mm: compaction: ensure that the compaction free scanner does not move to the next...
[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 next_mm:
1306                 ksm_scan.address = 0;
1307                 ksm_scan.rmap_list = &slot->rmap_list;
1308         }
1309
1310         mm = slot->mm;
1311         down_read(&mm->mmap_sem);
1312         if (ksm_test_exit(mm))
1313                 vma = NULL;
1314         else
1315                 vma = find_vma(mm, ksm_scan.address);
1316
1317         for (; vma; vma = vma->vm_next) {
1318                 if (!(vma->vm_flags & VM_MERGEABLE))
1319                         continue;
1320                 if (ksm_scan.address < vma->vm_start)
1321                         ksm_scan.address = vma->vm_start;
1322                 if (!vma->anon_vma)
1323                         ksm_scan.address = vma->vm_end;
1324
1325                 while (ksm_scan.address < vma->vm_end) {
1326                         if (ksm_test_exit(mm))
1327                                 break;
1328                         *page = follow_page(vma, ksm_scan.address, FOLL_GET);
1329                         if (IS_ERR_OR_NULL(*page)) {
1330                                 ksm_scan.address += PAGE_SIZE;
1331                                 cond_resched();
1332                                 continue;
1333                         }
1334                         if (PageAnon(*page) ||
1335                             page_trans_compound_anon(*page)) {
1336                                 flush_anon_page(vma, *page, ksm_scan.address);
1337                                 flush_dcache_page(*page);
1338                                 rmap_item = get_next_rmap_item(slot,
1339                                         ksm_scan.rmap_list, ksm_scan.address);
1340                                 if (rmap_item) {
1341                                         ksm_scan.rmap_list =
1342                                                         &rmap_item->rmap_list;
1343                                         ksm_scan.address += PAGE_SIZE;
1344                                 } else
1345                                         put_page(*page);
1346                                 up_read(&mm->mmap_sem);
1347                                 return rmap_item;
1348                         }
1349                         put_page(*page);
1350                         ksm_scan.address += PAGE_SIZE;
1351                         cond_resched();
1352                 }
1353         }
1354
1355         if (ksm_test_exit(mm)) {
1356                 ksm_scan.address = 0;
1357                 ksm_scan.rmap_list = &slot->rmap_list;
1358         }
1359         /*
1360          * Nuke all the rmap_items that are above this current rmap:
1361          * because there were no VM_MERGEABLE vmas with such addresses.
1362          */
1363         remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
1364
1365         spin_lock(&ksm_mmlist_lock);
1366         ksm_scan.mm_slot = list_entry(slot->mm_list.next,
1367                                                 struct mm_slot, mm_list);
1368         if (ksm_scan.address == 0) {
1369                 /*
1370                  * We've completed a full scan of all vmas, holding mmap_sem
1371                  * throughout, and found no VM_MERGEABLE: so do the same as
1372                  * __ksm_exit does to remove this mm from all our lists now.
1373                  * This applies either when cleaning up after __ksm_exit
1374                  * (but beware: we can reach here even before __ksm_exit),
1375                  * or when all VM_MERGEABLE areas have been unmapped (and
1376                  * mmap_sem then protects against race with MADV_MERGEABLE).
1377                  */
1378                 hlist_del(&slot->link);
1379                 list_del(&slot->mm_list);
1380                 spin_unlock(&ksm_mmlist_lock);
1381
1382                 free_mm_slot(slot);
1383                 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1384                 up_read(&mm->mmap_sem);
1385                 mmdrop(mm);
1386         } else {
1387                 spin_unlock(&ksm_mmlist_lock);
1388                 up_read(&mm->mmap_sem);
1389         }
1390
1391         /* Repeat until we've completed scanning the whole list */
1392         slot = ksm_scan.mm_slot;
1393         if (slot != &ksm_mm_head)
1394                 goto next_mm;
1395
1396         ksm_scan.seqnr++;
1397         return NULL;
1398 }
1399
1400 /**
1401  * ksm_do_scan  - the ksm scanner main worker function.
1402  * @scan_npages - number of pages we want to scan before we return.
1403  */
1404 static void ksm_do_scan(unsigned int scan_npages)
1405 {
1406         struct rmap_item *rmap_item;
1407         struct page *uninitialized_var(page);
1408
1409         while (scan_npages-- && likely(!freezing(current))) {
1410                 cond_resched();
1411                 rmap_item = scan_get_next_rmap_item(&page);
1412                 if (!rmap_item)
1413                         return;
1414                 if (!PageKsm(page) || !in_stable_tree(rmap_item))
1415                         cmp_and_merge_page(page, rmap_item);
1416                 put_page(page);
1417         }
1418 }
1419
1420 static int ksmd_should_run(void)
1421 {
1422         return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1423 }
1424
1425 static int ksm_scan_thread(void *nothing)
1426 {
1427         set_freezable();
1428         set_user_nice(current, 5);
1429
1430         while (!kthread_should_stop()) {
1431                 mutex_lock(&ksm_thread_mutex);
1432                 if (ksmd_should_run())
1433                         ksm_do_scan(ksm_thread_pages_to_scan);
1434                 mutex_unlock(&ksm_thread_mutex);
1435
1436                 try_to_freeze();
1437
1438                 if (ksmd_should_run()) {
1439                         schedule_timeout_interruptible(
1440                                 msecs_to_jiffies(ksm_thread_sleep_millisecs));
1441                 } else {
1442                         wait_event_freezable(ksm_thread_wait,
1443                                 ksmd_should_run() || kthread_should_stop());
1444                 }
1445         }
1446         return 0;
1447 }
1448
1449 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1450                 unsigned long end, int advice, unsigned long *vm_flags)
1451 {
1452         struct mm_struct *mm = vma->vm_mm;
1453         int err;
1454
1455         switch (advice) {
1456         case MADV_MERGEABLE:
1457                 /*
1458                  * Be somewhat over-protective for now!
1459                  */
1460                 if (*vm_flags & (VM_MERGEABLE | VM_SHARED  | VM_MAYSHARE   |
1461                                  VM_PFNMAP    | VM_IO      | VM_DONTEXPAND |
1462                                  VM_RESERVED  | VM_HUGETLB | VM_INSERTPAGE |
1463                                  VM_NONLINEAR | VM_MIXEDMAP | VM_SAO))
1464                         return 0;               /* just ignore the advice */
1465
1466                 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
1467                         err = __ksm_enter(mm);
1468                         if (err)
1469                                 return err;
1470                 }
1471
1472                 *vm_flags |= VM_MERGEABLE;
1473                 break;
1474
1475         case MADV_UNMERGEABLE:
1476                 if (!(*vm_flags & VM_MERGEABLE))
1477                         return 0;               /* just ignore the advice */
1478
1479                 if (vma->anon_vma) {
1480                         err = unmerge_ksm_pages(vma, start, end);
1481                         if (err)
1482                                 return err;
1483                 }
1484
1485                 *vm_flags &= ~VM_MERGEABLE;
1486                 break;
1487         }
1488
1489         return 0;
1490 }
1491
1492 int __ksm_enter(struct mm_struct *mm)
1493 {
1494         struct mm_slot *mm_slot;
1495         int needs_wakeup;
1496
1497         mm_slot = alloc_mm_slot();
1498         if (!mm_slot)
1499                 return -ENOMEM;
1500
1501         /* Check ksm_run too?  Would need tighter locking */
1502         needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1503
1504         spin_lock(&ksm_mmlist_lock);
1505         insert_to_mm_slots_hash(mm, mm_slot);
1506         /*
1507          * Insert just behind the scanning cursor, to let the area settle
1508          * down a little; when fork is followed by immediate exec, we don't
1509          * want ksmd to waste time setting up and tearing down an rmap_list.
1510          */
1511         list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
1512         spin_unlock(&ksm_mmlist_lock);
1513
1514         set_bit(MMF_VM_MERGEABLE, &mm->flags);
1515         atomic_inc(&mm->mm_count);
1516
1517         if (needs_wakeup)
1518                 wake_up_interruptible(&ksm_thread_wait);
1519
1520         return 0;
1521 }
1522
1523 void __ksm_exit(struct mm_struct *mm)
1524 {
1525         struct mm_slot *mm_slot;
1526         int easy_to_free = 0;
1527
1528         /*
1529          * This process is exiting: if it's straightforward (as is the
1530          * case when ksmd was never running), free mm_slot immediately.
1531          * But if it's at the cursor or has rmap_items linked to it, use
1532          * mmap_sem to synchronize with any break_cows before pagetables
1533          * are freed, and leave the mm_slot on the list for ksmd to free.
1534          * Beware: ksm may already have noticed it exiting and freed the slot.
1535          */
1536
1537         spin_lock(&ksm_mmlist_lock);
1538         mm_slot = get_mm_slot(mm);
1539         if (mm_slot && ksm_scan.mm_slot != mm_slot) {
1540                 if (!mm_slot->rmap_list) {
1541                         hlist_del(&mm_slot->link);
1542                         list_del(&mm_slot->mm_list);
1543                         easy_to_free = 1;
1544                 } else {
1545                         list_move(&mm_slot->mm_list,
1546                                   &ksm_scan.mm_slot->mm_list);
1547                 }
1548         }
1549         spin_unlock(&ksm_mmlist_lock);
1550
1551         if (easy_to_free) {
1552                 free_mm_slot(mm_slot);
1553                 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1554                 mmdrop(mm);
1555         } else if (mm_slot) {
1556                 down_write(&mm->mmap_sem);
1557                 up_write(&mm->mmap_sem);
1558         }
1559 }
1560
1561 struct page *ksm_does_need_to_copy(struct page *page,
1562                         struct vm_area_struct *vma, unsigned long address)
1563 {
1564         struct page *new_page;
1565
1566         new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
1567         if (new_page) {
1568                 copy_user_highpage(new_page, page, address, vma);
1569
1570                 SetPageDirty(new_page);
1571                 __SetPageUptodate(new_page);
1572                 SetPageSwapBacked(new_page);
1573                 __set_page_locked(new_page);
1574
1575                 if (page_evictable(new_page, vma))
1576                         lru_cache_add_lru(new_page, LRU_ACTIVE_ANON);
1577                 else
1578                         add_page_to_unevictable_list(new_page);
1579         }
1580
1581         return new_page;
1582 }
1583
1584 int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg,
1585                         unsigned long *vm_flags)
1586 {
1587         struct stable_node *stable_node;
1588         struct rmap_item *rmap_item;
1589         struct hlist_node *hlist;
1590         unsigned int mapcount = page_mapcount(page);
1591         int referenced = 0;
1592         int search_new_forks = 0;
1593
1594         VM_BUG_ON(!PageKsm(page));
1595         VM_BUG_ON(!PageLocked(page));
1596
1597         stable_node = page_stable_node(page);
1598         if (!stable_node)
1599                 return 0;
1600 again:
1601         hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1602                 struct anon_vma *anon_vma = rmap_item->anon_vma;
1603                 struct anon_vma_chain *vmac;
1604                 struct vm_area_struct *vma;
1605
1606                 anon_vma_lock(anon_vma);
1607                 list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1608                         vma = vmac->vma;
1609                         if (rmap_item->address < vma->vm_start ||
1610                             rmap_item->address >= vma->vm_end)
1611                                 continue;
1612                         /*
1613                          * Initially we examine only the vma which covers this
1614                          * rmap_item; but later, if there is still work to do,
1615                          * we examine covering vmas in other mms: in case they
1616                          * were forked from the original since ksmd passed.
1617                          */
1618                         if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1619                                 continue;
1620
1621                         if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
1622                                 continue;
1623
1624                         referenced += page_referenced_one(page, vma,
1625                                 rmap_item->address, &mapcount, vm_flags);
1626                         if (!search_new_forks || !mapcount)
1627                                 break;
1628                 }
1629                 anon_vma_unlock(anon_vma);
1630                 if (!mapcount)
1631                         goto out;
1632         }
1633         if (!search_new_forks++)
1634                 goto again;
1635 out:
1636         return referenced;
1637 }
1638
1639 int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
1640 {
1641         struct stable_node *stable_node;
1642         struct hlist_node *hlist;
1643         struct rmap_item *rmap_item;
1644         int ret = SWAP_AGAIN;
1645         int search_new_forks = 0;
1646
1647         VM_BUG_ON(!PageKsm(page));
1648         VM_BUG_ON(!PageLocked(page));
1649
1650         stable_node = page_stable_node(page);
1651         if (!stable_node)
1652                 return SWAP_FAIL;
1653 again:
1654         hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1655                 struct anon_vma *anon_vma = rmap_item->anon_vma;
1656                 struct anon_vma_chain *vmac;
1657                 struct vm_area_struct *vma;
1658
1659                 anon_vma_lock(anon_vma);
1660                 list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1661                         vma = vmac->vma;
1662                         if (rmap_item->address < vma->vm_start ||
1663                             rmap_item->address >= vma->vm_end)
1664                                 continue;
1665                         /*
1666                          * Initially we examine only the vma which covers this
1667                          * rmap_item; but later, if there is still work to do,
1668                          * we examine covering vmas in other mms: in case they
1669                          * were forked from the original since ksmd passed.
1670                          */
1671                         if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1672                                 continue;
1673
1674                         ret = try_to_unmap_one(page, vma,
1675                                         rmap_item->address, flags);
1676                         if (ret != SWAP_AGAIN || !page_mapped(page)) {
1677                                 anon_vma_unlock(anon_vma);
1678                                 goto out;
1679                         }
1680                 }
1681                 anon_vma_unlock(anon_vma);
1682         }
1683         if (!search_new_forks++)
1684                 goto again;
1685 out:
1686         return ret;
1687 }
1688
1689 #ifdef CONFIG_MIGRATION
1690 int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *,
1691                   struct vm_area_struct *, unsigned long, void *), void *arg)
1692 {
1693         struct stable_node *stable_node;
1694         struct hlist_node *hlist;
1695         struct rmap_item *rmap_item;
1696         int ret = SWAP_AGAIN;
1697         int search_new_forks = 0;
1698
1699         VM_BUG_ON(!PageKsm(page));
1700         VM_BUG_ON(!PageLocked(page));
1701
1702         stable_node = page_stable_node(page);
1703         if (!stable_node)
1704                 return ret;
1705 again:
1706         hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1707                 struct anon_vma *anon_vma = rmap_item->anon_vma;
1708                 struct anon_vma_chain *vmac;
1709                 struct vm_area_struct *vma;
1710
1711                 anon_vma_lock(anon_vma);
1712                 list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1713                         vma = vmac->vma;
1714                         if (rmap_item->address < vma->vm_start ||
1715                             rmap_item->address >= vma->vm_end)
1716                                 continue;
1717                         /*
1718                          * Initially we examine only the vma which covers this
1719                          * rmap_item; but later, if there is still work to do,
1720                          * we examine covering vmas in other mms: in case they
1721                          * were forked from the original since ksmd passed.
1722                          */
1723                         if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1724                                 continue;
1725
1726                         ret = rmap_one(page, vma, rmap_item->address, arg);
1727                         if (ret != SWAP_AGAIN) {
1728                                 anon_vma_unlock(anon_vma);
1729                                 goto out;
1730                         }
1731                 }
1732                 anon_vma_unlock(anon_vma);
1733         }
1734         if (!search_new_forks++)
1735                 goto again;
1736 out:
1737         return ret;
1738 }
1739
1740 void ksm_migrate_page(struct page *newpage, struct page *oldpage)
1741 {
1742         struct stable_node *stable_node;
1743
1744         VM_BUG_ON(!PageLocked(oldpage));
1745         VM_BUG_ON(!PageLocked(newpage));
1746         VM_BUG_ON(newpage->mapping != oldpage->mapping);
1747
1748         stable_node = page_stable_node(newpage);
1749         if (stable_node) {
1750                 VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage));
1751                 stable_node->kpfn = page_to_pfn(newpage);
1752         }
1753 }
1754 #endif /* CONFIG_MIGRATION */
1755
1756 #ifdef CONFIG_MEMORY_HOTREMOVE
1757 static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn,
1758                                                  unsigned long end_pfn)
1759 {
1760         struct rb_node *node;
1761
1762         for (node = rb_first(&root_stable_tree); node; node = rb_next(node)) {
1763                 struct stable_node *stable_node;
1764
1765                 stable_node = rb_entry(node, struct stable_node, node);
1766                 if (stable_node->kpfn >= start_pfn &&
1767                     stable_node->kpfn < end_pfn)
1768                         return stable_node;
1769         }
1770         return NULL;
1771 }
1772
1773 static int ksm_memory_callback(struct notifier_block *self,
1774                                unsigned long action, void *arg)
1775 {
1776         struct memory_notify *mn = arg;
1777         struct stable_node *stable_node;
1778
1779         switch (action) {
1780         case MEM_GOING_OFFLINE:
1781                 /*
1782                  * Keep it very simple for now: just lock out ksmd and
1783                  * MADV_UNMERGEABLE while any memory is going offline.
1784                  * mutex_lock_nested() is necessary because lockdep was alarmed
1785                  * that here we take ksm_thread_mutex inside notifier chain
1786                  * mutex, and later take notifier chain mutex inside
1787                  * ksm_thread_mutex to unlock it.   But that's safe because both
1788                  * are inside mem_hotplug_mutex.
1789                  */
1790                 mutex_lock_nested(&ksm_thread_mutex, SINGLE_DEPTH_NESTING);
1791                 break;
1792
1793         case MEM_OFFLINE:
1794                 /*
1795                  * Most of the work is done by page migration; but there might
1796                  * be a few stable_nodes left over, still pointing to struct
1797                  * pages which have been offlined: prune those from the tree.
1798                  */
1799                 while ((stable_node = ksm_check_stable_tree(mn->start_pfn,
1800                                         mn->start_pfn + mn->nr_pages)) != NULL)
1801                         remove_node_from_stable_tree(stable_node);
1802                 /* fallthrough */
1803
1804         case MEM_CANCEL_OFFLINE:
1805                 mutex_unlock(&ksm_thread_mutex);
1806                 break;
1807         }
1808         return NOTIFY_OK;
1809 }
1810 #endif /* CONFIG_MEMORY_HOTREMOVE */
1811
1812 #ifdef CONFIG_SYSFS
1813 /*
1814  * This all compiles without CONFIG_SYSFS, but is a waste of space.
1815  */
1816
1817 #define KSM_ATTR_RO(_name) \
1818         static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
1819 #define KSM_ATTR(_name) \
1820         static struct kobj_attribute _name##_attr = \
1821                 __ATTR(_name, 0644, _name##_show, _name##_store)
1822
1823 static ssize_t sleep_millisecs_show(struct kobject *kobj,
1824                                     struct kobj_attribute *attr, char *buf)
1825 {
1826         return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
1827 }
1828
1829 static ssize_t sleep_millisecs_store(struct kobject *kobj,
1830                                      struct kobj_attribute *attr,
1831                                      const char *buf, size_t count)
1832 {
1833         unsigned long msecs;
1834         int err;
1835
1836         err = strict_strtoul(buf, 10, &msecs);
1837         if (err || msecs > UINT_MAX)
1838                 return -EINVAL;
1839
1840         ksm_thread_sleep_millisecs = msecs;
1841
1842         return count;
1843 }
1844 KSM_ATTR(sleep_millisecs);
1845
1846 static ssize_t pages_to_scan_show(struct kobject *kobj,
1847                                   struct kobj_attribute *attr, char *buf)
1848 {
1849         return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
1850 }
1851
1852 static ssize_t pages_to_scan_store(struct kobject *kobj,
1853                                    struct kobj_attribute *attr,
1854                                    const char *buf, size_t count)
1855 {
1856         int err;
1857         unsigned long nr_pages;
1858
1859         err = strict_strtoul(buf, 10, &nr_pages);
1860         if (err || nr_pages > UINT_MAX)
1861                 return -EINVAL;
1862
1863         ksm_thread_pages_to_scan = nr_pages;
1864
1865         return count;
1866 }
1867 KSM_ATTR(pages_to_scan);
1868
1869 static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
1870                         char *buf)
1871 {
1872         return sprintf(buf, "%u\n", ksm_run);
1873 }
1874
1875 static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
1876                          const char *buf, size_t count)
1877 {
1878         int err;
1879         unsigned long flags;
1880
1881         err = strict_strtoul(buf, 10, &flags);
1882         if (err || flags > UINT_MAX)
1883                 return -EINVAL;
1884         if (flags > KSM_RUN_UNMERGE)
1885                 return -EINVAL;
1886
1887         /*
1888          * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
1889          * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
1890          * breaking COW to free the pages_shared (but leaves mm_slots
1891          * on the list for when ksmd may be set running again).
1892          */
1893
1894         mutex_lock(&ksm_thread_mutex);
1895         if (ksm_run != flags) {
1896                 ksm_run = flags;
1897                 if (flags & KSM_RUN_UNMERGE) {
1898                         int oom_score_adj;
1899
1900                         oom_score_adj = test_set_oom_score_adj(OOM_SCORE_ADJ_MAX);
1901                         err = unmerge_and_remove_all_rmap_items();
1902                         test_set_oom_score_adj(oom_score_adj);
1903                         if (err) {
1904                                 ksm_run = KSM_RUN_STOP;
1905                                 count = err;
1906                         }
1907                 }
1908         }
1909         mutex_unlock(&ksm_thread_mutex);
1910
1911         if (flags & KSM_RUN_MERGE)
1912                 wake_up_interruptible(&ksm_thread_wait);
1913
1914         return count;
1915 }
1916 KSM_ATTR(run);
1917
1918 static ssize_t pages_shared_show(struct kobject *kobj,
1919                                  struct kobj_attribute *attr, char *buf)
1920 {
1921         return sprintf(buf, "%lu\n", ksm_pages_shared);
1922 }
1923 KSM_ATTR_RO(pages_shared);
1924
1925 static ssize_t pages_sharing_show(struct kobject *kobj,
1926                                   struct kobj_attribute *attr, char *buf)
1927 {
1928         return sprintf(buf, "%lu\n", ksm_pages_sharing);
1929 }
1930 KSM_ATTR_RO(pages_sharing);
1931
1932 static ssize_t pages_unshared_show(struct kobject *kobj,
1933                                    struct kobj_attribute *attr, char *buf)
1934 {
1935         return sprintf(buf, "%lu\n", ksm_pages_unshared);
1936 }
1937 KSM_ATTR_RO(pages_unshared);
1938
1939 static ssize_t pages_volatile_show(struct kobject *kobj,
1940                                    struct kobj_attribute *attr, char *buf)
1941 {
1942         long ksm_pages_volatile;
1943
1944         ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
1945                                 - ksm_pages_sharing - ksm_pages_unshared;
1946         /*
1947          * It was not worth any locking to calculate that statistic,
1948          * but it might therefore sometimes be negative: conceal that.
1949          */
1950         if (ksm_pages_volatile < 0)
1951                 ksm_pages_volatile = 0;
1952         return sprintf(buf, "%ld\n", ksm_pages_volatile);
1953 }
1954 KSM_ATTR_RO(pages_volatile);
1955
1956 static ssize_t full_scans_show(struct kobject *kobj,
1957                                struct kobj_attribute *attr, char *buf)
1958 {
1959         return sprintf(buf, "%lu\n", ksm_scan.seqnr);
1960 }
1961 KSM_ATTR_RO(full_scans);
1962
1963 static struct attribute *ksm_attrs[] = {
1964         &sleep_millisecs_attr.attr,
1965         &pages_to_scan_attr.attr,
1966         &run_attr.attr,
1967         &pages_shared_attr.attr,
1968         &pages_sharing_attr.attr,
1969         &pages_unshared_attr.attr,
1970         &pages_volatile_attr.attr,
1971         &full_scans_attr.attr,
1972         NULL,
1973 };
1974
1975 static struct attribute_group ksm_attr_group = {
1976         .attrs = ksm_attrs,
1977         .name = "ksm",
1978 };
1979 #endif /* CONFIG_SYSFS */
1980
1981 static int __init ksm_init(void)
1982 {
1983         struct task_struct *ksm_thread;
1984         int err;
1985
1986         err = ksm_slab_init();
1987         if (err)
1988                 goto out;
1989
1990         ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
1991         if (IS_ERR(ksm_thread)) {
1992                 printk(KERN_ERR "ksm: creating kthread failed\n");
1993                 err = PTR_ERR(ksm_thread);
1994                 goto out_free;
1995         }
1996
1997 #ifdef CONFIG_SYSFS
1998         err = sysfs_create_group(mm_kobj, &ksm_attr_group);
1999         if (err) {
2000                 printk(KERN_ERR "ksm: register sysfs failed\n");
2001                 kthread_stop(ksm_thread);
2002                 goto out_free;
2003         }
2004 #else
2005         ksm_run = KSM_RUN_MERGE;        /* no way for user to start it */
2006
2007 #endif /* CONFIG_SYSFS */
2008
2009 #ifdef CONFIG_MEMORY_HOTREMOVE
2010         /*
2011          * Choose a high priority since the callback takes ksm_thread_mutex:
2012          * later callbacks could only be taking locks which nest within that.
2013          */
2014         hotplug_memory_notifier(ksm_memory_callback, 100);
2015 #endif
2016         return 0;
2017
2018 out_free:
2019         ksm_slab_free();
2020 out:
2021         return err;
2022 }
2023 module_init(ksm_init)