ksm: cleanup: introduce find_mergeable_vma()
[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/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
713         addr = page_address_in_vma(page, vma);
714         if (addr == -EFAULT)
715                 goto out;
716
717         BUG_ON(PageTransCompound(page));
718         ptep = page_check_address(page, mm, addr, &ptl, 0);
719         if (!ptep)
720                 goto out;
721
722         if (pte_write(*ptep) || pte_dirty(*ptep)) {
723                 pte_t entry;
724
725                 swapped = PageSwapCache(page);
726                 flush_cache_page(vma, addr, page_to_pfn(page));
727                 /*
728                  * Ok this is tricky, when get_user_pages_fast() run it doesn't
729                  * take any lock, therefore the check that we are going to make
730                  * with the pagecount against the mapcount is racey and
731                  * O_DIRECT can happen right after the check.
732                  * So we clear the pte and flush the tlb before the check
733                  * this assure us that no O_DIRECT can happen after the check
734                  * or in the middle of the check.
735                  */
736                 entry = ptep_clear_flush(vma, addr, ptep);
737                 /*
738                  * Check that no O_DIRECT or similar I/O is in progress on the
739                  * page
740                  */
741                 if (page_mapcount(page) + 1 + swapped != page_count(page)) {
742                         set_pte_at(mm, addr, ptep, entry);
743                         goto out_unlock;
744                 }
745                 if (pte_dirty(entry))
746                         set_page_dirty(page);
747                 entry = pte_mkclean(pte_wrprotect(entry));
748                 set_pte_at_notify(mm, addr, ptep, entry);
749         }
750         *orig_pte = *ptep;
751         err = 0;
752
753 out_unlock:
754         pte_unmap_unlock(ptep, ptl);
755 out:
756         return err;
757 }
758
759 /**
760  * replace_page - replace page in vma by new ksm page
761  * @vma:      vma that holds the pte pointing to page
762  * @page:     the page we are replacing by kpage
763  * @kpage:    the ksm page we replace page by
764  * @orig_pte: the original value of the pte
765  *
766  * Returns 0 on success, -EFAULT on failure.
767  */
768 static int replace_page(struct vm_area_struct *vma, struct page *page,
769                         struct page *kpage, pte_t orig_pte)
770 {
771         struct mm_struct *mm = vma->vm_mm;
772         pgd_t *pgd;
773         pud_t *pud;
774         pmd_t *pmd;
775         pte_t *ptep;
776         spinlock_t *ptl;
777         unsigned long addr;
778         int err = -EFAULT;
779
780         addr = page_address_in_vma(page, vma);
781         if (addr == -EFAULT)
782                 goto out;
783
784         pgd = pgd_offset(mm, addr);
785         if (!pgd_present(*pgd))
786                 goto out;
787
788         pud = pud_offset(pgd, addr);
789         if (!pud_present(*pud))
790                 goto out;
791
792         pmd = pmd_offset(pud, addr);
793         BUG_ON(pmd_trans_huge(*pmd));
794         if (!pmd_present(*pmd))
795                 goto out;
796
797         ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
798         if (!pte_same(*ptep, orig_pte)) {
799                 pte_unmap_unlock(ptep, ptl);
800                 goto out;
801         }
802
803         get_page(kpage);
804         page_add_anon_rmap(kpage, vma, addr);
805
806         flush_cache_page(vma, addr, pte_pfn(*ptep));
807         ptep_clear_flush(vma, addr, ptep);
808         set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
809
810         page_remove_rmap(page);
811         if (!page_mapped(page))
812                 try_to_free_swap(page);
813         put_page(page);
814
815         pte_unmap_unlock(ptep, ptl);
816         err = 0;
817 out:
818         return err;
819 }
820
821 static int page_trans_compound_anon_split(struct page *page)
822 {
823         int ret = 0;
824         struct page *transhuge_head = page_trans_compound_anon(page);
825         if (transhuge_head) {
826                 /* Get the reference on the head to split it. */
827                 if (get_page_unless_zero(transhuge_head)) {
828                         /*
829                          * Recheck we got the reference while the head
830                          * was still anonymous.
831                          */
832                         if (PageAnon(transhuge_head))
833                                 ret = split_huge_page(transhuge_head);
834                         else
835                                 /*
836                                  * Retry later if split_huge_page run
837                                  * from under us.
838                                  */
839                                 ret = 1;
840                         put_page(transhuge_head);
841                 } else
842                         /* Retry later if split_huge_page run from under us. */
843                         ret = 1;
844         }
845         return ret;
846 }
847
848 /*
849  * try_to_merge_one_page - take two pages and merge them into one
850  * @vma: the vma that holds the pte pointing to page
851  * @page: the PageAnon page that we want to replace with kpage
852  * @kpage: the PageKsm page that we want to map instead of page,
853  *         or NULL the first time when we want to use page as kpage.
854  *
855  * This function returns 0 if the pages were merged, -EFAULT otherwise.
856  */
857 static int try_to_merge_one_page(struct vm_area_struct *vma,
858                                  struct page *page, struct page *kpage)
859 {
860         pte_t orig_pte = __pte(0);
861         int err = -EFAULT;
862
863         if (page == kpage)                      /* ksm page forked */
864                 return 0;
865
866         if (!(vma->vm_flags & VM_MERGEABLE))
867                 goto out;
868         if (PageTransCompound(page) && page_trans_compound_anon_split(page))
869                 goto out;
870         BUG_ON(PageTransCompound(page));
871         if (!PageAnon(page))
872                 goto out;
873
874         /*
875          * We need the page lock to read a stable PageSwapCache in
876          * write_protect_page().  We use trylock_page() instead of
877          * lock_page() because we don't want to wait here - we
878          * prefer to continue scanning and merging different pages,
879          * then come back to this page when it is unlocked.
880          */
881         if (!trylock_page(page))
882                 goto out;
883         /*
884          * If this anonymous page is mapped only here, its pte may need
885          * to be write-protected.  If it's mapped elsewhere, all of its
886          * ptes are necessarily already write-protected.  But in either
887          * case, we need to lock and check page_count is not raised.
888          */
889         if (write_protect_page(vma, page, &orig_pte) == 0) {
890                 if (!kpage) {
891                         /*
892                          * While we hold page lock, upgrade page from
893                          * PageAnon+anon_vma to PageKsm+NULL stable_node:
894                          * stable_tree_insert() will update stable_node.
895                          */
896                         set_page_stable_node(page, NULL);
897                         mark_page_accessed(page);
898                         err = 0;
899                 } else if (pages_identical(page, kpage))
900                         err = replace_page(vma, page, kpage, orig_pte);
901         }
902
903         if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
904                 munlock_vma_page(page);
905                 if (!PageMlocked(kpage)) {
906                         unlock_page(page);
907                         lock_page(kpage);
908                         mlock_vma_page(kpage);
909                         page = kpage;           /* for final unlock */
910                 }
911         }
912
913         unlock_page(page);
914 out:
915         return err;
916 }
917
918 /*
919  * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
920  * but no new kernel page is allocated: kpage must already be a ksm page.
921  *
922  * This function returns 0 if the pages were merged, -EFAULT otherwise.
923  */
924 static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
925                                       struct page *page, struct page *kpage)
926 {
927         struct mm_struct *mm = rmap_item->mm;
928         struct vm_area_struct *vma;
929         int err = -EFAULT;
930
931         down_read(&mm->mmap_sem);
932         if (ksm_test_exit(mm))
933                 goto out;
934         vma = find_vma(mm, rmap_item->address);
935         if (!vma || vma->vm_start > rmap_item->address)
936                 goto out;
937
938         err = try_to_merge_one_page(vma, page, kpage);
939         if (err)
940                 goto out;
941
942         /* Must get reference to anon_vma while still holding mmap_sem */
943         rmap_item->anon_vma = vma->anon_vma;
944         get_anon_vma(vma->anon_vma);
945 out:
946         up_read(&mm->mmap_sem);
947         return err;
948 }
949
950 /*
951  * try_to_merge_two_pages - take two identical pages and prepare them
952  * to be merged into one page.
953  *
954  * This function returns the kpage if we successfully merged two identical
955  * pages into one ksm page, NULL otherwise.
956  *
957  * Note that this function upgrades page to ksm page: if one of the pages
958  * is already a ksm page, try_to_merge_with_ksm_page should be used.
959  */
960 static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
961                                            struct page *page,
962                                            struct rmap_item *tree_rmap_item,
963                                            struct page *tree_page)
964 {
965         int err;
966
967         err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
968         if (!err) {
969                 err = try_to_merge_with_ksm_page(tree_rmap_item,
970                                                         tree_page, page);
971                 /*
972                  * If that fails, we have a ksm page with only one pte
973                  * pointing to it: so break it.
974                  */
975                 if (err)
976                         break_cow(rmap_item);
977         }
978         return err ? NULL : page;
979 }
980
981 /*
982  * stable_tree_search - search for page inside the stable tree
983  *
984  * This function checks if there is a page inside the stable tree
985  * with identical content to the page that we are scanning right now.
986  *
987  * This function returns the stable tree node of identical content if found,
988  * NULL otherwise.
989  */
990 static struct page *stable_tree_search(struct page *page)
991 {
992         struct rb_node *node = root_stable_tree.rb_node;
993         struct stable_node *stable_node;
994
995         stable_node = page_stable_node(page);
996         if (stable_node) {                      /* ksm page forked */
997                 get_page(page);
998                 return page;
999         }
1000
1001         while (node) {
1002                 struct page *tree_page;
1003                 int ret;
1004
1005                 cond_resched();
1006                 stable_node = rb_entry(node, struct stable_node, node);
1007                 tree_page = get_ksm_page(stable_node);
1008                 if (!tree_page)
1009                         return NULL;
1010
1011                 ret = memcmp_pages(page, tree_page);
1012
1013                 if (ret < 0) {
1014                         put_page(tree_page);
1015                         node = node->rb_left;
1016                 } else if (ret > 0) {
1017                         put_page(tree_page);
1018                         node = node->rb_right;
1019                 } else
1020                         return tree_page;
1021         }
1022
1023         return NULL;
1024 }
1025
1026 /*
1027  * stable_tree_insert - insert rmap_item pointing to new ksm page
1028  * into the stable tree.
1029  *
1030  * This function returns the stable tree node just allocated on success,
1031  * NULL otherwise.
1032  */
1033 static struct stable_node *stable_tree_insert(struct page *kpage)
1034 {
1035         struct rb_node **new = &root_stable_tree.rb_node;
1036         struct rb_node *parent = NULL;
1037         struct stable_node *stable_node;
1038
1039         while (*new) {
1040                 struct page *tree_page;
1041                 int ret;
1042
1043                 cond_resched();
1044                 stable_node = rb_entry(*new, struct stable_node, node);
1045                 tree_page = get_ksm_page(stable_node);
1046                 if (!tree_page)
1047                         return NULL;
1048
1049                 ret = memcmp_pages(kpage, tree_page);
1050                 put_page(tree_page);
1051
1052                 parent = *new;
1053                 if (ret < 0)
1054                         new = &parent->rb_left;
1055                 else if (ret > 0)
1056                         new = &parent->rb_right;
1057                 else {
1058                         /*
1059                          * It is not a bug that stable_tree_search() didn't
1060                          * find this node: because at that time our page was
1061                          * not yet write-protected, so may have changed since.
1062                          */
1063                         return NULL;
1064                 }
1065         }
1066
1067         stable_node = alloc_stable_node();
1068         if (!stable_node)
1069                 return NULL;
1070
1071         rb_link_node(&stable_node->node, parent, new);
1072         rb_insert_color(&stable_node->node, &root_stable_tree);
1073
1074         INIT_HLIST_HEAD(&stable_node->hlist);
1075
1076         stable_node->kpfn = page_to_pfn(kpage);
1077         set_page_stable_node(kpage, stable_node);
1078
1079         return stable_node;
1080 }
1081
1082 /*
1083  * unstable_tree_search_insert - search for identical page,
1084  * else insert rmap_item into the unstable tree.
1085  *
1086  * This function searches for a page in the unstable tree identical to the
1087  * page currently being scanned; and if no identical page is found in the
1088  * tree, we insert rmap_item as a new object into the unstable tree.
1089  *
1090  * This function returns pointer to rmap_item found to be identical
1091  * to the currently scanned page, NULL otherwise.
1092  *
1093  * This function does both searching and inserting, because they share
1094  * the same walking algorithm in an rbtree.
1095  */
1096 static
1097 struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1098                                               struct page *page,
1099                                               struct page **tree_pagep)
1100
1101 {
1102         struct rb_node **new = &root_unstable_tree.rb_node;
1103         struct rb_node *parent = NULL;
1104
1105         while (*new) {
1106                 struct rmap_item *tree_rmap_item;
1107                 struct page *tree_page;
1108                 int ret;
1109
1110                 cond_resched();
1111                 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1112                 tree_page = get_mergeable_page(tree_rmap_item);
1113                 if (IS_ERR_OR_NULL(tree_page))
1114                         return NULL;
1115
1116                 /*
1117                  * Don't substitute a ksm page for a forked page.
1118                  */
1119                 if (page == tree_page) {
1120                         put_page(tree_page);
1121                         return NULL;
1122                 }
1123
1124                 ret = memcmp_pages(page, tree_page);
1125
1126                 parent = *new;
1127                 if (ret < 0) {
1128                         put_page(tree_page);
1129                         new = &parent->rb_left;
1130                 } else if (ret > 0) {
1131                         put_page(tree_page);
1132                         new = &parent->rb_right;
1133                 } else {
1134                         *tree_pagep = tree_page;
1135                         return tree_rmap_item;
1136                 }
1137         }
1138
1139         rmap_item->address |= UNSTABLE_FLAG;
1140         rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1141         rb_link_node(&rmap_item->node, parent, new);
1142         rb_insert_color(&rmap_item->node, &root_unstable_tree);
1143
1144         ksm_pages_unshared++;
1145         return NULL;
1146 }
1147
1148 /*
1149  * stable_tree_append - add another rmap_item to the linked list of
1150  * rmap_items hanging off a given node of the stable tree, all sharing
1151  * the same ksm page.
1152  */
1153 static void stable_tree_append(struct rmap_item *rmap_item,
1154                                struct stable_node *stable_node)
1155 {
1156         rmap_item->head = stable_node;
1157         rmap_item->address |= STABLE_FLAG;
1158         hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
1159
1160         if (rmap_item->hlist.next)
1161                 ksm_pages_sharing++;
1162         else
1163                 ksm_pages_shared++;
1164 }
1165
1166 /*
1167  * cmp_and_merge_page - first see if page can be merged into the stable tree;
1168  * if not, compare checksum to previous and if it's the same, see if page can
1169  * be inserted into the unstable tree, or merged with a page already there and
1170  * both transferred to the stable tree.
1171  *
1172  * @page: the page that we are searching identical page to.
1173  * @rmap_item: the reverse mapping into the virtual address of this page
1174  */
1175 static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1176 {
1177         struct rmap_item *tree_rmap_item;
1178         struct page *tree_page = NULL;
1179         struct stable_node *stable_node;
1180         struct page *kpage;
1181         unsigned int checksum;
1182         int err;
1183
1184         remove_rmap_item_from_tree(rmap_item);
1185
1186         /* We first start with searching the page inside the stable tree */
1187         kpage = stable_tree_search(page);
1188         if (kpage) {
1189                 err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
1190                 if (!err) {
1191                         /*
1192                          * The page was successfully merged:
1193                          * add its rmap_item to the stable tree.
1194                          */
1195                         lock_page(kpage);
1196                         stable_tree_append(rmap_item, page_stable_node(kpage));
1197                         unlock_page(kpage);
1198                 }
1199                 put_page(kpage);
1200                 return;
1201         }
1202
1203         /*
1204          * If the hash value of the page has changed from the last time
1205          * we calculated it, this page is changing frequently: therefore we
1206          * don't want to insert it in the unstable tree, and we don't want
1207          * to waste our time searching for something identical to it there.
1208          */
1209         checksum = calc_checksum(page);
1210         if (rmap_item->oldchecksum != checksum) {
1211                 rmap_item->oldchecksum = checksum;
1212                 return;
1213         }
1214
1215         tree_rmap_item =
1216                 unstable_tree_search_insert(rmap_item, page, &tree_page);
1217         if (tree_rmap_item) {
1218                 kpage = try_to_merge_two_pages(rmap_item, page,
1219                                                 tree_rmap_item, tree_page);
1220                 put_page(tree_page);
1221                 /*
1222                  * As soon as we merge this page, we want to remove the
1223                  * rmap_item of the page we have merged with from the unstable
1224                  * tree, and insert it instead as new node in the stable tree.
1225                  */
1226                 if (kpage) {
1227                         remove_rmap_item_from_tree(tree_rmap_item);
1228
1229                         lock_page(kpage);
1230                         stable_node = stable_tree_insert(kpage);
1231                         if (stable_node) {
1232                                 stable_tree_append(tree_rmap_item, stable_node);
1233                                 stable_tree_append(rmap_item, stable_node);
1234                         }
1235                         unlock_page(kpage);
1236
1237                         /*
1238                          * If we fail to insert the page into the stable tree,
1239                          * we will have 2 virtual addresses that are pointing
1240                          * to a ksm page left outside the stable tree,
1241                          * in which case we need to break_cow on both.
1242                          */
1243                         if (!stable_node) {
1244                                 break_cow(tree_rmap_item);
1245                                 break_cow(rmap_item);
1246                         }
1247                 }
1248         }
1249 }
1250
1251 static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
1252                                             struct rmap_item **rmap_list,
1253                                             unsigned long addr)
1254 {
1255         struct rmap_item *rmap_item;
1256
1257         while (*rmap_list) {
1258                 rmap_item = *rmap_list;
1259                 if ((rmap_item->address & PAGE_MASK) == addr)
1260                         return rmap_item;
1261                 if (rmap_item->address > addr)
1262                         break;
1263                 *rmap_list = rmap_item->rmap_list;
1264                 remove_rmap_item_from_tree(rmap_item);
1265                 free_rmap_item(rmap_item);
1266         }
1267
1268         rmap_item = alloc_rmap_item();
1269         if (rmap_item) {
1270                 /* It has already been zeroed */
1271                 rmap_item->mm = mm_slot->mm;
1272                 rmap_item->address = addr;
1273                 rmap_item->rmap_list = *rmap_list;
1274                 *rmap_list = rmap_item;
1275         }
1276         return rmap_item;
1277 }
1278
1279 static struct rmap_item *scan_get_next_rmap_item(struct page **page)
1280 {
1281         struct mm_struct *mm;
1282         struct mm_slot *slot;
1283         struct vm_area_struct *vma;
1284         struct rmap_item *rmap_item;
1285
1286         if (list_empty(&ksm_mm_head.mm_list))
1287                 return NULL;
1288
1289         slot = ksm_scan.mm_slot;
1290         if (slot == &ksm_mm_head) {
1291                 /*
1292                  * A number of pages can hang around indefinitely on per-cpu
1293                  * pagevecs, raised page count preventing write_protect_page
1294                  * from merging them.  Though it doesn't really matter much,
1295                  * it is puzzling to see some stuck in pages_volatile until
1296                  * other activity jostles them out, and they also prevented
1297                  * LTP's KSM test from succeeding deterministically; so drain
1298                  * them here (here rather than on entry to ksm_do_scan(),
1299                  * so we don't IPI too often when pages_to_scan is set low).
1300                  */
1301                 lru_add_drain_all();
1302
1303                 root_unstable_tree = RB_ROOT;
1304
1305                 spin_lock(&ksm_mmlist_lock);
1306                 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1307                 ksm_scan.mm_slot = slot;
1308                 spin_unlock(&ksm_mmlist_lock);
1309                 /*
1310                  * Although we tested list_empty() above, a racing __ksm_exit
1311                  * of the last mm on the list may have removed it since then.
1312                  */
1313                 if (slot == &ksm_mm_head)
1314                         return NULL;
1315 next_mm:
1316                 ksm_scan.address = 0;
1317                 ksm_scan.rmap_list = &slot->rmap_list;
1318         }
1319
1320         mm = slot->mm;
1321         down_read(&mm->mmap_sem);
1322         if (ksm_test_exit(mm))
1323                 vma = NULL;
1324         else
1325                 vma = find_vma(mm, ksm_scan.address);
1326
1327         for (; vma; vma = vma->vm_next) {
1328                 if (!(vma->vm_flags & VM_MERGEABLE))
1329                         continue;
1330                 if (ksm_scan.address < vma->vm_start)
1331                         ksm_scan.address = vma->vm_start;
1332                 if (!vma->anon_vma)
1333                         ksm_scan.address = vma->vm_end;
1334
1335                 while (ksm_scan.address < vma->vm_end) {
1336                         if (ksm_test_exit(mm))
1337                                 break;
1338                         *page = follow_page(vma, ksm_scan.address, FOLL_GET);
1339                         if (IS_ERR_OR_NULL(*page)) {
1340                                 ksm_scan.address += PAGE_SIZE;
1341                                 cond_resched();
1342                                 continue;
1343                         }
1344                         if (PageAnon(*page) ||
1345                             page_trans_compound_anon(*page)) {
1346                                 flush_anon_page(vma, *page, ksm_scan.address);
1347                                 flush_dcache_page(*page);
1348                                 rmap_item = get_next_rmap_item(slot,
1349                                         ksm_scan.rmap_list, ksm_scan.address);
1350                                 if (rmap_item) {
1351                                         ksm_scan.rmap_list =
1352                                                         &rmap_item->rmap_list;
1353                                         ksm_scan.address += PAGE_SIZE;
1354                                 } else
1355                                         put_page(*page);
1356                                 up_read(&mm->mmap_sem);
1357                                 return rmap_item;
1358                         }
1359                         put_page(*page);
1360                         ksm_scan.address += PAGE_SIZE;
1361                         cond_resched();
1362                 }
1363         }
1364
1365         if (ksm_test_exit(mm)) {
1366                 ksm_scan.address = 0;
1367                 ksm_scan.rmap_list = &slot->rmap_list;
1368         }
1369         /*
1370          * Nuke all the rmap_items that are above this current rmap:
1371          * because there were no VM_MERGEABLE vmas with such addresses.
1372          */
1373         remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
1374
1375         spin_lock(&ksm_mmlist_lock);
1376         ksm_scan.mm_slot = list_entry(slot->mm_list.next,
1377                                                 struct mm_slot, mm_list);
1378         if (ksm_scan.address == 0) {
1379                 /*
1380                  * We've completed a full scan of all vmas, holding mmap_sem
1381                  * throughout, and found no VM_MERGEABLE: so do the same as
1382                  * __ksm_exit does to remove this mm from all our lists now.
1383                  * This applies either when cleaning up after __ksm_exit
1384                  * (but beware: we can reach here even before __ksm_exit),
1385                  * or when all VM_MERGEABLE areas have been unmapped (and
1386                  * mmap_sem then protects against race with MADV_MERGEABLE).
1387                  */
1388                 hlist_del(&slot->link);
1389                 list_del(&slot->mm_list);
1390                 spin_unlock(&ksm_mmlist_lock);
1391
1392                 free_mm_slot(slot);
1393                 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1394                 up_read(&mm->mmap_sem);
1395                 mmdrop(mm);
1396         } else {
1397                 spin_unlock(&ksm_mmlist_lock);
1398                 up_read(&mm->mmap_sem);
1399         }
1400
1401         /* Repeat until we've completed scanning the whole list */
1402         slot = ksm_scan.mm_slot;
1403         if (slot != &ksm_mm_head)
1404                 goto next_mm;
1405
1406         ksm_scan.seqnr++;
1407         return NULL;
1408 }
1409
1410 /**
1411  * ksm_do_scan  - the ksm scanner main worker function.
1412  * @scan_npages - number of pages we want to scan before we return.
1413  */
1414 static void ksm_do_scan(unsigned int scan_npages)
1415 {
1416         struct rmap_item *rmap_item;
1417         struct page *uninitialized_var(page);
1418
1419         while (scan_npages-- && likely(!freezing(current))) {
1420                 cond_resched();
1421                 rmap_item = scan_get_next_rmap_item(&page);
1422                 if (!rmap_item)
1423                         return;
1424                 if (!PageKsm(page) || !in_stable_tree(rmap_item))
1425                         cmp_and_merge_page(page, rmap_item);
1426                 put_page(page);
1427         }
1428 }
1429
1430 static int ksmd_should_run(void)
1431 {
1432         return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1433 }
1434
1435 static int ksm_scan_thread(void *nothing)
1436 {
1437         set_freezable();
1438         set_user_nice(current, 5);
1439
1440         while (!kthread_should_stop()) {
1441                 mutex_lock(&ksm_thread_mutex);
1442                 if (ksmd_should_run())
1443                         ksm_do_scan(ksm_thread_pages_to_scan);
1444                 mutex_unlock(&ksm_thread_mutex);
1445
1446                 try_to_freeze();
1447
1448                 if (ksmd_should_run()) {
1449                         schedule_timeout_interruptible(
1450                                 msecs_to_jiffies(ksm_thread_sleep_millisecs));
1451                 } else {
1452                         wait_event_freezable(ksm_thread_wait,
1453                                 ksmd_should_run() || kthread_should_stop());
1454                 }
1455         }
1456         return 0;
1457 }
1458
1459 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1460                 unsigned long end, int advice, unsigned long *vm_flags)
1461 {
1462         struct mm_struct *mm = vma->vm_mm;
1463         int err;
1464
1465         switch (advice) {
1466         case MADV_MERGEABLE:
1467                 /*
1468                  * Be somewhat over-protective for now!
1469                  */
1470                 if (*vm_flags & (VM_MERGEABLE | VM_SHARED  | VM_MAYSHARE   |
1471                                  VM_PFNMAP    | VM_IO      | VM_DONTEXPAND |
1472                                  VM_RESERVED  | VM_HUGETLB | VM_INSERTPAGE |
1473                                  VM_NONLINEAR | VM_MIXEDMAP | VM_SAO))
1474                         return 0;               /* just ignore the advice */
1475
1476                 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
1477                         err = __ksm_enter(mm);
1478                         if (err)
1479                                 return err;
1480                 }
1481
1482                 *vm_flags |= VM_MERGEABLE;
1483                 break;
1484
1485         case MADV_UNMERGEABLE:
1486                 if (!(*vm_flags & VM_MERGEABLE))
1487                         return 0;               /* just ignore the advice */
1488
1489                 if (vma->anon_vma) {
1490                         err = unmerge_ksm_pages(vma, start, end);
1491                         if (err)
1492                                 return err;
1493                 }
1494
1495                 *vm_flags &= ~VM_MERGEABLE;
1496                 break;
1497         }
1498
1499         return 0;
1500 }
1501
1502 int __ksm_enter(struct mm_struct *mm)
1503 {
1504         struct mm_slot *mm_slot;
1505         int needs_wakeup;
1506
1507         mm_slot = alloc_mm_slot();
1508         if (!mm_slot)
1509                 return -ENOMEM;
1510
1511         /* Check ksm_run too?  Would need tighter locking */
1512         needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1513
1514         spin_lock(&ksm_mmlist_lock);
1515         insert_to_mm_slots_hash(mm, mm_slot);
1516         /*
1517          * Insert just behind the scanning cursor, to let the area settle
1518          * down a little; when fork is followed by immediate exec, we don't
1519          * want ksmd to waste time setting up and tearing down an rmap_list.
1520          */
1521         list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
1522         spin_unlock(&ksm_mmlist_lock);
1523
1524         set_bit(MMF_VM_MERGEABLE, &mm->flags);
1525         atomic_inc(&mm->mm_count);
1526
1527         if (needs_wakeup)
1528                 wake_up_interruptible(&ksm_thread_wait);
1529
1530         return 0;
1531 }
1532
1533 void __ksm_exit(struct mm_struct *mm)
1534 {
1535         struct mm_slot *mm_slot;
1536         int easy_to_free = 0;
1537
1538         /*
1539          * This process is exiting: if it's straightforward (as is the
1540          * case when ksmd was never running), free mm_slot immediately.
1541          * But if it's at the cursor or has rmap_items linked to it, use
1542          * mmap_sem to synchronize with any break_cows before pagetables
1543          * are freed, and leave the mm_slot on the list for ksmd to free.
1544          * Beware: ksm may already have noticed it exiting and freed the slot.
1545          */
1546
1547         spin_lock(&ksm_mmlist_lock);
1548         mm_slot = get_mm_slot(mm);
1549         if (mm_slot && ksm_scan.mm_slot != mm_slot) {
1550                 if (!mm_slot->rmap_list) {
1551                         hlist_del(&mm_slot->link);
1552                         list_del(&mm_slot->mm_list);
1553                         easy_to_free = 1;
1554                 } else {
1555                         list_move(&mm_slot->mm_list,
1556                                   &ksm_scan.mm_slot->mm_list);
1557                 }
1558         }
1559         spin_unlock(&ksm_mmlist_lock);
1560
1561         if (easy_to_free) {
1562                 free_mm_slot(mm_slot);
1563                 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1564                 mmdrop(mm);
1565         } else if (mm_slot) {
1566                 down_write(&mm->mmap_sem);
1567                 up_write(&mm->mmap_sem);
1568         }
1569 }
1570
1571 struct page *ksm_does_need_to_copy(struct page *page,
1572                         struct vm_area_struct *vma, unsigned long address)
1573 {
1574         struct page *new_page;
1575
1576         new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
1577         if (new_page) {
1578                 copy_user_highpage(new_page, page, address, vma);
1579
1580                 SetPageDirty(new_page);
1581                 __SetPageUptodate(new_page);
1582                 SetPageSwapBacked(new_page);
1583                 __set_page_locked(new_page);
1584
1585                 if (page_evictable(new_page, vma))
1586                         lru_cache_add_lru(new_page, LRU_ACTIVE_ANON);
1587                 else
1588                         add_page_to_unevictable_list(new_page);
1589         }
1590
1591         return new_page;
1592 }
1593
1594 int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg,
1595                         unsigned long *vm_flags)
1596 {
1597         struct stable_node *stable_node;
1598         struct rmap_item *rmap_item;
1599         struct hlist_node *hlist;
1600         unsigned int mapcount = page_mapcount(page);
1601         int referenced = 0;
1602         int search_new_forks = 0;
1603
1604         VM_BUG_ON(!PageKsm(page));
1605         VM_BUG_ON(!PageLocked(page));
1606
1607         stable_node = page_stable_node(page);
1608         if (!stable_node)
1609                 return 0;
1610 again:
1611         hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1612                 struct anon_vma *anon_vma = rmap_item->anon_vma;
1613                 struct anon_vma_chain *vmac;
1614                 struct vm_area_struct *vma;
1615
1616                 anon_vma_lock(anon_vma);
1617                 list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1618                         vma = vmac->vma;
1619                         if (rmap_item->address < vma->vm_start ||
1620                             rmap_item->address >= vma->vm_end)
1621                                 continue;
1622                         /*
1623                          * Initially we examine only the vma which covers this
1624                          * rmap_item; but later, if there is still work to do,
1625                          * we examine covering vmas in other mms: in case they
1626                          * were forked from the original since ksmd passed.
1627                          */
1628                         if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1629                                 continue;
1630
1631                         if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
1632                                 continue;
1633
1634                         referenced += page_referenced_one(page, vma,
1635                                 rmap_item->address, &mapcount, vm_flags);
1636                         if (!search_new_forks || !mapcount)
1637                                 break;
1638                 }
1639                 anon_vma_unlock(anon_vma);
1640                 if (!mapcount)
1641                         goto out;
1642         }
1643         if (!search_new_forks++)
1644                 goto again;
1645 out:
1646         return referenced;
1647 }
1648
1649 int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
1650 {
1651         struct stable_node *stable_node;
1652         struct hlist_node *hlist;
1653         struct rmap_item *rmap_item;
1654         int ret = SWAP_AGAIN;
1655         int search_new_forks = 0;
1656
1657         VM_BUG_ON(!PageKsm(page));
1658         VM_BUG_ON(!PageLocked(page));
1659
1660         stable_node = page_stable_node(page);
1661         if (!stable_node)
1662                 return SWAP_FAIL;
1663 again:
1664         hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1665                 struct anon_vma *anon_vma = rmap_item->anon_vma;
1666                 struct anon_vma_chain *vmac;
1667                 struct vm_area_struct *vma;
1668
1669                 anon_vma_lock(anon_vma);
1670                 list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1671                         vma = vmac->vma;
1672                         if (rmap_item->address < vma->vm_start ||
1673                             rmap_item->address >= vma->vm_end)
1674                                 continue;
1675                         /*
1676                          * Initially we examine only the vma which covers this
1677                          * rmap_item; but later, if there is still work to do,
1678                          * we examine covering vmas in other mms: in case they
1679                          * were forked from the original since ksmd passed.
1680                          */
1681                         if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1682                                 continue;
1683
1684                         ret = try_to_unmap_one(page, vma,
1685                                         rmap_item->address, flags);
1686                         if (ret != SWAP_AGAIN || !page_mapped(page)) {
1687                                 anon_vma_unlock(anon_vma);
1688                                 goto out;
1689                         }
1690                 }
1691                 anon_vma_unlock(anon_vma);
1692         }
1693         if (!search_new_forks++)
1694                 goto again;
1695 out:
1696         return ret;
1697 }
1698
1699 #ifdef CONFIG_MIGRATION
1700 int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *,
1701                   struct vm_area_struct *, unsigned long, void *), void *arg)
1702 {
1703         struct stable_node *stable_node;
1704         struct hlist_node *hlist;
1705         struct rmap_item *rmap_item;
1706         int ret = SWAP_AGAIN;
1707         int search_new_forks = 0;
1708
1709         VM_BUG_ON(!PageKsm(page));
1710         VM_BUG_ON(!PageLocked(page));
1711
1712         stable_node = page_stable_node(page);
1713         if (!stable_node)
1714                 return ret;
1715 again:
1716         hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1717                 struct anon_vma *anon_vma = rmap_item->anon_vma;
1718                 struct anon_vma_chain *vmac;
1719                 struct vm_area_struct *vma;
1720
1721                 anon_vma_lock(anon_vma);
1722                 list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1723                         vma = vmac->vma;
1724                         if (rmap_item->address < vma->vm_start ||
1725                             rmap_item->address >= vma->vm_end)
1726                                 continue;
1727                         /*
1728                          * Initially we examine only the vma which covers this
1729                          * rmap_item; but later, if there is still work to do,
1730                          * we examine covering vmas in other mms: in case they
1731                          * were forked from the original since ksmd passed.
1732                          */
1733                         if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1734                                 continue;
1735
1736                         ret = rmap_one(page, vma, rmap_item->address, arg);
1737                         if (ret != SWAP_AGAIN) {
1738                                 anon_vma_unlock(anon_vma);
1739                                 goto out;
1740                         }
1741                 }
1742                 anon_vma_unlock(anon_vma);
1743         }
1744         if (!search_new_forks++)
1745                 goto again;
1746 out:
1747         return ret;
1748 }
1749
1750 void ksm_migrate_page(struct page *newpage, struct page *oldpage)
1751 {
1752         struct stable_node *stable_node;
1753
1754         VM_BUG_ON(!PageLocked(oldpage));
1755         VM_BUG_ON(!PageLocked(newpage));
1756         VM_BUG_ON(newpage->mapping != oldpage->mapping);
1757
1758         stable_node = page_stable_node(newpage);
1759         if (stable_node) {
1760                 VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage));
1761                 stable_node->kpfn = page_to_pfn(newpage);
1762         }
1763 }
1764 #endif /* CONFIG_MIGRATION */
1765
1766 #ifdef CONFIG_MEMORY_HOTREMOVE
1767 static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn,
1768                                                  unsigned long end_pfn)
1769 {
1770         struct rb_node *node;
1771
1772         for (node = rb_first(&root_stable_tree); node; node = rb_next(node)) {
1773                 struct stable_node *stable_node;
1774
1775                 stable_node = rb_entry(node, struct stable_node, node);
1776                 if (stable_node->kpfn >= start_pfn &&
1777                     stable_node->kpfn < end_pfn)
1778                         return stable_node;
1779         }
1780         return NULL;
1781 }
1782
1783 static int ksm_memory_callback(struct notifier_block *self,
1784                                unsigned long action, void *arg)
1785 {
1786         struct memory_notify *mn = arg;
1787         struct stable_node *stable_node;
1788
1789         switch (action) {
1790         case MEM_GOING_OFFLINE:
1791                 /*
1792                  * Keep it very simple for now: just lock out ksmd and
1793                  * MADV_UNMERGEABLE while any memory is going offline.
1794                  * mutex_lock_nested() is necessary because lockdep was alarmed
1795                  * that here we take ksm_thread_mutex inside notifier chain
1796                  * mutex, and later take notifier chain mutex inside
1797                  * ksm_thread_mutex to unlock it.   But that's safe because both
1798                  * are inside mem_hotplug_mutex.
1799                  */
1800                 mutex_lock_nested(&ksm_thread_mutex, SINGLE_DEPTH_NESTING);
1801                 break;
1802
1803         case MEM_OFFLINE:
1804                 /*
1805                  * Most of the work is done by page migration; but there might
1806                  * be a few stable_nodes left over, still pointing to struct
1807                  * pages which have been offlined: prune those from the tree.
1808                  */
1809                 while ((stable_node = ksm_check_stable_tree(mn->start_pfn,
1810                                         mn->start_pfn + mn->nr_pages)) != NULL)
1811                         remove_node_from_stable_tree(stable_node);
1812                 /* fallthrough */
1813
1814         case MEM_CANCEL_OFFLINE:
1815                 mutex_unlock(&ksm_thread_mutex);
1816                 break;
1817         }
1818         return NOTIFY_OK;
1819 }
1820 #endif /* CONFIG_MEMORY_HOTREMOVE */
1821
1822 #ifdef CONFIG_SYSFS
1823 /*
1824  * This all compiles without CONFIG_SYSFS, but is a waste of space.
1825  */
1826
1827 #define KSM_ATTR_RO(_name) \
1828         static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
1829 #define KSM_ATTR(_name) \
1830         static struct kobj_attribute _name##_attr = \
1831                 __ATTR(_name, 0644, _name##_show, _name##_store)
1832
1833 static ssize_t sleep_millisecs_show(struct kobject *kobj,
1834                                     struct kobj_attribute *attr, char *buf)
1835 {
1836         return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
1837 }
1838
1839 static ssize_t sleep_millisecs_store(struct kobject *kobj,
1840                                      struct kobj_attribute *attr,
1841                                      const char *buf, size_t count)
1842 {
1843         unsigned long msecs;
1844         int err;
1845
1846         err = strict_strtoul(buf, 10, &msecs);
1847         if (err || msecs > UINT_MAX)
1848                 return -EINVAL;
1849
1850         ksm_thread_sleep_millisecs = msecs;
1851
1852         return count;
1853 }
1854 KSM_ATTR(sleep_millisecs);
1855
1856 static ssize_t pages_to_scan_show(struct kobject *kobj,
1857                                   struct kobj_attribute *attr, char *buf)
1858 {
1859         return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
1860 }
1861
1862 static ssize_t pages_to_scan_store(struct kobject *kobj,
1863                                    struct kobj_attribute *attr,
1864                                    const char *buf, size_t count)
1865 {
1866         int err;
1867         unsigned long nr_pages;
1868
1869         err = strict_strtoul(buf, 10, &nr_pages);
1870         if (err || nr_pages > UINT_MAX)
1871                 return -EINVAL;
1872
1873         ksm_thread_pages_to_scan = nr_pages;
1874
1875         return count;
1876 }
1877 KSM_ATTR(pages_to_scan);
1878
1879 static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
1880                         char *buf)
1881 {
1882         return sprintf(buf, "%u\n", ksm_run);
1883 }
1884
1885 static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
1886                          const char *buf, size_t count)
1887 {
1888         int err;
1889         unsigned long flags;
1890
1891         err = strict_strtoul(buf, 10, &flags);
1892         if (err || flags > UINT_MAX)
1893                 return -EINVAL;
1894         if (flags > KSM_RUN_UNMERGE)
1895                 return -EINVAL;
1896
1897         /*
1898          * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
1899          * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
1900          * breaking COW to free the pages_shared (but leaves mm_slots
1901          * on the list for when ksmd may be set running again).
1902          */
1903
1904         mutex_lock(&ksm_thread_mutex);
1905         if (ksm_run != flags) {
1906                 ksm_run = flags;
1907                 if (flags & KSM_RUN_UNMERGE) {
1908                         int oom_score_adj;
1909
1910                         oom_score_adj = test_set_oom_score_adj(OOM_SCORE_ADJ_MAX);
1911                         err = unmerge_and_remove_all_rmap_items();
1912                         compare_swap_oom_score_adj(OOM_SCORE_ADJ_MAX,
1913                                                                 oom_score_adj);
1914                         if (err) {
1915                                 ksm_run = KSM_RUN_STOP;
1916                                 count = err;
1917                         }
1918                 }
1919         }
1920         mutex_unlock(&ksm_thread_mutex);
1921
1922         if (flags & KSM_RUN_MERGE)
1923                 wake_up_interruptible(&ksm_thread_wait);
1924
1925         return count;
1926 }
1927 KSM_ATTR(run);
1928
1929 static ssize_t pages_shared_show(struct kobject *kobj,
1930                                  struct kobj_attribute *attr, char *buf)
1931 {
1932         return sprintf(buf, "%lu\n", ksm_pages_shared);
1933 }
1934 KSM_ATTR_RO(pages_shared);
1935
1936 static ssize_t pages_sharing_show(struct kobject *kobj,
1937                                   struct kobj_attribute *attr, char *buf)
1938 {
1939         return sprintf(buf, "%lu\n", ksm_pages_sharing);
1940 }
1941 KSM_ATTR_RO(pages_sharing);
1942
1943 static ssize_t pages_unshared_show(struct kobject *kobj,
1944                                    struct kobj_attribute *attr, char *buf)
1945 {
1946         return sprintf(buf, "%lu\n", ksm_pages_unshared);
1947 }
1948 KSM_ATTR_RO(pages_unshared);
1949
1950 static ssize_t pages_volatile_show(struct kobject *kobj,
1951                                    struct kobj_attribute *attr, char *buf)
1952 {
1953         long ksm_pages_volatile;
1954
1955         ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
1956                                 - ksm_pages_sharing - ksm_pages_unshared;
1957         /*
1958          * It was not worth any locking to calculate that statistic,
1959          * but it might therefore sometimes be negative: conceal that.
1960          */
1961         if (ksm_pages_volatile < 0)
1962                 ksm_pages_volatile = 0;
1963         return sprintf(buf, "%ld\n", ksm_pages_volatile);
1964 }
1965 KSM_ATTR_RO(pages_volatile);
1966
1967 static ssize_t full_scans_show(struct kobject *kobj,
1968                                struct kobj_attribute *attr, char *buf)
1969 {
1970         return sprintf(buf, "%lu\n", ksm_scan.seqnr);
1971 }
1972 KSM_ATTR_RO(full_scans);
1973
1974 static struct attribute *ksm_attrs[] = {
1975         &sleep_millisecs_attr.attr,
1976         &pages_to_scan_attr.attr,
1977         &run_attr.attr,
1978         &pages_shared_attr.attr,
1979         &pages_sharing_attr.attr,
1980         &pages_unshared_attr.attr,
1981         &pages_volatile_attr.attr,
1982         &full_scans_attr.attr,
1983         NULL,
1984 };
1985
1986 static struct attribute_group ksm_attr_group = {
1987         .attrs = ksm_attrs,
1988         .name = "ksm",
1989 };
1990 #endif /* CONFIG_SYSFS */
1991
1992 static int __init ksm_init(void)
1993 {
1994         struct task_struct *ksm_thread;
1995         int err;
1996
1997         err = ksm_slab_init();
1998         if (err)
1999                 goto out;
2000
2001         ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
2002         if (IS_ERR(ksm_thread)) {
2003                 printk(KERN_ERR "ksm: creating kthread failed\n");
2004                 err = PTR_ERR(ksm_thread);
2005                 goto out_free;
2006         }
2007
2008 #ifdef CONFIG_SYSFS
2009         err = sysfs_create_group(mm_kobj, &ksm_attr_group);
2010         if (err) {
2011                 printk(KERN_ERR "ksm: register sysfs failed\n");
2012                 kthread_stop(ksm_thread);
2013                 goto out_free;
2014         }
2015 #else
2016         ksm_run = KSM_RUN_MERGE;        /* no way for user to start it */
2017
2018 #endif /* CONFIG_SYSFS */
2019
2020 #ifdef CONFIG_MEMORY_HOTREMOVE
2021         /*
2022          * Choose a high priority since the callback takes ksm_thread_mutex:
2023          * later callbacks could only be taking locks which nest within that.
2024          */
2025         hotplug_memory_notifier(ksm_memory_callback, 100);
2026 #endif
2027         return 0;
2028
2029 out_free:
2030         ksm_slab_free();
2031 out:
2032         return err;
2033 }
2034 module_init(ksm_init)