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