Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net
[zen-stable.git] / mm / ksm.c
blob310544a379ae9c7b886b3b50815e5f3d5a991ba8
1 /*
2 * Memory merging support.
4 * This code enables dynamic sharing of identical pages found in different
5 * memory areas, even if they are not shared by fork()
7 * Copyright (C) 2008-2009 Red Hat, Inc.
8 * Authors:
9 * Izik Eidus
10 * Andrea Arcangeli
11 * Chris Wright
12 * Hugh Dickins
14 * This work is licensed under the terms of the GNU GPL, version 2.
17 #include <linux/errno.h>
18 #include <linux/mm.h>
19 #include <linux/fs.h>
20 #include <linux/mman.h>
21 #include <linux/sched.h>
22 #include <linux/rwsem.h>
23 #include <linux/pagemap.h>
24 #include <linux/rmap.h>
25 #include <linux/spinlock.h>
26 #include <linux/jhash.h>
27 #include <linux/delay.h>
28 #include <linux/kthread.h>
29 #include <linux/wait.h>
30 #include <linux/slab.h>
31 #include <linux/rbtree.h>
32 #include <linux/memory.h>
33 #include <linux/mmu_notifier.h>
34 #include <linux/swap.h>
35 #include <linux/ksm.h>
36 #include <linux/hash.h>
37 #include <linux/freezer.h>
38 #include <linux/oom.h>
40 #include <asm/tlbflush.h>
41 #include "internal.h"
44 * A few notes about the KSM scanning process,
45 * to make it easier to understand the data structures below:
47 * In order to reduce excessive scanning, KSM sorts the memory pages by their
48 * contents into a data structure that holds pointers to the pages' locations.
50 * Since the contents of the pages may change at any moment, KSM cannot just
51 * insert the pages into a normal sorted tree and expect it to find anything.
52 * Therefore KSM uses two data structures - the stable and the unstable tree.
54 * The stable tree holds pointers to all the merged pages (ksm pages), sorted
55 * by their contents. Because each such page is write-protected, searching on
56 * this tree is fully assured to be working (except when pages are unmapped),
57 * and therefore this tree is called the stable tree.
59 * In addition to the stable tree, KSM uses a second data structure called the
60 * unstable tree: this tree holds pointers to pages which have been found to
61 * be "unchanged for a period of time". The unstable tree sorts these pages
62 * by their contents, but since they are not write-protected, KSM cannot rely
63 * upon the unstable tree to work correctly - the unstable tree is liable to
64 * be corrupted as its contents are modified, and so it is called unstable.
66 * KSM solves this problem by several techniques:
68 * 1) The unstable tree is flushed every time KSM completes scanning all
69 * memory areas, and then the tree is rebuilt again from the beginning.
70 * 2) KSM will only insert into the unstable tree, pages whose hash value
71 * has not changed since the previous scan of all memory areas.
72 * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
73 * colors of the nodes and not on their contents, assuring that even when
74 * the tree gets "corrupted" it won't get out of balance, so scanning time
75 * remains the same (also, searching and inserting nodes in an rbtree uses
76 * the same algorithm, so we have no overhead when we flush and rebuild).
77 * 4) KSM never flushes the stable tree, which means that even if it were to
78 * take 10 attempts to find a page in the unstable tree, once it is found,
79 * it is secured in the stable tree. (When we scan a new page, we first
80 * compare it against the stable tree, and then against the unstable tree.)
83 /**
84 * struct mm_slot - ksm information per mm that is being scanned
85 * @link: link to the mm_slots hash list
86 * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
87 * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
88 * @mm: the mm that this information is valid for
90 struct mm_slot {
91 struct hlist_node link;
92 struct list_head mm_list;
93 struct rmap_item *rmap_list;
94 struct mm_struct *mm;
97 /**
98 * struct ksm_scan - cursor for scanning
99 * @mm_slot: the current mm_slot we are scanning
100 * @address: the next address inside that to be scanned
101 * @rmap_list: link to the next rmap to be scanned in the rmap_list
102 * @seqnr: count of completed full scans (needed when removing unstable node)
104 * There is only the one ksm_scan instance of this cursor structure.
106 struct ksm_scan {
107 struct mm_slot *mm_slot;
108 unsigned long address;
109 struct rmap_item **rmap_list;
110 unsigned long seqnr;
114 * struct stable_node - node of the stable rbtree
115 * @node: rb node of this ksm page in the stable tree
116 * @hlist: hlist head of rmap_items using this ksm page
117 * @kpfn: page frame number of this ksm page
119 struct stable_node {
120 struct rb_node node;
121 struct hlist_head hlist;
122 unsigned long kpfn;
126 * struct rmap_item - reverse mapping item for virtual addresses
127 * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
128 * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
129 * @mm: the memory structure this rmap_item is pointing into
130 * @address: the virtual address this rmap_item tracks (+ flags in low bits)
131 * @oldchecksum: previous checksum of the page at that virtual address
132 * @node: rb node of this rmap_item in the unstable tree
133 * @head: pointer to stable_node heading this list in the stable tree
134 * @hlist: link into hlist of rmap_items hanging off that stable_node
136 struct rmap_item {
137 struct rmap_item *rmap_list;
138 struct anon_vma *anon_vma; /* when stable */
139 struct mm_struct *mm;
140 unsigned long address; /* + low bits used for flags below */
141 unsigned int oldchecksum; /* when unstable */
142 union {
143 struct rb_node node; /* when node of unstable tree */
144 struct { /* when listed from stable tree */
145 struct stable_node *head;
146 struct hlist_node hlist;
151 #define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */
152 #define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */
153 #define STABLE_FLAG 0x200 /* is listed from the stable tree */
155 /* The stable and unstable tree heads */
156 static struct rb_root root_stable_tree = RB_ROOT;
157 static struct rb_root root_unstable_tree = RB_ROOT;
159 #define MM_SLOTS_HASH_SHIFT 10
160 #define MM_SLOTS_HASH_HEADS (1 << MM_SLOTS_HASH_SHIFT)
161 static struct hlist_head mm_slots_hash[MM_SLOTS_HASH_HEADS];
163 static struct mm_slot ksm_mm_head = {
164 .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
166 static struct ksm_scan ksm_scan = {
167 .mm_slot = &ksm_mm_head,
170 static struct kmem_cache *rmap_item_cache;
171 static struct kmem_cache *stable_node_cache;
172 static struct kmem_cache *mm_slot_cache;
174 /* The number of nodes in the stable tree */
175 static unsigned long ksm_pages_shared;
177 /* The number of page slots additionally sharing those nodes */
178 static unsigned long ksm_pages_sharing;
180 /* The number of nodes in the unstable tree */
181 static unsigned long ksm_pages_unshared;
183 /* The number of rmap_items in use: to calculate pages_volatile */
184 static unsigned long ksm_rmap_items;
186 /* Number of pages ksmd should scan in one batch */
187 static unsigned int ksm_thread_pages_to_scan = 100;
189 /* Milliseconds ksmd should sleep between batches */
190 static unsigned int ksm_thread_sleep_millisecs = 20;
192 #define KSM_RUN_STOP 0
193 #define KSM_RUN_MERGE 1
194 #define KSM_RUN_UNMERGE 2
195 static unsigned int ksm_run = KSM_RUN_STOP;
197 static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
198 static DEFINE_MUTEX(ksm_thread_mutex);
199 static DEFINE_SPINLOCK(ksm_mmlist_lock);
201 #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
202 sizeof(struct __struct), __alignof__(struct __struct),\
203 (__flags), NULL)
205 static int __init ksm_slab_init(void)
207 rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
208 if (!rmap_item_cache)
209 goto out;
211 stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
212 if (!stable_node_cache)
213 goto out_free1;
215 mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
216 if (!mm_slot_cache)
217 goto out_free2;
219 return 0;
221 out_free2:
222 kmem_cache_destroy(stable_node_cache);
223 out_free1:
224 kmem_cache_destroy(rmap_item_cache);
225 out:
226 return -ENOMEM;
229 static void __init ksm_slab_free(void)
231 kmem_cache_destroy(mm_slot_cache);
232 kmem_cache_destroy(stable_node_cache);
233 kmem_cache_destroy(rmap_item_cache);
234 mm_slot_cache = NULL;
237 static inline struct rmap_item *alloc_rmap_item(void)
239 struct rmap_item *rmap_item;
241 rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
242 if (rmap_item)
243 ksm_rmap_items++;
244 return rmap_item;
247 static inline void free_rmap_item(struct rmap_item *rmap_item)
249 ksm_rmap_items--;
250 rmap_item->mm = NULL; /* debug safety */
251 kmem_cache_free(rmap_item_cache, rmap_item);
254 static inline struct stable_node *alloc_stable_node(void)
256 return kmem_cache_alloc(stable_node_cache, GFP_KERNEL);
259 static inline void free_stable_node(struct stable_node *stable_node)
261 kmem_cache_free(stable_node_cache, stable_node);
264 static inline struct mm_slot *alloc_mm_slot(void)
266 if (!mm_slot_cache) /* initialization failed */
267 return NULL;
268 return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
271 static inline void free_mm_slot(struct mm_slot *mm_slot)
273 kmem_cache_free(mm_slot_cache, mm_slot);
276 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
278 struct mm_slot *mm_slot;
279 struct hlist_head *bucket;
280 struct hlist_node *node;
282 bucket = &mm_slots_hash[hash_ptr(mm, MM_SLOTS_HASH_SHIFT)];
283 hlist_for_each_entry(mm_slot, node, bucket, link) {
284 if (mm == mm_slot->mm)
285 return mm_slot;
287 return NULL;
290 static void insert_to_mm_slots_hash(struct mm_struct *mm,
291 struct mm_slot *mm_slot)
293 struct hlist_head *bucket;
295 bucket = &mm_slots_hash[hash_ptr(mm, MM_SLOTS_HASH_SHIFT)];
296 mm_slot->mm = mm;
297 hlist_add_head(&mm_slot->link, bucket);
300 static inline int in_stable_tree(struct rmap_item *rmap_item)
302 return rmap_item->address & STABLE_FLAG;
306 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
307 * page tables after it has passed through ksm_exit() - which, if necessary,
308 * takes mmap_sem briefly to serialize against them. ksm_exit() does not set
309 * a special flag: they can just back out as soon as mm_users goes to zero.
310 * ksm_test_exit() is used throughout to make this test for exit: in some
311 * places for correctness, in some places just to avoid unnecessary work.
313 static inline bool ksm_test_exit(struct mm_struct *mm)
315 return atomic_read(&mm->mm_users) == 0;
319 * We use break_ksm to break COW on a ksm page: it's a stripped down
321 * if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
322 * put_page(page);
324 * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
325 * in case the application has unmapped and remapped mm,addr meanwhile.
326 * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP
327 * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
329 static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
331 struct page *page;
332 int ret = 0;
334 do {
335 cond_resched();
336 page = follow_page(vma, addr, FOLL_GET);
337 if (IS_ERR_OR_NULL(page))
338 break;
339 if (PageKsm(page))
340 ret = handle_mm_fault(vma->vm_mm, vma, addr,
341 FAULT_FLAG_WRITE);
342 else
343 ret = VM_FAULT_WRITE;
344 put_page(page);
345 } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM)));
347 * We must loop because handle_mm_fault() may back out if there's
348 * any difficulty e.g. if pte accessed bit gets updated concurrently.
350 * VM_FAULT_WRITE is what we have been hoping for: it indicates that
351 * COW has been broken, even if the vma does not permit VM_WRITE;
352 * but note that a concurrent fault might break PageKsm for us.
354 * VM_FAULT_SIGBUS could occur if we race with truncation of the
355 * backing file, which also invalidates anonymous pages: that's
356 * okay, that truncation will have unmapped the PageKsm for us.
358 * VM_FAULT_OOM: at the time of writing (late July 2009), setting
359 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
360 * current task has TIF_MEMDIE set, and will be OOM killed on return
361 * to user; and ksmd, having no mm, would never be chosen for that.
363 * But if the mm is in a limited mem_cgroup, then the fault may fail
364 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
365 * even ksmd can fail in this way - though it's usually breaking ksm
366 * just to undo a merge it made a moment before, so unlikely to oom.
368 * That's a pity: we might therefore have more kernel pages allocated
369 * than we're counting as nodes in the stable tree; but ksm_do_scan
370 * will retry to break_cow on each pass, so should recover the page
371 * in due course. The important thing is to not let VM_MERGEABLE
372 * be cleared while any such pages might remain in the area.
374 return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
377 static void break_cow(struct rmap_item *rmap_item)
379 struct mm_struct *mm = rmap_item->mm;
380 unsigned long addr = rmap_item->address;
381 struct vm_area_struct *vma;
384 * It is not an accident that whenever we want to break COW
385 * to undo, we also need to drop a reference to the anon_vma.
387 put_anon_vma(rmap_item->anon_vma);
389 down_read(&mm->mmap_sem);
390 if (ksm_test_exit(mm))
391 goto out;
392 vma = find_vma(mm, addr);
393 if (!vma || vma->vm_start > addr)
394 goto out;
395 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
396 goto out;
397 break_ksm(vma, addr);
398 out:
399 up_read(&mm->mmap_sem);
402 static struct page *page_trans_compound_anon(struct page *page)
404 if (PageTransCompound(page)) {
405 struct page *head = compound_trans_head(page);
407 * head may actually be splitted and freed from under
408 * us but it's ok here.
410 if (PageAnon(head))
411 return head;
413 return NULL;
416 static struct page *get_mergeable_page(struct rmap_item *rmap_item)
418 struct mm_struct *mm = rmap_item->mm;
419 unsigned long addr = rmap_item->address;
420 struct vm_area_struct *vma;
421 struct page *page;
423 down_read(&mm->mmap_sem);
424 if (ksm_test_exit(mm))
425 goto out;
426 vma = find_vma(mm, addr);
427 if (!vma || vma->vm_start > addr)
428 goto out;
429 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
430 goto out;
432 page = follow_page(vma, addr, FOLL_GET);
433 if (IS_ERR_OR_NULL(page))
434 goto out;
435 if (PageAnon(page) || page_trans_compound_anon(page)) {
436 flush_anon_page(vma, page, addr);
437 flush_dcache_page(page);
438 } else {
439 put_page(page);
440 out: page = NULL;
442 up_read(&mm->mmap_sem);
443 return page;
446 static void remove_node_from_stable_tree(struct stable_node *stable_node)
448 struct rmap_item *rmap_item;
449 struct hlist_node *hlist;
451 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
452 if (rmap_item->hlist.next)
453 ksm_pages_sharing--;
454 else
455 ksm_pages_shared--;
456 put_anon_vma(rmap_item->anon_vma);
457 rmap_item->address &= PAGE_MASK;
458 cond_resched();
461 rb_erase(&stable_node->node, &root_stable_tree);
462 free_stable_node(stable_node);
466 * get_ksm_page: checks if the page indicated by the stable node
467 * is still its ksm page, despite having held no reference to it.
468 * In which case we can trust the content of the page, and it
469 * returns the gotten page; but if the page has now been zapped,
470 * remove the stale node from the stable tree and return NULL.
472 * You would expect the stable_node to hold a reference to the ksm page.
473 * But if it increments the page's count, swapping out has to wait for
474 * ksmd to come around again before it can free the page, which may take
475 * seconds or even minutes: much too unresponsive. So instead we use a
476 * "keyhole reference": access to the ksm page from the stable node peeps
477 * out through its keyhole to see if that page still holds the right key,
478 * pointing back to this stable node. This relies on freeing a PageAnon
479 * page to reset its page->mapping to NULL, and relies on no other use of
480 * a page to put something that might look like our key in page->mapping.
482 * include/linux/pagemap.h page_cache_get_speculative() is a good reference,
483 * but this is different - made simpler by ksm_thread_mutex being held, but
484 * interesting for assuming that no other use of the struct page could ever
485 * put our expected_mapping into page->mapping (or a field of the union which
486 * coincides with page->mapping). The RCU calls are not for KSM at all, but
487 * to keep the page_count protocol described with page_cache_get_speculative.
489 * Note: it is possible that get_ksm_page() will return NULL one moment,
490 * then page the next, if the page is in between page_freeze_refs() and
491 * page_unfreeze_refs(): this shouldn't be a problem anywhere, the page
492 * is on its way to being freed; but it is an anomaly to bear in mind.
494 static struct page *get_ksm_page(struct stable_node *stable_node)
496 struct page *page;
497 void *expected_mapping;
499 page = pfn_to_page(stable_node->kpfn);
500 expected_mapping = (void *)stable_node +
501 (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
502 rcu_read_lock();
503 if (page->mapping != expected_mapping)
504 goto stale;
505 if (!get_page_unless_zero(page))
506 goto stale;
507 if (page->mapping != expected_mapping) {
508 put_page(page);
509 goto stale;
511 rcu_read_unlock();
512 return page;
513 stale:
514 rcu_read_unlock();
515 remove_node_from_stable_tree(stable_node);
516 return NULL;
520 * Removing rmap_item from stable or unstable tree.
521 * This function will clean the information from the stable/unstable tree.
523 static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
525 if (rmap_item->address & STABLE_FLAG) {
526 struct stable_node *stable_node;
527 struct page *page;
529 stable_node = rmap_item->head;
530 page = get_ksm_page(stable_node);
531 if (!page)
532 goto out;
534 lock_page(page);
535 hlist_del(&rmap_item->hlist);
536 unlock_page(page);
537 put_page(page);
539 if (stable_node->hlist.first)
540 ksm_pages_sharing--;
541 else
542 ksm_pages_shared--;
544 put_anon_vma(rmap_item->anon_vma);
545 rmap_item->address &= PAGE_MASK;
547 } else if (rmap_item->address & UNSTABLE_FLAG) {
548 unsigned char age;
550 * Usually ksmd can and must skip the rb_erase, because
551 * root_unstable_tree was already reset to RB_ROOT.
552 * But be careful when an mm is exiting: do the rb_erase
553 * if this rmap_item was inserted by this scan, rather
554 * than left over from before.
556 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
557 BUG_ON(age > 1);
558 if (!age)
559 rb_erase(&rmap_item->node, &root_unstable_tree);
561 ksm_pages_unshared--;
562 rmap_item->address &= PAGE_MASK;
564 out:
565 cond_resched(); /* we're called from many long loops */
568 static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
569 struct rmap_item **rmap_list)
571 while (*rmap_list) {
572 struct rmap_item *rmap_item = *rmap_list;
573 *rmap_list = rmap_item->rmap_list;
574 remove_rmap_item_from_tree(rmap_item);
575 free_rmap_item(rmap_item);
580 * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather
581 * than check every pte of a given vma, the locking doesn't quite work for
582 * that - an rmap_item is assigned to the stable tree after inserting ksm
583 * page and upping mmap_sem. Nor does it fit with the way we skip dup'ing
584 * rmap_items from parent to child at fork time (so as not to waste time
585 * if exit comes before the next scan reaches it).
587 * Similarly, although we'd like to remove rmap_items (so updating counts
588 * and freeing memory) when unmerging an area, it's easier to leave that
589 * to the next pass of ksmd - consider, for example, how ksmd might be
590 * in cmp_and_merge_page on one of the rmap_items we would be removing.
592 static int unmerge_ksm_pages(struct vm_area_struct *vma,
593 unsigned long start, unsigned long end)
595 unsigned long addr;
596 int err = 0;
598 for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
599 if (ksm_test_exit(vma->vm_mm))
600 break;
601 if (signal_pending(current))
602 err = -ERESTARTSYS;
603 else
604 err = break_ksm(vma, addr);
606 return err;
609 #ifdef CONFIG_SYSFS
611 * Only called through the sysfs control interface:
613 static int unmerge_and_remove_all_rmap_items(void)
615 struct mm_slot *mm_slot;
616 struct mm_struct *mm;
617 struct vm_area_struct *vma;
618 int err = 0;
620 spin_lock(&ksm_mmlist_lock);
621 ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
622 struct mm_slot, mm_list);
623 spin_unlock(&ksm_mmlist_lock);
625 for (mm_slot = ksm_scan.mm_slot;
626 mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
627 mm = mm_slot->mm;
628 down_read(&mm->mmap_sem);
629 for (vma = mm->mmap; vma; vma = vma->vm_next) {
630 if (ksm_test_exit(mm))
631 break;
632 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
633 continue;
634 err = unmerge_ksm_pages(vma,
635 vma->vm_start, vma->vm_end);
636 if (err)
637 goto error;
640 remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
642 spin_lock(&ksm_mmlist_lock);
643 ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
644 struct mm_slot, mm_list);
645 if (ksm_test_exit(mm)) {
646 hlist_del(&mm_slot->link);
647 list_del(&mm_slot->mm_list);
648 spin_unlock(&ksm_mmlist_lock);
650 free_mm_slot(mm_slot);
651 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
652 up_read(&mm->mmap_sem);
653 mmdrop(mm);
654 } else {
655 spin_unlock(&ksm_mmlist_lock);
656 up_read(&mm->mmap_sem);
660 ksm_scan.seqnr = 0;
661 return 0;
663 error:
664 up_read(&mm->mmap_sem);
665 spin_lock(&ksm_mmlist_lock);
666 ksm_scan.mm_slot = &ksm_mm_head;
667 spin_unlock(&ksm_mmlist_lock);
668 return err;
670 #endif /* CONFIG_SYSFS */
672 static u32 calc_checksum(struct page *page)
674 u32 checksum;
675 void *addr = kmap_atomic(page, KM_USER0);
676 checksum = jhash2(addr, PAGE_SIZE / 4, 17);
677 kunmap_atomic(addr, KM_USER0);
678 return checksum;
681 static int memcmp_pages(struct page *page1, struct page *page2)
683 char *addr1, *addr2;
684 int ret;
686 addr1 = kmap_atomic(page1, KM_USER0);
687 addr2 = kmap_atomic(page2, KM_USER1);
688 ret = memcmp(addr1, addr2, PAGE_SIZE);
689 kunmap_atomic(addr2, KM_USER1);
690 kunmap_atomic(addr1, KM_USER0);
691 return ret;
694 static inline int pages_identical(struct page *page1, struct page *page2)
696 return !memcmp_pages(page1, page2);
699 static int write_protect_page(struct vm_area_struct *vma, struct page *page,
700 pte_t *orig_pte)
702 struct mm_struct *mm = vma->vm_mm;
703 unsigned long addr;
704 pte_t *ptep;
705 spinlock_t *ptl;
706 int swapped;
707 int err = -EFAULT;
709 addr = page_address_in_vma(page, vma);
710 if (addr == -EFAULT)
711 goto out;
713 BUG_ON(PageTransCompound(page));
714 ptep = page_check_address(page, mm, addr, &ptl, 0);
715 if (!ptep)
716 goto out;
718 if (pte_write(*ptep) || pte_dirty(*ptep)) {
719 pte_t entry;
721 swapped = PageSwapCache(page);
722 flush_cache_page(vma, addr, page_to_pfn(page));
724 * Ok this is tricky, when get_user_pages_fast() run it doesn't
725 * take any lock, therefore the check that we are going to make
726 * with the pagecount against the mapcount is racey and
727 * O_DIRECT can happen right after the check.
728 * So we clear the pte and flush the tlb before the check
729 * this assure us that no O_DIRECT can happen after the check
730 * or in the middle of the check.
732 entry = ptep_clear_flush(vma, addr, ptep);
734 * Check that no O_DIRECT or similar I/O is in progress on the
735 * page
737 if (page_mapcount(page) + 1 + swapped != page_count(page)) {
738 set_pte_at(mm, addr, ptep, entry);
739 goto out_unlock;
741 if (pte_dirty(entry))
742 set_page_dirty(page);
743 entry = pte_mkclean(pte_wrprotect(entry));
744 set_pte_at_notify(mm, addr, ptep, entry);
746 *orig_pte = *ptep;
747 err = 0;
749 out_unlock:
750 pte_unmap_unlock(ptep, ptl);
751 out:
752 return err;
756 * replace_page - replace page in vma by new ksm page
757 * @vma: vma that holds the pte pointing to page
758 * @page: the page we are replacing by kpage
759 * @kpage: the ksm page we replace page by
760 * @orig_pte: the original value of the pte
762 * Returns 0 on success, -EFAULT on failure.
764 static int replace_page(struct vm_area_struct *vma, struct page *page,
765 struct page *kpage, pte_t orig_pte)
767 struct mm_struct *mm = vma->vm_mm;
768 pgd_t *pgd;
769 pud_t *pud;
770 pmd_t *pmd;
771 pte_t *ptep;
772 spinlock_t *ptl;
773 unsigned long addr;
774 int err = -EFAULT;
776 addr = page_address_in_vma(page, vma);
777 if (addr == -EFAULT)
778 goto out;
780 pgd = pgd_offset(mm, addr);
781 if (!pgd_present(*pgd))
782 goto out;
784 pud = pud_offset(pgd, addr);
785 if (!pud_present(*pud))
786 goto out;
788 pmd = pmd_offset(pud, addr);
789 BUG_ON(pmd_trans_huge(*pmd));
790 if (!pmd_present(*pmd))
791 goto out;
793 ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
794 if (!pte_same(*ptep, orig_pte)) {
795 pte_unmap_unlock(ptep, ptl);
796 goto out;
799 get_page(kpage);
800 page_add_anon_rmap(kpage, vma, addr);
802 flush_cache_page(vma, addr, pte_pfn(*ptep));
803 ptep_clear_flush(vma, addr, ptep);
804 set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
806 page_remove_rmap(page);
807 if (!page_mapped(page))
808 try_to_free_swap(page);
809 put_page(page);
811 pte_unmap_unlock(ptep, ptl);
812 err = 0;
813 out:
814 return err;
817 static int page_trans_compound_anon_split(struct page *page)
819 int ret = 0;
820 struct page *transhuge_head = page_trans_compound_anon(page);
821 if (transhuge_head) {
822 /* Get the reference on the head to split it. */
823 if (get_page_unless_zero(transhuge_head)) {
825 * Recheck we got the reference while the head
826 * was still anonymous.
828 if (PageAnon(transhuge_head))
829 ret = split_huge_page(transhuge_head);
830 else
832 * Retry later if split_huge_page run
833 * from under us.
835 ret = 1;
836 put_page(transhuge_head);
837 } else
838 /* Retry later if split_huge_page run from under us. */
839 ret = 1;
841 return ret;
845 * try_to_merge_one_page - take two pages and merge them into one
846 * @vma: the vma that holds the pte pointing to page
847 * @page: the PageAnon page that we want to replace with kpage
848 * @kpage: the PageKsm page that we want to map instead of page,
849 * or NULL the first time when we want to use page as kpage.
851 * This function returns 0 if the pages were merged, -EFAULT otherwise.
853 static int try_to_merge_one_page(struct vm_area_struct *vma,
854 struct page *page, struct page *kpage)
856 pte_t orig_pte = __pte(0);
857 int err = -EFAULT;
859 if (page == kpage) /* ksm page forked */
860 return 0;
862 if (!(vma->vm_flags & VM_MERGEABLE))
863 goto out;
864 if (PageTransCompound(page) && page_trans_compound_anon_split(page))
865 goto out;
866 BUG_ON(PageTransCompound(page));
867 if (!PageAnon(page))
868 goto out;
871 * We need the page lock to read a stable PageSwapCache in
872 * write_protect_page(). We use trylock_page() instead of
873 * lock_page() because we don't want to wait here - we
874 * prefer to continue scanning and merging different pages,
875 * then come back to this page when it is unlocked.
877 if (!trylock_page(page))
878 goto out;
880 * If this anonymous page is mapped only here, its pte may need
881 * to be write-protected. If it's mapped elsewhere, all of its
882 * ptes are necessarily already write-protected. But in either
883 * case, we need to lock and check page_count is not raised.
885 if (write_protect_page(vma, page, &orig_pte) == 0) {
886 if (!kpage) {
888 * While we hold page lock, upgrade page from
889 * PageAnon+anon_vma to PageKsm+NULL stable_node:
890 * stable_tree_insert() will update stable_node.
892 set_page_stable_node(page, NULL);
893 mark_page_accessed(page);
894 err = 0;
895 } else if (pages_identical(page, kpage))
896 err = replace_page(vma, page, kpage, orig_pte);
899 if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
900 munlock_vma_page(page);
901 if (!PageMlocked(kpage)) {
902 unlock_page(page);
903 lock_page(kpage);
904 mlock_vma_page(kpage);
905 page = kpage; /* for final unlock */
909 unlock_page(page);
910 out:
911 return err;
915 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
916 * but no new kernel page is allocated: kpage must already be a ksm page.
918 * This function returns 0 if the pages were merged, -EFAULT otherwise.
920 static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
921 struct page *page, struct page *kpage)
923 struct mm_struct *mm = rmap_item->mm;
924 struct vm_area_struct *vma;
925 int err = -EFAULT;
927 down_read(&mm->mmap_sem);
928 if (ksm_test_exit(mm))
929 goto out;
930 vma = find_vma(mm, rmap_item->address);
931 if (!vma || vma->vm_start > rmap_item->address)
932 goto out;
934 err = try_to_merge_one_page(vma, page, kpage);
935 if (err)
936 goto out;
938 /* Must get reference to anon_vma while still holding mmap_sem */
939 rmap_item->anon_vma = vma->anon_vma;
940 get_anon_vma(vma->anon_vma);
941 out:
942 up_read(&mm->mmap_sem);
943 return err;
947 * try_to_merge_two_pages - take two identical pages and prepare them
948 * to be merged into one page.
950 * This function returns the kpage if we successfully merged two identical
951 * pages into one ksm page, NULL otherwise.
953 * Note that this function upgrades page to ksm page: if one of the pages
954 * is already a ksm page, try_to_merge_with_ksm_page should be used.
956 static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
957 struct page *page,
958 struct rmap_item *tree_rmap_item,
959 struct page *tree_page)
961 int err;
963 err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
964 if (!err) {
965 err = try_to_merge_with_ksm_page(tree_rmap_item,
966 tree_page, page);
968 * If that fails, we have a ksm page with only one pte
969 * pointing to it: so break it.
971 if (err)
972 break_cow(rmap_item);
974 return err ? NULL : page;
978 * stable_tree_search - search for page inside the stable tree
980 * This function checks if there is a page inside the stable tree
981 * with identical content to the page that we are scanning right now.
983 * This function returns the stable tree node of identical content if found,
984 * NULL otherwise.
986 static struct page *stable_tree_search(struct page *page)
988 struct rb_node *node = root_stable_tree.rb_node;
989 struct stable_node *stable_node;
991 stable_node = page_stable_node(page);
992 if (stable_node) { /* ksm page forked */
993 get_page(page);
994 return page;
997 while (node) {
998 struct page *tree_page;
999 int ret;
1001 cond_resched();
1002 stable_node = rb_entry(node, struct stable_node, node);
1003 tree_page = get_ksm_page(stable_node);
1004 if (!tree_page)
1005 return NULL;
1007 ret = memcmp_pages(page, tree_page);
1009 if (ret < 0) {
1010 put_page(tree_page);
1011 node = node->rb_left;
1012 } else if (ret > 0) {
1013 put_page(tree_page);
1014 node = node->rb_right;
1015 } else
1016 return tree_page;
1019 return NULL;
1023 * stable_tree_insert - insert rmap_item pointing to new ksm page
1024 * into the stable tree.
1026 * This function returns the stable tree node just allocated on success,
1027 * NULL otherwise.
1029 static struct stable_node *stable_tree_insert(struct page *kpage)
1031 struct rb_node **new = &root_stable_tree.rb_node;
1032 struct rb_node *parent = NULL;
1033 struct stable_node *stable_node;
1035 while (*new) {
1036 struct page *tree_page;
1037 int ret;
1039 cond_resched();
1040 stable_node = rb_entry(*new, struct stable_node, node);
1041 tree_page = get_ksm_page(stable_node);
1042 if (!tree_page)
1043 return NULL;
1045 ret = memcmp_pages(kpage, tree_page);
1046 put_page(tree_page);
1048 parent = *new;
1049 if (ret < 0)
1050 new = &parent->rb_left;
1051 else if (ret > 0)
1052 new = &parent->rb_right;
1053 else {
1055 * It is not a bug that stable_tree_search() didn't
1056 * find this node: because at that time our page was
1057 * not yet write-protected, so may have changed since.
1059 return NULL;
1063 stable_node = alloc_stable_node();
1064 if (!stable_node)
1065 return NULL;
1067 rb_link_node(&stable_node->node, parent, new);
1068 rb_insert_color(&stable_node->node, &root_stable_tree);
1070 INIT_HLIST_HEAD(&stable_node->hlist);
1072 stable_node->kpfn = page_to_pfn(kpage);
1073 set_page_stable_node(kpage, stable_node);
1075 return stable_node;
1079 * unstable_tree_search_insert - search for identical page,
1080 * else insert rmap_item into the unstable tree.
1082 * This function searches for a page in the unstable tree identical to the
1083 * page currently being scanned; and if no identical page is found in the
1084 * tree, we insert rmap_item as a new object into the unstable tree.
1086 * This function returns pointer to rmap_item found to be identical
1087 * to the currently scanned page, NULL otherwise.
1089 * This function does both searching and inserting, because they share
1090 * the same walking algorithm in an rbtree.
1092 static
1093 struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1094 struct page *page,
1095 struct page **tree_pagep)
1098 struct rb_node **new = &root_unstable_tree.rb_node;
1099 struct rb_node *parent = NULL;
1101 while (*new) {
1102 struct rmap_item *tree_rmap_item;
1103 struct page *tree_page;
1104 int ret;
1106 cond_resched();
1107 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1108 tree_page = get_mergeable_page(tree_rmap_item);
1109 if (IS_ERR_OR_NULL(tree_page))
1110 return NULL;
1113 * Don't substitute a ksm page for a forked page.
1115 if (page == tree_page) {
1116 put_page(tree_page);
1117 return NULL;
1120 ret = memcmp_pages(page, tree_page);
1122 parent = *new;
1123 if (ret < 0) {
1124 put_page(tree_page);
1125 new = &parent->rb_left;
1126 } else if (ret > 0) {
1127 put_page(tree_page);
1128 new = &parent->rb_right;
1129 } else {
1130 *tree_pagep = tree_page;
1131 return tree_rmap_item;
1135 rmap_item->address |= UNSTABLE_FLAG;
1136 rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1137 rb_link_node(&rmap_item->node, parent, new);
1138 rb_insert_color(&rmap_item->node, &root_unstable_tree);
1140 ksm_pages_unshared++;
1141 return NULL;
1145 * stable_tree_append - add another rmap_item to the linked list of
1146 * rmap_items hanging off a given node of the stable tree, all sharing
1147 * the same ksm page.
1149 static void stable_tree_append(struct rmap_item *rmap_item,
1150 struct stable_node *stable_node)
1152 rmap_item->head = stable_node;
1153 rmap_item->address |= STABLE_FLAG;
1154 hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
1156 if (rmap_item->hlist.next)
1157 ksm_pages_sharing++;
1158 else
1159 ksm_pages_shared++;
1163 * cmp_and_merge_page - first see if page can be merged into the stable tree;
1164 * if not, compare checksum to previous and if it's the same, see if page can
1165 * be inserted into the unstable tree, or merged with a page already there and
1166 * both transferred to the stable tree.
1168 * @page: the page that we are searching identical page to.
1169 * @rmap_item: the reverse mapping into the virtual address of this page
1171 static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1173 struct rmap_item *tree_rmap_item;
1174 struct page *tree_page = NULL;
1175 struct stable_node *stable_node;
1176 struct page *kpage;
1177 unsigned int checksum;
1178 int err;
1180 remove_rmap_item_from_tree(rmap_item);
1182 /* We first start with searching the page inside the stable tree */
1183 kpage = stable_tree_search(page);
1184 if (kpage) {
1185 err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
1186 if (!err) {
1188 * The page was successfully merged:
1189 * add its rmap_item to the stable tree.
1191 lock_page(kpage);
1192 stable_tree_append(rmap_item, page_stable_node(kpage));
1193 unlock_page(kpage);
1195 put_page(kpage);
1196 return;
1200 * If the hash value of the page has changed from the last time
1201 * we calculated it, this page is changing frequently: therefore we
1202 * don't want to insert it in the unstable tree, and we don't want
1203 * to waste our time searching for something identical to it there.
1205 checksum = calc_checksum(page);
1206 if (rmap_item->oldchecksum != checksum) {
1207 rmap_item->oldchecksum = checksum;
1208 return;
1211 tree_rmap_item =
1212 unstable_tree_search_insert(rmap_item, page, &tree_page);
1213 if (tree_rmap_item) {
1214 kpage = try_to_merge_two_pages(rmap_item, page,
1215 tree_rmap_item, tree_page);
1216 put_page(tree_page);
1218 * As soon as we merge this page, we want to remove the
1219 * rmap_item of the page we have merged with from the unstable
1220 * tree, and insert it instead as new node in the stable tree.
1222 if (kpage) {
1223 remove_rmap_item_from_tree(tree_rmap_item);
1225 lock_page(kpage);
1226 stable_node = stable_tree_insert(kpage);
1227 if (stable_node) {
1228 stable_tree_append(tree_rmap_item, stable_node);
1229 stable_tree_append(rmap_item, stable_node);
1231 unlock_page(kpage);
1234 * If we fail to insert the page into the stable tree,
1235 * we will have 2 virtual addresses that are pointing
1236 * to a ksm page left outside the stable tree,
1237 * in which case we need to break_cow on both.
1239 if (!stable_node) {
1240 break_cow(tree_rmap_item);
1241 break_cow(rmap_item);
1247 static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
1248 struct rmap_item **rmap_list,
1249 unsigned long addr)
1251 struct rmap_item *rmap_item;
1253 while (*rmap_list) {
1254 rmap_item = *rmap_list;
1255 if ((rmap_item->address & PAGE_MASK) == addr)
1256 return rmap_item;
1257 if (rmap_item->address > addr)
1258 break;
1259 *rmap_list = rmap_item->rmap_list;
1260 remove_rmap_item_from_tree(rmap_item);
1261 free_rmap_item(rmap_item);
1264 rmap_item = alloc_rmap_item();
1265 if (rmap_item) {
1266 /* It has already been zeroed */
1267 rmap_item->mm = mm_slot->mm;
1268 rmap_item->address = addr;
1269 rmap_item->rmap_list = *rmap_list;
1270 *rmap_list = rmap_item;
1272 return rmap_item;
1275 static struct rmap_item *scan_get_next_rmap_item(struct page **page)
1277 struct mm_struct *mm;
1278 struct mm_slot *slot;
1279 struct vm_area_struct *vma;
1280 struct rmap_item *rmap_item;
1282 if (list_empty(&ksm_mm_head.mm_list))
1283 return NULL;
1285 slot = ksm_scan.mm_slot;
1286 if (slot == &ksm_mm_head) {
1288 * A number of pages can hang around indefinitely on per-cpu
1289 * pagevecs, raised page count preventing write_protect_page
1290 * from merging them. Though it doesn't really matter much,
1291 * it is puzzling to see some stuck in pages_volatile until
1292 * other activity jostles them out, and they also prevented
1293 * LTP's KSM test from succeeding deterministically; so drain
1294 * them here (here rather than on entry to ksm_do_scan(),
1295 * so we don't IPI too often when pages_to_scan is set low).
1297 lru_add_drain_all();
1299 root_unstable_tree = RB_ROOT;
1301 spin_lock(&ksm_mmlist_lock);
1302 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1303 ksm_scan.mm_slot = slot;
1304 spin_unlock(&ksm_mmlist_lock);
1306 * Although we tested list_empty() above, a racing __ksm_exit
1307 * of the last mm on the list may have removed it since then.
1309 if (slot == &ksm_mm_head)
1310 return NULL;
1311 next_mm:
1312 ksm_scan.address = 0;
1313 ksm_scan.rmap_list = &slot->rmap_list;
1316 mm = slot->mm;
1317 down_read(&mm->mmap_sem);
1318 if (ksm_test_exit(mm))
1319 vma = NULL;
1320 else
1321 vma = find_vma(mm, ksm_scan.address);
1323 for (; vma; vma = vma->vm_next) {
1324 if (!(vma->vm_flags & VM_MERGEABLE))
1325 continue;
1326 if (ksm_scan.address < vma->vm_start)
1327 ksm_scan.address = vma->vm_start;
1328 if (!vma->anon_vma)
1329 ksm_scan.address = vma->vm_end;
1331 while (ksm_scan.address < vma->vm_end) {
1332 if (ksm_test_exit(mm))
1333 break;
1334 *page = follow_page(vma, ksm_scan.address, FOLL_GET);
1335 if (IS_ERR_OR_NULL(*page)) {
1336 ksm_scan.address += PAGE_SIZE;
1337 cond_resched();
1338 continue;
1340 if (PageAnon(*page) ||
1341 page_trans_compound_anon(*page)) {
1342 flush_anon_page(vma, *page, ksm_scan.address);
1343 flush_dcache_page(*page);
1344 rmap_item = get_next_rmap_item(slot,
1345 ksm_scan.rmap_list, ksm_scan.address);
1346 if (rmap_item) {
1347 ksm_scan.rmap_list =
1348 &rmap_item->rmap_list;
1349 ksm_scan.address += PAGE_SIZE;
1350 } else
1351 put_page(*page);
1352 up_read(&mm->mmap_sem);
1353 return rmap_item;
1355 put_page(*page);
1356 ksm_scan.address += PAGE_SIZE;
1357 cond_resched();
1361 if (ksm_test_exit(mm)) {
1362 ksm_scan.address = 0;
1363 ksm_scan.rmap_list = &slot->rmap_list;
1366 * Nuke all the rmap_items that are above this current rmap:
1367 * because there were no VM_MERGEABLE vmas with such addresses.
1369 remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
1371 spin_lock(&ksm_mmlist_lock);
1372 ksm_scan.mm_slot = list_entry(slot->mm_list.next,
1373 struct mm_slot, mm_list);
1374 if (ksm_scan.address == 0) {
1376 * We've completed a full scan of all vmas, holding mmap_sem
1377 * throughout, and found no VM_MERGEABLE: so do the same as
1378 * __ksm_exit does to remove this mm from all our lists now.
1379 * This applies either when cleaning up after __ksm_exit
1380 * (but beware: we can reach here even before __ksm_exit),
1381 * or when all VM_MERGEABLE areas have been unmapped (and
1382 * mmap_sem then protects against race with MADV_MERGEABLE).
1384 hlist_del(&slot->link);
1385 list_del(&slot->mm_list);
1386 spin_unlock(&ksm_mmlist_lock);
1388 free_mm_slot(slot);
1389 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1390 up_read(&mm->mmap_sem);
1391 mmdrop(mm);
1392 } else {
1393 spin_unlock(&ksm_mmlist_lock);
1394 up_read(&mm->mmap_sem);
1397 /* Repeat until we've completed scanning the whole list */
1398 slot = ksm_scan.mm_slot;
1399 if (slot != &ksm_mm_head)
1400 goto next_mm;
1402 ksm_scan.seqnr++;
1403 return NULL;
1407 * ksm_do_scan - the ksm scanner main worker function.
1408 * @scan_npages - number of pages we want to scan before we return.
1410 static void ksm_do_scan(unsigned int scan_npages)
1412 struct rmap_item *rmap_item;
1413 struct page *uninitialized_var(page);
1415 while (scan_npages-- && likely(!freezing(current))) {
1416 cond_resched();
1417 rmap_item = scan_get_next_rmap_item(&page);
1418 if (!rmap_item)
1419 return;
1420 if (!PageKsm(page) || !in_stable_tree(rmap_item))
1421 cmp_and_merge_page(page, rmap_item);
1422 put_page(page);
1426 static int ksmd_should_run(void)
1428 return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1431 static int ksm_scan_thread(void *nothing)
1433 set_freezable();
1434 set_user_nice(current, 5);
1436 while (!kthread_should_stop()) {
1437 mutex_lock(&ksm_thread_mutex);
1438 if (ksmd_should_run())
1439 ksm_do_scan(ksm_thread_pages_to_scan);
1440 mutex_unlock(&ksm_thread_mutex);
1442 try_to_freeze();
1444 if (ksmd_should_run()) {
1445 schedule_timeout_interruptible(
1446 msecs_to_jiffies(ksm_thread_sleep_millisecs));
1447 } else {
1448 wait_event_freezable(ksm_thread_wait,
1449 ksmd_should_run() || kthread_should_stop());
1452 return 0;
1455 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1456 unsigned long end, int advice, unsigned long *vm_flags)
1458 struct mm_struct *mm = vma->vm_mm;
1459 int err;
1461 switch (advice) {
1462 case MADV_MERGEABLE:
1464 * Be somewhat over-protective for now!
1466 if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE |
1467 VM_PFNMAP | VM_IO | VM_DONTEXPAND |
1468 VM_RESERVED | VM_HUGETLB | VM_INSERTPAGE |
1469 VM_NONLINEAR | VM_MIXEDMAP | VM_SAO))
1470 return 0; /* just ignore the advice */
1472 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
1473 err = __ksm_enter(mm);
1474 if (err)
1475 return err;
1478 *vm_flags |= VM_MERGEABLE;
1479 break;
1481 case MADV_UNMERGEABLE:
1482 if (!(*vm_flags & VM_MERGEABLE))
1483 return 0; /* just ignore the advice */
1485 if (vma->anon_vma) {
1486 err = unmerge_ksm_pages(vma, start, end);
1487 if (err)
1488 return err;
1491 *vm_flags &= ~VM_MERGEABLE;
1492 break;
1495 return 0;
1498 int __ksm_enter(struct mm_struct *mm)
1500 struct mm_slot *mm_slot;
1501 int needs_wakeup;
1503 mm_slot = alloc_mm_slot();
1504 if (!mm_slot)
1505 return -ENOMEM;
1507 /* Check ksm_run too? Would need tighter locking */
1508 needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1510 spin_lock(&ksm_mmlist_lock);
1511 insert_to_mm_slots_hash(mm, mm_slot);
1513 * Insert just behind the scanning cursor, to let the area settle
1514 * down a little; when fork is followed by immediate exec, we don't
1515 * want ksmd to waste time setting up and tearing down an rmap_list.
1517 list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
1518 spin_unlock(&ksm_mmlist_lock);
1520 set_bit(MMF_VM_MERGEABLE, &mm->flags);
1521 atomic_inc(&mm->mm_count);
1523 if (needs_wakeup)
1524 wake_up_interruptible(&ksm_thread_wait);
1526 return 0;
1529 void __ksm_exit(struct mm_struct *mm)
1531 struct mm_slot *mm_slot;
1532 int easy_to_free = 0;
1535 * This process is exiting: if it's straightforward (as is the
1536 * case when ksmd was never running), free mm_slot immediately.
1537 * But if it's at the cursor or has rmap_items linked to it, use
1538 * mmap_sem to synchronize with any break_cows before pagetables
1539 * are freed, and leave the mm_slot on the list for ksmd to free.
1540 * Beware: ksm may already have noticed it exiting and freed the slot.
1543 spin_lock(&ksm_mmlist_lock);
1544 mm_slot = get_mm_slot(mm);
1545 if (mm_slot && ksm_scan.mm_slot != mm_slot) {
1546 if (!mm_slot->rmap_list) {
1547 hlist_del(&mm_slot->link);
1548 list_del(&mm_slot->mm_list);
1549 easy_to_free = 1;
1550 } else {
1551 list_move(&mm_slot->mm_list,
1552 &ksm_scan.mm_slot->mm_list);
1555 spin_unlock(&ksm_mmlist_lock);
1557 if (easy_to_free) {
1558 free_mm_slot(mm_slot);
1559 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1560 mmdrop(mm);
1561 } else if (mm_slot) {
1562 down_write(&mm->mmap_sem);
1563 up_write(&mm->mmap_sem);
1567 struct page *ksm_does_need_to_copy(struct page *page,
1568 struct vm_area_struct *vma, unsigned long address)
1570 struct page *new_page;
1572 new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
1573 if (new_page) {
1574 copy_user_highpage(new_page, page, address, vma);
1576 SetPageDirty(new_page);
1577 __SetPageUptodate(new_page);
1578 SetPageSwapBacked(new_page);
1579 __set_page_locked(new_page);
1581 if (page_evictable(new_page, vma))
1582 lru_cache_add_lru(new_page, LRU_ACTIVE_ANON);
1583 else
1584 add_page_to_unevictable_list(new_page);
1587 return new_page;
1590 int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg,
1591 unsigned long *vm_flags)
1593 struct stable_node *stable_node;
1594 struct rmap_item *rmap_item;
1595 struct hlist_node *hlist;
1596 unsigned int mapcount = page_mapcount(page);
1597 int referenced = 0;
1598 int search_new_forks = 0;
1600 VM_BUG_ON(!PageKsm(page));
1601 VM_BUG_ON(!PageLocked(page));
1603 stable_node = page_stable_node(page);
1604 if (!stable_node)
1605 return 0;
1606 again:
1607 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1608 struct anon_vma *anon_vma = rmap_item->anon_vma;
1609 struct anon_vma_chain *vmac;
1610 struct vm_area_struct *vma;
1612 anon_vma_lock(anon_vma);
1613 list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1614 vma = vmac->vma;
1615 if (rmap_item->address < vma->vm_start ||
1616 rmap_item->address >= vma->vm_end)
1617 continue;
1619 * Initially we examine only the vma which covers this
1620 * rmap_item; but later, if there is still work to do,
1621 * we examine covering vmas in other mms: in case they
1622 * were forked from the original since ksmd passed.
1624 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1625 continue;
1627 if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
1628 continue;
1630 referenced += page_referenced_one(page, vma,
1631 rmap_item->address, &mapcount, vm_flags);
1632 if (!search_new_forks || !mapcount)
1633 break;
1635 anon_vma_unlock(anon_vma);
1636 if (!mapcount)
1637 goto out;
1639 if (!search_new_forks++)
1640 goto again;
1641 out:
1642 return referenced;
1645 int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
1647 struct stable_node *stable_node;
1648 struct hlist_node *hlist;
1649 struct rmap_item *rmap_item;
1650 int ret = SWAP_AGAIN;
1651 int search_new_forks = 0;
1653 VM_BUG_ON(!PageKsm(page));
1654 VM_BUG_ON(!PageLocked(page));
1656 stable_node = page_stable_node(page);
1657 if (!stable_node)
1658 return SWAP_FAIL;
1659 again:
1660 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1661 struct anon_vma *anon_vma = rmap_item->anon_vma;
1662 struct anon_vma_chain *vmac;
1663 struct vm_area_struct *vma;
1665 anon_vma_lock(anon_vma);
1666 list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1667 vma = vmac->vma;
1668 if (rmap_item->address < vma->vm_start ||
1669 rmap_item->address >= vma->vm_end)
1670 continue;
1672 * Initially we examine only the vma which covers this
1673 * rmap_item; but later, if there is still work to do,
1674 * we examine covering vmas in other mms: in case they
1675 * were forked from the original since ksmd passed.
1677 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1678 continue;
1680 ret = try_to_unmap_one(page, vma,
1681 rmap_item->address, flags);
1682 if (ret != SWAP_AGAIN || !page_mapped(page)) {
1683 anon_vma_unlock(anon_vma);
1684 goto out;
1687 anon_vma_unlock(anon_vma);
1689 if (!search_new_forks++)
1690 goto again;
1691 out:
1692 return ret;
1695 #ifdef CONFIG_MIGRATION
1696 int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *,
1697 struct vm_area_struct *, unsigned long, void *), void *arg)
1699 struct stable_node *stable_node;
1700 struct hlist_node *hlist;
1701 struct rmap_item *rmap_item;
1702 int ret = SWAP_AGAIN;
1703 int search_new_forks = 0;
1705 VM_BUG_ON(!PageKsm(page));
1706 VM_BUG_ON(!PageLocked(page));
1708 stable_node = page_stable_node(page);
1709 if (!stable_node)
1710 return ret;
1711 again:
1712 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1713 struct anon_vma *anon_vma = rmap_item->anon_vma;
1714 struct anon_vma_chain *vmac;
1715 struct vm_area_struct *vma;
1717 anon_vma_lock(anon_vma);
1718 list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1719 vma = vmac->vma;
1720 if (rmap_item->address < vma->vm_start ||
1721 rmap_item->address >= vma->vm_end)
1722 continue;
1724 * Initially we examine only the vma which covers this
1725 * rmap_item; but later, if there is still work to do,
1726 * we examine covering vmas in other mms: in case they
1727 * were forked from the original since ksmd passed.
1729 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1730 continue;
1732 ret = rmap_one(page, vma, rmap_item->address, arg);
1733 if (ret != SWAP_AGAIN) {
1734 anon_vma_unlock(anon_vma);
1735 goto out;
1738 anon_vma_unlock(anon_vma);
1740 if (!search_new_forks++)
1741 goto again;
1742 out:
1743 return ret;
1746 void ksm_migrate_page(struct page *newpage, struct page *oldpage)
1748 struct stable_node *stable_node;
1750 VM_BUG_ON(!PageLocked(oldpage));
1751 VM_BUG_ON(!PageLocked(newpage));
1752 VM_BUG_ON(newpage->mapping != oldpage->mapping);
1754 stable_node = page_stable_node(newpage);
1755 if (stable_node) {
1756 VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage));
1757 stable_node->kpfn = page_to_pfn(newpage);
1760 #endif /* CONFIG_MIGRATION */
1762 #ifdef CONFIG_MEMORY_HOTREMOVE
1763 static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn,
1764 unsigned long end_pfn)
1766 struct rb_node *node;
1768 for (node = rb_first(&root_stable_tree); node; node = rb_next(node)) {
1769 struct stable_node *stable_node;
1771 stable_node = rb_entry(node, struct stable_node, node);
1772 if (stable_node->kpfn >= start_pfn &&
1773 stable_node->kpfn < end_pfn)
1774 return stable_node;
1776 return NULL;
1779 static int ksm_memory_callback(struct notifier_block *self,
1780 unsigned long action, void *arg)
1782 struct memory_notify *mn = arg;
1783 struct stable_node *stable_node;
1785 switch (action) {
1786 case MEM_GOING_OFFLINE:
1788 * Keep it very simple for now: just lock out ksmd and
1789 * MADV_UNMERGEABLE while any memory is going offline.
1790 * mutex_lock_nested() is necessary because lockdep was alarmed
1791 * that here we take ksm_thread_mutex inside notifier chain
1792 * mutex, and later take notifier chain mutex inside
1793 * ksm_thread_mutex to unlock it. But that's safe because both
1794 * are inside mem_hotplug_mutex.
1796 mutex_lock_nested(&ksm_thread_mutex, SINGLE_DEPTH_NESTING);
1797 break;
1799 case MEM_OFFLINE:
1801 * Most of the work is done by page migration; but there might
1802 * be a few stable_nodes left over, still pointing to struct
1803 * pages which have been offlined: prune those from the tree.
1805 while ((stable_node = ksm_check_stable_tree(mn->start_pfn,
1806 mn->start_pfn + mn->nr_pages)) != NULL)
1807 remove_node_from_stable_tree(stable_node);
1808 /* fallthrough */
1810 case MEM_CANCEL_OFFLINE:
1811 mutex_unlock(&ksm_thread_mutex);
1812 break;
1814 return NOTIFY_OK;
1816 #endif /* CONFIG_MEMORY_HOTREMOVE */
1818 #ifdef CONFIG_SYSFS
1820 * This all compiles without CONFIG_SYSFS, but is a waste of space.
1823 #define KSM_ATTR_RO(_name) \
1824 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
1825 #define KSM_ATTR(_name) \
1826 static struct kobj_attribute _name##_attr = \
1827 __ATTR(_name, 0644, _name##_show, _name##_store)
1829 static ssize_t sleep_millisecs_show(struct kobject *kobj,
1830 struct kobj_attribute *attr, char *buf)
1832 return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
1835 static ssize_t sleep_millisecs_store(struct kobject *kobj,
1836 struct kobj_attribute *attr,
1837 const char *buf, size_t count)
1839 unsigned long msecs;
1840 int err;
1842 err = strict_strtoul(buf, 10, &msecs);
1843 if (err || msecs > UINT_MAX)
1844 return -EINVAL;
1846 ksm_thread_sleep_millisecs = msecs;
1848 return count;
1850 KSM_ATTR(sleep_millisecs);
1852 static ssize_t pages_to_scan_show(struct kobject *kobj,
1853 struct kobj_attribute *attr, char *buf)
1855 return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
1858 static ssize_t pages_to_scan_store(struct kobject *kobj,
1859 struct kobj_attribute *attr,
1860 const char *buf, size_t count)
1862 int err;
1863 unsigned long nr_pages;
1865 err = strict_strtoul(buf, 10, &nr_pages);
1866 if (err || nr_pages > UINT_MAX)
1867 return -EINVAL;
1869 ksm_thread_pages_to_scan = nr_pages;
1871 return count;
1873 KSM_ATTR(pages_to_scan);
1875 static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
1876 char *buf)
1878 return sprintf(buf, "%u\n", ksm_run);
1881 static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
1882 const char *buf, size_t count)
1884 int err;
1885 unsigned long flags;
1887 err = strict_strtoul(buf, 10, &flags);
1888 if (err || flags > UINT_MAX)
1889 return -EINVAL;
1890 if (flags > KSM_RUN_UNMERGE)
1891 return -EINVAL;
1894 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
1895 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
1896 * breaking COW to free the pages_shared (but leaves mm_slots
1897 * on the list for when ksmd may be set running again).
1900 mutex_lock(&ksm_thread_mutex);
1901 if (ksm_run != flags) {
1902 ksm_run = flags;
1903 if (flags & KSM_RUN_UNMERGE) {
1904 int oom_score_adj;
1906 oom_score_adj = test_set_oom_score_adj(OOM_SCORE_ADJ_MAX);
1907 err = unmerge_and_remove_all_rmap_items();
1908 compare_swap_oom_score_adj(OOM_SCORE_ADJ_MAX,
1909 oom_score_adj);
1910 if (err) {
1911 ksm_run = KSM_RUN_STOP;
1912 count = err;
1916 mutex_unlock(&ksm_thread_mutex);
1918 if (flags & KSM_RUN_MERGE)
1919 wake_up_interruptible(&ksm_thread_wait);
1921 return count;
1923 KSM_ATTR(run);
1925 static ssize_t pages_shared_show(struct kobject *kobj,
1926 struct kobj_attribute *attr, char *buf)
1928 return sprintf(buf, "%lu\n", ksm_pages_shared);
1930 KSM_ATTR_RO(pages_shared);
1932 static ssize_t pages_sharing_show(struct kobject *kobj,
1933 struct kobj_attribute *attr, char *buf)
1935 return sprintf(buf, "%lu\n", ksm_pages_sharing);
1937 KSM_ATTR_RO(pages_sharing);
1939 static ssize_t pages_unshared_show(struct kobject *kobj,
1940 struct kobj_attribute *attr, char *buf)
1942 return sprintf(buf, "%lu\n", ksm_pages_unshared);
1944 KSM_ATTR_RO(pages_unshared);
1946 static ssize_t pages_volatile_show(struct kobject *kobj,
1947 struct kobj_attribute *attr, char *buf)
1949 long ksm_pages_volatile;
1951 ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
1952 - ksm_pages_sharing - ksm_pages_unshared;
1954 * It was not worth any locking to calculate that statistic,
1955 * but it might therefore sometimes be negative: conceal that.
1957 if (ksm_pages_volatile < 0)
1958 ksm_pages_volatile = 0;
1959 return sprintf(buf, "%ld\n", ksm_pages_volatile);
1961 KSM_ATTR_RO(pages_volatile);
1963 static ssize_t full_scans_show(struct kobject *kobj,
1964 struct kobj_attribute *attr, char *buf)
1966 return sprintf(buf, "%lu\n", ksm_scan.seqnr);
1968 KSM_ATTR_RO(full_scans);
1970 static struct attribute *ksm_attrs[] = {
1971 &sleep_millisecs_attr.attr,
1972 &pages_to_scan_attr.attr,
1973 &run_attr.attr,
1974 &pages_shared_attr.attr,
1975 &pages_sharing_attr.attr,
1976 &pages_unshared_attr.attr,
1977 &pages_volatile_attr.attr,
1978 &full_scans_attr.attr,
1979 NULL,
1982 static struct attribute_group ksm_attr_group = {
1983 .attrs = ksm_attrs,
1984 .name = "ksm",
1986 #endif /* CONFIG_SYSFS */
1988 static int __init ksm_init(void)
1990 struct task_struct *ksm_thread;
1991 int err;
1993 err = ksm_slab_init();
1994 if (err)
1995 goto out;
1997 ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
1998 if (IS_ERR(ksm_thread)) {
1999 printk(KERN_ERR "ksm: creating kthread failed\n");
2000 err = PTR_ERR(ksm_thread);
2001 goto out_free;
2004 #ifdef CONFIG_SYSFS
2005 err = sysfs_create_group(mm_kobj, &ksm_attr_group);
2006 if (err) {
2007 printk(KERN_ERR "ksm: register sysfs failed\n");
2008 kthread_stop(ksm_thread);
2009 goto out_free;
2011 #else
2012 ksm_run = KSM_RUN_MERGE; /* no way for user to start it */
2014 #endif /* CONFIG_SYSFS */
2016 #ifdef CONFIG_MEMORY_HOTREMOVE
2018 * Choose a high priority since the callback takes ksm_thread_mutex:
2019 * later callbacks could only be taking locks which nest within that.
2021 hotplug_memory_notifier(ksm_memory_callback, 100);
2022 #endif
2023 return 0;
2025 out_free:
2026 ksm_slab_free();
2027 out:
2028 return err;
2030 module_init(ksm_init)