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Linux/mm/ksm.c

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  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 :c:type:`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 static int __init ksm_slab_init(void)
307 {
308         rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
309         if (!rmap_item_cache)
310                 goto out;
311 
312         stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
313         if (!stable_node_cache)
314                 goto out_free1;
315 
316         mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
317         if (!mm_slot_cache)
318                 goto out_free2;
319 
320         return 0;
321 
322 out_free2:
323         kmem_cache_destroy(stable_node_cache);
324 out_free1:
325         kmem_cache_destroy(rmap_item_cache);
326 out:
327         return -ENOMEM;
328 }
329 
330 static void __init ksm_slab_free(void)
331 {
332         kmem_cache_destroy(mm_slot_cache);
333         kmem_cache_destroy(stable_node_cache);
334         kmem_cache_destroy(rmap_item_cache);
335         mm_slot_cache = NULL;
336 }
337 
338 static __always_inline bool is_stable_node_chain(struct stable_node *chain)
339 {
340         return chain->rmap_hlist_len == STABLE_NODE_CHAIN;
341 }
342 
343 static __always_inline bool is_stable_node_dup(struct stable_node *dup)
344 {
345         return dup->head == STABLE_NODE_DUP_HEAD;
346 }
347 
348 static inline void stable_node_chain_add_dup(struct stable_node *dup,
349                                              struct stable_node *chain)
350 {
351         VM_BUG_ON(is_stable_node_dup(dup));
352         dup->head = STABLE_NODE_DUP_HEAD;
353         VM_BUG_ON(!is_stable_node_chain(chain));
354         hlist_add_head(&dup->hlist_dup, &chain->hlist);
355         ksm_stable_node_dups++;
356 }
357 
358 static inline void __stable_node_dup_del(struct stable_node *dup)
359 {
360         VM_BUG_ON(!is_stable_node_dup(dup));
361         hlist_del(&dup->hlist_dup);
362         ksm_stable_node_dups--;
363 }
364 
365 static inline void stable_node_dup_del(struct stable_node *dup)
366 {
367         VM_BUG_ON(is_stable_node_chain(dup));
368         if (is_stable_node_dup(dup))
369                 __stable_node_dup_del(dup);
370         else
371                 rb_erase(&dup->node, root_stable_tree + NUMA(dup->nid));
372 #ifdef CONFIG_DEBUG_VM
373         dup->head = NULL;
374 #endif
375 }
376 
377 static inline struct rmap_item *alloc_rmap_item(void)
378 {
379         struct rmap_item *rmap_item;
380 
381         rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL |
382                                                 __GFP_NORETRY | __GFP_NOWARN);
383         if (rmap_item)
384                 ksm_rmap_items++;
385         return rmap_item;
386 }
387 
388 static inline void free_rmap_item(struct rmap_item *rmap_item)
389 {
390         ksm_rmap_items--;
391         rmap_item->mm = NULL;   /* debug safety */
392         kmem_cache_free(rmap_item_cache, rmap_item);
393 }
394 
395 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         return kmem_cache_alloc(stable_node_cache, GFP_KERNEL | __GFP_HIGH);
403 }
404 
405 static inline void free_stable_node(struct stable_node *stable_node)
406 {
407         VM_BUG_ON(stable_node->rmap_hlist_len &&
408                   !is_stable_node_chain(stable_node));
409         kmem_cache_free(stable_node_cache, stable_node);
410 }
411 
412 static inline struct mm_slot *alloc_mm_slot(void)
413 {
414         if (!mm_slot_cache)     /* initialization failed */
415                 return NULL;
416         return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
417 }
418 
419 static inline void free_mm_slot(struct mm_slot *mm_slot)
420 {
421         kmem_cache_free(mm_slot_cache, mm_slot);
422 }
423 
424 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
425 {
426         struct mm_slot *slot;
427 
428         hash_for_each_possible(mm_slots_hash, slot, link, (unsigned long)mm)
429                 if (slot->mm == mm)
430                         return slot;
431 
432         return NULL;
433 }
434 
435 static void insert_to_mm_slots_hash(struct mm_struct *mm,
436                                     struct mm_slot *mm_slot)
437 {
438         mm_slot->mm = mm;
439         hash_add(mm_slots_hash, &mm_slot->link, (unsigned long)mm);
440 }
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_sem 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 static inline bool ksm_test_exit(struct mm_struct *mm)
451 {
452         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, 1, 1, &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 static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
471 {
472         struct page *page;
473         vm_fault_t ret = 0;
474 
475         do {
476                 cond_resched();
477                 page = follow_page(vma, addr,
478                                 FOLL_GET | FOLL_MIGRATION | FOLL_REMOTE);
479                 if (IS_ERR_OR_NULL(page))
480                         break;
481                 if (PageKsm(page))
482                         ret = handle_mm_fault(vma, addr,
483                                         FAULT_FLAG_WRITE | FAULT_FLAG_REMOTE);
484                 else
485                         ret = VM_FAULT_WRITE;
486                 put_page(page);
487         } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | VM_FAULT_OOM)));
488         /*
489          * We must loop because handle_mm_fault() may back out if there's
490          * any difficulty e.g. if pte accessed bit gets updated concurrently.
491          *
492          * VM_FAULT_WRITE is what we have been hoping for: it indicates that
493          * COW has been broken, even if the vma does not permit VM_WRITE;
494          * but note that a concurrent fault might break PageKsm for us.
495          *
496          * VM_FAULT_SIGBUS could occur if we race with truncation of the
497          * backing file, which also invalidates anonymous pages: that's
498          * okay, that truncation will have unmapped the PageKsm for us.
499          *
500          * VM_FAULT_OOM: at the time of writing (late July 2009), setting
501          * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
502          * current task has TIF_MEMDIE set, and will be OOM killed on return
503          * to user; and ksmd, having no mm, would never be chosen for that.
504          *
505          * But if the mm is in a limited mem_cgroup, then the fault may fail
506          * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
507          * even ksmd can fail in this way - though it's usually breaking ksm
508          * just to undo a merge it made a moment before, so unlikely to oom.
509          *
510          * That's a pity: we might therefore have more kernel pages allocated
511          * than we're counting as nodes in the stable tree; but ksm_do_scan
512          * will retry to break_cow on each pass, so should recover the page
513          * in due course.  The important thing is to not let VM_MERGEABLE
514          * be cleared while any such pages might remain in the area.
515          */
516         return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
517 }
518 
519 static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
520                 unsigned long addr)
521 {
522         struct vm_area_struct *vma;
523         if (ksm_test_exit(mm))
524                 return NULL;
525         vma = find_vma(mm, addr);
526         if (!vma || vma->vm_start > addr)
527                 return NULL;
528         if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
529                 return NULL;
530         return vma;
531 }
532 
533 static void break_cow(struct rmap_item *rmap_item)
534 {
535         struct mm_struct *mm = rmap_item->mm;
536         unsigned long addr = rmap_item->address;
537         struct vm_area_struct *vma;
538 
539         /*
540          * It is not an accident that whenever we want to break COW
541          * to undo, we also need to drop a reference to the anon_vma.
542          */
543         put_anon_vma(rmap_item->anon_vma);
544 
545         down_read(&mm->mmap_sem);
546         vma = find_mergeable_vma(mm, addr);
547         if (vma)
548                 break_ksm(vma, addr);
549         up_read(&mm->mmap_sem);
550 }
551 
552 static struct page *get_mergeable_page(struct rmap_item *rmap_item)
553 {
554         struct mm_struct *mm = rmap_item->mm;
555         unsigned long addr = rmap_item->address;
556         struct vm_area_struct *vma;
557         struct page *page;
558 
559         down_read(&mm->mmap_sem);
560         vma = find_mergeable_vma(mm, addr);
561         if (!vma)
562                 goto out;
563 
564         page = follow_page(vma, addr, FOLL_GET);
565         if (IS_ERR_OR_NULL(page))
566                 goto out;
567         if (PageAnon(page)) {
568                 flush_anon_page(vma, page, addr);
569                 flush_dcache_page(page);
570         } else {
571                 put_page(page);
572 out:
573                 page = NULL;
574         }
575         up_read(&mm->mmap_sem);
576         return page;
577 }
578 
579 /*
580  * This helper is used for getting right index into array of tree roots.
581  * When merge_across_nodes knob is set to 1, there are only two rb-trees for
582  * stable and unstable pages from all nodes with roots in index 0. Otherwise,
583  * every node has its own stable and unstable tree.
584  */
585 static inline int get_kpfn_nid(unsigned long kpfn)
586 {
587         return ksm_merge_across_nodes ? 0 : NUMA(pfn_to_nid(kpfn));
588 }
589 
590 static struct stable_node *alloc_stable_node_chain(struct stable_node *dup,
591                                                    struct rb_root *root)
592 {
593         struct stable_node *chain = alloc_stable_node();
594         VM_BUG_ON(is_stable_node_chain(dup));
595         if (likely(chain)) {
596                 INIT_HLIST_HEAD(&chain->hlist);
597                 chain->chain_prune_time = jiffies;
598                 chain->rmap_hlist_len = STABLE_NODE_CHAIN;
599 #if defined (CONFIG_DEBUG_VM) && defined(CONFIG_NUMA)
600                 chain->nid = NUMA_NO_NODE; /* debug */
601 #endif
602                 ksm_stable_node_chains++;
603 
604                 /*
605                  * Put the stable node chain in the first dimension of
606                  * the stable tree and at the same time remove the old
607                  * stable node.
608                  */
609                 rb_replace_node(&dup->node, &chain->node, root);
610 
611                 /*
612                  * Move the old stable node to the second dimension
613                  * queued in the hlist_dup. The invariant is that all
614                  * dup stable_nodes in the chain->hlist point to pages
615                  * that are wrprotected and have the exact same
616                  * content.
617                  */
618                 stable_node_chain_add_dup(dup, chain);
619         }
620         return chain;
621 }
622 
623 static inline void free_stable_node_chain(struct stable_node *chain,
624                                           struct rb_root *root)
625 {
626         rb_erase(&chain->node, root);
627         free_stable_node(chain);
628         ksm_stable_node_chains--;
629 }
630 
631 static void remove_node_from_stable_tree(struct stable_node *stable_node)
632 {
633         struct rmap_item *rmap_item;
634 
635         /* check it's not STABLE_NODE_CHAIN or negative */
636         BUG_ON(stable_node->rmap_hlist_len < 0);
637 
638         hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
639                 if (rmap_item->hlist.next)
640                         ksm_pages_sharing--;
641                 else
642                         ksm_pages_shared--;
643                 VM_BUG_ON(stable_node->rmap_hlist_len <= 0);
644                 stable_node->rmap_hlist_len--;
645                 put_anon_vma(rmap_item->anon_vma);
646                 rmap_item->address &= PAGE_MASK;
647                 cond_resched();
648         }
649 
650         /*
651          * We need the second aligned pointer of the migrate_nodes
652          * list_head to stay clear from the rb_parent_color union
653          * (aligned and different than any node) and also different
654          * from &migrate_nodes. This will verify that future list.h changes
655          * don't break STABLE_NODE_DUP_HEAD. Only recent gcc can handle it.
656          */
657 #if defined(GCC_VERSION) && GCC_VERSION >= 40903
658         BUILD_BUG_ON(STABLE_NODE_DUP_HEAD <= &migrate_nodes);
659         BUILD_BUG_ON(STABLE_NODE_DUP_HEAD >= &migrate_nodes + 1);
660 #endif
661 
662         if (stable_node->head == &migrate_nodes)
663                 list_del(&stable_node->list);
664         else
665                 stable_node_dup_del(stable_node);
666         free_stable_node(stable_node);
667 }
668 
669 enum get_ksm_page_flags {
670         GET_KSM_PAGE_NOLOCK,
671         GET_KSM_PAGE_LOCK,
672         GET_KSM_PAGE_TRYLOCK
673 };
674 
675 /*
676  * get_ksm_page: checks if the page indicated by the stable node
677  * is still its ksm page, despite having held no reference to it.
678  * In which case we can trust the content of the page, and it
679  * returns the gotten page; but if the page has now been zapped,
680  * remove the stale node from the stable tree and return NULL.
681  * But beware, the stable node's page might be being migrated.
682  *
683  * You would expect the stable_node to hold a reference to the ksm page.
684  * But if it increments the page's count, swapping out has to wait for
685  * ksmd to come around again before it can free the page, which may take
686  * seconds or even minutes: much too unresponsive.  So instead we use a
687  * "keyhole reference": access to the ksm page from the stable node peeps
688  * out through its keyhole to see if that page still holds the right key,
689  * pointing back to this stable node.  This relies on freeing a PageAnon
690  * page to reset its page->mapping to NULL, and relies on no other use of
691  * a page to put something that might look like our key in page->mapping.
692  * is on its way to being freed; but it is an anomaly to bear in mind.
693  */
694 static struct page *get_ksm_page(struct stable_node *stable_node,
695                                  enum get_ksm_page_flags flags)
696 {
697         struct page *page;
698         void *expected_mapping;
699         unsigned long kpfn;
700 
701         expected_mapping = (void *)((unsigned long)stable_node |
702                                         PAGE_MAPPING_KSM);
703 again:
704         kpfn = READ_ONCE(stable_node->kpfn); /* Address dependency. */
705         page = pfn_to_page(kpfn);
706         if (READ_ONCE(page->mapping) != expected_mapping)
707                 goto stale;
708 
709         /*
710          * We cannot do anything with the page while its refcount is 0.
711          * Usually 0 means free, or tail of a higher-order page: in which
712          * case this node is no longer referenced, and should be freed;
713          * however, it might mean that the page is under page_ref_freeze().
714          * The __remove_mapping() case is easy, again the node is now stale;
715          * the same is in reuse_ksm_page() case; but if page is swapcache
716          * in migrate_page_move_mapping(), it might still be our page,
717          * in which case it's essential to keep the node.
718          */
719         while (!get_page_unless_zero(page)) {
720                 /*
721                  * Another check for page->mapping != expected_mapping would
722                  * work here too.  We have chosen the !PageSwapCache test to
723                  * optimize the common case, when the page is or is about to
724                  * be freed: PageSwapCache is cleared (under spin_lock_irq)
725                  * in the ref_freeze section of __remove_mapping(); but Anon
726                  * page->mapping reset to NULL later, in free_pages_prepare().
727                  */
728                 if (!PageSwapCache(page))
729                         goto stale;
730                 cpu_relax();
731         }
732 
733         if (READ_ONCE(page->mapping) != expected_mapping) {
734                 put_page(page);
735                 goto stale;
736         }
737 
738         if (flags == GET_KSM_PAGE_TRYLOCK) {
739                 if (!trylock_page(page)) {
740                         put_page(page);
741                         return ERR_PTR(-EBUSY);
742                 }
743         } else if (flags == GET_KSM_PAGE_LOCK)
744                 lock_page(page);
745 
746         if (flags != GET_KSM_PAGE_NOLOCK) {
747                 if (READ_ONCE(page->mapping) != expected_mapping) {
748                         unlock_page(page);
749                         put_page(page);
750                         goto stale;
751                 }
752         }
753         return page;
754 
755 stale:
756         /*
757          * We come here from above when page->mapping or !PageSwapCache
758          * suggests that the node is stale; but it might be under migration.
759          * We need smp_rmb(), matching the smp_wmb() in ksm_migrate_page(),
760          * before checking whether node->kpfn has been changed.
761          */
762         smp_rmb();
763         if (READ_ONCE(stable_node->kpfn) != kpfn)
764                 goto again;
765         remove_node_from_stable_tree(stable_node);
766         return NULL;
767 }
768 
769 /*
770  * Removing rmap_item from stable or unstable tree.
771  * This function will clean the information from the stable/unstable tree.
772  */
773 static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
774 {
775         if (rmap_item->address & STABLE_FLAG) {
776                 struct stable_node *stable_node;
777                 struct page *page;
778 
779                 stable_node = rmap_item->head;
780                 page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
781                 if (!page)
782                         goto out;
783 
784                 hlist_del(&rmap_item->hlist);
785                 unlock_page(page);
786                 put_page(page);
787 
788                 if (!hlist_empty(&stable_node->hlist))
789                         ksm_pages_sharing--;
790                 else
791                         ksm_pages_shared--;
792                 VM_BUG_ON(stable_node->rmap_hlist_len <= 0);
793                 stable_node->rmap_hlist_len--;
794 
795                 put_anon_vma(rmap_item->anon_vma);
796                 rmap_item->address &= PAGE_MASK;
797 
798         } else if (rmap_item->address & UNSTABLE_FLAG) {
799                 unsigned char age;
800                 /*
801                  * Usually ksmd can and must skip the rb_erase, because
802                  * root_unstable_tree was already reset to RB_ROOT.
803                  * But be careful when an mm is exiting: do the rb_erase
804                  * if this rmap_item was inserted by this scan, rather
805                  * than left over from before.
806                  */
807                 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
808                 BUG_ON(age > 1);
809                 if (!age)
810                         rb_erase(&rmap_item->node,
811                                  root_unstable_tree + NUMA(rmap_item->nid));
812                 ksm_pages_unshared--;
813                 rmap_item->address &= PAGE_MASK;
814         }
815 out:
816         cond_resched();         /* we're called from many long loops */
817 }
818 
819 static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
820                                        struct rmap_item **rmap_list)
821 {
822         while (*rmap_list) {
823                 struct rmap_item *rmap_item = *rmap_list;
824                 *rmap_list = rmap_item->rmap_list;
825                 remove_rmap_item_from_tree(rmap_item);
826                 free_rmap_item(rmap_item);
827         }
828 }
829 
830 /*
831  * Though it's very tempting to unmerge rmap_items from stable tree rather
832  * than check every pte of a given vma, the locking doesn't quite work for
833  * that - an rmap_item is assigned to the stable tree after inserting ksm
834  * page and upping mmap_sem.  Nor does it fit with the way we skip dup'ing
835  * rmap_items from parent to child at fork time (so as not to waste time
836  * if exit comes before the next scan reaches it).
837  *
838  * Similarly, although we'd like to remove rmap_items (so updating counts
839  * and freeing memory) when unmerging an area, it's easier to leave that
840  * to the next pass of ksmd - consider, for example, how ksmd might be
841  * in cmp_and_merge_page on one of the rmap_items we would be removing.
842  */
843 static int unmerge_ksm_pages(struct vm_area_struct *vma,
844                              unsigned long start, unsigned long end)
845 {
846         unsigned long addr;
847         int err = 0;
848 
849         for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
850                 if (ksm_test_exit(vma->vm_mm))
851                         break;
852                 if (signal_pending(current))
853                         err = -ERESTARTSYS;
854                 else
855                         err = break_ksm(vma, addr);
856         }
857         return err;
858 }
859 
860 static inline struct stable_node *page_stable_node(struct page *page)
861 {
862         return PageKsm(page) ? page_rmapping(page) : NULL;
863 }
864 
865 static inline void set_page_stable_node(struct page *page,
866                                         struct stable_node *stable_node)
867 {
868         page->mapping = (void *)((unsigned long)stable_node | PAGE_MAPPING_KSM);
869 }
870 
871 #ifdef CONFIG_SYSFS
872 /*
873  * Only called through the sysfs control interface:
874  */
875 static int remove_stable_node(struct stable_node *stable_node)
876 {
877         struct page *page;
878         int err;
879 
880         page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
881         if (!page) {
882                 /*
883                  * get_ksm_page did remove_node_from_stable_tree itself.
884                  */
885                 return 0;
886         }
887 
888         /*
889          * Page could be still mapped if this races with __mmput() running in
890          * between ksm_exit() and exit_mmap(). Just refuse to let
891          * merge_across_nodes/max_page_sharing be switched.
892          */
893         err = -EBUSY;
894         if (!page_mapped(page)) {
895                 /*
896                  * The stable node did not yet appear stale to get_ksm_page(),
897                  * since that allows for an unmapped ksm page to be recognized
898                  * right up until it is freed; but the node is safe to remove.
899                  * This page might be in a pagevec waiting to be freed,
900                  * or it might be PageSwapCache (perhaps under writeback),
901                  * or it might have been removed from swapcache a moment ago.
902                  */
903                 set_page_stable_node(page, NULL);
904                 remove_node_from_stable_tree(stable_node);
905                 err = 0;
906         }
907 
908         unlock_page(page);
909         put_page(page);
910         return err;
911 }
912 
913 static int remove_stable_node_chain(struct stable_node *stable_node,
914                                     struct rb_root *root)
915 {
916         struct stable_node *dup;
917         struct hlist_node *hlist_safe;
918 
919         if (!is_stable_node_chain(stable_node)) {
920                 VM_BUG_ON(is_stable_node_dup(stable_node));
921                 if (remove_stable_node(stable_node))
922                         return true;
923                 else
924                         return false;
925         }
926 
927         hlist_for_each_entry_safe(dup, hlist_safe,
928                                   &stable_node->hlist, hlist_dup) {
929                 VM_BUG_ON(!is_stable_node_dup(dup));
930                 if (remove_stable_node(dup))
931                         return true;
932         }
933         BUG_ON(!hlist_empty(&stable_node->hlist));
934         free_stable_node_chain(stable_node, root);
935         return false;
936 }
937 
938 static int remove_all_stable_nodes(void)
939 {
940         struct stable_node *stable_node, *next;
941         int nid;
942         int err = 0;
943 
944         for (nid = 0; nid < ksm_nr_node_ids; nid++) {
945                 while (root_stable_tree[nid].rb_node) {
946                         stable_node = rb_entry(root_stable_tree[nid].rb_node,
947                                                 struct stable_node, node);
948                         if (remove_stable_node_chain(stable_node,
949                                                      root_stable_tree + nid)) {
950                                 err = -EBUSY;
951                                 break;  /* proceed to next nid */
952                         }
953                         cond_resched();
954                 }
955         }
956         list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
957                 if (remove_stable_node(stable_node))
958                         err = -EBUSY;
959                 cond_resched();
960         }
961         return err;
962 }
963 
964 static int unmerge_and_remove_all_rmap_items(void)
965 {
966         struct mm_slot *mm_slot;
967         struct mm_struct *mm;
968         struct vm_area_struct *vma;
969         int err = 0;
970 
971         spin_lock(&ksm_mmlist_lock);
972         ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
973                                                 struct mm_slot, mm_list);
974         spin_unlock(&ksm_mmlist_lock);
975 
976         for (mm_slot = ksm_scan.mm_slot;
977                         mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
978                 mm = mm_slot->mm;
979                 down_read(&mm->mmap_sem);
980                 for (vma = mm->mmap; vma; vma = vma->vm_next) {
981                         if (ksm_test_exit(mm))
982                                 break;
983                         if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
984                                 continue;
985                         err = unmerge_ksm_pages(vma,
986                                                 vma->vm_start, vma->vm_end);
987                         if (err)
988                                 goto error;
989                 }
990 
991                 remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
992                 up_read(&mm->mmap_sem);
993 
994                 spin_lock(&ksm_mmlist_lock);
995                 ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
996                                                 struct mm_slot, mm_list);
997                 if (ksm_test_exit(mm)) {
998                         hash_del(&mm_slot->link);
999                         list_del(&mm_slot->mm_list);
1000                         spin_unlock(&ksm_mmlist_lock);
1001 
1002                         free_mm_slot(mm_slot);
1003                         clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1004                         mmdrop(mm);
1005                 } else
1006                         spin_unlock(&ksm_mmlist_lock);
1007         }
1008 
1009         /* Clean up stable nodes, but don't worry if some are still busy */
1010         remove_all_stable_nodes();
1011         ksm_scan.seqnr = 0;
1012         return 0;
1013 
1014 error:
1015         up_read(&mm->mmap_sem);
1016         spin_lock(&ksm_mmlist_lock);
1017         ksm_scan.mm_slot = &ksm_mm_head;
1018         spin_unlock(&ksm_mmlist_lock);
1019         return err;
1020 }
1021 #endif /* CONFIG_SYSFS */
1022 
1023 static u32 calc_checksum(struct page *page)
1024 {
1025         u32 checksum;
1026         void *addr = kmap_atomic(page);
1027         checksum = xxhash(addr, PAGE_SIZE, 0);
1028         kunmap_atomic(addr);
1029         return checksum;
1030 }
1031 
1032 static int memcmp_pages(struct page *page1, struct page *page2)
1033 {
1034         char *addr1, *addr2;
1035         int ret;
1036 
1037         addr1 = kmap_atomic(page1);
1038         addr2 = kmap_atomic(page2);
1039         ret = memcmp(addr1, addr2, PAGE_SIZE);
1040         kunmap_atomic(addr2);
1041         kunmap_atomic(addr1);
1042         return ret;
1043 }
1044 
1045 static inline int pages_identical(struct page *page1, struct page *page2)
1046 {
1047         return !memcmp_pages(page1, page2);
1048 }
1049 
1050 static int write_protect_page(struct vm_area_struct *vma, struct page *page,
1051                               pte_t *orig_pte)
1052 {
1053         struct mm_struct *mm = vma->vm_mm;
1054         struct page_vma_mapped_walk pvmw = {
1055                 .page = page,
1056                 .vma = vma,
1057         };
1058         int swapped;
1059         int err = -EFAULT;
1060         struct mmu_notifier_range range;
1061 
1062         pvmw.address = page_address_in_vma(page, vma);
1063         if (pvmw.address == -EFAULT)
1064                 goto out;
1065 
1066         BUG_ON(PageTransCompound(page));
1067 
1068         mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm,
1069                                 pvmw.address,
1070                                 pvmw.address + PAGE_SIZE);
1071         mmu_notifier_invalidate_range_start(&range);
1072 
1073         if (!page_vma_mapped_walk(&pvmw))
1074                 goto out_mn;
1075         if (WARN_ONCE(!pvmw.pte, "Unexpected PMD mapping?"))
1076                 goto out_unlock;
1077 
1078         if (pte_write(*pvmw.pte) || pte_dirty(*pvmw.pte) ||
1079             (pte_protnone(*pvmw.pte) && pte_savedwrite(*pvmw.pte)) ||
1080                                                 mm_tlb_flush_pending(mm)) {
1081                 pte_t entry;
1082 
1083                 swapped = PageSwapCache(page);
1084                 flush_cache_page(vma, pvmw.address, page_to_pfn(page));
1085                 /*
1086                  * Ok this is tricky, when get_user_pages_fast() run it doesn't
1087                  * take any lock, therefore the check that we are going to make
1088                  * with the pagecount against the mapcount is racey and
1089                  * O_DIRECT can happen right after the check.
1090                  * So we clear the pte and flush the tlb before the check
1091                  * this assure us that no O_DIRECT can happen after the check
1092                  * or in the middle of the check.
1093                  *
1094                  * No need to notify as we are downgrading page table to read
1095                  * only not changing it to point to a new page.
1096                  *
1097                  * See Documentation/vm/mmu_notifier.rst
1098                  */
1099                 entry = ptep_clear_flush(vma, pvmw.address, pvmw.pte);
1100                 /*
1101                  * Check that no O_DIRECT or similar I/O is in progress on the
1102                  * page
1103                  */
1104                 if (page_mapcount(page) + 1 + swapped != page_count(page)) {
1105                         set_pte_at(mm, pvmw.address, pvmw.pte, entry);
1106                         goto out_unlock;
1107                 }
1108                 if (pte_dirty(entry))
1109                         set_page_dirty(page);
1110 
1111                 if (pte_protnone(entry))
1112                         entry = pte_mkclean(pte_clear_savedwrite(entry));
1113                 else
1114                         entry = pte_mkclean(pte_wrprotect(entry));
1115                 set_pte_at_notify(mm, pvmw.address, pvmw.pte, entry);
1116         }
1117         *orig_pte = *pvmw.pte;
1118         err = 0;
1119 
1120 out_unlock:
1121         page_vma_mapped_walk_done(&pvmw);
1122 out_mn:
1123         mmu_notifier_invalidate_range_end(&range);
1124 out:
1125         return err;
1126 }
1127 
1128 /**
1129  * replace_page - replace page in vma by new ksm page
1130  * @vma:      vma that holds the pte pointing to page
1131  * @page:     the page we are replacing by kpage
1132  * @kpage:    the ksm page we replace page by
1133  * @orig_pte: the original value of the pte
1134  *
1135  * Returns 0 on success, -EFAULT on failure.
1136  */
1137 static int replace_page(struct vm_area_struct *vma, struct page *page,
1138                         struct page *kpage, pte_t orig_pte)
1139 {
1140         struct mm_struct *mm = vma->vm_mm;
1141         pmd_t *pmd;
1142         pte_t *ptep;
1143         pte_t newpte;
1144         spinlock_t *ptl;
1145         unsigned long addr;
1146         int err = -EFAULT;
1147         struct mmu_notifier_range range;
1148 
1149         addr = page_address_in_vma(page, vma);
1150         if (addr == -EFAULT)
1151                 goto out;
1152 
1153         pmd = mm_find_pmd(mm, addr);
1154         if (!pmd)
1155                 goto out;
1156 
1157         mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm, addr,
1158                                 addr + PAGE_SIZE);
1159         mmu_notifier_invalidate_range_start(&range);
1160 
1161         ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
1162         if (!pte_same(*ptep, orig_pte)) {
1163                 pte_unmap_unlock(ptep, ptl);
1164                 goto out_mn;
1165         }
1166 
1167         /*
1168          * No need to check ksm_use_zero_pages here: we can only have a
1169          * zero_page here if ksm_use_zero_pages was enabled alreaady.
1170          */
1171         if (!is_zero_pfn(page_to_pfn(kpage))) {
1172                 get_page(kpage);
1173                 page_add_anon_rmap(kpage, vma, addr, false);
1174                 newpte = mk_pte(kpage, vma->vm_page_prot);
1175         } else {
1176                 newpte = pte_mkspecial(pfn_pte(page_to_pfn(kpage),
1177                                                vma->vm_page_prot));
1178                 /*
1179                  * We're replacing an anonymous page with a zero page, which is
1180                  * not anonymous. We need to do proper accounting otherwise we
1181                  * will get wrong values in /proc, and a BUG message in dmesg
1182                  * when tearing down the mm.
1183                  */
1184                 dec_mm_counter(mm, MM_ANONPAGES);
1185         }
1186 
1187         flush_cache_page(vma, addr, pte_pfn(*ptep));
1188         /*
1189          * No need to notify as we are replacing a read only page with another
1190          * read only page with the same content.
1191          *
1192          * See Documentation/vm/mmu_notifier.rst
1193          */
1194         ptep_clear_flush(vma, addr, ptep);
1195         set_pte_at_notify(mm, addr, ptep, newpte);
1196 
1197         page_remove_rmap(page, false);
1198         if (!page_mapped(page))
1199                 try_to_free_swap(page);
1200         put_page(page);
1201 
1202         pte_unmap_unlock(ptep, ptl);
1203         err = 0;
1204 out_mn:
1205         mmu_notifier_invalidate_range_end(&range);
1206 out:
1207         return err;
1208 }
1209 
1210 /*
1211  * try_to_merge_one_page - take two pages and merge them into one
1212  * @vma: the vma that holds the pte pointing to page
1213  * @page: the PageAnon page that we want to replace with kpage
1214  * @kpage: the PageKsm page that we want to map instead of page,
1215  *         or NULL the first time when we want to use page as kpage.
1216  *
1217  * This function returns 0 if the pages were merged, -EFAULT otherwise.
1218  */
1219 static int try_to_merge_one_page(struct vm_area_struct *vma,
1220                                  struct page *page, struct page *kpage)
1221 {
1222         pte_t orig_pte = __pte(0);
1223         int err = -EFAULT;
1224 
1225         if (page == kpage)                      /* ksm page forked */
1226                 return 0;
1227 
1228         if (!PageAnon(page))
1229                 goto out;
1230 
1231         /*
1232          * We need the page lock to read a stable PageSwapCache in
1233          * write_protect_page().  We use trylock_page() instead of
1234          * lock_page() because we don't want to wait here - we
1235          * prefer to continue scanning and merging different pages,
1236          * then come back to this page when it is unlocked.
1237          */
1238         if (!trylock_page(page))
1239                 goto out;
1240 
1241         if (PageTransCompound(page)) {
1242                 if (split_huge_page(page))
1243                         goto out_unlock;
1244         }
1245 
1246         /*
1247          * If this anonymous page is mapped only here, its pte may need
1248          * to be write-protected.  If it's mapped elsewhere, all of its
1249          * ptes are necessarily already write-protected.  But in either
1250          * case, we need to lock and check page_count is not raised.
1251          */
1252         if (write_protect_page(vma, page, &orig_pte) == 0) {
1253                 if (!kpage) {
1254                         /*
1255                          * While we hold page lock, upgrade page from
1256                          * PageAnon+anon_vma to PageKsm+NULL stable_node:
1257                          * stable_tree_insert() will update stable_node.
1258                          */
1259                         set_page_stable_node(page, NULL);
1260                         mark_page_accessed(page);
1261                         /*
1262                          * Page reclaim just frees a clean page with no dirty
1263                          * ptes: make sure that the ksm page would be swapped.
1264                          */
1265                         if (!PageDirty(page))
1266                                 SetPageDirty(page);
1267                         err = 0;
1268                 } else if (pages_identical(page, kpage))
1269                         err = replace_page(vma, page, kpage, orig_pte);
1270         }
1271 
1272         if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
1273                 munlock_vma_page(page);
1274                 if (!PageMlocked(kpage)) {
1275                         unlock_page(page);
1276                         lock_page(kpage);
1277                         mlock_vma_page(kpage);
1278                         page = kpage;           /* for final unlock */
1279                 }
1280         }
1281 
1282 out_unlock:
1283         unlock_page(page);
1284 out:
1285         return err;
1286 }
1287 
1288 /*
1289  * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
1290  * but no new kernel page is allocated: kpage must already be a ksm page.
1291  *
1292  * This function returns 0 if the pages were merged, -EFAULT otherwise.
1293  */
1294 static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
1295                                       struct page *page, struct page *kpage)
1296 {
1297         struct mm_struct *mm = rmap_item->mm;
1298         struct vm_area_struct *vma;
1299         int err = -EFAULT;
1300 
1301         down_read(&mm->mmap_sem);
1302         vma = find_mergeable_vma(mm, rmap_item->address);
1303         if (!vma)
1304                 goto out;
1305 
1306         err = try_to_merge_one_page(vma, page, kpage);
1307         if (err)
1308                 goto out;
1309 
1310         /* Unstable nid is in union with stable anon_vma: remove first */
1311         remove_rmap_item_from_tree(rmap_item);
1312 
1313         /* Must get reference to anon_vma while still holding mmap_sem */
1314         rmap_item->anon_vma = vma->anon_vma;
1315         get_anon_vma(vma->anon_vma);
1316 out:
1317         up_read(&mm->mmap_sem);
1318         return err;
1319 }
1320 
1321 /*
1322  * try_to_merge_two_pages - take two identical pages and prepare them
1323  * to be merged into one page.
1324  *
1325  * This function returns the kpage if we successfully merged two identical
1326  * pages into one ksm page, NULL otherwise.
1327  *
1328  * Note that this function upgrades page to ksm page: if one of the pages
1329  * is already a ksm page, try_to_merge_with_ksm_page should be used.
1330  */
1331 static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
1332                                            struct page *page,
1333                                            struct rmap_item *tree_rmap_item,
1334                                            struct page *tree_page)
1335 {
1336         int err;
1337 
1338         err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
1339         if (!err) {
1340                 err = try_to_merge_with_ksm_page(tree_rmap_item,
1341                                                         tree_page, page);
1342                 /*
1343                  * If that fails, we have a ksm page with only one pte
1344                  * pointing to it: so break it.
1345                  */
1346                 if (err)
1347                         break_cow(rmap_item);
1348         }
1349         return err ? NULL : page;
1350 }
1351 
1352 static __always_inline
1353 bool __is_page_sharing_candidate(struct stable_node *stable_node, int offset)
1354 {
1355         VM_BUG_ON(stable_node->rmap_hlist_len < 0);
1356         /*
1357          * Check that at least one mapping still exists, otherwise
1358          * there's no much point to merge and share with this
1359          * stable_node, as the underlying tree_page of the other
1360          * sharer is going to be freed soon.
1361          */
1362         return stable_node->rmap_hlist_len &&
1363                 stable_node->rmap_hlist_len + offset < ksm_max_page_sharing;
1364 }
1365 
1366 static __always_inline
1367 bool is_page_sharing_candidate(struct stable_node *stable_node)
1368 {
1369         return __is_page_sharing_candidate(stable_node, 0);
1370 }
1371 
1372 static struct page *stable_node_dup(struct stable_node **_stable_node_dup,
1373                                     struct stable_node **_stable_node,
1374                                     struct rb_root *root,
1375                                     bool prune_stale_stable_nodes)
1376 {
1377         struct stable_node *dup, *found = NULL, *stable_node = *_stable_node;
1378         struct hlist_node *hlist_safe;
1379         struct page *_tree_page, *tree_page = NULL;
1380         int nr = 0;
1381         int found_rmap_hlist_len;
1382 
1383         if (!prune_stale_stable_nodes ||
1384             time_before(jiffies, stable_node->chain_prune_time +
1385                         msecs_to_jiffies(
1386                                 ksm_stable_node_chains_prune_millisecs)))
1387                 prune_stale_stable_nodes = false;
1388         else
1389                 stable_node->chain_prune_time = jiffies;
1390 
1391         hlist_for_each_entry_safe(dup, hlist_safe,
1392                                   &stable_node->hlist, hlist_dup) {
1393                 cond_resched();
1394                 /*
1395                  * We must walk all stable_node_dup to prune the stale
1396                  * stable nodes during lookup.
1397                  *
1398                  * get_ksm_page can drop the nodes from the
1399                  * stable_node->hlist if they point to freed pages
1400                  * (that's why we do a _safe walk). The "dup"
1401                  * stable_node parameter itself will be freed from
1402                  * under us if it returns NULL.
1403                  */
1404                 _tree_page = get_ksm_page(dup, GET_KSM_PAGE_NOLOCK);
1405                 if (!_tree_page)
1406                         continue;
1407                 nr += 1;
1408                 if (is_page_sharing_candidate(dup)) {
1409                         if (!found ||
1410                             dup->rmap_hlist_len > found_rmap_hlist_len) {
1411                                 if (found)
1412                                         put_page(tree_page);
1413                                 found = dup;
1414                                 found_rmap_hlist_len = found->rmap_hlist_len;
1415                                 tree_page = _tree_page;
1416 
1417                                 /* skip put_page for found dup */
1418                                 if (!prune_stale_stable_nodes)
1419                                         break;
1420                                 continue;
1421                         }
1422                 }
1423                 put_page(_tree_page);
1424         }
1425 
1426         if (found) {
1427                 /*
1428                  * nr is counting all dups in the chain only if
1429                  * prune_stale_stable_nodes is true, otherwise we may
1430                  * break the loop at nr == 1 even if there are
1431                  * multiple entries.
1432                  */
1433                 if (prune_stale_stable_nodes && nr == 1) {
1434                         /*
1435                          * If there's not just one entry it would
1436                          * corrupt memory, better BUG_ON. In KSM
1437                          * context with no lock held it's not even
1438                          * fatal.
1439                          */
1440                         BUG_ON(stable_node->hlist.first->next);
1441 
1442                         /*
1443                          * There's just one entry and it is below the
1444                          * deduplication limit so drop the chain.
1445                          */
1446                         rb_replace_node(&stable_node->node, &found->node,
1447                                         root);
1448                         free_stable_node(stable_node);
1449                         ksm_stable_node_chains--;
1450                         ksm_stable_node_dups--;
1451                         /*
1452                          * NOTE: the caller depends on the stable_node
1453                          * to be equal to stable_node_dup if the chain
1454                          * was collapsed.
1455                          */
1456                         *_stable_node = found;
1457                         /*
1458                          * Just for robustneess as stable_node is
1459                          * otherwise left as a stable pointer, the
1460                          * compiler shall optimize it away at build
1461                          * time.
1462                          */
1463                         stable_node = NULL;
1464                 } else if (stable_node->hlist.first != &found->hlist_dup &&
1465                            __is_page_sharing_candidate(found, 1)) {
1466                         /*
1467                          * If the found stable_node dup can accept one
1468                          * more future merge (in addition to the one
1469                          * that is underway) and is not at the head of
1470                          * the chain, put it there so next search will
1471                          * be quicker in the !prune_stale_stable_nodes
1472                          * case.
1473                          *
1474                          * NOTE: it would be inaccurate to use nr > 1
1475                          * instead of checking the hlist.first pointer
1476                          * directly, because in the
1477                          * prune_stale_stable_nodes case "nr" isn't
1478                          * the position of the found dup in the chain,
1479                          * but the total number of dups in the chain.
1480                          */
1481                         hlist_del(&found->hlist_dup);
1482                         hlist_add_head(&found->hlist_dup,
1483                                        &stable_node->hlist);
1484                 }
1485         }
1486 
1487         *_stable_node_dup = found;
1488         return tree_page;
1489 }
1490 
1491 static struct stable_node *stable_node_dup_any(struct stable_node *stable_node,
1492                                                struct rb_root *root)
1493 {
1494         if (!is_stable_node_chain(stable_node))
1495                 return stable_node;
1496         if (hlist_empty(&stable_node->hlist)) {
1497                 free_stable_node_chain(stable_node, root);
1498                 return NULL;
1499         }
1500         return hlist_entry(stable_node->hlist.first,
1501                            typeof(*stable_node), hlist_dup);
1502 }
1503 
1504 /*
1505  * Like for get_ksm_page, this function can free the *_stable_node and
1506  * *_stable_node_dup if the returned tree_page is NULL.
1507  *
1508  * It can also free and overwrite *_stable_node with the found
1509  * stable_node_dup if the chain is collapsed (in which case
1510  * *_stable_node will be equal to *_stable_node_dup like if the chain
1511  * never existed). It's up to the caller to verify tree_page is not
1512  * NULL before dereferencing *_stable_node or *_stable_node_dup.
1513  *
1514  * *_stable_node_dup is really a second output parameter of this
1515  * function and will be overwritten in all cases, the caller doesn't
1516  * need to initialize it.
1517  */
1518 static struct page *__stable_node_chain(struct stable_node **_stable_node_dup,
1519                                         struct stable_node **_stable_node,
1520                                         struct rb_root *root,
1521                                         bool prune_stale_stable_nodes)
1522 {
1523         struct stable_node *stable_node = *_stable_node;
1524         if (!is_stable_node_chain(stable_node)) {
1525                 if (is_page_sharing_candidate(stable_node)) {
1526                         *_stable_node_dup = stable_node;
1527                         return get_ksm_page(stable_node, GET_KSM_PAGE_NOLOCK);
1528                 }
1529                 /*
1530                  * _stable_node_dup set to NULL means the stable_node
1531                  * reached the ksm_max_page_sharing limit.
1532                  */
1533                 *_stable_node_dup = NULL;
1534                 return NULL;
1535         }
1536         return stable_node_dup(_stable_node_dup, _stable_node, root,
1537                                prune_stale_stable_nodes);
1538 }
1539 
1540 static __always_inline struct page *chain_prune(struct stable_node **s_n_d,
1541                                                 struct stable_node **s_n,
1542                                                 struct rb_root *root)
1543 {
1544         return __stable_node_chain(s_n_d, s_n, root, true);
1545 }
1546 
1547 static __always_inline struct page *chain(struct stable_node **s_n_d,
1548                                           struct stable_node *s_n,
1549                                           struct rb_root *root)
1550 {
1551         struct stable_node *old_stable_node = s_n;
1552         struct page *tree_page;
1553 
1554         tree_page = __stable_node_chain(s_n_d, &s_n, root, false);
1555         /* not pruning dups so s_n cannot have changed */
1556         VM_BUG_ON(s_n != old_stable_node);
1557         return tree_page;
1558 }
1559 
1560 /*
1561  * stable_tree_search - search for page inside the stable tree
1562  *
1563  * This function checks if there is a page inside the stable tree
1564  * with identical content to the page that we are scanning right now.
1565  *
1566  * This function returns the stable tree node of identical content if found,
1567  * NULL otherwise.
1568  */
1569 static struct page *stable_tree_search(struct page *page)
1570 {
1571         int nid;
1572         struct rb_root *root;
1573         struct rb_node **new;
1574         struct rb_node *parent;
1575         struct stable_node *stable_node, *stable_node_dup, *stable_node_any;
1576         struct stable_node *page_node;
1577 
1578         page_node = page_stable_node(page);
1579         if (page_node && page_node->head != &migrate_nodes) {
1580                 /* ksm page forked */
1581                 get_page(page);
1582                 return page;
1583         }
1584 
1585         nid = get_kpfn_nid(page_to_pfn(page));
1586         root = root_stable_tree + nid;
1587 again:
1588         new = &root->rb_node;
1589         parent = NULL;
1590 
1591         while (*new) {
1592                 struct page *tree_page;
1593                 int ret;
1594 
1595                 cond_resched();
1596                 stable_node = rb_entry(*new, struct stable_node, node);
1597                 stable_node_any = NULL;
1598                 tree_page = chain_prune(&stable_node_dup, &stable_node, root);
1599                 /*
1600                  * NOTE: stable_node may have been freed by
1601                  * chain_prune() if the returned stable_node_dup is
1602                  * not NULL. stable_node_dup may have been inserted in
1603                  * the rbtree instead as a regular stable_node (in
1604                  * order to collapse the stable_node chain if a single
1605                  * stable_node dup was found in it). In such case the
1606                  * stable_node is overwritten by the calleee to point
1607                  * to the stable_node_dup that was collapsed in the
1608                  * stable rbtree and stable_node will be equal to
1609                  * stable_node_dup like if the chain never existed.
1610                  */
1611                 if (!stable_node_dup) {
1612                         /*
1613                          * Either all stable_node dups were full in
1614                          * this stable_node chain, or this chain was
1615                          * empty and should be rb_erased.
1616                          */
1617                         stable_node_any = stable_node_dup_any(stable_node,
1618                                                               root);
1619                         if (!stable_node_any) {
1620                                 /* rb_erase just run */
1621                                 goto again;
1622                         }
1623                         /*
1624                          * Take any of the stable_node dups page of
1625                          * this stable_node chain to let the tree walk
1626                          * continue. All KSM pages belonging to the
1627                          * stable_node dups in a stable_node chain
1628                          * have the same content and they're
1629                          * wrprotected at all times. Any will work
1630                          * fine to continue the walk.
1631                          */
1632                         tree_page = get_ksm_page(stable_node_any,
1633                                                  GET_KSM_PAGE_NOLOCK);
1634                 }
1635                 VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
1636                 if (!tree_page) {
1637                         /*
1638                          * If we walked over a stale stable_node,
1639                          * get_ksm_page() will call rb_erase() and it
1640                          * may rebalance the tree from under us. So
1641                          * restart the search from scratch. Returning
1642                          * NULL would be safe too, but we'd generate
1643                          * false negative insertions just because some
1644                          * stable_node was stale.
1645                          */
1646                         goto again;
1647                 }
1648 
1649                 ret = memcmp_pages(page, tree_page);
1650                 put_page(tree_page);
1651 
1652                 parent = *new;
1653                 if (ret < 0)
1654                         new = &parent->rb_left;
1655                 else if (ret > 0)
1656                         new = &parent->rb_right;
1657                 else {
1658                         if (page_node) {
1659                                 VM_BUG_ON(page_node->head != &migrate_nodes);
1660                                 /*
1661                                  * Test if the migrated page should be merged
1662                                  * into a stable node dup. If the mapcount is
1663                                  * 1 we can migrate it with another KSM page
1664                                  * without adding it to the chain.
1665                                  */
1666                                 if (page_mapcount(page) > 1)
1667                                         goto chain_append;
1668                         }
1669 
1670                         if (!stable_node_dup) {
1671                                 /*
1672                                  * If the stable_node is a chain and
1673                                  * we got a payload match in memcmp
1674                                  * but we cannot merge the scanned
1675                                  * page in any of the existing
1676                                  * stable_node dups because they're
1677                                  * all full, we need to wait the
1678                                  * scanned page to find itself a match
1679                                  * in the unstable tree to create a
1680                                  * brand new KSM page to add later to
1681                                  * the dups of this stable_node.
1682                                  */
1683                                 return NULL;
1684                         }
1685 
1686                         /*
1687                          * Lock and unlock the stable_node's page (which
1688                          * might already have been migrated) so that page
1689                          * migration is sure to notice its raised count.
1690                          * It would be more elegant to return stable_node
1691                          * than kpage, but that involves more changes.
1692                          */
1693                         tree_page = get_ksm_page(stable_node_dup,
1694                                                  GET_KSM_PAGE_TRYLOCK);
1695 
1696                         if (PTR_ERR(tree_page) == -EBUSY)
1697                                 return ERR_PTR(-EBUSY);
1698 
1699                         if (unlikely(!tree_page))
1700                                 /*
1701                                  * The tree may have been rebalanced,
1702                                  * so re-evaluate parent and new.
1703                                  */
1704                                 goto again;
1705                         unlock_page(tree_page);
1706 
1707                         if (get_kpfn_nid(stable_node_dup->kpfn) !=
1708                             NUMA(stable_node_dup->nid)) {
1709                                 put_page(tree_page);
1710                                 goto replace;
1711                         }
1712                         return tree_page;
1713                 }
1714         }
1715 
1716         if (!page_node)
1717                 return NULL;
1718 
1719         list_del(&page_node->list);
1720         DO_NUMA(page_node->nid = nid);
1721         rb_link_node(&page_node->node, parent, new);
1722         rb_insert_color(&page_node->node, root);
1723 out:
1724         if (is_page_sharing_candidate(page_node)) {
1725                 get_page(page);
1726                 return page;
1727         } else
1728                 return NULL;
1729 
1730 replace:
1731         /*
1732          * If stable_node was a chain and chain_prune collapsed it,
1733          * stable_node has been updated to be the new regular
1734          * stable_node. A collapse of the chain is indistinguishable
1735          * from the case there was no chain in the stable
1736          * rbtree. Otherwise stable_node is the chain and
1737          * stable_node_dup is the dup to replace.
1738          */
1739         if (stable_node_dup == stable_node) {
1740                 VM_BUG_ON(is_stable_node_chain(stable_node_dup));
1741                 VM_BUG_ON(is_stable_node_dup(stable_node_dup));
1742                 /* there is no chain */
1743                 if (page_node) {
1744                         VM_BUG_ON(page_node->head != &migrate_nodes);
1745                         list_del(&page_node->list);
1746                         DO_NUMA(page_node->nid = nid);
1747                         rb_replace_node(&stable_node_dup->node,
1748                                         &page_node->node,
1749                                         root);
1750                         if (is_page_sharing_candidate(page_node))
1751                                 get_page(page);
1752                         else
1753                                 page = NULL;
1754                 } else {
1755                         rb_erase(&stable_node_dup->node, root);
1756                         page = NULL;
1757                 }
1758         } else {
1759                 VM_BUG_ON(!is_stable_node_chain(stable_node));
1760                 __stable_node_dup_del(stable_node_dup);
1761                 if (page_node) {
1762                         VM_BUG_ON(page_node->head != &migrate_nodes);
1763                         list_del(&page_node->list);
1764                         DO_NUMA(page_node->nid = nid);
1765                         stable_node_chain_add_dup(page_node, stable_node);
1766                         if (is_page_sharing_candidate(page_node))
1767                                 get_page(page);
1768                         else
1769                                 page = NULL;
1770                 } else {
1771                         page = NULL;
1772                 }
1773         }
1774         stable_node_dup->head = &migrate_nodes;
1775         list_add(&stable_node_dup->list, stable_node_dup->head);
1776         return page;
1777 
1778 chain_append:
1779         /* stable_node_dup could be null if it reached the limit */
1780         if (!stable_node_dup)
1781                 stable_node_dup = stable_node_any;
1782         /*
1783          * If stable_node was a chain and chain_prune collapsed it,
1784          * stable_node has been updated to be the new regular
1785          * stable_node. A collapse of the chain is indistinguishable
1786          * from the case there was no chain in the stable
1787          * rbtree. Otherwise stable_node is the chain and
1788          * stable_node_dup is the dup to replace.
1789          */
1790         if (stable_node_dup == stable_node) {
1791                 VM_BUG_ON(is_stable_node_chain(stable_node_dup));
1792                 VM_BUG_ON(is_stable_node_dup(stable_node_dup));
1793                 /* chain is missing so create it */
1794                 stable_node = alloc_stable_node_chain(stable_node_dup,
1795                                                       root);
1796                 if (!stable_node)
1797                         return NULL;
1798         }
1799         /*
1800          * Add this stable_node dup that was
1801          * migrated to the stable_node chain
1802          * of the current nid for this page
1803          * content.
1804          */
1805         VM_BUG_ON(!is_stable_node_chain(stable_node));
1806         VM_BUG_ON(!is_stable_node_dup(stable_node_dup));
1807         VM_BUG_ON(page_node->head != &migrate_nodes);
1808         list_del(&page_node->list);
1809         DO_NUMA(page_node->nid = nid);
1810         stable_node_chain_add_dup(page_node, stable_node);
1811         goto out;
1812 }
1813 
1814 /*
1815  * stable_tree_insert - insert stable tree node pointing to new ksm page
1816  * into the stable tree.
1817  *
1818  * This function returns the stable tree node just allocated on success,
1819  * NULL otherwise.
1820  */
1821 static struct stable_node *stable_tree_insert(struct page *kpage)
1822 {
1823         int nid;
1824         unsigned long kpfn;
1825         struct rb_root *root;
1826         struct rb_node **new;
1827         struct rb_node *parent;
1828         struct stable_node *stable_node, *stable_node_dup, *stable_node_any;
1829         bool need_chain = false;
1830 
1831         kpfn = page_to_pfn(kpage);
1832         nid = get_kpfn_nid(kpfn);
1833         root = root_stable_tree + nid;
1834 again:
1835         parent = NULL;
1836         new = &root->rb_node;
1837 
1838         while (*new) {
1839                 struct page *tree_page;
1840                 int ret;
1841 
1842                 cond_resched();
1843                 stable_node = rb_entry(*new, struct stable_node, node);
1844                 stable_node_any = NULL;
1845                 tree_page = chain(&stable_node_dup, stable_node, root);
1846                 if (!stable_node_dup) {
1847                         /*
1848                          * Either all stable_node dups were full in
1849                          * this stable_node chain, or this chain was
1850                          * empty and should be rb_erased.
1851                          */
1852                         stable_node_any = stable_node_dup_any(stable_node,
1853                                                               root);
1854                         if (!stable_node_any) {
1855                                 /* rb_erase just run */
1856                                 goto again;
1857                         }
1858                         /*
1859                          * Take any of the stable_node dups page of
1860                          * this stable_node chain to let the tree walk
1861                          * continue. All KSM pages belonging to the
1862                          * stable_node dups in a stable_node chain
1863                          * have the same content and they're
1864                          * wrprotected at all times. Any will work
1865                          * fine to continue the walk.
1866                          */
1867                         tree_page = get_ksm_page(stable_node_any,
1868                                                  GET_KSM_PAGE_NOLOCK);
1869                 }
1870                 VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
1871                 if (!tree_page) {
1872                         /*
1873                          * If we walked over a stale stable_node,
1874                          * get_ksm_page() will call rb_erase() and it
1875                          * may rebalance the tree from under us. So
1876                          * restart the search from scratch. Returning
1877                          * NULL would be safe too, but we'd generate
1878                          * false negative insertions just because some
1879                          * stable_node was stale.
1880                          */
1881                         goto again;
1882                 }
1883 
1884                 ret = memcmp_pages(kpage, tree_page);
1885                 put_page(tree_page);
1886 
1887                 parent = *new;
1888                 if (ret < 0)
1889                         new = &parent->rb_left;
1890                 else if (ret > 0)
1891                         new = &parent->rb_right;
1892                 else {
1893                         need_chain = true;
1894                         break;
1895                 }
1896         }
1897 
1898         stable_node_dup = alloc_stable_node();
1899         if (!stable_node_dup)
1900                 return NULL;
1901 
1902         INIT_HLIST_HEAD(&stable_node_dup->hlist);
1903         stable_node_dup->kpfn = kpfn;
1904         set_page_stable_node(kpage, stable_node_dup);
1905         stable_node_dup->rmap_hlist_len = 0;
1906         DO_NUMA(stable_node_dup->nid = nid);
1907         if (!need_chain) {
1908                 rb_link_node(&stable_node_dup->node, parent, new);
1909                 rb_insert_color(&stable_node_dup->node, root);
1910         } else {
1911                 if (!is_stable_node_chain(stable_node)) {
1912                         struct stable_node *orig = stable_node;
1913                         /* chain is missing so create it */
1914                         stable_node = alloc_stable_node_chain(orig, root);
1915                         if (!stable_node) {
1916                                 free_stable_node(stable_node_dup);
1917                                 return NULL;
1918                         }
1919                 }
1920                 stable_node_chain_add_dup(stable_node_dup, stable_node);
1921         }
1922 
1923         return stable_node_dup;
1924 }
1925 
1926 /*
1927  * unstable_tree_search_insert - search for identical page,
1928  * else insert rmap_item into the unstable tree.
1929  *
1930  * This function searches for a page in the unstable tree identical to the
1931  * page currently being scanned; and if no identical page is found in the
1932  * tree, we insert rmap_item as a new object into the unstable tree.
1933  *
1934  * This function returns pointer to rmap_item found to be identical
1935  * to the currently scanned page, NULL otherwise.
1936  *
1937  * This function does both searching and inserting, because they share
1938  * the same walking algorithm in an rbtree.
1939  */
1940 static
1941 struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1942                                               struct page *page,
1943                                               struct page **tree_pagep)
1944 {
1945         struct rb_node **new;
1946         struct rb_root *root;
1947         struct rb_node *parent = NULL;
1948         int nid;
1949 
1950         nid = get_kpfn_nid(page_to_pfn(page));
1951         root = root_unstable_tree + nid;
1952         new = &root->rb_node;
1953 
1954         while (*new) {
1955                 struct rmap_item *tree_rmap_item;
1956                 struct page *tree_page;
1957                 int ret;
1958 
1959                 cond_resched();
1960                 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1961                 tree_page = get_mergeable_page(tree_rmap_item);
1962                 if (!tree_page)
1963                         return NULL;
1964 
1965                 /*
1966                  * Don't substitute a ksm page for a forked page.
1967                  */
1968                 if (page == tree_page) {
1969                         put_page(tree_page);
1970                         return NULL;
1971                 }
1972 
1973                 ret = memcmp_pages(page, tree_page);
1974 
1975                 parent = *new;
1976                 if (ret < 0) {
1977                         put_page(tree_page);
1978                         new = &parent->rb_left;
1979                 } else if (ret > 0) {
1980                         put_page(tree_page);
1981                         new = &parent->rb_right;
1982                 } else if (!ksm_merge_across_nodes &&
1983                            page_to_nid(tree_page) != nid) {
1984                         /*
1985                          * If tree_page has been migrated to another NUMA node,
1986                          * it will be flushed out and put in the right unstable
1987                          * tree next time: only merge with it when across_nodes.
1988                          */
1989                         put_page(tree_page);
1990                         return NULL;
1991                 } else {
1992                         *tree_pagep = tree_page;
1993                         return tree_rmap_item;
1994                 }
1995         }
1996 
1997         rmap_item->address |= UNSTABLE_FLAG;
1998         rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1999         DO_NUMA(rmap_item->nid = nid);
2000         rb_link_node(&rmap_item->node, parent, new);
2001         rb_insert_color(&rmap_item->node, root);
2002 
2003         ksm_pages_unshared++;
2004         return NULL;
2005 }
2006 
2007 /*
2008  * stable_tree_append - add another rmap_item to the linked list of
2009  * rmap_items hanging off a given node of the stable tree, all sharing
2010  * the same ksm page.
2011  */
2012 static void stable_tree_append(struct rmap_item *rmap_item,
2013                                struct stable_node *stable_node,
2014                                bool max_page_sharing_bypass)
2015 {
2016         /*
2017          * rmap won't find this mapping if we don't insert the
2018          * rmap_item in the right stable_node
2019          * duplicate. page_migration could break later if rmap breaks,
2020          * so we can as well crash here. We really need to check for
2021          * rmap_hlist_len == STABLE_NODE_CHAIN, but we can as well check
2022          * for other negative values as an undeflow if detected here
2023          * for the first time (and not when decreasing rmap_hlist_len)
2024          * would be sign of memory corruption in the stable_node.
2025          */
2026         BUG_ON(stable_node->rmap_hlist_len < 0);
2027 
2028         stable_node->rmap_hlist_len++;
2029         if (!max_page_sharing_bypass)
2030                 /* possibly non fatal but unexpected overflow, only warn */
2031                 WARN_ON_ONCE(stable_node->rmap_hlist_len >
2032                              ksm_max_page_sharing);
2033 
2034         rmap_item->head = stable_node;
2035         rmap_item->address |= STABLE_FLAG;
2036         hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
2037 
2038         if (rmap_item->hlist.next)
2039                 ksm_pages_sharing++;
2040         else
2041                 ksm_pages_shared++;
2042 }
2043 
2044 /*
2045  * cmp_and_merge_page - first see if page can be merged into the stable tree;
2046  * if not, compare checksum to previous and if it's the same, see if page can
2047  * be inserted into the unstable tree, or merged with a page already there and
2048  * both transferred to the stable tree.
2049  *
2050  * @page: the page that we are searching identical page to.
2051  * @rmap_item: the reverse mapping into the virtual address of this page
2052  */
2053 static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
2054 {
2055         struct mm_struct *mm = rmap_item->mm;
2056         struct rmap_item *tree_rmap_item;
2057         struct page *tree_page = NULL;
2058         struct stable_node *stable_node;
2059         struct page *kpage;
2060         unsigned int checksum;
2061         int err;
2062         bool max_page_sharing_bypass = false;
2063 
2064         stable_node = page_stable_node(page);
2065         if (stable_node) {
2066                 if (stable_node->head != &migrate_nodes &&
2067                     get_kpfn_nid(READ_ONCE(stable_node->kpfn)) !=
2068                     NUMA(stable_node->nid)) {
2069                         stable_node_dup_del(stable_node);
2070                         stable_node->head = &migrate_nodes;
2071                         list_add(&stable_node->list, stable_node->head);
2072                 }
2073                 if (stable_node->head != &migrate_nodes &&
2074                     rmap_item->head == stable_node)
2075                         return;
2076                 /*
2077                  * If it's a KSM fork, allow it to go over the sharing limit
2078                  * without warnings.
2079                  */
2080                 if (!is_page_sharing_candidate(stable_node))
2081                         max_page_sharing_bypass = true;
2082         }
2083 
2084         /* We first start with searching the page inside the stable tree */
2085         kpage = stable_tree_search(page);
2086         if (kpage == page && rmap_item->head == stable_node) {
2087                 put_page(kpage);
2088                 return;
2089         }
2090 
2091         remove_rmap_item_from_tree(rmap_item);
2092 
2093         if (kpage) {
2094                 if (PTR_ERR(kpage) == -EBUSY)
2095                         return;
2096 
2097                 err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
2098                 if (!err) {
2099                         /*
2100                          * The page was successfully merged:
2101                          * add its rmap_item to the stable tree.
2102                          */
2103                         lock_page(kpage);
2104                         stable_tree_append(rmap_item, page_stable_node(kpage),
2105                                            max_page_sharing_bypass);
2106                         unlock_page(kpage);
2107                 }
2108                 put_page(kpage);
2109                 return;
2110         }
2111 
2112         /*
2113          * If the hash value of the page has changed from the last time
2114          * we calculated it, this page is changing frequently: therefore we
2115          * don't want to insert it in the unstable tree, and we don't want
2116          * to waste our time searching for something identical to it there.
2117          */
2118         checksum = calc_checksum(page);
2119         if (rmap_item->oldchecksum != checksum) {
2120                 rmap_item->oldchecksum = checksum;
2121                 return;
2122         }
2123 
2124         /*
2125          * Same checksum as an empty page. We attempt to merge it with the
2126          * appropriate zero page if the user enabled this via sysfs.
2127          */
2128         if (ksm_use_zero_pages && (checksum == zero_checksum)) {
2129                 struct vm_area_struct *vma;
2130 
2131                 down_read(&mm->mmap_sem);
2132                 vma = find_mergeable_vma(mm, rmap_item->address);
2133                 err = try_to_merge_one_page(vma, page,
2134                                             ZERO_PAGE(rmap_item->address));
2135                 up_read(&mm->mmap_sem);
2136                 /*
2137                  * In case of failure, the page was not really empty, so we
2138                  * need to continue. Otherwise we're done.
2139                  */
2140                 if (!err)
2141                         return;
2142         }
2143         tree_rmap_item =
2144                 unstable_tree_search_insert(rmap_item, page, &tree_page);
2145         if (tree_rmap_item) {
2146                 bool split;
2147 
2148                 kpage = try_to_merge_two_pages(rmap_item, page,
2149                                                 tree_rmap_item, tree_page);
2150                 /*
2151                  * If both pages we tried to merge belong to the same compound
2152                  * page, then we actually ended up increasing the reference
2153                  * count of the same compound page twice, and split_huge_page
2154                  * failed.
2155                  * Here we set a flag if that happened, and we use it later to
2156                  * try split_huge_page again. Since we call put_page right
2157                  * afterwards, the reference count will be correct and
2158                  * split_huge_page should succeed.
2159                  */
2160                 split = PageTransCompound(page)
2161                         && compound_head(page) == compound_head(tree_page);
2162                 put_page(tree_page);
2163                 if (kpage) {
2164                         /*
2165                          * The pages were successfully merged: insert new
2166                          * node in the stable tree and add both rmap_items.
2167                          */
2168                         lock_page(kpage);
2169                         stable_node = stable_tree_insert(kpage);
2170                         if (stable_node) {
2171                                 stable_tree_append(tree_rmap_item, stable_node,
2172                                                    false);
2173                                 stable_tree_append(rmap_item, stable_node,
2174                                                    false);
2175                         }
2176                         unlock_page(kpage);
2177 
2178                         /*
2179                          * If we fail to insert the page into the stable tree,
2180                          * we will have 2 virtual addresses that are pointing
2181                          * to a ksm page left outside the stable tree,
2182                          * in which case we need to break_cow on both.
2183                          */
2184                         if (!stable_node) {
2185                                 break_cow(tree_rmap_item);
2186                                 break_cow(rmap_item);
2187                         }
2188                 } else if (split) {
2189                         /*
2190                          * We are here if we tried to merge two pages and
2191                          * failed because they both belonged to the same
2192                          * compound page. We will split the page now, but no
2193                          * merging will take place.
2194                          * We do not want to add the cost of a full lock; if
2195                          * the page is locked, it is better to skip it and
2196                          * perhaps try again later.
2197                          */
2198                         if (!trylock_page(page))
2199                                 return;
2200                         split_huge_page(page);
2201                         unlock_page(page);
2202                 }
2203         }
2204 }
2205 
2206 static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
2207                                             struct rmap_item **rmap_list,
2208                                             unsigned long addr)
2209 {
2210         struct rmap_item *rmap_item;
2211 
2212         while (*rmap_list) {
2213                 rmap_item = *rmap_list;
2214                 if ((rmap_item->address & PAGE_MASK) == addr)
2215                         return rmap_item;
2216                 if (rmap_item->address > addr)
2217                         break;
2218                 *rmap_list = rmap_item->rmap_list;
2219                 remove_rmap_item_from_tree(rmap_item);
2220                 free_rmap_item(rmap_item);
2221         }
2222 
2223         rmap_item = alloc_rmap_item();
2224         if (rmap_item) {
2225                 /* It has already been zeroed */
2226                 rmap_item->mm = mm_slot->mm;
2227                 rmap_item->address = addr;
2228                 rmap_item->rmap_list = *rmap_list;
2229                 *rmap_list = rmap_item;
2230         }
2231         return rmap_item;
2232 }
2233 
2234 static struct rmap_item *scan_get_next_rmap_item(struct page **page)
2235 {
2236         struct mm_struct *mm;
2237         struct mm_slot *slot;
2238         struct vm_area_struct *vma;
2239         struct rmap_item *rmap_item;
2240         int nid;
2241 
2242         if (list_empty(&ksm_mm_head.mm_list))
2243                 return NULL;
2244 
2245         slot = ksm_scan.mm_slot;
2246         if (slot == &ksm_mm_head) {
2247                 /*
2248                  * A number of pages can hang around indefinitely on per-cpu
2249                  * pagevecs, raised page count preventing write_protect_page
2250                  * from merging them.  Though it doesn't really matter much,
2251                  * it is puzzling to see some stuck in pages_volatile until
2252                  * other activity jostles them out, and they also prevented
2253                  * LTP's KSM test from succeeding deterministically; so drain
2254                  * them here (here rather than on entry to ksm_do_scan(),
2255                  * so we don't IPI too often when pages_to_scan is set low).
2256                  */
2257                 lru_add_drain_all();
2258 
2259                 /*
2260                  * Whereas stale stable_nodes on the stable_tree itself
2261                  * get pruned in the regular course of stable_tree_search(),
2262                  * those moved out to the migrate_nodes list can accumulate:
2263                  * so prune them once before each full scan.
2264                  */
2265                 if (!ksm_merge_across_nodes) {
2266                         struct stable_node *stable_node, *next;
2267                         struct page *page;
2268 
2269                         list_for_each_entry_safe(stable_node, next,
2270                                                  &migrate_nodes, list) {
2271                                 page = get_ksm_page(stable_node,
2272                                                     GET_KSM_PAGE_NOLOCK);
2273                                 if (page)
2274                                         put_page(page);
2275                                 cond_resched();
2276                         }
2277                 }
2278 
2279                 for (nid = 0; nid < ksm_nr_node_ids; nid++)
2280                         root_unstable_tree[nid] = RB_ROOT;
2281 
2282                 spin_lock(&ksm_mmlist_lock);
2283                 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
2284                 ksm_scan.mm_slot = slot;
2285                 spin_unlock(&ksm_mmlist_lock);
2286                 /*
2287                  * Although we tested list_empty() above, a racing __ksm_exit
2288                  * of the last mm on the list may have removed it since then.
2289                  */
2290                 if (slot == &ksm_mm_head)
2291                         return NULL;
2292 next_mm:
2293                 ksm_scan.address = 0;
2294                 ksm_scan.rmap_list = &slot->rmap_list;
2295         }
2296 
2297         mm = slot->mm;
2298         down_read(&mm->mmap_sem);
2299         if (ksm_test_exit(mm))
2300                 vma = NULL;
2301         else
2302                 vma = find_vma(mm, ksm_scan.address);
2303 
2304         for (; vma; vma = vma->vm_next) {
2305                 if (!(vma->vm_flags & VM_MERGEABLE))
2306                         continue;
2307                 if (ksm_scan.address < vma->vm_start)
2308                         ksm_scan.address = vma->vm_start;
2309                 if (!vma->anon_vma)
2310                         ksm_scan.address = vma->vm_end;
2311 
2312                 while (ksm_scan.address < vma->vm_end) {
2313                         if (ksm_test_exit(mm))
2314                                 break;
2315                         *page = follow_page(vma, ksm_scan.address, FOLL_GET);
2316                         if (IS_ERR_OR_NULL(*page)) {
2317                                 ksm_scan.address += PAGE_SIZE;
2318                                 cond_resched();
2319                                 continue;
2320                         }
2321                         if (PageAnon(*page)) {
2322                                 flush_anon_page(vma, *page, ksm_scan.address);
2323                                 flush_dcache_page(*page);
2324                                 rmap_item = get_next_rmap_item(slot,
2325                                         ksm_scan.rmap_list, ksm_scan.address);
2326                                 if (rmap_item) {
2327                                         ksm_scan.rmap_list =
2328                                                         &rmap_item->rmap_list;
2329                                         ksm_scan.address += PAGE_SIZE;
2330                                 } else
2331                                         put_page(*page);
2332                                 up_read(&mm->mmap_sem);
2333                                 return rmap_item;
2334                         }
2335                         put_page(*page);
2336                         ksm_scan.address += PAGE_SIZE;
2337                         cond_resched();
2338                 }
2339         }
2340 
2341         if (ksm_test_exit(mm)) {
2342                 ksm_scan.address = 0;
2343                 ksm_scan.rmap_list = &slot->rmap_list;
2344         }
2345         /*
2346          * Nuke all the rmap_items that are above this current rmap:
2347          * because there were no VM_MERGEABLE vmas with such addresses.
2348          */
2349         remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
2350 
2351         spin_lock(&ksm_mmlist_lock);
2352         ksm_scan.mm_slot = list_entry(slot->mm_list.next,
2353                                                 struct mm_slot, mm_list);
2354         if (ksm_scan.address == 0) {
2355                 /*
2356                  * We've completed a full scan of all vmas, holding mmap_sem
2357                  * throughout, and found no VM_MERGEABLE: so do the same as
2358                  * __ksm_exit does to remove this mm from all our lists now.
2359                  * This applies either when cleaning up after __ksm_exit
2360                  * (but beware: we can reach here even before __ksm_exit),
2361                  * or when all VM_MERGEABLE areas have been unmapped (and
2362                  * mmap_sem then protects against race with MADV_MERGEABLE).
2363                  */
2364                 hash_del(&slot->link);
2365                 list_del(&slot->mm_list);
2366                 spin_unlock(&ksm_mmlist_lock);
2367 
2368                 free_mm_slot(slot);
2369                 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
2370                 up_read(&mm->mmap_sem);
2371                 mmdrop(mm);
2372         } else {
2373                 up_read(&mm->mmap_sem);
2374                 /*
2375                  * up_read(&mm->mmap_sem) first because after
2376                  * spin_unlock(&ksm_mmlist_lock) run, the "mm" may
2377                  * already have been freed under us by __ksm_exit()
2378                  * because the "mm_slot" is still hashed and
2379                  * ksm_scan.mm_slot doesn't point to it anymore.
2380                  */
2381                 spin_unlock(&ksm_mmlist_lock);
2382         }
2383 
2384         /* Repeat until we've completed scanning the whole list */
2385         slot = ksm_scan.mm_slot;
2386         if (slot != &ksm_mm_head)
2387                 goto next_mm;
2388 
2389         ksm_scan.seqnr++;
2390         return NULL;
2391 }
2392 
2393 /**
2394  * ksm_do_scan  - the ksm scanner main worker function.
2395  * @scan_npages:  number of pages we want to scan before we return.
2396  */
2397 static void ksm_do_scan(unsigned int scan_npages)
2398 {
2399         struct rmap_item *rmap_item;
2400         struct page *uninitialized_var(page);
2401 
2402         while (scan_npages-- && likely(!freezing(current))) {
2403                 cond_resched();
2404                 rmap_item = scan_get_next_rmap_item(&page);
2405                 if (!rmap_item)
2406                         return;
2407                 cmp_and_merge_page(page, rmap_item);
2408                 put_page(page);
2409         }
2410 }
2411 
2412 static int ksmd_should_run(void)
2413 {
2414         return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
2415 }
2416 
2417 static int ksm_scan_thread(void *nothing)
2418 {
2419         unsigned int sleep_ms;
2420 
2421         set_freezable();
2422         set_user_nice(current, 5);
2423 
2424         while (!kthread_should_stop()) {
2425                 mutex_lock(&ksm_thread_mutex);
2426                 wait_while_offlining();
2427                 if (ksmd_should_run())
2428                         ksm_do_scan(ksm_thread_pages_to_scan);
2429                 mutex_unlock(&ksm_thread_mutex);
2430 
2431                 try_to_freeze();
2432 
2433                 if (ksmd_should_run()) {
2434                         sleep_ms = READ_ONCE(ksm_thread_sleep_millisecs);
2435                         wait_event_interruptible_timeout(ksm_iter_wait,
2436                                 sleep_ms != READ_ONCE(ksm_thread_sleep_millisecs),
2437                                 msecs_to_jiffies(sleep_ms));
2438                 } else {
2439                         wait_event_freezable(ksm_thread_wait,
2440                                 ksmd_should_run() || kthread_should_stop());
2441                 }
2442         }
2443         return 0;
2444 }
2445 
2446 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
2447                 unsigned long end, int advice, unsigned long *vm_flags)
2448 {
2449         struct mm_struct *mm = vma->vm_mm;
2450         int err;
2451 
2452         switch (advice) {
2453         case MADV_MERGEABLE:
2454                 /*
2455                  * Be somewhat over-protective for now!
2456                  */
2457                 if (*vm_flags & (VM_MERGEABLE | VM_SHARED  | VM_MAYSHARE   |
2458                                  VM_PFNMAP    | VM_IO      | VM_DONTEXPAND |
2459                                  VM_HUGETLB | VM_MIXEDMAP))
2460                         return 0;               /* just ignore the advice */
2461 
2462                 if (vma_is_dax(vma))
2463                         return 0;
2464 
2465 #ifdef VM_SAO
2466                 if (*vm_flags & VM_SAO)
2467                         return 0;
2468 #endif
2469 #ifdef VM_SPARC_ADI
2470                 if (*vm_flags & VM_SPARC_ADI)
2471                         return 0;
2472 #endif
2473 
2474                 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
2475                         err = __ksm_enter(mm);
2476                         if (err)
2477                                 return err;
2478                 }
2479 
2480                 *vm_flags |= VM_MERGEABLE;
2481                 break;
2482 
2483         case MADV_UNMERGEABLE:
2484                 if (!(*vm_flags & VM_MERGEABLE))
2485                         return 0;               /* just ignore the advice */
2486 
2487                 if (vma->anon_vma) {
2488                         err = unmerge_ksm_pages(vma, start, end);
2489                         if (err)
2490                                 return err;
2491                 }
2492 
2493                 *vm_flags &= ~VM_MERGEABLE;
2494                 break;
2495         }
2496 
2497         return 0;
2498 }
2499 
2500 int __ksm_enter(struct mm_struct *mm)
2501 {
2502         struct mm_slot *mm_slot;
2503         int needs_wakeup;
2504 
2505         mm_slot = alloc_mm_slot();
2506         if (!mm_slot)
2507                 return -ENOMEM;
2508 
2509         /* Check ksm_run too?  Would need tighter locking */
2510         needs_wakeup = list_empty(&ksm_mm_head.mm_list);
2511 
2512         spin_lock(&ksm_mmlist_lock);
2513         insert_to_mm_slots_hash(mm, mm_slot);
2514         /*
2515          * When KSM_RUN_MERGE (or KSM_RUN_STOP),
2516          * insert just behind the scanning cursor, to let the area settle
2517          * down a little; when fork is followed by immediate exec, we don't
2518          * want ksmd to waste time setting up and tearing down an rmap_list.
2519          *
2520          * But when KSM_RUN_UNMERGE, it's important to insert ahead of its
2521          * scanning cursor, otherwise KSM pages in newly forked mms will be
2522          * missed: then we might as well insert at the end of the list.
2523          */
2524         if (ksm_run & KSM_RUN_UNMERGE)
2525                 list_add_tail(&mm_slot->mm_list, &ksm_mm_head.mm_list);
2526         else
2527                 list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
2528         spin_unlock(&ksm_mmlist_lock);
2529 
2530         set_bit(MMF_VM_MERGEABLE, &mm->flags);
2531         mmgrab(mm);
2532 
2533         if (needs_wakeup)
2534                 wake_up_interruptible(&ksm_thread_wait);
2535 
2536         return 0;
2537 }
2538 
2539 void __ksm_exit(struct mm_struct *mm)
2540 {
2541         struct mm_slot *mm_slot;
2542         int easy_to_free = 0;
2543 
2544         /*
2545          * This process is exiting: if it's straightforward (as is the
2546          * case when ksmd was never running), free mm_slot immediately.
2547          * But if it's at the cursor or has rmap_items linked to it, use
2548          * mmap_sem to synchronize with any break_cows before pagetables
2549          * are freed, and leave the mm_slot on the list for ksmd to free.
2550          * Beware: ksm may already have noticed it exiting and freed the slot.
2551          */
2552 
2553         spin_lock(&ksm_mmlist_lock);
2554         mm_slot = get_mm_slot(mm);
2555         if (mm_slot && ksm_scan.mm_slot != mm_slot) {
2556                 if (!mm_slot->rmap_list) {
2557                         hash_del(&mm_slot->link);
2558                         list_del(&mm_slot->mm_list);
2559                         easy_to_free = 1;
2560                 } else {
2561                         list_move(&mm_slot->mm_list,
2562                                   &ksm_scan.mm_slot->mm_list);
2563                 }
2564         }
2565         spin_unlock(&ksm_mmlist_lock);
2566 
2567         if (easy_to_free) {
2568                 free_mm_slot(mm_slot);
2569                 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
2570                 mmdrop(mm);
2571         } else if (mm_slot) {
2572                 down_write(&mm->mmap_sem);
2573                 up_write(&mm->mmap_sem);
2574         }
2575 }
2576 
2577 struct page *ksm_might_need_to_copy(struct page *page,
2578                         struct vm_area_struct *vma, unsigned long address)
2579 {
2580         struct anon_vma *anon_vma = page_anon_vma(page);
2581         struct page *new_page;
2582 
2583         if (PageKsm(page)) {
2584                 if (page_stable_node(page) &&
2585                     !(ksm_run & KSM_RUN_UNMERGE))
2586                         return page;    /* no need to copy it */
2587         } else if (!anon_vma) {
2588                 return page;            /* no need to copy it */
2589         } else if (anon_vma->root == vma->anon_vma->root &&
2590                  page->index == linear_page_index(vma, address)) {
2591                 return page;            /* still no need to copy it */
2592         }
2593         if (!PageUptodate(page))
2594                 return page;            /* let do_swap_page report the error */
2595 
2596         new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
2597         if (new_page) {
2598                 copy_user_highpage(new_page, page, address, vma);
2599 
2600                 SetPageDirty(new_page);
2601                 __SetPageUptodate(new_page);
2602                 __SetPageLocked(new_page);
2603         }
2604 
2605         return new_page;
2606 }
2607 
2608 void rmap_walk_ksm(struct page *page, struct rmap_walk_control *rwc)
2609 {
2610         struct stable_node *stable_node;
2611         struct rmap_item *rmap_item;
2612         int search_new_forks = 0;
2613 
2614         VM_BUG_ON_PAGE(!PageKsm(page), page);
2615 
2616         /*
2617          * Rely on the page lock to protect against concurrent modifications
2618          * to that page's node of the stable tree.
2619          */
2620         VM_BUG_ON_PAGE(!PageLocked(page), page);
2621 
2622         stable_node = page_stable_node(page);
2623         if (!stable_node)
2624                 return;
2625 again:
2626         hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
2627                 struct anon_vma *anon_vma = rmap_item->anon_vma;
2628                 struct anon_vma_chain *vmac;
2629                 struct vm_area_struct *vma;
2630 
2631                 cond_resched();
2632                 anon_vma_lock_read(anon_vma);
2633                 anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
2634                                                0, ULONG_MAX) {
2635                         unsigned long addr;
2636 
2637                         cond_resched();
2638                         vma = vmac->vma;
2639 
2640                         /* Ignore the stable/unstable/sqnr flags */
2641                         addr = rmap_item->address & ~KSM_FLAG_MASK;
2642 
2643                         if (addr < vma->vm_start || addr >= vma->vm_end)
2644                                 continue;
2645                         /*
2646                          * Initially we examine only the vma which covers this
2647                          * rmap_item; but later, if there is still work to do,
2648                          * we examine covering vmas in other mms: in case they
2649                          * were forked from the original since ksmd passed.
2650                          */
2651                         if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
2652                                 continue;
2653 
2654                         if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
2655                                 continue;
2656 
2657                         if (!rwc->rmap_one(page, vma, addr, rwc->arg)) {
2658                                 anon_vma_unlock_read(anon_vma);
2659                                 return;
2660                         }
2661                         if (rwc->done && rwc->done(page)) {
2662                                 anon_vma_unlock_read(anon_vma);
2663                                 return;
2664                         }
2665                 }
2666                 anon_vma_unlock_read(anon_vma);
2667         }
2668         if (!search_new_forks++)
2669                 goto again;
2670 }
2671 
2672 bool reuse_ksm_page(struct page *page,
2673                     struct vm_area_struct *vma,
2674                     unsigned long address)
2675 {
2676 #ifdef CONFIG_DEBUG_VM
2677         if (WARN_ON(is_zero_pfn(page_to_pfn(page))) ||
2678                         WARN_ON(!page_mapped(page)) ||
2679                         WARN_ON(!PageLocked(page))) {
2680                 dump_page(page, "reuse_ksm_page");
2681                 return false;
2682         }
2683 #endif
2684 
2685         if (PageSwapCache(page) || !page_stable_node(page))
2686                 return false;
2687         /* Prohibit parallel get_ksm_page() */
2688         if (!page_ref_freeze(page, 1))
2689                 return false;
2690 
2691         page_move_anon_rmap(page, vma);
2692         page->index = linear_page_index(vma, address);
2693         page_ref_unfreeze(page, 1);
2694 
2695         return true;
2696 }
2697 #ifdef CONFIG_MIGRATION
2698 void ksm_migrate_page(struct page *newpage, struct page *oldpage)
2699 {
2700         struct stable_node *stable_node;
2701 
2702         VM_BUG_ON_PAGE(!PageLocked(oldpage), oldpage);
2703         VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
2704         VM_BUG_ON_PAGE(newpage->mapping != oldpage->mapping, newpage);
2705 
2706         stable_node = page_stable_node(newpage);
2707         if (stable_node) {
2708                 VM_BUG_ON_PAGE(stable_node->kpfn != page_to_pfn(oldpage), oldpage);
2709                 stable_node->kpfn = page_to_pfn(newpage);
2710                 /*
2711                  * newpage->mapping was set in advance; now we need smp_wmb()
2712                  * to make sure that the new stable_node->kpfn is visible
2713                  * to get_ksm_page() before it can see that oldpage->mapping
2714                  * has gone stale (or that PageSwapCache has been cleared).
2715                  */
2716                 smp_wmb();
2717                 set_page_stable_node(oldpage, NULL);
2718         }
2719 }
2720 #endif /* CONFIG_MIGRATION */
2721 
2722 #ifdef CONFIG_MEMORY_HOTREMOVE
2723 static void wait_while_offlining(void)
2724 {
2725         while (ksm_run & KSM_RUN_OFFLINE) {
2726                 mutex_unlock(&ksm_thread_mutex);
2727                 wait_on_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE),
2728                             TASK_UNINTERRUPTIBLE);
2729                 mutex_lock(&ksm_thread_mutex);
2730         }
2731 }
2732 
2733 static bool stable_node_dup_remove_range(struct stable_node *stable_node,
2734                                          unsigned long start_pfn,
2735                                          unsigned long end_pfn)
2736 {
2737         if (stable_node->kpfn >= start_pfn &&
2738             stable_node->kpfn < end_pfn) {
2739                 /*
2740                  * Don't get_ksm_page, page has already gone:
2741                  * which is why we keep kpfn instead of page*
2742                  */
2743                 remove_node_from_stable_tree(stable_node);
2744                 return true;
2745         }
2746         return false;
2747 }
2748 
2749 static bool stable_node_chain_remove_range(struct stable_node *stable_node,
2750                                            unsigned long start_pfn,
2751                                            unsigned long end_pfn,
2752                                            struct rb_root *root)
2753 {
2754         struct stable_node *dup;
2755         struct hlist_node *hlist_safe;
2756 
2757         if (!is_stable_node_chain(stable_node)) {
2758                 VM_BUG_ON(is_stable_node_dup(stable_node));
2759                 return stable_node_dup_remove_range(stable_node, start_pfn,
2760                                                     end_pfn);
2761         }
2762 
2763         hlist_for_each_entry_safe(dup, hlist_safe,
2764                                   &stable_node->hlist, hlist_dup) {
2765                 VM_BUG_ON(!is_stable_node_dup(dup));
2766                 stable_node_dup_remove_range(dup, start_pfn, end_pfn);
2767         }
2768         if (hlist_empty(&stable_node->hlist)) {
2769                 free_stable_node_chain(stable_node, root);
2770                 return true; /* notify caller that tree was rebalanced */
2771         } else
2772                 return false;
2773 }
2774 
2775 static void ksm_check_stable_tree(unsigned long start_pfn,
2776                                   unsigned long end_pfn)
2777 {
2778         struct stable_node *stable_node, *next;
2779         struct rb_node *node;
2780         int nid;
2781 
2782         for (nid = 0; nid < ksm_nr_node_ids; nid++) {
2783                 node = rb_first(root_stable_tree + nid);
2784                 while (node) {
2785                         stable_node = rb_entry(node, struct stable_node, node);
2786                         if (stable_node_chain_remove_range(stable_node,
2787                                                            start_pfn, end_pfn,
2788                                                            root_stable_tree +
2789                                                            nid))
2790                                 node = rb_first(root_stable_tree + nid);
2791                         else
2792                                 node = rb_next(node);
2793                         cond_resched();
2794                 }
2795         }
2796         list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
2797                 if (stable_node->kpfn >= start_pfn &&
2798                     stable_node->kpfn < end_pfn)
2799                         remove_node_from_stable_tree(stable_node);
2800                 cond_resched();
2801         }
2802 }
2803 
2804 static int ksm_memory_callback(struct notifier_block *self,
2805                                unsigned long action, void *arg)
2806 {
2807         struct memory_notify *mn = arg;
2808 
2809         switch (action) {
2810         case MEM_GOING_OFFLINE:
2811                 /*
2812                  * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
2813                  * and remove_all_stable_nodes() while memory is going offline:
2814                  * it is unsafe for them to touch the stable tree at this time.
2815                  * But unmerge_ksm_pages(), rmap lookups and other entry points
2816                  * which do not need the ksm_thread_mutex are all safe.
2817                  */
2818                 mutex_lock(&ksm_thread_mutex);
2819                 ksm_run |= KSM_RUN_OFFLINE;
2820                 mutex_unlock(&ksm_thread_mutex);
2821                 break;
2822 
2823         case MEM_OFFLINE:
2824                 /*
2825                  * Most of the work is done by page migration; but there might
2826                  * be a few stable_nodes left over, still pointing to struct
2827                  * pages which have been offlined: prune those from the tree,
2828                  * otherwise get_ksm_page() might later try to access a
2829                  * non-existent struct page.
2830                  */
2831                 ksm_check_stable_tree(mn->start_pfn,
2832                                       mn->start_pfn + mn->nr_pages);
2833                 /* fallthrough */
2834 
2835         case MEM_CANCEL_OFFLINE:
2836                 mutex_lock(&ksm_thread_mutex);
2837                 ksm_run &= ~KSM_RUN_OFFLINE;
2838                 mutex_unlock(&ksm_thread_mutex);
2839 
2840                 smp_mb();       /* wake_up_bit advises this */
2841                 wake_up_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE));
2842                 break;
2843         }
2844         return NOTIFY_OK;
2845 }
2846 #else
2847 static void wait_while_offlining(void)
2848 {
2849 }
2850 #endif /* CONFIG_MEMORY_HOTREMOVE */
2851 
2852 #ifdef CONFIG_SYSFS
2853 /*
2854  * This all compiles without CONFIG_SYSFS, but is a waste of space.
2855  */
2856 
2857 #define KSM_ATTR_RO(_name) \
2858         static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
2859 #define KSM_ATTR(_name) \
2860         static struct kobj_attribute _name##_attr = \
2861                 __ATTR(_name, 0644, _name##_show, _name##_store)
2862 
2863 static ssize_t sleep_millisecs_show(struct kobject *kobj,
2864                                     struct kobj_attribute *attr, char *buf)
2865 {
2866         return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
2867 }
2868 
2869 static ssize_t sleep_millisecs_store(struct kobject *kobj,
2870                                      struct kobj_attribute *attr,
2871                                      const char *buf, size_t count)
2872 {
2873         unsigned long msecs;
2874         int err;
2875 
2876         err = kstrtoul(buf, 10, &msecs);
2877         if (err || msecs > UINT_MAX)
2878                 return -EINVAL;
2879 
2880         ksm_thread_sleep_millisecs = msecs;
2881         wake_up_interruptible(&ksm_iter_wait);
2882 
2883         return count;
2884 }
2885 KSM_ATTR(sleep_millisecs);
2886 
2887 static ssize_t pages_to_scan_show(struct kobject *kobj,
2888                                   struct kobj_attribute *attr, char *buf)
2889 {
2890         return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
2891 }
2892 
2893 static ssize_t pages_to_scan_store(struct kobject *kobj,
2894                                    struct kobj_attribute *attr,
2895                                    const char *buf, size_t count)
2896 {
2897         int err;
2898         unsigned long nr_pages;
2899 
2900         err = kstrtoul(buf, 10, &nr_pages);
2901         if (err || nr_pages > UINT_MAX)
2902                 return -EINVAL;
2903 
2904         ksm_thread_pages_to_scan = nr_pages;
2905 
2906         return count;
2907 }
2908 KSM_ATTR(pages_to_scan);
2909 
2910 static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
2911                         char *buf)
2912 {
2913         return sprintf(buf, "%lu\n", ksm_run);
2914 }
2915 
2916 static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
2917                          const char *buf, size_t count)
2918 {
2919         int err;
2920         unsigned long flags;
2921 
2922         err = kstrtoul(buf, 10, &flags);
2923         if (err || flags > UINT_MAX)
2924                 return -EINVAL;
2925         if (flags > KSM_RUN_UNMERGE)
2926                 return -EINVAL;
2927 
2928         /*
2929          * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
2930          * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
2931          * breaking COW to free the pages_shared (but leaves mm_slots
2932          * on the list for when ksmd may be set running again).
2933          */
2934 
2935         mutex_lock(&ksm_thread_mutex);
2936         wait_while_offlining();
2937         if (ksm_run != flags) {
2938                 ksm_run = flags;
2939                 if (flags & KSM_RUN_UNMERGE) {
2940                         set_current_oom_origin();
2941                         err = unmerge_and_remove_all_rmap_items();
2942                         clear_current_oom_origin();
2943                         if (err) {
2944                                 ksm_run = KSM_RUN_STOP;
2945                                 count = err;
2946                         }
2947                 }
2948         }
2949         mutex_unlock(&ksm_thread_mutex);
2950 
2951         if (flags & KSM_RUN_MERGE)
2952                 wake_up_interruptible(&ksm_thread_wait);
2953 
2954         return count;
2955 }
2956 KSM_ATTR(run);
2957 
2958 #ifdef CONFIG_NUMA
2959 static ssize_t merge_across_nodes_show(struct kobject *kobj,
2960                                 struct kobj_attribute *attr, char *buf)
2961 {
2962         return sprintf(buf, "%u\n", ksm_merge_across_nodes);
2963 }
2964 
2965 static ssize_t merge_across_nodes_store(struct kobject *kobj,
2966                                    struct kobj_attribute *attr,
2967                                    const char *buf, size_t count)
2968 {
2969         int err;
2970         unsigned long knob;
2971 
2972         err = kstrtoul(buf, 10, &knob);
2973         if (err)
2974                 return err;
2975         if (knob > 1)
2976                 return -EINVAL;
2977 
2978         mutex_lock(&ksm_thread_mutex);
2979         wait_while_offlining();
2980         if (ksm_merge_across_nodes != knob) {
2981                 if (ksm_pages_shared || remove_all_stable_nodes())
2982                         err = -EBUSY;
2983                 else if (root_stable_tree == one_stable_tree) {
2984                         struct rb_root *buf;
2985                         /*
2986                          * This is the first time that we switch away from the
2987                          * default of merging across nodes: must now allocate
2988                          * a buffer to hold as many roots as may be needed.
2989                          * Allocate stable and unstable together:
2990                          * MAXSMP NODES_SHIFT 10 will use 16kB.
2991                          */
2992                         buf = kcalloc(nr_node_ids + nr_node_ids, sizeof(*buf),
2993                                       GFP_KERNEL);
2994                         /* Let us assume that RB_ROOT is NULL is zero */
2995                         if (!buf)
2996                                 err = -ENOMEM;
2997                         else {
2998                                 root_stable_tree = buf;
2999                                 root_unstable_tree = buf + nr_node_ids;
3000                                 /* Stable tree is empty but not the unstable */
3001                                 root_unstable_tree[0] = one_unstable_tree[0];
3002                         }
3003                 }
3004                 if (!err) {
3005                         ksm_merge_across_nodes = knob;
3006                         ksm_nr_node_ids = knob ? 1 : nr_node_ids;
3007                 }
3008         }
3009         mutex_unlock(&ksm_thread_mutex);
3010 
3011         return err ? err : count;
3012 }
3013 KSM_ATTR(merge_across_nodes);
3014 #endif
3015 
3016 static ssize_t use_zero_pages_show(struct kobject *kobj,
3017                                 struct kobj_attribute *attr, char *buf)
3018 {
3019         return sprintf(buf, "%u\n", ksm_use_zero_pages);
3020 }
3021 static ssize_t use_zero_pages_store(struct kobject *kobj,
3022                                    struct kobj_attribute *attr,
3023                                    const char *buf, size_t count)
3024 {
3025         int err;
3026         bool value;
3027 
3028         err = kstrtobool(buf, &value);
3029         if (err)
3030                 return -EINVAL;
3031 
3032         ksm_use_zero_pages = value;
3033 
3034         return count;
3035 }
3036 KSM_ATTR(use_zero_pages);
3037 
3038 static ssize_t max_page_sharing_show(struct kobject *kobj,
3039                                      struct kobj_attribute *attr, char *buf)
3040 {
3041         return sprintf(buf, "%u\n", ksm_max_page_sharing);
3042 }
3043 
3044 static ssize_t max_page_sharing_store(struct kobject *kobj,
3045                                       struct kobj_attribute *attr,
3046                                       const char *buf, size_t count)
3047 {
3048         int err;
3049         int knob;
3050 
3051         err = kstrtoint(buf, 10, &knob);
3052         if (err)
3053                 return err;
3054         /*
3055          * When a KSM page is created it is shared by 2 mappings. This
3056          * being a signed comparison, it implicitly verifies it's not
3057          * negative.
3058          */
3059         if (knob < 2)
3060                 return -EINVAL;
3061 
3062         if (READ_ONCE(ksm_max_page_sharing) == knob)
3063                 return count;
3064 
3065         mutex_lock(&ksm_thread_mutex);
3066         wait_while_offlining();
3067         if (ksm_max_page_sharing != knob) {
3068                 if (ksm_pages_shared || remove_all_stable_nodes())
3069                         err = -EBUSY;
3070                 else
3071                         ksm_max_page_sharing = knob;
3072         }
3073         mutex_unlock(&ksm_thread_mutex);
3074 
3075         return err ? err : count;
3076 }
3077 KSM_ATTR(max_page_sharing);
3078 
3079 static ssize_t pages_shared_show(struct kobject *kobj,
3080                                  struct kobj_attribute *attr, char *buf)
3081 {
3082         return sprintf(buf, "%lu\n", ksm_pages_shared);
3083 }
3084 KSM_ATTR_RO(pages_shared);
3085 
3086 static ssize_t pages_sharing_show(struct kobject *kobj,
3087                                   struct kobj_attribute *attr, char *buf)
3088 {
3089         return sprintf(buf, "%lu\n", ksm_pages_sharing);
3090 }
3091 KSM_ATTR_RO(pages_sharing);
3092 
3093 static ssize_t pages_unshared_show(struct kobject *kobj,
3094                                    struct kobj_attribute *attr, char *buf)
3095 {
3096         return sprintf(buf, "%lu\n", ksm_pages_unshared);
3097 }
3098 KSM_ATTR_RO(pages_unshared);
3099 
3100 static ssize_t pages_volatile_show(struct kobject *kobj,
3101                                    struct kobj_attribute *attr, char *buf)
3102 {
3103         long ksm_pages_volatile;
3104 
3105         ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
3106                                 - ksm_pages_sharing - ksm_pages_unshared;
3107         /*
3108          * It was not worth any locking to calculate that statistic,
3109          * but it might therefore sometimes be negative: conceal that.
3110          */
3111         if (ksm_pages_volatile < 0)
3112                 ksm_pages_volatile = 0;
3113         return sprintf(buf, "%ld\n", ksm_pages_volatile);
3114 }
3115 KSM_ATTR_RO(pages_volatile);
3116 
3117 static ssize_t stable_node_dups_show(struct kobject *kobj,
3118                                      struct kobj_attribute *attr, char *buf)
3119 {
3120         return sprintf(buf, "%lu\n", ksm_stable_node_dups);
3121 }
3122 KSM_ATTR_RO(stable_node_dups);
3123 
3124 static ssize_t stable_node_chains_show(struct kobject *kobj,
3125                                        struct kobj_attribute *attr, char *buf)
3126 {
3127         return sprintf(buf, "%lu\n", ksm_stable_node_chains);
3128 }
3129 KSM_ATTR_RO(stable_node_chains);
3130 
3131 static ssize_t
3132 stable_node_chains_prune_millisecs_show(struct kobject *kobj,
3133                                         struct kobj_attribute *attr,
3134                                         char *buf)
3135 {
3136         return sprintf(buf, "%u\n", ksm_stable_node_chains_prune_millisecs);
3137 }
3138 
3139 static ssize_t
3140 stable_node_chains_prune_millisecs_store(struct kobject *kobj,
3141                                          struct kobj_attribute *attr,
3142                                          const char *buf, size_t count)
3143 {
3144         unsigned long msecs;
3145         int err;
3146 
3147         err = kstrtoul(buf, 10, &msecs);
3148         if (err || msecs > UINT_MAX)
3149                 return -EINVAL;
3150 
3151         ksm_stable_node_chains_prune_millisecs = msecs;
3152 
3153         return count;
3154 }
3155 KSM_ATTR(stable_node_chains_prune_millisecs);
3156 
3157 static ssize_t full_scans_show(struct kobject *kobj,
3158                                struct kobj_attribute *attr, char *buf)
3159 {
3160         return sprintf(buf, "%lu\n", ksm_scan.seqnr);
3161 }
3162 KSM_ATTR_RO(full_scans);
3163 
3164 static struct attribute *ksm_attrs[] = {
3165         &sleep_millisecs_attr.attr,
3166         &pages_to_scan_attr.attr,
3167         &run_attr.attr,
3168         &pages_shared_attr.attr,
3169         &pages_sharing_attr.attr,
3170         &pages_unshared_attr.attr,
3171         &pages_volatile_attr.attr,
3172         &full_scans_attr.attr,
3173 #ifdef CONFIG_NUMA
3174         &merge_across_nodes_attr.attr,
3175 #endif
3176         &max_page_sharing_attr.attr,
3177         &stable_node_chains_attr.attr,
3178         &stable_node_dups_attr.attr,
3179         &stable_node_chains_prune_millisecs_attr.attr,
3180         &use_zero_pages_attr.attr,
3181         NULL,
3182 };
3183 
3184 static const struct attribute_group ksm_attr_group = {
3185         .attrs = ksm_attrs,
3186         .name = "ksm",
3187 };
3188 #endif /* CONFIG_SYSFS */
3189 
3190 static int __init ksm_init(void)
3191 {
3192         struct task_struct *ksm_thread;
3193         int err;
3194 
3195         /* The correct value depends on page size and endianness */
3196         zero_checksum = calc_checksum(ZERO_PAGE(0));
3197         /* Default to false for backwards compatibility */
3198         ksm_use_zero_pages = false;
3199 
3200         err = ksm_slab_init();
3201         if (err)
3202                 goto out;
3203 
3204         ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
3205         if (IS_ERR(ksm_thread)) {
3206                 pr_err("ksm: creating kthread failed\n");
3207                 err = PTR_ERR(ksm_thread);
3208                 goto out_free;
3209         }
3210 
3211 #ifdef CONFIG_SYSFS
3212         err = sysfs_create_group(mm_kobj, &ksm_attr_group);
3213         if (err) {
3214                 pr_err("ksm: register sysfs failed\n");
3215                 kthread_stop(ksm_thread);
3216                 goto out_free;
3217         }
3218 #else
3219         ksm_run = KSM_RUN_MERGE;        /* no way for user to start it */
3220 
3221 #endif /* CONFIG_SYSFS */
3222 
3223 #ifdef CONFIG_MEMORY_HOTREMOVE
3224         /* There is no significance to this priority 100 */
3225         hotplug_memory_notifier(ksm_memory_callback, 100);
3226 #endif
3227         return 0;
3228 
3229 out_free:
3230         ksm_slab_free();
3231 out:
3232         return err;
3233 }
3234 subsys_initcall(ksm_init);
3235 

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