ksm: more on default values
[linux-3.10.git] / mm / ksm.c
1 /*
2  * Memory merging support.
3  *
4  * This code enables dynamic sharing of identical pages found in different
5  * memory areas, even if they are not shared by fork()
6  *
7  * Copyright (C) 2008-2009 Red Hat, Inc.
8  * Authors:
9  *      Izik Eidus
10  *      Andrea Arcangeli
11  *      Chris Wright
12  *      Hugh Dickins
13  *
14  * This work is licensed under the terms of the GNU GPL, version 2.
15  */
16
17 #include <linux/errno.h>
18 #include <linux/mm.h>
19 #include <linux/fs.h>
20 #include <linux/mman.h>
21 #include <linux/sched.h>
22 #include <linux/rwsem.h>
23 #include <linux/pagemap.h>
24 #include <linux/rmap.h>
25 #include <linux/spinlock.h>
26 #include <linux/jhash.h>
27 #include <linux/delay.h>
28 #include <linux/kthread.h>
29 #include <linux/wait.h>
30 #include <linux/slab.h>
31 #include <linux/rbtree.h>
32 #include <linux/mmu_notifier.h>
33 #include <linux/swap.h>
34 #include <linux/ksm.h>
35
36 #include <asm/tlbflush.h>
37
38 /*
39  * A few notes about the KSM scanning process,
40  * to make it easier to understand the data structures below:
41  *
42  * In order to reduce excessive scanning, KSM sorts the memory pages by their
43  * contents into a data structure that holds pointers to the pages' locations.
44  *
45  * Since the contents of the pages may change at any moment, KSM cannot just
46  * insert the pages into a normal sorted tree and expect it to find anything.
47  * Therefore KSM uses two data structures - the stable and the unstable tree.
48  *
49  * The stable tree holds pointers to all the merged pages (ksm pages), sorted
50  * by their contents.  Because each such page is write-protected, searching on
51  * this tree is fully assured to be working (except when pages are unmapped),
52  * and therefore this tree is called the stable tree.
53  *
54  * In addition to the stable tree, KSM uses a second data structure called the
55  * unstable tree: this tree holds pointers to pages which have been found to
56  * be "unchanged for a period of time".  The unstable tree sorts these pages
57  * by their contents, but since they are not write-protected, KSM cannot rely
58  * upon the unstable tree to work correctly - the unstable tree is liable to
59  * be corrupted as its contents are modified, and so it is called unstable.
60  *
61  * KSM solves this problem by several techniques:
62  *
63  * 1) The unstable tree is flushed every time KSM completes scanning all
64  *    memory areas, and then the tree is rebuilt again from the beginning.
65  * 2) KSM will only insert into the unstable tree, pages whose hash value
66  *    has not changed since the previous scan of all memory areas.
67  * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
68  *    colors of the nodes and not on their contents, assuring that even when
69  *    the tree gets "corrupted" it won't get out of balance, so scanning time
70  *    remains the same (also, searching and inserting nodes in an rbtree uses
71  *    the same algorithm, so we have no overhead when we flush and rebuild).
72  * 4) KSM never flushes the stable tree, which means that even if it were to
73  *    take 10 attempts to find a page in the unstable tree, once it is found,
74  *    it is secured in the stable tree.  (When we scan a new page, we first
75  *    compare it against the stable tree, and then against the unstable tree.)
76  */
77
78 /**
79  * struct mm_slot - ksm information per mm that is being scanned
80  * @link: link to the mm_slots hash list
81  * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
82  * @rmap_list: head for this mm_slot's list of rmap_items
83  * @mm: the mm that this information is valid for
84  */
85 struct mm_slot {
86         struct hlist_node link;
87         struct list_head mm_list;
88         struct list_head rmap_list;
89         struct mm_struct *mm;
90 };
91
92 /**
93  * struct ksm_scan - cursor for scanning
94  * @mm_slot: the current mm_slot we are scanning
95  * @address: the next address inside that to be scanned
96  * @rmap_item: the current rmap that we are scanning inside the rmap_list
97  * @seqnr: count of completed full scans (needed when removing unstable node)
98  *
99  * There is only the one ksm_scan instance of this cursor structure.
100  */
101 struct ksm_scan {
102         struct mm_slot *mm_slot;
103         unsigned long address;
104         struct rmap_item *rmap_item;
105         unsigned long seqnr;
106 };
107
108 /**
109  * struct rmap_item - reverse mapping item for virtual addresses
110  * @link: link into mm_slot's rmap_list (rmap_list is per mm)
111  * @mm: the memory structure this rmap_item is pointing into
112  * @address: the virtual address this rmap_item tracks (+ flags in low bits)
113  * @oldchecksum: previous checksum of the page at that virtual address
114  * @node: rb_node of this rmap_item in either unstable or stable tree
115  * @next: next rmap_item hanging off the same node of the stable tree
116  * @prev: previous rmap_item hanging off the same node of the stable tree
117  */
118 struct rmap_item {
119         struct list_head link;
120         struct mm_struct *mm;
121         unsigned long address;          /* + low bits used for flags below */
122         union {
123                 unsigned int oldchecksum;               /* when unstable */
124                 struct rmap_item *next;                 /* when stable */
125         };
126         union {
127                 struct rb_node node;                    /* when tree node */
128                 struct rmap_item *prev;                 /* in stable list */
129         };
130 };
131
132 #define SEQNR_MASK      0x0ff   /* low bits of unstable tree seqnr */
133 #define NODE_FLAG       0x100   /* is a node of unstable or stable tree */
134 #define STABLE_FLAG     0x200   /* is a node or list item of stable tree */
135
136 /* The stable and unstable tree heads */
137 static struct rb_root root_stable_tree = RB_ROOT;
138 static struct rb_root root_unstable_tree = RB_ROOT;
139
140 #define MM_SLOTS_HASH_HEADS 1024
141 static struct hlist_head *mm_slots_hash;
142
143 static struct mm_slot ksm_mm_head = {
144         .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
145 };
146 static struct ksm_scan ksm_scan = {
147         .mm_slot = &ksm_mm_head,
148 };
149
150 static struct kmem_cache *rmap_item_cache;
151 static struct kmem_cache *mm_slot_cache;
152
153 /* The number of nodes in the stable tree */
154 static unsigned long ksm_pages_shared;
155
156 /* The number of page slots additionally sharing those nodes */
157 static unsigned long ksm_pages_sharing;
158
159 /* The number of nodes in the unstable tree */
160 static unsigned long ksm_pages_unshared;
161
162 /* The number of rmap_items in use: to calculate pages_volatile */
163 static unsigned long ksm_rmap_items;
164
165 /* Limit on the number of unswappable pages used */
166 static unsigned long ksm_max_kernel_pages;
167
168 /* Number of pages ksmd should scan in one batch */
169 static unsigned int ksm_thread_pages_to_scan = 100;
170
171 /* Milliseconds ksmd should sleep between batches */
172 static unsigned int ksm_thread_sleep_millisecs = 20;
173
174 #define KSM_RUN_STOP    0
175 #define KSM_RUN_MERGE   1
176 #define KSM_RUN_UNMERGE 2
177 static unsigned int ksm_run = KSM_RUN_STOP;
178
179 static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
180 static DEFINE_MUTEX(ksm_thread_mutex);
181 static DEFINE_SPINLOCK(ksm_mmlist_lock);
182
183 #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
184                 sizeof(struct __struct), __alignof__(struct __struct),\
185                 (__flags), NULL)
186
187 static int __init ksm_slab_init(void)
188 {
189         rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
190         if (!rmap_item_cache)
191                 goto out;
192
193         mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
194         if (!mm_slot_cache)
195                 goto out_free;
196
197         return 0;
198
199 out_free:
200         kmem_cache_destroy(rmap_item_cache);
201 out:
202         return -ENOMEM;
203 }
204
205 static void __init ksm_slab_free(void)
206 {
207         kmem_cache_destroy(mm_slot_cache);
208         kmem_cache_destroy(rmap_item_cache);
209         mm_slot_cache = NULL;
210 }
211
212 static inline struct rmap_item *alloc_rmap_item(void)
213 {
214         struct rmap_item *rmap_item;
215
216         rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
217         if (rmap_item)
218                 ksm_rmap_items++;
219         return rmap_item;
220 }
221
222 static inline void free_rmap_item(struct rmap_item *rmap_item)
223 {
224         ksm_rmap_items--;
225         rmap_item->mm = NULL;   /* debug safety */
226         kmem_cache_free(rmap_item_cache, rmap_item);
227 }
228
229 static inline struct mm_slot *alloc_mm_slot(void)
230 {
231         if (!mm_slot_cache)     /* initialization failed */
232                 return NULL;
233         return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
234 }
235
236 static inline void free_mm_slot(struct mm_slot *mm_slot)
237 {
238         kmem_cache_free(mm_slot_cache, mm_slot);
239 }
240
241 static int __init mm_slots_hash_init(void)
242 {
243         mm_slots_hash = kzalloc(MM_SLOTS_HASH_HEADS * sizeof(struct hlist_head),
244                                 GFP_KERNEL);
245         if (!mm_slots_hash)
246                 return -ENOMEM;
247         return 0;
248 }
249
250 static void __init mm_slots_hash_free(void)
251 {
252         kfree(mm_slots_hash);
253 }
254
255 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
256 {
257         struct mm_slot *mm_slot;
258         struct hlist_head *bucket;
259         struct hlist_node *node;
260
261         bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
262                                 % MM_SLOTS_HASH_HEADS];
263         hlist_for_each_entry(mm_slot, node, bucket, link) {
264                 if (mm == mm_slot->mm)
265                         return mm_slot;
266         }
267         return NULL;
268 }
269
270 static void insert_to_mm_slots_hash(struct mm_struct *mm,
271                                     struct mm_slot *mm_slot)
272 {
273         struct hlist_head *bucket;
274
275         bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
276                                 % MM_SLOTS_HASH_HEADS];
277         mm_slot->mm = mm;
278         INIT_LIST_HEAD(&mm_slot->rmap_list);
279         hlist_add_head(&mm_slot->link, bucket);
280 }
281
282 static inline int in_stable_tree(struct rmap_item *rmap_item)
283 {
284         return rmap_item->address & STABLE_FLAG;
285 }
286
287 /*
288  * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
289  * page tables after it has passed through ksm_exit() - which, if necessary,
290  * takes mmap_sem briefly to serialize against them.  ksm_exit() does not set
291  * a special flag: they can just back out as soon as mm_users goes to zero.
292  * ksm_test_exit() is used throughout to make this test for exit: in some
293  * places for correctness, in some places just to avoid unnecessary work.
294  */
295 static inline bool ksm_test_exit(struct mm_struct *mm)
296 {
297         return atomic_read(&mm->mm_users) == 0;
298 }
299
300 /*
301  * We use break_ksm to break COW on a ksm page: it's a stripped down
302  *
303  *      if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
304  *              put_page(page);
305  *
306  * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
307  * in case the application has unmapped and remapped mm,addr meanwhile.
308  * Could a ksm page appear anywhere else?  Actually yes, in a VM_PFNMAP
309  * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
310  */
311 static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
312 {
313         struct page *page;
314         int ret = 0;
315
316         do {
317                 cond_resched();
318                 page = follow_page(vma, addr, FOLL_GET);
319                 if (!page)
320                         break;
321                 if (PageKsm(page))
322                         ret = handle_mm_fault(vma->vm_mm, vma, addr,
323                                                         FAULT_FLAG_WRITE);
324                 else
325                         ret = VM_FAULT_WRITE;
326                 put_page(page);
327         } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM)));
328         /*
329          * We must loop because handle_mm_fault() may back out if there's
330          * any difficulty e.g. if pte accessed bit gets updated concurrently.
331          *
332          * VM_FAULT_WRITE is what we have been hoping for: it indicates that
333          * COW has been broken, even if the vma does not permit VM_WRITE;
334          * but note that a concurrent fault might break PageKsm for us.
335          *
336          * VM_FAULT_SIGBUS could occur if we race with truncation of the
337          * backing file, which also invalidates anonymous pages: that's
338          * okay, that truncation will have unmapped the PageKsm for us.
339          *
340          * VM_FAULT_OOM: at the time of writing (late July 2009), setting
341          * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
342          * current task has TIF_MEMDIE set, and will be OOM killed on return
343          * to user; and ksmd, having no mm, would never be chosen for that.
344          *
345          * But if the mm is in a limited mem_cgroup, then the fault may fail
346          * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
347          * even ksmd can fail in this way - though it's usually breaking ksm
348          * just to undo a merge it made a moment before, so unlikely to oom.
349          *
350          * That's a pity: we might therefore have more kernel pages allocated
351          * than we're counting as nodes in the stable tree; but ksm_do_scan
352          * will retry to break_cow on each pass, so should recover the page
353          * in due course.  The important thing is to not let VM_MERGEABLE
354          * be cleared while any such pages might remain in the area.
355          */
356         return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
357 }
358
359 static void break_cow(struct mm_struct *mm, unsigned long addr)
360 {
361         struct vm_area_struct *vma;
362
363         down_read(&mm->mmap_sem);
364         if (ksm_test_exit(mm))
365                 goto out;
366         vma = find_vma(mm, addr);
367         if (!vma || vma->vm_start > addr)
368                 goto out;
369         if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
370                 goto out;
371         break_ksm(vma, addr);
372 out:
373         up_read(&mm->mmap_sem);
374 }
375
376 static struct page *get_mergeable_page(struct rmap_item *rmap_item)
377 {
378         struct mm_struct *mm = rmap_item->mm;
379         unsigned long addr = rmap_item->address;
380         struct vm_area_struct *vma;
381         struct page *page;
382
383         down_read(&mm->mmap_sem);
384         if (ksm_test_exit(mm))
385                 goto out;
386         vma = find_vma(mm, addr);
387         if (!vma || vma->vm_start > addr)
388                 goto out;
389         if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
390                 goto out;
391
392         page = follow_page(vma, addr, FOLL_GET);
393         if (!page)
394                 goto out;
395         if (PageAnon(page)) {
396                 flush_anon_page(vma, page, addr);
397                 flush_dcache_page(page);
398         } else {
399                 put_page(page);
400 out:            page = NULL;
401         }
402         up_read(&mm->mmap_sem);
403         return page;
404 }
405
406 /*
407  * get_ksm_page: checks if the page at the virtual address in rmap_item
408  * is still PageKsm, in which case we can trust the content of the page,
409  * and it returns the gotten page; but NULL if the page has been zapped.
410  */
411 static struct page *get_ksm_page(struct rmap_item *rmap_item)
412 {
413         struct page *page;
414
415         page = get_mergeable_page(rmap_item);
416         if (page && !PageKsm(page)) {
417                 put_page(page);
418                 page = NULL;
419         }
420         return page;
421 }
422
423 /*
424  * Removing rmap_item from stable or unstable tree.
425  * This function will clean the information from the stable/unstable tree.
426  */
427 static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
428 {
429         if (in_stable_tree(rmap_item)) {
430                 struct rmap_item *next_item = rmap_item->next;
431
432                 if (rmap_item->address & NODE_FLAG) {
433                         if (next_item) {
434                                 rb_replace_node(&rmap_item->node,
435                                                 &next_item->node,
436                                                 &root_stable_tree);
437                                 next_item->address |= NODE_FLAG;
438                                 ksm_pages_sharing--;
439                         } else {
440                                 rb_erase(&rmap_item->node, &root_stable_tree);
441                                 ksm_pages_shared--;
442                         }
443                 } else {
444                         struct rmap_item *prev_item = rmap_item->prev;
445
446                         BUG_ON(prev_item->next != rmap_item);
447                         prev_item->next = next_item;
448                         if (next_item) {
449                                 BUG_ON(next_item->prev != rmap_item);
450                                 next_item->prev = rmap_item->prev;
451                         }
452                         ksm_pages_sharing--;
453                 }
454
455                 rmap_item->next = NULL;
456
457         } else if (rmap_item->address & NODE_FLAG) {
458                 unsigned char age;
459                 /*
460                  * Usually ksmd can and must skip the rb_erase, because
461                  * root_unstable_tree was already reset to RB_ROOT.
462                  * But be careful when an mm is exiting: do the rb_erase
463                  * if this rmap_item was inserted by this scan, rather
464                  * than left over from before.
465                  */
466                 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
467                 BUG_ON(age > 1);
468                 if (!age)
469                         rb_erase(&rmap_item->node, &root_unstable_tree);
470                 ksm_pages_unshared--;
471         }
472
473         rmap_item->address &= PAGE_MASK;
474
475         cond_resched();         /* we're called from many long loops */
476 }
477
478 static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
479                                        struct list_head *cur)
480 {
481         struct rmap_item *rmap_item;
482
483         while (cur != &mm_slot->rmap_list) {
484                 rmap_item = list_entry(cur, struct rmap_item, link);
485                 cur = cur->next;
486                 remove_rmap_item_from_tree(rmap_item);
487                 list_del(&rmap_item->link);
488                 free_rmap_item(rmap_item);
489         }
490 }
491
492 /*
493  * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather
494  * than check every pte of a given vma, the locking doesn't quite work for
495  * that - an rmap_item is assigned to the stable tree after inserting ksm
496  * page and upping mmap_sem.  Nor does it fit with the way we skip dup'ing
497  * rmap_items from parent to child at fork time (so as not to waste time
498  * if exit comes before the next scan reaches it).
499  *
500  * Similarly, although we'd like to remove rmap_items (so updating counts
501  * and freeing memory) when unmerging an area, it's easier to leave that
502  * to the next pass of ksmd - consider, for example, how ksmd might be
503  * in cmp_and_merge_page on one of the rmap_items we would be removing.
504  */
505 static int unmerge_ksm_pages(struct vm_area_struct *vma,
506                              unsigned long start, unsigned long end)
507 {
508         unsigned long addr;
509         int err = 0;
510
511         for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
512                 if (ksm_test_exit(vma->vm_mm))
513                         break;
514                 if (signal_pending(current))
515                         err = -ERESTARTSYS;
516                 else
517                         err = break_ksm(vma, addr);
518         }
519         return err;
520 }
521
522 #ifdef CONFIG_SYSFS
523 /*
524  * Only called through the sysfs control interface:
525  */
526 static int unmerge_and_remove_all_rmap_items(void)
527 {
528         struct mm_slot *mm_slot;
529         struct mm_struct *mm;
530         struct vm_area_struct *vma;
531         int err = 0;
532
533         spin_lock(&ksm_mmlist_lock);
534         ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
535                                                 struct mm_slot, mm_list);
536         spin_unlock(&ksm_mmlist_lock);
537
538         for (mm_slot = ksm_scan.mm_slot;
539                         mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
540                 mm = mm_slot->mm;
541                 down_read(&mm->mmap_sem);
542                 for (vma = mm->mmap; vma; vma = vma->vm_next) {
543                         if (ksm_test_exit(mm))
544                                 break;
545                         if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
546                                 continue;
547                         err = unmerge_ksm_pages(vma,
548                                                 vma->vm_start, vma->vm_end);
549                         if (err)
550                                 goto error;
551                 }
552
553                 remove_trailing_rmap_items(mm_slot, mm_slot->rmap_list.next);
554
555                 spin_lock(&ksm_mmlist_lock);
556                 ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
557                                                 struct mm_slot, mm_list);
558                 if (ksm_test_exit(mm)) {
559                         hlist_del(&mm_slot->link);
560                         list_del(&mm_slot->mm_list);
561                         spin_unlock(&ksm_mmlist_lock);
562
563                         free_mm_slot(mm_slot);
564                         clear_bit(MMF_VM_MERGEABLE, &mm->flags);
565                         up_read(&mm->mmap_sem);
566                         mmdrop(mm);
567                 } else {
568                         spin_unlock(&ksm_mmlist_lock);
569                         up_read(&mm->mmap_sem);
570                 }
571         }
572
573         ksm_scan.seqnr = 0;
574         return 0;
575
576 error:
577         up_read(&mm->mmap_sem);
578         spin_lock(&ksm_mmlist_lock);
579         ksm_scan.mm_slot = &ksm_mm_head;
580         spin_unlock(&ksm_mmlist_lock);
581         return err;
582 }
583 #endif /* CONFIG_SYSFS */
584
585 static u32 calc_checksum(struct page *page)
586 {
587         u32 checksum;
588         void *addr = kmap_atomic(page, KM_USER0);
589         checksum = jhash2(addr, PAGE_SIZE / 4, 17);
590         kunmap_atomic(addr, KM_USER0);
591         return checksum;
592 }
593
594 static int memcmp_pages(struct page *page1, struct page *page2)
595 {
596         char *addr1, *addr2;
597         int ret;
598
599         addr1 = kmap_atomic(page1, KM_USER0);
600         addr2 = kmap_atomic(page2, KM_USER1);
601         ret = memcmp(addr1, addr2, PAGE_SIZE);
602         kunmap_atomic(addr2, KM_USER1);
603         kunmap_atomic(addr1, KM_USER0);
604         return ret;
605 }
606
607 static inline int pages_identical(struct page *page1, struct page *page2)
608 {
609         return !memcmp_pages(page1, page2);
610 }
611
612 static int write_protect_page(struct vm_area_struct *vma, struct page *page,
613                               pte_t *orig_pte)
614 {
615         struct mm_struct *mm = vma->vm_mm;
616         unsigned long addr;
617         pte_t *ptep;
618         spinlock_t *ptl;
619         int swapped;
620         int err = -EFAULT;
621
622         addr = page_address_in_vma(page, vma);
623         if (addr == -EFAULT)
624                 goto out;
625
626         ptep = page_check_address(page, mm, addr, &ptl, 0);
627         if (!ptep)
628                 goto out;
629
630         if (pte_write(*ptep)) {
631                 pte_t entry;
632
633                 swapped = PageSwapCache(page);
634                 flush_cache_page(vma, addr, page_to_pfn(page));
635                 /*
636                  * Ok this is tricky, when get_user_pages_fast() run it doesnt
637                  * take any lock, therefore the check that we are going to make
638                  * with the pagecount against the mapcount is racey and
639                  * O_DIRECT can happen right after the check.
640                  * So we clear the pte and flush the tlb before the check
641                  * this assure us that no O_DIRECT can happen after the check
642                  * or in the middle of the check.
643                  */
644                 entry = ptep_clear_flush(vma, addr, ptep);
645                 /*
646                  * Check that no O_DIRECT or similar I/O is in progress on the
647                  * page
648                  */
649                 if ((page_mapcount(page) + 2 + swapped) != page_count(page)) {
650                         set_pte_at_notify(mm, addr, ptep, entry);
651                         goto out_unlock;
652                 }
653                 entry = pte_wrprotect(entry);
654                 set_pte_at_notify(mm, addr, ptep, entry);
655         }
656         *orig_pte = *ptep;
657         err = 0;
658
659 out_unlock:
660         pte_unmap_unlock(ptep, ptl);
661 out:
662         return err;
663 }
664
665 /**
666  * replace_page - replace page in vma by new ksm page
667  * @vma:      vma that holds the pte pointing to oldpage
668  * @oldpage:  the page we are replacing by newpage
669  * @newpage:  the ksm page we replace oldpage by
670  * @orig_pte: the original value of the pte
671  *
672  * Returns 0 on success, -EFAULT on failure.
673  */
674 static int replace_page(struct vm_area_struct *vma, struct page *oldpage,
675                         struct page *newpage, pte_t orig_pte)
676 {
677         struct mm_struct *mm = vma->vm_mm;
678         pgd_t *pgd;
679         pud_t *pud;
680         pmd_t *pmd;
681         pte_t *ptep;
682         spinlock_t *ptl;
683         unsigned long addr;
684         pgprot_t prot;
685         int err = -EFAULT;
686
687         prot = vm_get_page_prot(vma->vm_flags & ~VM_WRITE);
688
689         addr = page_address_in_vma(oldpage, vma);
690         if (addr == -EFAULT)
691                 goto out;
692
693         pgd = pgd_offset(mm, addr);
694         if (!pgd_present(*pgd))
695                 goto out;
696
697         pud = pud_offset(pgd, addr);
698         if (!pud_present(*pud))
699                 goto out;
700
701         pmd = pmd_offset(pud, addr);
702         if (!pmd_present(*pmd))
703                 goto out;
704
705         ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
706         if (!pte_same(*ptep, orig_pte)) {
707                 pte_unmap_unlock(ptep, ptl);
708                 goto out;
709         }
710
711         get_page(newpage);
712         page_add_ksm_rmap(newpage);
713
714         flush_cache_page(vma, addr, pte_pfn(*ptep));
715         ptep_clear_flush(vma, addr, ptep);
716         set_pte_at_notify(mm, addr, ptep, mk_pte(newpage, prot));
717
718         page_remove_rmap(oldpage);
719         put_page(oldpage);
720
721         pte_unmap_unlock(ptep, ptl);
722         err = 0;
723 out:
724         return err;
725 }
726
727 /*
728  * try_to_merge_one_page - take two pages and merge them into one
729  * @vma: the vma that hold the pte pointing into oldpage
730  * @oldpage: the page that we want to replace with newpage
731  * @newpage: the page that we want to map instead of oldpage
732  *
733  * Note:
734  * oldpage should be a PageAnon page, while newpage should be a PageKsm page,
735  * or a newly allocated kernel page which page_add_ksm_rmap will make PageKsm.
736  *
737  * This function returns 0 if the pages were merged, -EFAULT otherwise.
738  */
739 static int try_to_merge_one_page(struct vm_area_struct *vma,
740                                  struct page *oldpage,
741                                  struct page *newpage)
742 {
743         pte_t orig_pte = __pte(0);
744         int err = -EFAULT;
745
746         if (!(vma->vm_flags & VM_MERGEABLE))
747                 goto out;
748
749         if (!PageAnon(oldpage))
750                 goto out;
751
752         get_page(newpage);
753         get_page(oldpage);
754
755         /*
756          * We need the page lock to read a stable PageSwapCache in
757          * write_protect_page().  We use trylock_page() instead of
758          * lock_page() because we don't want to wait here - we
759          * prefer to continue scanning and merging different pages,
760          * then come back to this page when it is unlocked.
761          */
762         if (!trylock_page(oldpage))
763                 goto out_putpage;
764         /*
765          * If this anonymous page is mapped only here, its pte may need
766          * to be write-protected.  If it's mapped elsewhere, all of its
767          * ptes are necessarily already write-protected.  But in either
768          * case, we need to lock and check page_count is not raised.
769          */
770         if (write_protect_page(vma, oldpage, &orig_pte)) {
771                 unlock_page(oldpage);
772                 goto out_putpage;
773         }
774         unlock_page(oldpage);
775
776         if (pages_identical(oldpage, newpage))
777                 err = replace_page(vma, oldpage, newpage, orig_pte);
778
779 out_putpage:
780         put_page(oldpage);
781         put_page(newpage);
782 out:
783         return err;
784 }
785
786 /*
787  * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
788  * but no new kernel page is allocated: kpage must already be a ksm page.
789  */
790 static int try_to_merge_with_ksm_page(struct mm_struct *mm1,
791                                       unsigned long addr1,
792                                       struct page *page1,
793                                       struct page *kpage)
794 {
795         struct vm_area_struct *vma;
796         int err = -EFAULT;
797
798         down_read(&mm1->mmap_sem);
799         if (ksm_test_exit(mm1))
800                 goto out;
801
802         vma = find_vma(mm1, addr1);
803         if (!vma || vma->vm_start > addr1)
804                 goto out;
805
806         err = try_to_merge_one_page(vma, page1, kpage);
807 out:
808         up_read(&mm1->mmap_sem);
809         return err;
810 }
811
812 /*
813  * try_to_merge_two_pages - take two identical pages and prepare them
814  * to be merged into one page.
815  *
816  * This function returns 0 if we successfully mapped two identical pages
817  * into one page, -EFAULT otherwise.
818  *
819  * Note that this function allocates a new kernel page: if one of the pages
820  * is already a ksm page, try_to_merge_with_ksm_page should be used.
821  */
822 static int try_to_merge_two_pages(struct mm_struct *mm1, unsigned long addr1,
823                                   struct page *page1, struct mm_struct *mm2,
824                                   unsigned long addr2, struct page *page2)
825 {
826         struct vm_area_struct *vma;
827         struct page *kpage;
828         int err = -EFAULT;
829
830         /*
831          * The number of nodes in the stable tree
832          * is the number of kernel pages that we hold.
833          */
834         if (ksm_max_kernel_pages &&
835             ksm_max_kernel_pages <= ksm_pages_shared)
836                 return err;
837
838         kpage = alloc_page(GFP_HIGHUSER);
839         if (!kpage)
840                 return err;
841
842         down_read(&mm1->mmap_sem);
843         if (ksm_test_exit(mm1)) {
844                 up_read(&mm1->mmap_sem);
845                 goto out;
846         }
847         vma = find_vma(mm1, addr1);
848         if (!vma || vma->vm_start > addr1) {
849                 up_read(&mm1->mmap_sem);
850                 goto out;
851         }
852
853         copy_user_highpage(kpage, page1, addr1, vma);
854         err = try_to_merge_one_page(vma, page1, kpage);
855         up_read(&mm1->mmap_sem);
856
857         if (!err) {
858                 err = try_to_merge_with_ksm_page(mm2, addr2, page2, kpage);
859                 /*
860                  * If that fails, we have a ksm page with only one pte
861                  * pointing to it: so break it.
862                  */
863                 if (err)
864                         break_cow(mm1, addr1);
865         }
866 out:
867         put_page(kpage);
868         return err;
869 }
870
871 /*
872  * stable_tree_search - search page inside the stable tree
873  * @page: the page that we are searching identical pages to.
874  * @page2: pointer into identical page that we are holding inside the stable
875  *         tree that we have found.
876  * @rmap_item: the reverse mapping item
877  *
878  * This function checks if there is a page inside the stable tree
879  * with identical content to the page that we are scanning right now.
880  *
881  * This function return rmap_item pointer to the identical item if found,
882  * NULL otherwise.
883  */
884 static struct rmap_item *stable_tree_search(struct page *page,
885                                             struct page **page2,
886                                             struct rmap_item *rmap_item)
887 {
888         struct rb_node *node = root_stable_tree.rb_node;
889
890         while (node) {
891                 struct rmap_item *tree_rmap_item, *next_rmap_item;
892                 int ret;
893
894                 tree_rmap_item = rb_entry(node, struct rmap_item, node);
895                 while (tree_rmap_item) {
896                         BUG_ON(!in_stable_tree(tree_rmap_item));
897                         cond_resched();
898                         page2[0] = get_ksm_page(tree_rmap_item);
899                         if (page2[0])
900                                 break;
901                         next_rmap_item = tree_rmap_item->next;
902                         remove_rmap_item_from_tree(tree_rmap_item);
903                         tree_rmap_item = next_rmap_item;
904                 }
905                 if (!tree_rmap_item)
906                         return NULL;
907
908                 ret = memcmp_pages(page, page2[0]);
909
910                 if (ret < 0) {
911                         put_page(page2[0]);
912                         node = node->rb_left;
913                 } else if (ret > 0) {
914                         put_page(page2[0]);
915                         node = node->rb_right;
916                 } else {
917                         return tree_rmap_item;
918                 }
919         }
920
921         return NULL;
922 }
923
924 /*
925  * stable_tree_insert - insert rmap_item pointing to new ksm page
926  * into the stable tree.
927  *
928  * @page: the page that we are searching identical page to inside the stable
929  *        tree.
930  * @rmap_item: pointer to the reverse mapping item.
931  *
932  * This function returns rmap_item if success, NULL otherwise.
933  */
934 static struct rmap_item *stable_tree_insert(struct page *page,
935                                             struct rmap_item *rmap_item)
936 {
937         struct rb_node **new = &root_stable_tree.rb_node;
938         struct rb_node *parent = NULL;
939
940         while (*new) {
941                 struct rmap_item *tree_rmap_item, *next_rmap_item;
942                 struct page *tree_page;
943                 int ret;
944
945                 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
946                 while (tree_rmap_item) {
947                         BUG_ON(!in_stable_tree(tree_rmap_item));
948                         cond_resched();
949                         tree_page = get_ksm_page(tree_rmap_item);
950                         if (tree_page)
951                                 break;
952                         next_rmap_item = tree_rmap_item->next;
953                         remove_rmap_item_from_tree(tree_rmap_item);
954                         tree_rmap_item = next_rmap_item;
955                 }
956                 if (!tree_rmap_item)
957                         return NULL;
958
959                 ret = memcmp_pages(page, tree_page);
960                 put_page(tree_page);
961
962                 parent = *new;
963                 if (ret < 0)
964                         new = &parent->rb_left;
965                 else if (ret > 0)
966                         new = &parent->rb_right;
967                 else {
968                         /*
969                          * It is not a bug that stable_tree_search() didn't
970                          * find this node: because at that time our page was
971                          * not yet write-protected, so may have changed since.
972                          */
973                         return NULL;
974                 }
975         }
976
977         rmap_item->address |= NODE_FLAG | STABLE_FLAG;
978         rmap_item->next = NULL;
979         rb_link_node(&rmap_item->node, parent, new);
980         rb_insert_color(&rmap_item->node, &root_stable_tree);
981
982         ksm_pages_shared++;
983         return rmap_item;
984 }
985
986 /*
987  * unstable_tree_search_insert - search and insert items into the unstable tree.
988  *
989  * @page: the page that we are going to search for identical page or to insert
990  *        into the unstable tree
991  * @page2: pointer into identical page that was found inside the unstable tree
992  * @rmap_item: the reverse mapping item of page
993  *
994  * This function searches for a page in the unstable tree identical to the
995  * page currently being scanned; and if no identical page is found in the
996  * tree, we insert rmap_item as a new object into the unstable tree.
997  *
998  * This function returns pointer to rmap_item found to be identical
999  * to the currently scanned page, NULL otherwise.
1000  *
1001  * This function does both searching and inserting, because they share
1002  * the same walking algorithm in an rbtree.
1003  */
1004 static struct rmap_item *unstable_tree_search_insert(struct page *page,
1005                                                 struct page **page2,
1006                                                 struct rmap_item *rmap_item)
1007 {
1008         struct rb_node **new = &root_unstable_tree.rb_node;
1009         struct rb_node *parent = NULL;
1010
1011         while (*new) {
1012                 struct rmap_item *tree_rmap_item;
1013                 int ret;
1014
1015                 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1016                 page2[0] = get_mergeable_page(tree_rmap_item);
1017                 if (!page2[0])
1018                         return NULL;
1019
1020                 /*
1021                  * Don't substitute an unswappable ksm page
1022                  * just for one good swappable forked page.
1023                  */
1024                 if (page == page2[0]) {
1025                         put_page(page2[0]);
1026                         return NULL;
1027                 }
1028
1029                 ret = memcmp_pages(page, page2[0]);
1030
1031                 parent = *new;
1032                 if (ret < 0) {
1033                         put_page(page2[0]);
1034                         new = &parent->rb_left;
1035                 } else if (ret > 0) {
1036                         put_page(page2[0]);
1037                         new = &parent->rb_right;
1038                 } else {
1039                         return tree_rmap_item;
1040                 }
1041         }
1042
1043         rmap_item->address |= NODE_FLAG;
1044         rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1045         rb_link_node(&rmap_item->node, parent, new);
1046         rb_insert_color(&rmap_item->node, &root_unstable_tree);
1047
1048         ksm_pages_unshared++;
1049         return NULL;
1050 }
1051
1052 /*
1053  * stable_tree_append - add another rmap_item to the linked list of
1054  * rmap_items hanging off a given node of the stable tree, all sharing
1055  * the same ksm page.
1056  */
1057 static void stable_tree_append(struct rmap_item *rmap_item,
1058                                struct rmap_item *tree_rmap_item)
1059 {
1060         rmap_item->next = tree_rmap_item->next;
1061         rmap_item->prev = tree_rmap_item;
1062
1063         if (tree_rmap_item->next)
1064                 tree_rmap_item->next->prev = rmap_item;
1065
1066         tree_rmap_item->next = rmap_item;
1067         rmap_item->address |= STABLE_FLAG;
1068
1069         ksm_pages_sharing++;
1070 }
1071
1072 /*
1073  * cmp_and_merge_page - first see if page can be merged into the stable tree;
1074  * if not, compare checksum to previous and if it's the same, see if page can
1075  * be inserted into the unstable tree, or merged with a page already there and
1076  * both transferred to the stable tree.
1077  *
1078  * @page: the page that we are searching identical page to.
1079  * @rmap_item: the reverse mapping into the virtual address of this page
1080  */
1081 static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1082 {
1083         struct page *page2[1];
1084         struct rmap_item *tree_rmap_item;
1085         unsigned int checksum;
1086         int err;
1087
1088         if (in_stable_tree(rmap_item))
1089                 remove_rmap_item_from_tree(rmap_item);
1090
1091         /* We first start with searching the page inside the stable tree */
1092         tree_rmap_item = stable_tree_search(page, page2, rmap_item);
1093         if (tree_rmap_item) {
1094                 if (page == page2[0])                   /* forked */
1095                         err = 0;
1096                 else
1097                         err = try_to_merge_with_ksm_page(rmap_item->mm,
1098                                                          rmap_item->address,
1099                                                          page, page2[0]);
1100                 put_page(page2[0]);
1101
1102                 if (!err) {
1103                         /*
1104                          * The page was successfully merged:
1105                          * add its rmap_item to the stable tree.
1106                          */
1107                         stable_tree_append(rmap_item, tree_rmap_item);
1108                 }
1109                 return;
1110         }
1111
1112         /*
1113          * A ksm page might have got here by fork, but its other
1114          * references have already been removed from the stable tree.
1115          * Or it might be left over from a break_ksm which failed
1116          * when the mem_cgroup had reached its limit: try again now.
1117          */
1118         if (PageKsm(page))
1119                 break_cow(rmap_item->mm, rmap_item->address);
1120
1121         /*
1122          * In case the hash value of the page was changed from the last time we
1123          * have calculated it, this page to be changed frequely, therefore we
1124          * don't want to insert it to the unstable tree, and we don't want to
1125          * waste our time to search if there is something identical to it there.
1126          */
1127         checksum = calc_checksum(page);
1128         if (rmap_item->oldchecksum != checksum) {
1129                 rmap_item->oldchecksum = checksum;
1130                 return;
1131         }
1132
1133         tree_rmap_item = unstable_tree_search_insert(page, page2, rmap_item);
1134         if (tree_rmap_item) {
1135                 err = try_to_merge_two_pages(rmap_item->mm,
1136                                              rmap_item->address, page,
1137                                              tree_rmap_item->mm,
1138                                              tree_rmap_item->address, page2[0]);
1139                 /*
1140                  * As soon as we merge this page, we want to remove the
1141                  * rmap_item of the page we have merged with from the unstable
1142                  * tree, and insert it instead as new node in the stable tree.
1143                  */
1144                 if (!err) {
1145                         rb_erase(&tree_rmap_item->node, &root_unstable_tree);
1146                         tree_rmap_item->address &= ~NODE_FLAG;
1147                         ksm_pages_unshared--;
1148
1149                         /*
1150                          * If we fail to insert the page into the stable tree,
1151                          * we will have 2 virtual addresses that are pointing
1152                          * to a ksm page left outside the stable tree,
1153                          * in which case we need to break_cow on both.
1154                          */
1155                         if (stable_tree_insert(page2[0], tree_rmap_item))
1156                                 stable_tree_append(rmap_item, tree_rmap_item);
1157                         else {
1158                                 break_cow(tree_rmap_item->mm,
1159                                                 tree_rmap_item->address);
1160                                 break_cow(rmap_item->mm, rmap_item->address);
1161                         }
1162                 }
1163
1164                 put_page(page2[0]);
1165         }
1166 }
1167
1168 static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
1169                                             struct list_head *cur,
1170                                             unsigned long addr)
1171 {
1172         struct rmap_item *rmap_item;
1173
1174         while (cur != &mm_slot->rmap_list) {
1175                 rmap_item = list_entry(cur, struct rmap_item, link);
1176                 if ((rmap_item->address & PAGE_MASK) == addr) {
1177                         if (!in_stable_tree(rmap_item))
1178                                 remove_rmap_item_from_tree(rmap_item);
1179                         return rmap_item;
1180                 }
1181                 if (rmap_item->address > addr)
1182                         break;
1183                 cur = cur->next;
1184                 remove_rmap_item_from_tree(rmap_item);
1185                 list_del(&rmap_item->link);
1186                 free_rmap_item(rmap_item);
1187         }
1188
1189         rmap_item = alloc_rmap_item();
1190         if (rmap_item) {
1191                 /* It has already been zeroed */
1192                 rmap_item->mm = mm_slot->mm;
1193                 rmap_item->address = addr;
1194                 list_add_tail(&rmap_item->link, cur);
1195         }
1196         return rmap_item;
1197 }
1198
1199 static struct rmap_item *scan_get_next_rmap_item(struct page **page)
1200 {
1201         struct mm_struct *mm;
1202         struct mm_slot *slot;
1203         struct vm_area_struct *vma;
1204         struct rmap_item *rmap_item;
1205
1206         if (list_empty(&ksm_mm_head.mm_list))
1207                 return NULL;
1208
1209         slot = ksm_scan.mm_slot;
1210         if (slot == &ksm_mm_head) {
1211                 root_unstable_tree = RB_ROOT;
1212
1213                 spin_lock(&ksm_mmlist_lock);
1214                 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1215                 ksm_scan.mm_slot = slot;
1216                 spin_unlock(&ksm_mmlist_lock);
1217 next_mm:
1218                 ksm_scan.address = 0;
1219                 ksm_scan.rmap_item = list_entry(&slot->rmap_list,
1220                                                 struct rmap_item, link);
1221         }
1222
1223         mm = slot->mm;
1224         down_read(&mm->mmap_sem);
1225         if (ksm_test_exit(mm))
1226                 vma = NULL;
1227         else
1228                 vma = find_vma(mm, ksm_scan.address);
1229
1230         for (; vma; vma = vma->vm_next) {
1231                 if (!(vma->vm_flags & VM_MERGEABLE))
1232                         continue;
1233                 if (ksm_scan.address < vma->vm_start)
1234                         ksm_scan.address = vma->vm_start;
1235                 if (!vma->anon_vma)
1236                         ksm_scan.address = vma->vm_end;
1237
1238                 while (ksm_scan.address < vma->vm_end) {
1239                         if (ksm_test_exit(mm))
1240                                 break;
1241                         *page = follow_page(vma, ksm_scan.address, FOLL_GET);
1242                         if (*page && PageAnon(*page)) {
1243                                 flush_anon_page(vma, *page, ksm_scan.address);
1244                                 flush_dcache_page(*page);
1245                                 rmap_item = get_next_rmap_item(slot,
1246                                         ksm_scan.rmap_item->link.next,
1247                                         ksm_scan.address);
1248                                 if (rmap_item) {
1249                                         ksm_scan.rmap_item = rmap_item;
1250                                         ksm_scan.address += PAGE_SIZE;
1251                                 } else
1252                                         put_page(*page);
1253                                 up_read(&mm->mmap_sem);
1254                                 return rmap_item;
1255                         }
1256                         if (*page)
1257                                 put_page(*page);
1258                         ksm_scan.address += PAGE_SIZE;
1259                         cond_resched();
1260                 }
1261         }
1262
1263         if (ksm_test_exit(mm)) {
1264                 ksm_scan.address = 0;
1265                 ksm_scan.rmap_item = list_entry(&slot->rmap_list,
1266                                                 struct rmap_item, link);
1267         }
1268         /*
1269          * Nuke all the rmap_items that are above this current rmap:
1270          * because there were no VM_MERGEABLE vmas with such addresses.
1271          */
1272         remove_trailing_rmap_items(slot, ksm_scan.rmap_item->link.next);
1273
1274         spin_lock(&ksm_mmlist_lock);
1275         ksm_scan.mm_slot = list_entry(slot->mm_list.next,
1276                                                 struct mm_slot, mm_list);
1277         if (ksm_scan.address == 0) {
1278                 /*
1279                  * We've completed a full scan of all vmas, holding mmap_sem
1280                  * throughout, and found no VM_MERGEABLE: so do the same as
1281                  * __ksm_exit does to remove this mm from all our lists now.
1282                  * This applies either when cleaning up after __ksm_exit
1283                  * (but beware: we can reach here even before __ksm_exit),
1284                  * or when all VM_MERGEABLE areas have been unmapped (and
1285                  * mmap_sem then protects against race with MADV_MERGEABLE).
1286                  */
1287                 hlist_del(&slot->link);
1288                 list_del(&slot->mm_list);
1289                 spin_unlock(&ksm_mmlist_lock);
1290
1291                 free_mm_slot(slot);
1292                 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1293                 up_read(&mm->mmap_sem);
1294                 mmdrop(mm);
1295         } else {
1296                 spin_unlock(&ksm_mmlist_lock);
1297                 up_read(&mm->mmap_sem);
1298         }
1299
1300         /* Repeat until we've completed scanning the whole list */
1301         slot = ksm_scan.mm_slot;
1302         if (slot != &ksm_mm_head)
1303                 goto next_mm;
1304
1305         ksm_scan.seqnr++;
1306         return NULL;
1307 }
1308
1309 /**
1310  * ksm_do_scan  - the ksm scanner main worker function.
1311  * @scan_npages - number of pages we want to scan before we return.
1312  */
1313 static void ksm_do_scan(unsigned int scan_npages)
1314 {
1315         struct rmap_item *rmap_item;
1316         struct page *page;
1317
1318         while (scan_npages--) {
1319                 cond_resched();
1320                 rmap_item = scan_get_next_rmap_item(&page);
1321                 if (!rmap_item)
1322                         return;
1323                 if (!PageKsm(page) || !in_stable_tree(rmap_item))
1324                         cmp_and_merge_page(page, rmap_item);
1325                 else if (page_mapcount(page) == 1) {
1326                         /*
1327                          * Replace now-unshared ksm page by ordinary page.
1328                          */
1329                         break_cow(rmap_item->mm, rmap_item->address);
1330                         remove_rmap_item_from_tree(rmap_item);
1331                         rmap_item->oldchecksum = calc_checksum(page);
1332                 }
1333                 put_page(page);
1334         }
1335 }
1336
1337 static int ksmd_should_run(void)
1338 {
1339         return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1340 }
1341
1342 static int ksm_scan_thread(void *nothing)
1343 {
1344         set_user_nice(current, 5);
1345
1346         while (!kthread_should_stop()) {
1347                 mutex_lock(&ksm_thread_mutex);
1348                 if (ksmd_should_run())
1349                         ksm_do_scan(ksm_thread_pages_to_scan);
1350                 mutex_unlock(&ksm_thread_mutex);
1351
1352                 if (ksmd_should_run()) {
1353                         schedule_timeout_interruptible(
1354                                 msecs_to_jiffies(ksm_thread_sleep_millisecs));
1355                 } else {
1356                         wait_event_interruptible(ksm_thread_wait,
1357                                 ksmd_should_run() || kthread_should_stop());
1358                 }
1359         }
1360         return 0;
1361 }
1362
1363 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1364                 unsigned long end, int advice, unsigned long *vm_flags)
1365 {
1366         struct mm_struct *mm = vma->vm_mm;
1367         int err;
1368
1369         switch (advice) {
1370         case MADV_MERGEABLE:
1371                 /*
1372                  * Be somewhat over-protective for now!
1373                  */
1374                 if (*vm_flags & (VM_MERGEABLE | VM_SHARED  | VM_MAYSHARE   |
1375                                  VM_PFNMAP    | VM_IO      | VM_DONTEXPAND |
1376                                  VM_RESERVED  | VM_HUGETLB | VM_INSERTPAGE |
1377                                  VM_MIXEDMAP  | VM_SAO))
1378                         return 0;               /* just ignore the advice */
1379
1380                 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
1381                         err = __ksm_enter(mm);
1382                         if (err)
1383                                 return err;
1384                 }
1385
1386                 *vm_flags |= VM_MERGEABLE;
1387                 break;
1388
1389         case MADV_UNMERGEABLE:
1390                 if (!(*vm_flags & VM_MERGEABLE))
1391                         return 0;               /* just ignore the advice */
1392
1393                 if (vma->anon_vma) {
1394                         err = unmerge_ksm_pages(vma, start, end);
1395                         if (err)
1396                                 return err;
1397                 }
1398
1399                 *vm_flags &= ~VM_MERGEABLE;
1400                 break;
1401         }
1402
1403         return 0;
1404 }
1405
1406 int __ksm_enter(struct mm_struct *mm)
1407 {
1408         struct mm_slot *mm_slot;
1409         int needs_wakeup;
1410
1411         mm_slot = alloc_mm_slot();
1412         if (!mm_slot)
1413                 return -ENOMEM;
1414
1415         /* Check ksm_run too?  Would need tighter locking */
1416         needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1417
1418         spin_lock(&ksm_mmlist_lock);
1419         insert_to_mm_slots_hash(mm, mm_slot);
1420         /*
1421          * Insert just behind the scanning cursor, to let the area settle
1422          * down a little; when fork is followed by immediate exec, we don't
1423          * want ksmd to waste time setting up and tearing down an rmap_list.
1424          */
1425         list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
1426         spin_unlock(&ksm_mmlist_lock);
1427
1428         set_bit(MMF_VM_MERGEABLE, &mm->flags);
1429         atomic_inc(&mm->mm_count);
1430
1431         if (needs_wakeup)
1432                 wake_up_interruptible(&ksm_thread_wait);
1433
1434         return 0;
1435 }
1436
1437 void __ksm_exit(struct mm_struct *mm)
1438 {
1439         struct mm_slot *mm_slot;
1440         int easy_to_free = 0;
1441
1442         /*
1443          * This process is exiting: if it's straightforward (as is the
1444          * case when ksmd was never running), free mm_slot immediately.
1445          * But if it's at the cursor or has rmap_items linked to it, use
1446          * mmap_sem to synchronize with any break_cows before pagetables
1447          * are freed, and leave the mm_slot on the list for ksmd to free.
1448          * Beware: ksm may already have noticed it exiting and freed the slot.
1449          */
1450
1451         spin_lock(&ksm_mmlist_lock);
1452         mm_slot = get_mm_slot(mm);
1453         if (mm_slot && ksm_scan.mm_slot != mm_slot) {
1454                 if (list_empty(&mm_slot->rmap_list)) {
1455                         hlist_del(&mm_slot->link);
1456                         list_del(&mm_slot->mm_list);
1457                         easy_to_free = 1;
1458                 } else {
1459                         list_move(&mm_slot->mm_list,
1460                                   &ksm_scan.mm_slot->mm_list);
1461                 }
1462         }
1463         spin_unlock(&ksm_mmlist_lock);
1464
1465         if (easy_to_free) {
1466                 free_mm_slot(mm_slot);
1467                 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1468                 mmdrop(mm);
1469         } else if (mm_slot) {
1470                 down_write(&mm->mmap_sem);
1471                 up_write(&mm->mmap_sem);
1472         }
1473 }
1474
1475 #ifdef CONFIG_SYSFS
1476 /*
1477  * This all compiles without CONFIG_SYSFS, but is a waste of space.
1478  */
1479
1480 #define KSM_ATTR_RO(_name) \
1481         static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
1482 #define KSM_ATTR(_name) \
1483         static struct kobj_attribute _name##_attr = \
1484                 __ATTR(_name, 0644, _name##_show, _name##_store)
1485
1486 static ssize_t sleep_millisecs_show(struct kobject *kobj,
1487                                     struct kobj_attribute *attr, char *buf)
1488 {
1489         return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
1490 }
1491
1492 static ssize_t sleep_millisecs_store(struct kobject *kobj,
1493                                      struct kobj_attribute *attr,
1494                                      const char *buf, size_t count)
1495 {
1496         unsigned long msecs;
1497         int err;
1498
1499         err = strict_strtoul(buf, 10, &msecs);
1500         if (err || msecs > UINT_MAX)
1501                 return -EINVAL;
1502
1503         ksm_thread_sleep_millisecs = msecs;
1504
1505         return count;
1506 }
1507 KSM_ATTR(sleep_millisecs);
1508
1509 static ssize_t pages_to_scan_show(struct kobject *kobj,
1510                                   struct kobj_attribute *attr, char *buf)
1511 {
1512         return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
1513 }
1514
1515 static ssize_t pages_to_scan_store(struct kobject *kobj,
1516                                    struct kobj_attribute *attr,
1517                                    const char *buf, size_t count)
1518 {
1519         int err;
1520         unsigned long nr_pages;
1521
1522         err = strict_strtoul(buf, 10, &nr_pages);
1523         if (err || nr_pages > UINT_MAX)
1524                 return -EINVAL;
1525
1526         ksm_thread_pages_to_scan = nr_pages;
1527
1528         return count;
1529 }
1530 KSM_ATTR(pages_to_scan);
1531
1532 static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
1533                         char *buf)
1534 {
1535         return sprintf(buf, "%u\n", ksm_run);
1536 }
1537
1538 static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
1539                          const char *buf, size_t count)
1540 {
1541         int err;
1542         unsigned long flags;
1543
1544         err = strict_strtoul(buf, 10, &flags);
1545         if (err || flags > UINT_MAX)
1546                 return -EINVAL;
1547         if (flags > KSM_RUN_UNMERGE)
1548                 return -EINVAL;
1549
1550         /*
1551          * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
1552          * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
1553          * breaking COW to free the unswappable pages_shared (but leaves
1554          * mm_slots on the list for when ksmd may be set running again).
1555          */
1556
1557         mutex_lock(&ksm_thread_mutex);
1558         if (ksm_run != flags) {
1559                 ksm_run = flags;
1560                 if (flags & KSM_RUN_UNMERGE) {
1561                         current->flags |= PF_OOM_ORIGIN;
1562                         err = unmerge_and_remove_all_rmap_items();
1563                         current->flags &= ~PF_OOM_ORIGIN;
1564                         if (err) {
1565                                 ksm_run = KSM_RUN_STOP;
1566                                 count = err;
1567                         }
1568                 }
1569         }
1570         mutex_unlock(&ksm_thread_mutex);
1571
1572         if (flags & KSM_RUN_MERGE)
1573                 wake_up_interruptible(&ksm_thread_wait);
1574
1575         return count;
1576 }
1577 KSM_ATTR(run);
1578
1579 static ssize_t max_kernel_pages_store(struct kobject *kobj,
1580                                       struct kobj_attribute *attr,
1581                                       const char *buf, size_t count)
1582 {
1583         int err;
1584         unsigned long nr_pages;
1585
1586         err = strict_strtoul(buf, 10, &nr_pages);
1587         if (err)
1588                 return -EINVAL;
1589
1590         ksm_max_kernel_pages = nr_pages;
1591
1592         return count;
1593 }
1594
1595 static ssize_t max_kernel_pages_show(struct kobject *kobj,
1596                                      struct kobj_attribute *attr, char *buf)
1597 {
1598         return sprintf(buf, "%lu\n", ksm_max_kernel_pages);
1599 }
1600 KSM_ATTR(max_kernel_pages);
1601
1602 static ssize_t pages_shared_show(struct kobject *kobj,
1603                                  struct kobj_attribute *attr, char *buf)
1604 {
1605         return sprintf(buf, "%lu\n", ksm_pages_shared);
1606 }
1607 KSM_ATTR_RO(pages_shared);
1608
1609 static ssize_t pages_sharing_show(struct kobject *kobj,
1610                                   struct kobj_attribute *attr, char *buf)
1611 {
1612         return sprintf(buf, "%lu\n", ksm_pages_sharing);
1613 }
1614 KSM_ATTR_RO(pages_sharing);
1615
1616 static ssize_t pages_unshared_show(struct kobject *kobj,
1617                                    struct kobj_attribute *attr, char *buf)
1618 {
1619         return sprintf(buf, "%lu\n", ksm_pages_unshared);
1620 }
1621 KSM_ATTR_RO(pages_unshared);
1622
1623 static ssize_t pages_volatile_show(struct kobject *kobj,
1624                                    struct kobj_attribute *attr, char *buf)
1625 {
1626         long ksm_pages_volatile;
1627
1628         ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
1629                                 - ksm_pages_sharing - ksm_pages_unshared;
1630         /*
1631          * It was not worth any locking to calculate that statistic,
1632          * but it might therefore sometimes be negative: conceal that.
1633          */
1634         if (ksm_pages_volatile < 0)
1635                 ksm_pages_volatile = 0;
1636         return sprintf(buf, "%ld\n", ksm_pages_volatile);
1637 }
1638 KSM_ATTR_RO(pages_volatile);
1639
1640 static ssize_t full_scans_show(struct kobject *kobj,
1641                                struct kobj_attribute *attr, char *buf)
1642 {
1643         return sprintf(buf, "%lu\n", ksm_scan.seqnr);
1644 }
1645 KSM_ATTR_RO(full_scans);
1646
1647 static struct attribute *ksm_attrs[] = {
1648         &sleep_millisecs_attr.attr,
1649         &pages_to_scan_attr.attr,
1650         &run_attr.attr,
1651         &max_kernel_pages_attr.attr,
1652         &pages_shared_attr.attr,
1653         &pages_sharing_attr.attr,
1654         &pages_unshared_attr.attr,
1655         &pages_volatile_attr.attr,
1656         &full_scans_attr.attr,
1657         NULL,
1658 };
1659
1660 static struct attribute_group ksm_attr_group = {
1661         .attrs = ksm_attrs,
1662         .name = "ksm",
1663 };
1664 #endif /* CONFIG_SYSFS */
1665
1666 static int __init ksm_init(void)
1667 {
1668         struct task_struct *ksm_thread;
1669         int err;
1670
1671         ksm_max_kernel_pages = totalram_pages / 4;
1672
1673         err = ksm_slab_init();
1674         if (err)
1675                 goto out;
1676
1677         err = mm_slots_hash_init();
1678         if (err)
1679                 goto out_free1;
1680
1681         ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
1682         if (IS_ERR(ksm_thread)) {
1683                 printk(KERN_ERR "ksm: creating kthread failed\n");
1684                 err = PTR_ERR(ksm_thread);
1685                 goto out_free2;
1686         }
1687
1688 #ifdef CONFIG_SYSFS
1689         err = sysfs_create_group(mm_kobj, &ksm_attr_group);
1690         if (err) {
1691                 printk(KERN_ERR "ksm: register sysfs failed\n");
1692                 kthread_stop(ksm_thread);
1693                 goto out_free2;
1694         }
1695 #else
1696         ksm_run = KSM_RUN_MERGE;        /* no way for user to start it */
1697
1698 #endif /* CONFIG_SYSFS */
1699
1700         return 0;
1701
1702 out_free2:
1703         mm_slots_hash_free();
1704 out_free1:
1705         ksm_slab_free();
1706 out:
1707         return err;
1708 }
1709 module_init(ksm_init)