memcg: clear pc->mem_cgroup if necessary.
[linux-2.6.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/memcontrol.h>
32 #include <linux/rbtree.h>
33 #include <linux/memory.h>
34 #include <linux/mmu_notifier.h>
35 #include <linux/swap.h>
36 #include <linux/ksm.h>
37 #include <linux/hash.h>
38 #include <linux/freezer.h>
39 #include <linux/oom.h>
40
41 #include <asm/tlbflush.h>
42 #include "internal.h"
43
44 /*
45  * A few notes about the KSM scanning process,
46  * to make it easier to understand the data structures below:
47  *
48  * In order to reduce excessive scanning, KSM sorts the memory pages by their
49  * contents into a data structure that holds pointers to the pages' locations.
50  *
51  * Since the contents of the pages may change at any moment, KSM cannot just
52  * insert the pages into a normal sorted tree and expect it to find anything.
53  * Therefore KSM uses two data structures - the stable and the unstable tree.
54  *
55  * The stable tree holds pointers to all the merged pages (ksm pages), sorted
56  * by their contents.  Because each such page is write-protected, searching on
57  * this tree is fully assured to be working (except when pages are unmapped),
58  * and therefore this tree is called the stable tree.
59  *
60  * In addition to the stable tree, KSM uses a second data structure called the
61  * unstable tree: this tree holds pointers to pages which have been found to
62  * be "unchanged for a period of time".  The unstable tree sorts these pages
63  * by their contents, but since they are not write-protected, KSM cannot rely
64  * upon the unstable tree to work correctly - the unstable tree is liable to
65  * be corrupted as its contents are modified, and so it is called unstable.
66  *
67  * KSM solves this problem by several techniques:
68  *
69  * 1) The unstable tree is flushed every time KSM completes scanning all
70  *    memory areas, and then the tree is rebuilt again from the beginning.
71  * 2) KSM will only insert into the unstable tree, pages whose hash value
72  *    has not changed since the previous scan of all memory areas.
73  * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
74  *    colors of the nodes and not on their contents, assuring that even when
75  *    the tree gets "corrupted" it won't get out of balance, so scanning time
76  *    remains the same (also, searching and inserting nodes in an rbtree uses
77  *    the same algorithm, so we have no overhead when we flush and rebuild).
78  * 4) KSM never flushes the stable tree, which means that even if it were to
79  *    take 10 attempts to find a page in the unstable tree, once it is found,
80  *    it is secured in the stable tree.  (When we scan a new page, we first
81  *    compare it against the stable tree, and then against the unstable tree.)
82  */
83
84 /**
85  * struct mm_slot - ksm information per mm that is being scanned
86  * @link: link to the mm_slots hash list
87  * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
88  * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
89  * @mm: the mm that this information is valid for
90  */
91 struct mm_slot {
92         struct hlist_node link;
93         struct list_head mm_list;
94         struct rmap_item *rmap_list;
95         struct mm_struct *mm;
96 };
97
98 /**
99  * struct ksm_scan - cursor for scanning
100  * @mm_slot: the current mm_slot we are scanning
101  * @address: the next address inside that to be scanned
102  * @rmap_list: link to the next rmap to be scanned in the rmap_list
103  * @seqnr: count of completed full scans (needed when removing unstable node)
104  *
105  * There is only the one ksm_scan instance of this cursor structure.
106  */
107 struct ksm_scan {
108         struct mm_slot *mm_slot;
109         unsigned long address;
110         struct rmap_item **rmap_list;
111         unsigned long seqnr;
112 };
113
114 /**
115  * struct stable_node - node of the stable rbtree
116  * @node: rb node of this ksm page in the stable tree
117  * @hlist: hlist head of rmap_items using this ksm page
118  * @kpfn: page frame number of this ksm page
119  */
120 struct stable_node {
121         struct rb_node node;
122         struct hlist_head hlist;
123         unsigned long kpfn;
124 };
125
126 /**
127  * struct rmap_item - reverse mapping item for virtual addresses
128  * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
129  * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
130  * @mm: the memory structure this rmap_item is pointing into
131  * @address: the virtual address this rmap_item tracks (+ flags in low bits)
132  * @oldchecksum: previous checksum of the page at that virtual address
133  * @node: rb node of this rmap_item in the unstable tree
134  * @head: pointer to stable_node heading this list in the stable tree
135  * @hlist: link into hlist of rmap_items hanging off that stable_node
136  */
137 struct rmap_item {
138         struct rmap_item *rmap_list;
139         struct anon_vma *anon_vma;      /* when stable */
140         struct mm_struct *mm;
141         unsigned long address;          /* + low bits used for flags below */
142         unsigned int oldchecksum;       /* when unstable */
143         union {
144                 struct rb_node node;    /* when node of unstable tree */
145                 struct {                /* when listed from stable tree */
146                         struct stable_node *head;
147                         struct hlist_node hlist;
148                 };
149         };
150 };
151
152 #define SEQNR_MASK      0x0ff   /* low bits of unstable tree seqnr */
153 #define UNSTABLE_FLAG   0x100   /* is a node of the unstable tree */
154 #define STABLE_FLAG     0x200   /* is listed from the stable tree */
155
156 /* The stable and unstable tree heads */
157 static struct rb_root root_stable_tree = RB_ROOT;
158 static struct rb_root root_unstable_tree = RB_ROOT;
159
160 #define MM_SLOTS_HASH_SHIFT 10
161 #define MM_SLOTS_HASH_HEADS (1 << MM_SLOTS_HASH_SHIFT)
162 static struct hlist_head mm_slots_hash[MM_SLOTS_HASH_HEADS];
163
164 static struct mm_slot ksm_mm_head = {
165         .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
166 };
167 static struct ksm_scan ksm_scan = {
168         .mm_slot = &ksm_mm_head,
169 };
170
171 static struct kmem_cache *rmap_item_cache;
172 static struct kmem_cache *stable_node_cache;
173 static struct kmem_cache *mm_slot_cache;
174
175 /* The number of nodes in the stable tree */
176 static unsigned long ksm_pages_shared;
177
178 /* The number of page slots additionally sharing those nodes */
179 static unsigned long ksm_pages_sharing;
180
181 /* The number of nodes in the unstable tree */
182 static unsigned long ksm_pages_unshared;
183
184 /* The number of rmap_items in use: to calculate pages_volatile */
185 static unsigned long ksm_rmap_items;
186
187 /* Number of pages ksmd should scan in one batch */
188 static unsigned int ksm_thread_pages_to_scan = 100;
189
190 /* Milliseconds ksmd should sleep between batches */
191 static unsigned int ksm_thread_sleep_millisecs = 20;
192
193 #define KSM_RUN_STOP    0
194 #define KSM_RUN_MERGE   1
195 #define KSM_RUN_UNMERGE 2
196 static unsigned int ksm_run = KSM_RUN_STOP;
197
198 static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
199 static DEFINE_MUTEX(ksm_thread_mutex);
200 static DEFINE_SPINLOCK(ksm_mmlist_lock);
201
202 #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
203                 sizeof(struct __struct), __alignof__(struct __struct),\
204                 (__flags), NULL)
205
206 static int __init ksm_slab_init(void)
207 {
208         rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
209         if (!rmap_item_cache)
210                 goto out;
211
212         stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
213         if (!stable_node_cache)
214                 goto out_free1;
215
216         mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
217         if (!mm_slot_cache)
218                 goto out_free2;
219
220         return 0;
221
222 out_free2:
223         kmem_cache_destroy(stable_node_cache);
224 out_free1:
225         kmem_cache_destroy(rmap_item_cache);
226 out:
227         return -ENOMEM;
228 }
229
230 static void __init ksm_slab_free(void)
231 {
232         kmem_cache_destroy(mm_slot_cache);
233         kmem_cache_destroy(stable_node_cache);
234         kmem_cache_destroy(rmap_item_cache);
235         mm_slot_cache = NULL;
236 }
237
238 static inline struct rmap_item *alloc_rmap_item(void)
239 {
240         struct rmap_item *rmap_item;
241
242         rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
243         if (rmap_item)
244                 ksm_rmap_items++;
245         return rmap_item;
246 }
247
248 static inline void free_rmap_item(struct rmap_item *rmap_item)
249 {
250         ksm_rmap_items--;
251         rmap_item->mm = NULL;   /* debug safety */
252         kmem_cache_free(rmap_item_cache, rmap_item);
253 }
254
255 static inline struct stable_node *alloc_stable_node(void)
256 {
257         return kmem_cache_alloc(stable_node_cache, GFP_KERNEL);
258 }
259
260 static inline void free_stable_node(struct stable_node *stable_node)
261 {
262         kmem_cache_free(stable_node_cache, stable_node);
263 }
264
265 static inline struct mm_slot *alloc_mm_slot(void)
266 {
267         if (!mm_slot_cache)     /* initialization failed */
268                 return NULL;
269         return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
270 }
271
272 static inline void free_mm_slot(struct mm_slot *mm_slot)
273 {
274         kmem_cache_free(mm_slot_cache, mm_slot);
275 }
276
277 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
278 {
279         struct mm_slot *mm_slot;
280         struct hlist_head *bucket;
281         struct hlist_node *node;
282
283         bucket = &mm_slots_hash[hash_ptr(mm, MM_SLOTS_HASH_SHIFT)];
284         hlist_for_each_entry(mm_slot, node, bucket, link) {
285                 if (mm == mm_slot->mm)
286                         return mm_slot;
287         }
288         return NULL;
289 }
290
291 static void insert_to_mm_slots_hash(struct mm_struct *mm,
292                                     struct mm_slot *mm_slot)
293 {
294         struct hlist_head *bucket;
295
296         bucket = &mm_slots_hash[hash_ptr(mm, MM_SLOTS_HASH_SHIFT)];
297         mm_slot->mm = mm;
298         hlist_add_head(&mm_slot->link, bucket);
299 }
300
301 static inline int in_stable_tree(struct rmap_item *rmap_item)
302 {
303         return rmap_item->address & STABLE_FLAG;
304 }
305
306 /*
307  * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
308  * page tables after it has passed through ksm_exit() - which, if necessary,
309  * takes mmap_sem briefly to serialize against them.  ksm_exit() does not set
310  * a special flag: they can just back out as soon as mm_users goes to zero.
311  * ksm_test_exit() is used throughout to make this test for exit: in some
312  * places for correctness, in some places just to avoid unnecessary work.
313  */
314 static inline bool ksm_test_exit(struct mm_struct *mm)
315 {
316         return atomic_read(&mm->mm_users) == 0;
317 }
318
319 /*
320  * We use break_ksm to break COW on a ksm page: it's a stripped down
321  *
322  *      if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
323  *              put_page(page);
324  *
325  * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
326  * in case the application has unmapped and remapped mm,addr meanwhile.
327  * Could a ksm page appear anywhere else?  Actually yes, in a VM_PFNMAP
328  * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
329  */
330 static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
331 {
332         struct page *page;
333         int ret = 0;
334
335         do {
336                 cond_resched();
337                 page = follow_page(vma, addr, FOLL_GET);
338                 if (IS_ERR_OR_NULL(page))
339                         break;
340                 if (PageKsm(page))
341                         ret = handle_mm_fault(vma->vm_mm, vma, addr,
342                                                         FAULT_FLAG_WRITE);
343                 else
344                         ret = VM_FAULT_WRITE;
345                 put_page(page);
346         } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM)));
347         /*
348          * We must loop because handle_mm_fault() may back out if there's
349          * any difficulty e.g. if pte accessed bit gets updated concurrently.
350          *
351          * VM_FAULT_WRITE is what we have been hoping for: it indicates that
352          * COW has been broken, even if the vma does not permit VM_WRITE;
353          * but note that a concurrent fault might break PageKsm for us.
354          *
355          * VM_FAULT_SIGBUS could occur if we race with truncation of the
356          * backing file, which also invalidates anonymous pages: that's
357          * okay, that truncation will have unmapped the PageKsm for us.
358          *
359          * VM_FAULT_OOM: at the time of writing (late July 2009), setting
360          * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
361          * current task has TIF_MEMDIE set, and will be OOM killed on return
362          * to user; and ksmd, having no mm, would never be chosen for that.
363          *
364          * But if the mm is in a limited mem_cgroup, then the fault may fail
365          * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
366          * even ksmd can fail in this way - though it's usually breaking ksm
367          * just to undo a merge it made a moment before, so unlikely to oom.
368          *
369          * That's a pity: we might therefore have more kernel pages allocated
370          * than we're counting as nodes in the stable tree; but ksm_do_scan
371          * will retry to break_cow on each pass, so should recover the page
372          * in due course.  The important thing is to not let VM_MERGEABLE
373          * be cleared while any such pages might remain in the area.
374          */
375         return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
376 }
377
378 static void break_cow(struct rmap_item *rmap_item)
379 {
380         struct mm_struct *mm = rmap_item->mm;
381         unsigned long addr = rmap_item->address;
382         struct vm_area_struct *vma;
383
384         /*
385          * It is not an accident that whenever we want to break COW
386          * to undo, we also need to drop a reference to the anon_vma.
387          */
388         put_anon_vma(rmap_item->anon_vma);
389
390         down_read(&mm->mmap_sem);
391         if (ksm_test_exit(mm))
392                 goto out;
393         vma = find_vma(mm, addr);
394         if (!vma || vma->vm_start > addr)
395                 goto out;
396         if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
397                 goto out;
398         break_ksm(vma, addr);
399 out:
400         up_read(&mm->mmap_sem);
401 }
402
403 static struct page *page_trans_compound_anon(struct page *page)
404 {
405         if (PageTransCompound(page)) {
406                 struct page *head = compound_trans_head(page);
407                 /*
408                  * head may actually be splitted and freed from under
409                  * us but it's ok here.
410                  */
411                 if (PageAnon(head))
412                         return head;
413         }
414         return NULL;
415 }
416
417 static struct page *get_mergeable_page(struct rmap_item *rmap_item)
418 {
419         struct mm_struct *mm = rmap_item->mm;
420         unsigned long addr = rmap_item->address;
421         struct vm_area_struct *vma;
422         struct page *page;
423
424         down_read(&mm->mmap_sem);
425         if (ksm_test_exit(mm))
426                 goto out;
427         vma = find_vma(mm, addr);
428         if (!vma || vma->vm_start > addr)
429                 goto out;
430         if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
431                 goto out;
432
433         page = follow_page(vma, addr, FOLL_GET);
434         if (IS_ERR_OR_NULL(page))
435                 goto out;
436         if (PageAnon(page) || page_trans_compound_anon(page)) {
437                 flush_anon_page(vma, page, addr);
438                 flush_dcache_page(page);
439         } else {
440                 put_page(page);
441 out:            page = NULL;
442         }
443         up_read(&mm->mmap_sem);
444         return page;
445 }
446
447 static void remove_node_from_stable_tree(struct stable_node *stable_node)
448 {
449         struct rmap_item *rmap_item;
450         struct hlist_node *hlist;
451
452         hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
453                 if (rmap_item->hlist.next)
454                         ksm_pages_sharing--;
455                 else
456                         ksm_pages_shared--;
457                 put_anon_vma(rmap_item->anon_vma);
458                 rmap_item->address &= PAGE_MASK;
459                 cond_resched();
460         }
461
462         rb_erase(&stable_node->node, &root_stable_tree);
463         free_stable_node(stable_node);
464 }
465
466 /*
467  * get_ksm_page: checks if the page indicated by the stable node
468  * is still its ksm page, despite having held no reference to it.
469  * In which case we can trust the content of the page, and it
470  * returns the gotten page; but if the page has now been zapped,
471  * remove the stale node from the stable tree and return NULL.
472  *
473  * You would expect the stable_node to hold a reference to the ksm page.
474  * But if it increments the page's count, swapping out has to wait for
475  * ksmd to come around again before it can free the page, which may take
476  * seconds or even minutes: much too unresponsive.  So instead we use a
477  * "keyhole reference": access to the ksm page from the stable node peeps
478  * out through its keyhole to see if that page still holds the right key,
479  * pointing back to this stable node.  This relies on freeing a PageAnon
480  * page to reset its page->mapping to NULL, and relies on no other use of
481  * a page to put something that might look like our key in page->mapping.
482  *
483  * include/linux/pagemap.h page_cache_get_speculative() is a good reference,
484  * but this is different - made simpler by ksm_thread_mutex being held, but
485  * interesting for assuming that no other use of the struct page could ever
486  * put our expected_mapping into page->mapping (or a field of the union which
487  * coincides with page->mapping).  The RCU calls are not for KSM at all, but
488  * to keep the page_count protocol described with page_cache_get_speculative.
489  *
490  * Note: it is possible that get_ksm_page() will return NULL one moment,
491  * then page the next, if the page is in between page_freeze_refs() and
492  * page_unfreeze_refs(): this shouldn't be a problem anywhere, the page
493  * is on its way to being freed; but it is an anomaly to bear in mind.
494  */
495 static struct page *get_ksm_page(struct stable_node *stable_node)
496 {
497         struct page *page;
498         void *expected_mapping;
499
500         page = pfn_to_page(stable_node->kpfn);
501         expected_mapping = (void *)stable_node +
502                                 (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
503         rcu_read_lock();
504         if (page->mapping != expected_mapping)
505                 goto stale;
506         if (!get_page_unless_zero(page))
507                 goto stale;
508         if (page->mapping != expected_mapping) {
509                 put_page(page);
510                 goto stale;
511         }
512         rcu_read_unlock();
513         return page;
514 stale:
515         rcu_read_unlock();
516         remove_node_from_stable_tree(stable_node);
517         return NULL;
518 }
519
520 /*
521  * Removing rmap_item from stable or unstable tree.
522  * This function will clean the information from the stable/unstable tree.
523  */
524 static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
525 {
526         if (rmap_item->address & STABLE_FLAG) {
527                 struct stable_node *stable_node;
528                 struct page *page;
529
530                 stable_node = rmap_item->head;
531                 page = get_ksm_page(stable_node);
532                 if (!page)
533                         goto out;
534
535                 lock_page(page);
536                 hlist_del(&rmap_item->hlist);
537                 unlock_page(page);
538                 put_page(page);
539
540                 if (stable_node->hlist.first)
541                         ksm_pages_sharing--;
542                 else
543                         ksm_pages_shared--;
544
545                 put_anon_vma(rmap_item->anon_vma);
546                 rmap_item->address &= PAGE_MASK;
547
548         } else if (rmap_item->address & UNSTABLE_FLAG) {
549                 unsigned char age;
550                 /*
551                  * Usually ksmd can and must skip the rb_erase, because
552                  * root_unstable_tree was already reset to RB_ROOT.
553                  * But be careful when an mm is exiting: do the rb_erase
554                  * if this rmap_item was inserted by this scan, rather
555                  * than left over from before.
556                  */
557                 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
558                 BUG_ON(age > 1);
559                 if (!age)
560                         rb_erase(&rmap_item->node, &root_unstable_tree);
561
562                 ksm_pages_unshared--;
563                 rmap_item->address &= PAGE_MASK;
564         }
565 out:
566         cond_resched();         /* we're called from many long loops */
567 }
568
569 static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
570                                        struct rmap_item **rmap_list)
571 {
572         while (*rmap_list) {
573                 struct rmap_item *rmap_item = *rmap_list;
574                 *rmap_list = rmap_item->rmap_list;
575                 remove_rmap_item_from_tree(rmap_item);
576                 free_rmap_item(rmap_item);
577         }
578 }
579
580 /*
581  * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather
582  * than check every pte of a given vma, the locking doesn't quite work for
583  * that - an rmap_item is assigned to the stable tree after inserting ksm
584  * page and upping mmap_sem.  Nor does it fit with the way we skip dup'ing
585  * rmap_items from parent to child at fork time (so as not to waste time
586  * if exit comes before the next scan reaches it).
587  *
588  * Similarly, although we'd like to remove rmap_items (so updating counts
589  * and freeing memory) when unmerging an area, it's easier to leave that
590  * to the next pass of ksmd - consider, for example, how ksmd might be
591  * in cmp_and_merge_page on one of the rmap_items we would be removing.
592  */
593 static int unmerge_ksm_pages(struct vm_area_struct *vma,
594                              unsigned long start, unsigned long end)
595 {
596         unsigned long addr;
597         int err = 0;
598
599         for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
600                 if (ksm_test_exit(vma->vm_mm))
601                         break;
602                 if (signal_pending(current))
603                         err = -ERESTARTSYS;
604                 else
605                         err = break_ksm(vma, addr);
606         }
607         return err;
608 }
609
610 #ifdef CONFIG_SYSFS
611 /*
612  * Only called through the sysfs control interface:
613  */
614 static int unmerge_and_remove_all_rmap_items(void)
615 {
616         struct mm_slot *mm_slot;
617         struct mm_struct *mm;
618         struct vm_area_struct *vma;
619         int err = 0;
620
621         spin_lock(&ksm_mmlist_lock);
622         ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
623                                                 struct mm_slot, mm_list);
624         spin_unlock(&ksm_mmlist_lock);
625
626         for (mm_slot = ksm_scan.mm_slot;
627                         mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
628                 mm = mm_slot->mm;
629                 down_read(&mm->mmap_sem);
630                 for (vma = mm->mmap; vma; vma = vma->vm_next) {
631                         if (ksm_test_exit(mm))
632                                 break;
633                         if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
634                                 continue;
635                         err = unmerge_ksm_pages(vma,
636                                                 vma->vm_start, vma->vm_end);
637                         if (err)
638                                 goto error;
639                 }
640
641                 remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
642
643                 spin_lock(&ksm_mmlist_lock);
644                 ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
645                                                 struct mm_slot, mm_list);
646                 if (ksm_test_exit(mm)) {
647                         hlist_del(&mm_slot->link);
648                         list_del(&mm_slot->mm_list);
649                         spin_unlock(&ksm_mmlist_lock);
650
651                         free_mm_slot(mm_slot);
652                         clear_bit(MMF_VM_MERGEABLE, &mm->flags);
653                         up_read(&mm->mmap_sem);
654                         mmdrop(mm);
655                 } else {
656                         spin_unlock(&ksm_mmlist_lock);
657                         up_read(&mm->mmap_sem);
658                 }
659         }
660
661         ksm_scan.seqnr = 0;
662         return 0;
663
664 error:
665         up_read(&mm->mmap_sem);
666         spin_lock(&ksm_mmlist_lock);
667         ksm_scan.mm_slot = &ksm_mm_head;
668         spin_unlock(&ksm_mmlist_lock);
669         return err;
670 }
671 #endif /* CONFIG_SYSFS */
672
673 static u32 calc_checksum(struct page *page)
674 {
675         u32 checksum;
676         void *addr = kmap_atomic(page, KM_USER0);
677         checksum = jhash2(addr, PAGE_SIZE / 4, 17);
678         kunmap_atomic(addr, KM_USER0);
679         return checksum;
680 }
681
682 static int memcmp_pages(struct page *page1, struct page *page2)
683 {
684         char *addr1, *addr2;
685         int ret;
686
687         addr1 = kmap_atomic(page1, KM_USER0);
688         addr2 = kmap_atomic(page2, KM_USER1);
689         ret = memcmp(addr1, addr2, PAGE_SIZE);
690         kunmap_atomic(addr2, KM_USER1);
691         kunmap_atomic(addr1, KM_USER0);
692         return ret;
693 }
694
695 static inline int pages_identical(struct page *page1, struct page *page2)
696 {
697         return !memcmp_pages(page1, page2);
698 }
699
700 static int write_protect_page(struct vm_area_struct *vma, struct page *page,
701                               pte_t *orig_pte)
702 {
703         struct mm_struct *mm = vma->vm_mm;
704         unsigned long addr;
705         pte_t *ptep;
706         spinlock_t *ptl;
707         int swapped;
708         int err = -EFAULT;
709
710         addr = page_address_in_vma(page, vma);
711         if (addr == -EFAULT)
712                 goto out;
713
714         BUG_ON(PageTransCompound(page));
715         ptep = page_check_address(page, mm, addr, &ptl, 0);
716         if (!ptep)
717                 goto out;
718
719         if (pte_write(*ptep) || pte_dirty(*ptep)) {
720                 pte_t entry;
721
722                 swapped = PageSwapCache(page);
723                 flush_cache_page(vma, addr, page_to_pfn(page));
724                 /*
725                  * Ok this is tricky, when get_user_pages_fast() run it doesn't
726                  * take any lock, therefore the check that we are going to make
727                  * with the pagecount against the mapcount is racey and
728                  * O_DIRECT can happen right after the check.
729                  * So we clear the pte and flush the tlb before the check
730                  * this assure us that no O_DIRECT can happen after the check
731                  * or in the middle of the check.
732                  */
733                 entry = ptep_clear_flush(vma, addr, ptep);
734                 /*
735                  * Check that no O_DIRECT or similar I/O is in progress on the
736                  * page
737                  */
738                 if (page_mapcount(page) + 1 + swapped != page_count(page)) {
739                         set_pte_at(mm, addr, ptep, entry);
740                         goto out_unlock;
741                 }
742                 if (pte_dirty(entry))
743                         set_page_dirty(page);
744                 entry = pte_mkclean(pte_wrprotect(entry));
745                 set_pte_at_notify(mm, addr, ptep, entry);
746         }
747         *orig_pte = *ptep;
748         err = 0;
749
750 out_unlock:
751         pte_unmap_unlock(ptep, ptl);
752 out:
753         return err;
754 }
755
756 /**
757  * replace_page - replace page in vma by new ksm page
758  * @vma:      vma that holds the pte pointing to page
759  * @page:     the page we are replacing by kpage
760  * @kpage:    the ksm page we replace page by
761  * @orig_pte: the original value of the pte
762  *
763  * Returns 0 on success, -EFAULT on failure.
764  */
765 static int replace_page(struct vm_area_struct *vma, struct page *page,
766                         struct page *kpage, pte_t orig_pte)
767 {
768         struct mm_struct *mm = vma->vm_mm;
769         pgd_t *pgd;
770         pud_t *pud;
771         pmd_t *pmd;
772         pte_t *ptep;
773         spinlock_t *ptl;
774         unsigned long addr;
775         int err = -EFAULT;
776
777         addr = page_address_in_vma(page, vma);
778         if (addr == -EFAULT)
779                 goto out;
780
781         pgd = pgd_offset(mm, addr);
782         if (!pgd_present(*pgd))
783                 goto out;
784
785         pud = pud_offset(pgd, addr);
786         if (!pud_present(*pud))
787                 goto out;
788
789         pmd = pmd_offset(pud, addr);
790         BUG_ON(pmd_trans_huge(*pmd));
791         if (!pmd_present(*pmd))
792                 goto out;
793
794         ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
795         if (!pte_same(*ptep, orig_pte)) {
796                 pte_unmap_unlock(ptep, ptl);
797                 goto out;
798         }
799
800         get_page(kpage);
801         page_add_anon_rmap(kpage, vma, addr);
802
803         flush_cache_page(vma, addr, pte_pfn(*ptep));
804         ptep_clear_flush(vma, addr, ptep);
805         set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
806
807         page_remove_rmap(page);
808         if (!page_mapped(page))
809                 try_to_free_swap(page);
810         put_page(page);
811
812         pte_unmap_unlock(ptep, ptl);
813         err = 0;
814 out:
815         return err;
816 }
817
818 static int page_trans_compound_anon_split(struct page *page)
819 {
820         int ret = 0;
821         struct page *transhuge_head = page_trans_compound_anon(page);
822         if (transhuge_head) {
823                 /* Get the reference on the head to split it. */
824                 if (get_page_unless_zero(transhuge_head)) {
825                         /*
826                          * Recheck we got the reference while the head
827                          * was still anonymous.
828                          */
829                         if (PageAnon(transhuge_head))
830                                 ret = split_huge_page(transhuge_head);
831                         else
832                                 /*
833                                  * Retry later if split_huge_page run
834                                  * from under us.
835                                  */
836                                 ret = 1;
837                         put_page(transhuge_head);
838                 } else
839                         /* Retry later if split_huge_page run from under us. */
840                         ret = 1;
841         }
842         return ret;
843 }
844
845 /*
846  * try_to_merge_one_page - take two pages and merge them into one
847  * @vma: the vma that holds the pte pointing to page
848  * @page: the PageAnon page that we want to replace with kpage
849  * @kpage: the PageKsm page that we want to map instead of page,
850  *         or NULL the first time when we want to use page as kpage.
851  *
852  * This function returns 0 if the pages were merged, -EFAULT otherwise.
853  */
854 static int try_to_merge_one_page(struct vm_area_struct *vma,
855                                  struct page *page, struct page *kpage)
856 {
857         pte_t orig_pte = __pte(0);
858         int err = -EFAULT;
859
860         if (page == kpage)                      /* ksm page forked */
861                 return 0;
862
863         if (!(vma->vm_flags & VM_MERGEABLE))
864                 goto out;
865         if (PageTransCompound(page) && page_trans_compound_anon_split(page))
866                 goto out;
867         BUG_ON(PageTransCompound(page));
868         if (!PageAnon(page))
869                 goto out;
870
871         /*
872          * We need the page lock to read a stable PageSwapCache in
873          * write_protect_page().  We use trylock_page() instead of
874          * lock_page() because we don't want to wait here - we
875          * prefer to continue scanning and merging different pages,
876          * then come back to this page when it is unlocked.
877          */
878         if (!trylock_page(page))
879                 goto out;
880         /*
881          * If this anonymous page is mapped only here, its pte may need
882          * to be write-protected.  If it's mapped elsewhere, all of its
883          * ptes are necessarily already write-protected.  But in either
884          * case, we need to lock and check page_count is not raised.
885          */
886         if (write_protect_page(vma, page, &orig_pte) == 0) {
887                 if (!kpage) {
888                         /*
889                          * While we hold page lock, upgrade page from
890                          * PageAnon+anon_vma to PageKsm+NULL stable_node:
891                          * stable_tree_insert() will update stable_node.
892                          */
893                         set_page_stable_node(page, NULL);
894                         mark_page_accessed(page);
895                         err = 0;
896                 } else if (pages_identical(page, kpage))
897                         err = replace_page(vma, page, kpage, orig_pte);
898         }
899
900         if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
901                 munlock_vma_page(page);
902                 if (!PageMlocked(kpage)) {
903                         unlock_page(page);
904                         lock_page(kpage);
905                         mlock_vma_page(kpage);
906                         page = kpage;           /* for final unlock */
907                 }
908         }
909
910         unlock_page(page);
911 out:
912         return err;
913 }
914
915 /*
916  * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
917  * but no new kernel page is allocated: kpage must already be a ksm page.
918  *
919  * This function returns 0 if the pages were merged, -EFAULT otherwise.
920  */
921 static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
922                                       struct page *page, struct page *kpage)
923 {
924         struct mm_struct *mm = rmap_item->mm;
925         struct vm_area_struct *vma;
926         int err = -EFAULT;
927
928         down_read(&mm->mmap_sem);
929         if (ksm_test_exit(mm))
930                 goto out;
931         vma = find_vma(mm, rmap_item->address);
932         if (!vma || vma->vm_start > rmap_item->address)
933                 goto out;
934
935         err = try_to_merge_one_page(vma, page, kpage);
936         if (err)
937                 goto out;
938
939         /* Must get reference to anon_vma while still holding mmap_sem */
940         rmap_item->anon_vma = vma->anon_vma;
941         get_anon_vma(vma->anon_vma);
942 out:
943         up_read(&mm->mmap_sem);
944         return err;
945 }
946
947 /*
948  * try_to_merge_two_pages - take two identical pages and prepare them
949  * to be merged into one page.
950  *
951  * This function returns the kpage if we successfully merged two identical
952  * pages into one ksm page, NULL otherwise.
953  *
954  * Note that this function upgrades page to ksm page: if one of the pages
955  * is already a ksm page, try_to_merge_with_ksm_page should be used.
956  */
957 static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
958                                            struct page *page,
959                                            struct rmap_item *tree_rmap_item,
960                                            struct page *tree_page)
961 {
962         int err;
963
964         err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
965         if (!err) {
966                 err = try_to_merge_with_ksm_page(tree_rmap_item,
967                                                         tree_page, page);
968                 /*
969                  * If that fails, we have a ksm page with only one pte
970                  * pointing to it: so break it.
971                  */
972                 if (err)
973                         break_cow(rmap_item);
974         }
975         return err ? NULL : page;
976 }
977
978 /*
979  * stable_tree_search - search for page inside the stable tree
980  *
981  * This function checks if there is a page inside the stable tree
982  * with identical content to the page that we are scanning right now.
983  *
984  * This function returns the stable tree node of identical content if found,
985  * NULL otherwise.
986  */
987 static struct page *stable_tree_search(struct page *page)
988 {
989         struct rb_node *node = root_stable_tree.rb_node;
990         struct stable_node *stable_node;
991
992         stable_node = page_stable_node(page);
993         if (stable_node) {                      /* ksm page forked */
994                 get_page(page);
995                 return page;
996         }
997
998         while (node) {
999                 struct page *tree_page;
1000                 int ret;
1001
1002                 cond_resched();
1003                 stable_node = rb_entry(node, struct stable_node, node);
1004                 tree_page = get_ksm_page(stable_node);
1005                 if (!tree_page)
1006                         return NULL;
1007
1008                 ret = memcmp_pages(page, tree_page);
1009
1010                 if (ret < 0) {
1011                         put_page(tree_page);
1012                         node = node->rb_left;
1013                 } else if (ret > 0) {
1014                         put_page(tree_page);
1015                         node = node->rb_right;
1016                 } else
1017                         return tree_page;
1018         }
1019
1020         return NULL;
1021 }
1022
1023 /*
1024  * stable_tree_insert - insert rmap_item pointing to new ksm page
1025  * into the stable tree.
1026  *
1027  * This function returns the stable tree node just allocated on success,
1028  * NULL otherwise.
1029  */
1030 static struct stable_node *stable_tree_insert(struct page *kpage)
1031 {
1032         struct rb_node **new = &root_stable_tree.rb_node;
1033         struct rb_node *parent = NULL;
1034         struct stable_node *stable_node;
1035
1036         while (*new) {
1037                 struct page *tree_page;
1038                 int ret;
1039
1040                 cond_resched();
1041                 stable_node = rb_entry(*new, struct stable_node, node);
1042                 tree_page = get_ksm_page(stable_node);
1043                 if (!tree_page)
1044                         return NULL;
1045
1046                 ret = memcmp_pages(kpage, tree_page);
1047                 put_page(tree_page);
1048
1049                 parent = *new;
1050                 if (ret < 0)
1051                         new = &parent->rb_left;
1052                 else if (ret > 0)
1053                         new = &parent->rb_right;
1054                 else {
1055                         /*
1056                          * It is not a bug that stable_tree_search() didn't
1057                          * find this node: because at that time our page was
1058                          * not yet write-protected, so may have changed since.
1059                          */
1060                         return NULL;
1061                 }
1062         }
1063
1064         stable_node = alloc_stable_node();
1065         if (!stable_node)
1066                 return NULL;
1067
1068         rb_link_node(&stable_node->node, parent, new);
1069         rb_insert_color(&stable_node->node, &root_stable_tree);
1070
1071         INIT_HLIST_HEAD(&stable_node->hlist);
1072
1073         stable_node->kpfn = page_to_pfn(kpage);
1074         set_page_stable_node(kpage, stable_node);
1075
1076         return stable_node;
1077 }
1078
1079 /*
1080  * unstable_tree_search_insert - search for identical page,
1081  * else insert rmap_item into the unstable tree.
1082  *
1083  * This function searches for a page in the unstable tree identical to the
1084  * page currently being scanned; and if no identical page is found in the
1085  * tree, we insert rmap_item as a new object into the unstable tree.
1086  *
1087  * This function returns pointer to rmap_item found to be identical
1088  * to the currently scanned page, NULL otherwise.
1089  *
1090  * This function does both searching and inserting, because they share
1091  * the same walking algorithm in an rbtree.
1092  */
1093 static
1094 struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1095                                               struct page *page,
1096                                               struct page **tree_pagep)
1097
1098 {
1099         struct rb_node **new = &root_unstable_tree.rb_node;
1100         struct rb_node *parent = NULL;
1101
1102         while (*new) {
1103                 struct rmap_item *tree_rmap_item;
1104                 struct page *tree_page;
1105                 int ret;
1106
1107                 cond_resched();
1108                 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1109                 tree_page = get_mergeable_page(tree_rmap_item);
1110                 if (IS_ERR_OR_NULL(tree_page))
1111                         return NULL;
1112
1113                 /*
1114                  * Don't substitute a ksm page for a forked page.
1115                  */
1116                 if (page == tree_page) {
1117                         put_page(tree_page);
1118                         return NULL;
1119                 }
1120
1121                 ret = memcmp_pages(page, tree_page);
1122
1123                 parent = *new;
1124                 if (ret < 0) {
1125                         put_page(tree_page);
1126                         new = &parent->rb_left;
1127                 } else if (ret > 0) {
1128                         put_page(tree_page);
1129                         new = &parent->rb_right;
1130                 } else {
1131                         *tree_pagep = tree_page;
1132                         return tree_rmap_item;
1133                 }
1134         }
1135
1136         rmap_item->address |= UNSTABLE_FLAG;
1137         rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1138         rb_link_node(&rmap_item->node, parent, new);
1139         rb_insert_color(&rmap_item->node, &root_unstable_tree);
1140
1141         ksm_pages_unshared++;
1142         return NULL;
1143 }
1144
1145 /*
1146  * stable_tree_append - add another rmap_item to the linked list of
1147  * rmap_items hanging off a given node of the stable tree, all sharing
1148  * the same ksm page.
1149  */
1150 static void stable_tree_append(struct rmap_item *rmap_item,
1151                                struct stable_node *stable_node)
1152 {
1153         rmap_item->head = stable_node;
1154         rmap_item->address |= STABLE_FLAG;
1155         hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
1156
1157         if (rmap_item->hlist.next)
1158                 ksm_pages_sharing++;
1159         else
1160                 ksm_pages_shared++;
1161 }
1162
1163 /*
1164  * cmp_and_merge_page - first see if page can be merged into the stable tree;
1165  * if not, compare checksum to previous and if it's the same, see if page can
1166  * be inserted into the unstable tree, or merged with a page already there and
1167  * both transferred to the stable tree.
1168  *
1169  * @page: the page that we are searching identical page to.
1170  * @rmap_item: the reverse mapping into the virtual address of this page
1171  */
1172 static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1173 {
1174         struct rmap_item *tree_rmap_item;
1175         struct page *tree_page = NULL;
1176         struct stable_node *stable_node;
1177         struct page *kpage;
1178         unsigned int checksum;
1179         int err;
1180
1181         remove_rmap_item_from_tree(rmap_item);
1182
1183         /* We first start with searching the page inside the stable tree */
1184         kpage = stable_tree_search(page);
1185         if (kpage) {
1186                 err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
1187                 if (!err) {
1188                         /*
1189                          * The page was successfully merged:
1190                          * add its rmap_item to the stable tree.
1191                          */
1192                         lock_page(kpage);
1193                         stable_tree_append(rmap_item, page_stable_node(kpage));
1194                         unlock_page(kpage);
1195                 }
1196                 put_page(kpage);
1197                 return;
1198         }
1199
1200         /*
1201          * If the hash value of the page has changed from the last time
1202          * we calculated it, this page is changing frequently: therefore we
1203          * don't want to insert it in the unstable tree, and we don't want
1204          * to waste our time searching for something identical to it there.
1205          */
1206         checksum = calc_checksum(page);
1207         if (rmap_item->oldchecksum != checksum) {
1208                 rmap_item->oldchecksum = checksum;
1209                 return;
1210         }
1211
1212         tree_rmap_item =
1213                 unstable_tree_search_insert(rmap_item, page, &tree_page);
1214         if (tree_rmap_item) {
1215                 kpage = try_to_merge_two_pages(rmap_item, page,
1216                                                 tree_rmap_item, tree_page);
1217                 put_page(tree_page);
1218                 /*
1219                  * As soon as we merge this page, we want to remove the
1220                  * rmap_item of the page we have merged with from the unstable
1221                  * tree, and insert it instead as new node in the stable tree.
1222                  */
1223                 if (kpage) {
1224                         remove_rmap_item_from_tree(tree_rmap_item);
1225
1226                         lock_page(kpage);
1227                         stable_node = stable_tree_insert(kpage);
1228                         if (stable_node) {
1229                                 stable_tree_append(tree_rmap_item, stable_node);
1230                                 stable_tree_append(rmap_item, stable_node);
1231                         }
1232                         unlock_page(kpage);
1233
1234                         /*
1235                          * If we fail to insert the page into the stable tree,
1236                          * we will have 2 virtual addresses that are pointing
1237                          * to a ksm page left outside the stable tree,
1238                          * in which case we need to break_cow on both.
1239                          */
1240                         if (!stable_node) {
1241                                 break_cow(tree_rmap_item);
1242                                 break_cow(rmap_item);
1243                         }
1244                 }
1245         }
1246 }
1247
1248 static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
1249                                             struct rmap_item **rmap_list,
1250                                             unsigned long addr)
1251 {
1252         struct rmap_item *rmap_item;
1253
1254         while (*rmap_list) {
1255                 rmap_item = *rmap_list;
1256                 if ((rmap_item->address & PAGE_MASK) == addr)
1257                         return rmap_item;
1258                 if (rmap_item->address > addr)
1259                         break;
1260                 *rmap_list = rmap_item->rmap_list;
1261                 remove_rmap_item_from_tree(rmap_item);
1262                 free_rmap_item(rmap_item);
1263         }
1264
1265         rmap_item = alloc_rmap_item();
1266         if (rmap_item) {
1267                 /* It has already been zeroed */
1268                 rmap_item->mm = mm_slot->mm;
1269                 rmap_item->address = addr;
1270                 rmap_item->rmap_list = *rmap_list;
1271                 *rmap_list = rmap_item;
1272         }
1273         return rmap_item;
1274 }
1275
1276 static struct rmap_item *scan_get_next_rmap_item(struct page **page)
1277 {
1278         struct mm_struct *mm;
1279         struct mm_slot *slot;
1280         struct vm_area_struct *vma;
1281         struct rmap_item *rmap_item;
1282
1283         if (list_empty(&ksm_mm_head.mm_list))
1284                 return NULL;
1285
1286         slot = ksm_scan.mm_slot;
1287         if (slot == &ksm_mm_head) {
1288                 /*
1289                  * A number of pages can hang around indefinitely on per-cpu
1290                  * pagevecs, raised page count preventing write_protect_page
1291                  * from merging them.  Though it doesn't really matter much,
1292                  * it is puzzling to see some stuck in pages_volatile until
1293                  * other activity jostles them out, and they also prevented
1294                  * LTP's KSM test from succeeding deterministically; so drain
1295                  * them here (here rather than on entry to ksm_do_scan(),
1296                  * so we don't IPI too often when pages_to_scan is set low).
1297                  */
1298                 lru_add_drain_all();
1299
1300                 root_unstable_tree = RB_ROOT;
1301
1302                 spin_lock(&ksm_mmlist_lock);
1303                 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1304                 ksm_scan.mm_slot = slot;
1305                 spin_unlock(&ksm_mmlist_lock);
1306                 /*
1307                  * Although we tested list_empty() above, a racing __ksm_exit
1308                  * of the last mm on the list may have removed it since then.
1309                  */
1310                 if (slot == &ksm_mm_head)
1311                         return NULL;
1312 next_mm:
1313                 ksm_scan.address = 0;
1314                 ksm_scan.rmap_list = &slot->rmap_list;
1315         }
1316
1317         mm = slot->mm;
1318         down_read(&mm->mmap_sem);
1319         if (ksm_test_exit(mm))
1320                 vma = NULL;
1321         else
1322                 vma = find_vma(mm, ksm_scan.address);
1323
1324         for (; vma; vma = vma->vm_next) {
1325                 if (!(vma->vm_flags & VM_MERGEABLE))
1326                         continue;
1327                 if (ksm_scan.address < vma->vm_start)
1328                         ksm_scan.address = vma->vm_start;
1329                 if (!vma->anon_vma)
1330                         ksm_scan.address = vma->vm_end;
1331
1332                 while (ksm_scan.address < vma->vm_end) {
1333                         if (ksm_test_exit(mm))
1334                                 break;
1335                         *page = follow_page(vma, ksm_scan.address, FOLL_GET);
1336                         if (IS_ERR_OR_NULL(*page)) {
1337                                 ksm_scan.address += PAGE_SIZE;
1338                                 cond_resched();
1339                                 continue;
1340                         }
1341                         if (PageAnon(*page) ||
1342                             page_trans_compound_anon(*page)) {
1343                                 flush_anon_page(vma, *page, ksm_scan.address);
1344                                 flush_dcache_page(*page);
1345                                 rmap_item = get_next_rmap_item(slot,
1346                                         ksm_scan.rmap_list, ksm_scan.address);
1347                                 if (rmap_item) {
1348                                         ksm_scan.rmap_list =
1349                                                         &rmap_item->rmap_list;
1350                                         ksm_scan.address += PAGE_SIZE;
1351                                 } else
1352                                         put_page(*page);
1353                                 up_read(&mm->mmap_sem);
1354                                 return rmap_item;
1355                         }
1356                         put_page(*page);
1357                         ksm_scan.address += PAGE_SIZE;
1358                         cond_resched();
1359                 }
1360         }
1361
1362         if (ksm_test_exit(mm)) {
1363                 ksm_scan.address = 0;
1364                 ksm_scan.rmap_list = &slot->rmap_list;
1365         }
1366         /*
1367          * Nuke all the rmap_items that are above this current rmap:
1368          * because there were no VM_MERGEABLE vmas with such addresses.
1369          */
1370         remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
1371
1372         spin_lock(&ksm_mmlist_lock);
1373         ksm_scan.mm_slot = list_entry(slot->mm_list.next,
1374                                                 struct mm_slot, mm_list);
1375         if (ksm_scan.address == 0) {
1376                 /*
1377                  * We've completed a full scan of all vmas, holding mmap_sem
1378                  * throughout, and found no VM_MERGEABLE: so do the same as
1379                  * __ksm_exit does to remove this mm from all our lists now.
1380                  * This applies either when cleaning up after __ksm_exit
1381                  * (but beware: we can reach here even before __ksm_exit),
1382                  * or when all VM_MERGEABLE areas have been unmapped (and
1383                  * mmap_sem then protects against race with MADV_MERGEABLE).
1384                  */
1385                 hlist_del(&slot->link);
1386                 list_del(&slot->mm_list);
1387                 spin_unlock(&ksm_mmlist_lock);
1388
1389                 free_mm_slot(slot);
1390                 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1391                 up_read(&mm->mmap_sem);
1392                 mmdrop(mm);
1393         } else {
1394                 spin_unlock(&ksm_mmlist_lock);
1395                 up_read(&mm->mmap_sem);
1396         }
1397
1398         /* Repeat until we've completed scanning the whole list */
1399         slot = ksm_scan.mm_slot;
1400         if (slot != &ksm_mm_head)
1401                 goto next_mm;
1402
1403         ksm_scan.seqnr++;
1404         return NULL;
1405 }
1406
1407 /**
1408  * ksm_do_scan  - the ksm scanner main worker function.
1409  * @scan_npages - number of pages we want to scan before we return.
1410  */
1411 static void ksm_do_scan(unsigned int scan_npages)
1412 {
1413         struct rmap_item *rmap_item;
1414         struct page *uninitialized_var(page);
1415
1416         while (scan_npages-- && likely(!freezing(current))) {
1417                 cond_resched();
1418                 rmap_item = scan_get_next_rmap_item(&page);
1419                 if (!rmap_item)
1420                         return;
1421                 if (!PageKsm(page) || !in_stable_tree(rmap_item))
1422                         cmp_and_merge_page(page, rmap_item);
1423                 put_page(page);
1424         }
1425 }
1426
1427 static int ksmd_should_run(void)
1428 {
1429         return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1430 }
1431
1432 static int ksm_scan_thread(void *nothing)
1433 {
1434         set_freezable();
1435         set_user_nice(current, 5);
1436
1437         while (!kthread_should_stop()) {
1438                 mutex_lock(&ksm_thread_mutex);
1439                 if (ksmd_should_run())
1440                         ksm_do_scan(ksm_thread_pages_to_scan);
1441                 mutex_unlock(&ksm_thread_mutex);
1442
1443                 try_to_freeze();
1444
1445                 if (ksmd_should_run()) {
1446                         schedule_timeout_interruptible(
1447                                 msecs_to_jiffies(ksm_thread_sleep_millisecs));
1448                 } else {
1449                         wait_event_freezable(ksm_thread_wait,
1450                                 ksmd_should_run() || kthread_should_stop());
1451                 }
1452         }
1453         return 0;
1454 }
1455
1456 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1457                 unsigned long end, int advice, unsigned long *vm_flags)
1458 {
1459         struct mm_struct *mm = vma->vm_mm;
1460         int err;
1461
1462         switch (advice) {
1463         case MADV_MERGEABLE:
1464                 /*
1465                  * Be somewhat over-protective for now!
1466                  */
1467                 if (*vm_flags & (VM_MERGEABLE | VM_SHARED  | VM_MAYSHARE   |
1468                                  VM_PFNMAP    | VM_IO      | VM_DONTEXPAND |
1469                                  VM_RESERVED  | VM_HUGETLB | VM_INSERTPAGE |
1470                                  VM_NONLINEAR | VM_MIXEDMAP | VM_SAO))
1471                         return 0;               /* just ignore the advice */
1472
1473                 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
1474                         err = __ksm_enter(mm);
1475                         if (err)
1476                                 return err;
1477                 }
1478
1479                 *vm_flags |= VM_MERGEABLE;
1480                 break;
1481
1482         case MADV_UNMERGEABLE:
1483                 if (!(*vm_flags & VM_MERGEABLE))
1484                         return 0;               /* just ignore the advice */
1485
1486                 if (vma->anon_vma) {
1487                         err = unmerge_ksm_pages(vma, start, end);
1488                         if (err)
1489                                 return err;
1490                 }
1491
1492                 *vm_flags &= ~VM_MERGEABLE;
1493                 break;
1494         }
1495
1496         return 0;
1497 }
1498
1499 int __ksm_enter(struct mm_struct *mm)
1500 {
1501         struct mm_slot *mm_slot;
1502         int needs_wakeup;
1503
1504         mm_slot = alloc_mm_slot();
1505         if (!mm_slot)
1506                 return -ENOMEM;
1507
1508         /* Check ksm_run too?  Would need tighter locking */
1509         needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1510
1511         spin_lock(&ksm_mmlist_lock);
1512         insert_to_mm_slots_hash(mm, mm_slot);
1513         /*
1514          * Insert just behind the scanning cursor, to let the area settle
1515          * down a little; when fork is followed by immediate exec, we don't
1516          * want ksmd to waste time setting up and tearing down an rmap_list.
1517          */
1518         list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
1519         spin_unlock(&ksm_mmlist_lock);
1520
1521         set_bit(MMF_VM_MERGEABLE, &mm->flags);
1522         atomic_inc(&mm->mm_count);
1523
1524         if (needs_wakeup)
1525                 wake_up_interruptible(&ksm_thread_wait);
1526
1527         return 0;
1528 }
1529
1530 void __ksm_exit(struct mm_struct *mm)
1531 {
1532         struct mm_slot *mm_slot;
1533         int easy_to_free = 0;
1534
1535         /*
1536          * This process is exiting: if it's straightforward (as is the
1537          * case when ksmd was never running), free mm_slot immediately.
1538          * But if it's at the cursor or has rmap_items linked to it, use
1539          * mmap_sem to synchronize with any break_cows before pagetables
1540          * are freed, and leave the mm_slot on the list for ksmd to free.
1541          * Beware: ksm may already have noticed it exiting and freed the slot.
1542          */
1543
1544         spin_lock(&ksm_mmlist_lock);
1545         mm_slot = get_mm_slot(mm);
1546         if (mm_slot && ksm_scan.mm_slot != mm_slot) {
1547                 if (!mm_slot->rmap_list) {
1548                         hlist_del(&mm_slot->link);
1549                         list_del(&mm_slot->mm_list);
1550                         easy_to_free = 1;
1551                 } else {
1552                         list_move(&mm_slot->mm_list,
1553                                   &ksm_scan.mm_slot->mm_list);
1554                 }
1555         }
1556         spin_unlock(&ksm_mmlist_lock);
1557
1558         if (easy_to_free) {
1559                 free_mm_slot(mm_slot);
1560                 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1561                 mmdrop(mm);
1562         } else if (mm_slot) {
1563                 down_write(&mm->mmap_sem);
1564                 up_write(&mm->mmap_sem);
1565         }
1566 }
1567
1568 struct page *ksm_does_need_to_copy(struct page *page,
1569                         struct vm_area_struct *vma, unsigned long address)
1570 {
1571         struct page *new_page;
1572
1573         new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
1574         if (new_page) {
1575                 /*
1576                  * The memcg-specific accounting when moving
1577                  * pages around the LRU lists relies on the
1578                  * page's owner (memcg) to be valid.  Usually,
1579                  * pages are assigned to a new owner before
1580                  * being put on the LRU list, but since this
1581                  * is not the case here, the stale owner from
1582                  * a previous allocation cycle must be reset.
1583                  */
1584                 mem_cgroup_reset_owner(new_page);
1585                 copy_user_highpage(new_page, page, address, vma);
1586
1587                 SetPageDirty(new_page);
1588                 __SetPageUptodate(new_page);
1589                 SetPageSwapBacked(new_page);
1590                 __set_page_locked(new_page);
1591
1592                 if (page_evictable(new_page, vma))
1593                         lru_cache_add_lru(new_page, LRU_ACTIVE_ANON);
1594                 else
1595                         add_page_to_unevictable_list(new_page);
1596         }
1597
1598         return new_page;
1599 }
1600
1601 int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg,
1602                         unsigned long *vm_flags)
1603 {
1604         struct stable_node *stable_node;
1605         struct rmap_item *rmap_item;
1606         struct hlist_node *hlist;
1607         unsigned int mapcount = page_mapcount(page);
1608         int referenced = 0;
1609         int search_new_forks = 0;
1610
1611         VM_BUG_ON(!PageKsm(page));
1612         VM_BUG_ON(!PageLocked(page));
1613
1614         stable_node = page_stable_node(page);
1615         if (!stable_node)
1616                 return 0;
1617 again:
1618         hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1619                 struct anon_vma *anon_vma = rmap_item->anon_vma;
1620                 struct anon_vma_chain *vmac;
1621                 struct vm_area_struct *vma;
1622
1623                 anon_vma_lock(anon_vma);
1624                 list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1625                         vma = vmac->vma;
1626                         if (rmap_item->address < vma->vm_start ||
1627                             rmap_item->address >= vma->vm_end)
1628                                 continue;
1629                         /*
1630                          * Initially we examine only the vma which covers this
1631                          * rmap_item; but later, if there is still work to do,
1632                          * we examine covering vmas in other mms: in case they
1633                          * were forked from the original since ksmd passed.
1634                          */
1635                         if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1636                                 continue;
1637
1638                         if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
1639                                 continue;
1640
1641                         referenced += page_referenced_one(page, vma,
1642                                 rmap_item->address, &mapcount, vm_flags);
1643                         if (!search_new_forks || !mapcount)
1644                                 break;
1645                 }
1646                 anon_vma_unlock(anon_vma);
1647                 if (!mapcount)
1648                         goto out;
1649         }
1650         if (!search_new_forks++)
1651                 goto again;
1652 out:
1653         return referenced;
1654 }
1655
1656 int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
1657 {
1658         struct stable_node *stable_node;
1659         struct hlist_node *hlist;
1660         struct rmap_item *rmap_item;
1661         int ret = SWAP_AGAIN;
1662         int search_new_forks = 0;
1663
1664         VM_BUG_ON(!PageKsm(page));
1665         VM_BUG_ON(!PageLocked(page));
1666
1667         stable_node = page_stable_node(page);
1668         if (!stable_node)
1669                 return SWAP_FAIL;
1670 again:
1671         hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1672                 struct anon_vma *anon_vma = rmap_item->anon_vma;
1673                 struct anon_vma_chain *vmac;
1674                 struct vm_area_struct *vma;
1675
1676                 anon_vma_lock(anon_vma);
1677                 list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1678                         vma = vmac->vma;
1679                         if (rmap_item->address < vma->vm_start ||
1680                             rmap_item->address >= vma->vm_end)
1681                                 continue;
1682                         /*
1683                          * Initially we examine only the vma which covers this
1684                          * rmap_item; but later, if there is still work to do,
1685                          * we examine covering vmas in other mms: in case they
1686                          * were forked from the original since ksmd passed.
1687                          */
1688                         if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1689                                 continue;
1690
1691                         ret = try_to_unmap_one(page, vma,
1692                                         rmap_item->address, flags);
1693                         if (ret != SWAP_AGAIN || !page_mapped(page)) {
1694                                 anon_vma_unlock(anon_vma);
1695                                 goto out;
1696                         }
1697                 }
1698                 anon_vma_unlock(anon_vma);
1699         }
1700         if (!search_new_forks++)
1701                 goto again;
1702 out:
1703         return ret;
1704 }
1705
1706 #ifdef CONFIG_MIGRATION
1707 int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *,
1708                   struct vm_area_struct *, unsigned long, void *), void *arg)
1709 {
1710         struct stable_node *stable_node;
1711         struct hlist_node *hlist;
1712         struct rmap_item *rmap_item;
1713         int ret = SWAP_AGAIN;
1714         int search_new_forks = 0;
1715
1716         VM_BUG_ON(!PageKsm(page));
1717         VM_BUG_ON(!PageLocked(page));
1718
1719         stable_node = page_stable_node(page);
1720         if (!stable_node)
1721                 return ret;
1722 again:
1723         hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1724                 struct anon_vma *anon_vma = rmap_item->anon_vma;
1725                 struct anon_vma_chain *vmac;
1726                 struct vm_area_struct *vma;
1727
1728                 anon_vma_lock(anon_vma);
1729                 list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1730                         vma = vmac->vma;
1731                         if (rmap_item->address < vma->vm_start ||
1732                             rmap_item->address >= vma->vm_end)
1733                                 continue;
1734                         /*
1735                          * Initially we examine only the vma which covers this
1736                          * rmap_item; but later, if there is still work to do,
1737                          * we examine covering vmas in other mms: in case they
1738                          * were forked from the original since ksmd passed.
1739                          */
1740                         if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1741                                 continue;
1742
1743                         ret = rmap_one(page, vma, rmap_item->address, arg);
1744                         if (ret != SWAP_AGAIN) {
1745                                 anon_vma_unlock(anon_vma);
1746                                 goto out;
1747                         }
1748                 }
1749                 anon_vma_unlock(anon_vma);
1750         }
1751         if (!search_new_forks++)
1752                 goto again;
1753 out:
1754         return ret;
1755 }
1756
1757 void ksm_migrate_page(struct page *newpage, struct page *oldpage)
1758 {
1759         struct stable_node *stable_node;
1760
1761         VM_BUG_ON(!PageLocked(oldpage));
1762         VM_BUG_ON(!PageLocked(newpage));
1763         VM_BUG_ON(newpage->mapping != oldpage->mapping);
1764
1765         stable_node = page_stable_node(newpage);
1766         if (stable_node) {
1767                 VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage));
1768                 stable_node->kpfn = page_to_pfn(newpage);
1769         }
1770 }
1771 #endif /* CONFIG_MIGRATION */
1772
1773 #ifdef CONFIG_MEMORY_HOTREMOVE
1774 static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn,
1775                                                  unsigned long end_pfn)
1776 {
1777         struct rb_node *node;
1778
1779         for (node = rb_first(&root_stable_tree); node; node = rb_next(node)) {
1780                 struct stable_node *stable_node;
1781
1782                 stable_node = rb_entry(node, struct stable_node, node);
1783                 if (stable_node->kpfn >= start_pfn &&
1784                     stable_node->kpfn < end_pfn)
1785                         return stable_node;
1786         }
1787         return NULL;
1788 }
1789
1790 static int ksm_memory_callback(struct notifier_block *self,
1791                                unsigned long action, void *arg)
1792 {
1793         struct memory_notify *mn = arg;
1794         struct stable_node *stable_node;
1795
1796         switch (action) {
1797         case MEM_GOING_OFFLINE:
1798                 /*
1799                  * Keep it very simple for now: just lock out ksmd and
1800                  * MADV_UNMERGEABLE while any memory is going offline.
1801                  * mutex_lock_nested() is necessary because lockdep was alarmed
1802                  * that here we take ksm_thread_mutex inside notifier chain
1803                  * mutex, and later take notifier chain mutex inside
1804                  * ksm_thread_mutex to unlock it.   But that's safe because both
1805                  * are inside mem_hotplug_mutex.
1806                  */
1807                 mutex_lock_nested(&ksm_thread_mutex, SINGLE_DEPTH_NESTING);
1808                 break;
1809
1810         case MEM_OFFLINE:
1811                 /*
1812                  * Most of the work is done by page migration; but there might
1813                  * be a few stable_nodes left over, still pointing to struct
1814                  * pages which have been offlined: prune those from the tree.
1815                  */
1816                 while ((stable_node = ksm_check_stable_tree(mn->start_pfn,
1817                                         mn->start_pfn + mn->nr_pages)) != NULL)
1818                         remove_node_from_stable_tree(stable_node);
1819                 /* fallthrough */
1820
1821         case MEM_CANCEL_OFFLINE:
1822                 mutex_unlock(&ksm_thread_mutex);
1823                 break;
1824         }
1825         return NOTIFY_OK;
1826 }
1827 #endif /* CONFIG_MEMORY_HOTREMOVE */
1828
1829 #ifdef CONFIG_SYSFS
1830 /*
1831  * This all compiles without CONFIG_SYSFS, but is a waste of space.
1832  */
1833
1834 #define KSM_ATTR_RO(_name) \
1835         static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
1836 #define KSM_ATTR(_name) \
1837         static struct kobj_attribute _name##_attr = \
1838                 __ATTR(_name, 0644, _name##_show, _name##_store)
1839
1840 static ssize_t sleep_millisecs_show(struct kobject *kobj,
1841                                     struct kobj_attribute *attr, char *buf)
1842 {
1843         return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
1844 }
1845
1846 static ssize_t sleep_millisecs_store(struct kobject *kobj,
1847                                      struct kobj_attribute *attr,
1848                                      const char *buf, size_t count)
1849 {
1850         unsigned long msecs;
1851         int err;
1852
1853         err = strict_strtoul(buf, 10, &msecs);
1854         if (err || msecs > UINT_MAX)
1855                 return -EINVAL;
1856
1857         ksm_thread_sleep_millisecs = msecs;
1858
1859         return count;
1860 }
1861 KSM_ATTR(sleep_millisecs);
1862
1863 static ssize_t pages_to_scan_show(struct kobject *kobj,
1864                                   struct kobj_attribute *attr, char *buf)
1865 {
1866         return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
1867 }
1868
1869 static ssize_t pages_to_scan_store(struct kobject *kobj,
1870                                    struct kobj_attribute *attr,
1871                                    const char *buf, size_t count)
1872 {
1873         int err;
1874         unsigned long nr_pages;
1875
1876         err = strict_strtoul(buf, 10, &nr_pages);
1877         if (err || nr_pages > UINT_MAX)
1878                 return -EINVAL;
1879
1880         ksm_thread_pages_to_scan = nr_pages;
1881
1882         return count;
1883 }
1884 KSM_ATTR(pages_to_scan);
1885
1886 static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
1887                         char *buf)
1888 {
1889         return sprintf(buf, "%u\n", ksm_run);
1890 }
1891
1892 static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
1893                          const char *buf, size_t count)
1894 {
1895         int err;
1896         unsigned long flags;
1897
1898         err = strict_strtoul(buf, 10, &flags);
1899         if (err || flags > UINT_MAX)
1900                 return -EINVAL;
1901         if (flags > KSM_RUN_UNMERGE)
1902                 return -EINVAL;
1903
1904         /*
1905          * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
1906          * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
1907          * breaking COW to free the pages_shared (but leaves mm_slots
1908          * on the list for when ksmd may be set running again).
1909          */
1910
1911         mutex_lock(&ksm_thread_mutex);
1912         if (ksm_run != flags) {
1913                 ksm_run = flags;
1914                 if (flags & KSM_RUN_UNMERGE) {
1915                         int oom_score_adj;
1916
1917                         oom_score_adj = test_set_oom_score_adj(OOM_SCORE_ADJ_MAX);
1918                         err = unmerge_and_remove_all_rmap_items();
1919                         compare_swap_oom_score_adj(OOM_SCORE_ADJ_MAX,
1920                                                                 oom_score_adj);
1921                         if (err) {
1922                                 ksm_run = KSM_RUN_STOP;
1923                                 count = err;
1924                         }
1925                 }
1926         }
1927         mutex_unlock(&ksm_thread_mutex);
1928
1929         if (flags & KSM_RUN_MERGE)
1930                 wake_up_interruptible(&ksm_thread_wait);
1931
1932         return count;
1933 }
1934 KSM_ATTR(run);
1935
1936 static ssize_t pages_shared_show(struct kobject *kobj,
1937                                  struct kobj_attribute *attr, char *buf)
1938 {
1939         return sprintf(buf, "%lu\n", ksm_pages_shared);
1940 }
1941 KSM_ATTR_RO(pages_shared);
1942
1943 static ssize_t pages_sharing_show(struct kobject *kobj,
1944                                   struct kobj_attribute *attr, char *buf)
1945 {
1946         return sprintf(buf, "%lu\n", ksm_pages_sharing);
1947 }
1948 KSM_ATTR_RO(pages_sharing);
1949
1950 static ssize_t pages_unshared_show(struct kobject *kobj,
1951                                    struct kobj_attribute *attr, char *buf)
1952 {
1953         return sprintf(buf, "%lu\n", ksm_pages_unshared);
1954 }
1955 KSM_ATTR_RO(pages_unshared);
1956
1957 static ssize_t pages_volatile_show(struct kobject *kobj,
1958                                    struct kobj_attribute *attr, char *buf)
1959 {
1960         long ksm_pages_volatile;
1961
1962         ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
1963                                 - ksm_pages_sharing - ksm_pages_unshared;
1964         /*
1965          * It was not worth any locking to calculate that statistic,
1966          * but it might therefore sometimes be negative: conceal that.
1967          */
1968         if (ksm_pages_volatile < 0)
1969                 ksm_pages_volatile = 0;
1970         return sprintf(buf, "%ld\n", ksm_pages_volatile);
1971 }
1972 KSM_ATTR_RO(pages_volatile);
1973
1974 static ssize_t full_scans_show(struct kobject *kobj,
1975                                struct kobj_attribute *attr, char *buf)
1976 {
1977         return sprintf(buf, "%lu\n", ksm_scan.seqnr);
1978 }
1979 KSM_ATTR_RO(full_scans);
1980
1981 static struct attribute *ksm_attrs[] = {
1982         &sleep_millisecs_attr.attr,
1983         &pages_to_scan_attr.attr,
1984         &run_attr.attr,
1985         &pages_shared_attr.attr,
1986         &pages_sharing_attr.attr,
1987         &pages_unshared_attr.attr,
1988         &pages_volatile_attr.attr,
1989         &full_scans_attr.attr,
1990         NULL,
1991 };
1992
1993 static struct attribute_group ksm_attr_group = {
1994         .attrs = ksm_attrs,
1995         .name = "ksm",
1996 };
1997 #endif /* CONFIG_SYSFS */
1998
1999 static int __init ksm_init(void)
2000 {
2001         struct task_struct *ksm_thread;
2002         int err;
2003
2004         err = ksm_slab_init();
2005         if (err)
2006                 goto out;
2007
2008         ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
2009         if (IS_ERR(ksm_thread)) {
2010                 printk(KERN_ERR "ksm: creating kthread failed\n");
2011                 err = PTR_ERR(ksm_thread);
2012                 goto out_free;
2013         }
2014
2015 #ifdef CONFIG_SYSFS
2016         err = sysfs_create_group(mm_kobj, &ksm_attr_group);
2017         if (err) {
2018                 printk(KERN_ERR "ksm: register sysfs failed\n");
2019                 kthread_stop(ksm_thread);
2020                 goto out_free;
2021         }
2022 #else
2023         ksm_run = KSM_RUN_MERGE;        /* no way for user to start it */
2024
2025 #endif /* CONFIG_SYSFS */
2026
2027 #ifdef CONFIG_MEMORY_HOTREMOVE
2028         /*
2029          * Choose a high priority since the callback takes ksm_thread_mutex:
2030          * later callbacks could only be taking locks which nest within that.
2031          */
2032         hotplug_memory_notifier(ksm_memory_callback, 100);
2033 #endif
2034         return 0;
2035
2036 out_free:
2037         ksm_slab_free();
2038 out:
2039         return err;
2040 }
2041 module_init(ksm_init)