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Linux/mm/ksm.c

  1 /*
  2  * Memory merging support.
  3  *
  4  * This code enables dynamic sharing of identical pages found in different
  5  * memory areas, even if they are not shared by fork()
  6  *
  7  * Copyright (C) 2008-2009 Red Hat, Inc.
  8  * Authors:
  9  *      Izik Eidus
 10  *      Andrea Arcangeli
 11  *      Chris Wright
 12  *      Hugh Dickins
 13  *
 14  * This work is licensed under the terms of the GNU GPL, version 2.
 15  */
 16 
 17 #include <linux/errno.h>
 18 #include <linux/mm.h>
 19 #include <linux/fs.h>
 20 #include <linux/mman.h>
 21 #include <linux/sched.h>
 22 #include <linux/rwsem.h>
 23 #include <linux/pagemap.h>
 24 #include <linux/rmap.h>
 25 #include <linux/spinlock.h>
 26 #include <linux/jhash.h>
 27 #include <linux/delay.h>
 28 #include <linux/kthread.h>
 29 #include <linux/wait.h>
 30 #include <linux/slab.h>
 31 #include <linux/rbtree.h>
 32 #include <linux/memory.h>
 33 #include <linux/mmu_notifier.h>
 34 #include <linux/swap.h>
 35 #include <linux/ksm.h>
 36 #include <linux/hashtable.h>
 37 #include <linux/freezer.h>
 38 #include <linux/oom.h>
 39 #include <linux/numa.h>
 40 
 41 #include <asm/tlbflush.h>
 42 #include "internal.h"
 43 
 44 #ifdef CONFIG_NUMA
 45 #define NUMA(x)         (x)
 46 #define DO_NUMA(x)      do { (x); } while (0)
 47 #else
 48 #define NUMA(x)         (0)
 49 #define DO_NUMA(x)      do { } while (0)
 50 #endif
 51 
 52 /*
 53  * A few notes about the KSM scanning process,
 54  * to make it easier to understand the data structures below:
 55  *
 56  * In order to reduce excessive scanning, KSM sorts the memory pages by their
 57  * contents into a data structure that holds pointers to the pages' locations.
 58  *
 59  * Since the contents of the pages may change at any moment, KSM cannot just
 60  * insert the pages into a normal sorted tree and expect it to find anything.
 61  * Therefore KSM uses two data structures - the stable and the unstable tree.
 62  *
 63  * The stable tree holds pointers to all the merged pages (ksm pages), sorted
 64  * by their contents.  Because each such page is write-protected, searching on
 65  * this tree is fully assured to be working (except when pages are unmapped),
 66  * and therefore this tree is called the stable tree.
 67  *
 68  * In addition to the stable tree, KSM uses a second data structure called the
 69  * unstable tree: this tree holds pointers to pages which have been found to
 70  * be "unchanged for a period of time".  The unstable tree sorts these pages
 71  * by their contents, but since they are not write-protected, KSM cannot rely
 72  * upon the unstable tree to work correctly - the unstable tree is liable to
 73  * be corrupted as its contents are modified, and so it is called unstable.
 74  *
 75  * KSM solves this problem by several techniques:
 76  *
 77  * 1) The unstable tree is flushed every time KSM completes scanning all
 78  *    memory areas, and then the tree is rebuilt again from the beginning.
 79  * 2) KSM will only insert into the unstable tree, pages whose hash value
 80  *    has not changed since the previous scan of all memory areas.
 81  * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
 82  *    colors of the nodes and not on their contents, assuring that even when
 83  *    the tree gets "corrupted" it won't get out of balance, so scanning time
 84  *    remains the same (also, searching and inserting nodes in an rbtree uses
 85  *    the same algorithm, so we have no overhead when we flush and rebuild).
 86  * 4) KSM never flushes the stable tree, which means that even if it were to
 87  *    take 10 attempts to find a page in the unstable tree, once it is found,
 88  *    it is secured in the stable tree.  (When we scan a new page, we first
 89  *    compare it against the stable tree, and then against the unstable tree.)
 90  *
 91  * If the merge_across_nodes tunable is unset, then KSM maintains multiple
 92  * stable trees and multiple unstable trees: one of each for each NUMA node.
 93  */
 94 
 95 /**
 96  * struct mm_slot - ksm information per mm that is being scanned
 97  * @link: link to the mm_slots hash list
 98  * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
 99  * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
100  * @mm: the mm that this information is valid for
101  */
102 struct mm_slot {
103         struct hlist_node link;
104         struct list_head mm_list;
105         struct rmap_item *rmap_list;
106         struct mm_struct *mm;
107 };
108 
109 /**
110  * struct ksm_scan - cursor for scanning
111  * @mm_slot: the current mm_slot we are scanning
112  * @address: the next address inside that to be scanned
113  * @rmap_list: link to the next rmap to be scanned in the rmap_list
114  * @seqnr: count of completed full scans (needed when removing unstable node)
115  *
116  * There is only the one ksm_scan instance of this cursor structure.
117  */
118 struct ksm_scan {
119         struct mm_slot *mm_slot;
120         unsigned long address;
121         struct rmap_item **rmap_list;
122         unsigned long seqnr;
123 };
124 
125 /**
126  * struct stable_node - node of the stable rbtree
127  * @node: rb node of this ksm page in the stable tree
128  * @head: (overlaying parent) &migrate_nodes indicates temporarily on that list
129  * @list: linked into migrate_nodes, pending placement in the proper node tree
130  * @hlist: hlist head of rmap_items using this ksm page
131  * @kpfn: page frame number of this ksm page (perhaps temporarily on wrong nid)
132  * @nid: NUMA node id of stable tree in which linked (may not match kpfn)
133  */
134 struct stable_node {
135         union {
136                 struct rb_node node;    /* when node of stable tree */
137                 struct {                /* when listed for migration */
138                         struct list_head *head;
139                         struct list_head list;
140                 };
141         };
142         struct hlist_head hlist;
143         unsigned long kpfn;
144 #ifdef CONFIG_NUMA
145         int nid;
146 #endif
147 };
148 
149 /**
150  * struct rmap_item - reverse mapping item for virtual addresses
151  * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
152  * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
153  * @nid: NUMA node id of unstable tree in which linked (may not match page)
154  * @mm: the memory structure this rmap_item is pointing into
155  * @address: the virtual address this rmap_item tracks (+ flags in low bits)
156  * @oldchecksum: previous checksum of the page at that virtual address
157  * @node: rb node of this rmap_item in the unstable tree
158  * @head: pointer to stable_node heading this list in the stable tree
159  * @hlist: link into hlist of rmap_items hanging off that stable_node
160  */
161 struct rmap_item {
162         struct rmap_item *rmap_list;
163         union {
164                 struct anon_vma *anon_vma;      /* when stable */
165 #ifdef CONFIG_NUMA
166                 int nid;                /* when node of unstable tree */
167 #endif
168         };
169         struct mm_struct *mm;
170         unsigned long address;          /* + low bits used for flags below */
171         unsigned int oldchecksum;       /* when unstable */
172         union {
173                 struct rb_node node;    /* when node of unstable tree */
174                 struct {                /* when listed from stable tree */
175                         struct stable_node *head;
176                         struct hlist_node hlist;
177                 };
178         };
179 };
180 
181 #define SEQNR_MASK      0x0ff   /* low bits of unstable tree seqnr */
182 #define UNSTABLE_FLAG   0x100   /* is a node of the unstable tree */
183 #define STABLE_FLAG     0x200   /* is listed from the stable tree */
184 
185 /* The stable and unstable tree heads */
186 static struct rb_root one_stable_tree[1] = { RB_ROOT };
187 static struct rb_root one_unstable_tree[1] = { RB_ROOT };
188 static struct rb_root *root_stable_tree = one_stable_tree;
189 static struct rb_root *root_unstable_tree = one_unstable_tree;
190 
191 /* Recently migrated nodes of stable tree, pending proper placement */
192 static LIST_HEAD(migrate_nodes);
193 
194 #define MM_SLOTS_HASH_BITS 10
195 static DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
196 
197 static struct mm_slot ksm_mm_head = {
198         .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
199 };
200 static struct ksm_scan ksm_scan = {
201         .mm_slot = &ksm_mm_head,
202 };
203 
204 static struct kmem_cache *rmap_item_cache;
205 static struct kmem_cache *stable_node_cache;
206 static struct kmem_cache *mm_slot_cache;
207 
208 /* The number of nodes in the stable tree */
209 static unsigned long ksm_pages_shared;
210 
211 /* The number of page slots additionally sharing those nodes */
212 static unsigned long ksm_pages_sharing;
213 
214 /* The number of nodes in the unstable tree */
215 static unsigned long ksm_pages_unshared;
216 
217 /* The number of rmap_items in use: to calculate pages_volatile */
218 static unsigned long ksm_rmap_items;
219 
220 /* Number of pages ksmd should scan in one batch */
221 static unsigned int ksm_thread_pages_to_scan = 100;
222 
223 /* Milliseconds ksmd should sleep between batches */
224 static unsigned int ksm_thread_sleep_millisecs = 20;
225 
226 #ifdef CONFIG_NUMA
227 /* Zeroed when merging across nodes is not allowed */
228 static unsigned int ksm_merge_across_nodes = 1;
229 static int ksm_nr_node_ids = 1;
230 #else
231 #define ksm_merge_across_nodes  1U
232 #define ksm_nr_node_ids         1
233 #endif
234 
235 #define KSM_RUN_STOP    0
236 #define KSM_RUN_MERGE   1
237 #define KSM_RUN_UNMERGE 2
238 #define KSM_RUN_OFFLINE 4
239 static unsigned long ksm_run = KSM_RUN_STOP;
240 static void wait_while_offlining(void);
241 
242 static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
243 static DEFINE_MUTEX(ksm_thread_mutex);
244 static DEFINE_SPINLOCK(ksm_mmlist_lock);
245 
246 #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
247                 sizeof(struct __struct), __alignof__(struct __struct),\
248                 (__flags), NULL)
249 
250 static int __init ksm_slab_init(void)
251 {
252         rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
253         if (!rmap_item_cache)
254                 goto out;
255 
256         stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
257         if (!stable_node_cache)
258                 goto out_free1;
259 
260         mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
261         if (!mm_slot_cache)
262                 goto out_free2;
263 
264         return 0;
265 
266 out_free2:
267         kmem_cache_destroy(stable_node_cache);
268 out_free1:
269         kmem_cache_destroy(rmap_item_cache);
270 out:
271         return -ENOMEM;
272 }
273 
274 static void __init ksm_slab_free(void)
275 {
276         kmem_cache_destroy(mm_slot_cache);
277         kmem_cache_destroy(stable_node_cache);
278         kmem_cache_destroy(rmap_item_cache);
279         mm_slot_cache = NULL;
280 }
281 
282 static inline struct rmap_item *alloc_rmap_item(void)
283 {
284         struct rmap_item *rmap_item;
285 
286         rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL |
287                                                 __GFP_NORETRY | __GFP_NOWARN);
288         if (rmap_item)
289                 ksm_rmap_items++;
290         return rmap_item;
291 }
292 
293 static inline void free_rmap_item(struct rmap_item *rmap_item)
294 {
295         ksm_rmap_items--;
296         rmap_item->mm = NULL;   /* debug safety */
297         kmem_cache_free(rmap_item_cache, rmap_item);
298 }
299 
300 static inline struct stable_node *alloc_stable_node(void)
301 {
302         /*
303          * The allocation can take too long with GFP_KERNEL when memory is under
304          * pressure, which may lead to hung task warnings.  Adding __GFP_HIGH
305          * grants access to memory reserves, helping to avoid this problem.
306          */
307         return kmem_cache_alloc(stable_node_cache, GFP_KERNEL | __GFP_HIGH);
308 }
309 
310 static inline void free_stable_node(struct stable_node *stable_node)
311 {
312         kmem_cache_free(stable_node_cache, stable_node);
313 }
314 
315 static inline struct mm_slot *alloc_mm_slot(void)
316 {
317         if (!mm_slot_cache)     /* initialization failed */
318                 return NULL;
319         return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
320 }
321 
322 static inline void free_mm_slot(struct mm_slot *mm_slot)
323 {
324         kmem_cache_free(mm_slot_cache, mm_slot);
325 }
326 
327 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
328 {
329         struct mm_slot *slot;
330 
331         hash_for_each_possible(mm_slots_hash, slot, link, (unsigned long)mm)
332                 if (slot->mm == mm)
333                         return slot;
334 
335         return NULL;
336 }
337 
338 static void insert_to_mm_slots_hash(struct mm_struct *mm,
339                                     struct mm_slot *mm_slot)
340 {
341         mm_slot->mm = mm;
342         hash_add(mm_slots_hash, &mm_slot->link, (unsigned long)mm);
343 }
344 
345 /*
346  * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
347  * page tables after it has passed through ksm_exit() - which, if necessary,
348  * takes mmap_sem briefly to serialize against them.  ksm_exit() does not set
349  * a special flag: they can just back out as soon as mm_users goes to zero.
350  * ksm_test_exit() is used throughout to make this test for exit: in some
351  * places for correctness, in some places just to avoid unnecessary work.
352  */
353 static inline bool ksm_test_exit(struct mm_struct *mm)
354 {
355         return atomic_read(&mm->mm_users) == 0;
356 }
357 
358 /*
359  * We use break_ksm to break COW on a ksm page: it's a stripped down
360  *
361  *      if (get_user_pages(addr, 1, 1, 1, &page, NULL) == 1)
362  *              put_page(page);
363  *
364  * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
365  * in case the application has unmapped and remapped mm,addr meanwhile.
366  * Could a ksm page appear anywhere else?  Actually yes, in a VM_PFNMAP
367  * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
368  *
369  * FAULT_FLAG/FOLL_REMOTE are because we do this outside the context
370  * of the process that owns 'vma'.  We also do not want to enforce
371  * protection keys here anyway.
372  */
373 static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
374 {
375         struct page *page;
376         int ret = 0;
377 
378         do {
379                 cond_resched();
380                 page = follow_page(vma, addr,
381                                 FOLL_GET | FOLL_MIGRATION | FOLL_REMOTE);
382                 if (IS_ERR_OR_NULL(page))
383                         break;
384                 if (PageKsm(page))
385                         ret = handle_mm_fault(vma, addr,
386                                         FAULT_FLAG_WRITE | FAULT_FLAG_REMOTE);
387                 else
388                         ret = VM_FAULT_WRITE;
389                 put_page(page);
390         } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | VM_FAULT_OOM)));
391         /*
392          * We must loop because handle_mm_fault() may back out if there's
393          * any difficulty e.g. if pte accessed bit gets updated concurrently.
394          *
395          * VM_FAULT_WRITE is what we have been hoping for: it indicates that
396          * COW has been broken, even if the vma does not permit VM_WRITE;
397          * but note that a concurrent fault might break PageKsm for us.
398          *
399          * VM_FAULT_SIGBUS could occur if we race with truncation of the
400          * backing file, which also invalidates anonymous pages: that's
401          * okay, that truncation will have unmapped the PageKsm for us.
402          *
403          * VM_FAULT_OOM: at the time of writing (late July 2009), setting
404          * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
405          * current task has TIF_MEMDIE set, and will be OOM killed on return
406          * to user; and ksmd, having no mm, would never be chosen for that.
407          *
408          * But if the mm is in a limited mem_cgroup, then the fault may fail
409          * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
410          * even ksmd can fail in this way - though it's usually breaking ksm
411          * just to undo a merge it made a moment before, so unlikely to oom.
412          *
413          * That's a pity: we might therefore have more kernel pages allocated
414          * than we're counting as nodes in the stable tree; but ksm_do_scan
415          * will retry to break_cow on each pass, so should recover the page
416          * in due course.  The important thing is to not let VM_MERGEABLE
417          * be cleared while any such pages might remain in the area.
418          */
419         return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
420 }
421 
422 static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
423                 unsigned long addr)
424 {
425         struct vm_area_struct *vma;
426         if (ksm_test_exit(mm))
427                 return NULL;
428         vma = find_vma(mm, addr);
429         if (!vma || vma->vm_start > addr)
430                 return NULL;
431         if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
432                 return NULL;
433         return vma;
434 }
435 
436 static void break_cow(struct rmap_item *rmap_item)
437 {
438         struct mm_struct *mm = rmap_item->mm;
439         unsigned long addr = rmap_item->address;
440         struct vm_area_struct *vma;
441 
442         /*
443          * It is not an accident that whenever we want to break COW
444          * to undo, we also need to drop a reference to the anon_vma.
445          */
446         put_anon_vma(rmap_item->anon_vma);
447 
448         down_read(&mm->mmap_sem);
449         vma = find_mergeable_vma(mm, addr);
450         if (vma)
451                 break_ksm(vma, addr);
452         up_read(&mm->mmap_sem);
453 }
454 
455 static struct page *get_mergeable_page(struct rmap_item *rmap_item)
456 {
457         struct mm_struct *mm = rmap_item->mm;
458         unsigned long addr = rmap_item->address;
459         struct vm_area_struct *vma;
460         struct page *page;
461 
462         down_read(&mm->mmap_sem);
463         vma = find_mergeable_vma(mm, addr);
464         if (!vma)
465                 goto out;
466 
467         page = follow_page(vma, addr, FOLL_GET);
468         if (IS_ERR_OR_NULL(page))
469                 goto out;
470         if (PageAnon(page)) {
471                 flush_anon_page(vma, page, addr);
472                 flush_dcache_page(page);
473         } else {
474                 put_page(page);
475 out:
476                 page = NULL;
477         }
478         up_read(&mm->mmap_sem);
479         return page;
480 }
481 
482 /*
483  * This helper is used for getting right index into array of tree roots.
484  * When merge_across_nodes knob is set to 1, there are only two rb-trees for
485  * stable and unstable pages from all nodes with roots in index 0. Otherwise,
486  * every node has its own stable and unstable tree.
487  */
488 static inline int get_kpfn_nid(unsigned long kpfn)
489 {
490         return ksm_merge_across_nodes ? 0 : NUMA(pfn_to_nid(kpfn));
491 }
492 
493 static void remove_node_from_stable_tree(struct stable_node *stable_node)
494 {
495         struct rmap_item *rmap_item;
496 
497         hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
498                 if (rmap_item->hlist.next)
499                         ksm_pages_sharing--;
500                 else
501                         ksm_pages_shared--;
502                 put_anon_vma(rmap_item->anon_vma);
503                 rmap_item->address &= PAGE_MASK;
504                 cond_resched();
505         }
506 
507         if (stable_node->head == &migrate_nodes)
508                 list_del(&stable_node->list);
509         else
510                 rb_erase(&stable_node->node,
511                          root_stable_tree + NUMA(stable_node->nid));
512         free_stable_node(stable_node);
513 }
514 
515 /*
516  * get_ksm_page: checks if the page indicated by the stable node
517  * is still its ksm page, despite having held no reference to it.
518  * In which case we can trust the content of the page, and it
519  * returns the gotten page; but if the page has now been zapped,
520  * remove the stale node from the stable tree and return NULL.
521  * But beware, the stable node's page might be being migrated.
522  *
523  * You would expect the stable_node to hold a reference to the ksm page.
524  * But if it increments the page's count, swapping out has to wait for
525  * ksmd to come around again before it can free the page, which may take
526  * seconds or even minutes: much too unresponsive.  So instead we use a
527  * "keyhole reference": access to the ksm page from the stable node peeps
528  * out through its keyhole to see if that page still holds the right key,
529  * pointing back to this stable node.  This relies on freeing a PageAnon
530  * page to reset its page->mapping to NULL, and relies on no other use of
531  * a page to put something that might look like our key in page->mapping.
532  * is on its way to being freed; but it is an anomaly to bear in mind.
533  */
534 static struct page *get_ksm_page(struct stable_node *stable_node, bool lock_it)
535 {
536         struct page *page;
537         void *expected_mapping;
538         unsigned long kpfn;
539 
540         expected_mapping = (void *)((unsigned long)stable_node |
541                                         PAGE_MAPPING_KSM);
542 again:
543         kpfn = READ_ONCE(stable_node->kpfn);
544         page = pfn_to_page(kpfn);
545 
546         /*
547          * page is computed from kpfn, so on most architectures reading
548          * page->mapping is naturally ordered after reading node->kpfn,
549          * but on Alpha we need to be more careful.
550          */
551         smp_read_barrier_depends();
552         if (READ_ONCE(page->mapping) != expected_mapping)
553                 goto stale;
554 
555         /*
556          * We cannot do anything with the page while its refcount is 0.
557          * Usually 0 means free, or tail of a higher-order page: in which
558          * case this node is no longer referenced, and should be freed;
559          * however, it might mean that the page is under page_freeze_refs().
560          * The __remove_mapping() case is easy, again the node is now stale;
561          * but if page is swapcache in migrate_page_move_mapping(), it might
562          * still be our page, in which case it's essential to keep the node.
563          */
564         while (!get_page_unless_zero(page)) {
565                 /*
566                  * Another check for page->mapping != expected_mapping would
567                  * work here too.  We have chosen the !PageSwapCache test to
568                  * optimize the common case, when the page is or is about to
569                  * be freed: PageSwapCache is cleared (under spin_lock_irq)
570                  * in the freeze_refs section of __remove_mapping(); but Anon
571                  * page->mapping reset to NULL later, in free_pages_prepare().
572                  */
573                 if (!PageSwapCache(page))
574                         goto stale;
575                 cpu_relax();
576         }
577 
578         if (READ_ONCE(page->mapping) != expected_mapping) {
579                 put_page(page);
580                 goto stale;
581         }
582 
583         if (lock_it) {
584                 lock_page(page);
585                 if (READ_ONCE(page->mapping) != expected_mapping) {
586                         unlock_page(page);
587                         put_page(page);
588                         goto stale;
589                 }
590         }
591         return page;
592 
593 stale:
594         /*
595          * We come here from above when page->mapping or !PageSwapCache
596          * suggests that the node is stale; but it might be under migration.
597          * We need smp_rmb(), matching the smp_wmb() in ksm_migrate_page(),
598          * before checking whether node->kpfn has been changed.
599          */
600         smp_rmb();
601         if (READ_ONCE(stable_node->kpfn) != kpfn)
602                 goto again;
603         remove_node_from_stable_tree(stable_node);
604         return NULL;
605 }
606 
607 /*
608  * Removing rmap_item from stable or unstable tree.
609  * This function will clean the information from the stable/unstable tree.
610  */
611 static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
612 {
613         if (rmap_item->address & STABLE_FLAG) {
614                 struct stable_node *stable_node;
615                 struct page *page;
616 
617                 stable_node = rmap_item->head;
618                 page = get_ksm_page(stable_node, true);
619                 if (!page)
620                         goto out;
621 
622                 hlist_del(&rmap_item->hlist);
623                 unlock_page(page);
624                 put_page(page);
625 
626                 if (!hlist_empty(&stable_node->hlist))
627                         ksm_pages_sharing--;
628                 else
629                         ksm_pages_shared--;
630 
631                 put_anon_vma(rmap_item->anon_vma);
632                 rmap_item->address &= PAGE_MASK;
633 
634         } else if (rmap_item->address & UNSTABLE_FLAG) {
635                 unsigned char age;
636                 /*
637                  * Usually ksmd can and must skip the rb_erase, because
638                  * root_unstable_tree was already reset to RB_ROOT.
639                  * But be careful when an mm is exiting: do the rb_erase
640                  * if this rmap_item was inserted by this scan, rather
641                  * than left over from before.
642                  */
643                 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
644                 BUG_ON(age > 1);
645                 if (!age)
646                         rb_erase(&rmap_item->node,
647                                  root_unstable_tree + NUMA(rmap_item->nid));
648                 ksm_pages_unshared--;
649                 rmap_item->address &= PAGE_MASK;
650         }
651 out:
652         cond_resched();         /* we're called from many long loops */
653 }
654 
655 static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
656                                        struct rmap_item **rmap_list)
657 {
658         while (*rmap_list) {
659                 struct rmap_item *rmap_item = *rmap_list;
660                 *rmap_list = rmap_item->rmap_list;
661                 remove_rmap_item_from_tree(rmap_item);
662                 free_rmap_item(rmap_item);
663         }
664 }
665 
666 /*
667  * Though it's very tempting to unmerge rmap_items from stable tree rather
668  * than check every pte of a given vma, the locking doesn't quite work for
669  * that - an rmap_item is assigned to the stable tree after inserting ksm
670  * page and upping mmap_sem.  Nor does it fit with the way we skip dup'ing
671  * rmap_items from parent to child at fork time (so as not to waste time
672  * if exit comes before the next scan reaches it).
673  *
674  * Similarly, although we'd like to remove rmap_items (so updating counts
675  * and freeing memory) when unmerging an area, it's easier to leave that
676  * to the next pass of ksmd - consider, for example, how ksmd might be
677  * in cmp_and_merge_page on one of the rmap_items we would be removing.
678  */
679 static int unmerge_ksm_pages(struct vm_area_struct *vma,
680                              unsigned long start, unsigned long end)
681 {
682         unsigned long addr;
683         int err = 0;
684 
685         for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
686                 if (ksm_test_exit(vma->vm_mm))
687                         break;
688                 if (signal_pending(current))
689                         err = -ERESTARTSYS;
690                 else
691                         err = break_ksm(vma, addr);
692         }
693         return err;
694 }
695 
696 #ifdef CONFIG_SYSFS
697 /*
698  * Only called through the sysfs control interface:
699  */
700 static int remove_stable_node(struct stable_node *stable_node)
701 {
702         struct page *page;
703         int err;
704 
705         page = get_ksm_page(stable_node, true);
706         if (!page) {
707                 /*
708                  * get_ksm_page did remove_node_from_stable_tree itself.
709                  */
710                 return 0;
711         }
712 
713         if (WARN_ON_ONCE(page_mapped(page))) {
714                 /*
715                  * This should not happen: but if it does, just refuse to let
716                  * merge_across_nodes be switched - there is no need to panic.
717                  */
718                 err = -EBUSY;
719         } else {
720                 /*
721                  * The stable node did not yet appear stale to get_ksm_page(),
722                  * since that allows for an unmapped ksm page to be recognized
723                  * right up until it is freed; but the node is safe to remove.
724                  * This page might be in a pagevec waiting to be freed,
725                  * or it might be PageSwapCache (perhaps under writeback),
726                  * or it might have been removed from swapcache a moment ago.
727                  */
728                 set_page_stable_node(page, NULL);
729                 remove_node_from_stable_tree(stable_node);
730                 err = 0;
731         }
732 
733         unlock_page(page);
734         put_page(page);
735         return err;
736 }
737 
738 static int remove_all_stable_nodes(void)
739 {
740         struct stable_node *stable_node, *next;
741         int nid;
742         int err = 0;
743 
744         for (nid = 0; nid < ksm_nr_node_ids; nid++) {
745                 while (root_stable_tree[nid].rb_node) {
746                         stable_node = rb_entry(root_stable_tree[nid].rb_node,
747                                                 struct stable_node, node);
748                         if (remove_stable_node(stable_node)) {
749                                 err = -EBUSY;
750                                 break;  /* proceed to next nid */
751                         }
752                         cond_resched();
753                 }
754         }
755         list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
756                 if (remove_stable_node(stable_node))
757                         err = -EBUSY;
758                 cond_resched();
759         }
760         return err;
761 }
762 
763 static int unmerge_and_remove_all_rmap_items(void)
764 {
765         struct mm_slot *mm_slot;
766         struct mm_struct *mm;
767         struct vm_area_struct *vma;
768         int err = 0;
769 
770         spin_lock(&ksm_mmlist_lock);
771         ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
772                                                 struct mm_slot, mm_list);
773         spin_unlock(&ksm_mmlist_lock);
774 
775         for (mm_slot = ksm_scan.mm_slot;
776                         mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
777                 mm = mm_slot->mm;
778                 down_read(&mm->mmap_sem);
779                 for (vma = mm->mmap; vma; vma = vma->vm_next) {
780                         if (ksm_test_exit(mm))
781                                 break;
782                         if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
783                                 continue;
784                         err = unmerge_ksm_pages(vma,
785                                                 vma->vm_start, vma->vm_end);
786                         if (err)
787                                 goto error;
788                 }
789 
790                 remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
791                 up_read(&mm->mmap_sem);
792 
793                 spin_lock(&ksm_mmlist_lock);
794                 ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
795                                                 struct mm_slot, mm_list);
796                 if (ksm_test_exit(mm)) {
797                         hash_del(&mm_slot->link);
798                         list_del(&mm_slot->mm_list);
799                         spin_unlock(&ksm_mmlist_lock);
800 
801                         free_mm_slot(mm_slot);
802                         clear_bit(MMF_VM_MERGEABLE, &mm->flags);
803                         mmdrop(mm);
804                 } else
805                         spin_unlock(&ksm_mmlist_lock);
806         }
807 
808         /* Clean up stable nodes, but don't worry if some are still busy */
809         remove_all_stable_nodes();
810         ksm_scan.seqnr = 0;
811         return 0;
812 
813 error:
814         up_read(&mm->mmap_sem);
815         spin_lock(&ksm_mmlist_lock);
816         ksm_scan.mm_slot = &ksm_mm_head;
817         spin_unlock(&ksm_mmlist_lock);
818         return err;
819 }
820 #endif /* CONFIG_SYSFS */
821 
822 static u32 calc_checksum(struct page *page)
823 {
824         u32 checksum;
825         void *addr = kmap_atomic(page);
826         checksum = jhash2(addr, PAGE_SIZE / 4, 17);
827         kunmap_atomic(addr);
828         return checksum;
829 }
830 
831 static int memcmp_pages(struct page *page1, struct page *page2)
832 {
833         char *addr1, *addr2;
834         int ret;
835 
836         addr1 = kmap_atomic(page1);
837         addr2 = kmap_atomic(page2);
838         ret = memcmp(addr1, addr2, PAGE_SIZE);
839         kunmap_atomic(addr2);
840         kunmap_atomic(addr1);
841         return ret;
842 }
843 
844 static inline int pages_identical(struct page *page1, struct page *page2)
845 {
846         return !memcmp_pages(page1, page2);
847 }
848 
849 static int write_protect_page(struct vm_area_struct *vma, struct page *page,
850                               pte_t *orig_pte)
851 {
852         struct mm_struct *mm = vma->vm_mm;
853         unsigned long addr;
854         pte_t *ptep;
855         spinlock_t *ptl;
856         int swapped;
857         int err = -EFAULT;
858         unsigned long mmun_start;       /* For mmu_notifiers */
859         unsigned long mmun_end;         /* For mmu_notifiers */
860 
861         addr = page_address_in_vma(page, vma);
862         if (addr == -EFAULT)
863                 goto out;
864 
865         BUG_ON(PageTransCompound(page));
866 
867         mmun_start = addr;
868         mmun_end   = addr + PAGE_SIZE;
869         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
870 
871         ptep = page_check_address(page, mm, addr, &ptl, 0);
872         if (!ptep)
873                 goto out_mn;
874 
875         if (pte_write(*ptep) || pte_dirty(*ptep)) {
876                 pte_t entry;
877 
878                 swapped = PageSwapCache(page);
879                 flush_cache_page(vma, addr, page_to_pfn(page));
880                 /*
881                  * Ok this is tricky, when get_user_pages_fast() run it doesn't
882                  * take any lock, therefore the check that we are going to make
883                  * with the pagecount against the mapcount is racey and
884                  * O_DIRECT can happen right after the check.
885                  * So we clear the pte and flush the tlb before the check
886                  * this assure us that no O_DIRECT can happen after the check
887                  * or in the middle of the check.
888                  */
889                 entry = ptep_clear_flush_notify(vma, addr, ptep);
890                 /*
891                  * Check that no O_DIRECT or similar I/O is in progress on the
892                  * page
893                  */
894                 if (page_mapcount(page) + 1 + swapped != page_count(page)) {
895                         set_pte_at(mm, addr, ptep, entry);
896                         goto out_unlock;
897                 }
898                 if (pte_dirty(entry))
899                         set_page_dirty(page);
900                 entry = pte_mkclean(pte_wrprotect(entry));
901                 set_pte_at_notify(mm, addr, ptep, entry);
902         }
903         *orig_pte = *ptep;
904         err = 0;
905 
906 out_unlock:
907         pte_unmap_unlock(ptep, ptl);
908 out_mn:
909         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
910 out:
911         return err;
912 }
913 
914 /**
915  * replace_page - replace page in vma by new ksm page
916  * @vma:      vma that holds the pte pointing to page
917  * @page:     the page we are replacing by kpage
918  * @kpage:    the ksm page we replace page by
919  * @orig_pte: the original value of the pte
920  *
921  * Returns 0 on success, -EFAULT on failure.
922  */
923 static int replace_page(struct vm_area_struct *vma, struct page *page,
924                         struct page *kpage, pte_t orig_pte)
925 {
926         struct mm_struct *mm = vma->vm_mm;
927         pmd_t *pmd;
928         pte_t *ptep;
929         spinlock_t *ptl;
930         unsigned long addr;
931         int err = -EFAULT;
932         unsigned long mmun_start;       /* For mmu_notifiers */
933         unsigned long mmun_end;         /* For mmu_notifiers */
934 
935         addr = page_address_in_vma(page, vma);
936         if (addr == -EFAULT)
937                 goto out;
938 
939         pmd = mm_find_pmd(mm, addr);
940         if (!pmd)
941                 goto out;
942 
943         mmun_start = addr;
944         mmun_end   = addr + PAGE_SIZE;
945         mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
946 
947         ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
948         if (!pte_same(*ptep, orig_pte)) {
949                 pte_unmap_unlock(ptep, ptl);
950                 goto out_mn;
951         }
952 
953         get_page(kpage);
954         page_add_anon_rmap(kpage, vma, addr, false);
955 
956         flush_cache_page(vma, addr, pte_pfn(*ptep));
957         ptep_clear_flush_notify(vma, addr, ptep);
958         set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
959 
960         page_remove_rmap(page, false);
961         if (!page_mapped(page))
962                 try_to_free_swap(page);
963         put_page(page);
964 
965         pte_unmap_unlock(ptep, ptl);
966         err = 0;
967 out_mn:
968         mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
969 out:
970         return err;
971 }
972 
973 /*
974  * try_to_merge_one_page - take two pages and merge them into one
975  * @vma: the vma that holds the pte pointing to page
976  * @page: the PageAnon page that we want to replace with kpage
977  * @kpage: the PageKsm page that we want to map instead of page,
978  *         or NULL the first time when we want to use page as kpage.
979  *
980  * This function returns 0 if the pages were merged, -EFAULT otherwise.
981  */
982 static int try_to_merge_one_page(struct vm_area_struct *vma,
983                                  struct page *page, struct page *kpage)
984 {
985         pte_t orig_pte = __pte(0);
986         int err = -EFAULT;
987 
988         if (page == kpage)                      /* ksm page forked */
989                 return 0;
990 
991         if (!PageAnon(page))
992                 goto out;
993 
994         /*
995          * We need the page lock to read a stable PageSwapCache in
996          * write_protect_page().  We use trylock_page() instead of
997          * lock_page() because we don't want to wait here - we
998          * prefer to continue scanning and merging different pages,
999          * then come back to this page when it is unlocked.
1000          */
1001         if (!trylock_page(page))
1002                 goto out;
1003 
1004         if (PageTransCompound(page)) {
1005                 err = split_huge_page(page);
1006                 if (err)
1007                         goto out_unlock;
1008         }
1009 
1010         /*
1011          * If this anonymous page is mapped only here, its pte may need
1012          * to be write-protected.  If it's mapped elsewhere, all of its
1013          * ptes are necessarily already write-protected.  But in either
1014          * case, we need to lock and check page_count is not raised.
1015          */
1016         if (write_protect_page(vma, page, &orig_pte) == 0) {
1017                 if (!kpage) {
1018                         /*
1019                          * While we hold page lock, upgrade page from
1020                          * PageAnon+anon_vma to PageKsm+NULL stable_node:
1021                          * stable_tree_insert() will update stable_node.
1022                          */
1023                         set_page_stable_node(page, NULL);
1024                         mark_page_accessed(page);
1025                         /*
1026                          * Page reclaim just frees a clean page with no dirty
1027                          * ptes: make sure that the ksm page would be swapped.
1028                          */
1029                         if (!PageDirty(page))
1030                                 SetPageDirty(page);
1031                         err = 0;
1032                 } else if (pages_identical(page, kpage))
1033                         err = replace_page(vma, page, kpage, orig_pte);
1034         }
1035 
1036         if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
1037                 munlock_vma_page(page);
1038                 if (!PageMlocked(kpage)) {
1039                         unlock_page(page);
1040                         lock_page(kpage);
1041                         mlock_vma_page(kpage);
1042                         page = kpage;           /* for final unlock */
1043                 }
1044         }
1045 
1046 out_unlock:
1047         unlock_page(page);
1048 out:
1049         return err;
1050 }
1051 
1052 /*
1053  * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
1054  * but no new kernel page is allocated: kpage must already be a ksm page.
1055  *
1056  * This function returns 0 if the pages were merged, -EFAULT otherwise.
1057  */
1058 static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
1059                                       struct page *page, struct page *kpage)
1060 {
1061         struct mm_struct *mm = rmap_item->mm;
1062         struct vm_area_struct *vma;
1063         int err = -EFAULT;
1064 
1065         down_read(&mm->mmap_sem);
1066         vma = find_mergeable_vma(mm, rmap_item->address);
1067         if (!vma)
1068                 goto out;
1069 
1070         err = try_to_merge_one_page(vma, page, kpage);
1071         if (err)
1072                 goto out;
1073 
1074         /* Unstable nid is in union with stable anon_vma: remove first */
1075         remove_rmap_item_from_tree(rmap_item);
1076 
1077         /* Must get reference to anon_vma while still holding mmap_sem */
1078         rmap_item->anon_vma = vma->anon_vma;
1079         get_anon_vma(vma->anon_vma);
1080 out:
1081         up_read(&mm->mmap_sem);
1082         return err;
1083 }
1084 
1085 /*
1086  * try_to_merge_two_pages - take two identical pages and prepare them
1087  * to be merged into one page.
1088  *
1089  * This function returns the kpage if we successfully merged two identical
1090  * pages into one ksm page, NULL otherwise.
1091  *
1092  * Note that this function upgrades page to ksm page: if one of the pages
1093  * is already a ksm page, try_to_merge_with_ksm_page should be used.
1094  */
1095 static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
1096                                            struct page *page,
1097                                            struct rmap_item *tree_rmap_item,
1098                                            struct page *tree_page)
1099 {
1100         int err;
1101 
1102         err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
1103         if (!err) {
1104                 err = try_to_merge_with_ksm_page(tree_rmap_item,
1105                                                         tree_page, page);
1106                 /*
1107                  * If that fails, we have a ksm page with only one pte
1108                  * pointing to it: so break it.
1109                  */
1110                 if (err)
1111                         break_cow(rmap_item);
1112         }
1113         return err ? NULL : page;
1114 }
1115 
1116 /*
1117  * stable_tree_search - search for page inside the stable tree
1118  *
1119  * This function checks if there is a page inside the stable tree
1120  * with identical content to the page that we are scanning right now.
1121  *
1122  * This function returns the stable tree node of identical content if found,
1123  * NULL otherwise.
1124  */
1125 static struct page *stable_tree_search(struct page *page)
1126 {
1127         int nid;
1128         struct rb_root *root;
1129         struct rb_node **new;
1130         struct rb_node *parent;
1131         struct stable_node *stable_node;
1132         struct stable_node *page_node;
1133 
1134         page_node = page_stable_node(page);
1135         if (page_node && page_node->head != &migrate_nodes) {
1136                 /* ksm page forked */
1137                 get_page(page);
1138                 return page;
1139         }
1140 
1141         nid = get_kpfn_nid(page_to_pfn(page));
1142         root = root_stable_tree + nid;
1143 again:
1144         new = &root->rb_node;
1145         parent = NULL;
1146 
1147         while (*new) {
1148                 struct page *tree_page;
1149                 int ret;
1150 
1151                 cond_resched();
1152                 stable_node = rb_entry(*new, struct stable_node, node);
1153                 tree_page = get_ksm_page(stable_node, false);
1154                 if (!tree_page) {
1155                         /*
1156                          * If we walked over a stale stable_node,
1157                          * get_ksm_page() will call rb_erase() and it
1158                          * may rebalance the tree from under us. So
1159                          * restart the search from scratch. Returning
1160                          * NULL would be safe too, but we'd generate
1161                          * false negative insertions just because some
1162                          * stable_node was stale.
1163                          */
1164                         goto again;
1165                 }
1166 
1167                 ret = memcmp_pages(page, tree_page);
1168                 put_page(tree_page);
1169 
1170                 parent = *new;
1171                 if (ret < 0)
1172                         new = &parent->rb_left;
1173                 else if (ret > 0)
1174                         new = &parent->rb_right;
1175                 else {
1176                         /*
1177                          * Lock and unlock the stable_node's page (which
1178                          * might already have been migrated) so that page
1179                          * migration is sure to notice its raised count.
1180                          * It would be more elegant to return stable_node
1181                          * than kpage, but that involves more changes.
1182                          */
1183                         tree_page = get_ksm_page(stable_node, true);
1184                         if (tree_page) {
1185                                 unlock_page(tree_page);
1186                                 if (get_kpfn_nid(stable_node->kpfn) !=
1187                                                 NUMA(stable_node->nid)) {
1188                                         put_page(tree_page);
1189                                         goto replace;
1190                                 }
1191                                 return tree_page;
1192                         }
1193                         /*
1194                          * There is now a place for page_node, but the tree may
1195                          * have been rebalanced, so re-evaluate parent and new.
1196                          */
1197                         if (page_node)
1198                                 goto again;
1199                         return NULL;
1200                 }
1201         }
1202 
1203         if (!page_node)
1204                 return NULL;
1205 
1206         list_del(&page_node->list);
1207         DO_NUMA(page_node->nid = nid);
1208         rb_link_node(&page_node->node, parent, new);
1209         rb_insert_color(&page_node->node, root);
1210         get_page(page);
1211         return page;
1212 
1213 replace:
1214         if (page_node) {
1215                 list_del(&page_node->list);
1216                 DO_NUMA(page_node->nid = nid);
1217                 rb_replace_node(&stable_node->node, &page_node->node, root);
1218                 get_page(page);
1219         } else {
1220                 rb_erase(&stable_node->node, root);
1221                 page = NULL;
1222         }
1223         stable_node->head = &migrate_nodes;
1224         list_add(&stable_node->list, stable_node->head);
1225         return page;
1226 }
1227 
1228 /*
1229  * stable_tree_insert - insert stable tree node pointing to new ksm page
1230  * into the stable tree.
1231  *
1232  * This function returns the stable tree node just allocated on success,
1233  * NULL otherwise.
1234  */
1235 static struct stable_node *stable_tree_insert(struct page *kpage)
1236 {
1237         int nid;
1238         unsigned long kpfn;
1239         struct rb_root *root;
1240         struct rb_node **new;
1241         struct rb_node *parent;
1242         struct stable_node *stable_node;
1243 
1244         kpfn = page_to_pfn(kpage);
1245         nid = get_kpfn_nid(kpfn);
1246         root = root_stable_tree + nid;
1247 again:
1248         parent = NULL;
1249         new = &root->rb_node;
1250 
1251         while (*new) {
1252                 struct page *tree_page;
1253                 int ret;
1254 
1255                 cond_resched();
1256                 stable_node = rb_entry(*new, struct stable_node, node);
1257                 tree_page = get_ksm_page(stable_node, false);
1258                 if (!tree_page) {
1259                         /*
1260                          * If we walked over a stale stable_node,
1261                          * get_ksm_page() will call rb_erase() and it
1262                          * may rebalance the tree from under us. So
1263                          * restart the search from scratch. Returning
1264                          * NULL would be safe too, but we'd generate
1265                          * false negative insertions just because some
1266                          * stable_node was stale.
1267                          */
1268                         goto again;
1269                 }
1270 
1271                 ret = memcmp_pages(kpage, tree_page);
1272                 put_page(tree_page);
1273 
1274                 parent = *new;
1275                 if (ret < 0)
1276                         new = &parent->rb_left;
1277                 else if (ret > 0)
1278                         new = &parent->rb_right;
1279                 else {
1280                         /*
1281                          * It is not a bug that stable_tree_search() didn't
1282                          * find this node: because at that time our page was
1283                          * not yet write-protected, so may have changed since.
1284                          */
1285                         return NULL;
1286                 }
1287         }
1288 
1289         stable_node = alloc_stable_node();
1290         if (!stable_node)
1291                 return NULL;
1292 
1293         INIT_HLIST_HEAD(&stable_node->hlist);
1294         stable_node->kpfn = kpfn;
1295         set_page_stable_node(kpage, stable_node);
1296         DO_NUMA(stable_node->nid = nid);
1297         rb_link_node(&stable_node->node, parent, new);
1298         rb_insert_color(&stable_node->node, root);
1299 
1300         return stable_node;
1301 }
1302 
1303 /*
1304  * unstable_tree_search_insert - search for identical page,
1305  * else insert rmap_item into the unstable tree.
1306  *
1307  * This function searches for a page in the unstable tree identical to the
1308  * page currently being scanned; and if no identical page is found in the
1309  * tree, we insert rmap_item as a new object into the unstable tree.
1310  *
1311  * This function returns pointer to rmap_item found to be identical
1312  * to the currently scanned page, NULL otherwise.
1313  *
1314  * This function does both searching and inserting, because they share
1315  * the same walking algorithm in an rbtree.
1316  */
1317 static
1318 struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1319                                               struct page *page,
1320                                               struct page **tree_pagep)
1321 {
1322         struct rb_node **new;
1323         struct rb_root *root;
1324         struct rb_node *parent = NULL;
1325         int nid;
1326 
1327         nid = get_kpfn_nid(page_to_pfn(page));
1328         root = root_unstable_tree + nid;
1329         new = &root->rb_node;
1330 
1331         while (*new) {
1332                 struct rmap_item *tree_rmap_item;
1333                 struct page *tree_page;
1334                 int ret;
1335 
1336                 cond_resched();
1337                 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1338                 tree_page = get_mergeable_page(tree_rmap_item);
1339                 if (!tree_page)
1340                         return NULL;
1341 
1342                 /*
1343                  * Don't substitute a ksm page for a forked page.
1344                  */
1345                 if (page == tree_page) {
1346                         put_page(tree_page);
1347                         return NULL;
1348                 }
1349 
1350                 ret = memcmp_pages(page, tree_page);
1351 
1352                 parent = *new;
1353                 if (ret < 0) {
1354                         put_page(tree_page);
1355                         new = &parent->rb_left;
1356                 } else if (ret > 0) {
1357                         put_page(tree_page);
1358                         new = &parent->rb_right;
1359                 } else if (!ksm_merge_across_nodes &&
1360                            page_to_nid(tree_page) != nid) {
1361                         /*
1362                          * If tree_page has been migrated to another NUMA node,
1363                          * it will be flushed out and put in the right unstable
1364                          * tree next time: only merge with it when across_nodes.
1365                          */
1366                         put_page(tree_page);
1367                         return NULL;
1368                 } else {
1369                         *tree_pagep = tree_page;
1370                         return tree_rmap_item;
1371                 }
1372         }
1373 
1374         rmap_item->address |= UNSTABLE_FLAG;
1375         rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1376         DO_NUMA(rmap_item->nid = nid);
1377         rb_link_node(&rmap_item->node, parent, new);
1378         rb_insert_color(&rmap_item->node, root);
1379 
1380         ksm_pages_unshared++;
1381         return NULL;
1382 }
1383 
1384 /*
1385  * stable_tree_append - add another rmap_item to the linked list of
1386  * rmap_items hanging off a given node of the stable tree, all sharing
1387  * the same ksm page.
1388  */
1389 static void stable_tree_append(struct rmap_item *rmap_item,
1390                                struct stable_node *stable_node)
1391 {
1392         rmap_item->head = stable_node;
1393         rmap_item->address |= STABLE_FLAG;
1394         hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
1395 
1396         if (rmap_item->hlist.next)
1397                 ksm_pages_sharing++;
1398         else
1399                 ksm_pages_shared++;
1400 }
1401 
1402 /*
1403  * cmp_and_merge_page - first see if page can be merged into the stable tree;
1404  * if not, compare checksum to previous and if it's the same, see if page can
1405  * be inserted into the unstable tree, or merged with a page already there and
1406  * both transferred to the stable tree.
1407  *
1408  * @page: the page that we are searching identical page to.
1409  * @rmap_item: the reverse mapping into the virtual address of this page
1410  */
1411 static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1412 {
1413         struct rmap_item *tree_rmap_item;
1414         struct page *tree_page = NULL;
1415         struct stable_node *stable_node;
1416         struct page *kpage;
1417         unsigned int checksum;
1418         int err;
1419 
1420         stable_node = page_stable_node(page);
1421         if (stable_node) {
1422                 if (stable_node->head != &migrate_nodes &&
1423                     get_kpfn_nid(stable_node->kpfn) != NUMA(stable_node->nid)) {
1424                         rb_erase(&stable_node->node,
1425                                  root_stable_tree + NUMA(stable_node->nid));
1426                         stable_node->head = &migrate_nodes;
1427                         list_add(&stable_node->list, stable_node->head);
1428                 }
1429                 if (stable_node->head != &migrate_nodes &&
1430                     rmap_item->head == stable_node)
1431                         return;
1432         }
1433 
1434         /* We first start with searching the page inside the stable tree */
1435         kpage = stable_tree_search(page);
1436         if (kpage == page && rmap_item->head == stable_node) {
1437                 put_page(kpage);
1438                 return;
1439         }
1440 
1441         remove_rmap_item_from_tree(rmap_item);
1442 
1443         if (kpage) {
1444                 err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
1445                 if (!err) {
1446                         /*
1447                          * The page was successfully merged:
1448                          * add its rmap_item to the stable tree.
1449                          */
1450                         lock_page(kpage);
1451                         stable_tree_append(rmap_item, page_stable_node(kpage));
1452                         unlock_page(kpage);
1453                 }
1454                 put_page(kpage);
1455                 return;
1456         }
1457 
1458         /*
1459          * If the hash value of the page has changed from the last time
1460          * we calculated it, this page is changing frequently: therefore we
1461          * don't want to insert it in the unstable tree, and we don't want
1462          * to waste our time searching for something identical to it there.
1463          */
1464         checksum = calc_checksum(page);
1465         if (rmap_item->oldchecksum != checksum) {
1466                 rmap_item->oldchecksum = checksum;
1467                 return;
1468         }
1469 
1470         tree_rmap_item =
1471                 unstable_tree_search_insert(rmap_item, page, &tree_page);
1472         if (tree_rmap_item) {
1473                 kpage = try_to_merge_two_pages(rmap_item, page,
1474                                                 tree_rmap_item, tree_page);
1475                 put_page(tree_page);
1476                 if (kpage) {
1477                         /*
1478                          * The pages were successfully merged: insert new
1479                          * node in the stable tree and add both rmap_items.
1480                          */
1481                         lock_page(kpage);
1482                         stable_node = stable_tree_insert(kpage);
1483                         if (stable_node) {
1484                                 stable_tree_append(tree_rmap_item, stable_node);
1485                                 stable_tree_append(rmap_item, stable_node);
1486                         }
1487                         unlock_page(kpage);
1488 
1489                         /*
1490                          * If we fail to insert the page into the stable tree,
1491                          * we will have 2 virtual addresses that are pointing
1492                          * to a ksm page left outside the stable tree,
1493                          * in which case we need to break_cow on both.
1494                          */
1495                         if (!stable_node) {
1496                                 break_cow(tree_rmap_item);
1497                                 break_cow(rmap_item);
1498                         }
1499                 }
1500         }
1501 }
1502 
1503 static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
1504                                             struct rmap_item **rmap_list,
1505                                             unsigned long addr)
1506 {
1507         struct rmap_item *rmap_item;
1508 
1509         while (*rmap_list) {
1510                 rmap_item = *rmap_list;
1511                 if ((rmap_item->address & PAGE_MASK) == addr)
1512                         return rmap_item;
1513                 if (rmap_item->address > addr)
1514                         break;
1515                 *rmap_list = rmap_item->rmap_list;
1516                 remove_rmap_item_from_tree(rmap_item);
1517                 free_rmap_item(rmap_item);
1518         }
1519 
1520         rmap_item = alloc_rmap_item();
1521         if (rmap_item) {
1522                 /* It has already been zeroed */
1523                 rmap_item->mm = mm_slot->mm;
1524                 rmap_item->address = addr;
1525                 rmap_item->rmap_list = *rmap_list;
1526                 *rmap_list = rmap_item;
1527         }
1528         return rmap_item;
1529 }
1530 
1531 static struct rmap_item *scan_get_next_rmap_item(struct page **page)
1532 {
1533         struct mm_struct *mm;
1534         struct mm_slot *slot;
1535         struct vm_area_struct *vma;
1536         struct rmap_item *rmap_item;
1537         int nid;
1538 
1539         if (list_empty(&ksm_mm_head.mm_list))
1540                 return NULL;
1541 
1542         slot = ksm_scan.mm_slot;
1543         if (slot == &ksm_mm_head) {
1544                 /*
1545                  * A number of pages can hang around indefinitely on per-cpu
1546                  * pagevecs, raised page count preventing write_protect_page
1547                  * from merging them.  Though it doesn't really matter much,
1548                  * it is puzzling to see some stuck in pages_volatile until
1549                  * other activity jostles them out, and they also prevented
1550                  * LTP's KSM test from succeeding deterministically; so drain
1551                  * them here (here rather than on entry to ksm_do_scan(),
1552                  * so we don't IPI too often when pages_to_scan is set low).
1553                  */
1554                 lru_add_drain_all();
1555 
1556                 /*
1557                  * Whereas stale stable_nodes on the stable_tree itself
1558                  * get pruned in the regular course of stable_tree_search(),
1559                  * those moved out to the migrate_nodes list can accumulate:
1560                  * so prune them once before each full scan.
1561                  */
1562                 if (!ksm_merge_across_nodes) {
1563                         struct stable_node *stable_node, *next;
1564                         struct page *page;
1565 
1566                         list_for_each_entry_safe(stable_node, next,
1567                                                  &migrate_nodes, list) {
1568                                 page = get_ksm_page(stable_node, false);
1569                                 if (page)
1570                                         put_page(page);
1571                                 cond_resched();
1572                         }
1573                 }
1574 
1575                 for (nid = 0; nid < ksm_nr_node_ids; nid++)
1576                         root_unstable_tree[nid] = RB_ROOT;
1577 
1578                 spin_lock(&ksm_mmlist_lock);
1579                 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1580                 ksm_scan.mm_slot = slot;
1581                 spin_unlock(&ksm_mmlist_lock);
1582                 /*
1583                  * Although we tested list_empty() above, a racing __ksm_exit
1584                  * of the last mm on the list may have removed it since then.
1585                  */
1586                 if (slot == &ksm_mm_head)
1587                         return NULL;
1588 next_mm:
1589                 ksm_scan.address = 0;
1590                 ksm_scan.rmap_list = &slot->rmap_list;
1591         }
1592 
1593         mm = slot->mm;
1594         down_read(&mm->mmap_sem);
1595         if (ksm_test_exit(mm))
1596                 vma = NULL;
1597         else
1598                 vma = find_vma(mm, ksm_scan.address);
1599 
1600         for (; vma; vma = vma->vm_next) {
1601                 if (!(vma->vm_flags & VM_MERGEABLE))
1602                         continue;
1603                 if (ksm_scan.address < vma->vm_start)
1604                         ksm_scan.address = vma->vm_start;
1605                 if (!vma->anon_vma)
1606                         ksm_scan.address = vma->vm_end;
1607 
1608                 while (ksm_scan.address < vma->vm_end) {
1609                         if (ksm_test_exit(mm))
1610                                 break;
1611                         *page = follow_page(vma, ksm_scan.address, FOLL_GET);
1612                         if (IS_ERR_OR_NULL(*page)) {
1613                                 ksm_scan.address += PAGE_SIZE;
1614                                 cond_resched();
1615                                 continue;
1616                         }
1617                         if (PageAnon(*page)) {
1618                                 flush_anon_page(vma, *page, ksm_scan.address);
1619                                 flush_dcache_page(*page);
1620                                 rmap_item = get_next_rmap_item(slot,
1621                                         ksm_scan.rmap_list, ksm_scan.address);
1622                                 if (rmap_item) {
1623                                         ksm_scan.rmap_list =
1624                                                         &rmap_item->rmap_list;
1625                                         ksm_scan.address += PAGE_SIZE;
1626                                 } else
1627                                         put_page(*page);
1628                                 up_read(&mm->mmap_sem);
1629                                 return rmap_item;
1630                         }
1631                         put_page(*page);
1632                         ksm_scan.address += PAGE_SIZE;
1633                         cond_resched();
1634                 }
1635         }
1636 
1637         if (ksm_test_exit(mm)) {
1638                 ksm_scan.address = 0;
1639                 ksm_scan.rmap_list = &slot->rmap_list;
1640         }
1641         /*
1642          * Nuke all the rmap_items that are above this current rmap:
1643          * because there were no VM_MERGEABLE vmas with such addresses.
1644          */
1645         remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
1646 
1647         spin_lock(&ksm_mmlist_lock);
1648         ksm_scan.mm_slot = list_entry(slot->mm_list.next,
1649                                                 struct mm_slot, mm_list);
1650         if (ksm_scan.address == 0) {
1651                 /*
1652                  * We've completed a full scan of all vmas, holding mmap_sem
1653                  * throughout, and found no VM_MERGEABLE: so do the same as
1654                  * __ksm_exit does to remove this mm from all our lists now.
1655                  * This applies either when cleaning up after __ksm_exit
1656                  * (but beware: we can reach here even before __ksm_exit),
1657                  * or when all VM_MERGEABLE areas have been unmapped (and
1658                  * mmap_sem then protects against race with MADV_MERGEABLE).
1659                  */
1660                 hash_del(&slot->link);
1661                 list_del(&slot->mm_list);
1662                 spin_unlock(&ksm_mmlist_lock);
1663 
1664                 free_mm_slot(slot);
1665                 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1666                 up_read(&mm->mmap_sem);
1667                 mmdrop(mm);
1668         } else {
1669                 up_read(&mm->mmap_sem);
1670                 /*
1671                  * up_read(&mm->mmap_sem) first because after
1672                  * spin_unlock(&ksm_mmlist_lock) run, the "mm" may
1673                  * already have been freed under us by __ksm_exit()
1674                  * because the "mm_slot" is still hashed and
1675                  * ksm_scan.mm_slot doesn't point to it anymore.
1676                  */
1677                 spin_unlock(&ksm_mmlist_lock);
1678         }
1679 
1680         /* Repeat until we've completed scanning the whole list */
1681         slot = ksm_scan.mm_slot;
1682         if (slot != &ksm_mm_head)
1683                 goto next_mm;
1684 
1685         ksm_scan.seqnr++;
1686         return NULL;
1687 }
1688 
1689 /**
1690  * ksm_do_scan  - the ksm scanner main worker function.
1691  * @scan_npages - number of pages we want to scan before we return.
1692  */
1693 static void ksm_do_scan(unsigned int scan_npages)
1694 {
1695         struct rmap_item *rmap_item;
1696         struct page *uninitialized_var(page);
1697 
1698         while (scan_npages-- && likely(!freezing(current))) {
1699                 cond_resched();
1700                 rmap_item = scan_get_next_rmap_item(&page);
1701                 if (!rmap_item)
1702                         return;
1703                 cmp_and_merge_page(page, rmap_item);
1704                 put_page(page);
1705         }
1706 }
1707 
1708 static int ksmd_should_run(void)
1709 {
1710         return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1711 }
1712 
1713 static int ksm_scan_thread(void *nothing)
1714 {
1715         set_freezable();
1716         set_user_nice(current, 5);
1717 
1718         while (!kthread_should_stop()) {
1719                 mutex_lock(&ksm_thread_mutex);
1720                 wait_while_offlining();
1721                 if (ksmd_should_run())
1722                         ksm_do_scan(ksm_thread_pages_to_scan);
1723                 mutex_unlock(&ksm_thread_mutex);
1724 
1725                 try_to_freeze();
1726 
1727                 if (ksmd_should_run()) {
1728                         schedule_timeout_interruptible(
1729                                 msecs_to_jiffies(ksm_thread_sleep_millisecs));
1730                 } else {
1731                         wait_event_freezable(ksm_thread_wait,
1732                                 ksmd_should_run() || kthread_should_stop());
1733                 }
1734         }
1735         return 0;
1736 }
1737 
1738 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1739                 unsigned long end, int advice, unsigned long *vm_flags)
1740 {
1741         struct mm_struct *mm = vma->vm_mm;
1742         int err;
1743 
1744         switch (advice) {
1745         case MADV_MERGEABLE:
1746                 /*
1747                  * Be somewhat over-protective for now!
1748                  */
1749                 if (*vm_flags & (VM_MERGEABLE | VM_SHARED  | VM_MAYSHARE   |
1750                                  VM_PFNMAP    | VM_IO      | VM_DONTEXPAND |
1751                                  VM_HUGETLB | VM_MIXEDMAP))
1752                         return 0;               /* just ignore the advice */
1753 
1754 #ifdef VM_SAO
1755                 if (*vm_flags & VM_SAO)
1756                         return 0;
1757 #endif
1758 
1759                 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
1760                         err = __ksm_enter(mm);
1761                         if (err)
1762                                 return err;
1763                 }
1764 
1765                 *vm_flags |= VM_MERGEABLE;
1766                 break;
1767 
1768         case MADV_UNMERGEABLE:
1769                 if (!(*vm_flags & VM_MERGEABLE))
1770                         return 0;               /* just ignore the advice */
1771 
1772                 if (vma->anon_vma) {
1773                         err = unmerge_ksm_pages(vma, start, end);
1774                         if (err)
1775                                 return err;
1776                 }
1777 
1778                 *vm_flags &= ~VM_MERGEABLE;
1779                 break;
1780         }
1781 
1782         return 0;
1783 }
1784 
1785 int __ksm_enter(struct mm_struct *mm)
1786 {
1787         struct mm_slot *mm_slot;
1788         int needs_wakeup;
1789 
1790         mm_slot = alloc_mm_slot();
1791         if (!mm_slot)
1792                 return -ENOMEM;
1793 
1794         /* Check ksm_run too?  Would need tighter locking */
1795         needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1796 
1797         spin_lock(&ksm_mmlist_lock);
1798         insert_to_mm_slots_hash(mm, mm_slot);
1799         /*
1800          * When KSM_RUN_MERGE (or KSM_RUN_STOP),
1801          * insert just behind the scanning cursor, to let the area settle
1802          * down a little; when fork is followed by immediate exec, we don't
1803          * want ksmd to waste time setting up and tearing down an rmap_list.
1804          *
1805          * But when KSM_RUN_UNMERGE, it's important to insert ahead of its
1806          * scanning cursor, otherwise KSM pages in newly forked mms will be
1807          * missed: then we might as well insert at the end of the list.
1808          */
1809         if (ksm_run & KSM_RUN_UNMERGE)
1810                 list_add_tail(&mm_slot->mm_list, &ksm_mm_head.mm_list);
1811         else
1812                 list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
1813         spin_unlock(&ksm_mmlist_lock);
1814 
1815         set_bit(MMF_VM_MERGEABLE, &mm->flags);
1816         atomic_inc(&mm->mm_count);
1817 
1818         if (needs_wakeup)
1819                 wake_up_interruptible(&ksm_thread_wait);
1820 
1821         return 0;
1822 }
1823 
1824 void __ksm_exit(struct mm_struct *mm)
1825 {
1826         struct mm_slot *mm_slot;
1827         int easy_to_free = 0;
1828 
1829         /*
1830          * This process is exiting: if it's straightforward (as is the
1831          * case when ksmd was never running), free mm_slot immediately.
1832          * But if it's at the cursor or has rmap_items linked to it, use
1833          * mmap_sem to synchronize with any break_cows before pagetables
1834          * are freed, and leave the mm_slot on the list for ksmd to free.
1835          * Beware: ksm may already have noticed it exiting and freed the slot.
1836          */
1837 
1838         spin_lock(&ksm_mmlist_lock);
1839         mm_slot = get_mm_slot(mm);
1840         if (mm_slot && ksm_scan.mm_slot != mm_slot) {
1841                 if (!mm_slot->rmap_list) {
1842                         hash_del(&mm_slot->link);
1843                         list_del(&mm_slot->mm_list);
1844                         easy_to_free = 1;
1845                 } else {
1846                         list_move(&mm_slot->mm_list,
1847                                   &ksm_scan.mm_slot->mm_list);
1848                 }
1849         }
1850         spin_unlock(&ksm_mmlist_lock);
1851 
1852         if (easy_to_free) {
1853                 free_mm_slot(mm_slot);
1854                 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1855                 mmdrop(mm);
1856         } else if (mm_slot) {
1857                 down_write(&mm->mmap_sem);
1858                 up_write(&mm->mmap_sem);
1859         }
1860 }
1861 
1862 struct page *ksm_might_need_to_copy(struct page *page,
1863                         struct vm_area_struct *vma, unsigned long address)
1864 {
1865         struct anon_vma *anon_vma = page_anon_vma(page);
1866         struct page *new_page;
1867 
1868         if (PageKsm(page)) {
1869                 if (page_stable_node(page) &&
1870                     !(ksm_run & KSM_RUN_UNMERGE))
1871                         return page;    /* no need to copy it */
1872         } else if (!anon_vma) {
1873                 return page;            /* no need to copy it */
1874         } else if (anon_vma->root == vma->anon_vma->root &&
1875                  page->index == linear_page_index(vma, address)) {
1876                 return page;            /* still no need to copy it */
1877         }
1878         if (!PageUptodate(page))
1879                 return page;            /* let do_swap_page report the error */
1880 
1881         new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
1882         if (new_page) {
1883                 copy_user_highpage(new_page, page, address, vma);
1884 
1885                 SetPageDirty(new_page);
1886                 __SetPageUptodate(new_page);
1887                 __SetPageLocked(new_page);
1888         }
1889 
1890         return new_page;
1891 }
1892 
1893 int rmap_walk_ksm(struct page *page, struct rmap_walk_control *rwc)
1894 {
1895         struct stable_node *stable_node;
1896         struct rmap_item *rmap_item;
1897         int ret = SWAP_AGAIN;
1898         int search_new_forks = 0;
1899 
1900         VM_BUG_ON_PAGE(!PageKsm(page), page);
1901 
1902         /*
1903          * Rely on the page lock to protect against concurrent modifications
1904          * to that page's node of the stable tree.
1905          */
1906         VM_BUG_ON_PAGE(!PageLocked(page), page);
1907 
1908         stable_node = page_stable_node(page);
1909         if (!stable_node)
1910                 return ret;
1911 again:
1912         hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
1913                 struct anon_vma *anon_vma = rmap_item->anon_vma;
1914                 struct anon_vma_chain *vmac;
1915                 struct vm_area_struct *vma;
1916 
1917                 cond_resched();
1918                 anon_vma_lock_read(anon_vma);
1919                 anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
1920                                                0, ULONG_MAX) {
1921                         cond_resched();
1922                         vma = vmac->vma;
1923                         if (rmap_item->address < vma->vm_start ||
1924                             rmap_item->address >= vma->vm_end)
1925                                 continue;
1926                         /*
1927                          * Initially we examine only the vma which covers this
1928                          * rmap_item; but later, if there is still work to do,
1929                          * we examine covering vmas in other mms: in case they
1930                          * were forked from the original since ksmd passed.
1931                          */
1932                         if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1933                                 continue;
1934 
1935                         if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
1936                                 continue;
1937 
1938                         ret = rwc->rmap_one(page, vma,
1939                                         rmap_item->address, rwc->arg);
1940                         if (ret != SWAP_AGAIN) {
1941                                 anon_vma_unlock_read(anon_vma);
1942                                 goto out;
1943                         }
1944                         if (rwc->done && rwc->done(page)) {
1945                                 anon_vma_unlock_read(anon_vma);
1946                                 goto out;
1947                         }
1948                 }
1949                 anon_vma_unlock_read(anon_vma);
1950         }
1951         if (!search_new_forks++)
1952                 goto again;
1953 out:
1954         return ret;
1955 }
1956 
1957 #ifdef CONFIG_MIGRATION
1958 void ksm_migrate_page(struct page *newpage, struct page *oldpage)
1959 {
1960         struct stable_node *stable_node;
1961 
1962         VM_BUG_ON_PAGE(!PageLocked(oldpage), oldpage);
1963         VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
1964         VM_BUG_ON_PAGE(newpage->mapping != oldpage->mapping, newpage);
1965 
1966         stable_node = page_stable_node(newpage);
1967         if (stable_node) {
1968                 VM_BUG_ON_PAGE(stable_node->kpfn != page_to_pfn(oldpage), oldpage);
1969                 stable_node->kpfn = page_to_pfn(newpage);
1970                 /*
1971                  * newpage->mapping was set in advance; now we need smp_wmb()
1972                  * to make sure that the new stable_node->kpfn is visible
1973                  * to get_ksm_page() before it can see that oldpage->mapping
1974                  * has gone stale (or that PageSwapCache has been cleared).
1975                  */
1976                 smp_wmb();
1977                 set_page_stable_node(oldpage, NULL);
1978         }
1979 }
1980 #endif /* CONFIG_MIGRATION */
1981 
1982 #ifdef CONFIG_MEMORY_HOTREMOVE
1983 static void wait_while_offlining(void)
1984 {
1985         while (ksm_run & KSM_RUN_OFFLINE) {
1986                 mutex_unlock(&ksm_thread_mutex);
1987                 wait_on_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE),
1988                             TASK_UNINTERRUPTIBLE);
1989                 mutex_lock(&ksm_thread_mutex);
1990         }
1991 }
1992 
1993 static void ksm_check_stable_tree(unsigned long start_pfn,
1994                                   unsigned long end_pfn)
1995 {
1996         struct stable_node *stable_node, *next;
1997         struct rb_node *node;
1998         int nid;
1999 
2000         for (nid = 0; nid < ksm_nr_node_ids; nid++) {
2001                 node = rb_first(root_stable_tree + nid);
2002                 while (node) {
2003                         stable_node = rb_entry(node, struct stable_node, node);
2004                         if (stable_node->kpfn >= start_pfn &&
2005                             stable_node->kpfn < end_pfn) {
2006                                 /*
2007                                  * Don't get_ksm_page, page has already gone:
2008                                  * which is why we keep kpfn instead of page*
2009                                  */
2010                                 remove_node_from_stable_tree(stable_node);
2011                                 node = rb_first(root_stable_tree + nid);
2012                         } else
2013                                 node = rb_next(node);
2014                         cond_resched();
2015                 }
2016         }
2017         list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
2018                 if (stable_node->kpfn >= start_pfn &&
2019                     stable_node->kpfn < end_pfn)
2020                         remove_node_from_stable_tree(stable_node);
2021                 cond_resched();
2022         }
2023 }
2024 
2025 static int ksm_memory_callback(struct notifier_block *self,
2026                                unsigned long action, void *arg)
2027 {
2028         struct memory_notify *mn = arg;
2029 
2030         switch (action) {
2031         case MEM_GOING_OFFLINE:
2032                 /*
2033                  * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
2034                  * and remove_all_stable_nodes() while memory is going offline:
2035                  * it is unsafe for them to touch the stable tree at this time.
2036                  * But unmerge_ksm_pages(), rmap lookups and other entry points
2037                  * which do not need the ksm_thread_mutex are all safe.
2038                  */
2039                 mutex_lock(&ksm_thread_mutex);
2040                 ksm_run |= KSM_RUN_OFFLINE;
2041                 mutex_unlock(&ksm_thread_mutex);
2042                 break;
2043 
2044         case MEM_OFFLINE:
2045                 /*
2046                  * Most of the work is done by page migration; but there might
2047                  * be a few stable_nodes left over, still pointing to struct
2048                  * pages which have been offlined: prune those from the tree,
2049                  * otherwise get_ksm_page() might later try to access a
2050                  * non-existent struct page.
2051                  */
2052                 ksm_check_stable_tree(mn->start_pfn,
2053                                       mn->start_pfn + mn->nr_pages);
2054                 /* fallthrough */
2055 
2056         case MEM_CANCEL_OFFLINE:
2057                 mutex_lock(&ksm_thread_mutex);
2058                 ksm_run &= ~KSM_RUN_OFFLINE;
2059                 mutex_unlock(&ksm_thread_mutex);
2060 
2061                 smp_mb();       /* wake_up_bit advises this */
2062                 wake_up_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE));
2063                 break;
2064         }
2065         return NOTIFY_OK;
2066 }
2067 #else
2068 static void wait_while_offlining(void)
2069 {
2070 }
2071 #endif /* CONFIG_MEMORY_HOTREMOVE */
2072 
2073 #ifdef CONFIG_SYSFS
2074 /*
2075  * This all compiles without CONFIG_SYSFS, but is a waste of space.
2076  */
2077 
2078 #define KSM_ATTR_RO(_name) \
2079         static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
2080 #define KSM_ATTR(_name) \
2081         static struct kobj_attribute _name##_attr = \
2082                 __ATTR(_name, 0644, _name##_show, _name##_store)
2083 
2084 static ssize_t sleep_millisecs_show(struct kobject *kobj,
2085                                     struct kobj_attribute *attr, char *buf)
2086 {
2087         return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
2088 }
2089 
2090 static ssize_t sleep_millisecs_store(struct kobject *kobj,
2091                                      struct kobj_attribute *attr,
2092                                      const char *buf, size_t count)
2093 {
2094         unsigned long msecs;
2095         int err;
2096 
2097         err = kstrtoul(buf, 10, &msecs);
2098         if (err || msecs > UINT_MAX)
2099                 return -EINVAL;
2100 
2101         ksm_thread_sleep_millisecs = msecs;
2102 
2103         return count;
2104 }
2105 KSM_ATTR(sleep_millisecs);
2106 
2107 static ssize_t pages_to_scan_show(struct kobject *kobj,
2108                                   struct kobj_attribute *attr, char *buf)
2109 {
2110         return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
2111 }
2112 
2113 static ssize_t pages_to_scan_store(struct kobject *kobj,
2114                                    struct kobj_attribute *attr,
2115                                    const char *buf, size_t count)
2116 {
2117         int err;
2118         unsigned long nr_pages;
2119 
2120         err = kstrtoul(buf, 10, &nr_pages);
2121         if (err || nr_pages > UINT_MAX)
2122                 return -EINVAL;
2123 
2124         ksm_thread_pages_to_scan = nr_pages;
2125 
2126         return count;
2127 }
2128 KSM_ATTR(pages_to_scan);
2129 
2130 static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
2131                         char *buf)
2132 {
2133         return sprintf(buf, "%lu\n", ksm_run);
2134 }
2135 
2136 static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
2137                          const char *buf, size_t count)
2138 {
2139         int err;
2140         unsigned long flags;
2141 
2142         err = kstrtoul(buf, 10, &flags);
2143         if (err || flags > UINT_MAX)
2144                 return -EINVAL;
2145         if (flags > KSM_RUN_UNMERGE)
2146                 return -EINVAL;
2147 
2148         /*
2149          * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
2150          * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
2151          * breaking COW to free the pages_shared (but leaves mm_slots
2152          * on the list for when ksmd may be set running again).
2153          */
2154 
2155         mutex_lock(&ksm_thread_mutex);
2156         wait_while_offlining();
2157         if (ksm_run != flags) {
2158                 ksm_run = flags;
2159                 if (flags & KSM_RUN_UNMERGE) {
2160                         set_current_oom_origin();
2161                         err = unmerge_and_remove_all_rmap_items();
2162                         clear_current_oom_origin();
2163                         if (err) {
2164                                 ksm_run = KSM_RUN_STOP;
2165                                 count = err;
2166                         }
2167                 }
2168         }
2169         mutex_unlock(&ksm_thread_mutex);
2170 
2171         if (flags & KSM_RUN_MERGE)
2172                 wake_up_interruptible(&ksm_thread_wait);
2173 
2174         return count;
2175 }
2176 KSM_ATTR(run);
2177 
2178 #ifdef CONFIG_NUMA
2179 static ssize_t merge_across_nodes_show(struct kobject *kobj,
2180                                 struct kobj_attribute *attr, char *buf)
2181 {
2182         return sprintf(buf, "%u\n", ksm_merge_across_nodes);
2183 }
2184 
2185 static ssize_t merge_across_nodes_store(struct kobject *kobj,
2186                                    struct kobj_attribute *attr,
2187                                    const char *buf, size_t count)
2188 {
2189         int err;
2190         unsigned long knob;
2191 
2192         err = kstrtoul(buf, 10, &knob);
2193         if (err)
2194                 return err;
2195         if (knob > 1)
2196                 return -EINVAL;
2197 
2198         mutex_lock(&ksm_thread_mutex);
2199         wait_while_offlining();
2200         if (ksm_merge_across_nodes != knob) {
2201                 if (ksm_pages_shared || remove_all_stable_nodes())
2202                         err = -EBUSY;
2203                 else if (root_stable_tree == one_stable_tree) {
2204                         struct rb_root *buf;
2205                         /*
2206                          * This is the first time that we switch away from the
2207                          * default of merging across nodes: must now allocate
2208                          * a buffer to hold as many roots as may be needed.
2209                          * Allocate stable and unstable together:
2210                          * MAXSMP NODES_SHIFT 10 will use 16kB.
2211                          */
2212                         buf = kcalloc(nr_node_ids + nr_node_ids, sizeof(*buf),
2213                                       GFP_KERNEL);
2214                         /* Let us assume that RB_ROOT is NULL is zero */
2215                         if (!buf)
2216                                 err = -ENOMEM;
2217                         else {
2218                                 root_stable_tree = buf;
2219                                 root_unstable_tree = buf + nr_node_ids;
2220                                 /* Stable tree is empty but not the unstable */
2221                                 root_unstable_tree[0] = one_unstable_tree[0];
2222                         }
2223                 }
2224                 if (!err) {
2225                         ksm_merge_across_nodes = knob;
2226                         ksm_nr_node_ids = knob ? 1 : nr_node_ids;
2227                 }
2228         }
2229         mutex_unlock(&ksm_thread_mutex);
2230 
2231         return err ? err : count;
2232 }
2233 KSM_ATTR(merge_across_nodes);
2234 #endif
2235 
2236 static ssize_t pages_shared_show(struct kobject *kobj,
2237                                  struct kobj_attribute *attr, char *buf)
2238 {
2239         return sprintf(buf, "%lu\n", ksm_pages_shared);
2240 }
2241 KSM_ATTR_RO(pages_shared);
2242 
2243 static ssize_t pages_sharing_show(struct kobject *kobj,
2244                                   struct kobj_attribute *attr, char *buf)
2245 {
2246         return sprintf(buf, "%lu\n", ksm_pages_sharing);
2247 }
2248 KSM_ATTR_RO(pages_sharing);
2249 
2250 static ssize_t pages_unshared_show(struct kobject *kobj,
2251                                    struct kobj_attribute *attr, char *buf)
2252 {
2253         return sprintf(buf, "%lu\n", ksm_pages_unshared);
2254 }
2255 KSM_ATTR_RO(pages_unshared);
2256 
2257 static ssize_t pages_volatile_show(struct kobject *kobj,
2258                                    struct kobj_attribute *attr, char *buf)
2259 {
2260         long ksm_pages_volatile;
2261 
2262         ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
2263                                 - ksm_pages_sharing - ksm_pages_unshared;
2264         /*
2265          * It was not worth any locking to calculate that statistic,
2266          * but it might therefore sometimes be negative: conceal that.
2267          */
2268         if (ksm_pages_volatile < 0)
2269                 ksm_pages_volatile = 0;
2270         return sprintf(buf, "%ld\n", ksm_pages_volatile);
2271 }
2272 KSM_ATTR_RO(pages_volatile);
2273 
2274 static ssize_t full_scans_show(struct kobject *kobj,
2275                                struct kobj_attribute *attr, char *buf)
2276 {
2277         return sprintf(buf, "%lu\n", ksm_scan.seqnr);
2278 }
2279 KSM_ATTR_RO(full_scans);
2280 
2281 static struct attribute *ksm_attrs[] = {
2282         &sleep_millisecs_attr.attr,
2283         &pages_to_scan_attr.attr,
2284         &run_attr.attr,
2285         &pages_shared_attr.attr,
2286         &pages_sharing_attr.attr,
2287         &pages_unshared_attr.attr,
2288         &pages_volatile_attr.attr,
2289         &full_scans_attr.attr,
2290 #ifdef CONFIG_NUMA
2291         &merge_across_nodes_attr.attr,
2292 #endif
2293         NULL,
2294 };
2295 
2296 static struct attribute_group ksm_attr_group = {
2297         .attrs = ksm_attrs,
2298         .name = "ksm",
2299 };
2300 #endif /* CONFIG_SYSFS */
2301 
2302 static int __init ksm_init(void)
2303 {
2304         struct task_struct *ksm_thread;
2305         int err;
2306 
2307         err = ksm_slab_init();
2308         if (err)
2309                 goto out;
2310 
2311         ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
2312         if (IS_ERR(ksm_thread)) {
2313                 pr_err("ksm: creating kthread failed\n");
2314                 err = PTR_ERR(ksm_thread);
2315                 goto out_free;
2316         }
2317 
2318 #ifdef CONFIG_SYSFS
2319         err = sysfs_create_group(mm_kobj, &ksm_attr_group);
2320         if (err) {
2321                 pr_err("ksm: register sysfs failed\n");
2322                 kthread_stop(ksm_thread);
2323                 goto out_free;
2324         }
2325 #else
2326         ksm_run = KSM_RUN_MERGE;        /* no way for user to start it */
2327 
2328 #endif /* CONFIG_SYSFS */
2329 
2330 #ifdef CONFIG_MEMORY_HOTREMOVE
2331         /* There is no significance to this priority 100 */
2332         hotplug_memory_notifier(ksm_memory_callback, 100);
2333 #endif
2334         return 0;
2335 
2336 out_free:
2337         ksm_slab_free();
2338 out:
2339         return err;
2340 }
2341 subsys_initcall(ksm_init);
2342 

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