LCOV - code coverage report
Current view: top level - mm - ksm.c (source / functions) Hit Total Coverage
Test: landlock.info Lines: 39 1194 3.3 %
Date: 2021-04-22 12:43:58 Functions: 4 74 5.4 %

          Line data    Source code
       1             : // SPDX-License-Identifier: GPL-2.0-only
       2             : /*
       3             :  * Memory merging support.
       4             :  *
       5             :  * This code enables dynamic sharing of identical pages found in different
       6             :  * memory areas, even if they are not shared by fork()
       7             :  *
       8             :  * Copyright (C) 2008-2009 Red Hat, Inc.
       9             :  * Authors:
      10             :  *      Izik Eidus
      11             :  *      Andrea Arcangeli
      12             :  *      Chris Wright
      13             :  *      Hugh Dickins
      14             :  */
      15             : 
      16             : #include <linux/errno.h>
      17             : #include <linux/mm.h>
      18             : #include <linux/fs.h>
      19             : #include <linux/mman.h>
      20             : #include <linux/sched.h>
      21             : #include <linux/sched/mm.h>
      22             : #include <linux/sched/coredump.h>
      23             : #include <linux/rwsem.h>
      24             : #include <linux/pagemap.h>
      25             : #include <linux/rmap.h>
      26             : #include <linux/spinlock.h>
      27             : #include <linux/xxhash.h>
      28             : #include <linux/delay.h>
      29             : #include <linux/kthread.h>
      30             : #include <linux/wait.h>
      31             : #include <linux/slab.h>
      32             : #include <linux/rbtree.h>
      33             : #include <linux/memory.h>
      34             : #include <linux/mmu_notifier.h>
      35             : #include <linux/swap.h>
      36             : #include <linux/ksm.h>
      37             : #include <linux/hashtable.h>
      38             : #include <linux/freezer.h>
      39             : #include <linux/oom.h>
      40             : #include <linux/numa.h>
      41             : 
      42             : #include <asm/tlbflush.h>
      43             : #include "internal.h"
      44             : 
      45             : #ifdef CONFIG_NUMA
      46             : #define NUMA(x)         (x)
      47             : #define DO_NUMA(x)      do { (x); } while (0)
      48             : #else
      49             : #define NUMA(x)         (0)
      50             : #define DO_NUMA(x)      do { } while (0)
      51             : #endif
      52             : 
      53             : /**
      54             :  * DOC: Overview
      55             :  *
      56             :  * A few notes about the KSM scanning process,
      57             :  * to make it easier to understand the data structures below:
      58             :  *
      59             :  * In order to reduce excessive scanning, KSM sorts the memory pages by their
      60             :  * contents into a data structure that holds pointers to the pages' locations.
      61             :  *
      62             :  * Since the contents of the pages may change at any moment, KSM cannot just
      63             :  * insert the pages into a normal sorted tree and expect it to find anything.
      64             :  * Therefore KSM uses two data structures - the stable and the unstable tree.
      65             :  *
      66             :  * The stable tree holds pointers to all the merged pages (ksm pages), sorted
      67             :  * by their contents.  Because each such page is write-protected, searching on
      68             :  * this tree is fully assured to be working (except when pages are unmapped),
      69             :  * and therefore this tree is called the stable tree.
      70             :  *
      71             :  * The stable tree node includes information required for reverse
      72             :  * mapping from a KSM page to virtual addresses that map this page.
      73             :  *
      74             :  * In order to avoid large latencies of the rmap walks on KSM pages,
      75             :  * KSM maintains two types of nodes in the stable tree:
      76             :  *
      77             :  * * the regular nodes that keep the reverse mapping structures in a
      78             :  *   linked list
      79             :  * * the "chains" that link nodes ("dups") that represent the same
      80             :  *   write protected memory content, but each "dup" corresponds to a
      81             :  *   different KSM page copy of that content
      82             :  *
      83             :  * Internally, the regular nodes, "dups" and "chains" are represented
      84             :  * using the same struct stable_node structure.
      85             :  *
      86             :  * In addition to the stable tree, KSM uses a second data structure called the
      87             :  * unstable tree: this tree holds pointers to pages which have been found to
      88             :  * be "unchanged for a period of time".  The unstable tree sorts these pages
      89             :  * by their contents, but since they are not write-protected, KSM cannot rely
      90             :  * upon the unstable tree to work correctly - the unstable tree is liable to
      91             :  * be corrupted as its contents are modified, and so it is called unstable.
      92             :  *
      93             :  * KSM solves this problem by several techniques:
      94             :  *
      95             :  * 1) The unstable tree is flushed every time KSM completes scanning all
      96             :  *    memory areas, and then the tree is rebuilt again from the beginning.
      97             :  * 2) KSM will only insert into the unstable tree, pages whose hash value
      98             :  *    has not changed since the previous scan of all memory areas.
      99             :  * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
     100             :  *    colors of the nodes and not on their contents, assuring that even when
     101             :  *    the tree gets "corrupted" it won't get out of balance, so scanning time
     102             :  *    remains the same (also, searching and inserting nodes in an rbtree uses
     103             :  *    the same algorithm, so we have no overhead when we flush and rebuild).
     104             :  * 4) KSM never flushes the stable tree, which means that even if it were to
     105             :  *    take 10 attempts to find a page in the unstable tree, once it is found,
     106             :  *    it is secured in the stable tree.  (When we scan a new page, we first
     107             :  *    compare it against the stable tree, and then against the unstable tree.)
     108             :  *
     109             :  * If the merge_across_nodes tunable is unset, then KSM maintains multiple
     110             :  * stable trees and multiple unstable trees: one of each for each NUMA node.
     111             :  */
     112             : 
     113             : /**
     114             :  * struct mm_slot - ksm information per mm that is being scanned
     115             :  * @link: link to the mm_slots hash list
     116             :  * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
     117             :  * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
     118             :  * @mm: the mm that this information is valid for
     119             :  */
     120             : struct mm_slot {
     121             :         struct hlist_node link;
     122             :         struct list_head mm_list;
     123             :         struct rmap_item *rmap_list;
     124             :         struct mm_struct *mm;
     125             : };
     126             : 
     127             : /**
     128             :  * struct ksm_scan - cursor for scanning
     129             :  * @mm_slot: the current mm_slot we are scanning
     130             :  * @address: the next address inside that to be scanned
     131             :  * @rmap_list: link to the next rmap to be scanned in the rmap_list
     132             :  * @seqnr: count of completed full scans (needed when removing unstable node)
     133             :  *
     134             :  * There is only the one ksm_scan instance of this cursor structure.
     135             :  */
     136             : struct ksm_scan {
     137             :         struct mm_slot *mm_slot;
     138             :         unsigned long address;
     139             :         struct rmap_item **rmap_list;
     140             :         unsigned long seqnr;
     141             : };
     142             : 
     143             : /**
     144             :  * struct stable_node - node of the stable rbtree
     145             :  * @node: rb node of this ksm page in the stable tree
     146             :  * @head: (overlaying parent) &migrate_nodes indicates temporarily on that list
     147             :  * @hlist_dup: linked into the stable_node->hlist with a stable_node chain
     148             :  * @list: linked into migrate_nodes, pending placement in the proper node tree
     149             :  * @hlist: hlist head of rmap_items using this ksm page
     150             :  * @kpfn: page frame number of this ksm page (perhaps temporarily on wrong nid)
     151             :  * @chain_prune_time: time of the last full garbage collection
     152             :  * @rmap_hlist_len: number of rmap_item entries in hlist or STABLE_NODE_CHAIN
     153             :  * @nid: NUMA node id of stable tree in which linked (may not match kpfn)
     154             :  */
     155             : struct stable_node {
     156             :         union {
     157             :                 struct rb_node node;    /* when node of stable tree */
     158             :                 struct {                /* when listed for migration */
     159             :                         struct list_head *head;
     160             :                         struct {
     161             :                                 struct hlist_node hlist_dup;
     162             :                                 struct list_head list;
     163             :                         };
     164             :                 };
     165             :         };
     166             :         struct hlist_head hlist;
     167             :         union {
     168             :                 unsigned long kpfn;
     169             :                 unsigned long chain_prune_time;
     170             :         };
     171             :         /*
     172             :          * STABLE_NODE_CHAIN can be any negative number in
     173             :          * rmap_hlist_len negative range, but better not -1 to be able
     174             :          * to reliably detect underflows.
     175             :          */
     176             : #define STABLE_NODE_CHAIN -1024
     177             :         int rmap_hlist_len;
     178             : #ifdef CONFIG_NUMA
     179             :         int nid;
     180             : #endif
     181             : };
     182             : 
     183             : /**
     184             :  * struct rmap_item - reverse mapping item for virtual addresses
     185             :  * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
     186             :  * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
     187             :  * @nid: NUMA node id of unstable tree in which linked (may not match page)
     188             :  * @mm: the memory structure this rmap_item is pointing into
     189             :  * @address: the virtual address this rmap_item tracks (+ flags in low bits)
     190             :  * @oldchecksum: previous checksum of the page at that virtual address
     191             :  * @node: rb node of this rmap_item in the unstable tree
     192             :  * @head: pointer to stable_node heading this list in the stable tree
     193             :  * @hlist: link into hlist of rmap_items hanging off that stable_node
     194             :  */
     195             : struct rmap_item {
     196             :         struct rmap_item *rmap_list;
     197             :         union {
     198             :                 struct anon_vma *anon_vma;      /* when stable */
     199             : #ifdef CONFIG_NUMA
     200             :                 int nid;                /* when node of unstable tree */
     201             : #endif
     202             :         };
     203             :         struct mm_struct *mm;
     204             :         unsigned long address;          /* + low bits used for flags below */
     205             :         unsigned int oldchecksum;       /* when unstable */
     206             :         union {
     207             :                 struct rb_node node;    /* when node of unstable tree */
     208             :                 struct {                /* when listed from stable tree */
     209             :                         struct stable_node *head;
     210             :                         struct hlist_node hlist;
     211             :                 };
     212             :         };
     213             : };
     214             : 
     215             : #define SEQNR_MASK      0x0ff   /* low bits of unstable tree seqnr */
     216             : #define UNSTABLE_FLAG   0x100   /* is a node of the unstable tree */
     217             : #define STABLE_FLAG     0x200   /* is listed from the stable tree */
     218             : #define KSM_FLAG_MASK   (SEQNR_MASK|UNSTABLE_FLAG|STABLE_FLAG)
     219             :                                 /* to mask all the flags */
     220             : 
     221             : /* The stable and unstable tree heads */
     222             : static struct rb_root one_stable_tree[1] = { RB_ROOT };
     223             : static struct rb_root one_unstable_tree[1] = { RB_ROOT };
     224             : static struct rb_root *root_stable_tree = one_stable_tree;
     225             : static struct rb_root *root_unstable_tree = one_unstable_tree;
     226             : 
     227             : /* Recently migrated nodes of stable tree, pending proper placement */
     228             : static LIST_HEAD(migrate_nodes);
     229             : #define STABLE_NODE_DUP_HEAD ((struct list_head *)&migrate_nodes.prev)
     230             : 
     231             : #define MM_SLOTS_HASH_BITS 10
     232             : static DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
     233             : 
     234             : static struct mm_slot ksm_mm_head = {
     235             :         .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
     236             : };
     237             : static struct ksm_scan ksm_scan = {
     238             :         .mm_slot = &ksm_mm_head,
     239             : };
     240             : 
     241             : static struct kmem_cache *rmap_item_cache;
     242             : static struct kmem_cache *stable_node_cache;
     243             : static struct kmem_cache *mm_slot_cache;
     244             : 
     245             : /* The number of nodes in the stable tree */
     246             : static unsigned long ksm_pages_shared;
     247             : 
     248             : /* The number of page slots additionally sharing those nodes */
     249             : static unsigned long ksm_pages_sharing;
     250             : 
     251             : /* The number of nodes in the unstable tree */
     252             : static unsigned long ksm_pages_unshared;
     253             : 
     254             : /* The number of rmap_items in use: to calculate pages_volatile */
     255             : static unsigned long ksm_rmap_items;
     256             : 
     257             : /* The number of stable_node chains */
     258             : static unsigned long ksm_stable_node_chains;
     259             : 
     260             : /* The number of stable_node dups linked to the stable_node chains */
     261             : static unsigned long ksm_stable_node_dups;
     262             : 
     263             : /* Delay in pruning stale stable_node_dups in the stable_node_chains */
     264             : static int ksm_stable_node_chains_prune_millisecs = 2000;
     265             : 
     266             : /* Maximum number of page slots sharing a stable node */
     267             : static int ksm_max_page_sharing = 256;
     268             : 
     269             : /* Number of pages ksmd should scan in one batch */
     270             : static unsigned int ksm_thread_pages_to_scan = 100;
     271             : 
     272             : /* Milliseconds ksmd should sleep between batches */
     273             : static unsigned int ksm_thread_sleep_millisecs = 20;
     274             : 
     275             : /* Checksum of an empty (zeroed) page */
     276             : static unsigned int zero_checksum __read_mostly;
     277             : 
     278             : /* Whether to merge empty (zeroed) pages with actual zero pages */
     279             : static bool ksm_use_zero_pages __read_mostly;
     280             : 
     281             : #ifdef CONFIG_NUMA
     282             : /* Zeroed when merging across nodes is not allowed */
     283             : static unsigned int ksm_merge_across_nodes = 1;
     284             : static int ksm_nr_node_ids = 1;
     285             : #else
     286             : #define ksm_merge_across_nodes  1U
     287             : #define ksm_nr_node_ids         1
     288             : #endif
     289             : 
     290             : #define KSM_RUN_STOP    0
     291             : #define KSM_RUN_MERGE   1
     292             : #define KSM_RUN_UNMERGE 2
     293             : #define KSM_RUN_OFFLINE 4
     294             : static unsigned long ksm_run = KSM_RUN_STOP;
     295             : static void wait_while_offlining(void);
     296             : 
     297             : static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
     298             : static DECLARE_WAIT_QUEUE_HEAD(ksm_iter_wait);
     299             : static DEFINE_MUTEX(ksm_thread_mutex);
     300             : static DEFINE_SPINLOCK(ksm_mmlist_lock);
     301             : 
     302             : #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
     303             :                 sizeof(struct __struct), __alignof__(struct __struct),\
     304             :                 (__flags), NULL)
     305             : 
     306           1 : static int __init ksm_slab_init(void)
     307             : {
     308           1 :         rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
     309           1 :         if (!rmap_item_cache)
     310           0 :                 goto out;
     311             : 
     312           1 :         stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
     313           1 :         if (!stable_node_cache)
     314           0 :                 goto out_free1;
     315             : 
     316           1 :         mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
     317           1 :         if (!mm_slot_cache)
     318           0 :                 goto out_free2;
     319             : 
     320             :         return 0;
     321             : 
     322           0 : out_free2:
     323           0 :         kmem_cache_destroy(stable_node_cache);
     324           0 : out_free1:
     325           0 :         kmem_cache_destroy(rmap_item_cache);
     326             : out:
     327             :         return -ENOMEM;
     328             : }
     329             : 
     330           0 : static void __init ksm_slab_free(void)
     331             : {
     332           0 :         kmem_cache_destroy(mm_slot_cache);
     333           0 :         kmem_cache_destroy(stable_node_cache);
     334           0 :         kmem_cache_destroy(rmap_item_cache);
     335           0 :         mm_slot_cache = NULL;
     336           0 : }
     337             : 
     338           0 : static __always_inline bool is_stable_node_chain(struct stable_node *chain)
     339             : {
     340           0 :         return chain->rmap_hlist_len == STABLE_NODE_CHAIN;
     341             : }
     342             : 
     343           0 : static __always_inline bool is_stable_node_dup(struct stable_node *dup)
     344             : {
     345           0 :         return dup->head == STABLE_NODE_DUP_HEAD;
     346             : }
     347             : 
     348           0 : static inline void stable_node_chain_add_dup(struct stable_node *dup,
     349             :                                              struct stable_node *chain)
     350             : {
     351           0 :         VM_BUG_ON(is_stable_node_dup(dup));
     352           0 :         dup->head = STABLE_NODE_DUP_HEAD;
     353           0 :         VM_BUG_ON(!is_stable_node_chain(chain));
     354           0 :         hlist_add_head(&dup->hlist_dup, &chain->hlist);
     355           0 :         ksm_stable_node_dups++;
     356           0 : }
     357             : 
     358           0 : static inline void __stable_node_dup_del(struct stable_node *dup)
     359             : {
     360           0 :         VM_BUG_ON(!is_stable_node_dup(dup));
     361           0 :         hlist_del(&dup->hlist_dup);
     362           0 :         ksm_stable_node_dups--;
     363           0 : }
     364             : 
     365           0 : static inline void stable_node_dup_del(struct stable_node *dup)
     366             : {
     367           0 :         VM_BUG_ON(is_stable_node_chain(dup));
     368           0 :         if (is_stable_node_dup(dup))
     369           0 :                 __stable_node_dup_del(dup);
     370             :         else
     371           0 :                 rb_erase(&dup->node, root_stable_tree + NUMA(dup->nid));
     372             : #ifdef CONFIG_DEBUG_VM
     373           0 :         dup->head = NULL;
     374             : #endif
     375           0 : }
     376             : 
     377           0 : static inline struct rmap_item *alloc_rmap_item(void)
     378             : {
     379           0 :         struct rmap_item *rmap_item;
     380             : 
     381           0 :         rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL |
     382             :                                                 __GFP_NORETRY | __GFP_NOWARN);
     383           0 :         if (rmap_item)
     384           0 :                 ksm_rmap_items++;
     385           0 :         return rmap_item;
     386             : }
     387             : 
     388           0 : static inline void free_rmap_item(struct rmap_item *rmap_item)
     389             : {
     390           0 :         ksm_rmap_items--;
     391           0 :         rmap_item->mm = NULL;        /* debug safety */
     392           0 :         kmem_cache_free(rmap_item_cache, rmap_item);
     393           0 : }
     394             : 
     395           0 : static inline struct stable_node *alloc_stable_node(void)
     396             : {
     397             :         /*
     398             :          * The allocation can take too long with GFP_KERNEL when memory is under
     399             :          * pressure, which may lead to hung task warnings.  Adding __GFP_HIGH
     400             :          * grants access to memory reserves, helping to avoid this problem.
     401             :          */
     402           0 :         return kmem_cache_alloc(stable_node_cache, GFP_KERNEL | __GFP_HIGH);
     403             : }
     404             : 
     405           0 : static inline void free_stable_node(struct stable_node *stable_node)
     406             : {
     407           0 :         VM_BUG_ON(stable_node->rmap_hlist_len &&
     408             :                   !is_stable_node_chain(stable_node));
     409           0 :         kmem_cache_free(stable_node_cache, stable_node);
     410           0 : }
     411             : 
     412           0 : static inline struct mm_slot *alloc_mm_slot(void)
     413             : {
     414           0 :         if (!mm_slot_cache)     /* initialization failed */
     415             :                 return NULL;
     416           0 :         return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
     417             : }
     418             : 
     419           0 : static inline void free_mm_slot(struct mm_slot *mm_slot)
     420             : {
     421           0 :         kmem_cache_free(mm_slot_cache, mm_slot);
     422             : }
     423             : 
     424           0 : static struct mm_slot *get_mm_slot(struct mm_struct *mm)
     425             : {
     426           0 :         struct mm_slot *slot;
     427             : 
     428           0 :         hash_for_each_possible(mm_slots_hash, slot, link, (unsigned long)mm)
     429           0 :                 if (slot->mm == mm)
     430           0 :                         return slot;
     431             : 
     432             :         return NULL;
     433             : }
     434             : 
     435           0 : static void insert_to_mm_slots_hash(struct mm_struct *mm,
     436             :                                     struct mm_slot *mm_slot)
     437             : {
     438           0 :         mm_slot->mm = mm;
     439           0 :         hash_add(mm_slots_hash, &mm_slot->link, (unsigned long)mm);
     440           0 : }
     441             : 
     442             : /*
     443             :  * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
     444             :  * page tables after it has passed through ksm_exit() - which, if necessary,
     445             :  * takes mmap_lock briefly to serialize against them.  ksm_exit() does not set
     446             :  * a special flag: they can just back out as soon as mm_users goes to zero.
     447             :  * ksm_test_exit() is used throughout to make this test for exit: in some
     448             :  * places for correctness, in some places just to avoid unnecessary work.
     449             :  */
     450           0 : static inline bool ksm_test_exit(struct mm_struct *mm)
     451             : {
     452           0 :         return atomic_read(&mm->mm_users) == 0;
     453             : }
     454             : 
     455             : /*
     456             :  * We use break_ksm to break COW on a ksm page: it's a stripped down
     457             :  *
     458             :  *      if (get_user_pages(addr, 1, FOLL_WRITE, &page, NULL) == 1)
     459             :  *              put_page(page);
     460             :  *
     461             :  * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
     462             :  * in case the application has unmapped and remapped mm,addr meanwhile.
     463             :  * Could a ksm page appear anywhere else?  Actually yes, in a VM_PFNMAP
     464             :  * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
     465             :  *
     466             :  * FAULT_FLAG/FOLL_REMOTE are because we do this outside the context
     467             :  * of the process that owns 'vma'.  We also do not want to enforce
     468             :  * protection keys here anyway.
     469             :  */
     470           0 : static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
     471             : {
     472           0 :         struct page *page;
     473           0 :         vm_fault_t ret = 0;
     474             : 
     475           0 :         do {
     476           0 :                 cond_resched();
     477           0 :                 page = follow_page(vma, addr,
     478             :                                 FOLL_GET | FOLL_MIGRATION | FOLL_REMOTE);
     479           0 :                 if (IS_ERR_OR_NULL(page))
     480             :                         break;
     481           0 :                 if (PageKsm(page))
     482           0 :                         ret = handle_mm_fault(vma, addr,
     483             :                                               FAULT_FLAG_WRITE | FAULT_FLAG_REMOTE,
     484             :                                               NULL);
     485             :                 else
     486             :                         ret = VM_FAULT_WRITE;
     487           0 :                 put_page(page);
     488           0 :         } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | VM_FAULT_OOM)));
     489             :         /*
     490             :          * We must loop because handle_mm_fault() may back out if there's
     491             :          * any difficulty e.g. if pte accessed bit gets updated concurrently.
     492             :          *
     493             :          * VM_FAULT_WRITE is what we have been hoping for: it indicates that
     494             :          * COW has been broken, even if the vma does not permit VM_WRITE;
     495             :          * but note that a concurrent fault might break PageKsm for us.
     496             :          *
     497             :          * VM_FAULT_SIGBUS could occur if we race with truncation of the
     498             :          * backing file, which also invalidates anonymous pages: that's
     499             :          * okay, that truncation will have unmapped the PageKsm for us.
     500             :          *
     501             :          * VM_FAULT_OOM: at the time of writing (late July 2009), setting
     502             :          * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
     503             :          * current task has TIF_MEMDIE set, and will be OOM killed on return
     504             :          * to user; and ksmd, having no mm, would never be chosen for that.
     505             :          *
     506             :          * But if the mm is in a limited mem_cgroup, then the fault may fail
     507             :          * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
     508             :          * even ksmd can fail in this way - though it's usually breaking ksm
     509             :          * just to undo a merge it made a moment before, so unlikely to oom.
     510             :          *
     511             :          * That's a pity: we might therefore have more kernel pages allocated
     512             :          * than we're counting as nodes in the stable tree; but ksm_do_scan
     513             :          * will retry to break_cow on each pass, so should recover the page
     514             :          * in due course.  The important thing is to not let VM_MERGEABLE
     515             :          * be cleared while any such pages might remain in the area.
     516             :          */
     517           0 :         return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
     518             : }
     519             : 
     520           0 : static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
     521             :                 unsigned long addr)
     522             : {
     523           0 :         struct vm_area_struct *vma;
     524           0 :         if (ksm_test_exit(mm))
     525             :                 return NULL;
     526           0 :         vma = find_vma(mm, addr);
     527           0 :         if (!vma || vma->vm_start > addr)
     528             :                 return NULL;
     529           0 :         if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
     530           0 :                 return NULL;
     531             :         return vma;
     532             : }
     533             : 
     534           0 : static void break_cow(struct rmap_item *rmap_item)
     535             : {
     536           0 :         struct mm_struct *mm = rmap_item->mm;
     537           0 :         unsigned long addr = rmap_item->address;
     538           0 :         struct vm_area_struct *vma;
     539             : 
     540             :         /*
     541             :          * It is not an accident that whenever we want to break COW
     542             :          * to undo, we also need to drop a reference to the anon_vma.
     543             :          */
     544           0 :         put_anon_vma(rmap_item->anon_vma);
     545             : 
     546           0 :         mmap_read_lock(mm);
     547           0 :         vma = find_mergeable_vma(mm, addr);
     548           0 :         if (vma)
     549           0 :                 break_ksm(vma, addr);
     550           0 :         mmap_read_unlock(mm);
     551           0 : }
     552             : 
     553           0 : static struct page *get_mergeable_page(struct rmap_item *rmap_item)
     554             : {
     555           0 :         struct mm_struct *mm = rmap_item->mm;
     556           0 :         unsigned long addr = rmap_item->address;
     557           0 :         struct vm_area_struct *vma;
     558           0 :         struct page *page;
     559             : 
     560           0 :         mmap_read_lock(mm);
     561           0 :         vma = find_mergeable_vma(mm, addr);
     562           0 :         if (!vma)
     563           0 :                 goto out;
     564             : 
     565           0 :         page = follow_page(vma, addr, FOLL_GET);
     566           0 :         if (IS_ERR_OR_NULL(page))
     567           0 :                 goto out;
     568           0 :         if (PageAnon(page)) {
     569           0 :                 flush_anon_page(vma, page, addr);
     570           0 :                 flush_dcache_page(page);
     571             :         } else {
     572           0 :                 put_page(page);
     573             : out:
     574             :                 page = NULL;
     575             :         }
     576           0 :         mmap_read_unlock(mm);
     577           0 :         return page;
     578             : }
     579             : 
     580             : /*
     581             :  * This helper is used for getting right index into array of tree roots.
     582             :  * When merge_across_nodes knob is set to 1, there are only two rb-trees for
     583             :  * stable and unstable pages from all nodes with roots in index 0. Otherwise,
     584             :  * every node has its own stable and unstable tree.
     585             :  */
     586           0 : static inline int get_kpfn_nid(unsigned long kpfn)
     587             : {
     588           0 :         return ksm_merge_across_nodes ? 0 : NUMA(pfn_to_nid(kpfn));
     589             : }
     590             : 
     591           0 : static struct stable_node *alloc_stable_node_chain(struct stable_node *dup,
     592             :                                                    struct rb_root *root)
     593             : {
     594           0 :         struct stable_node *chain = alloc_stable_node();
     595           0 :         VM_BUG_ON(is_stable_node_chain(dup));
     596           0 :         if (likely(chain)) {
     597           0 :                 INIT_HLIST_HEAD(&chain->hlist);
     598           0 :                 chain->chain_prune_time = jiffies;
     599           0 :                 chain->rmap_hlist_len = STABLE_NODE_CHAIN;
     600             : #if defined (CONFIG_DEBUG_VM) && defined(CONFIG_NUMA)
     601           0 :                 chain->nid = NUMA_NO_NODE; /* debug */
     602             : #endif
     603           0 :                 ksm_stable_node_chains++;
     604             : 
     605             :                 /*
     606             :                  * Put the stable node chain in the first dimension of
     607             :                  * the stable tree and at the same time remove the old
     608             :                  * stable node.
     609             :                  */
     610           0 :                 rb_replace_node(&dup->node, &chain->node, root);
     611             : 
     612             :                 /*
     613             :                  * Move the old stable node to the second dimension
     614             :                  * queued in the hlist_dup. The invariant is that all
     615             :                  * dup stable_nodes in the chain->hlist point to pages
     616             :                  * that are write protected and have the exact same
     617             :                  * content.
     618             :                  */
     619           0 :                 stable_node_chain_add_dup(dup, chain);
     620             :         }
     621           0 :         return chain;
     622             : }
     623             : 
     624           0 : static inline void free_stable_node_chain(struct stable_node *chain,
     625             :                                           struct rb_root *root)
     626             : {
     627           0 :         rb_erase(&chain->node, root);
     628           0 :         free_stable_node(chain);
     629           0 :         ksm_stable_node_chains--;
     630           0 : }
     631             : 
     632           0 : static void remove_node_from_stable_tree(struct stable_node *stable_node)
     633             : {
     634           0 :         struct rmap_item *rmap_item;
     635             : 
     636             :         /* check it's not STABLE_NODE_CHAIN or negative */
     637           0 :         BUG_ON(stable_node->rmap_hlist_len < 0);
     638             : 
     639           0 :         hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
     640           0 :                 if (rmap_item->hlist.next)
     641           0 :                         ksm_pages_sharing--;
     642             :                 else
     643           0 :                         ksm_pages_shared--;
     644           0 :                 VM_BUG_ON(stable_node->rmap_hlist_len <= 0);
     645           0 :                 stable_node->rmap_hlist_len--;
     646           0 :                 put_anon_vma(rmap_item->anon_vma);
     647           0 :                 rmap_item->address &= PAGE_MASK;
     648           0 :                 cond_resched();
     649             :         }
     650             : 
     651             :         /*
     652             :          * We need the second aligned pointer of the migrate_nodes
     653             :          * list_head to stay clear from the rb_parent_color union
     654             :          * (aligned and different than any node) and also different
     655             :          * from &migrate_nodes. This will verify that future list.h changes
     656             :          * don't break STABLE_NODE_DUP_HEAD. Only recent gcc can handle it.
     657             :          */
     658             : #if defined(GCC_VERSION) && GCC_VERSION >= 40903
     659           0 :         BUILD_BUG_ON(STABLE_NODE_DUP_HEAD <= &migrate_nodes);
     660           0 :         BUILD_BUG_ON(STABLE_NODE_DUP_HEAD >= &migrate_nodes + 1);
     661             : #endif
     662             : 
     663           0 :         if (stable_node->head == &migrate_nodes)
     664           0 :                 list_del(&stable_node->list);
     665             :         else
     666           0 :                 stable_node_dup_del(stable_node);
     667           0 :         free_stable_node(stable_node);
     668           0 : }
     669             : 
     670             : enum get_ksm_page_flags {
     671             :         GET_KSM_PAGE_NOLOCK,
     672             :         GET_KSM_PAGE_LOCK,
     673             :         GET_KSM_PAGE_TRYLOCK
     674             : };
     675             : 
     676             : /*
     677             :  * get_ksm_page: checks if the page indicated by the stable node
     678             :  * is still its ksm page, despite having held no reference to it.
     679             :  * In which case we can trust the content of the page, and it
     680             :  * returns the gotten page; but if the page has now been zapped,
     681             :  * remove the stale node from the stable tree and return NULL.
     682             :  * But beware, the stable node's page might be being migrated.
     683             :  *
     684             :  * You would expect the stable_node to hold a reference to the ksm page.
     685             :  * But if it increments the page's count, swapping out has to wait for
     686             :  * ksmd to come around again before it can free the page, which may take
     687             :  * seconds or even minutes: much too unresponsive.  So instead we use a
     688             :  * "keyhole reference": access to the ksm page from the stable node peeps
     689             :  * out through its keyhole to see if that page still holds the right key,
     690             :  * pointing back to this stable node.  This relies on freeing a PageAnon
     691             :  * page to reset its page->mapping to NULL, and relies on no other use of
     692             :  * a page to put something that might look like our key in page->mapping.
     693             :  * is on its way to being freed; but it is an anomaly to bear in mind.
     694             :  */
     695           0 : static struct page *get_ksm_page(struct stable_node *stable_node,
     696             :                                  enum get_ksm_page_flags flags)
     697             : {
     698           0 :         struct page *page;
     699           0 :         void *expected_mapping;
     700           0 :         unsigned long kpfn;
     701             : 
     702           0 :         expected_mapping = (void *)((unsigned long)stable_node |
     703             :                                         PAGE_MAPPING_KSM);
     704           0 : again:
     705           0 :         kpfn = READ_ONCE(stable_node->kpfn); /* Address dependency. */
     706           0 :         page = pfn_to_page(kpfn);
     707           0 :         if (READ_ONCE(page->mapping) != expected_mapping)
     708           0 :                 goto stale;
     709             : 
     710             :         /*
     711             :          * We cannot do anything with the page while its refcount is 0.
     712             :          * Usually 0 means free, or tail of a higher-order page: in which
     713             :          * case this node is no longer referenced, and should be freed;
     714             :          * however, it might mean that the page is under page_ref_freeze().
     715             :          * The __remove_mapping() case is easy, again the node is now stale;
     716             :          * the same is in reuse_ksm_page() case; but if page is swapcache
     717             :          * in migrate_page_move_mapping(), it might still be our page,
     718             :          * in which case it's essential to keep the node.
     719             :          */
     720           0 :         while (!get_page_unless_zero(page)) {
     721             :                 /*
     722             :                  * Another check for page->mapping != expected_mapping would
     723             :                  * work here too.  We have chosen the !PageSwapCache test to
     724             :                  * optimize the common case, when the page is or is about to
     725             :                  * be freed: PageSwapCache is cleared (under spin_lock_irq)
     726             :                  * in the ref_freeze section of __remove_mapping(); but Anon
     727             :                  * page->mapping reset to NULL later, in free_pages_prepare().
     728             :                  */
     729           0 :                 if (!PageSwapCache(page))
     730           0 :                         goto stale;
     731             :                 cpu_relax();
     732             :         }
     733             : 
     734           0 :         if (READ_ONCE(page->mapping) != expected_mapping) {
     735           0 :                 put_page(page);
     736           0 :                 goto stale;
     737             :         }
     738             : 
     739           0 :         if (flags == GET_KSM_PAGE_TRYLOCK) {
     740           0 :                 if (!trylock_page(page)) {
     741           0 :                         put_page(page);
     742           0 :                         return ERR_PTR(-EBUSY);
     743             :                 }
     744           0 :         } else if (flags == GET_KSM_PAGE_LOCK)
     745           0 :                 lock_page(page);
     746             : 
     747           0 :         if (flags != GET_KSM_PAGE_NOLOCK) {
     748           0 :                 if (READ_ONCE(page->mapping) != expected_mapping) {
     749           0 :                         unlock_page(page);
     750           0 :                         put_page(page);
     751           0 :                         goto stale;
     752             :                 }
     753             :         }
     754             :         return page;
     755             : 
     756           0 : stale:
     757             :         /*
     758             :          * We come here from above when page->mapping or !PageSwapCache
     759             :          * suggests that the node is stale; but it might be under migration.
     760             :          * We need smp_rmb(), matching the smp_wmb() in ksm_migrate_page(),
     761             :          * before checking whether node->kpfn has been changed.
     762             :          */
     763           0 :         smp_rmb();
     764           0 :         if (READ_ONCE(stable_node->kpfn) != kpfn)
     765           0 :                 goto again;
     766           0 :         remove_node_from_stable_tree(stable_node);
     767           0 :         return NULL;
     768             : }
     769             : 
     770             : /*
     771             :  * Removing rmap_item from stable or unstable tree.
     772             :  * This function will clean the information from the stable/unstable tree.
     773             :  */
     774           0 : static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
     775             : {
     776           0 :         if (rmap_item->address & STABLE_FLAG) {
     777           0 :                 struct stable_node *stable_node;
     778           0 :                 struct page *page;
     779             : 
     780           0 :                 stable_node = rmap_item->head;
     781           0 :                 page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
     782           0 :                 if (!page)
     783           0 :                         goto out;
     784             : 
     785           0 :                 hlist_del(&rmap_item->hlist);
     786           0 :                 unlock_page(page);
     787           0 :                 put_page(page);
     788             : 
     789           0 :                 if (!hlist_empty(&stable_node->hlist))
     790           0 :                         ksm_pages_sharing--;
     791             :                 else
     792           0 :                         ksm_pages_shared--;
     793           0 :                 VM_BUG_ON(stable_node->rmap_hlist_len <= 0);
     794           0 :                 stable_node->rmap_hlist_len--;
     795             : 
     796           0 :                 put_anon_vma(rmap_item->anon_vma);
     797           0 :                 rmap_item->address &= PAGE_MASK;
     798             : 
     799           0 :         } else if (rmap_item->address & UNSTABLE_FLAG) {
     800           0 :                 unsigned char age;
     801             :                 /*
     802             :                  * Usually ksmd can and must skip the rb_erase, because
     803             :                  * root_unstable_tree was already reset to RB_ROOT.
     804             :                  * But be careful when an mm is exiting: do the rb_erase
     805             :                  * if this rmap_item was inserted by this scan, rather
     806             :                  * than left over from before.
     807             :                  */
     808           0 :                 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
     809           0 :                 BUG_ON(age > 1);
     810           0 :                 if (!age)
     811           0 :                         rb_erase(&rmap_item->node,
     812           0 :                                  root_unstable_tree + NUMA(rmap_item->nid));
     813           0 :                 ksm_pages_unshared--;
     814           0 :                 rmap_item->address &= PAGE_MASK;
     815             :         }
     816           0 : out:
     817           0 :         cond_resched();         /* we're called from many long loops */
     818           0 : }
     819             : 
     820           0 : static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
     821             :                                        struct rmap_item **rmap_list)
     822             : {
     823           0 :         while (*rmap_list) {
     824           0 :                 struct rmap_item *rmap_item = *rmap_list;
     825           0 :                 *rmap_list = rmap_item->rmap_list;
     826           0 :                 remove_rmap_item_from_tree(rmap_item);
     827           0 :                 free_rmap_item(rmap_item);
     828             :         }
     829           0 : }
     830             : 
     831             : /*
     832             :  * Though it's very tempting to unmerge rmap_items from stable tree rather
     833             :  * than check every pte of a given vma, the locking doesn't quite work for
     834             :  * that - an rmap_item is assigned to the stable tree after inserting ksm
     835             :  * page and upping mmap_lock.  Nor does it fit with the way we skip dup'ing
     836             :  * rmap_items from parent to child at fork time (so as not to waste time
     837             :  * if exit comes before the next scan reaches it).
     838             :  *
     839             :  * Similarly, although we'd like to remove rmap_items (so updating counts
     840             :  * and freeing memory) when unmerging an area, it's easier to leave that
     841             :  * to the next pass of ksmd - consider, for example, how ksmd might be
     842             :  * in cmp_and_merge_page on one of the rmap_items we would be removing.
     843             :  */
     844           0 : static int unmerge_ksm_pages(struct vm_area_struct *vma,
     845             :                              unsigned long start, unsigned long end)
     846             : {
     847           0 :         unsigned long addr;
     848           0 :         int err = 0;
     849             : 
     850           0 :         for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
     851           0 :                 if (ksm_test_exit(vma->vm_mm))
     852             :                         break;
     853           0 :                 if (signal_pending(current))
     854             :                         err = -ERESTARTSYS;
     855             :                 else
     856           0 :                         err = break_ksm(vma, addr);
     857             :         }
     858           0 :         return err;
     859             : }
     860             : 
     861           0 : static inline struct stable_node *page_stable_node(struct page *page)
     862             : {
     863           0 :         return PageKsm(page) ? page_rmapping(page) : NULL;
     864             : }
     865             : 
     866           0 : static inline void set_page_stable_node(struct page *page,
     867             :                                         struct stable_node *stable_node)
     868             : {
     869           0 :         page->mapping = (void *)((unsigned long)stable_node | PAGE_MAPPING_KSM);
     870           0 : }
     871             : 
     872             : #ifdef CONFIG_SYSFS
     873             : /*
     874             :  * Only called through the sysfs control interface:
     875             :  */
     876           0 : static int remove_stable_node(struct stable_node *stable_node)
     877             : {
     878           0 :         struct page *page;
     879           0 :         int err;
     880             : 
     881           0 :         page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
     882           0 :         if (!page) {
     883             :                 /*
     884             :                  * get_ksm_page did remove_node_from_stable_tree itself.
     885             :                  */
     886             :                 return 0;
     887             :         }
     888             : 
     889             :         /*
     890             :          * Page could be still mapped if this races with __mmput() running in
     891             :          * between ksm_exit() and exit_mmap(). Just refuse to let
     892             :          * merge_across_nodes/max_page_sharing be switched.
     893             :          */
     894           0 :         err = -EBUSY;
     895           0 :         if (!page_mapped(page)) {
     896             :                 /*
     897             :                  * The stable node did not yet appear stale to get_ksm_page(),
     898             :                  * since that allows for an unmapped ksm page to be recognized
     899             :                  * right up until it is freed; but the node is safe to remove.
     900             :                  * This page might be in a pagevec waiting to be freed,
     901             :                  * or it might be PageSwapCache (perhaps under writeback),
     902             :                  * or it might have been removed from swapcache a moment ago.
     903             :                  */
     904           0 :                 set_page_stable_node(page, NULL);
     905           0 :                 remove_node_from_stable_tree(stable_node);
     906           0 :                 err = 0;
     907             :         }
     908             : 
     909           0 :         unlock_page(page);
     910           0 :         put_page(page);
     911           0 :         return err;
     912             : }
     913             : 
     914           0 : static int remove_stable_node_chain(struct stable_node *stable_node,
     915             :                                     struct rb_root *root)
     916             : {
     917           0 :         struct stable_node *dup;
     918           0 :         struct hlist_node *hlist_safe;
     919             : 
     920           0 :         if (!is_stable_node_chain(stable_node)) {
     921           0 :                 VM_BUG_ON(is_stable_node_dup(stable_node));
     922           0 :                 if (remove_stable_node(stable_node))
     923             :                         return true;
     924             :                 else
     925           0 :                         return false;
     926             :         }
     927             : 
     928           0 :         hlist_for_each_entry_safe(dup, hlist_safe,
     929             :                                   &stable_node->hlist, hlist_dup) {
     930           0 :                 VM_BUG_ON(!is_stable_node_dup(dup));
     931           0 :                 if (remove_stable_node(dup))
     932             :                         return true;
     933             :         }
     934           0 :         BUG_ON(!hlist_empty(&stable_node->hlist));
     935           0 :         free_stable_node_chain(stable_node, root);
     936           0 :         return false;
     937             : }
     938             : 
     939           0 : static int remove_all_stable_nodes(void)
     940             : {
     941           0 :         struct stable_node *stable_node, *next;
     942           0 :         int nid;
     943           0 :         int err = 0;
     944             : 
     945           0 :         for (nid = 0; nid < ksm_nr_node_ids; nid++) {
     946           0 :                 while (root_stable_tree[nid].rb_node) {
     947           0 :                         stable_node = rb_entry(root_stable_tree[nid].rb_node,
     948             :                                                 struct stable_node, node);
     949           0 :                         if (remove_stable_node_chain(stable_node,
     950             :                                                      root_stable_tree + nid)) {
     951             :                                 err = -EBUSY;
     952             :                                 break;  /* proceed to next nid */
     953             :                         }
     954           0 :                         cond_resched();
     955             :                 }
     956             :         }
     957           0 :         list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
     958           0 :                 if (remove_stable_node(stable_node))
     959           0 :                         err = -EBUSY;
     960           0 :                 cond_resched();
     961             :         }
     962           0 :         return err;
     963             : }
     964             : 
     965           0 : static int unmerge_and_remove_all_rmap_items(void)
     966             : {
     967           0 :         struct mm_slot *mm_slot;
     968           0 :         struct mm_struct *mm;
     969           0 :         struct vm_area_struct *vma;
     970           0 :         int err = 0;
     971             : 
     972           0 :         spin_lock(&ksm_mmlist_lock);
     973           0 :         ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
     974             :                                                 struct mm_slot, mm_list);
     975           0 :         spin_unlock(&ksm_mmlist_lock);
     976             : 
     977           0 :         for (mm_slot = ksm_scan.mm_slot;
     978           0 :                         mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
     979           0 :                 mm = mm_slot->mm;
     980           0 :                 mmap_read_lock(mm);
     981           0 :                 for (vma = mm->mmap; vma; vma = vma->vm_next) {
     982           0 :                         if (ksm_test_exit(mm))
     983             :                                 break;
     984           0 :                         if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
     985           0 :                                 continue;
     986           0 :                         err = unmerge_ksm_pages(vma,
     987             :                                                 vma->vm_start, vma->vm_end);
     988           0 :                         if (err)
     989           0 :                                 goto error;
     990             :                 }
     991             : 
     992           0 :                 remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
     993           0 :                 mmap_read_unlock(mm);
     994             : 
     995           0 :                 spin_lock(&ksm_mmlist_lock);
     996           0 :                 ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
     997             :                                                 struct mm_slot, mm_list);
     998           0 :                 if (ksm_test_exit(mm)) {
     999           0 :                         hash_del(&mm_slot->link);
    1000           0 :                         list_del(&mm_slot->mm_list);
    1001           0 :                         spin_unlock(&ksm_mmlist_lock);
    1002             : 
    1003           0 :                         free_mm_slot(mm_slot);
    1004           0 :                         clear_bit(MMF_VM_MERGEABLE, &mm->flags);
    1005           0 :                         mmdrop(mm);
    1006             :                 } else
    1007           0 :                         spin_unlock(&ksm_mmlist_lock);
    1008             :         }
    1009             : 
    1010             :         /* Clean up stable nodes, but don't worry if some are still busy */
    1011           0 :         remove_all_stable_nodes();
    1012           0 :         ksm_scan.seqnr = 0;
    1013           0 :         return 0;
    1014             : 
    1015           0 : error:
    1016           0 :         mmap_read_unlock(mm);
    1017           0 :         spin_lock(&ksm_mmlist_lock);
    1018           0 :         ksm_scan.mm_slot = &ksm_mm_head;
    1019           0 :         spin_unlock(&ksm_mmlist_lock);
    1020           0 :         return err;
    1021             : }
    1022             : #endif /* CONFIG_SYSFS */
    1023             : 
    1024           1 : static u32 calc_checksum(struct page *page)
    1025             : {
    1026           1 :         u32 checksum;
    1027           1 :         void *addr = kmap_atomic(page);
    1028           1 :         checksum = xxhash(addr, PAGE_SIZE, 0);
    1029           1 :         kunmap_atomic(addr);
    1030           1 :         return checksum;
    1031             : }
    1032             : 
    1033           0 : static int write_protect_page(struct vm_area_struct *vma, struct page *page,
    1034             :                               pte_t *orig_pte)
    1035             : {
    1036           0 :         struct mm_struct *mm = vma->vm_mm;
    1037           0 :         struct page_vma_mapped_walk pvmw = {
    1038             :                 .page = page,
    1039             :                 .vma = vma,
    1040             :         };
    1041           0 :         int swapped;
    1042           0 :         int err = -EFAULT;
    1043           0 :         struct mmu_notifier_range range;
    1044             : 
    1045           0 :         pvmw.address = page_address_in_vma(page, vma);
    1046           0 :         if (pvmw.address == -EFAULT)
    1047           0 :                 goto out;
    1048             : 
    1049           0 :         BUG_ON(PageTransCompound(page));
    1050             : 
    1051           0 :         mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm,
    1052             :                                 pvmw.address,
    1053             :                                 pvmw.address + PAGE_SIZE);
    1054           0 :         mmu_notifier_invalidate_range_start(&range);
    1055             : 
    1056           0 :         if (!page_vma_mapped_walk(&pvmw))
    1057           0 :                 goto out_mn;
    1058           0 :         if (WARN_ONCE(!pvmw.pte, "Unexpected PMD mapping?"))
    1059           0 :                 goto out_unlock;
    1060             : 
    1061           0 :         if (pte_write(*pvmw.pte) || pte_dirty(*pvmw.pte) ||
    1062           0 :             (pte_protnone(*pvmw.pte) && pte_savedwrite(*pvmw.pte)) ||
    1063           0 :                                                 mm_tlb_flush_pending(mm)) {
    1064           0 :                 pte_t entry;
    1065             : 
    1066           0 :                 swapped = PageSwapCache(page);
    1067           0 :                 flush_cache_page(vma, pvmw.address, page_to_pfn(page));
    1068             :                 /*
    1069             :                  * Ok this is tricky, when get_user_pages_fast() run it doesn't
    1070             :                  * take any lock, therefore the check that we are going to make
    1071             :                  * with the pagecount against the mapcount is racey and
    1072             :                  * O_DIRECT can happen right after the check.
    1073             :                  * So we clear the pte and flush the tlb before the check
    1074             :                  * this assure us that no O_DIRECT can happen after the check
    1075             :                  * or in the middle of the check.
    1076             :                  *
    1077             :                  * No need to notify as we are downgrading page table to read
    1078             :                  * only not changing it to point to a new page.
    1079             :                  *
    1080             :                  * See Documentation/vm/mmu_notifier.rst
    1081             :                  */
    1082           0 :                 entry = ptep_clear_flush(vma, pvmw.address, pvmw.pte);
    1083             :                 /*
    1084             :                  * Check that no O_DIRECT or similar I/O is in progress on the
    1085             :                  * page
    1086             :                  */
    1087           0 :                 if (page_mapcount(page) + 1 + swapped != page_count(page)) {
    1088           0 :                         set_pte_at(mm, pvmw.address, pvmw.pte, entry);
    1089           0 :                         goto out_unlock;
    1090             :                 }
    1091           0 :                 if (pte_dirty(entry))
    1092           0 :                         set_page_dirty(page);
    1093             : 
    1094           0 :                 if (pte_protnone(entry))
    1095             :                         entry = pte_mkclean(pte_clear_savedwrite(entry));
    1096             :                 else
    1097           0 :                         entry = pte_mkclean(pte_wrprotect(entry));
    1098           0 :                 set_pte_at_notify(mm, pvmw.address, pvmw.pte, entry);
    1099             :         }
    1100           0 :         *orig_pte = *pvmw.pte;
    1101           0 :         err = 0;
    1102             : 
    1103           0 : out_unlock:
    1104           0 :         page_vma_mapped_walk_done(&pvmw);
    1105             : out_mn:
    1106           0 :         mmu_notifier_invalidate_range_end(&range);
    1107           0 : out:
    1108           0 :         return err;
    1109             : }
    1110             : 
    1111             : /**
    1112             :  * replace_page - replace page in vma by new ksm page
    1113             :  * @vma:      vma that holds the pte pointing to page
    1114             :  * @page:     the page we are replacing by kpage
    1115             :  * @kpage:    the ksm page we replace page by
    1116             :  * @orig_pte: the original value of the pte
    1117             :  *
    1118             :  * Returns 0 on success, -EFAULT on failure.
    1119             :  */
    1120           0 : static int replace_page(struct vm_area_struct *vma, struct page *page,
    1121             :                         struct page *kpage, pte_t orig_pte)
    1122             : {
    1123           0 :         struct mm_struct *mm = vma->vm_mm;
    1124           0 :         pmd_t *pmd;
    1125           0 :         pte_t *ptep;
    1126           0 :         pte_t newpte;
    1127           0 :         spinlock_t *ptl;
    1128           0 :         unsigned long addr;
    1129           0 :         int err = -EFAULT;
    1130           0 :         struct mmu_notifier_range range;
    1131             : 
    1132           0 :         addr = page_address_in_vma(page, vma);
    1133           0 :         if (addr == -EFAULT)
    1134           0 :                 goto out;
    1135             : 
    1136           0 :         pmd = mm_find_pmd(mm, addr);
    1137           0 :         if (!pmd)
    1138           0 :                 goto out;
    1139             : 
    1140           0 :         mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm, addr,
    1141             :                                 addr + PAGE_SIZE);
    1142           0 :         mmu_notifier_invalidate_range_start(&range);
    1143             : 
    1144           0 :         ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
    1145           0 :         if (!pte_same(*ptep, orig_pte)) {
    1146           0 :                 pte_unmap_unlock(ptep, ptl);
    1147           0 :                 goto out_mn;
    1148             :         }
    1149             : 
    1150             :         /*
    1151             :          * No need to check ksm_use_zero_pages here: we can only have a
    1152             :          * zero_page here if ksm_use_zero_pages was enabled already.
    1153             :          */
    1154           0 :         if (!is_zero_pfn(page_to_pfn(kpage))) {
    1155           0 :                 get_page(kpage);
    1156           0 :                 page_add_anon_rmap(kpage, vma, addr, false);
    1157           0 :                 newpte = mk_pte(kpage, vma->vm_page_prot);
    1158             :         } else {
    1159           0 :                 newpte = pte_mkspecial(pfn_pte(page_to_pfn(kpage),
    1160             :                                                vma->vm_page_prot));
    1161             :                 /*
    1162             :                  * We're replacing an anonymous page with a zero page, which is
    1163             :                  * not anonymous. We need to do proper accounting otherwise we
    1164             :                  * will get wrong values in /proc, and a BUG message in dmesg
    1165             :                  * when tearing down the mm.
    1166             :                  */
    1167           0 :                 dec_mm_counter(mm, MM_ANONPAGES);
    1168             :         }
    1169             : 
    1170           0 :         flush_cache_page(vma, addr, pte_pfn(*ptep));
    1171             :         /*
    1172             :          * No need to notify as we are replacing a read only page with another
    1173             :          * read only page with the same content.
    1174             :          *
    1175             :          * See Documentation/vm/mmu_notifier.rst
    1176             :          */
    1177           0 :         ptep_clear_flush(vma, addr, ptep);
    1178           0 :         set_pte_at_notify(mm, addr, ptep, newpte);
    1179             : 
    1180           0 :         page_remove_rmap(page, false);
    1181           0 :         if (!page_mapped(page))
    1182           0 :                 try_to_free_swap(page);
    1183           0 :         put_page(page);
    1184             : 
    1185           0 :         pte_unmap_unlock(ptep, ptl);
    1186           0 :         err = 0;
    1187             : out_mn:
    1188           0 :         mmu_notifier_invalidate_range_end(&range);
    1189           0 : out:
    1190           0 :         return err;
    1191             : }
    1192             : 
    1193             : /*
    1194             :  * try_to_merge_one_page - take two pages and merge them into one
    1195             :  * @vma: the vma that holds the pte pointing to page
    1196             :  * @page: the PageAnon page that we want to replace with kpage
    1197             :  * @kpage: the PageKsm page that we want to map instead of page,
    1198             :  *         or NULL the first time when we want to use page as kpage.
    1199             :  *
    1200             :  * This function returns 0 if the pages were merged, -EFAULT otherwise.
    1201             :  */
    1202           0 : static int try_to_merge_one_page(struct vm_area_struct *vma,
    1203             :                                  struct page *page, struct page *kpage)
    1204             : {
    1205           0 :         pte_t orig_pte = __pte(0);
    1206           0 :         int err = -EFAULT;
    1207             : 
    1208           0 :         if (page == kpage)                      /* ksm page forked */
    1209             :                 return 0;
    1210             : 
    1211           0 :         if (!PageAnon(page))
    1212           0 :                 goto out;
    1213             : 
    1214             :         /*
    1215             :          * We need the page lock to read a stable PageSwapCache in
    1216             :          * write_protect_page().  We use trylock_page() instead of
    1217             :          * lock_page() because we don't want to wait here - we
    1218             :          * prefer to continue scanning and merging different pages,
    1219             :          * then come back to this page when it is unlocked.
    1220             :          */
    1221           0 :         if (!trylock_page(page))
    1222           0 :                 goto out;
    1223             : 
    1224           0 :         if (PageTransCompound(page)) {
    1225           0 :                 if (split_huge_page(page))
    1226           0 :                         goto out_unlock;
    1227             :         }
    1228             : 
    1229             :         /*
    1230             :          * If this anonymous page is mapped only here, its pte may need
    1231             :          * to be write-protected.  If it's mapped elsewhere, all of its
    1232             :          * ptes are necessarily already write-protected.  But in either
    1233             :          * case, we need to lock and check page_count is not raised.
    1234             :          */
    1235           0 :         if (write_protect_page(vma, page, &orig_pte) == 0) {
    1236           0 :                 if (!kpage) {
    1237             :                         /*
    1238             :                          * While we hold page lock, upgrade page from
    1239             :                          * PageAnon+anon_vma to PageKsm+NULL stable_node:
    1240             :                          * stable_tree_insert() will update stable_node.
    1241             :                          */
    1242           0 :                         set_page_stable_node(page, NULL);
    1243           0 :                         mark_page_accessed(page);
    1244             :                         /*
    1245             :                          * Page reclaim just frees a clean page with no dirty
    1246             :                          * ptes: make sure that the ksm page would be swapped.
    1247             :                          */
    1248           0 :                         if (!PageDirty(page))
    1249           0 :                                 SetPageDirty(page);
    1250             :                         err = 0;
    1251           0 :                 } else if (pages_identical(page, kpage))
    1252           0 :                         err = replace_page(vma, page, kpage, orig_pte);
    1253             :         }
    1254             : 
    1255           0 :         if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
    1256           0 :                 munlock_vma_page(page);
    1257           0 :                 if (!PageMlocked(kpage)) {
    1258           0 :                         unlock_page(page);
    1259           0 :                         lock_page(kpage);
    1260           0 :                         mlock_vma_page(kpage);
    1261           0 :                         page = kpage;           /* for final unlock */
    1262             :                 }
    1263             :         }
    1264             : 
    1265           0 : out_unlock:
    1266           0 :         unlock_page(page);
    1267             : out:
    1268             :         return err;
    1269             : }
    1270             : 
    1271             : /*
    1272             :  * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
    1273             :  * but no new kernel page is allocated: kpage must already be a ksm page.
    1274             :  *
    1275             :  * This function returns 0 if the pages were merged, -EFAULT otherwise.
    1276             :  */
    1277           0 : static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
    1278             :                                       struct page *page, struct page *kpage)
    1279             : {
    1280           0 :         struct mm_struct *mm = rmap_item->mm;
    1281           0 :         struct vm_area_struct *vma;
    1282           0 :         int err = -EFAULT;
    1283             : 
    1284           0 :         mmap_read_lock(mm);
    1285           0 :         vma = find_mergeable_vma(mm, rmap_item->address);
    1286           0 :         if (!vma)
    1287           0 :                 goto out;
    1288             : 
    1289           0 :         err = try_to_merge_one_page(vma, page, kpage);
    1290           0 :         if (err)
    1291           0 :                 goto out;
    1292             : 
    1293             :         /* Unstable nid is in union with stable anon_vma: remove first */
    1294           0 :         remove_rmap_item_from_tree(rmap_item);
    1295             : 
    1296             :         /* Must get reference to anon_vma while still holding mmap_lock */
    1297           0 :         rmap_item->anon_vma = vma->anon_vma;
    1298           0 :         get_anon_vma(vma->anon_vma);
    1299           0 : out:
    1300           0 :         mmap_read_unlock(mm);
    1301           0 :         return err;
    1302             : }
    1303             : 
    1304             : /*
    1305             :  * try_to_merge_two_pages - take two identical pages and prepare them
    1306             :  * to be merged into one page.
    1307             :  *
    1308             :  * This function returns the kpage if we successfully merged two identical
    1309             :  * pages into one ksm page, NULL otherwise.
    1310             :  *
    1311             :  * Note that this function upgrades page to ksm page: if one of the pages
    1312             :  * is already a ksm page, try_to_merge_with_ksm_page should be used.
    1313             :  */
    1314           0 : static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
    1315             :                                            struct page *page,
    1316             :                                            struct rmap_item *tree_rmap_item,
    1317             :                                            struct page *tree_page)
    1318             : {
    1319           0 :         int err;
    1320             : 
    1321           0 :         err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
    1322           0 :         if (!err) {
    1323           0 :                 err = try_to_merge_with_ksm_page(tree_rmap_item,
    1324             :                                                         tree_page, page);
    1325             :                 /*
    1326             :                  * If that fails, we have a ksm page with only one pte
    1327             :                  * pointing to it: so break it.
    1328             :                  */
    1329           0 :                 if (err)
    1330           0 :                         break_cow(rmap_item);
    1331             :         }
    1332           0 :         return err ? NULL : page;
    1333             : }
    1334             : 
    1335             : static __always_inline
    1336           0 : bool __is_page_sharing_candidate(struct stable_node *stable_node, int offset)
    1337             : {
    1338           0 :         VM_BUG_ON(stable_node->rmap_hlist_len < 0);
    1339             :         /*
    1340             :          * Check that at least one mapping still exists, otherwise
    1341             :          * there's no much point to merge and share with this
    1342             :          * stable_node, as the underlying tree_page of the other
    1343             :          * sharer is going to be freed soon.
    1344             :          */
    1345           0 :         return stable_node->rmap_hlist_len &&
    1346           0 :                 stable_node->rmap_hlist_len + offset < ksm_max_page_sharing;
    1347             : }
    1348             : 
    1349             : static __always_inline
    1350           0 : bool is_page_sharing_candidate(struct stable_node *stable_node)
    1351             : {
    1352           0 :         return __is_page_sharing_candidate(stable_node, 0);
    1353             : }
    1354             : 
    1355           0 : static struct page *stable_node_dup(struct stable_node **_stable_node_dup,
    1356             :                                     struct stable_node **_stable_node,
    1357             :                                     struct rb_root *root,
    1358             :                                     bool prune_stale_stable_nodes)
    1359             : {
    1360           0 :         struct stable_node *dup, *found = NULL, *stable_node = *_stable_node;
    1361           0 :         struct hlist_node *hlist_safe;
    1362           0 :         struct page *_tree_page, *tree_page = NULL;
    1363           0 :         int nr = 0;
    1364           0 :         int found_rmap_hlist_len;
    1365             : 
    1366           0 :         if (!prune_stale_stable_nodes ||
    1367           0 :             time_before(jiffies, stable_node->chain_prune_time +
    1368             :                         msecs_to_jiffies(
    1369             :                                 ksm_stable_node_chains_prune_millisecs)))
    1370             :                 prune_stale_stable_nodes = false;
    1371             :         else
    1372           0 :                 stable_node->chain_prune_time = jiffies;
    1373             : 
    1374           0 :         hlist_for_each_entry_safe(dup, hlist_safe,
    1375             :                                   &stable_node->hlist, hlist_dup) {
    1376           0 :                 cond_resched();
    1377             :                 /*
    1378             :                  * We must walk all stable_node_dup to prune the stale
    1379             :                  * stable nodes during lookup.
    1380             :                  *
    1381             :                  * get_ksm_page can drop the nodes from the
    1382             :                  * stable_node->hlist if they point to freed pages
    1383             :                  * (that's why we do a _safe walk). The "dup"
    1384             :                  * stable_node parameter itself will be freed from
    1385             :                  * under us if it returns NULL.
    1386             :                  */
    1387           0 :                 _tree_page = get_ksm_page(dup, GET_KSM_PAGE_NOLOCK);
    1388           0 :                 if (!_tree_page)
    1389           0 :                         continue;
    1390           0 :                 nr += 1;
    1391           0 :                 if (is_page_sharing_candidate(dup)) {
    1392           0 :                         if (!found ||
    1393             :                             dup->rmap_hlist_len > found_rmap_hlist_len) {
    1394           0 :                                 if (found)
    1395           0 :                                         put_page(tree_page);
    1396           0 :                                 found = dup;
    1397           0 :                                 found_rmap_hlist_len = found->rmap_hlist_len;
    1398           0 :                                 tree_page = _tree_page;
    1399             : 
    1400             :                                 /* skip put_page for found dup */
    1401           0 :                                 if (!prune_stale_stable_nodes)
    1402             :                                         break;
    1403           0 :                                 continue;
    1404             :                         }
    1405             :                 }
    1406           0 :                 put_page(_tree_page);
    1407             :         }
    1408             : 
    1409           0 :         if (found) {
    1410             :                 /*
    1411             :                  * nr is counting all dups in the chain only if
    1412             :                  * prune_stale_stable_nodes is true, otherwise we may
    1413             :                  * break the loop at nr == 1 even if there are
    1414             :                  * multiple entries.
    1415             :                  */
    1416           0 :                 if (prune_stale_stable_nodes && nr == 1) {
    1417             :                         /*
    1418             :                          * If there's not just one entry it would
    1419             :                          * corrupt memory, better BUG_ON. In KSM
    1420             :                          * context with no lock held it's not even
    1421             :                          * fatal.
    1422             :                          */
    1423           0 :                         BUG_ON(stable_node->hlist.first->next);
    1424             : 
    1425             :                         /*
    1426             :                          * There's just one entry and it is below the
    1427             :                          * deduplication limit so drop the chain.
    1428             :                          */
    1429           0 :                         rb_replace_node(&stable_node->node, &found->node,
    1430             :                                         root);
    1431           0 :                         free_stable_node(stable_node);
    1432           0 :                         ksm_stable_node_chains--;
    1433           0 :                         ksm_stable_node_dups--;
    1434             :                         /*
    1435             :                          * NOTE: the caller depends on the stable_node
    1436             :                          * to be equal to stable_node_dup if the chain
    1437             :                          * was collapsed.
    1438             :                          */
    1439           0 :                         *_stable_node = found;
    1440             :                         /*
    1441             :                          * Just for robustneess as stable_node is
    1442             :                          * otherwise left as a stable pointer, the
    1443             :                          * compiler shall optimize it away at build
    1444             :                          * time.
    1445             :                          */
    1446           0 :                         stable_node = NULL;
    1447           0 :                 } else if (stable_node->hlist.first != &found->hlist_dup &&
    1448           0 :                            __is_page_sharing_candidate(found, 1)) {
    1449             :                         /*
    1450             :                          * If the found stable_node dup can accept one
    1451             :                          * more future merge (in addition to the one
    1452             :                          * that is underway) and is not at the head of
    1453             :                          * the chain, put it there so next search will
    1454             :                          * be quicker in the !prune_stale_stable_nodes
    1455             :                          * case.
    1456             :                          *
    1457             :                          * NOTE: it would be inaccurate to use nr > 1
    1458             :                          * instead of checking the hlist.first pointer
    1459             :                          * directly, because in the
    1460             :                          * prune_stale_stable_nodes case "nr" isn't
    1461             :                          * the position of the found dup in the chain,
    1462             :                          * but the total number of dups in the chain.
    1463             :                          */
    1464           0 :                         hlist_del(&found->hlist_dup);
    1465           0 :                         hlist_add_head(&found->hlist_dup,
    1466             :                                        &stable_node->hlist);
    1467             :                 }
    1468             :         }
    1469             : 
    1470           0 :         *_stable_node_dup = found;
    1471           0 :         return tree_page;
    1472             : }
    1473             : 
    1474           0 : static struct stable_node *stable_node_dup_any(struct stable_node *stable_node,
    1475             :                                                struct rb_root *root)
    1476             : {
    1477           0 :         if (!is_stable_node_chain(stable_node))
    1478             :                 return stable_node;
    1479           0 :         if (hlist_empty(&stable_node->hlist)) {
    1480           0 :                 free_stable_node_chain(stable_node, root);
    1481           0 :                 return NULL;
    1482             :         }
    1483           0 :         return hlist_entry(stable_node->hlist.first,
    1484             :                            typeof(*stable_node), hlist_dup);
    1485             : }
    1486             : 
    1487             : /*
    1488             :  * Like for get_ksm_page, this function can free the *_stable_node and
    1489             :  * *_stable_node_dup if the returned tree_page is NULL.
    1490             :  *
    1491             :  * It can also free and overwrite *_stable_node with the found
    1492             :  * stable_node_dup if the chain is collapsed (in which case
    1493             :  * *_stable_node will be equal to *_stable_node_dup like if the chain
    1494             :  * never existed). It's up to the caller to verify tree_page is not
    1495             :  * NULL before dereferencing *_stable_node or *_stable_node_dup.
    1496             :  *
    1497             :  * *_stable_node_dup is really a second output parameter of this
    1498             :  * function and will be overwritten in all cases, the caller doesn't
    1499             :  * need to initialize it.
    1500             :  */
    1501           0 : static struct page *__stable_node_chain(struct stable_node **_stable_node_dup,
    1502             :                                         struct stable_node **_stable_node,
    1503             :                                         struct rb_root *root,
    1504             :                                         bool prune_stale_stable_nodes)
    1505             : {
    1506           0 :         struct stable_node *stable_node = *_stable_node;
    1507           0 :         if (!is_stable_node_chain(stable_node)) {
    1508           0 :                 if (is_page_sharing_candidate(stable_node)) {
    1509           0 :                         *_stable_node_dup = stable_node;
    1510           0 :                         return get_ksm_page(stable_node, GET_KSM_PAGE_NOLOCK);
    1511             :                 }
    1512             :                 /*
    1513             :                  * _stable_node_dup set to NULL means the stable_node
    1514             :                  * reached the ksm_max_page_sharing limit.
    1515             :                  */
    1516           0 :                 *_stable_node_dup = NULL;
    1517           0 :                 return NULL;
    1518             :         }
    1519           0 :         return stable_node_dup(_stable_node_dup, _stable_node, root,
    1520             :                                prune_stale_stable_nodes);
    1521             : }
    1522             : 
    1523           0 : static __always_inline struct page *chain_prune(struct stable_node **s_n_d,
    1524             :                                                 struct stable_node **s_n,
    1525             :                                                 struct rb_root *root)
    1526             : {
    1527           0 :         return __stable_node_chain(s_n_d, s_n, root, true);
    1528             : }
    1529             : 
    1530           0 : static __always_inline struct page *chain(struct stable_node **s_n_d,
    1531             :                                           struct stable_node *s_n,
    1532             :                                           struct rb_root *root)
    1533             : {
    1534           0 :         struct stable_node *old_stable_node = s_n;
    1535           0 :         struct page *tree_page;
    1536             : 
    1537           0 :         tree_page = __stable_node_chain(s_n_d, &s_n, root, false);
    1538             :         /* not pruning dups so s_n cannot have changed */
    1539           0 :         VM_BUG_ON(s_n != old_stable_node);
    1540           0 :         return tree_page;
    1541             : }
    1542             : 
    1543             : /*
    1544             :  * stable_tree_search - search for page inside the stable tree
    1545             :  *
    1546             :  * This function checks if there is a page inside the stable tree
    1547             :  * with identical content to the page that we are scanning right now.
    1548             :  *
    1549             :  * This function returns the stable tree node of identical content if found,
    1550             :  * NULL otherwise.
    1551             :  */
    1552           0 : static struct page *stable_tree_search(struct page *page)
    1553             : {
    1554           0 :         int nid;
    1555           0 :         struct rb_root *root;
    1556           0 :         struct rb_node **new;
    1557           0 :         struct rb_node *parent;
    1558           0 :         struct stable_node *stable_node, *stable_node_dup, *stable_node_any;
    1559           0 :         struct stable_node *page_node;
    1560             : 
    1561           0 :         page_node = page_stable_node(page);
    1562           0 :         if (page_node && page_node->head != &migrate_nodes) {
    1563             :                 /* ksm page forked */
    1564           0 :                 get_page(page);
    1565           0 :                 return page;
    1566             :         }
    1567             : 
    1568           0 :         nid = get_kpfn_nid(page_to_pfn(page));
    1569           0 :         root = root_stable_tree + nid;
    1570             : again:
    1571           0 :         new = &root->rb_node;
    1572           0 :         parent = NULL;
    1573             : 
    1574           0 :         while (*new) {
    1575           0 :                 struct page *tree_page;
    1576           0 :                 int ret;
    1577             : 
    1578           0 :                 cond_resched();
    1579           0 :                 stable_node = rb_entry(*new, struct stable_node, node);
    1580           0 :                 stable_node_any = NULL;
    1581           0 :                 tree_page = chain_prune(&stable_node_dup, &stable_node, root);
    1582             :                 /*
    1583             :                  * NOTE: stable_node may have been freed by
    1584             :                  * chain_prune() if the returned stable_node_dup is
    1585             :                  * not NULL. stable_node_dup may have been inserted in
    1586             :                  * the rbtree instead as a regular stable_node (in
    1587             :                  * order to collapse the stable_node chain if a single
    1588             :                  * stable_node dup was found in it). In such case the
    1589             :                  * stable_node is overwritten by the calleee to point
    1590             :                  * to the stable_node_dup that was collapsed in the
    1591             :                  * stable rbtree and stable_node will be equal to
    1592             :                  * stable_node_dup like if the chain never existed.
    1593             :                  */
    1594           0 :                 if (!stable_node_dup) {
    1595             :                         /*
    1596             :                          * Either all stable_node dups were full in
    1597             :                          * this stable_node chain, or this chain was
    1598             :                          * empty and should be rb_erased.
    1599             :                          */
    1600           0 :                         stable_node_any = stable_node_dup_any(stable_node,
    1601             :                                                               root);
    1602           0 :                         if (!stable_node_any) {
    1603             :                                 /* rb_erase just run */
    1604           0 :                                 goto again;
    1605             :                         }
    1606             :                         /*
    1607             :                          * Take any of the stable_node dups page of
    1608             :                          * this stable_node chain to let the tree walk
    1609             :                          * continue. All KSM pages belonging to the
    1610             :                          * stable_node dups in a stable_node chain
    1611             :                          * have the same content and they're
    1612             :                          * write protected at all times. Any will work
    1613             :                          * fine to continue the walk.
    1614             :                          */
    1615           0 :                         tree_page = get_ksm_page(stable_node_any,
    1616             :                                                  GET_KSM_PAGE_NOLOCK);
    1617             :                 }
    1618           0 :                 VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
    1619           0 :                 if (!tree_page) {
    1620             :                         /*
    1621             :                          * If we walked over a stale stable_node,
    1622             :                          * get_ksm_page() will call rb_erase() and it
    1623             :                          * may rebalance the tree from under us. So
    1624             :                          * restart the search from scratch. Returning
    1625             :                          * NULL would be safe too, but we'd generate
    1626             :                          * false negative insertions just because some
    1627             :                          * stable_node was stale.
    1628             :                          */
    1629           0 :                         goto again;
    1630             :                 }
    1631             : 
    1632           0 :                 ret = memcmp_pages(page, tree_page);
    1633           0 :                 put_page(tree_page);
    1634             : 
    1635           0 :                 parent = *new;
    1636           0 :                 if (ret < 0)
    1637           0 :                         new = &parent->rb_left;
    1638           0 :                 else if (ret > 0)
    1639           0 :                         new = &parent->rb_right;
    1640             :                 else {
    1641           0 :                         if (page_node) {
    1642           0 :                                 VM_BUG_ON(page_node->head != &migrate_nodes);
    1643             :                                 /*
    1644             :                                  * Test if the migrated page should be merged
    1645             :                                  * into a stable node dup. If the mapcount is
    1646             :                                  * 1 we can migrate it with another KSM page
    1647             :                                  * without adding it to the chain.
    1648             :                                  */
    1649           0 :                                 if (page_mapcount(page) > 1)
    1650           0 :                                         goto chain_append;
    1651             :                         }
    1652             : 
    1653           0 :                         if (!stable_node_dup) {
    1654             :                                 /*
    1655             :                                  * If the stable_node is a chain and
    1656             :                                  * we got a payload match in memcmp
    1657             :                                  * but we cannot merge the scanned
    1658             :                                  * page in any of the existing
    1659             :                                  * stable_node dups because they're
    1660             :                                  * all full, we need to wait the
    1661             :                                  * scanned page to find itself a match
    1662             :                                  * in the unstable tree to create a
    1663             :                                  * brand new KSM page to add later to
    1664             :                                  * the dups of this stable_node.
    1665             :                                  */
    1666             :                                 return NULL;
    1667             :                         }
    1668             : 
    1669             :                         /*
    1670             :                          * Lock and unlock the stable_node's page (which
    1671             :                          * might already have been migrated) so that page
    1672             :                          * migration is sure to notice its raised count.
    1673             :                          * It would be more elegant to return stable_node
    1674             :                          * than kpage, but that involves more changes.
    1675             :                          */
    1676           0 :                         tree_page = get_ksm_page(stable_node_dup,
    1677             :                                                  GET_KSM_PAGE_TRYLOCK);
    1678             : 
    1679           0 :                         if (PTR_ERR(tree_page) == -EBUSY)
    1680           0 :                                 return ERR_PTR(-EBUSY);
    1681             : 
    1682           0 :                         if (unlikely(!tree_page))
    1683             :                                 /*
    1684             :                                  * The tree may have been rebalanced,
    1685             :                                  * so re-evaluate parent and new.
    1686             :                                  */
    1687           0 :                                 goto again;
    1688           0 :                         unlock_page(tree_page);
    1689             : 
    1690           0 :                         if (get_kpfn_nid(stable_node_dup->kpfn) !=
    1691           0 :                             NUMA(stable_node_dup->nid)) {
    1692           0 :                                 put_page(tree_page);
    1693           0 :                                 goto replace;
    1694             :                         }
    1695             :                         return tree_page;
    1696             :                 }
    1697             :         }
    1698             : 
    1699           0 :         if (!page_node)
    1700             :                 return NULL;
    1701             : 
    1702           0 :         list_del(&page_node->list);
    1703           0 :         DO_NUMA(page_node->nid = nid);
    1704           0 :         rb_link_node(&page_node->node, parent, new);
    1705           0 :         rb_insert_color(&page_node->node, root);
    1706           0 : out:
    1707           0 :         if (is_page_sharing_candidate(page_node)) {
    1708           0 :                 get_page(page);
    1709           0 :                 return page;
    1710             :         } else
    1711             :                 return NULL;
    1712             : 
    1713           0 : replace:
    1714             :         /*
    1715             :          * If stable_node was a chain and chain_prune collapsed it,
    1716             :          * stable_node has been updated to be the new regular
    1717             :          * stable_node. A collapse of the chain is indistinguishable
    1718             :          * from the case there was no chain in the stable
    1719             :          * rbtree. Otherwise stable_node is the chain and
    1720             :          * stable_node_dup is the dup to replace.
    1721             :          */
    1722           0 :         if (stable_node_dup == stable_node) {
    1723           0 :                 VM_BUG_ON(is_stable_node_chain(stable_node_dup));
    1724           0 :                 VM_BUG_ON(is_stable_node_dup(stable_node_dup));
    1725             :                 /* there is no chain */
    1726           0 :                 if (page_node) {
    1727           0 :                         VM_BUG_ON(page_node->head != &migrate_nodes);
    1728           0 :                         list_del(&page_node->list);
    1729           0 :                         DO_NUMA(page_node->nid = nid);
    1730           0 :                         rb_replace_node(&stable_node_dup->node,
    1731             :                                         &page_node->node,
    1732             :                                         root);
    1733           0 :                         if (is_page_sharing_candidate(page_node))
    1734           0 :                                 get_page(page);
    1735             :                         else
    1736             :                                 page = NULL;
    1737             :                 } else {
    1738           0 :                         rb_erase(&stable_node_dup->node, root);
    1739           0 :                         page = NULL;
    1740             :                 }
    1741             :         } else {
    1742           0 :                 VM_BUG_ON(!is_stable_node_chain(stable_node));
    1743           0 :                 __stable_node_dup_del(stable_node_dup);
    1744           0 :                 if (page_node) {
    1745           0 :                         VM_BUG_ON(page_node->head != &migrate_nodes);
    1746           0 :                         list_del(&page_node->list);
    1747           0 :                         DO_NUMA(page_node->nid = nid);
    1748           0 :                         stable_node_chain_add_dup(page_node, stable_node);
    1749           0 :                         if (is_page_sharing_candidate(page_node))
    1750           0 :                                 get_page(page);
    1751             :                         else
    1752             :                                 page = NULL;
    1753             :                 } else {
    1754             :                         page = NULL;
    1755             :                 }
    1756             :         }
    1757           0 :         stable_node_dup->head = &migrate_nodes;
    1758           0 :         list_add(&stable_node_dup->list, stable_node_dup->head);
    1759           0 :         return page;
    1760             : 
    1761           0 : chain_append:
    1762             :         /* stable_node_dup could be null if it reached the limit */
    1763           0 :         if (!stable_node_dup)
    1764           0 :                 stable_node_dup = stable_node_any;
    1765             :         /*
    1766             :          * If stable_node was a chain and chain_prune collapsed it,
    1767             :          * stable_node has been updated to be the new regular
    1768             :          * stable_node. A collapse of the chain is indistinguishable
    1769             :          * from the case there was no chain in the stable
    1770             :          * rbtree. Otherwise stable_node is the chain and
    1771             :          * stable_node_dup is the dup to replace.
    1772             :          */
    1773           0 :         if (stable_node_dup == stable_node) {
    1774           0 :                 VM_BUG_ON(is_stable_node_chain(stable_node_dup));
    1775           0 :                 VM_BUG_ON(is_stable_node_dup(stable_node_dup));
    1776             :                 /* chain is missing so create it */
    1777           0 :                 stable_node = alloc_stable_node_chain(stable_node_dup,
    1778             :                                                       root);
    1779           0 :                 if (!stable_node)
    1780             :                         return NULL;
    1781             :         }
    1782             :         /*
    1783             :          * Add this stable_node dup that was
    1784             :          * migrated to the stable_node chain
    1785             :          * of the current nid for this page
    1786             :          * content.
    1787             :          */
    1788           0 :         VM_BUG_ON(!is_stable_node_chain(stable_node));
    1789           0 :         VM_BUG_ON(!is_stable_node_dup(stable_node_dup));
    1790           0 :         VM_BUG_ON(page_node->head != &migrate_nodes);
    1791           0 :         list_del(&page_node->list);
    1792           0 :         DO_NUMA(page_node->nid = nid);
    1793           0 :         stable_node_chain_add_dup(page_node, stable_node);
    1794           0 :         goto out;
    1795             : }
    1796             : 
    1797             : /*
    1798             :  * stable_tree_insert - insert stable tree node pointing to new ksm page
    1799             :  * into the stable tree.
    1800             :  *
    1801             :  * This function returns the stable tree node just allocated on success,
    1802             :  * NULL otherwise.
    1803             :  */
    1804           0 : static struct stable_node *stable_tree_insert(struct page *kpage)
    1805             : {
    1806           0 :         int nid;
    1807           0 :         unsigned long kpfn;
    1808           0 :         struct rb_root *root;
    1809           0 :         struct rb_node **new;
    1810           0 :         struct rb_node *parent;
    1811           0 :         struct stable_node *stable_node, *stable_node_dup, *stable_node_any;
    1812           0 :         bool need_chain = false;
    1813             : 
    1814           0 :         kpfn = page_to_pfn(kpage);
    1815           0 :         nid = get_kpfn_nid(kpfn);
    1816           0 :         root = root_stable_tree + nid;
    1817             : again:
    1818           0 :         parent = NULL;
    1819           0 :         new = &root->rb_node;
    1820             : 
    1821           0 :         while (*new) {
    1822           0 :                 struct page *tree_page;
    1823           0 :                 int ret;
    1824             : 
    1825           0 :                 cond_resched();
    1826           0 :                 stable_node = rb_entry(*new, struct stable_node, node);
    1827           0 :                 stable_node_any = NULL;
    1828           0 :                 tree_page = chain(&stable_node_dup, stable_node, root);
    1829           0 :                 if (!stable_node_dup) {
    1830             :                         /*
    1831             :                          * Either all stable_node dups were full in
    1832             :                          * this stable_node chain, or this chain was
    1833             :                          * empty and should be rb_erased.
    1834             :                          */
    1835           0 :                         stable_node_any = stable_node_dup_any(stable_node,
    1836             :                                                               root);
    1837           0 :                         if (!stable_node_any) {
    1838             :                                 /* rb_erase just run */
    1839           0 :                                 goto again;
    1840             :                         }
    1841             :                         /*
    1842             :                          * Take any of the stable_node dups page of
    1843             :                          * this stable_node chain to let the tree walk
    1844             :                          * continue. All KSM pages belonging to the
    1845             :                          * stable_node dups in a stable_node chain
    1846             :                          * have the same content and they're
    1847             :                          * write protected at all times. Any will work
    1848             :                          * fine to continue the walk.
    1849             :                          */
    1850           0 :                         tree_page = get_ksm_page(stable_node_any,
    1851             :                                                  GET_KSM_PAGE_NOLOCK);
    1852             :                 }
    1853           0 :                 VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
    1854           0 :                 if (!tree_page) {
    1855             :                         /*
    1856             :                          * If we walked over a stale stable_node,
    1857             :                          * get_ksm_page() will call rb_erase() and it
    1858             :                          * may rebalance the tree from under us. So
    1859             :                          * restart the search from scratch. Returning
    1860             :                          * NULL would be safe too, but we'd generate
    1861             :                          * false negative insertions just because some
    1862             :                          * stable_node was stale.
    1863             :                          */
    1864           0 :                         goto again;
    1865             :                 }
    1866             : 
    1867           0 :                 ret = memcmp_pages(kpage, tree_page);
    1868           0 :                 put_page(tree_page);
    1869             : 
    1870           0 :                 parent = *new;
    1871           0 :                 if (ret < 0)
    1872           0 :                         new = &parent->rb_left;
    1873           0 :                 else if (ret > 0)
    1874           0 :                         new = &parent->rb_right;
    1875             :                 else {
    1876             :                         need_chain = true;
    1877             :                         break;
    1878             :                 }
    1879             :         }
    1880             : 
    1881           0 :         stable_node_dup = alloc_stable_node();
    1882           0 :         if (!stable_node_dup)
    1883             :                 return NULL;
    1884             : 
    1885           0 :         INIT_HLIST_HEAD(&stable_node_dup->hlist);
    1886           0 :         stable_node_dup->kpfn = kpfn;
    1887           0 :         set_page_stable_node(kpage, stable_node_dup);
    1888           0 :         stable_node_dup->rmap_hlist_len = 0;
    1889           0 :         DO_NUMA(stable_node_dup->nid = nid);
    1890           0 :         if (!need_chain) {
    1891           0 :                 rb_link_node(&stable_node_dup->node, parent, new);
    1892           0 :                 rb_insert_color(&stable_node_dup->node, root);
    1893             :         } else {
    1894           0 :                 if (!is_stable_node_chain(stable_node)) {
    1895           0 :                         struct stable_node *orig = stable_node;
    1896             :                         /* chain is missing so create it */
    1897           0 :                         stable_node = alloc_stable_node_chain(orig, root);
    1898           0 :                         if (!stable_node) {
    1899           0 :                                 free_stable_node(stable_node_dup);
    1900           0 :                                 return NULL;
    1901             :                         }
    1902             :                 }
    1903           0 :                 stable_node_chain_add_dup(stable_node_dup, stable_node);
    1904             :         }
    1905             : 
    1906           0 :         return stable_node_dup;
    1907             : }
    1908             : 
    1909             : /*
    1910             :  * unstable_tree_search_insert - search for identical page,
    1911             :  * else insert rmap_item into the unstable tree.
    1912             :  *
    1913             :  * This function searches for a page in the unstable tree identical to the
    1914             :  * page currently being scanned; and if no identical page is found in the
    1915             :  * tree, we insert rmap_item as a new object into the unstable tree.
    1916             :  *
    1917             :  * This function returns pointer to rmap_item found to be identical
    1918             :  * to the currently scanned page, NULL otherwise.
    1919             :  *
    1920             :  * This function does both searching and inserting, because they share
    1921             :  * the same walking algorithm in an rbtree.
    1922             :  */
    1923             : static
    1924           0 : struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
    1925             :                                               struct page *page,
    1926             :                                               struct page **tree_pagep)
    1927             : {
    1928           0 :         struct rb_node **new;
    1929           0 :         struct rb_root *root;
    1930           0 :         struct rb_node *parent = NULL;
    1931           0 :         int nid;
    1932             : 
    1933           0 :         nid = get_kpfn_nid(page_to_pfn(page));
    1934           0 :         root = root_unstable_tree + nid;
    1935           0 :         new = &root->rb_node;
    1936             : 
    1937           0 :         while (*new) {
    1938           0 :                 struct rmap_item *tree_rmap_item;
    1939           0 :                 struct page *tree_page;
    1940           0 :                 int ret;
    1941             : 
    1942           0 :                 cond_resched();
    1943           0 :                 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
    1944           0 :                 tree_page = get_mergeable_page(tree_rmap_item);
    1945           0 :                 if (!tree_page)
    1946             :                         return NULL;
    1947             : 
    1948             :                 /*
    1949             :                  * Don't substitute a ksm page for a forked page.
    1950             :                  */
    1951           0 :                 if (page == tree_page) {
    1952           0 :                         put_page(tree_page);
    1953           0 :                         return NULL;
    1954             :                 }
    1955             : 
    1956           0 :                 ret = memcmp_pages(page, tree_page);
    1957             : 
    1958           0 :                 parent = *new;
    1959           0 :                 if (ret < 0) {
    1960           0 :                         put_page(tree_page);
    1961           0 :                         new = &parent->rb_left;
    1962           0 :                 } else if (ret > 0) {
    1963           0 :                         put_page(tree_page);
    1964           0 :                         new = &parent->rb_right;
    1965           0 :                 } else if (!ksm_merge_across_nodes &&
    1966           0 :                            page_to_nid(tree_page) != nid) {
    1967             :                         /*
    1968             :                          * If tree_page has been migrated to another NUMA node,
    1969             :                          * it will be flushed out and put in the right unstable
    1970             :                          * tree next time: only merge with it when across_nodes.
    1971             :                          */
    1972           0 :                         put_page(tree_page);
    1973           0 :                         return NULL;
    1974             :                 } else {
    1975           0 :                         *tree_pagep = tree_page;
    1976           0 :                         return tree_rmap_item;
    1977             :                 }
    1978             :         }
    1979             : 
    1980           0 :         rmap_item->address |= UNSTABLE_FLAG;
    1981           0 :         rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
    1982           0 :         DO_NUMA(rmap_item->nid = nid);
    1983           0 :         rb_link_node(&rmap_item->node, parent, new);
    1984           0 :         rb_insert_color(&rmap_item->node, root);
    1985             : 
    1986           0 :         ksm_pages_unshared++;
    1987           0 :         return NULL;
    1988             : }
    1989             : 
    1990             : /*
    1991             :  * stable_tree_append - add another rmap_item to the linked list of
    1992             :  * rmap_items hanging off a given node of the stable tree, all sharing
    1993             :  * the same ksm page.
    1994             :  */
    1995           0 : static void stable_tree_append(struct rmap_item *rmap_item,
    1996             :                                struct stable_node *stable_node,
    1997             :                                bool max_page_sharing_bypass)
    1998             : {
    1999             :         /*
    2000             :          * rmap won't find this mapping if we don't insert the
    2001             :          * rmap_item in the right stable_node
    2002             :          * duplicate. page_migration could break later if rmap breaks,
    2003             :          * so we can as well crash here. We really need to check for
    2004             :          * rmap_hlist_len == STABLE_NODE_CHAIN, but we can as well check
    2005             :          * for other negative values as an underflow if detected here
    2006             :          * for the first time (and not when decreasing rmap_hlist_len)
    2007             :          * would be sign of memory corruption in the stable_node.
    2008             :          */
    2009           0 :         BUG_ON(stable_node->rmap_hlist_len < 0);
    2010             : 
    2011           0 :         stable_node->rmap_hlist_len++;
    2012           0 :         if (!max_page_sharing_bypass)
    2013             :                 /* possibly non fatal but unexpected overflow, only warn */
    2014           0 :                 WARN_ON_ONCE(stable_node->rmap_hlist_len >
    2015             :                              ksm_max_page_sharing);
    2016             : 
    2017           0 :         rmap_item->head = stable_node;
    2018           0 :         rmap_item->address |= STABLE_FLAG;
    2019           0 :         hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
    2020             : 
    2021           0 :         if (rmap_item->hlist.next)
    2022           0 :                 ksm_pages_sharing++;
    2023             :         else
    2024           0 :                 ksm_pages_shared++;
    2025           0 : }
    2026             : 
    2027             : /*
    2028             :  * cmp_and_merge_page - first see if page can be merged into the stable tree;
    2029             :  * if not, compare checksum to previous and if it's the same, see if page can
    2030             :  * be inserted into the unstable tree, or merged with a page already there and
    2031             :  * both transferred to the stable tree.
    2032             :  *
    2033             :  * @page: the page that we are searching identical page to.
    2034             :  * @rmap_item: the reverse mapping into the virtual address of this page
    2035             :  */
    2036           0 : static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
    2037             : {
    2038           0 :         struct mm_struct *mm = rmap_item->mm;
    2039           0 :         struct rmap_item *tree_rmap_item;
    2040           0 :         struct page *tree_page = NULL;
    2041           0 :         struct stable_node *stable_node;
    2042           0 :         struct page *kpage;
    2043           0 :         unsigned int checksum;
    2044           0 :         int err;
    2045           0 :         bool max_page_sharing_bypass = false;
    2046             : 
    2047           0 :         stable_node = page_stable_node(page);
    2048           0 :         if (stable_node) {
    2049           0 :                 if (stable_node->head != &migrate_nodes &&
    2050           0 :                     get_kpfn_nid(READ_ONCE(stable_node->kpfn)) !=
    2051           0 :                     NUMA(stable_node->nid)) {
    2052           0 :                         stable_node_dup_del(stable_node);
    2053           0 :                         stable_node->head = &migrate_nodes;
    2054           0 :                         list_add(&stable_node->list, stable_node->head);
    2055             :                 }
    2056           0 :                 if (stable_node->head != &migrate_nodes &&
    2057           0 :                     rmap_item->head == stable_node)
    2058           0 :                         return;
    2059             :                 /*
    2060             :                  * If it's a KSM fork, allow it to go over the sharing limit
    2061             :                  * without warnings.
    2062             :                  */
    2063           0 :                 if (!is_page_sharing_candidate(stable_node))
    2064           0 :                         max_page_sharing_bypass = true;
    2065             :         }
    2066             : 
    2067             :         /* We first start with searching the page inside the stable tree */
    2068           0 :         kpage = stable_tree_search(page);
    2069           0 :         if (kpage == page && rmap_item->head == stable_node) {
    2070           0 :                 put_page(kpage);
    2071           0 :                 return;
    2072             :         }
    2073             : 
    2074           0 :         remove_rmap_item_from_tree(rmap_item);
    2075             : 
    2076           0 :         if (kpage) {
    2077           0 :                 if (PTR_ERR(kpage) == -EBUSY)
    2078             :                         return;
    2079             : 
    2080           0 :                 err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
    2081           0 :                 if (!err) {
    2082             :                         /*
    2083             :                          * The page was successfully merged:
    2084             :                          * add its rmap_item to the stable tree.
    2085             :                          */
    2086           0 :                         lock_page(kpage);
    2087           0 :                         stable_tree_append(rmap_item, page_stable_node(kpage),
    2088             :                                            max_page_sharing_bypass);
    2089           0 :                         unlock_page(kpage);
    2090             :                 }
    2091           0 :                 put_page(kpage);
    2092           0 :                 return;
    2093             :         }
    2094             : 
    2095             :         /*
    2096             :          * If the hash value of the page has changed from the last time
    2097             :          * we calculated it, this page is changing frequently: therefore we
    2098             :          * don't want to insert it in the unstable tree, and we don't want
    2099             :          * to waste our time searching for something identical to it there.
    2100             :          */
    2101           0 :         checksum = calc_checksum(page);
    2102           0 :         if (rmap_item->oldchecksum != checksum) {
    2103           0 :                 rmap_item->oldchecksum = checksum;
    2104           0 :                 return;
    2105             :         }
    2106             : 
    2107             :         /*
    2108             :          * Same checksum as an empty page. We attempt to merge it with the
    2109             :          * appropriate zero page if the user enabled this via sysfs.
    2110             :          */
    2111           0 :         if (ksm_use_zero_pages && (checksum == zero_checksum)) {
    2112           0 :                 struct vm_area_struct *vma;
    2113             : 
    2114           0 :                 mmap_read_lock(mm);
    2115           0 :                 vma = find_mergeable_vma(mm, rmap_item->address);
    2116           0 :                 if (vma) {
    2117           0 :                         err = try_to_merge_one_page(vma, page,
    2118           0 :                                         ZERO_PAGE(rmap_item->address));
    2119             :                 } else {
    2120             :                         /*
    2121             :                          * If the vma is out of date, we do not need to
    2122             :                          * continue.
    2123             :                          */
    2124             :                         err = 0;
    2125             :                 }
    2126           0 :                 mmap_read_unlock(mm);
    2127             :                 /*
    2128             :                  * In case of failure, the page was not really empty, so we
    2129             :                  * need to continue. Otherwise we're done.
    2130             :                  */
    2131           0 :                 if (!err)
    2132             :                         return;
    2133             :         }
    2134           0 :         tree_rmap_item =
    2135           0 :                 unstable_tree_search_insert(rmap_item, page, &tree_page);
    2136           0 :         if (tree_rmap_item) {
    2137           0 :                 bool split;
    2138             : 
    2139           0 :                 kpage = try_to_merge_two_pages(rmap_item, page,
    2140             :                                                 tree_rmap_item, tree_page);
    2141             :                 /*
    2142             :                  * If both pages we tried to merge belong to the same compound
    2143             :                  * page, then we actually ended up increasing the reference
    2144             :                  * count of the same compound page twice, and split_huge_page
    2145             :                  * failed.
    2146             :                  * Here we set a flag if that happened, and we use it later to
    2147             :                  * try split_huge_page again. Since we call put_page right
    2148             :                  * afterwards, the reference count will be correct and
    2149             :                  * split_huge_page should succeed.
    2150             :                  */
    2151           0 :                 split = PageTransCompound(page)
    2152           0 :                         && compound_head(page) == compound_head(tree_page);
    2153           0 :                 put_page(tree_page);
    2154           0 :                 if (kpage) {
    2155             :                         /*
    2156             :                          * The pages were successfully merged: insert new
    2157             :                          * node in the stable tree and add both rmap_items.
    2158             :                          */
    2159           0 :                         lock_page(kpage);
    2160           0 :                         stable_node = stable_tree_insert(kpage);
    2161           0 :                         if (stable_node) {
    2162           0 :                                 stable_tree_append(tree_rmap_item, stable_node,
    2163             :                                                    false);
    2164           0 :                                 stable_tree_append(rmap_item, stable_node,
    2165             :                                                    false);
    2166             :                         }
    2167           0 :                         unlock_page(kpage);
    2168             : 
    2169             :                         /*
    2170             :                          * If we fail to insert the page into the stable tree,
    2171             :                          * we will have 2 virtual addresses that are pointing
    2172             :                          * to a ksm page left outside the stable tree,
    2173             :                          * in which case we need to break_cow on both.
    2174             :                          */
    2175           0 :                         if (!stable_node) {
    2176           0 :                                 break_cow(tree_rmap_item);
    2177           0 :                                 break_cow(rmap_item);
    2178             :                         }
    2179           0 :                 } else if (split) {
    2180             :                         /*
    2181             :                          * We are here if we tried to merge two pages and
    2182             :                          * failed because they both belonged to the same
    2183             :                          * compound page. We will split the page now, but no
    2184             :                          * merging will take place.
    2185             :                          * We do not want to add the cost of a full lock; if
    2186             :                          * the page is locked, it is better to skip it and
    2187             :                          * perhaps try again later.
    2188             :                          */
    2189           0 :                         if (!trylock_page(page))
    2190             :                                 return;
    2191           0 :                         split_huge_page(page);
    2192           0 :                         unlock_page(page);
    2193             :                 }
    2194             :         }
    2195             : }
    2196             : 
    2197           0 : static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
    2198             :                                             struct rmap_item **rmap_list,
    2199             :                                             unsigned long addr)
    2200             : {
    2201           0 :         struct rmap_item *rmap_item;
    2202             : 
    2203           0 :         while (*rmap_list) {
    2204           0 :                 rmap_item = *rmap_list;
    2205           0 :                 if ((rmap_item->address & PAGE_MASK) == addr)
    2206           0 :                         return rmap_item;
    2207           0 :                 if (rmap_item->address > addr)
    2208             :                         break;
    2209           0 :                 *rmap_list = rmap_item->rmap_list;
    2210           0 :                 remove_rmap_item_from_tree(rmap_item);
    2211           0 :                 free_rmap_item(rmap_item);
    2212             :         }
    2213             : 
    2214           0 :         rmap_item = alloc_rmap_item();
    2215           0 :         if (rmap_item) {
    2216             :                 /* It has already been zeroed */
    2217           0 :                 rmap_item->mm = mm_slot->mm;
    2218           0 :                 rmap_item->address = addr;
    2219           0 :                 rmap_item->rmap_list = *rmap_list;
    2220           0 :                 *rmap_list = rmap_item;
    2221             :         }
    2222             :         return rmap_item;
    2223             : }
    2224             : 
    2225           0 : static struct rmap_item *scan_get_next_rmap_item(struct page **page)
    2226             : {
    2227           0 :         struct mm_struct *mm;
    2228           0 :         struct mm_slot *slot;
    2229           0 :         struct vm_area_struct *vma;
    2230           0 :         struct rmap_item *rmap_item;
    2231           0 :         int nid;
    2232             : 
    2233           0 :         if (list_empty(&ksm_mm_head.mm_list))
    2234             :                 return NULL;
    2235             : 
    2236           0 :         slot = ksm_scan.mm_slot;
    2237           0 :         if (slot == &ksm_mm_head) {
    2238             :                 /*
    2239             :                  * A number of pages can hang around indefinitely on per-cpu
    2240             :                  * pagevecs, raised page count preventing write_protect_page
    2241             :                  * from merging them.  Though it doesn't really matter much,
    2242             :                  * it is puzzling to see some stuck in pages_volatile until
    2243             :                  * other activity jostles them out, and they also prevented
    2244             :                  * LTP's KSM test from succeeding deterministically; so drain
    2245             :                  * them here (here rather than on entry to ksm_do_scan(),
    2246             :                  * so we don't IPI too often when pages_to_scan is set low).
    2247             :                  */
    2248           0 :                 lru_add_drain_all();
    2249             : 
    2250             :                 /*
    2251             :                  * Whereas stale stable_nodes on the stable_tree itself
    2252             :                  * get pruned in the regular course of stable_tree_search(),
    2253             :                  * those moved out to the migrate_nodes list can accumulate:
    2254             :                  * so prune them once before each full scan.
    2255             :                  */
    2256           0 :                 if (!ksm_merge_across_nodes) {
    2257           0 :                         struct stable_node *stable_node, *next;
    2258           0 :                         struct page *page;
    2259             : 
    2260           0 :                         list_for_each_entry_safe(stable_node, next,
    2261             :                                                  &migrate_nodes, list) {
    2262           0 :                                 page = get_ksm_page(stable_node,
    2263             :                                                     GET_KSM_PAGE_NOLOCK);
    2264           0 :                                 if (page)
    2265           0 :                                         put_page(page);
    2266           0 :                                 cond_resched();
    2267             :                         }
    2268             :                 }
    2269             : 
    2270           0 :                 for (nid = 0; nid < ksm_nr_node_ids; nid++)
    2271           0 :                         root_unstable_tree[nid] = RB_ROOT;
    2272             : 
    2273           0 :                 spin_lock(&ksm_mmlist_lock);
    2274           0 :                 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
    2275           0 :                 ksm_scan.mm_slot = slot;
    2276           0 :                 spin_unlock(&ksm_mmlist_lock);
    2277             :                 /*
    2278             :                  * Although we tested list_empty() above, a racing __ksm_exit
    2279             :                  * of the last mm on the list may have removed it since then.
    2280             :                  */
    2281           0 :                 if (slot == &ksm_mm_head)
    2282             :                         return NULL;
    2283           0 : next_mm:
    2284           0 :                 ksm_scan.address = 0;
    2285           0 :                 ksm_scan.rmap_list = &slot->rmap_list;
    2286             :         }
    2287             : 
    2288           0 :         mm = slot->mm;
    2289           0 :         mmap_read_lock(mm);
    2290           0 :         if (ksm_test_exit(mm))
    2291             :                 vma = NULL;
    2292             :         else
    2293           0 :                 vma = find_vma(mm, ksm_scan.address);
    2294             : 
    2295           0 :         for (; vma; vma = vma->vm_next) {
    2296           0 :                 if (!(vma->vm_flags & VM_MERGEABLE))
    2297           0 :                         continue;
    2298           0 :                 if (ksm_scan.address < vma->vm_start)
    2299           0 :                         ksm_scan.address = vma->vm_start;
    2300           0 :                 if (!vma->anon_vma)
    2301           0 :                         ksm_scan.address = vma->vm_end;
    2302             : 
    2303           0 :                 while (ksm_scan.address < vma->vm_end) {
    2304           0 :                         if (ksm_test_exit(mm))
    2305             :                                 break;
    2306           0 :                         *page = follow_page(vma, ksm_scan.address, FOLL_GET);
    2307           0 :                         if (IS_ERR_OR_NULL(*page)) {
    2308           0 :                                 ksm_scan.address += PAGE_SIZE;
    2309           0 :                                 cond_resched();
    2310           0 :                                 continue;
    2311             :                         }
    2312           0 :                         if (PageAnon(*page)) {
    2313           0 :                                 flush_anon_page(vma, *page, ksm_scan.address);
    2314           0 :                                 flush_dcache_page(*page);
    2315           0 :                                 rmap_item = get_next_rmap_item(slot,
    2316             :                                         ksm_scan.rmap_list, ksm_scan.address);
    2317           0 :                                 if (rmap_item) {
    2318           0 :                                         ksm_scan.rmap_list =
    2319           0 :                                                         &rmap_item->rmap_list;
    2320           0 :                                         ksm_scan.address += PAGE_SIZE;
    2321             :                                 } else
    2322           0 :                                         put_page(*page);
    2323           0 :                                 mmap_read_unlock(mm);
    2324           0 :                                 return rmap_item;
    2325             :                         }
    2326           0 :                         put_page(*page);
    2327           0 :                         ksm_scan.address += PAGE_SIZE;
    2328           0 :                         cond_resched();
    2329             :                 }
    2330             :         }
    2331             : 
    2332           0 :         if (ksm_test_exit(mm)) {
    2333           0 :                 ksm_scan.address = 0;
    2334           0 :                 ksm_scan.rmap_list = &slot->rmap_list;
    2335             :         }
    2336             :         /*
    2337             :          * Nuke all the rmap_items that are above this current rmap:
    2338             :          * because there were no VM_MERGEABLE vmas with such addresses.
    2339             :          */
    2340           0 :         remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
    2341             : 
    2342           0 :         spin_lock(&ksm_mmlist_lock);
    2343           0 :         ksm_scan.mm_slot = list_entry(slot->mm_list.next,
    2344             :                                                 struct mm_slot, mm_list);
    2345           0 :         if (ksm_scan.address == 0) {
    2346             :                 /*
    2347             :                  * We've completed a full scan of all vmas, holding mmap_lock
    2348             :                  * throughout, and found no VM_MERGEABLE: so do the same as
    2349             :                  * __ksm_exit does to remove this mm from all our lists now.
    2350             :                  * This applies either when cleaning up after __ksm_exit
    2351             :                  * (but beware: we can reach here even before __ksm_exit),
    2352             :                  * or when all VM_MERGEABLE areas have been unmapped (and
    2353             :                  * mmap_lock then protects against race with MADV_MERGEABLE).
    2354             :                  */
    2355           0 :                 hash_del(&slot->link);
    2356           0 :                 list_del(&slot->mm_list);
    2357           0 :                 spin_unlock(&ksm_mmlist_lock);
    2358             : 
    2359           0 :                 free_mm_slot(slot);
    2360           0 :                 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
    2361           0 :                 mmap_read_unlock(mm);
    2362           0 :                 mmdrop(mm);
    2363             :         } else {
    2364           0 :                 mmap_read_unlock(mm);
    2365             :                 /*
    2366             :                  * mmap_read_unlock(mm) first because after
    2367             :                  * spin_unlock(&ksm_mmlist_lock) run, the "mm" may
    2368             :                  * already have been freed under us by __ksm_exit()
    2369             :                  * because the "mm_slot" is still hashed and
    2370             :                  * ksm_scan.mm_slot doesn't point to it anymore.
    2371             :                  */
    2372           0 :                 spin_unlock(&ksm_mmlist_lock);
    2373             :         }
    2374             : 
    2375             :         /* Repeat until we've completed scanning the whole list */
    2376           0 :         slot = ksm_scan.mm_slot;
    2377           0 :         if (slot != &ksm_mm_head)
    2378           0 :                 goto next_mm;
    2379             : 
    2380           0 :         ksm_scan.seqnr++;
    2381           0 :         return NULL;
    2382             : }
    2383             : 
    2384             : /**
    2385             :  * ksm_do_scan  - the ksm scanner main worker function.
    2386             :  * @scan_npages:  number of pages we want to scan before we return.
    2387             :  */
    2388           0 : static void ksm_do_scan(unsigned int scan_npages)
    2389             : {
    2390           0 :         struct rmap_item *rmap_item;
    2391           0 :         struct page *page;
    2392             : 
    2393           0 :         while (scan_npages-- && likely(!freezing(current))) {
    2394           0 :                 cond_resched();
    2395           0 :                 rmap_item = scan_get_next_rmap_item(&page);
    2396           0 :                 if (!rmap_item)
    2397           0 :                         return;
    2398           0 :                 cmp_and_merge_page(page, rmap_item);
    2399           0 :                 put_page(page);
    2400             :         }
    2401             : }
    2402             : 
    2403           4 : static int ksmd_should_run(void)
    2404             : {
    2405           0 :         return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
    2406             : }
    2407             : 
    2408           1 : static int ksm_scan_thread(void *nothing)
    2409             : {
    2410           1 :         unsigned int sleep_ms;
    2411             : 
    2412           1 :         set_freezable();
    2413           1 :         set_user_nice(current, 5);
    2414             : 
    2415           1 :         while (!kthread_should_stop()) {
    2416           1 :                 mutex_lock(&ksm_thread_mutex);
    2417           1 :                 wait_while_offlining();
    2418           1 :                 if (ksmd_should_run())
    2419           0 :                         ksm_do_scan(ksm_thread_pages_to_scan);
    2420           1 :                 mutex_unlock(&ksm_thread_mutex);
    2421             : 
    2422           1 :                 try_to_freeze();
    2423             : 
    2424           1 :                 if (ksmd_should_run()) {
    2425           0 :                         sleep_ms = READ_ONCE(ksm_thread_sleep_millisecs);
    2426           0 :                         wait_event_interruptible_timeout(ksm_iter_wait,
    2427             :                                 sleep_ms != READ_ONCE(ksm_thread_sleep_millisecs),
    2428             :                                 msecs_to_jiffies(sleep_ms));
    2429             :                 } else {
    2430           1 :                         wait_event_freezable(ksm_thread_wait,
    2431             :                                 ksmd_should_run() || kthread_should_stop());
    2432             :                 }
    2433             :         }
    2434           0 :         return 0;
    2435             : }
    2436             : 
    2437           0 : int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
    2438             :                 unsigned long end, int advice, unsigned long *vm_flags)
    2439             : {
    2440           0 :         struct mm_struct *mm = vma->vm_mm;
    2441           0 :         int err;
    2442             : 
    2443           0 :         switch (advice) {
    2444           0 :         case MADV_MERGEABLE:
    2445             :                 /*
    2446             :                  * Be somewhat over-protective for now!
    2447             :                  */
    2448           0 :                 if (*vm_flags & (VM_MERGEABLE | VM_SHARED  | VM_MAYSHARE   |
    2449             :                                  VM_PFNMAP    | VM_IO      | VM_DONTEXPAND |
    2450             :                                  VM_HUGETLB | VM_MIXEDMAP))
    2451             :                         return 0;               /* just ignore the advice */
    2452             : 
    2453           0 :                 if (vma_is_dax(vma))
    2454             :                         return 0;
    2455             : 
    2456             : #ifdef VM_SAO
    2457             :                 if (*vm_flags & VM_SAO)
    2458             :                         return 0;
    2459             : #endif
    2460             : #ifdef VM_SPARC_ADI
    2461             :                 if (*vm_flags & VM_SPARC_ADI)
    2462             :                         return 0;
    2463             : #endif
    2464             : 
    2465           0 :                 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
    2466           0 :                         err = __ksm_enter(mm);
    2467           0 :                         if (err)
    2468             :                                 return err;
    2469             :                 }
    2470             : 
    2471           0 :                 *vm_flags |= VM_MERGEABLE;
    2472           0 :                 break;
    2473             : 
    2474           0 :         case MADV_UNMERGEABLE:
    2475           0 :                 if (!(*vm_flags & VM_MERGEABLE))
    2476             :                         return 0;               /* just ignore the advice */
    2477             : 
    2478           0 :                 if (vma->anon_vma) {
    2479           0 :                         err = unmerge_ksm_pages(vma, start, end);
    2480           0 :                         if (err)
    2481             :                                 return err;
    2482             :                 }
    2483             : 
    2484           0 :                 *vm_flags &= ~VM_MERGEABLE;
    2485           0 :                 break;
    2486             :         }
    2487             : 
    2488             :         return 0;
    2489             : }
    2490             : EXPORT_SYMBOL_GPL(ksm_madvise);
    2491             : 
    2492           0 : int __ksm_enter(struct mm_struct *mm)
    2493             : {
    2494           0 :         struct mm_slot *mm_slot;
    2495           0 :         int needs_wakeup;
    2496             : 
    2497           0 :         mm_slot = alloc_mm_slot();
    2498           0 :         if (!mm_slot)
    2499             :                 return -ENOMEM;
    2500             : 
    2501             :         /* Check ksm_run too?  Would need tighter locking */
    2502           0 :         needs_wakeup = list_empty(&ksm_mm_head.mm_list);
    2503             : 
    2504           0 :         spin_lock(&ksm_mmlist_lock);
    2505           0 :         insert_to_mm_slots_hash(mm, mm_slot);
    2506             :         /*
    2507             :          * When KSM_RUN_MERGE (or KSM_RUN_STOP),
    2508             :          * insert just behind the scanning cursor, to let the area settle
    2509             :          * down a little; when fork is followed by immediate exec, we don't
    2510             :          * want ksmd to waste time setting up and tearing down an rmap_list.
    2511             :          *
    2512             :          * But when KSM_RUN_UNMERGE, it's important to insert ahead of its
    2513             :          * scanning cursor, otherwise KSM pages in newly forked mms will be
    2514             :          * missed: then we might as well insert at the end of the list.
    2515             :          */
    2516           0 :         if (ksm_run & KSM_RUN_UNMERGE)
    2517           0 :                 list_add_tail(&mm_slot->mm_list, &ksm_mm_head.mm_list);
    2518             :         else
    2519           0 :                 list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
    2520           0 :         spin_unlock(&ksm_mmlist_lock);
    2521             : 
    2522           0 :         set_bit(MMF_VM_MERGEABLE, &mm->flags);
    2523           0 :         mmgrab(mm);
    2524             : 
    2525           0 :         if (needs_wakeup)
    2526           0 :                 wake_up_interruptible(&ksm_thread_wait);
    2527             : 
    2528             :         return 0;
    2529             : }
    2530             : 
    2531           0 : void __ksm_exit(struct mm_struct *mm)
    2532             : {
    2533           0 :         struct mm_slot *mm_slot;
    2534           0 :         int easy_to_free = 0;
    2535             : 
    2536             :         /*
    2537             :          * This process is exiting: if it's straightforward (as is the
    2538             :          * case when ksmd was never running), free mm_slot immediately.
    2539             :          * But if it's at the cursor or has rmap_items linked to it, use
    2540             :          * mmap_lock to synchronize with any break_cows before pagetables
    2541             :          * are freed, and leave the mm_slot on the list for ksmd to free.
    2542             :          * Beware: ksm may already have noticed it exiting and freed the slot.
    2543             :          */
    2544             : 
    2545           0 :         spin_lock(&ksm_mmlist_lock);
    2546           0 :         mm_slot = get_mm_slot(mm);
    2547           0 :         if (mm_slot && ksm_scan.mm_slot != mm_slot) {
    2548           0 :                 if (!mm_slot->rmap_list) {
    2549           0 :                         hash_del(&mm_slot->link);
    2550           0 :                         list_del(&mm_slot->mm_list);
    2551           0 :                         easy_to_free = 1;
    2552             :                 } else {
    2553           0 :                         list_move(&mm_slot->mm_list,
    2554             :                                   &ksm_scan.mm_slot->mm_list);
    2555             :                 }
    2556             :         }
    2557           0 :         spin_unlock(&ksm_mmlist_lock);
    2558             : 
    2559           0 :         if (easy_to_free) {
    2560           0 :                 free_mm_slot(mm_slot);
    2561           0 :                 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
    2562           0 :                 mmdrop(mm);
    2563           0 :         } else if (mm_slot) {
    2564           0 :                 mmap_write_lock(mm);
    2565           0 :                 mmap_write_unlock(mm);
    2566             :         }
    2567           0 : }
    2568             : 
    2569           0 : struct page *ksm_might_need_to_copy(struct page *page,
    2570             :                         struct vm_area_struct *vma, unsigned long address)
    2571             : {
    2572           0 :         struct anon_vma *anon_vma = page_anon_vma(page);
    2573           0 :         struct page *new_page;
    2574             : 
    2575           0 :         if (PageKsm(page)) {
    2576           0 :                 if (page_stable_node(page) &&
    2577           0 :                     !(ksm_run & KSM_RUN_UNMERGE))
    2578             :                         return page;    /* no need to copy it */
    2579           0 :         } else if (!anon_vma) {
    2580             :                 return page;            /* no need to copy it */
    2581           0 :         } else if (anon_vma->root == vma->anon_vma->root &&
    2582           0 :                  page->index == linear_page_index(vma, address)) {
    2583             :                 return page;            /* still no need to copy it */
    2584             :         }
    2585           0 :         if (!PageUptodate(page))
    2586             :                 return page;            /* let do_swap_page report the error */
    2587             : 
    2588           0 :         new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
    2589           0 :         if (new_page && mem_cgroup_charge(new_page, vma->vm_mm, GFP_KERNEL)) {
    2590             :                 put_page(new_page);
    2591             :                 new_page = NULL;
    2592             :         }
    2593           0 :         if (new_page) {
    2594           0 :                 copy_user_highpage(new_page, page, address, vma);
    2595             : 
    2596           0 :                 SetPageDirty(new_page);
    2597           0 :                 __SetPageUptodate(new_page);
    2598           0 :                 __SetPageLocked(new_page);
    2599             :         }
    2600             : 
    2601             :         return new_page;
    2602             : }
    2603             : 
    2604           0 : void rmap_walk_ksm(struct page *page, struct rmap_walk_control *rwc)
    2605             : {
    2606           0 :         struct stable_node *stable_node;
    2607           0 :         struct rmap_item *rmap_item;
    2608           0 :         int search_new_forks = 0;
    2609             : 
    2610           0 :         VM_BUG_ON_PAGE(!PageKsm(page), page);
    2611             : 
    2612             :         /*
    2613             :          * Rely on the page lock to protect against concurrent modifications
    2614             :          * to that page's node of the stable tree.
    2615             :          */
    2616           0 :         VM_BUG_ON_PAGE(!PageLocked(page), page);
    2617             : 
    2618           0 :         stable_node = page_stable_node(page);
    2619           0 :         if (!stable_node)
    2620             :                 return;
    2621           0 : again:
    2622           0 :         hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
    2623           0 :                 struct anon_vma *anon_vma = rmap_item->anon_vma;
    2624           0 :                 struct anon_vma_chain *vmac;
    2625           0 :                 struct vm_area_struct *vma;
    2626             : 
    2627           0 :                 cond_resched();
    2628           0 :                 anon_vma_lock_read(anon_vma);
    2629           0 :                 anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
    2630             :                                                0, ULONG_MAX) {
    2631           0 :                         unsigned long addr;
    2632             : 
    2633           0 :                         cond_resched();
    2634           0 :                         vma = vmac->vma;
    2635             : 
    2636             :                         /* Ignore the stable/unstable/sqnr flags */
    2637           0 :                         addr = rmap_item->address & ~KSM_FLAG_MASK;
    2638             : 
    2639           0 :                         if (addr < vma->vm_start || addr >= vma->vm_end)
    2640           0 :                                 continue;
    2641             :                         /*
    2642             :                          * Initially we examine only the vma which covers this
    2643             :                          * rmap_item; but later, if there is still work to do,
    2644             :                          * we examine covering vmas in other mms: in case they
    2645             :                          * were forked from the original since ksmd passed.
    2646             :                          */
    2647           0 :                         if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
    2648           0 :                                 continue;
    2649             : 
    2650           0 :                         if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
    2651           0 :                                 continue;
    2652             : 
    2653           0 :                         if (!rwc->rmap_one(page, vma, addr, rwc->arg)) {
    2654           0 :                                 anon_vma_unlock_read(anon_vma);
    2655           0 :                                 return;
    2656             :                         }
    2657           0 :                         if (rwc->done && rwc->done(page)) {
    2658           0 :                                 anon_vma_unlock_read(anon_vma);
    2659           0 :                                 return;
    2660             :                         }
    2661             :                 }
    2662           0 :                 anon_vma_unlock_read(anon_vma);
    2663             :         }
    2664           0 :         if (!search_new_forks++)
    2665           0 :                 goto again;
    2666             : }
    2667             : 
    2668             : #ifdef CONFIG_MIGRATION
    2669           0 : void ksm_migrate_page(struct page *newpage, struct page *oldpage)
    2670             : {
    2671           0 :         struct stable_node *stable_node;
    2672             : 
    2673           0 :         VM_BUG_ON_PAGE(!PageLocked(oldpage), oldpage);
    2674           0 :         VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
    2675           0 :         VM_BUG_ON_PAGE(newpage->mapping != oldpage->mapping, newpage);
    2676             : 
    2677           0 :         stable_node = page_stable_node(newpage);
    2678           0 :         if (stable_node) {
    2679           0 :                 VM_BUG_ON_PAGE(stable_node->kpfn != page_to_pfn(oldpage), oldpage);
    2680           0 :                 stable_node->kpfn = page_to_pfn(newpage);
    2681             :                 /*
    2682             :                  * newpage->mapping was set in advance; now we need smp_wmb()
    2683             :                  * to make sure that the new stable_node->kpfn is visible
    2684             :                  * to get_ksm_page() before it can see that oldpage->mapping
    2685             :                  * has gone stale (or that PageSwapCache has been cleared).
    2686             :                  */
    2687           0 :                 smp_wmb();
    2688           0 :                 set_page_stable_node(oldpage, NULL);
    2689             :         }
    2690           0 : }
    2691             : #endif /* CONFIG_MIGRATION */
    2692             : 
    2693             : #ifdef CONFIG_MEMORY_HOTREMOVE
    2694             : static void wait_while_offlining(void)
    2695             : {
    2696             :         while (ksm_run & KSM_RUN_OFFLINE) {
    2697             :                 mutex_unlock(&ksm_thread_mutex);
    2698             :                 wait_on_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE),
    2699             :                             TASK_UNINTERRUPTIBLE);
    2700             :                 mutex_lock(&ksm_thread_mutex);
    2701             :         }
    2702             : }
    2703             : 
    2704             : static bool stable_node_dup_remove_range(struct stable_node *stable_node,
    2705             :                                          unsigned long start_pfn,
    2706             :                                          unsigned long end_pfn)
    2707             : {
    2708             :         if (stable_node->kpfn >= start_pfn &&
    2709             :             stable_node->kpfn < end_pfn) {
    2710             :                 /*
    2711             :                  * Don't get_ksm_page, page has already gone:
    2712             :                  * which is why we keep kpfn instead of page*
    2713             :                  */
    2714             :                 remove_node_from_stable_tree(stable_node);
    2715             :                 return true;
    2716             :         }
    2717             :         return false;
    2718             : }
    2719             : 
    2720             : static bool stable_node_chain_remove_range(struct stable_node *stable_node,
    2721             :                                            unsigned long start_pfn,
    2722             :                                            unsigned long end_pfn,
    2723             :                                            struct rb_root *root)
    2724             : {
    2725             :         struct stable_node *dup;
    2726             :         struct hlist_node *hlist_safe;
    2727             : 
    2728             :         if (!is_stable_node_chain(stable_node)) {
    2729             :                 VM_BUG_ON(is_stable_node_dup(stable_node));
    2730             :                 return stable_node_dup_remove_range(stable_node, start_pfn,
    2731             :                                                     end_pfn);
    2732             :         }
    2733             : 
    2734             :         hlist_for_each_entry_safe(dup, hlist_safe,
    2735             :                                   &stable_node->hlist, hlist_dup) {
    2736             :                 VM_BUG_ON(!is_stable_node_dup(dup));
    2737             :                 stable_node_dup_remove_range(dup, start_pfn, end_pfn);
    2738             :         }
    2739             :         if (hlist_empty(&stable_node->hlist)) {
    2740             :                 free_stable_node_chain(stable_node, root);
    2741             :                 return true; /* notify caller that tree was rebalanced */
    2742             :         } else
    2743             :                 return false;
    2744             : }
    2745             : 
    2746             : static void ksm_check_stable_tree(unsigned long start_pfn,
    2747             :                                   unsigned long end_pfn)
    2748             : {
    2749             :         struct stable_node *stable_node, *next;
    2750             :         struct rb_node *node;
    2751             :         int nid;
    2752             : 
    2753             :         for (nid = 0; nid < ksm_nr_node_ids; nid++) {
    2754             :                 node = rb_first(root_stable_tree + nid);
    2755             :                 while (node) {
    2756             :                         stable_node = rb_entry(node, struct stable_node, node);
    2757             :                         if (stable_node_chain_remove_range(stable_node,
    2758             :                                                            start_pfn, end_pfn,
    2759             :                                                            root_stable_tree +
    2760             :                                                            nid))
    2761             :                                 node = rb_first(root_stable_tree + nid);
    2762             :                         else
    2763             :                                 node = rb_next(node);
    2764             :                         cond_resched();
    2765             :                 }
    2766             :         }
    2767             :         list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
    2768             :                 if (stable_node->kpfn >= start_pfn &&
    2769             :                     stable_node->kpfn < end_pfn)
    2770             :                         remove_node_from_stable_tree(stable_node);
    2771             :                 cond_resched();
    2772             :         }
    2773             : }
    2774             : 
    2775             : static int ksm_memory_callback(struct notifier_block *self,
    2776             :                                unsigned long action, void *arg)
    2777             : {
    2778             :         struct memory_notify *mn = arg;
    2779             : 
    2780             :         switch (action) {
    2781             :         case MEM_GOING_OFFLINE:
    2782             :                 /*
    2783             :                  * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
    2784             :                  * and remove_all_stable_nodes() while memory is going offline:
    2785             :                  * it is unsafe for them to touch the stable tree at this time.
    2786             :                  * But unmerge_ksm_pages(), rmap lookups and other entry points
    2787             :                  * which do not need the ksm_thread_mutex are all safe.
    2788             :                  */
    2789             :                 mutex_lock(&ksm_thread_mutex);
    2790             :                 ksm_run |= KSM_RUN_OFFLINE;
    2791             :                 mutex_unlock(&ksm_thread_mutex);
    2792             :                 break;
    2793             : 
    2794             :         case MEM_OFFLINE:
    2795             :                 /*
    2796             :                  * Most of the work is done by page migration; but there might
    2797             :                  * be a few stable_nodes left over, still pointing to struct
    2798             :                  * pages which have been offlined: prune those from the tree,
    2799             :                  * otherwise get_ksm_page() might later try to access a
    2800             :                  * non-existent struct page.
    2801             :                  */
    2802             :                 ksm_check_stable_tree(mn->start_pfn,
    2803             :                                       mn->start_pfn + mn->nr_pages);
    2804             :                 fallthrough;
    2805             :         case MEM_CANCEL_OFFLINE:
    2806             :                 mutex_lock(&ksm_thread_mutex);
    2807             :                 ksm_run &= ~KSM_RUN_OFFLINE;
    2808             :                 mutex_unlock(&ksm_thread_mutex);
    2809             : 
    2810             :                 smp_mb();       /* wake_up_bit advises this */
    2811             :                 wake_up_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE));
    2812             :                 break;
    2813             :         }
    2814             :         return NOTIFY_OK;
    2815             : }
    2816             : #else
    2817           1 : static void wait_while_offlining(void)
    2818             : {
    2819           1 : }
    2820             : #endif /* CONFIG_MEMORY_HOTREMOVE */
    2821             : 
    2822             : #ifdef CONFIG_SYSFS
    2823             : /*
    2824             :  * This all compiles without CONFIG_SYSFS, but is a waste of space.
    2825             :  */
    2826             : 
    2827             : #define KSM_ATTR_RO(_name) \
    2828             :         static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
    2829             : #define KSM_ATTR(_name) \
    2830             :         static struct kobj_attribute _name##_attr = \
    2831             :                 __ATTR(_name, 0644, _name##_show, _name##_store)
    2832             : 
    2833           0 : static ssize_t sleep_millisecs_show(struct kobject *kobj,
    2834             :                                     struct kobj_attribute *attr, char *buf)
    2835             : {
    2836           0 :         return sysfs_emit(buf, "%u\n", ksm_thread_sleep_millisecs);
    2837             : }
    2838             : 
    2839           0 : static ssize_t sleep_millisecs_store(struct kobject *kobj,
    2840             :                                      struct kobj_attribute *attr,
    2841             :                                      const char *buf, size_t count)
    2842             : {
    2843           0 :         unsigned int msecs;
    2844           0 :         int err;
    2845             : 
    2846           0 :         err = kstrtouint(buf, 10, &msecs);
    2847           0 :         if (err)
    2848             :                 return -EINVAL;
    2849             : 
    2850           0 :         ksm_thread_sleep_millisecs = msecs;
    2851           0 :         wake_up_interruptible(&ksm_iter_wait);
    2852             : 
    2853           0 :         return count;
    2854             : }
    2855             : KSM_ATTR(sleep_millisecs);
    2856             : 
    2857           0 : static ssize_t pages_to_scan_show(struct kobject *kobj,
    2858             :                                   struct kobj_attribute *attr, char *buf)
    2859             : {
    2860           0 :         return sysfs_emit(buf, "%u\n", ksm_thread_pages_to_scan);
    2861             : }
    2862             : 
    2863           0 : static ssize_t pages_to_scan_store(struct kobject *kobj,
    2864             :                                    struct kobj_attribute *attr,
    2865             :                                    const char *buf, size_t count)
    2866             : {
    2867           0 :         unsigned int nr_pages;
    2868           0 :         int err;
    2869             : 
    2870           0 :         err = kstrtouint(buf, 10, &nr_pages);
    2871           0 :         if (err)
    2872             :                 return -EINVAL;
    2873             : 
    2874           0 :         ksm_thread_pages_to_scan = nr_pages;
    2875             : 
    2876           0 :         return count;
    2877             : }
    2878             : KSM_ATTR(pages_to_scan);
    2879             : 
    2880           0 : static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
    2881             :                         char *buf)
    2882             : {
    2883           0 :         return sysfs_emit(buf, "%lu\n", ksm_run);
    2884             : }
    2885             : 
    2886           0 : static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
    2887             :                          const char *buf, size_t count)
    2888             : {
    2889           0 :         unsigned int flags;
    2890           0 :         int err;
    2891             : 
    2892           0 :         err = kstrtouint(buf, 10, &flags);
    2893           0 :         if (err)
    2894             :                 return -EINVAL;
    2895           0 :         if (flags > KSM_RUN_UNMERGE)
    2896             :                 return -EINVAL;
    2897             : 
    2898             :         /*
    2899             :          * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
    2900             :          * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
    2901             :          * breaking COW to free the pages_shared (but leaves mm_slots
    2902             :          * on the list for when ksmd may be set running again).
    2903             :          */
    2904             : 
    2905           0 :         mutex_lock(&ksm_thread_mutex);
    2906           0 :         wait_while_offlining();
    2907           0 :         if (ksm_run != flags) {
    2908           0 :                 ksm_run = flags;
    2909           0 :                 if (flags & KSM_RUN_UNMERGE) {
    2910           0 :                         set_current_oom_origin();
    2911           0 :                         err = unmerge_and_remove_all_rmap_items();
    2912           0 :                         clear_current_oom_origin();
    2913           0 :                         if (err) {
    2914           0 :                                 ksm_run = KSM_RUN_STOP;
    2915           0 :                                 count = err;
    2916             :                         }
    2917             :                 }
    2918             :         }
    2919           0 :         mutex_unlock(&ksm_thread_mutex);
    2920             : 
    2921           0 :         if (flags & KSM_RUN_MERGE)
    2922           0 :                 wake_up_interruptible(&ksm_thread_wait);
    2923             : 
    2924           0 :         return count;
    2925             : }
    2926             : KSM_ATTR(run);
    2927             : 
    2928             : #ifdef CONFIG_NUMA
    2929           0 : static ssize_t merge_across_nodes_show(struct kobject *kobj,
    2930             :                                        struct kobj_attribute *attr, char *buf)
    2931             : {
    2932           0 :         return sysfs_emit(buf, "%u\n", ksm_merge_across_nodes);
    2933             : }
    2934             : 
    2935           0 : static ssize_t merge_across_nodes_store(struct kobject *kobj,
    2936             :                                    struct kobj_attribute *attr,
    2937             :                                    const char *buf, size_t count)
    2938             : {
    2939           0 :         int err;
    2940           0 :         unsigned long knob;
    2941             : 
    2942           0 :         err = kstrtoul(buf, 10, &knob);
    2943           0 :         if (err)
    2944           0 :                 return err;
    2945           0 :         if (knob > 1)
    2946             :                 return -EINVAL;
    2947             : 
    2948           0 :         mutex_lock(&ksm_thread_mutex);
    2949           0 :         wait_while_offlining();
    2950           0 :         if (ksm_merge_across_nodes != knob) {
    2951           0 :                 if (ksm_pages_shared || remove_all_stable_nodes())
    2952             :                         err = -EBUSY;
    2953           0 :                 else if (root_stable_tree == one_stable_tree) {
    2954           0 :                         struct rb_root *buf;
    2955             :                         /*
    2956             :                          * This is the first time that we switch away from the
    2957             :                          * default of merging across nodes: must now allocate
    2958             :                          * a buffer to hold as many roots as may be needed.
    2959             :                          * Allocate stable and unstable together:
    2960             :                          * MAXSMP NODES_SHIFT 10 will use 16kB.
    2961             :                          */
    2962           0 :                         buf = kcalloc(nr_node_ids + nr_node_ids, sizeof(*buf),
    2963             :                                       GFP_KERNEL);
    2964             :                         /* Let us assume that RB_ROOT is NULL is zero */
    2965           0 :                         if (!buf)
    2966             :                                 err = -ENOMEM;
    2967             :                         else {
    2968           0 :                                 root_stable_tree = buf;
    2969           0 :                                 root_unstable_tree = buf + nr_node_ids;
    2970             :                                 /* Stable tree is empty but not the unstable */
    2971           0 :                                 root_unstable_tree[0] = one_unstable_tree[0];
    2972             :                         }
    2973             :                 }
    2974           0 :                 if (!err) {
    2975           0 :                         ksm_merge_across_nodes = knob;
    2976           0 :                         ksm_nr_node_ids = knob ? 1 : nr_node_ids;
    2977             :                 }
    2978             :         }
    2979           0 :         mutex_unlock(&ksm_thread_mutex);
    2980             : 
    2981           0 :         return err ? err : count;
    2982             : }
    2983             : KSM_ATTR(merge_across_nodes);
    2984             : #endif
    2985             : 
    2986           0 : static ssize_t use_zero_pages_show(struct kobject *kobj,
    2987             :                                    struct kobj_attribute *attr, char *buf)
    2988             : {
    2989           0 :         return sysfs_emit(buf, "%u\n", ksm_use_zero_pages);
    2990             : }
    2991           0 : static ssize_t use_zero_pages_store(struct kobject *kobj,
    2992             :                                    struct kobj_attribute *attr,
    2993             :                                    const char *buf, size_t count)
    2994             : {
    2995           0 :         int err;
    2996           0 :         bool value;
    2997             : 
    2998           0 :         err = kstrtobool(buf, &value);
    2999           0 :         if (err)
    3000             :                 return -EINVAL;
    3001             : 
    3002           0 :         ksm_use_zero_pages = value;
    3003             : 
    3004           0 :         return count;
    3005             : }
    3006             : KSM_ATTR(use_zero_pages);
    3007             : 
    3008           0 : static ssize_t max_page_sharing_show(struct kobject *kobj,
    3009             :                                      struct kobj_attribute *attr, char *buf)
    3010             : {
    3011           0 :         return sysfs_emit(buf, "%u\n", ksm_max_page_sharing);
    3012             : }
    3013             : 
    3014           0 : static ssize_t max_page_sharing_store(struct kobject *kobj,
    3015             :                                       struct kobj_attribute *attr,
    3016             :                                       const char *buf, size_t count)
    3017             : {
    3018           0 :         int err;
    3019           0 :         int knob;
    3020             : 
    3021           0 :         err = kstrtoint(buf, 10, &knob);
    3022           0 :         if (err)
    3023           0 :                 return err;
    3024             :         /*
    3025             :          * When a KSM page is created it is shared by 2 mappings. This
    3026             :          * being a signed comparison, it implicitly verifies it's not
    3027             :          * negative.
    3028             :          */
    3029           0 :         if (knob < 2)
    3030             :                 return -EINVAL;
    3031             : 
    3032           0 :         if (READ_ONCE(ksm_max_page_sharing) == knob)
    3033           0 :                 return count;
    3034             : 
    3035           0 :         mutex_lock(&ksm_thread_mutex);
    3036           0 :         wait_while_offlining();
    3037           0 :         if (ksm_max_page_sharing != knob) {
    3038           0 :                 if (ksm_pages_shared || remove_all_stable_nodes())
    3039             :                         err = -EBUSY;
    3040             :                 else
    3041           0 :                         ksm_max_page_sharing = knob;
    3042             :         }
    3043           0 :         mutex_unlock(&ksm_thread_mutex);
    3044             : 
    3045           0 :         return err ? err : count;
    3046             : }
    3047             : KSM_ATTR(max_page_sharing);
    3048             : 
    3049           0 : static ssize_t pages_shared_show(struct kobject *kobj,
    3050             :                                  struct kobj_attribute *attr, char *buf)
    3051             : {
    3052           0 :         return sysfs_emit(buf, "%lu\n", ksm_pages_shared);
    3053             : }
    3054             : KSM_ATTR_RO(pages_shared);
    3055             : 
    3056           0 : static ssize_t pages_sharing_show(struct kobject *kobj,
    3057             :                                   struct kobj_attribute *attr, char *buf)
    3058             : {
    3059           0 :         return sysfs_emit(buf, "%lu\n", ksm_pages_sharing);
    3060             : }
    3061             : KSM_ATTR_RO(pages_sharing);
    3062             : 
    3063           0 : static ssize_t pages_unshared_show(struct kobject *kobj,
    3064             :                                    struct kobj_attribute *attr, char *buf)
    3065             : {
    3066           0 :         return sysfs_emit(buf, "%lu\n", ksm_pages_unshared);
    3067             : }
    3068             : KSM_ATTR_RO(pages_unshared);
    3069             : 
    3070           0 : static ssize_t pages_volatile_show(struct kobject *kobj,
    3071             :                                    struct kobj_attribute *attr, char *buf)
    3072             : {
    3073           0 :         long ksm_pages_volatile;
    3074             : 
    3075           0 :         ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
    3076           0 :                                 - ksm_pages_sharing - ksm_pages_unshared;
    3077             :         /*
    3078             :          * It was not worth any locking to calculate that statistic,
    3079             :          * but it might therefore sometimes be negative: conceal that.
    3080             :          */
    3081           0 :         if (ksm_pages_volatile < 0)
    3082             :                 ksm_pages_volatile = 0;
    3083           0 :         return sysfs_emit(buf, "%ld\n", ksm_pages_volatile);
    3084             : }
    3085             : KSM_ATTR_RO(pages_volatile);
    3086             : 
    3087           0 : static ssize_t stable_node_dups_show(struct kobject *kobj,
    3088             :                                      struct kobj_attribute *attr, char *buf)
    3089             : {
    3090           0 :         return sysfs_emit(buf, "%lu\n", ksm_stable_node_dups);
    3091             : }
    3092             : KSM_ATTR_RO(stable_node_dups);
    3093             : 
    3094           0 : static ssize_t stable_node_chains_show(struct kobject *kobj,
    3095             :                                        struct kobj_attribute *attr, char *buf)
    3096             : {
    3097           0 :         return sysfs_emit(buf, "%lu\n", ksm_stable_node_chains);
    3098             : }
    3099             : KSM_ATTR_RO(stable_node_chains);
    3100             : 
    3101             : static ssize_t
    3102           0 : stable_node_chains_prune_millisecs_show(struct kobject *kobj,
    3103             :                                         struct kobj_attribute *attr,
    3104             :                                         char *buf)
    3105             : {
    3106           0 :         return sysfs_emit(buf, "%u\n", ksm_stable_node_chains_prune_millisecs);
    3107             : }
    3108             : 
    3109             : static ssize_t
    3110           0 : stable_node_chains_prune_millisecs_store(struct kobject *kobj,
    3111             :                                          struct kobj_attribute *attr,
    3112             :                                          const char *buf, size_t count)
    3113             : {
    3114           0 :         unsigned long msecs;
    3115           0 :         int err;
    3116             : 
    3117           0 :         err = kstrtoul(buf, 10, &msecs);
    3118           0 :         if (err || msecs > UINT_MAX)
    3119             :                 return -EINVAL;
    3120             : 
    3121           0 :         ksm_stable_node_chains_prune_millisecs = msecs;
    3122             : 
    3123           0 :         return count;
    3124             : }
    3125             : KSM_ATTR(stable_node_chains_prune_millisecs);
    3126             : 
    3127           0 : static ssize_t full_scans_show(struct kobject *kobj,
    3128             :                                struct kobj_attribute *attr, char *buf)
    3129             : {
    3130           0 :         return sysfs_emit(buf, "%lu\n", ksm_scan.seqnr);
    3131             : }
    3132             : KSM_ATTR_RO(full_scans);
    3133             : 
    3134             : static struct attribute *ksm_attrs[] = {
    3135             :         &sleep_millisecs_attr.attr,
    3136             :         &pages_to_scan_attr.attr,
    3137             :         &run_attr.attr,
    3138             :         &pages_shared_attr.attr,
    3139             :         &pages_sharing_attr.attr,
    3140             :         &pages_unshared_attr.attr,
    3141             :         &pages_volatile_attr.attr,
    3142             :         &full_scans_attr.attr,
    3143             : #ifdef CONFIG_NUMA
    3144             :         &merge_across_nodes_attr.attr,
    3145             : #endif
    3146             :         &max_page_sharing_attr.attr,
    3147             :         &stable_node_chains_attr.attr,
    3148             :         &stable_node_dups_attr.attr,
    3149             :         &stable_node_chains_prune_millisecs_attr.attr,
    3150             :         &use_zero_pages_attr.attr,
    3151             :         NULL,
    3152             : };
    3153             : 
    3154             : static const struct attribute_group ksm_attr_group = {
    3155             :         .attrs = ksm_attrs,
    3156             :         .name = "ksm",
    3157             : };
    3158             : #endif /* CONFIG_SYSFS */
    3159             : 
    3160           1 : static int __init ksm_init(void)
    3161             : {
    3162           1 :         struct task_struct *ksm_thread;
    3163           1 :         int err;
    3164             : 
    3165             :         /* The correct value depends on page size and endianness */
    3166           2 :         zero_checksum = calc_checksum(ZERO_PAGE(0));
    3167             :         /* Default to false for backwards compatibility */
    3168           1 :         ksm_use_zero_pages = false;
    3169             : 
    3170           1 :         err = ksm_slab_init();
    3171           1 :         if (err)
    3172           0 :                 goto out;
    3173             : 
    3174           1 :         ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
    3175           1 :         if (IS_ERR(ksm_thread)) {
    3176           0 :                 pr_err("ksm: creating kthread failed\n");
    3177           0 :                 err = PTR_ERR(ksm_thread);
    3178           0 :                 goto out_free;
    3179             :         }
    3180             : 
    3181             : #ifdef CONFIG_SYSFS
    3182           1 :         err = sysfs_create_group(mm_kobj, &ksm_attr_group);
    3183           1 :         if (err) {
    3184           0 :                 pr_err("ksm: register sysfs failed\n");
    3185           0 :                 kthread_stop(ksm_thread);
    3186           0 :                 goto out_free;
    3187             :         }
    3188             : #else
    3189             :         ksm_run = KSM_RUN_MERGE;        /* no way for user to start it */
    3190             : 
    3191             : #endif /* CONFIG_SYSFS */
    3192             : 
    3193             : #ifdef CONFIG_MEMORY_HOTREMOVE
    3194             :         /* There is no significance to this priority 100 */
    3195             :         hotplug_memory_notifier(ksm_memory_callback, 100);
    3196             : #endif
    3197             :         return 0;
    3198             : 
    3199           0 : out_free:
    3200           0 :         ksm_slab_free();
    3201             : out:
    3202             :         return err;
    3203             : }
    3204             : subsys_initcall(ksm_init);

Generated by: LCOV version 1.14