dfdc292d3626d43ab638871e103dcba9899d29b5
[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/mmu_notifier.h>
33 #include <linux/swap.h>
34 #include <linux/ksm.h>
35
36 #include <asm/tlbflush.h>
37 #include "internal.h"
38
39 /*
40  * A few notes about the KSM scanning process,
41  * to make it easier to understand the data structures below:
42  *
43  * In order to reduce excessive scanning, KSM sorts the memory pages by their
44  * contents into a data structure that holds pointers to the pages' locations.
45  *
46  * Since the contents of the pages may change at any moment, KSM cannot just
47  * insert the pages into a normal sorted tree and expect it to find anything.
48  * Therefore KSM uses two data structures - the stable and the unstable tree.
49  *
50  * The stable tree holds pointers to all the merged pages (ksm pages), sorted
51  * by their contents.  Because each such page is write-protected, searching on
52  * this tree is fully assured to be working (except when pages are unmapped),
53  * and therefore this tree is called the stable tree.
54  *
55  * In addition to the stable tree, KSM uses a second data structure called the
56  * unstable tree: this tree holds pointers to pages which have been found to
57  * be "unchanged for a period of time".  The unstable tree sorts these pages
58  * by their contents, but since they are not write-protected, KSM cannot rely
59  * upon the unstable tree to work correctly - the unstable tree is liable to
60  * be corrupted as its contents are modified, and so it is called unstable.
61  *
62  * KSM solves this problem by several techniques:
63  *
64  * 1) The unstable tree is flushed every time KSM completes scanning all
65  *    memory areas, and then the tree is rebuilt again from the beginning.
66  * 2) KSM will only insert into the unstable tree, pages whose hash value
67  *    has not changed since the previous scan of all memory areas.
68  * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
69  *    colors of the nodes and not on their contents, assuring that even when
70  *    the tree gets "corrupted" it won't get out of balance, so scanning time
71  *    remains the same (also, searching and inserting nodes in an rbtree uses
72  *    the same algorithm, so we have no overhead when we flush and rebuild).
73  * 4) KSM never flushes the stable tree, which means that even if it were to
74  *    take 10 attempts to find a page in the unstable tree, once it is found,
75  *    it is secured in the stable tree.  (When we scan a new page, we first
76  *    compare it against the stable tree, and then against the unstable tree.)
77  */
78
79 /**
80  * struct mm_slot - ksm information per mm that is being scanned
81  * @link: link to the mm_slots hash list
82  * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
83  * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
84  * @mm: the mm that this information is valid for
85  */
86 struct mm_slot {
87         struct hlist_node link;
88         struct list_head mm_list;
89         struct rmap_item *rmap_list;
90         struct mm_struct *mm;
91 };
92
93 /**
94  * struct ksm_scan - cursor for scanning
95  * @mm_slot: the current mm_slot we are scanning
96  * @address: the next address inside that to be scanned
97  * @rmap_list: link to the next rmap to be scanned in the rmap_list
98  * @seqnr: count of completed full scans (needed when removing unstable node)
99  *
100  * There is only the one ksm_scan instance of this cursor structure.
101  */
102 struct ksm_scan {
103         struct mm_slot *mm_slot;
104         unsigned long address;
105         struct rmap_item **rmap_list;
106         unsigned long seqnr;
107 };
108
109 /**
110  * struct stable_node - node of the stable rbtree
111  * @page: pointer to struct page of the ksm page
112  * @node: rb node of this ksm page in the stable tree
113  * @hlist: hlist head of rmap_items using this ksm page
114  */
115 struct stable_node {
116         struct page *page;
117         struct rb_node node;
118         struct hlist_head hlist;
119 };
120
121 /**
122  * struct rmap_item - reverse mapping item for virtual addresses
123  * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
124  * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
125  * @mm: the memory structure this rmap_item is pointing into
126  * @address: the virtual address this rmap_item tracks (+ flags in low bits)
127  * @oldchecksum: previous checksum of the page at that virtual address
128  * @node: rb node of this rmap_item in the unstable tree
129  * @head: pointer to stable_node heading this list in the stable tree
130  * @hlist: link into hlist of rmap_items hanging off that stable_node
131  */
132 struct rmap_item {
133         struct rmap_item *rmap_list;
134         struct anon_vma *anon_vma;      /* when stable */
135         struct mm_struct *mm;
136         unsigned long address;          /* + low bits used for flags below */
137         unsigned int oldchecksum;       /* when unstable */
138         union {
139                 struct rb_node node;    /* when node of unstable tree */
140                 struct {                /* when listed from stable tree */
141                         struct stable_node *head;
142                         struct hlist_node hlist;
143                 };
144         };
145 };
146
147 #define SEQNR_MASK      0x0ff   /* low bits of unstable tree seqnr */
148 #define UNSTABLE_FLAG   0x100   /* is a node of the unstable tree */
149 #define STABLE_FLAG     0x200   /* is listed from the stable tree */
150
151 /* The stable and unstable tree heads */
152 static struct rb_root root_stable_tree = RB_ROOT;
153 static struct rb_root root_unstable_tree = RB_ROOT;
154
155 #define MM_SLOTS_HASH_HEADS 1024
156 static struct hlist_head *mm_slots_hash;
157
158 static struct mm_slot ksm_mm_head = {
159         .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
160 };
161 static struct ksm_scan ksm_scan = {
162         .mm_slot = &ksm_mm_head,
163 };
164
165 static struct kmem_cache *rmap_item_cache;
166 static struct kmem_cache *stable_node_cache;
167 static struct kmem_cache *mm_slot_cache;
168
169 /* The number of nodes in the stable tree */
170 static unsigned long ksm_pages_shared;
171
172 /* The number of page slots additionally sharing those nodes */
173 static unsigned long ksm_pages_sharing;
174
175 /* The number of nodes in the unstable tree */
176 static unsigned long ksm_pages_unshared;
177
178 /* The number of rmap_items in use: to calculate pages_volatile */
179 static unsigned long ksm_rmap_items;
180
181 /* Limit on the number of unswappable pages used */
182 static unsigned long ksm_max_kernel_pages;
183
184 /* Number of pages ksmd should scan in one batch */
185 static unsigned int ksm_thread_pages_to_scan = 100;
186
187 /* Milliseconds ksmd should sleep between batches */
188 static unsigned int ksm_thread_sleep_millisecs = 20;
189
190 #define KSM_RUN_STOP    0
191 #define KSM_RUN_MERGE   1
192 #define KSM_RUN_UNMERGE 2
193 static unsigned int ksm_run = KSM_RUN_STOP;
194
195 static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
196 static DEFINE_MUTEX(ksm_thread_mutex);
197 static DEFINE_SPINLOCK(ksm_mmlist_lock);
198
199 #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
200                 sizeof(struct __struct), __alignof__(struct __struct),\
201                 (__flags), NULL)
202
203 static int __init ksm_slab_init(void)
204 {
205         rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
206         if (!rmap_item_cache)
207                 goto out;
208
209         stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
210         if (!stable_node_cache)
211                 goto out_free1;
212
213         mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
214         if (!mm_slot_cache)
215                 goto out_free2;
216
217         return 0;
218
219 out_free2:
220         kmem_cache_destroy(stable_node_cache);
221 out_free1:
222         kmem_cache_destroy(rmap_item_cache);
223 out:
224         return -ENOMEM;
225 }
226
227 static void __init ksm_slab_free(void)
228 {
229         kmem_cache_destroy(mm_slot_cache);
230         kmem_cache_destroy(stable_node_cache);
231         kmem_cache_destroy(rmap_item_cache);
232         mm_slot_cache = NULL;
233 }
234
235 static inline struct rmap_item *alloc_rmap_item(void)
236 {
237         struct rmap_item *rmap_item;
238
239         rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
240         if (rmap_item)
241                 ksm_rmap_items++;
242         return rmap_item;
243 }
244
245 static inline void free_rmap_item(struct rmap_item *rmap_item)
246 {
247         ksm_rmap_items--;
248         rmap_item->mm = NULL;   /* debug safety */
249         kmem_cache_free(rmap_item_cache, rmap_item);
250 }
251
252 static inline struct stable_node *alloc_stable_node(void)
253 {
254         return kmem_cache_alloc(stable_node_cache, GFP_KERNEL);
255 }
256
257 static inline void free_stable_node(struct stable_node *stable_node)
258 {
259         kmem_cache_free(stable_node_cache, stable_node);
260 }
261
262 static inline struct mm_slot *alloc_mm_slot(void)
263 {
264         if (!mm_slot_cache)     /* initialization failed */
265                 return NULL;
266         return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
267 }
268
269 static inline void free_mm_slot(struct mm_slot *mm_slot)
270 {
271         kmem_cache_free(mm_slot_cache, mm_slot);
272 }
273
274 static int __init mm_slots_hash_init(void)
275 {
276         mm_slots_hash = kzalloc(MM_SLOTS_HASH_HEADS * sizeof(struct hlist_head),
277                                 GFP_KERNEL);
278         if (!mm_slots_hash)
279                 return -ENOMEM;
280         return 0;
281 }
282
283 static void __init mm_slots_hash_free(void)
284 {
285         kfree(mm_slots_hash);
286 }
287
288 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
289 {
290         struct mm_slot *mm_slot;
291         struct hlist_head *bucket;
292         struct hlist_node *node;
293
294         bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
295                                 % MM_SLOTS_HASH_HEADS];
296         hlist_for_each_entry(mm_slot, node, bucket, link) {
297                 if (mm == mm_slot->mm)
298                         return mm_slot;
299         }
300         return NULL;
301 }
302
303 static void insert_to_mm_slots_hash(struct mm_struct *mm,
304                                     struct mm_slot *mm_slot)
305 {
306         struct hlist_head *bucket;
307
308         bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
309                                 % MM_SLOTS_HASH_HEADS];
310         mm_slot->mm = mm;
311         hlist_add_head(&mm_slot->link, bucket);
312 }
313
314 static inline int in_stable_tree(struct rmap_item *rmap_item)
315 {
316         return rmap_item->address & STABLE_FLAG;
317 }
318
319 static void hold_anon_vma(struct rmap_item *rmap_item,
320                           struct anon_vma *anon_vma)
321 {
322         rmap_item->anon_vma = anon_vma;
323         atomic_inc(&anon_vma->ksm_refcount);
324 }
325
326 static void drop_anon_vma(struct rmap_item *rmap_item)
327 {
328         struct anon_vma *anon_vma = rmap_item->anon_vma;
329
330         if (atomic_dec_and_lock(&anon_vma->ksm_refcount, &anon_vma->lock)) {
331                 int empty = list_empty(&anon_vma->head);
332                 spin_unlock(&anon_vma->lock);
333                 if (empty)
334                         anon_vma_free(anon_vma);
335         }
336 }
337
338 /*
339  * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
340  * page tables after it has passed through ksm_exit() - which, if necessary,
341  * takes mmap_sem briefly to serialize against them.  ksm_exit() does not set
342  * a special flag: they can just back out as soon as mm_users goes to zero.
343  * ksm_test_exit() is used throughout to make this test for exit: in some
344  * places for correctness, in some places just to avoid unnecessary work.
345  */
346 static inline bool ksm_test_exit(struct mm_struct *mm)
347 {
348         return atomic_read(&mm->mm_users) == 0;
349 }
350
351 /*
352  * We use break_ksm to break COW on a ksm page: it's a stripped down
353  *
354  *      if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
355  *              put_page(page);
356  *
357  * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
358  * in case the application has unmapped and remapped mm,addr meanwhile.
359  * Could a ksm page appear anywhere else?  Actually yes, in a VM_PFNMAP
360  * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
361  */
362 static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
363 {
364         struct page *page;
365         int ret = 0;
366
367         do {
368                 cond_resched();
369                 page = follow_page(vma, addr, FOLL_GET);
370                 if (!page)
371                         break;
372                 if (PageKsm(page))
373                         ret = handle_mm_fault(vma->vm_mm, vma, addr,
374                                                         FAULT_FLAG_WRITE);
375                 else
376                         ret = VM_FAULT_WRITE;
377                 put_page(page);
378         } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM)));
379         /*
380          * We must loop because handle_mm_fault() may back out if there's
381          * any difficulty e.g. if pte accessed bit gets updated concurrently.
382          *
383          * VM_FAULT_WRITE is what we have been hoping for: it indicates that
384          * COW has been broken, even if the vma does not permit VM_WRITE;
385          * but note that a concurrent fault might break PageKsm for us.
386          *
387          * VM_FAULT_SIGBUS could occur if we race with truncation of the
388          * backing file, which also invalidates anonymous pages: that's
389          * okay, that truncation will have unmapped the PageKsm for us.
390          *
391          * VM_FAULT_OOM: at the time of writing (late July 2009), setting
392          * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
393          * current task has TIF_MEMDIE set, and will be OOM killed on return
394          * to user; and ksmd, having no mm, would never be chosen for that.
395          *
396          * But if the mm is in a limited mem_cgroup, then the fault may fail
397          * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
398          * even ksmd can fail in this way - though it's usually breaking ksm
399          * just to undo a merge it made a moment before, so unlikely to oom.
400          *
401          * That's a pity: we might therefore have more kernel pages allocated
402          * than we're counting as nodes in the stable tree; but ksm_do_scan
403          * will retry to break_cow on each pass, so should recover the page
404          * in due course.  The important thing is to not let VM_MERGEABLE
405          * be cleared while any such pages might remain in the area.
406          */
407         return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
408 }
409
410 static void break_cow(struct rmap_item *rmap_item)
411 {
412         struct mm_struct *mm = rmap_item->mm;
413         unsigned long addr = rmap_item->address;
414         struct vm_area_struct *vma;
415
416         /*
417          * It is not an accident that whenever we want to break COW
418          * to undo, we also need to drop a reference to the anon_vma.
419          */
420         drop_anon_vma(rmap_item);
421
422         down_read(&mm->mmap_sem);
423         if (ksm_test_exit(mm))
424                 goto out;
425         vma = find_vma(mm, addr);
426         if (!vma || vma->vm_start > addr)
427                 goto out;
428         if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
429                 goto out;
430         break_ksm(vma, addr);
431 out:
432         up_read(&mm->mmap_sem);
433 }
434
435 static struct page *get_mergeable_page(struct rmap_item *rmap_item)
436 {
437         struct mm_struct *mm = rmap_item->mm;
438         unsigned long addr = rmap_item->address;
439         struct vm_area_struct *vma;
440         struct page *page;
441
442         down_read(&mm->mmap_sem);
443         if (ksm_test_exit(mm))
444                 goto out;
445         vma = find_vma(mm, addr);
446         if (!vma || vma->vm_start > addr)
447                 goto out;
448         if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
449                 goto out;
450
451         page = follow_page(vma, addr, FOLL_GET);
452         if (!page)
453                 goto out;
454         if (PageAnon(page)) {
455                 flush_anon_page(vma, page, addr);
456                 flush_dcache_page(page);
457         } else {
458                 put_page(page);
459 out:            page = NULL;
460         }
461         up_read(&mm->mmap_sem);
462         return page;
463 }
464
465 static void remove_node_from_stable_tree(struct stable_node *stable_node)
466 {
467         struct rmap_item *rmap_item;
468         struct hlist_node *hlist;
469
470         hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
471                 if (rmap_item->hlist.next)
472                         ksm_pages_sharing--;
473                 else
474                         ksm_pages_shared--;
475                 drop_anon_vma(rmap_item);
476                 rmap_item->address &= PAGE_MASK;
477                 cond_resched();
478         }
479
480         rb_erase(&stable_node->node, &root_stable_tree);
481         free_stable_node(stable_node);
482 }
483
484 /*
485  * get_ksm_page: checks if the page indicated by the stable node
486  * is still its ksm page, despite having held no reference to it.
487  * In which case we can trust the content of the page, and it
488  * returns the gotten page; but if the page has now been zapped,
489  * remove the stale node from the stable tree and return NULL.
490  *
491  * You would expect the stable_node to hold a reference to the ksm page.
492  * But if it increments the page's count, swapping out has to wait for
493  * ksmd to come around again before it can free the page, which may take
494  * seconds or even minutes: much too unresponsive.  So instead we use a
495  * "keyhole reference": access to the ksm page from the stable node peeps
496  * out through its keyhole to see if that page still holds the right key,
497  * pointing back to this stable node.  This relies on freeing a PageAnon
498  * page to reset its page->mapping to NULL, and relies on no other use of
499  * a page to put something that might look like our key in page->mapping.
500  *
501  * include/linux/pagemap.h page_cache_get_speculative() is a good reference,
502  * but this is different - made simpler by ksm_thread_mutex being held, but
503  * interesting for assuming that no other use of the struct page could ever
504  * put our expected_mapping into page->mapping (or a field of the union which
505  * coincides with page->mapping).  The RCU calls are not for KSM at all, but
506  * to keep the page_count protocol described with page_cache_get_speculative.
507  *
508  * Note: it is possible that get_ksm_page() will return NULL one moment,
509  * then page the next, if the page is in between page_freeze_refs() and
510  * page_unfreeze_refs(): this shouldn't be a problem anywhere, the page
511  * is on its way to being freed; but it is an anomaly to bear in mind.
512  */
513 static struct page *get_ksm_page(struct stable_node *stable_node)
514 {
515         struct page *page;
516         void *expected_mapping;
517
518         page = stable_node->page;
519         expected_mapping = (void *)stable_node +
520                                 (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
521         rcu_read_lock();
522         if (page->mapping != expected_mapping)
523                 goto stale;
524         if (!get_page_unless_zero(page))
525                 goto stale;
526         if (page->mapping != expected_mapping) {
527                 put_page(page);
528                 goto stale;
529         }
530         rcu_read_unlock();
531         return page;
532 stale:
533         rcu_read_unlock();
534         remove_node_from_stable_tree(stable_node);
535         return NULL;
536 }
537
538 /*
539  * Removing rmap_item from stable or unstable tree.
540  * This function will clean the information from the stable/unstable tree.
541  */
542 static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
543 {
544         if (rmap_item->address & STABLE_FLAG) {
545                 struct stable_node *stable_node;
546                 struct page *page;
547
548                 stable_node = rmap_item->head;
549                 page = get_ksm_page(stable_node);
550                 if (!page)
551                         goto out;
552
553                 lock_page(page);
554                 hlist_del(&rmap_item->hlist);
555                 unlock_page(page);
556                 put_page(page);
557
558                 if (stable_node->hlist.first)
559                         ksm_pages_sharing--;
560                 else
561                         ksm_pages_shared--;
562
563                 drop_anon_vma(rmap_item);
564                 rmap_item->address &= PAGE_MASK;
565
566         } else if (rmap_item->address & UNSTABLE_FLAG) {
567                 unsigned char age;
568                 /*
569                  * Usually ksmd can and must skip the rb_erase, because
570                  * root_unstable_tree was already reset to RB_ROOT.
571                  * But be careful when an mm is exiting: do the rb_erase
572                  * if this rmap_item was inserted by this scan, rather
573                  * than left over from before.
574                  */
575                 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
576                 BUG_ON(age > 1);
577                 if (!age)
578                         rb_erase(&rmap_item->node, &root_unstable_tree);
579
580                 ksm_pages_unshared--;
581                 rmap_item->address &= PAGE_MASK;
582         }
583 out:
584         cond_resched();         /* we're called from many long loops */
585 }
586
587 static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
588                                        struct rmap_item **rmap_list)
589 {
590         while (*rmap_list) {
591                 struct rmap_item *rmap_item = *rmap_list;
592                 *rmap_list = rmap_item->rmap_list;
593                 remove_rmap_item_from_tree(rmap_item);
594                 free_rmap_item(rmap_item);
595         }
596 }
597
598 /*
599  * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather
600  * than check every pte of a given vma, the locking doesn't quite work for
601  * that - an rmap_item is assigned to the stable tree after inserting ksm
602  * page and upping mmap_sem.  Nor does it fit with the way we skip dup'ing
603  * rmap_items from parent to child at fork time (so as not to waste time
604  * if exit comes before the next scan reaches it).
605  *
606  * Similarly, although we'd like to remove rmap_items (so updating counts
607  * and freeing memory) when unmerging an area, it's easier to leave that
608  * to the next pass of ksmd - consider, for example, how ksmd might be
609  * in cmp_and_merge_page on one of the rmap_items we would be removing.
610  */
611 static int unmerge_ksm_pages(struct vm_area_struct *vma,
612                              unsigned long start, unsigned long end)
613 {
614         unsigned long addr;
615         int err = 0;
616
617         for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
618                 if (ksm_test_exit(vma->vm_mm))
619                         break;
620                 if (signal_pending(current))
621                         err = -ERESTARTSYS;
622                 else
623                         err = break_ksm(vma, addr);
624         }
625         return err;
626 }
627
628 #ifdef CONFIG_SYSFS
629 /*
630  * Only called through the sysfs control interface:
631  */
632 static int unmerge_and_remove_all_rmap_items(void)
633 {
634         struct mm_slot *mm_slot;
635         struct mm_struct *mm;
636         struct vm_area_struct *vma;
637         int err = 0;
638
639         spin_lock(&ksm_mmlist_lock);
640         ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
641                                                 struct mm_slot, mm_list);
642         spin_unlock(&ksm_mmlist_lock);
643
644         for (mm_slot = ksm_scan.mm_slot;
645                         mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
646                 mm = mm_slot->mm;
647                 down_read(&mm->mmap_sem);
648                 for (vma = mm->mmap; vma; vma = vma->vm_next) {
649                         if (ksm_test_exit(mm))
650                                 break;
651                         if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
652                                 continue;
653                         err = unmerge_ksm_pages(vma,
654                                                 vma->vm_start, vma->vm_end);
655                         if (err)
656                                 goto error;
657                 }
658
659                 remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
660
661                 spin_lock(&ksm_mmlist_lock);
662                 ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
663                                                 struct mm_slot, mm_list);
664                 if (ksm_test_exit(mm)) {
665                         hlist_del(&mm_slot->link);
666                         list_del(&mm_slot->mm_list);
667                         spin_unlock(&ksm_mmlist_lock);
668
669                         free_mm_slot(mm_slot);
670                         clear_bit(MMF_VM_MERGEABLE, &mm->flags);
671                         up_read(&mm->mmap_sem);
672                         mmdrop(mm);
673                 } else {
674                         spin_unlock(&ksm_mmlist_lock);
675                         up_read(&mm->mmap_sem);
676                 }
677         }
678
679         ksm_scan.seqnr = 0;
680         return 0;
681
682 error:
683         up_read(&mm->mmap_sem);
684         spin_lock(&ksm_mmlist_lock);
685         ksm_scan.mm_slot = &ksm_mm_head;
686         spin_unlock(&ksm_mmlist_lock);
687         return err;
688 }
689 #endif /* CONFIG_SYSFS */
690
691 static u32 calc_checksum(struct page *page)
692 {
693         u32 checksum;
694         void *addr = kmap_atomic(page, KM_USER0);
695         checksum = jhash2(addr, PAGE_SIZE / 4, 17);
696         kunmap_atomic(addr, KM_USER0);
697         return checksum;
698 }
699
700 static int memcmp_pages(struct page *page1, struct page *page2)
701 {
702         char *addr1, *addr2;
703         int ret;
704
705         addr1 = kmap_atomic(page1, KM_USER0);
706         addr2 = kmap_atomic(page2, KM_USER1);
707         ret = memcmp(addr1, addr2, PAGE_SIZE);
708         kunmap_atomic(addr2, KM_USER1);
709         kunmap_atomic(addr1, KM_USER0);
710         return ret;
711 }
712
713 static inline int pages_identical(struct page *page1, struct page *page2)
714 {
715         return !memcmp_pages(page1, page2);
716 }
717
718 static int write_protect_page(struct vm_area_struct *vma, struct page *page,
719                               pte_t *orig_pte)
720 {
721         struct mm_struct *mm = vma->vm_mm;
722         unsigned long addr;
723         pte_t *ptep;
724         spinlock_t *ptl;
725         int swapped;
726         int err = -EFAULT;
727
728         addr = page_address_in_vma(page, vma);
729         if (addr == -EFAULT)
730                 goto out;
731
732         ptep = page_check_address(page, mm, addr, &ptl, 0);
733         if (!ptep)
734                 goto out;
735
736         if (pte_write(*ptep)) {
737                 pte_t entry;
738
739                 swapped = PageSwapCache(page);
740                 flush_cache_page(vma, addr, page_to_pfn(page));
741                 /*
742                  * Ok this is tricky, when get_user_pages_fast() run it doesnt
743                  * take any lock, therefore the check that we are going to make
744                  * with the pagecount against the mapcount is racey and
745                  * O_DIRECT can happen right after the check.
746                  * So we clear the pte and flush the tlb before the check
747                  * this assure us that no O_DIRECT can happen after the check
748                  * or in the middle of the check.
749                  */
750                 entry = ptep_clear_flush(vma, addr, ptep);
751                 /*
752                  * Check that no O_DIRECT or similar I/O is in progress on the
753                  * page
754                  */
755                 if (page_mapcount(page) + 1 + swapped != page_count(page)) {
756                         set_pte_at_notify(mm, addr, ptep, entry);
757                         goto out_unlock;
758                 }
759                 entry = pte_wrprotect(entry);
760                 set_pte_at_notify(mm, addr, ptep, entry);
761         }
762         *orig_pte = *ptep;
763         err = 0;
764
765 out_unlock:
766         pte_unmap_unlock(ptep, ptl);
767 out:
768         return err;
769 }
770
771 /**
772  * replace_page - replace page in vma by new ksm page
773  * @vma:      vma that holds the pte pointing to page
774  * @page:     the page we are replacing by kpage
775  * @kpage:    the ksm page we replace page by
776  * @orig_pte: the original value of the pte
777  *
778  * Returns 0 on success, -EFAULT on failure.
779  */
780 static int replace_page(struct vm_area_struct *vma, struct page *page,
781                         struct page *kpage, pte_t orig_pte)
782 {
783         struct mm_struct *mm = vma->vm_mm;
784         pgd_t *pgd;
785         pud_t *pud;
786         pmd_t *pmd;
787         pte_t *ptep;
788         spinlock_t *ptl;
789         unsigned long addr;
790         int err = -EFAULT;
791
792         addr = page_address_in_vma(page, vma);
793         if (addr == -EFAULT)
794                 goto out;
795
796         pgd = pgd_offset(mm, addr);
797         if (!pgd_present(*pgd))
798                 goto out;
799
800         pud = pud_offset(pgd, addr);
801         if (!pud_present(*pud))
802                 goto out;
803
804         pmd = pmd_offset(pud, addr);
805         if (!pmd_present(*pmd))
806                 goto out;
807
808         ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
809         if (!pte_same(*ptep, orig_pte)) {
810                 pte_unmap_unlock(ptep, ptl);
811                 goto out;
812         }
813
814         get_page(kpage);
815         page_add_anon_rmap(kpage, vma, addr);
816
817         flush_cache_page(vma, addr, pte_pfn(*ptep));
818         ptep_clear_flush(vma, addr, ptep);
819         set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
820
821         page_remove_rmap(page);
822         put_page(page);
823
824         pte_unmap_unlock(ptep, ptl);
825         err = 0;
826 out:
827         return err;
828 }
829
830 /*
831  * try_to_merge_one_page - take two pages and merge them into one
832  * @vma: the vma that holds the pte pointing to page
833  * @page: the PageAnon page that we want to replace with kpage
834  * @kpage: the PageKsm page that we want to map instead of page,
835  *         or NULL the first time when we want to use page as kpage.
836  *
837  * This function returns 0 if the pages were merged, -EFAULT otherwise.
838  */
839 static int try_to_merge_one_page(struct vm_area_struct *vma,
840                                  struct page *page, struct page *kpage)
841 {
842         pte_t orig_pte = __pte(0);
843         int err = -EFAULT;
844
845         if (page == kpage)                      /* ksm page forked */
846                 return 0;
847
848         if (!(vma->vm_flags & VM_MERGEABLE))
849                 goto out;
850         if (!PageAnon(page))
851                 goto out;
852
853         /*
854          * We need the page lock to read a stable PageSwapCache in
855          * write_protect_page().  We use trylock_page() instead of
856          * lock_page() because we don't want to wait here - we
857          * prefer to continue scanning and merging different pages,
858          * then come back to this page when it is unlocked.
859          */
860         if (!trylock_page(page))
861                 goto out;
862         /*
863          * If this anonymous page is mapped only here, its pte may need
864          * to be write-protected.  If it's mapped elsewhere, all of its
865          * ptes are necessarily already write-protected.  But in either
866          * case, we need to lock and check page_count is not raised.
867          */
868         if (write_protect_page(vma, page, &orig_pte) == 0) {
869                 if (!kpage) {
870                         /*
871                          * While we hold page lock, upgrade page from
872                          * PageAnon+anon_vma to PageKsm+NULL stable_node:
873                          * stable_tree_insert() will update stable_node.
874                          */
875                         set_page_stable_node(page, NULL);
876                         mark_page_accessed(page);
877                         err = 0;
878                 } else if (pages_identical(page, kpage))
879                         err = replace_page(vma, page, kpage, orig_pte);
880         }
881
882         if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
883                 munlock_vma_page(page);
884                 if (!PageMlocked(kpage)) {
885                         unlock_page(page);
886                         lock_page(kpage);
887                         mlock_vma_page(kpage);
888                         page = kpage;           /* for final unlock */
889                 }
890         }
891
892         unlock_page(page);
893 out:
894         return err;
895 }
896
897 /*
898  * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
899  * but no new kernel page is allocated: kpage must already be a ksm page.
900  *
901  * This function returns 0 if the pages were merged, -EFAULT otherwise.
902  */
903 static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
904                                       struct page *page, struct page *kpage)
905 {
906         struct mm_struct *mm = rmap_item->mm;
907         struct vm_area_struct *vma;
908         int err = -EFAULT;
909
910         down_read(&mm->mmap_sem);
911         if (ksm_test_exit(mm))
912                 goto out;
913         vma = find_vma(mm, rmap_item->address);
914         if (!vma || vma->vm_start > rmap_item->address)
915                 goto out;
916
917         err = try_to_merge_one_page(vma, page, kpage);
918         if (err)
919                 goto out;
920
921         /* Must get reference to anon_vma while still holding mmap_sem */
922         hold_anon_vma(rmap_item, vma->anon_vma);
923 out:
924         up_read(&mm->mmap_sem);
925         return err;
926 }
927
928 /*
929  * try_to_merge_two_pages - take two identical pages and prepare them
930  * to be merged into one page.
931  *
932  * This function returns the kpage if we successfully merged two identical
933  * pages into one ksm page, NULL otherwise.
934  *
935  * Note that this function upgrades page to ksm page: if one of the pages
936  * is already a ksm page, try_to_merge_with_ksm_page should be used.
937  */
938 static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
939                                            struct page *page,
940                                            struct rmap_item *tree_rmap_item,
941                                            struct page *tree_page)
942 {
943         int err;
944
945         /*
946          * The number of nodes in the stable tree
947          * is the number of kernel pages that we hold.
948          */
949         if (ksm_max_kernel_pages &&
950             ksm_max_kernel_pages <= ksm_pages_shared)
951                 return NULL;
952
953         err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
954         if (!err) {
955                 err = try_to_merge_with_ksm_page(tree_rmap_item,
956                                                         tree_page, page);
957                 /*
958                  * If that fails, we have a ksm page with only one pte
959                  * pointing to it: so break it.
960                  */
961                 if (err)
962                         break_cow(rmap_item);
963         }
964         return err ? NULL : page;
965 }
966
967 /*
968  * stable_tree_search - search for page inside the stable tree
969  *
970  * This function checks if there is a page inside the stable tree
971  * with identical content to the page that we are scanning right now.
972  *
973  * This function returns the stable tree node of identical content if found,
974  * NULL otherwise.
975  */
976 static struct stable_node *stable_tree_search(struct page *page)
977 {
978         struct rb_node *node = root_stable_tree.rb_node;
979         struct stable_node *stable_node;
980
981         stable_node = page_stable_node(page);
982         if (stable_node) {                      /* ksm page forked */
983                 get_page(page);
984                 return stable_node;
985         }
986
987         while (node) {
988                 struct page *tree_page;
989                 int ret;
990
991                 cond_resched();
992                 stable_node = rb_entry(node, struct stable_node, node);
993                 tree_page = get_ksm_page(stable_node);
994                 if (!tree_page)
995                         return NULL;
996
997                 ret = memcmp_pages(page, tree_page);
998
999                 if (ret < 0) {
1000                         put_page(tree_page);
1001                         node = node->rb_left;
1002                 } else if (ret > 0) {
1003                         put_page(tree_page);
1004                         node = node->rb_right;
1005                 } else
1006                         return stable_node;
1007         }
1008
1009         return NULL;
1010 }
1011
1012 /*
1013  * stable_tree_insert - insert rmap_item pointing to new ksm page
1014  * into the stable tree.
1015  *
1016  * This function returns the stable tree node just allocated on success,
1017  * NULL otherwise.
1018  */
1019 static struct stable_node *stable_tree_insert(struct page *kpage)
1020 {
1021         struct rb_node **new = &root_stable_tree.rb_node;
1022         struct rb_node *parent = NULL;
1023         struct stable_node *stable_node;
1024
1025         while (*new) {
1026                 struct page *tree_page;
1027                 int ret;
1028
1029                 cond_resched();
1030                 stable_node = rb_entry(*new, struct stable_node, node);
1031                 tree_page = get_ksm_page(stable_node);
1032                 if (!tree_page)
1033                         return NULL;
1034
1035                 ret = memcmp_pages(kpage, tree_page);
1036                 put_page(tree_page);
1037
1038                 parent = *new;
1039                 if (ret < 0)
1040                         new = &parent->rb_left;
1041                 else if (ret > 0)
1042                         new = &parent->rb_right;
1043                 else {
1044                         /*
1045                          * It is not a bug that stable_tree_search() didn't
1046                          * find this node: because at that time our page was
1047                          * not yet write-protected, so may have changed since.
1048                          */
1049                         return NULL;
1050                 }
1051         }
1052
1053         stable_node = alloc_stable_node();
1054         if (!stable_node)
1055                 return NULL;
1056
1057         rb_link_node(&stable_node->node, parent, new);
1058         rb_insert_color(&stable_node->node, &root_stable_tree);
1059
1060         INIT_HLIST_HEAD(&stable_node->hlist);
1061
1062         stable_node->page = kpage;
1063         set_page_stable_node(kpage, stable_node);
1064
1065         return stable_node;
1066 }
1067
1068 /*
1069  * unstable_tree_search_insert - search for identical page,
1070  * else insert rmap_item into the unstable tree.
1071  *
1072  * This function searches for a page in the unstable tree identical to the
1073  * page currently being scanned; and if no identical page is found in the
1074  * tree, we insert rmap_item as a new object into the unstable tree.
1075  *
1076  * This function returns pointer to rmap_item found to be identical
1077  * to the currently scanned page, NULL otherwise.
1078  *
1079  * This function does both searching and inserting, because they share
1080  * the same walking algorithm in an rbtree.
1081  */
1082 static
1083 struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1084                                               struct page *page,
1085                                               struct page **tree_pagep)
1086
1087 {
1088         struct rb_node **new = &root_unstable_tree.rb_node;
1089         struct rb_node *parent = NULL;
1090
1091         while (*new) {
1092                 struct rmap_item *tree_rmap_item;
1093                 struct page *tree_page;
1094                 int ret;
1095
1096                 cond_resched();
1097                 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1098                 tree_page = get_mergeable_page(tree_rmap_item);
1099                 if (!tree_page)
1100                         return NULL;
1101
1102                 /*
1103                  * Don't substitute a ksm page for a forked page.
1104                  */
1105                 if (page == tree_page) {
1106                         put_page(tree_page);
1107                         return NULL;
1108                 }
1109
1110                 ret = memcmp_pages(page, tree_page);
1111
1112                 parent = *new;
1113                 if (ret < 0) {
1114                         put_page(tree_page);
1115                         new = &parent->rb_left;
1116                 } else if (ret > 0) {
1117                         put_page(tree_page);
1118                         new = &parent->rb_right;
1119                 } else {
1120                         *tree_pagep = tree_page;
1121                         return tree_rmap_item;
1122                 }
1123         }
1124
1125         rmap_item->address |= UNSTABLE_FLAG;
1126         rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1127         rb_link_node(&rmap_item->node, parent, new);
1128         rb_insert_color(&rmap_item->node, &root_unstable_tree);
1129
1130         ksm_pages_unshared++;
1131         return NULL;
1132 }
1133
1134 /*
1135  * stable_tree_append - add another rmap_item to the linked list of
1136  * rmap_items hanging off a given node of the stable tree, all sharing
1137  * the same ksm page.
1138  */
1139 static void stable_tree_append(struct rmap_item *rmap_item,
1140                                struct stable_node *stable_node)
1141 {
1142         rmap_item->head = stable_node;
1143         rmap_item->address |= STABLE_FLAG;
1144         hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
1145
1146         if (rmap_item->hlist.next)
1147                 ksm_pages_sharing++;
1148         else
1149                 ksm_pages_shared++;
1150 }
1151
1152 /*
1153  * cmp_and_merge_page - first see if page can be merged into the stable tree;
1154  * if not, compare checksum to previous and if it's the same, see if page can
1155  * be inserted into the unstable tree, or merged with a page already there and
1156  * both transferred to the stable tree.
1157  *
1158  * @page: the page that we are searching identical page to.
1159  * @rmap_item: the reverse mapping into the virtual address of this page
1160  */
1161 static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1162 {
1163         struct rmap_item *tree_rmap_item;
1164         struct page *tree_page = NULL;
1165         struct stable_node *stable_node;
1166         struct page *kpage;
1167         unsigned int checksum;
1168         int err;
1169
1170         remove_rmap_item_from_tree(rmap_item);
1171
1172         /* We first start with searching the page inside the stable tree */
1173         stable_node = stable_tree_search(page);
1174         if (stable_node) {
1175                 kpage = stable_node->page;
1176                 err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
1177                 if (!err) {
1178                         /*
1179                          * The page was successfully merged:
1180                          * add its rmap_item to the stable tree.
1181                          */
1182                         lock_page(kpage);
1183                         stable_tree_append(rmap_item, stable_node);
1184                         unlock_page(kpage);
1185                 }
1186                 put_page(kpage);
1187                 return;
1188         }
1189
1190         /*
1191          * If the hash value of the page has changed from the last time
1192          * we calculated it, this page is changing frequently: therefore we
1193          * don't want to insert it in the unstable tree, and we don't want
1194          * to waste our time searching for something identical to it there.
1195          */
1196         checksum = calc_checksum(page);
1197         if (rmap_item->oldchecksum != checksum) {
1198                 rmap_item->oldchecksum = checksum;
1199                 return;
1200         }
1201
1202         tree_rmap_item =
1203                 unstable_tree_search_insert(rmap_item, page, &tree_page);
1204         if (tree_rmap_item) {
1205                 kpage = try_to_merge_two_pages(rmap_item, page,
1206                                                 tree_rmap_item, tree_page);
1207                 put_page(tree_page);
1208                 /*
1209                  * As soon as we merge this page, we want to remove the
1210                  * rmap_item of the page we have merged with from the unstable
1211                  * tree, and insert it instead as new node in the stable tree.
1212                  */
1213                 if (kpage) {
1214                         remove_rmap_item_from_tree(tree_rmap_item);
1215
1216                         lock_page(kpage);
1217                         stable_node = stable_tree_insert(kpage);
1218                         if (stable_node) {
1219                                 stable_tree_append(tree_rmap_item, stable_node);
1220                                 stable_tree_append(rmap_item, stable_node);
1221                         }
1222                         unlock_page(kpage);
1223
1224                         /*
1225                          * If we fail to insert the page into the stable tree,
1226                          * we will have 2 virtual addresses that are pointing
1227                          * to a ksm page left outside the stable tree,
1228                          * in which case we need to break_cow on both.
1229                          */
1230                         if (!stable_node) {
1231                                 break_cow(tree_rmap_item);
1232                                 break_cow(rmap_item);
1233                         }
1234                 }
1235         }
1236 }
1237
1238 static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
1239                                             struct rmap_item **rmap_list,
1240                                             unsigned long addr)
1241 {
1242         struct rmap_item *rmap_item;
1243
1244         while (*rmap_list) {
1245                 rmap_item = *rmap_list;
1246                 if ((rmap_item->address & PAGE_MASK) == addr)
1247                         return rmap_item;
1248                 if (rmap_item->address > addr)
1249                         break;
1250                 *rmap_list = rmap_item->rmap_list;
1251                 remove_rmap_item_from_tree(rmap_item);
1252                 free_rmap_item(rmap_item);
1253         }
1254
1255         rmap_item = alloc_rmap_item();
1256         if (rmap_item) {
1257                 /* It has already been zeroed */
1258                 rmap_item->mm = mm_slot->mm;
1259                 rmap_item->address = addr;
1260                 rmap_item->rmap_list = *rmap_list;
1261                 *rmap_list = rmap_item;
1262         }
1263         return rmap_item;
1264 }
1265
1266 static struct rmap_item *scan_get_next_rmap_item(struct page **page)
1267 {
1268         struct mm_struct *mm;
1269         struct mm_slot *slot;
1270         struct vm_area_struct *vma;
1271         struct rmap_item *rmap_item;
1272
1273         if (list_empty(&ksm_mm_head.mm_list))
1274                 return NULL;
1275
1276         slot = ksm_scan.mm_slot;
1277         if (slot == &ksm_mm_head) {
1278                 root_unstable_tree = RB_ROOT;
1279
1280                 spin_lock(&ksm_mmlist_lock);
1281                 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1282                 ksm_scan.mm_slot = slot;
1283                 spin_unlock(&ksm_mmlist_lock);
1284 next_mm:
1285                 ksm_scan.address = 0;
1286                 ksm_scan.rmap_list = &slot->rmap_list;
1287         }
1288
1289         mm = slot->mm;
1290         down_read(&mm->mmap_sem);
1291         if (ksm_test_exit(mm))
1292                 vma = NULL;
1293         else
1294                 vma = find_vma(mm, ksm_scan.address);
1295
1296         for (; vma; vma = vma->vm_next) {
1297                 if (!(vma->vm_flags & VM_MERGEABLE))
1298                         continue;
1299                 if (ksm_scan.address < vma->vm_start)
1300                         ksm_scan.address = vma->vm_start;
1301                 if (!vma->anon_vma)
1302                         ksm_scan.address = vma->vm_end;
1303
1304                 while (ksm_scan.address < vma->vm_end) {
1305                         if (ksm_test_exit(mm))
1306                                 break;
1307                         *page = follow_page(vma, ksm_scan.address, FOLL_GET);
1308                         if (*page && PageAnon(*page)) {
1309                                 flush_anon_page(vma, *page, ksm_scan.address);
1310                                 flush_dcache_page(*page);
1311                                 rmap_item = get_next_rmap_item(slot,
1312                                         ksm_scan.rmap_list, ksm_scan.address);
1313                                 if (rmap_item) {
1314                                         ksm_scan.rmap_list =
1315                                                         &rmap_item->rmap_list;
1316                                         ksm_scan.address += PAGE_SIZE;
1317                                 } else
1318                                         put_page(*page);
1319                                 up_read(&mm->mmap_sem);
1320                                 return rmap_item;
1321                         }
1322                         if (*page)
1323                                 put_page(*page);
1324                         ksm_scan.address += PAGE_SIZE;
1325                         cond_resched();
1326                 }
1327         }
1328
1329         if (ksm_test_exit(mm)) {
1330                 ksm_scan.address = 0;
1331                 ksm_scan.rmap_list = &slot->rmap_list;
1332         }
1333         /*
1334          * Nuke all the rmap_items that are above this current rmap:
1335          * because there were no VM_MERGEABLE vmas with such addresses.
1336          */
1337         remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
1338
1339         spin_lock(&ksm_mmlist_lock);
1340         ksm_scan.mm_slot = list_entry(slot->mm_list.next,
1341                                                 struct mm_slot, mm_list);
1342         if (ksm_scan.address == 0) {
1343                 /*
1344                  * We've completed a full scan of all vmas, holding mmap_sem
1345                  * throughout, and found no VM_MERGEABLE: so do the same as
1346                  * __ksm_exit does to remove this mm from all our lists now.
1347                  * This applies either when cleaning up after __ksm_exit
1348                  * (but beware: we can reach here even before __ksm_exit),
1349                  * or when all VM_MERGEABLE areas have been unmapped (and
1350                  * mmap_sem then protects against race with MADV_MERGEABLE).
1351                  */
1352                 hlist_del(&slot->link);
1353                 list_del(&slot->mm_list);
1354                 spin_unlock(&ksm_mmlist_lock);
1355
1356                 free_mm_slot(slot);
1357                 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1358                 up_read(&mm->mmap_sem);
1359                 mmdrop(mm);
1360         } else {
1361                 spin_unlock(&ksm_mmlist_lock);
1362                 up_read(&mm->mmap_sem);
1363         }
1364
1365         /* Repeat until we've completed scanning the whole list */
1366         slot = ksm_scan.mm_slot;
1367         if (slot != &ksm_mm_head)
1368                 goto next_mm;
1369
1370         ksm_scan.seqnr++;
1371         return NULL;
1372 }
1373
1374 /**
1375  * ksm_do_scan  - the ksm scanner main worker function.
1376  * @scan_npages - number of pages we want to scan before we return.
1377  */
1378 static void ksm_do_scan(unsigned int scan_npages)
1379 {
1380         struct rmap_item *rmap_item;
1381         struct page *page;
1382
1383         while (scan_npages--) {
1384                 cond_resched();
1385                 rmap_item = scan_get_next_rmap_item(&page);
1386                 if (!rmap_item)
1387                         return;
1388                 if (!PageKsm(page) || !in_stable_tree(rmap_item))
1389                         cmp_and_merge_page(page, rmap_item);
1390                 put_page(page);
1391         }
1392 }
1393
1394 static int ksmd_should_run(void)
1395 {
1396         return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1397 }
1398
1399 static int ksm_scan_thread(void *nothing)
1400 {
1401         set_user_nice(current, 5);
1402
1403         while (!kthread_should_stop()) {
1404                 mutex_lock(&ksm_thread_mutex);
1405                 if (ksmd_should_run())
1406                         ksm_do_scan(ksm_thread_pages_to_scan);
1407                 mutex_unlock(&ksm_thread_mutex);
1408
1409                 if (ksmd_should_run()) {
1410                         schedule_timeout_interruptible(
1411                                 msecs_to_jiffies(ksm_thread_sleep_millisecs));
1412                 } else {
1413                         wait_event_interruptible(ksm_thread_wait,
1414                                 ksmd_should_run() || kthread_should_stop());
1415                 }
1416         }
1417         return 0;
1418 }
1419
1420 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1421                 unsigned long end, int advice, unsigned long *vm_flags)
1422 {
1423         struct mm_struct *mm = vma->vm_mm;
1424         int err;
1425
1426         switch (advice) {
1427         case MADV_MERGEABLE:
1428                 /*
1429                  * Be somewhat over-protective for now!
1430                  */
1431                 if (*vm_flags & (VM_MERGEABLE | VM_SHARED  | VM_MAYSHARE   |
1432                                  VM_PFNMAP    | VM_IO      | VM_DONTEXPAND |
1433                                  VM_RESERVED  | VM_HUGETLB | VM_INSERTPAGE |
1434                                  VM_NONLINEAR | VM_MIXEDMAP | VM_SAO))
1435                         return 0;               /* just ignore the advice */
1436
1437                 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
1438                         err = __ksm_enter(mm);
1439                         if (err)
1440                                 return err;
1441                 }
1442
1443                 *vm_flags |= VM_MERGEABLE;
1444                 break;
1445
1446         case MADV_UNMERGEABLE:
1447                 if (!(*vm_flags & VM_MERGEABLE))
1448                         return 0;               /* just ignore the advice */
1449
1450                 if (vma->anon_vma) {
1451                         err = unmerge_ksm_pages(vma, start, end);
1452                         if (err)
1453                                 return err;
1454                 }
1455
1456                 *vm_flags &= ~VM_MERGEABLE;
1457                 break;
1458         }
1459
1460         return 0;
1461 }
1462
1463 int __ksm_enter(struct mm_struct *mm)
1464 {
1465         struct mm_slot *mm_slot;
1466         int needs_wakeup;
1467
1468         mm_slot = alloc_mm_slot();
1469         if (!mm_slot)
1470                 return -ENOMEM;
1471
1472         /* Check ksm_run too?  Would need tighter locking */
1473         needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1474
1475         spin_lock(&ksm_mmlist_lock);
1476         insert_to_mm_slots_hash(mm, mm_slot);
1477         /*
1478          * Insert just behind the scanning cursor, to let the area settle
1479          * down a little; when fork is followed by immediate exec, we don't
1480          * want ksmd to waste time setting up and tearing down an rmap_list.
1481          */
1482         list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
1483         spin_unlock(&ksm_mmlist_lock);
1484
1485         set_bit(MMF_VM_MERGEABLE, &mm->flags);
1486         atomic_inc(&mm->mm_count);
1487
1488         if (needs_wakeup)
1489                 wake_up_interruptible(&ksm_thread_wait);
1490
1491         return 0;
1492 }
1493
1494 void __ksm_exit(struct mm_struct *mm)
1495 {
1496         struct mm_slot *mm_slot;
1497         int easy_to_free = 0;
1498
1499         /*
1500          * This process is exiting: if it's straightforward (as is the
1501          * case when ksmd was never running), free mm_slot immediately.
1502          * But if it's at the cursor or has rmap_items linked to it, use
1503          * mmap_sem to synchronize with any break_cows before pagetables
1504          * are freed, and leave the mm_slot on the list for ksmd to free.
1505          * Beware: ksm may already have noticed it exiting and freed the slot.
1506          */
1507
1508         spin_lock(&ksm_mmlist_lock);
1509         mm_slot = get_mm_slot(mm);
1510         if (mm_slot && ksm_scan.mm_slot != mm_slot) {
1511                 if (!mm_slot->rmap_list) {
1512                         hlist_del(&mm_slot->link);
1513                         list_del(&mm_slot->mm_list);
1514                         easy_to_free = 1;
1515                 } else {
1516                         list_move(&mm_slot->mm_list,
1517                                   &ksm_scan.mm_slot->mm_list);
1518                 }
1519         }
1520         spin_unlock(&ksm_mmlist_lock);
1521
1522         if (easy_to_free) {
1523                 free_mm_slot(mm_slot);
1524                 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1525                 mmdrop(mm);
1526         } else if (mm_slot) {
1527                 down_write(&mm->mmap_sem);
1528                 up_write(&mm->mmap_sem);
1529         }
1530 }
1531
1532 struct page *ksm_does_need_to_copy(struct page *page,
1533                         struct vm_area_struct *vma, unsigned long address)
1534 {
1535         struct page *new_page;
1536
1537         unlock_page(page);      /* any racers will COW it, not modify it */
1538
1539         new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
1540         if (new_page) {
1541                 copy_user_highpage(new_page, page, address, vma);
1542
1543                 SetPageDirty(new_page);
1544                 __SetPageUptodate(new_page);
1545                 SetPageSwapBacked(new_page);
1546                 __set_page_locked(new_page);
1547
1548                 if (page_evictable(new_page, vma))
1549                         lru_cache_add_lru(new_page, LRU_ACTIVE_ANON);
1550                 else
1551                         add_page_to_unevictable_list(new_page);
1552         }
1553
1554         page_cache_release(page);
1555         return new_page;
1556 }
1557
1558 int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg,
1559                         unsigned long *vm_flags)
1560 {
1561         struct stable_node *stable_node;
1562         struct rmap_item *rmap_item;
1563         struct hlist_node *hlist;
1564         unsigned int mapcount = page_mapcount(page);
1565         int referenced = 0;
1566         int search_new_forks = 0;
1567
1568         VM_BUG_ON(!PageKsm(page));
1569         VM_BUG_ON(!PageLocked(page));
1570
1571         stable_node = page_stable_node(page);
1572         if (!stable_node)
1573                 return 0;
1574 again:
1575         hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1576                 struct anon_vma *anon_vma = rmap_item->anon_vma;
1577                 struct vm_area_struct *vma;
1578
1579                 spin_lock(&anon_vma->lock);
1580                 list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
1581                         if (rmap_item->address < vma->vm_start ||
1582                             rmap_item->address >= vma->vm_end)
1583                                 continue;
1584                         /*
1585                          * Initially we examine only the vma which covers this
1586                          * rmap_item; but later, if there is still work to do,
1587                          * we examine covering vmas in other mms: in case they
1588                          * were forked from the original since ksmd passed.
1589                          */
1590                         if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1591                                 continue;
1592
1593                         if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
1594                                 continue;
1595
1596                         referenced += page_referenced_one(page, vma,
1597                                 rmap_item->address, &mapcount, vm_flags);
1598                         if (!search_new_forks || !mapcount)
1599                                 break;
1600                 }
1601                 spin_unlock(&anon_vma->lock);
1602                 if (!mapcount)
1603                         goto out;
1604         }
1605         if (!search_new_forks++)
1606                 goto again;
1607 out:
1608         return referenced;
1609 }
1610
1611 int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
1612 {
1613         struct stable_node *stable_node;
1614         struct hlist_node *hlist;
1615         struct rmap_item *rmap_item;
1616         int ret = SWAP_AGAIN;
1617         int search_new_forks = 0;
1618
1619         VM_BUG_ON(!PageKsm(page));
1620         VM_BUG_ON(!PageLocked(page));
1621
1622         stable_node = page_stable_node(page);
1623         if (!stable_node)
1624                 return SWAP_FAIL;
1625 again:
1626         hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1627                 struct anon_vma *anon_vma = rmap_item->anon_vma;
1628                 struct vm_area_struct *vma;
1629
1630                 spin_lock(&anon_vma->lock);
1631                 list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
1632                         if (rmap_item->address < vma->vm_start ||
1633                             rmap_item->address >= vma->vm_end)
1634                                 continue;
1635                         /*
1636                          * Initially we examine only the vma which covers this
1637                          * rmap_item; but later, if there is still work to do,
1638                          * we examine covering vmas in other mms: in case they
1639                          * were forked from the original since ksmd passed.
1640                          */
1641                         if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1642                                 continue;
1643
1644                         ret = try_to_unmap_one(page, vma,
1645                                         rmap_item->address, flags);
1646                         if (ret != SWAP_AGAIN || !page_mapped(page)) {
1647                                 spin_unlock(&anon_vma->lock);
1648                                 goto out;
1649                         }
1650                 }
1651                 spin_unlock(&anon_vma->lock);
1652         }
1653         if (!search_new_forks++)
1654                 goto again;
1655 out:
1656         return ret;
1657 }
1658
1659 #ifdef CONFIG_MIGRATION
1660 int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *,
1661                   struct vm_area_struct *, unsigned long, void *), void *arg)
1662 {
1663         struct stable_node *stable_node;
1664         struct hlist_node *hlist;
1665         struct rmap_item *rmap_item;
1666         int ret = SWAP_AGAIN;
1667         int search_new_forks = 0;
1668
1669         VM_BUG_ON(!PageKsm(page));
1670         VM_BUG_ON(!PageLocked(page));
1671
1672         stable_node = page_stable_node(page);
1673         if (!stable_node)
1674                 return ret;
1675 again:
1676         hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1677                 struct anon_vma *anon_vma = rmap_item->anon_vma;
1678                 struct vm_area_struct *vma;
1679
1680                 spin_lock(&anon_vma->lock);
1681                 list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
1682                         if (rmap_item->address < vma->vm_start ||
1683                             rmap_item->address >= vma->vm_end)
1684                                 continue;
1685                         /*
1686                          * Initially we examine only the vma which covers this
1687                          * rmap_item; but later, if there is still work to do,
1688                          * we examine covering vmas in other mms: in case they
1689                          * were forked from the original since ksmd passed.
1690                          */
1691                         if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1692                                 continue;
1693
1694                         ret = rmap_one(page, vma, rmap_item->address, arg);
1695                         if (ret != SWAP_AGAIN) {
1696                                 spin_unlock(&anon_vma->lock);
1697                                 goto out;
1698                         }
1699                 }
1700                 spin_unlock(&anon_vma->lock);
1701         }
1702         if (!search_new_forks++)
1703                 goto again;
1704 out:
1705         return ret;
1706 }
1707
1708 void ksm_migrate_page(struct page *newpage, struct page *oldpage)
1709 {
1710         struct stable_node *stable_node;
1711
1712         VM_BUG_ON(!PageLocked(oldpage));
1713         VM_BUG_ON(!PageLocked(newpage));
1714         VM_BUG_ON(newpage->mapping != oldpage->mapping);
1715
1716         stable_node = page_stable_node(newpage);
1717         if (stable_node) {
1718                 VM_BUG_ON(stable_node->page != oldpage);
1719                 stable_node->page = newpage;
1720         }
1721 }
1722 #endif /* CONFIG_MIGRATION */
1723
1724 #ifdef CONFIG_SYSFS
1725 /*
1726  * This all compiles without CONFIG_SYSFS, but is a waste of space.
1727  */
1728
1729 #define KSM_ATTR_RO(_name) \
1730         static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
1731 #define KSM_ATTR(_name) \
1732         static struct kobj_attribute _name##_attr = \
1733                 __ATTR(_name, 0644, _name##_show, _name##_store)
1734
1735 static ssize_t sleep_millisecs_show(struct kobject *kobj,
1736                                     struct kobj_attribute *attr, char *buf)
1737 {
1738         return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
1739 }
1740
1741 static ssize_t sleep_millisecs_store(struct kobject *kobj,
1742                                      struct kobj_attribute *attr,
1743                                      const char *buf, size_t count)
1744 {
1745         unsigned long msecs;
1746         int err;
1747
1748         err = strict_strtoul(buf, 10, &msecs);
1749         if (err || msecs > UINT_MAX)
1750                 return -EINVAL;
1751
1752         ksm_thread_sleep_millisecs = msecs;
1753
1754         return count;
1755 }
1756 KSM_ATTR(sleep_millisecs);
1757
1758 static ssize_t pages_to_scan_show(struct kobject *kobj,
1759                                   struct kobj_attribute *attr, char *buf)
1760 {
1761         return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
1762 }
1763
1764 static ssize_t pages_to_scan_store(struct kobject *kobj,
1765                                    struct kobj_attribute *attr,
1766                                    const char *buf, size_t count)
1767 {
1768         int err;
1769         unsigned long nr_pages;
1770
1771         err = strict_strtoul(buf, 10, &nr_pages);
1772         if (err || nr_pages > UINT_MAX)
1773                 return -EINVAL;
1774
1775         ksm_thread_pages_to_scan = nr_pages;
1776
1777         return count;
1778 }
1779 KSM_ATTR(pages_to_scan);
1780
1781 static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
1782                         char *buf)
1783 {
1784         return sprintf(buf, "%u\n", ksm_run);
1785 }
1786
1787 static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
1788                          const char *buf, size_t count)
1789 {
1790         int err;
1791         unsigned long flags;
1792
1793         err = strict_strtoul(buf, 10, &flags);
1794         if (err || flags > UINT_MAX)
1795                 return -EINVAL;
1796         if (flags > KSM_RUN_UNMERGE)
1797                 return -EINVAL;
1798
1799         /*
1800          * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
1801          * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
1802          * breaking COW to free the unswappable pages_shared (but leaves
1803          * mm_slots on the list for when ksmd may be set running again).
1804          */
1805
1806         mutex_lock(&ksm_thread_mutex);
1807         if (ksm_run != flags) {
1808                 ksm_run = flags;
1809                 if (flags & KSM_RUN_UNMERGE) {
1810                         current->flags |= PF_OOM_ORIGIN;
1811                         err = unmerge_and_remove_all_rmap_items();
1812                         current->flags &= ~PF_OOM_ORIGIN;
1813                         if (err) {
1814                                 ksm_run = KSM_RUN_STOP;
1815                                 count = err;
1816                         }
1817                 }
1818         }
1819         mutex_unlock(&ksm_thread_mutex);
1820
1821         if (flags & KSM_RUN_MERGE)
1822                 wake_up_interruptible(&ksm_thread_wait);
1823
1824         return count;
1825 }
1826 KSM_ATTR(run);
1827
1828 static ssize_t max_kernel_pages_store(struct kobject *kobj,
1829                                       struct kobj_attribute *attr,
1830                                       const char *buf, size_t count)
1831 {
1832         int err;
1833         unsigned long nr_pages;
1834
1835         err = strict_strtoul(buf, 10, &nr_pages);
1836         if (err)
1837                 return -EINVAL;
1838
1839         ksm_max_kernel_pages = nr_pages;
1840
1841         return count;
1842 }
1843
1844 static ssize_t max_kernel_pages_show(struct kobject *kobj,
1845                                      struct kobj_attribute *attr, char *buf)
1846 {
1847         return sprintf(buf, "%lu\n", ksm_max_kernel_pages);
1848 }
1849 KSM_ATTR(max_kernel_pages);
1850
1851 static ssize_t pages_shared_show(struct kobject *kobj,
1852                                  struct kobj_attribute *attr, char *buf)
1853 {
1854         return sprintf(buf, "%lu\n", ksm_pages_shared);
1855 }
1856 KSM_ATTR_RO(pages_shared);
1857
1858 static ssize_t pages_sharing_show(struct kobject *kobj,
1859                                   struct kobj_attribute *attr, char *buf)
1860 {
1861         return sprintf(buf, "%lu\n", ksm_pages_sharing);
1862 }
1863 KSM_ATTR_RO(pages_sharing);
1864
1865 static ssize_t pages_unshared_show(struct kobject *kobj,
1866                                    struct kobj_attribute *attr, char *buf)
1867 {
1868         return sprintf(buf, "%lu\n", ksm_pages_unshared);
1869 }
1870 KSM_ATTR_RO(pages_unshared);
1871
1872 static ssize_t pages_volatile_show(struct kobject *kobj,
1873                                    struct kobj_attribute *attr, char *buf)
1874 {
1875         long ksm_pages_volatile;
1876
1877         ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
1878                                 - ksm_pages_sharing - ksm_pages_unshared;
1879         /*
1880          * It was not worth any locking to calculate that statistic,
1881          * but it might therefore sometimes be negative: conceal that.
1882          */
1883         if (ksm_pages_volatile < 0)
1884                 ksm_pages_volatile = 0;
1885         return sprintf(buf, "%ld\n", ksm_pages_volatile);
1886 }
1887 KSM_ATTR_RO(pages_volatile);
1888
1889 static ssize_t full_scans_show(struct kobject *kobj,
1890                                struct kobj_attribute *attr, char *buf)
1891 {
1892         return sprintf(buf, "%lu\n", ksm_scan.seqnr);
1893 }
1894 KSM_ATTR_RO(full_scans);
1895
1896 static struct attribute *ksm_attrs[] = {
1897         &sleep_millisecs_attr.attr,
1898         &pages_to_scan_attr.attr,
1899         &run_attr.attr,
1900         &max_kernel_pages_attr.attr,
1901         &pages_shared_attr.attr,
1902         &pages_sharing_attr.attr,
1903         &pages_unshared_attr.attr,
1904         &pages_volatile_attr.attr,
1905         &full_scans_attr.attr,
1906         NULL,
1907 };
1908
1909 static struct attribute_group ksm_attr_group = {
1910         .attrs = ksm_attrs,
1911         .name = "ksm",
1912 };
1913 #endif /* CONFIG_SYSFS */
1914
1915 static int __init ksm_init(void)
1916 {
1917         struct task_struct *ksm_thread;
1918         int err;
1919
1920         ksm_max_kernel_pages = totalram_pages / 4;
1921
1922         err = ksm_slab_init();
1923         if (err)
1924                 goto out;
1925
1926         err = mm_slots_hash_init();
1927         if (err)
1928                 goto out_free1;
1929
1930         ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
1931         if (IS_ERR(ksm_thread)) {
1932                 printk(KERN_ERR "ksm: creating kthread failed\n");
1933                 err = PTR_ERR(ksm_thread);
1934                 goto out_free2;
1935         }
1936
1937 #ifdef CONFIG_SYSFS
1938         err = sysfs_create_group(mm_kobj, &ksm_attr_group);
1939         if (err) {
1940                 printk(KERN_ERR "ksm: register sysfs failed\n");
1941                 kthread_stop(ksm_thread);
1942                 goto out_free2;
1943         }
1944 #else
1945         ksm_run = KSM_RUN_MERGE;        /* no way for user to start it */
1946
1947 #endif /* CONFIG_SYSFS */
1948
1949         return 0;
1950
1951 out_free2:
1952         mm_slots_hash_free();
1953 out_free1:
1954         ksm_slab_free();
1955 out:
1956         return err;
1957 }
1958 module_init(ksm_init)