thp: add compound_trans_head() helper
[linux-3.10.git] / 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/hash.h>
37 #include <linux/freezer.h>
38
39 #include <asm/tlbflush.h>
40 #include "internal.h"
41
42 /*
43  * A few notes about the KSM scanning process,
44  * to make it easier to understand the data structures below:
45  *
46  * In order to reduce excessive scanning, KSM sorts the memory pages by their
47  * contents into a data structure that holds pointers to the pages' locations.
48  *
49  * Since the contents of the pages may change at any moment, KSM cannot just
50  * insert the pages into a normal sorted tree and expect it to find anything.
51  * Therefore KSM uses two data structures - the stable and the unstable tree.
52  *
53  * The stable tree holds pointers to all the merged pages (ksm pages), sorted
54  * by their contents.  Because each such page is write-protected, searching on
55  * this tree is fully assured to be working (except when pages are unmapped),
56  * and therefore this tree is called the stable tree.
57  *
58  * In addition to the stable tree, KSM uses a second data structure called the
59  * unstable tree: this tree holds pointers to pages which have been found to
60  * be "unchanged for a period of time".  The unstable tree sorts these pages
61  * by their contents, but since they are not write-protected, KSM cannot rely
62  * upon the unstable tree to work correctly - the unstable tree is liable to
63  * be corrupted as its contents are modified, and so it is called unstable.
64  *
65  * KSM solves this problem by several techniques:
66  *
67  * 1) The unstable tree is flushed every time KSM completes scanning all
68  *    memory areas, and then the tree is rebuilt again from the beginning.
69  * 2) KSM will only insert into the unstable tree, pages whose hash value
70  *    has not changed since the previous scan of all memory areas.
71  * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
72  *    colors of the nodes and not on their contents, assuring that even when
73  *    the tree gets "corrupted" it won't get out of balance, so scanning time
74  *    remains the same (also, searching and inserting nodes in an rbtree uses
75  *    the same algorithm, so we have no overhead when we flush and rebuild).
76  * 4) KSM never flushes the stable tree, which means that even if it were to
77  *    take 10 attempts to find a page in the unstable tree, once it is found,
78  *    it is secured in the stable tree.  (When we scan a new page, we first
79  *    compare it against the stable tree, and then against the unstable tree.)
80  */
81
82 /**
83  * struct mm_slot - ksm information per mm that is being scanned
84  * @link: link to the mm_slots hash list
85  * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
86  * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
87  * @mm: the mm that this information is valid for
88  */
89 struct mm_slot {
90         struct hlist_node link;
91         struct list_head mm_list;
92         struct rmap_item *rmap_list;
93         struct mm_struct *mm;
94 };
95
96 /**
97  * struct ksm_scan - cursor for scanning
98  * @mm_slot: the current mm_slot we are scanning
99  * @address: the next address inside that to be scanned
100  * @rmap_list: link to the next rmap to be scanned in the rmap_list
101  * @seqnr: count of completed full scans (needed when removing unstable node)
102  *
103  * There is only the one ksm_scan instance of this cursor structure.
104  */
105 struct ksm_scan {
106         struct mm_slot *mm_slot;
107         unsigned long address;
108         struct rmap_item **rmap_list;
109         unsigned long seqnr;
110 };
111
112 /**
113  * struct stable_node - node of the stable rbtree
114  * @node: rb node of this ksm page in the stable tree
115  * @hlist: hlist head of rmap_items using this ksm page
116  * @kpfn: page frame number of this ksm page
117  */
118 struct stable_node {
119         struct rb_node node;
120         struct hlist_head hlist;
121         unsigned long kpfn;
122 };
123
124 /**
125  * struct rmap_item - reverse mapping item for virtual addresses
126  * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
127  * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
128  * @mm: the memory structure this rmap_item is pointing into
129  * @address: the virtual address this rmap_item tracks (+ flags in low bits)
130  * @oldchecksum: previous checksum of the page at that virtual address
131  * @node: rb node of this rmap_item in the unstable tree
132  * @head: pointer to stable_node heading this list in the stable tree
133  * @hlist: link into hlist of rmap_items hanging off that stable_node
134  */
135 struct rmap_item {
136         struct rmap_item *rmap_list;
137         struct anon_vma *anon_vma;      /* when stable */
138         struct mm_struct *mm;
139         unsigned long address;          /* + low bits used for flags below */
140         unsigned int oldchecksum;       /* when unstable */
141         union {
142                 struct rb_node node;    /* when node of unstable tree */
143                 struct {                /* when listed from stable tree */
144                         struct stable_node *head;
145                         struct hlist_node hlist;
146                 };
147         };
148 };
149
150 #define SEQNR_MASK      0x0ff   /* low bits of unstable tree seqnr */
151 #define UNSTABLE_FLAG   0x100   /* is a node of the unstable tree */
152 #define STABLE_FLAG     0x200   /* is listed from the stable tree */
153
154 /* The stable and unstable tree heads */
155 static struct rb_root root_stable_tree = RB_ROOT;
156 static struct rb_root root_unstable_tree = RB_ROOT;
157
158 #define MM_SLOTS_HASH_SHIFT 10
159 #define MM_SLOTS_HASH_HEADS (1 << MM_SLOTS_HASH_SHIFT)
160 static struct hlist_head mm_slots_hash[MM_SLOTS_HASH_HEADS];
161
162 static struct mm_slot ksm_mm_head = {
163         .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
164 };
165 static struct ksm_scan ksm_scan = {
166         .mm_slot = &ksm_mm_head,
167 };
168
169 static struct kmem_cache *rmap_item_cache;
170 static struct kmem_cache *stable_node_cache;
171 static struct kmem_cache *mm_slot_cache;
172
173 /* The number of nodes in the stable tree */
174 static unsigned long ksm_pages_shared;
175
176 /* The number of page slots additionally sharing those nodes */
177 static unsigned long ksm_pages_sharing;
178
179 /* The number of nodes in the unstable tree */
180 static unsigned long ksm_pages_unshared;
181
182 /* The number of rmap_items in use: to calculate pages_volatile */
183 static unsigned long ksm_rmap_items;
184
185 /* Number of pages ksmd should scan in one batch */
186 static unsigned int ksm_thread_pages_to_scan = 100;
187
188 /* Milliseconds ksmd should sleep between batches */
189 static unsigned int ksm_thread_sleep_millisecs = 20;
190
191 #define KSM_RUN_STOP    0
192 #define KSM_RUN_MERGE   1
193 #define KSM_RUN_UNMERGE 2
194 static unsigned int ksm_run = KSM_RUN_STOP;
195
196 static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
197 static DEFINE_MUTEX(ksm_thread_mutex);
198 static DEFINE_SPINLOCK(ksm_mmlist_lock);
199
200 #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
201                 sizeof(struct __struct), __alignof__(struct __struct),\
202                 (__flags), NULL)
203
204 static int __init ksm_slab_init(void)
205 {
206         rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
207         if (!rmap_item_cache)
208                 goto out;
209
210         stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
211         if (!stable_node_cache)
212                 goto out_free1;
213
214         mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
215         if (!mm_slot_cache)
216                 goto out_free2;
217
218         return 0;
219
220 out_free2:
221         kmem_cache_destroy(stable_node_cache);
222 out_free1:
223         kmem_cache_destroy(rmap_item_cache);
224 out:
225         return -ENOMEM;
226 }
227
228 static void __init ksm_slab_free(void)
229 {
230         kmem_cache_destroy(mm_slot_cache);
231         kmem_cache_destroy(stable_node_cache);
232         kmem_cache_destroy(rmap_item_cache);
233         mm_slot_cache = NULL;
234 }
235
236 static inline struct rmap_item *alloc_rmap_item(void)
237 {
238         struct rmap_item *rmap_item;
239
240         rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
241         if (rmap_item)
242                 ksm_rmap_items++;
243         return rmap_item;
244 }
245
246 static inline void free_rmap_item(struct rmap_item *rmap_item)
247 {
248         ksm_rmap_items--;
249         rmap_item->mm = NULL;   /* debug safety */
250         kmem_cache_free(rmap_item_cache, rmap_item);
251 }
252
253 static inline struct stable_node *alloc_stable_node(void)
254 {
255         return kmem_cache_alloc(stable_node_cache, GFP_KERNEL);
256 }
257
258 static inline void free_stable_node(struct stable_node *stable_node)
259 {
260         kmem_cache_free(stable_node_cache, stable_node);
261 }
262
263 static inline struct mm_slot *alloc_mm_slot(void)
264 {
265         if (!mm_slot_cache)     /* initialization failed */
266                 return NULL;
267         return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
268 }
269
270 static inline void free_mm_slot(struct mm_slot *mm_slot)
271 {
272         kmem_cache_free(mm_slot_cache, mm_slot);
273 }
274
275 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
276 {
277         struct mm_slot *mm_slot;
278         struct hlist_head *bucket;
279         struct hlist_node *node;
280
281         bucket = &mm_slots_hash[hash_ptr(mm, MM_SLOTS_HASH_SHIFT)];
282         hlist_for_each_entry(mm_slot, node, bucket, link) {
283                 if (mm == mm_slot->mm)
284                         return mm_slot;
285         }
286         return NULL;
287 }
288
289 static void insert_to_mm_slots_hash(struct mm_struct *mm,
290                                     struct mm_slot *mm_slot)
291 {
292         struct hlist_head *bucket;
293
294         bucket = &mm_slots_hash[hash_ptr(mm, MM_SLOTS_HASH_SHIFT)];
295         mm_slot->mm = mm;
296         hlist_add_head(&mm_slot->link, bucket);
297 }
298
299 static inline int in_stable_tree(struct rmap_item *rmap_item)
300 {
301         return rmap_item->address & STABLE_FLAG;
302 }
303
304 static void hold_anon_vma(struct rmap_item *rmap_item,
305                           struct anon_vma *anon_vma)
306 {
307         rmap_item->anon_vma = anon_vma;
308         get_anon_vma(anon_vma);
309 }
310
311 static void ksm_drop_anon_vma(struct rmap_item *rmap_item)
312 {
313         struct anon_vma *anon_vma = rmap_item->anon_vma;
314
315         drop_anon_vma(anon_vma);
316 }
317
318 /*
319  * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
320  * page tables after it has passed through ksm_exit() - which, if necessary,
321  * takes mmap_sem briefly to serialize against them.  ksm_exit() does not set
322  * a special flag: they can just back out as soon as mm_users goes to zero.
323  * ksm_test_exit() is used throughout to make this test for exit: in some
324  * places for correctness, in some places just to avoid unnecessary work.
325  */
326 static inline bool ksm_test_exit(struct mm_struct *mm)
327 {
328         return atomic_read(&mm->mm_users) == 0;
329 }
330
331 /*
332  * We use break_ksm to break COW on a ksm page: it's a stripped down
333  *
334  *      if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
335  *              put_page(page);
336  *
337  * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
338  * in case the application has unmapped and remapped mm,addr meanwhile.
339  * Could a ksm page appear anywhere else?  Actually yes, in a VM_PFNMAP
340  * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
341  */
342 static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
343 {
344         struct page *page;
345         int ret = 0;
346
347         do {
348                 cond_resched();
349                 page = follow_page(vma, addr, FOLL_GET);
350                 if (IS_ERR_OR_NULL(page))
351                         break;
352                 if (PageKsm(page))
353                         ret = handle_mm_fault(vma->vm_mm, vma, addr,
354                                                         FAULT_FLAG_WRITE);
355                 else
356                         ret = VM_FAULT_WRITE;
357                 put_page(page);
358         } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM)));
359         /*
360          * We must loop because handle_mm_fault() may back out if there's
361          * any difficulty e.g. if pte accessed bit gets updated concurrently.
362          *
363          * VM_FAULT_WRITE is what we have been hoping for: it indicates that
364          * COW has been broken, even if the vma does not permit VM_WRITE;
365          * but note that a concurrent fault might break PageKsm for us.
366          *
367          * VM_FAULT_SIGBUS could occur if we race with truncation of the
368          * backing file, which also invalidates anonymous pages: that's
369          * okay, that truncation will have unmapped the PageKsm for us.
370          *
371          * VM_FAULT_OOM: at the time of writing (late July 2009), setting
372          * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
373          * current task has TIF_MEMDIE set, and will be OOM killed on return
374          * to user; and ksmd, having no mm, would never be chosen for that.
375          *
376          * But if the mm is in a limited mem_cgroup, then the fault may fail
377          * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
378          * even ksmd can fail in this way - though it's usually breaking ksm
379          * just to undo a merge it made a moment before, so unlikely to oom.
380          *
381          * That's a pity: we might therefore have more kernel pages allocated
382          * than we're counting as nodes in the stable tree; but ksm_do_scan
383          * will retry to break_cow on each pass, so should recover the page
384          * in due course.  The important thing is to not let VM_MERGEABLE
385          * be cleared while any such pages might remain in the area.
386          */
387         return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
388 }
389
390 static void break_cow(struct rmap_item *rmap_item)
391 {
392         struct mm_struct *mm = rmap_item->mm;
393         unsigned long addr = rmap_item->address;
394         struct vm_area_struct *vma;
395
396         /*
397          * It is not an accident that whenever we want to break COW
398          * to undo, we also need to drop a reference to the anon_vma.
399          */
400         ksm_drop_anon_vma(rmap_item);
401
402         down_read(&mm->mmap_sem);
403         if (ksm_test_exit(mm))
404                 goto out;
405         vma = find_vma(mm, addr);
406         if (!vma || vma->vm_start > addr)
407                 goto out;
408         if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
409                 goto out;
410         break_ksm(vma, addr);
411 out:
412         up_read(&mm->mmap_sem);
413 }
414
415 static struct page *page_trans_compound_anon(struct page *page)
416 {
417         if (PageTransCompound(page)) {
418                 struct page *head = compound_trans_head(page);
419                 /*
420                  * head may actually be splitted and freed from under
421                  * us but it's ok here.
422                  */
423                 if (PageAnon(head))
424                         return head;
425         }
426         return NULL;
427 }
428
429 static struct page *get_mergeable_page(struct rmap_item *rmap_item)
430 {
431         struct mm_struct *mm = rmap_item->mm;
432         unsigned long addr = rmap_item->address;
433         struct vm_area_struct *vma;
434         struct page *page;
435
436         down_read(&mm->mmap_sem);
437         if (ksm_test_exit(mm))
438                 goto out;
439         vma = find_vma(mm, addr);
440         if (!vma || vma->vm_start > addr)
441                 goto out;
442         if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
443                 goto out;
444
445         page = follow_page(vma, addr, FOLL_GET);
446         if (IS_ERR_OR_NULL(page))
447                 goto out;
448         if (PageAnon(page) || page_trans_compound_anon(page)) {
449                 flush_anon_page(vma, page, addr);
450                 flush_dcache_page(page);
451         } else {
452                 put_page(page);
453 out:            page = NULL;
454         }
455         up_read(&mm->mmap_sem);
456         return page;
457 }
458
459 static void remove_node_from_stable_tree(struct stable_node *stable_node)
460 {
461         struct rmap_item *rmap_item;
462         struct hlist_node *hlist;
463
464         hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
465                 if (rmap_item->hlist.next)
466                         ksm_pages_sharing--;
467                 else
468                         ksm_pages_shared--;
469                 ksm_drop_anon_vma(rmap_item);
470                 rmap_item->address &= PAGE_MASK;
471                 cond_resched();
472         }
473
474         rb_erase(&stable_node->node, &root_stable_tree);
475         free_stable_node(stable_node);
476 }
477
478 /*
479  * get_ksm_page: checks if the page indicated by the stable node
480  * is still its ksm page, despite having held no reference to it.
481  * In which case we can trust the content of the page, and it
482  * returns the gotten page; but if the page has now been zapped,
483  * remove the stale node from the stable tree and return NULL.
484  *
485  * You would expect the stable_node to hold a reference to the ksm page.
486  * But if it increments the page's count, swapping out has to wait for
487  * ksmd to come around again before it can free the page, which may take
488  * seconds or even minutes: much too unresponsive.  So instead we use a
489  * "keyhole reference": access to the ksm page from the stable node peeps
490  * out through its keyhole to see if that page still holds the right key,
491  * pointing back to this stable node.  This relies on freeing a PageAnon
492  * page to reset its page->mapping to NULL, and relies on no other use of
493  * a page to put something that might look like our key in page->mapping.
494  *
495  * include/linux/pagemap.h page_cache_get_speculative() is a good reference,
496  * but this is different - made simpler by ksm_thread_mutex being held, but
497  * interesting for assuming that no other use of the struct page could ever
498  * put our expected_mapping into page->mapping (or a field of the union which
499  * coincides with page->mapping).  The RCU calls are not for KSM at all, but
500  * to keep the page_count protocol described with page_cache_get_speculative.
501  *
502  * Note: it is possible that get_ksm_page() will return NULL one moment,
503  * then page the next, if the page is in between page_freeze_refs() and
504  * page_unfreeze_refs(): this shouldn't be a problem anywhere, the page
505  * is on its way to being freed; but it is an anomaly to bear in mind.
506  */
507 static struct page *get_ksm_page(struct stable_node *stable_node)
508 {
509         struct page *page;
510         void *expected_mapping;
511
512         page = pfn_to_page(stable_node->kpfn);
513         expected_mapping = (void *)stable_node +
514                                 (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
515         rcu_read_lock();
516         if (page->mapping != expected_mapping)
517                 goto stale;
518         if (!get_page_unless_zero(page))
519                 goto stale;
520         if (page->mapping != expected_mapping) {
521                 put_page(page);
522                 goto stale;
523         }
524         rcu_read_unlock();
525         return page;
526 stale:
527         rcu_read_unlock();
528         remove_node_from_stable_tree(stable_node);
529         return NULL;
530 }
531
532 /*
533  * Removing rmap_item from stable or unstable tree.
534  * This function will clean the information from the stable/unstable tree.
535  */
536 static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
537 {
538         if (rmap_item->address & STABLE_FLAG) {
539                 struct stable_node *stable_node;
540                 struct page *page;
541
542                 stable_node = rmap_item->head;
543                 page = get_ksm_page(stable_node);
544                 if (!page)
545                         goto out;
546
547                 lock_page(page);
548                 hlist_del(&rmap_item->hlist);
549                 unlock_page(page);
550                 put_page(page);
551
552                 if (stable_node->hlist.first)
553                         ksm_pages_sharing--;
554                 else
555                         ksm_pages_shared--;
556
557                 ksm_drop_anon_vma(rmap_item);
558                 rmap_item->address &= PAGE_MASK;
559
560         } else if (rmap_item->address & UNSTABLE_FLAG) {
561                 unsigned char age;
562                 /*
563                  * Usually ksmd can and must skip the rb_erase, because
564                  * root_unstable_tree was already reset to RB_ROOT.
565                  * But be careful when an mm is exiting: do the rb_erase
566                  * if this rmap_item was inserted by this scan, rather
567                  * than left over from before.
568                  */
569                 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
570                 BUG_ON(age > 1);
571                 if (!age)
572                         rb_erase(&rmap_item->node, &root_unstable_tree);
573
574                 ksm_pages_unshared--;
575                 rmap_item->address &= PAGE_MASK;
576         }
577 out:
578         cond_resched();         /* we're called from many long loops */
579 }
580
581 static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
582                                        struct rmap_item **rmap_list)
583 {
584         while (*rmap_list) {
585                 struct rmap_item *rmap_item = *rmap_list;
586                 *rmap_list = rmap_item->rmap_list;
587                 remove_rmap_item_from_tree(rmap_item);
588                 free_rmap_item(rmap_item);
589         }
590 }
591
592 /*
593  * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather
594  * than check every pte of a given vma, the locking doesn't quite work for
595  * that - an rmap_item is assigned to the stable tree after inserting ksm
596  * page and upping mmap_sem.  Nor does it fit with the way we skip dup'ing
597  * rmap_items from parent to child at fork time (so as not to waste time
598  * if exit comes before the next scan reaches it).
599  *
600  * Similarly, although we'd like to remove rmap_items (so updating counts
601  * and freeing memory) when unmerging an area, it's easier to leave that
602  * to the next pass of ksmd - consider, for example, how ksmd might be
603  * in cmp_and_merge_page on one of the rmap_items we would be removing.
604  */
605 static int unmerge_ksm_pages(struct vm_area_struct *vma,
606                              unsigned long start, unsigned long end)
607 {
608         unsigned long addr;
609         int err = 0;
610
611         for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
612                 if (ksm_test_exit(vma->vm_mm))
613                         break;
614                 if (signal_pending(current))
615                         err = -ERESTARTSYS;
616                 else
617                         err = break_ksm(vma, addr);
618         }
619         return err;
620 }
621
622 #ifdef CONFIG_SYSFS
623 /*
624  * Only called through the sysfs control interface:
625  */
626 static int unmerge_and_remove_all_rmap_items(void)
627 {
628         struct mm_slot *mm_slot;
629         struct mm_struct *mm;
630         struct vm_area_struct *vma;
631         int err = 0;
632
633         spin_lock(&ksm_mmlist_lock);
634         ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
635                                                 struct mm_slot, mm_list);
636         spin_unlock(&ksm_mmlist_lock);
637
638         for (mm_slot = ksm_scan.mm_slot;
639                         mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
640                 mm = mm_slot->mm;
641                 down_read(&mm->mmap_sem);
642                 for (vma = mm->mmap; vma; vma = vma->vm_next) {
643                         if (ksm_test_exit(mm))
644                                 break;
645                         if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
646                                 continue;
647                         err = unmerge_ksm_pages(vma,
648                                                 vma->vm_start, vma->vm_end);
649                         if (err)
650                                 goto error;
651                 }
652
653                 remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
654
655                 spin_lock(&ksm_mmlist_lock);
656                 ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
657                                                 struct mm_slot, mm_list);
658                 if (ksm_test_exit(mm)) {
659                         hlist_del(&mm_slot->link);
660                         list_del(&mm_slot->mm_list);
661                         spin_unlock(&ksm_mmlist_lock);
662
663                         free_mm_slot(mm_slot);
664                         clear_bit(MMF_VM_MERGEABLE, &mm->flags);
665                         up_read(&mm->mmap_sem);
666                         mmdrop(mm);
667                 } else {
668                         spin_unlock(&ksm_mmlist_lock);
669                         up_read(&mm->mmap_sem);
670                 }
671         }
672
673         ksm_scan.seqnr = 0;
674         return 0;
675
676 error:
677         up_read(&mm->mmap_sem);
678         spin_lock(&ksm_mmlist_lock);
679         ksm_scan.mm_slot = &ksm_mm_head;
680         spin_unlock(&ksm_mmlist_lock);
681         return err;
682 }
683 #endif /* CONFIG_SYSFS */
684
685 static u32 calc_checksum(struct page *page)
686 {
687         u32 checksum;
688         void *addr = kmap_atomic(page, KM_USER0);
689         checksum = jhash2(addr, PAGE_SIZE / 4, 17);
690         kunmap_atomic(addr, KM_USER0);
691         return checksum;
692 }
693
694 static int memcmp_pages(struct page *page1, struct page *page2)
695 {
696         char *addr1, *addr2;
697         int ret;
698
699         addr1 = kmap_atomic(page1, KM_USER0);
700         addr2 = kmap_atomic(page2, KM_USER1);
701         ret = memcmp(addr1, addr2, PAGE_SIZE);
702         kunmap_atomic(addr2, KM_USER1);
703         kunmap_atomic(addr1, KM_USER0);
704         return ret;
705 }
706
707 static inline int pages_identical(struct page *page1, struct page *page2)
708 {
709         return !memcmp_pages(page1, page2);
710 }
711
712 static int write_protect_page(struct vm_area_struct *vma, struct page *page,
713                               pte_t *orig_pte)
714 {
715         struct mm_struct *mm = vma->vm_mm;
716         unsigned long addr;
717         pte_t *ptep;
718         spinlock_t *ptl;
719         int swapped;
720         int err = -EFAULT;
721
722         addr = page_address_in_vma(page, vma);
723         if (addr == -EFAULT)
724                 goto out;
725
726         BUG_ON(PageTransCompound(page));
727         ptep = page_check_address(page, mm, addr, &ptl, 0);
728         if (!ptep)
729                 goto out;
730
731         if (pte_write(*ptep) || pte_dirty(*ptep)) {
732                 pte_t entry;
733
734                 swapped = PageSwapCache(page);
735                 flush_cache_page(vma, addr, page_to_pfn(page));
736                 /*
737                  * Ok this is tricky, when get_user_pages_fast() run it doesnt
738                  * take any lock, therefore the check that we are going to make
739                  * with the pagecount against the mapcount is racey and
740                  * O_DIRECT can happen right after the check.
741                  * So we clear the pte and flush the tlb before the check
742                  * this assure us that no O_DIRECT can happen after the check
743                  * or in the middle of the check.
744                  */
745                 entry = ptep_clear_flush(vma, addr, ptep);
746                 /*
747                  * Check that no O_DIRECT or similar I/O is in progress on the
748                  * page
749                  */
750                 if (page_mapcount(page) + 1 + swapped != page_count(page)) {
751                         set_pte_at(mm, addr, ptep, entry);
752                         goto out_unlock;
753                 }
754                 if (pte_dirty(entry))
755                         set_page_dirty(page);
756                 entry = pte_mkclean(pte_wrprotect(entry));
757                 set_pte_at_notify(mm, addr, ptep, entry);
758         }
759         *orig_pte = *ptep;
760         err = 0;
761
762 out_unlock:
763         pte_unmap_unlock(ptep, ptl);
764 out:
765         return err;
766 }
767
768 /**
769  * replace_page - replace page in vma by new ksm page
770  * @vma:      vma that holds the pte pointing to page
771  * @page:     the page we are replacing by kpage
772  * @kpage:    the ksm page we replace page by
773  * @orig_pte: the original value of the pte
774  *
775  * Returns 0 on success, -EFAULT on failure.
776  */
777 static int replace_page(struct vm_area_struct *vma, struct page *page,
778                         struct page *kpage, pte_t orig_pte)
779 {
780         struct mm_struct *mm = vma->vm_mm;
781         pgd_t *pgd;
782         pud_t *pud;
783         pmd_t *pmd;
784         pte_t *ptep;
785         spinlock_t *ptl;
786         unsigned long addr;
787         int err = -EFAULT;
788
789         addr = page_address_in_vma(page, vma);
790         if (addr == -EFAULT)
791                 goto out;
792
793         pgd = pgd_offset(mm, addr);
794         if (!pgd_present(*pgd))
795                 goto out;
796
797         pud = pud_offset(pgd, addr);
798         if (!pud_present(*pud))
799                 goto out;
800
801         pmd = pmd_offset(pud, addr);
802         BUG_ON(pmd_trans_huge(*pmd));
803         if (!pmd_present(*pmd))
804                 goto out;
805
806         ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
807         if (!pte_same(*ptep, orig_pte)) {
808                 pte_unmap_unlock(ptep, ptl);
809                 goto out;
810         }
811
812         get_page(kpage);
813         page_add_anon_rmap(kpage, vma, addr);
814
815         flush_cache_page(vma, addr, pte_pfn(*ptep));
816         ptep_clear_flush(vma, addr, ptep);
817         set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
818
819         page_remove_rmap(page);
820         if (!page_mapped(page))
821                 try_to_free_swap(page);
822         put_page(page);
823
824         pte_unmap_unlock(ptep, ptl);
825         err = 0;
826 out:
827         return err;
828 }
829
830 static int page_trans_compound_anon_split(struct page *page)
831 {
832         int ret = 0;
833         struct page *transhuge_head = page_trans_compound_anon(page);
834         if (transhuge_head) {
835                 /* Get the reference on the head to split it. */
836                 if (get_page_unless_zero(transhuge_head)) {
837                         /*
838                          * Recheck we got the reference while the head
839                          * was still anonymous.
840                          */
841                         if (PageAnon(transhuge_head))
842                                 ret = split_huge_page(transhuge_head);
843                         else
844                                 /*
845                                  * Retry later if split_huge_page run
846                                  * from under us.
847                                  */
848                                 ret = 1;
849                         put_page(transhuge_head);
850                 } else
851                         /* Retry later if split_huge_page run from under us. */
852                         ret = 1;
853         }
854         return ret;
855 }
856
857 /*
858  * try_to_merge_one_page - take two pages and merge them into one
859  * @vma: the vma that holds the pte pointing to page
860  * @page: the PageAnon page that we want to replace with kpage
861  * @kpage: the PageKsm page that we want to map instead of page,
862  *         or NULL the first time when we want to use page as kpage.
863  *
864  * This function returns 0 if the pages were merged, -EFAULT otherwise.
865  */
866 static int try_to_merge_one_page(struct vm_area_struct *vma,
867                                  struct page *page, struct page *kpage)
868 {
869         pte_t orig_pte = __pte(0);
870         int err = -EFAULT;
871
872         if (page == kpage)                      /* ksm page forked */
873                 return 0;
874
875         if (!(vma->vm_flags & VM_MERGEABLE))
876                 goto out;
877         if (PageTransCompound(page) && page_trans_compound_anon_split(page))
878                 goto out;
879         BUG_ON(PageTransCompound(page));
880         if (!PageAnon(page))
881                 goto out;
882
883         /*
884          * We need the page lock to read a stable PageSwapCache in
885          * write_protect_page().  We use trylock_page() instead of
886          * lock_page() because we don't want to wait here - we
887          * prefer to continue scanning and merging different pages,
888          * then come back to this page when it is unlocked.
889          */
890         if (!trylock_page(page))
891                 goto out;
892         /*
893          * If this anonymous page is mapped only here, its pte may need
894          * to be write-protected.  If it's mapped elsewhere, all of its
895          * ptes are necessarily already write-protected.  But in either
896          * case, we need to lock and check page_count is not raised.
897          */
898         if (write_protect_page(vma, page, &orig_pte) == 0) {
899                 if (!kpage) {
900                         /*
901                          * While we hold page lock, upgrade page from
902                          * PageAnon+anon_vma to PageKsm+NULL stable_node:
903                          * stable_tree_insert() will update stable_node.
904                          */
905                         set_page_stable_node(page, NULL);
906                         mark_page_accessed(page);
907                         err = 0;
908                 } else if (pages_identical(page, kpage))
909                         err = replace_page(vma, page, kpage, orig_pte);
910         }
911
912         if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
913                 munlock_vma_page(page);
914                 if (!PageMlocked(kpage)) {
915                         unlock_page(page);
916                         lock_page(kpage);
917                         mlock_vma_page(kpage);
918                         page = kpage;           /* for final unlock */
919                 }
920         }
921
922         unlock_page(page);
923 out:
924         return err;
925 }
926
927 /*
928  * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
929  * but no new kernel page is allocated: kpage must already be a ksm page.
930  *
931  * This function returns 0 if the pages were merged, -EFAULT otherwise.
932  */
933 static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
934                                       struct page *page, struct page *kpage)
935 {
936         struct mm_struct *mm = rmap_item->mm;
937         struct vm_area_struct *vma;
938         int err = -EFAULT;
939
940         down_read(&mm->mmap_sem);
941         if (ksm_test_exit(mm))
942                 goto out;
943         vma = find_vma(mm, rmap_item->address);
944         if (!vma || vma->vm_start > rmap_item->address)
945                 goto out;
946
947         err = try_to_merge_one_page(vma, page, kpage);
948         if (err)
949                 goto out;
950
951         /* Must get reference to anon_vma while still holding mmap_sem */
952         hold_anon_vma(rmap_item, vma->anon_vma);
953 out:
954         up_read(&mm->mmap_sem);
955         return err;
956 }
957
958 /*
959  * try_to_merge_two_pages - take two identical pages and prepare them
960  * to be merged into one page.
961  *
962  * This function returns the kpage if we successfully merged two identical
963  * pages into one ksm page, NULL otherwise.
964  *
965  * Note that this function upgrades page to ksm page: if one of the pages
966  * is already a ksm page, try_to_merge_with_ksm_page should be used.
967  */
968 static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
969                                            struct page *page,
970                                            struct rmap_item *tree_rmap_item,
971                                            struct page *tree_page)
972 {
973         int err;
974
975         err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
976         if (!err) {
977                 err = try_to_merge_with_ksm_page(tree_rmap_item,
978                                                         tree_page, page);
979                 /*
980                  * If that fails, we have a ksm page with only one pte
981                  * pointing to it: so break it.
982                  */
983                 if (err)
984                         break_cow(rmap_item);
985         }
986         return err ? NULL : page;
987 }
988
989 /*
990  * stable_tree_search - search for page inside the stable tree
991  *
992  * This function checks if there is a page inside the stable tree
993  * with identical content to the page that we are scanning right now.
994  *
995  * This function returns the stable tree node of identical content if found,
996  * NULL otherwise.
997  */
998 static struct page *stable_tree_search(struct page *page)
999 {
1000         struct rb_node *node = root_stable_tree.rb_node;
1001         struct stable_node *stable_node;
1002
1003         stable_node = page_stable_node(page);
1004         if (stable_node) {                      /* ksm page forked */
1005                 get_page(page);
1006                 return page;
1007         }
1008
1009         while (node) {
1010                 struct page *tree_page;
1011                 int ret;
1012
1013                 cond_resched();
1014                 stable_node = rb_entry(node, struct stable_node, node);
1015                 tree_page = get_ksm_page(stable_node);
1016                 if (!tree_page)
1017                         return NULL;
1018
1019                 ret = memcmp_pages(page, tree_page);
1020
1021                 if (ret < 0) {
1022                         put_page(tree_page);
1023                         node = node->rb_left;
1024                 } else if (ret > 0) {
1025                         put_page(tree_page);
1026                         node = node->rb_right;
1027                 } else
1028                         return tree_page;
1029         }
1030
1031         return NULL;
1032 }
1033
1034 /*
1035  * stable_tree_insert - insert rmap_item pointing to new ksm page
1036  * into the stable tree.
1037  *
1038  * This function returns the stable tree node just allocated on success,
1039  * NULL otherwise.
1040  */
1041 static struct stable_node *stable_tree_insert(struct page *kpage)
1042 {
1043         struct rb_node **new = &root_stable_tree.rb_node;
1044         struct rb_node *parent = NULL;
1045         struct stable_node *stable_node;
1046
1047         while (*new) {
1048                 struct page *tree_page;
1049                 int ret;
1050
1051                 cond_resched();
1052                 stable_node = rb_entry(*new, struct stable_node, node);
1053                 tree_page = get_ksm_page(stable_node);
1054                 if (!tree_page)
1055                         return NULL;
1056
1057                 ret = memcmp_pages(kpage, tree_page);
1058                 put_page(tree_page);
1059
1060                 parent = *new;
1061                 if (ret < 0)
1062                         new = &parent->rb_left;
1063                 else if (ret > 0)
1064                         new = &parent->rb_right;
1065                 else {
1066                         /*
1067                          * It is not a bug that stable_tree_search() didn't
1068                          * find this node: because at that time our page was
1069                          * not yet write-protected, so may have changed since.
1070                          */
1071                         return NULL;
1072                 }
1073         }
1074
1075         stable_node = alloc_stable_node();
1076         if (!stable_node)
1077                 return NULL;
1078
1079         rb_link_node(&stable_node->node, parent, new);
1080         rb_insert_color(&stable_node->node, &root_stable_tree);
1081
1082         INIT_HLIST_HEAD(&stable_node->hlist);
1083
1084         stable_node->kpfn = page_to_pfn(kpage);
1085         set_page_stable_node(kpage, stable_node);
1086
1087         return stable_node;
1088 }
1089
1090 /*
1091  * unstable_tree_search_insert - search for identical page,
1092  * else insert rmap_item into the unstable tree.
1093  *
1094  * This function searches for a page in the unstable tree identical to the
1095  * page currently being scanned; and if no identical page is found in the
1096  * tree, we insert rmap_item as a new object into the unstable tree.
1097  *
1098  * This function returns pointer to rmap_item found to be identical
1099  * to the currently scanned page, NULL otherwise.
1100  *
1101  * This function does both searching and inserting, because they share
1102  * the same walking algorithm in an rbtree.
1103  */
1104 static
1105 struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1106                                               struct page *page,
1107                                               struct page **tree_pagep)
1108
1109 {
1110         struct rb_node **new = &root_unstable_tree.rb_node;
1111         struct rb_node *parent = NULL;
1112
1113         while (*new) {
1114                 struct rmap_item *tree_rmap_item;
1115                 struct page *tree_page;
1116                 int ret;
1117
1118                 cond_resched();
1119                 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1120                 tree_page = get_mergeable_page(tree_rmap_item);
1121                 if (IS_ERR_OR_NULL(tree_page))
1122                         return NULL;
1123
1124                 /*
1125                  * Don't substitute a ksm page for a forked page.
1126                  */
1127                 if (page == tree_page) {
1128                         put_page(tree_page);
1129                         return NULL;
1130                 }
1131
1132                 ret = memcmp_pages(page, tree_page);
1133
1134                 parent = *new;
1135                 if (ret < 0) {
1136                         put_page(tree_page);
1137                         new = &parent->rb_left;
1138                 } else if (ret > 0) {
1139                         put_page(tree_page);
1140                         new = &parent->rb_right;
1141                 } else {
1142                         *tree_pagep = tree_page;
1143                         return tree_rmap_item;
1144                 }
1145         }
1146
1147         rmap_item->address |= UNSTABLE_FLAG;
1148         rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1149         rb_link_node(&rmap_item->node, parent, new);
1150         rb_insert_color(&rmap_item->node, &root_unstable_tree);
1151
1152         ksm_pages_unshared++;
1153         return NULL;
1154 }
1155
1156 /*
1157  * stable_tree_append - add another rmap_item to the linked list of
1158  * rmap_items hanging off a given node of the stable tree, all sharing
1159  * the same ksm page.
1160  */
1161 static void stable_tree_append(struct rmap_item *rmap_item,
1162                                struct stable_node *stable_node)
1163 {
1164         rmap_item->head = stable_node;
1165         rmap_item->address |= STABLE_FLAG;
1166         hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
1167
1168         if (rmap_item->hlist.next)
1169                 ksm_pages_sharing++;
1170         else
1171                 ksm_pages_shared++;
1172 }
1173
1174 /*
1175  * cmp_and_merge_page - first see if page can be merged into the stable tree;
1176  * if not, compare checksum to previous and if it's the same, see if page can
1177  * be inserted into the unstable tree, or merged with a page already there and
1178  * both transferred to the stable tree.
1179  *
1180  * @page: the page that we are searching identical page to.
1181  * @rmap_item: the reverse mapping into the virtual address of this page
1182  */
1183 static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1184 {
1185         struct rmap_item *tree_rmap_item;
1186         struct page *tree_page = NULL;
1187         struct stable_node *stable_node;
1188         struct page *kpage;
1189         unsigned int checksum;
1190         int err;
1191
1192         remove_rmap_item_from_tree(rmap_item);
1193
1194         /* We first start with searching the page inside the stable tree */
1195         kpage = stable_tree_search(page);
1196         if (kpage) {
1197                 err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
1198                 if (!err) {
1199                         /*
1200                          * The page was successfully merged:
1201                          * add its rmap_item to the stable tree.
1202                          */
1203                         lock_page(kpage);
1204                         stable_tree_append(rmap_item, page_stable_node(kpage));
1205                         unlock_page(kpage);
1206                 }
1207                 put_page(kpage);
1208                 return;
1209         }
1210
1211         /*
1212          * If the hash value of the page has changed from the last time
1213          * we calculated it, this page is changing frequently: therefore we
1214          * don't want to insert it in the unstable tree, and we don't want
1215          * to waste our time searching for something identical to it there.
1216          */
1217         checksum = calc_checksum(page);
1218         if (rmap_item->oldchecksum != checksum) {
1219                 rmap_item->oldchecksum = checksum;
1220                 return;
1221         }
1222
1223         tree_rmap_item =
1224                 unstable_tree_search_insert(rmap_item, page, &tree_page);
1225         if (tree_rmap_item) {
1226                 kpage = try_to_merge_two_pages(rmap_item, page,
1227                                                 tree_rmap_item, tree_page);
1228                 put_page(tree_page);
1229                 /*
1230                  * As soon as we merge this page, we want to remove the
1231                  * rmap_item of the page we have merged with from the unstable
1232                  * tree, and insert it instead as new node in the stable tree.
1233                  */
1234                 if (kpage) {
1235                         remove_rmap_item_from_tree(tree_rmap_item);
1236
1237                         lock_page(kpage);
1238                         stable_node = stable_tree_insert(kpage);
1239                         if (stable_node) {
1240                                 stable_tree_append(tree_rmap_item, stable_node);
1241                                 stable_tree_append(rmap_item, stable_node);
1242                         }
1243                         unlock_page(kpage);
1244
1245                         /*
1246                          * If we fail to insert the page into the stable tree,
1247                          * we will have 2 virtual addresses that are pointing
1248                          * to a ksm page left outside the stable tree,
1249                          * in which case we need to break_cow on both.
1250                          */
1251                         if (!stable_node) {
1252                                 break_cow(tree_rmap_item);
1253                                 break_cow(rmap_item);
1254                         }
1255                 }
1256         }
1257 }
1258
1259 static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
1260                                             struct rmap_item **rmap_list,
1261                                             unsigned long addr)
1262 {
1263         struct rmap_item *rmap_item;
1264
1265         while (*rmap_list) {
1266                 rmap_item = *rmap_list;
1267                 if ((rmap_item->address & PAGE_MASK) == addr)
1268                         return rmap_item;
1269                 if (rmap_item->address > addr)
1270                         break;
1271                 *rmap_list = rmap_item->rmap_list;
1272                 remove_rmap_item_from_tree(rmap_item);
1273                 free_rmap_item(rmap_item);
1274         }
1275
1276         rmap_item = alloc_rmap_item();
1277         if (rmap_item) {
1278                 /* It has already been zeroed */
1279                 rmap_item->mm = mm_slot->mm;
1280                 rmap_item->address = addr;
1281                 rmap_item->rmap_list = *rmap_list;
1282                 *rmap_list = rmap_item;
1283         }
1284         return rmap_item;
1285 }
1286
1287 static struct rmap_item *scan_get_next_rmap_item(struct page **page)
1288 {
1289         struct mm_struct *mm;
1290         struct mm_slot *slot;
1291         struct vm_area_struct *vma;
1292         struct rmap_item *rmap_item;
1293
1294         if (list_empty(&ksm_mm_head.mm_list))
1295                 return NULL;
1296
1297         slot = ksm_scan.mm_slot;
1298         if (slot == &ksm_mm_head) {
1299                 root_unstable_tree = RB_ROOT;
1300
1301                 spin_lock(&ksm_mmlist_lock);
1302                 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1303                 ksm_scan.mm_slot = slot;
1304                 spin_unlock(&ksm_mmlist_lock);
1305 next_mm:
1306                 ksm_scan.address = 0;
1307                 ksm_scan.rmap_list = &slot->rmap_list;
1308         }
1309
1310         mm = slot->mm;
1311         down_read(&mm->mmap_sem);
1312         if (ksm_test_exit(mm))
1313                 vma = NULL;
1314         else
1315                 vma = find_vma(mm, ksm_scan.address);
1316
1317         for (; vma; vma = vma->vm_next) {
1318                 if (!(vma->vm_flags & VM_MERGEABLE))
1319                         continue;
1320                 if (ksm_scan.address < vma->vm_start)
1321                         ksm_scan.address = vma->vm_start;
1322                 if (!vma->anon_vma)
1323                         ksm_scan.address = vma->vm_end;
1324
1325                 while (ksm_scan.address < vma->vm_end) {
1326                         if (ksm_test_exit(mm))
1327                                 break;
1328                         *page = follow_page(vma, ksm_scan.address, FOLL_GET);
1329                         if (IS_ERR_OR_NULL(*page)) {
1330                                 ksm_scan.address += PAGE_SIZE;
1331                                 cond_resched();
1332                                 continue;
1333                         }
1334                         if (PageAnon(*page) ||
1335                             page_trans_compound_anon(*page)) {
1336                                 flush_anon_page(vma, *page, ksm_scan.address);
1337                                 flush_dcache_page(*page);
1338                                 rmap_item = get_next_rmap_item(slot,
1339                                         ksm_scan.rmap_list, ksm_scan.address);
1340                                 if (rmap_item) {
1341                                         ksm_scan.rmap_list =
1342                                                         &rmap_item->rmap_list;
1343                                         ksm_scan.address += PAGE_SIZE;
1344                                 } else
1345                                         put_page(*page);
1346                                 up_read(&mm->mmap_sem);
1347                                 return rmap_item;
1348                         }
1349                         put_page(*page);
1350                         ksm_scan.address += PAGE_SIZE;
1351                         cond_resched();
1352                 }
1353         }
1354
1355         if (ksm_test_exit(mm)) {
1356                 ksm_scan.address = 0;
1357                 ksm_scan.rmap_list = &slot->rmap_list;
1358         }
1359         /*
1360          * Nuke all the rmap_items that are above this current rmap:
1361          * because there were no VM_MERGEABLE vmas with such addresses.
1362          */
1363         remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
1364
1365         spin_lock(&ksm_mmlist_lock);
1366         ksm_scan.mm_slot = list_entry(slot->mm_list.next,
1367                                                 struct mm_slot, mm_list);
1368         if (ksm_scan.address == 0) {
1369                 /*
1370                  * We've completed a full scan of all vmas, holding mmap_sem
1371                  * throughout, and found no VM_MERGEABLE: so do the same as
1372                  * __ksm_exit does to remove this mm from all our lists now.
1373                  * This applies either when cleaning up after __ksm_exit
1374                  * (but beware: we can reach here even before __ksm_exit),
1375                  * or when all VM_MERGEABLE areas have been unmapped (and
1376                  * mmap_sem then protects against race with MADV_MERGEABLE).
1377                  */
1378                 hlist_del(&slot->link);
1379                 list_del(&slot->mm_list);
1380                 spin_unlock(&ksm_mmlist_lock);
1381
1382                 free_mm_slot(slot);
1383                 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1384                 up_read(&mm->mmap_sem);
1385                 mmdrop(mm);
1386         } else {
1387                 spin_unlock(&ksm_mmlist_lock);
1388                 up_read(&mm->mmap_sem);
1389         }
1390
1391         /* Repeat until we've completed scanning the whole list */
1392         slot = ksm_scan.mm_slot;
1393         if (slot != &ksm_mm_head)
1394                 goto next_mm;
1395
1396         ksm_scan.seqnr++;
1397         return NULL;
1398 }
1399
1400 /**
1401  * ksm_do_scan  - the ksm scanner main worker function.
1402  * @scan_npages - number of pages we want to scan before we return.
1403  */
1404 static void ksm_do_scan(unsigned int scan_npages)
1405 {
1406         struct rmap_item *rmap_item;
1407         struct page *uninitialized_var(page);
1408
1409         while (scan_npages-- && likely(!freezing(current))) {
1410                 cond_resched();
1411                 rmap_item = scan_get_next_rmap_item(&page);
1412                 if (!rmap_item)
1413                         return;
1414                 if (!PageKsm(page) || !in_stable_tree(rmap_item))
1415                         cmp_and_merge_page(page, rmap_item);
1416                 put_page(page);
1417         }
1418 }
1419
1420 static int ksmd_should_run(void)
1421 {
1422         return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1423 }
1424
1425 static int ksm_scan_thread(void *nothing)
1426 {
1427         set_freezable();
1428         set_user_nice(current, 5);
1429
1430         while (!kthread_should_stop()) {
1431                 mutex_lock(&ksm_thread_mutex);
1432                 if (ksmd_should_run())
1433                         ksm_do_scan(ksm_thread_pages_to_scan);
1434                 mutex_unlock(&ksm_thread_mutex);
1435
1436                 try_to_freeze();
1437
1438                 if (ksmd_should_run()) {
1439                         schedule_timeout_interruptible(
1440                                 msecs_to_jiffies(ksm_thread_sleep_millisecs));
1441                 } else {
1442                         wait_event_freezable(ksm_thread_wait,
1443                                 ksmd_should_run() || kthread_should_stop());
1444                 }
1445         }
1446         return 0;
1447 }
1448
1449 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1450                 unsigned long end, int advice, unsigned long *vm_flags)
1451 {
1452         struct mm_struct *mm = vma->vm_mm;
1453         int err;
1454
1455         switch (advice) {
1456         case MADV_MERGEABLE:
1457                 /*
1458                  * Be somewhat over-protective for now!
1459                  */
1460                 if (*vm_flags & (VM_MERGEABLE | VM_SHARED  | VM_MAYSHARE   |
1461                                  VM_PFNMAP    | VM_IO      | VM_DONTEXPAND |
1462                                  VM_RESERVED  | VM_HUGETLB | VM_INSERTPAGE |
1463                                  VM_NONLINEAR | VM_MIXEDMAP | VM_SAO))
1464                         return 0;               /* just ignore the advice */
1465
1466                 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
1467                         err = __ksm_enter(mm);
1468                         if (err)
1469                                 return err;
1470                 }
1471
1472                 *vm_flags |= VM_MERGEABLE;
1473                 break;
1474
1475         case MADV_UNMERGEABLE:
1476                 if (!(*vm_flags & VM_MERGEABLE))
1477                         return 0;               /* just ignore the advice */
1478
1479                 if (vma->anon_vma) {
1480                         err = unmerge_ksm_pages(vma, start, end);
1481                         if (err)
1482                                 return err;
1483                 }
1484
1485                 *vm_flags &= ~VM_MERGEABLE;
1486                 break;
1487         }
1488
1489         return 0;
1490 }
1491
1492 int __ksm_enter(struct mm_struct *mm)
1493 {
1494         struct mm_slot *mm_slot;
1495         int needs_wakeup;
1496
1497         mm_slot = alloc_mm_slot();
1498         if (!mm_slot)
1499                 return -ENOMEM;
1500
1501         /* Check ksm_run too?  Would need tighter locking */
1502         needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1503
1504         spin_lock(&ksm_mmlist_lock);
1505         insert_to_mm_slots_hash(mm, mm_slot);
1506         /*
1507          * Insert just behind the scanning cursor, to let the area settle
1508          * down a little; when fork is followed by immediate exec, we don't
1509          * want ksmd to waste time setting up and tearing down an rmap_list.
1510          */
1511         list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
1512         spin_unlock(&ksm_mmlist_lock);
1513
1514         set_bit(MMF_VM_MERGEABLE, &mm->flags);
1515         atomic_inc(&mm->mm_count);
1516
1517         if (needs_wakeup)
1518                 wake_up_interruptible(&ksm_thread_wait);
1519
1520         return 0;
1521 }
1522
1523 void __ksm_exit(struct mm_struct *mm)
1524 {
1525         struct mm_slot *mm_slot;
1526         int easy_to_free = 0;
1527
1528         /*
1529          * This process is exiting: if it's straightforward (as is the
1530          * case when ksmd was never running), free mm_slot immediately.
1531          * But if it's at the cursor or has rmap_items linked to it, use
1532          * mmap_sem to synchronize with any break_cows before pagetables
1533          * are freed, and leave the mm_slot on the list for ksmd to free.
1534          * Beware: ksm may already have noticed it exiting and freed the slot.
1535          */
1536
1537         spin_lock(&ksm_mmlist_lock);
1538         mm_slot = get_mm_slot(mm);
1539         if (mm_slot && ksm_scan.mm_slot != mm_slot) {
1540                 if (!mm_slot->rmap_list) {
1541                         hlist_del(&mm_slot->link);
1542                         list_del(&mm_slot->mm_list);
1543                         easy_to_free = 1;
1544                 } else {
1545                         list_move(&mm_slot->mm_list,
1546                                   &ksm_scan.mm_slot->mm_list);
1547                 }
1548         }
1549         spin_unlock(&ksm_mmlist_lock);
1550
1551         if (easy_to_free) {
1552                 free_mm_slot(mm_slot);
1553                 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1554                 mmdrop(mm);
1555         } else if (mm_slot) {
1556                 down_write(&mm->mmap_sem);
1557                 up_write(&mm->mmap_sem);
1558         }
1559 }
1560
1561 struct page *ksm_does_need_to_copy(struct page *page,
1562                         struct vm_area_struct *vma, unsigned long address)
1563 {
1564         struct page *new_page;
1565
1566         new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
1567         if (new_page) {
1568                 copy_user_highpage(new_page, page, address, vma);
1569
1570                 SetPageDirty(new_page);
1571                 __SetPageUptodate(new_page);
1572                 SetPageSwapBacked(new_page);
1573                 __set_page_locked(new_page);
1574
1575                 if (page_evictable(new_page, vma))
1576                         lru_cache_add_lru(new_page, LRU_ACTIVE_ANON);
1577                 else
1578                         add_page_to_unevictable_list(new_page);
1579         }
1580
1581         return new_page;
1582 }
1583
1584 int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg,
1585                         unsigned long *vm_flags)
1586 {
1587         struct stable_node *stable_node;
1588         struct rmap_item *rmap_item;
1589         struct hlist_node *hlist;
1590         unsigned int mapcount = page_mapcount(page);
1591         int referenced = 0;
1592         int search_new_forks = 0;
1593
1594         VM_BUG_ON(!PageKsm(page));
1595         VM_BUG_ON(!PageLocked(page));
1596
1597         stable_node = page_stable_node(page);
1598         if (!stable_node)
1599                 return 0;
1600 again:
1601         hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1602                 struct anon_vma *anon_vma = rmap_item->anon_vma;
1603                 struct anon_vma_chain *vmac;
1604                 struct vm_area_struct *vma;
1605
1606                 anon_vma_lock(anon_vma);
1607                 list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1608                         vma = vmac->vma;
1609                         if (rmap_item->address < vma->vm_start ||
1610                             rmap_item->address >= vma->vm_end)
1611                                 continue;
1612                         /*
1613                          * Initially we examine only the vma which covers this
1614                          * rmap_item; but later, if there is still work to do,
1615                          * we examine covering vmas in other mms: in case they
1616                          * were forked from the original since ksmd passed.
1617                          */
1618                         if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1619                                 continue;
1620
1621                         if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
1622                                 continue;
1623
1624                         referenced += page_referenced_one(page, vma,
1625                                 rmap_item->address, &mapcount, vm_flags);
1626                         if (!search_new_forks || !mapcount)
1627                                 break;
1628                 }
1629                 anon_vma_unlock(anon_vma);
1630                 if (!mapcount)
1631                         goto out;
1632         }
1633         if (!search_new_forks++)
1634                 goto again;
1635 out:
1636         return referenced;
1637 }
1638
1639 int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
1640 {
1641         struct stable_node *stable_node;
1642         struct hlist_node *hlist;
1643         struct rmap_item *rmap_item;
1644         int ret = SWAP_AGAIN;
1645         int search_new_forks = 0;
1646
1647         VM_BUG_ON(!PageKsm(page));
1648         VM_BUG_ON(!PageLocked(page));
1649
1650         stable_node = page_stable_node(page);
1651         if (!stable_node)
1652                 return SWAP_FAIL;
1653 again:
1654         hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1655                 struct anon_vma *anon_vma = rmap_item->anon_vma;
1656                 struct anon_vma_chain *vmac;
1657                 struct vm_area_struct *vma;
1658
1659                 anon_vma_lock(anon_vma);
1660                 list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1661                         vma = vmac->vma;
1662                         if (rmap_item->address < vma->vm_start ||
1663                             rmap_item->address >= vma->vm_end)
1664                                 continue;
1665                         /*
1666                          * Initially we examine only the vma which covers this
1667                          * rmap_item; but later, if there is still work to do,
1668                          * we examine covering vmas in other mms: in case they
1669                          * were forked from the original since ksmd passed.
1670                          */
1671                         if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1672                                 continue;
1673
1674                         ret = try_to_unmap_one(page, vma,
1675                                         rmap_item->address, flags);
1676                         if (ret != SWAP_AGAIN || !page_mapped(page)) {
1677                                 anon_vma_unlock(anon_vma);
1678                                 goto out;
1679                         }
1680                 }
1681                 anon_vma_unlock(anon_vma);
1682         }
1683         if (!search_new_forks++)
1684                 goto again;
1685 out:
1686         return ret;
1687 }
1688
1689 #ifdef CONFIG_MIGRATION
1690 int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *,
1691                   struct vm_area_struct *, unsigned long, void *), void *arg)
1692 {
1693         struct stable_node *stable_node;
1694         struct hlist_node *hlist;
1695         struct rmap_item *rmap_item;
1696         int ret = SWAP_AGAIN;
1697         int search_new_forks = 0;
1698
1699         VM_BUG_ON(!PageKsm(page));
1700         VM_BUG_ON(!PageLocked(page));
1701
1702         stable_node = page_stable_node(page);
1703         if (!stable_node)
1704                 return ret;
1705 again:
1706         hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1707                 struct anon_vma *anon_vma = rmap_item->anon_vma;
1708                 struct anon_vma_chain *vmac;
1709                 struct vm_area_struct *vma;
1710
1711                 anon_vma_lock(anon_vma);
1712                 list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1713                         vma = vmac->vma;
1714                         if (rmap_item->address < vma->vm_start ||
1715                             rmap_item->address >= vma->vm_end)
1716                                 continue;
1717                         /*
1718                          * Initially we examine only the vma which covers this
1719                          * rmap_item; but later, if there is still work to do,
1720                          * we examine covering vmas in other mms: in case they
1721                          * were forked from the original since ksmd passed.
1722                          */
1723                         if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1724                                 continue;
1725
1726                         ret = rmap_one(page, vma, rmap_item->address, arg);
1727                         if (ret != SWAP_AGAIN) {
1728                                 anon_vma_unlock(anon_vma);
1729                                 goto out;
1730                         }
1731                 }
1732                 anon_vma_unlock(anon_vma);
1733         }
1734         if (!search_new_forks++)
1735                 goto again;
1736 out:
1737         return ret;
1738 }
1739
1740 void ksm_migrate_page(struct page *newpage, struct page *oldpage)
1741 {
1742         struct stable_node *stable_node;
1743
1744         VM_BUG_ON(!PageLocked(oldpage));
1745         VM_BUG_ON(!PageLocked(newpage));
1746         VM_BUG_ON(newpage->mapping != oldpage->mapping);
1747
1748         stable_node = page_stable_node(newpage);
1749         if (stable_node) {
1750                 VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage));
1751                 stable_node->kpfn = page_to_pfn(newpage);
1752         }
1753 }
1754 #endif /* CONFIG_MIGRATION */
1755
1756 #ifdef CONFIG_MEMORY_HOTREMOVE
1757 static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn,
1758                                                  unsigned long end_pfn)
1759 {
1760         struct rb_node *node;
1761
1762         for (node = rb_first(&root_stable_tree); node; node = rb_next(node)) {
1763                 struct stable_node *stable_node;
1764
1765                 stable_node = rb_entry(node, struct stable_node, node);
1766                 if (stable_node->kpfn >= start_pfn &&
1767                     stable_node->kpfn < end_pfn)
1768                         return stable_node;
1769         }
1770         return NULL;
1771 }
1772
1773 static int ksm_memory_callback(struct notifier_block *self,
1774                                unsigned long action, void *arg)
1775 {
1776         struct memory_notify *mn = arg;
1777         struct stable_node *stable_node;
1778
1779         switch (action) {
1780         case MEM_GOING_OFFLINE:
1781                 /*
1782                  * Keep it very simple for now: just lock out ksmd and
1783                  * MADV_UNMERGEABLE while any memory is going offline.
1784                  * mutex_lock_nested() is necessary because lockdep was alarmed
1785                  * that here we take ksm_thread_mutex inside notifier chain
1786                  * mutex, and later take notifier chain mutex inside
1787                  * ksm_thread_mutex to unlock it.   But that's safe because both
1788                  * are inside mem_hotplug_mutex.
1789                  */
1790                 mutex_lock_nested(&ksm_thread_mutex, SINGLE_DEPTH_NESTING);
1791                 break;
1792
1793         case MEM_OFFLINE:
1794                 /*
1795                  * Most of the work is done by page migration; but there might
1796                  * be a few stable_nodes left over, still pointing to struct
1797                  * pages which have been offlined: prune those from the tree.
1798                  */
1799                 while ((stable_node = ksm_check_stable_tree(mn->start_pfn,
1800                                         mn->start_pfn + mn->nr_pages)) != NULL)
1801                         remove_node_from_stable_tree(stable_node);
1802                 /* fallthrough */
1803
1804         case MEM_CANCEL_OFFLINE:
1805                 mutex_unlock(&ksm_thread_mutex);
1806                 break;
1807         }
1808         return NOTIFY_OK;
1809 }
1810 #endif /* CONFIG_MEMORY_HOTREMOVE */
1811
1812 #ifdef CONFIG_SYSFS
1813 /*
1814  * This all compiles without CONFIG_SYSFS, but is a waste of space.
1815  */
1816
1817 #define KSM_ATTR_RO(_name) \
1818         static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
1819 #define KSM_ATTR(_name) \
1820         static struct kobj_attribute _name##_attr = \
1821                 __ATTR(_name, 0644, _name##_show, _name##_store)
1822
1823 static ssize_t sleep_millisecs_show(struct kobject *kobj,
1824                                     struct kobj_attribute *attr, char *buf)
1825 {
1826         return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
1827 }
1828
1829 static ssize_t sleep_millisecs_store(struct kobject *kobj,
1830                                      struct kobj_attribute *attr,
1831                                      const char *buf, size_t count)
1832 {
1833         unsigned long msecs;
1834         int err;
1835
1836         err = strict_strtoul(buf, 10, &msecs);
1837         if (err || msecs > UINT_MAX)
1838                 return -EINVAL;
1839
1840         ksm_thread_sleep_millisecs = msecs;
1841
1842         return count;
1843 }
1844 KSM_ATTR(sleep_millisecs);
1845
1846 static ssize_t pages_to_scan_show(struct kobject *kobj,
1847                                   struct kobj_attribute *attr, char *buf)
1848 {
1849         return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
1850 }
1851
1852 static ssize_t pages_to_scan_store(struct kobject *kobj,
1853                                    struct kobj_attribute *attr,
1854                                    const char *buf, size_t count)
1855 {
1856         int err;
1857         unsigned long nr_pages;
1858
1859         err = strict_strtoul(buf, 10, &nr_pages);
1860         if (err || nr_pages > UINT_MAX)
1861                 return -EINVAL;
1862
1863         ksm_thread_pages_to_scan = nr_pages;
1864
1865         return count;
1866 }
1867 KSM_ATTR(pages_to_scan);
1868
1869 static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
1870                         char *buf)
1871 {
1872         return sprintf(buf, "%u\n", ksm_run);
1873 }
1874
1875 static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
1876                          const char *buf, size_t count)
1877 {
1878         int err;
1879         unsigned long flags;
1880
1881         err = strict_strtoul(buf, 10, &flags);
1882         if (err || flags > UINT_MAX)
1883                 return -EINVAL;
1884         if (flags > KSM_RUN_UNMERGE)
1885                 return -EINVAL;
1886
1887         /*
1888          * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
1889          * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
1890          * breaking COW to free the pages_shared (but leaves mm_slots
1891          * on the list for when ksmd may be set running again).
1892          */
1893
1894         mutex_lock(&ksm_thread_mutex);
1895         if (ksm_run != flags) {
1896                 ksm_run = flags;
1897                 if (flags & KSM_RUN_UNMERGE) {
1898                         current->flags |= PF_OOM_ORIGIN;
1899                         err = unmerge_and_remove_all_rmap_items();
1900                         current->flags &= ~PF_OOM_ORIGIN;
1901                         if (err) {
1902                                 ksm_run = KSM_RUN_STOP;
1903                                 count = err;
1904                         }
1905                 }
1906         }
1907         mutex_unlock(&ksm_thread_mutex);
1908
1909         if (flags & KSM_RUN_MERGE)
1910                 wake_up_interruptible(&ksm_thread_wait);
1911
1912         return count;
1913 }
1914 KSM_ATTR(run);
1915
1916 static ssize_t pages_shared_show(struct kobject *kobj,
1917                                  struct kobj_attribute *attr, char *buf)
1918 {
1919         return sprintf(buf, "%lu\n", ksm_pages_shared);
1920 }
1921 KSM_ATTR_RO(pages_shared);
1922
1923 static ssize_t pages_sharing_show(struct kobject *kobj,
1924                                   struct kobj_attribute *attr, char *buf)
1925 {
1926         return sprintf(buf, "%lu\n", ksm_pages_sharing);
1927 }
1928 KSM_ATTR_RO(pages_sharing);
1929
1930 static ssize_t pages_unshared_show(struct kobject *kobj,
1931                                    struct kobj_attribute *attr, char *buf)
1932 {
1933         return sprintf(buf, "%lu\n", ksm_pages_unshared);
1934 }
1935 KSM_ATTR_RO(pages_unshared);
1936
1937 static ssize_t pages_volatile_show(struct kobject *kobj,
1938                                    struct kobj_attribute *attr, char *buf)
1939 {
1940         long ksm_pages_volatile;
1941
1942         ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
1943                                 - ksm_pages_sharing - ksm_pages_unshared;
1944         /*
1945          * It was not worth any locking to calculate that statistic,
1946          * but it might therefore sometimes be negative: conceal that.
1947          */
1948         if (ksm_pages_volatile < 0)
1949                 ksm_pages_volatile = 0;
1950         return sprintf(buf, "%ld\n", ksm_pages_volatile);
1951 }
1952 KSM_ATTR_RO(pages_volatile);
1953
1954 static ssize_t full_scans_show(struct kobject *kobj,
1955                                struct kobj_attribute *attr, char *buf)
1956 {
1957         return sprintf(buf, "%lu\n", ksm_scan.seqnr);
1958 }
1959 KSM_ATTR_RO(full_scans);
1960
1961 static struct attribute *ksm_attrs[] = {
1962         &sleep_millisecs_attr.attr,
1963         &pages_to_scan_attr.attr,
1964         &run_attr.attr,
1965         &pages_shared_attr.attr,
1966         &pages_sharing_attr.attr,
1967         &pages_unshared_attr.attr,
1968         &pages_volatile_attr.attr,
1969         &full_scans_attr.attr,
1970         NULL,
1971 };
1972
1973 static struct attribute_group ksm_attr_group = {
1974         .attrs = ksm_attrs,
1975         .name = "ksm",
1976 };
1977 #endif /* CONFIG_SYSFS */
1978
1979 static int __init ksm_init(void)
1980 {
1981         struct task_struct *ksm_thread;
1982         int err;
1983
1984         err = ksm_slab_init();
1985         if (err)
1986                 goto out;
1987
1988         ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
1989         if (IS_ERR(ksm_thread)) {
1990                 printk(KERN_ERR "ksm: creating kthread failed\n");
1991                 err = PTR_ERR(ksm_thread);
1992                 goto out_free;
1993         }
1994
1995 #ifdef CONFIG_SYSFS
1996         err = sysfs_create_group(mm_kobj, &ksm_attr_group);
1997         if (err) {
1998                 printk(KERN_ERR "ksm: register sysfs failed\n");
1999                 kthread_stop(ksm_thread);
2000                 goto out_free;
2001         }
2002 #else
2003         ksm_run = KSM_RUN_MERGE;        /* no way for user to start it */
2004
2005 #endif /* CONFIG_SYSFS */
2006
2007 #ifdef CONFIG_MEMORY_HOTREMOVE
2008         /*
2009          * Choose a high priority since the callback takes ksm_thread_mutex:
2010          * later callbacks could only be taking locks which nest within that.
2011          */
2012         hotplug_memory_notifier(ksm_memory_callback, 100);
2013 #endif
2014         return 0;
2015
2016 out_free:
2017         ksm_slab_free();
2018 out:
2019         return err;
2020 }
2021 module_init(ksm_init)