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