Linux 2.6.35-rc1
[orion.git] / mm / ksm.c
blob6c3e99b4ae7c0726851ea5281fbb39f90f7b9ea2
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>
37 #include <asm/tlbflush.h>
38 #include "internal.h"
41 * A few notes about the KSM scanning process,
42 * to make it easier to understand the data structures below:
44 * In order to reduce excessive scanning, KSM sorts the memory pages by their
45 * contents into a data structure that holds pointers to the pages' locations.
47 * Since the contents of the pages may change at any moment, KSM cannot just
48 * insert the pages into a normal sorted tree and expect it to find anything.
49 * Therefore KSM uses two data structures - the stable and the unstable tree.
51 * The stable tree holds pointers to all the merged pages (ksm pages), sorted
52 * by their contents. Because each such page is write-protected, searching on
53 * this tree is fully assured to be working (except when pages are unmapped),
54 * and therefore this tree is called the stable tree.
56 * In addition to the stable tree, KSM uses a second data structure called the
57 * unstable tree: this tree holds pointers to pages which have been found to
58 * be "unchanged for a period of time". The unstable tree sorts these pages
59 * by their contents, but since they are not write-protected, KSM cannot rely
60 * upon the unstable tree to work correctly - the unstable tree is liable to
61 * be corrupted as its contents are modified, and so it is called unstable.
63 * KSM solves this problem by several techniques:
65 * 1) The unstable tree is flushed every time KSM completes scanning all
66 * memory areas, and then the tree is rebuilt again from the beginning.
67 * 2) KSM will only insert into the unstable tree, pages whose hash value
68 * has not changed since the previous scan of all memory areas.
69 * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
70 * colors of the nodes and not on their contents, assuring that even when
71 * the tree gets "corrupted" it won't get out of balance, so scanning time
72 * remains the same (also, searching and inserting nodes in an rbtree uses
73 * the same algorithm, so we have no overhead when we flush and rebuild).
74 * 4) KSM never flushes the stable tree, which means that even if it were to
75 * take 10 attempts to find a page in the unstable tree, once it is found,
76 * it is secured in the stable tree. (When we scan a new page, we first
77 * compare it against the stable tree, and then against the unstable tree.)
80 /**
81 * struct mm_slot - ksm information per mm that is being scanned
82 * @link: link to the mm_slots hash list
83 * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
84 * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
85 * @mm: the mm that this information is valid for
87 struct mm_slot {
88 struct hlist_node link;
89 struct list_head mm_list;
90 struct rmap_item *rmap_list;
91 struct mm_struct *mm;
94 /**
95 * struct ksm_scan - cursor for scanning
96 * @mm_slot: the current mm_slot we are scanning
97 * @address: the next address inside that to be scanned
98 * @rmap_list: link to the next rmap to be scanned in the rmap_list
99 * @seqnr: count of completed full scans (needed when removing unstable node)
101 * There is only the one ksm_scan instance of this cursor structure.
103 struct ksm_scan {
104 struct mm_slot *mm_slot;
105 unsigned long address;
106 struct rmap_item **rmap_list;
107 unsigned long seqnr;
111 * struct stable_node - node of the stable rbtree
112 * @node: rb node of this ksm page in the stable tree
113 * @hlist: hlist head of rmap_items using this ksm page
114 * @kpfn: page frame number of this ksm page
116 struct stable_node {
117 struct rb_node node;
118 struct hlist_head hlist;
119 unsigned long kpfn;
123 * struct rmap_item - reverse mapping item for virtual addresses
124 * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
125 * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
126 * @mm: the memory structure this rmap_item is pointing into
127 * @address: the virtual address this rmap_item tracks (+ flags in low bits)
128 * @oldchecksum: previous checksum of the page at that virtual address
129 * @node: rb node of this rmap_item in the unstable tree
130 * @head: pointer to stable_node heading this list in the stable tree
131 * @hlist: link into hlist of rmap_items hanging off that stable_node
133 struct rmap_item {
134 struct rmap_item *rmap_list;
135 struct anon_vma *anon_vma; /* when stable */
136 struct mm_struct *mm;
137 unsigned long address; /* + low bits used for flags below */
138 unsigned int oldchecksum; /* when unstable */
139 union {
140 struct rb_node node; /* when node of unstable tree */
141 struct { /* when listed from stable tree */
142 struct stable_node *head;
143 struct hlist_node hlist;
148 #define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */
149 #define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */
150 #define STABLE_FLAG 0x200 /* is listed from the stable tree */
152 /* The stable and unstable tree heads */
153 static struct rb_root root_stable_tree = RB_ROOT;
154 static struct rb_root root_unstable_tree = RB_ROOT;
156 #define MM_SLOTS_HASH_HEADS 1024
157 static struct hlist_head *mm_slots_hash;
159 static struct mm_slot ksm_mm_head = {
160 .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
162 static struct ksm_scan ksm_scan = {
163 .mm_slot = &ksm_mm_head,
166 static struct kmem_cache *rmap_item_cache;
167 static struct kmem_cache *stable_node_cache;
168 static struct kmem_cache *mm_slot_cache;
170 /* The number of nodes in the stable tree */
171 static unsigned long ksm_pages_shared;
173 /* The number of page slots additionally sharing those nodes */
174 static unsigned long ksm_pages_sharing;
176 /* The number of nodes in the unstable tree */
177 static unsigned long ksm_pages_unshared;
179 /* The number of rmap_items in use: to calculate pages_volatile */
180 static unsigned long ksm_rmap_items;
182 /* Number of pages ksmd should scan in one batch */
183 static unsigned int ksm_thread_pages_to_scan = 100;
185 /* Milliseconds ksmd should sleep between batches */
186 static unsigned int ksm_thread_sleep_millisecs = 20;
188 #define KSM_RUN_STOP 0
189 #define KSM_RUN_MERGE 1
190 #define KSM_RUN_UNMERGE 2
191 static unsigned int ksm_run = KSM_RUN_STOP;
193 static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
194 static DEFINE_MUTEX(ksm_thread_mutex);
195 static DEFINE_SPINLOCK(ksm_mmlist_lock);
197 #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
198 sizeof(struct __struct), __alignof__(struct __struct),\
199 (__flags), NULL)
201 static int __init ksm_slab_init(void)
203 rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
204 if (!rmap_item_cache)
205 goto out;
207 stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
208 if (!stable_node_cache)
209 goto out_free1;
211 mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
212 if (!mm_slot_cache)
213 goto out_free2;
215 return 0;
217 out_free2:
218 kmem_cache_destroy(stable_node_cache);
219 out_free1:
220 kmem_cache_destroy(rmap_item_cache);
221 out:
222 return -ENOMEM;
225 static void __init ksm_slab_free(void)
227 kmem_cache_destroy(mm_slot_cache);
228 kmem_cache_destroy(stable_node_cache);
229 kmem_cache_destroy(rmap_item_cache);
230 mm_slot_cache = NULL;
233 static inline struct rmap_item *alloc_rmap_item(void)
235 struct rmap_item *rmap_item;
237 rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
238 if (rmap_item)
239 ksm_rmap_items++;
240 return rmap_item;
243 static inline void free_rmap_item(struct rmap_item *rmap_item)
245 ksm_rmap_items--;
246 rmap_item->mm = NULL; /* debug safety */
247 kmem_cache_free(rmap_item_cache, rmap_item);
250 static inline struct stable_node *alloc_stable_node(void)
252 return kmem_cache_alloc(stable_node_cache, GFP_KERNEL);
255 static inline void free_stable_node(struct stable_node *stable_node)
257 kmem_cache_free(stable_node_cache, stable_node);
260 static inline struct mm_slot *alloc_mm_slot(void)
262 if (!mm_slot_cache) /* initialization failed */
263 return NULL;
264 return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
267 static inline void free_mm_slot(struct mm_slot *mm_slot)
269 kmem_cache_free(mm_slot_cache, mm_slot);
272 static int __init mm_slots_hash_init(void)
274 mm_slots_hash = kzalloc(MM_SLOTS_HASH_HEADS * sizeof(struct hlist_head),
275 GFP_KERNEL);
276 if (!mm_slots_hash)
277 return -ENOMEM;
278 return 0;
281 static void __init mm_slots_hash_free(void)
283 kfree(mm_slots_hash);
286 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
288 struct mm_slot *mm_slot;
289 struct hlist_head *bucket;
290 struct hlist_node *node;
292 bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
293 % MM_SLOTS_HASH_HEADS];
294 hlist_for_each_entry(mm_slot, node, bucket, link) {
295 if (mm == mm_slot->mm)
296 return mm_slot;
298 return NULL;
301 static void insert_to_mm_slots_hash(struct mm_struct *mm,
302 struct mm_slot *mm_slot)
304 struct hlist_head *bucket;
306 bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
307 % MM_SLOTS_HASH_HEADS];
308 mm_slot->mm = mm;
309 hlist_add_head(&mm_slot->link, bucket);
312 static inline int in_stable_tree(struct rmap_item *rmap_item)
314 return rmap_item->address & STABLE_FLAG;
317 static void hold_anon_vma(struct rmap_item *rmap_item,
318 struct anon_vma *anon_vma)
320 rmap_item->anon_vma = anon_vma;
321 atomic_inc(&anon_vma->external_refcount);
324 static void drop_anon_vma(struct rmap_item *rmap_item)
326 struct anon_vma *anon_vma = rmap_item->anon_vma;
328 if (atomic_dec_and_lock(&anon_vma->external_refcount, &anon_vma->lock)) {
329 int empty = list_empty(&anon_vma->head);
330 spin_unlock(&anon_vma->lock);
331 if (empty)
332 anon_vma_free(anon_vma);
337 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
338 * page tables after it has passed through ksm_exit() - which, if necessary,
339 * takes mmap_sem briefly to serialize against them. ksm_exit() does not set
340 * a special flag: they can just back out as soon as mm_users goes to zero.
341 * ksm_test_exit() is used throughout to make this test for exit: in some
342 * places for correctness, in some places just to avoid unnecessary work.
344 static inline bool ksm_test_exit(struct mm_struct *mm)
346 return atomic_read(&mm->mm_users) == 0;
350 * We use break_ksm to break COW on a ksm page: it's a stripped down
352 * if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
353 * put_page(page);
355 * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
356 * in case the application has unmapped and remapped mm,addr meanwhile.
357 * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP
358 * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
360 static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
362 struct page *page;
363 int ret = 0;
365 do {
366 cond_resched();
367 page = follow_page(vma, addr, FOLL_GET);
368 if (IS_ERR_OR_NULL(page))
369 break;
370 if (PageKsm(page))
371 ret = handle_mm_fault(vma->vm_mm, vma, addr,
372 FAULT_FLAG_WRITE);
373 else
374 ret = VM_FAULT_WRITE;
375 put_page(page);
376 } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM)));
378 * We must loop because handle_mm_fault() may back out if there's
379 * any difficulty e.g. if pte accessed bit gets updated concurrently.
381 * VM_FAULT_WRITE is what we have been hoping for: it indicates that
382 * COW has been broken, even if the vma does not permit VM_WRITE;
383 * but note that a concurrent fault might break PageKsm for us.
385 * VM_FAULT_SIGBUS could occur if we race with truncation of the
386 * backing file, which also invalidates anonymous pages: that's
387 * okay, that truncation will have unmapped the PageKsm for us.
389 * VM_FAULT_OOM: at the time of writing (late July 2009), setting
390 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
391 * current task has TIF_MEMDIE set, and will be OOM killed on return
392 * to user; and ksmd, having no mm, would never be chosen for that.
394 * But if the mm is in a limited mem_cgroup, then the fault may fail
395 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
396 * even ksmd can fail in this way - though it's usually breaking ksm
397 * just to undo a merge it made a moment before, so unlikely to oom.
399 * That's a pity: we might therefore have more kernel pages allocated
400 * than we're counting as nodes in the stable tree; but ksm_do_scan
401 * will retry to break_cow on each pass, so should recover the page
402 * in due course. The important thing is to not let VM_MERGEABLE
403 * be cleared while any such pages might remain in the area.
405 return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
408 static void break_cow(struct rmap_item *rmap_item)
410 struct mm_struct *mm = rmap_item->mm;
411 unsigned long addr = rmap_item->address;
412 struct vm_area_struct *vma;
415 * It is not an accident that whenever we want to break COW
416 * to undo, we also need to drop a reference to the anon_vma.
418 drop_anon_vma(rmap_item);
420 down_read(&mm->mmap_sem);
421 if (ksm_test_exit(mm))
422 goto out;
423 vma = find_vma(mm, addr);
424 if (!vma || vma->vm_start > addr)
425 goto out;
426 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
427 goto out;
428 break_ksm(vma, addr);
429 out:
430 up_read(&mm->mmap_sem);
433 static struct page *get_mergeable_page(struct rmap_item *rmap_item)
435 struct mm_struct *mm = rmap_item->mm;
436 unsigned long addr = rmap_item->address;
437 struct vm_area_struct *vma;
438 struct page *page;
440 down_read(&mm->mmap_sem);
441 if (ksm_test_exit(mm))
442 goto out;
443 vma = find_vma(mm, addr);
444 if (!vma || vma->vm_start > addr)
445 goto out;
446 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
447 goto out;
449 page = follow_page(vma, addr, FOLL_GET);
450 if (IS_ERR_OR_NULL(page))
451 goto out;
452 if (PageAnon(page)) {
453 flush_anon_page(vma, page, addr);
454 flush_dcache_page(page);
455 } else {
456 put_page(page);
457 out: page = NULL;
459 up_read(&mm->mmap_sem);
460 return page;
463 static void remove_node_from_stable_tree(struct stable_node *stable_node)
465 struct rmap_item *rmap_item;
466 struct hlist_node *hlist;
468 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
469 if (rmap_item->hlist.next)
470 ksm_pages_sharing--;
471 else
472 ksm_pages_shared--;
473 drop_anon_vma(rmap_item);
474 rmap_item->address &= PAGE_MASK;
475 cond_resched();
478 rb_erase(&stable_node->node, &root_stable_tree);
479 free_stable_node(stable_node);
483 * get_ksm_page: checks if the page indicated by the stable node
484 * is still its ksm page, despite having held no reference to it.
485 * In which case we can trust the content of the page, and it
486 * returns the gotten page; but if the page has now been zapped,
487 * remove the stale node from the stable tree and return NULL.
489 * You would expect the stable_node to hold a reference to the ksm page.
490 * But if it increments the page's count, swapping out has to wait for
491 * ksmd to come around again before it can free the page, which may take
492 * seconds or even minutes: much too unresponsive. So instead we use a
493 * "keyhole reference": access to the ksm page from the stable node peeps
494 * out through its keyhole to see if that page still holds the right key,
495 * pointing back to this stable node. This relies on freeing a PageAnon
496 * page to reset its page->mapping to NULL, and relies on no other use of
497 * a page to put something that might look like our key in page->mapping.
499 * include/linux/pagemap.h page_cache_get_speculative() is a good reference,
500 * but this is different - made simpler by ksm_thread_mutex being held, but
501 * interesting for assuming that no other use of the struct page could ever
502 * put our expected_mapping into page->mapping (or a field of the union which
503 * coincides with page->mapping). The RCU calls are not for KSM at all, but
504 * to keep the page_count protocol described with page_cache_get_speculative.
506 * Note: it is possible that get_ksm_page() will return NULL one moment,
507 * then page the next, if the page is in between page_freeze_refs() and
508 * page_unfreeze_refs(): this shouldn't be a problem anywhere, the page
509 * is on its way to being freed; but it is an anomaly to bear in mind.
511 static struct page *get_ksm_page(struct stable_node *stable_node)
513 struct page *page;
514 void *expected_mapping;
516 page = pfn_to_page(stable_node->kpfn);
517 expected_mapping = (void *)stable_node +
518 (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
519 rcu_read_lock();
520 if (page->mapping != expected_mapping)
521 goto stale;
522 if (!get_page_unless_zero(page))
523 goto stale;
524 if (page->mapping != expected_mapping) {
525 put_page(page);
526 goto stale;
528 rcu_read_unlock();
529 return page;
530 stale:
531 rcu_read_unlock();
532 remove_node_from_stable_tree(stable_node);
533 return NULL;
537 * Removing rmap_item from stable or unstable tree.
538 * This function will clean the information from the stable/unstable tree.
540 static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
542 if (rmap_item->address & STABLE_FLAG) {
543 struct stable_node *stable_node;
544 struct page *page;
546 stable_node = rmap_item->head;
547 page = get_ksm_page(stable_node);
548 if (!page)
549 goto out;
551 lock_page(page);
552 hlist_del(&rmap_item->hlist);
553 unlock_page(page);
554 put_page(page);
556 if (stable_node->hlist.first)
557 ksm_pages_sharing--;
558 else
559 ksm_pages_shared--;
561 drop_anon_vma(rmap_item);
562 rmap_item->address &= PAGE_MASK;
564 } else if (rmap_item->address & UNSTABLE_FLAG) {
565 unsigned char age;
567 * Usually ksmd can and must skip the rb_erase, because
568 * root_unstable_tree was already reset to RB_ROOT.
569 * But be careful when an mm is exiting: do the rb_erase
570 * if this rmap_item was inserted by this scan, rather
571 * than left over from before.
573 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
574 BUG_ON(age > 1);
575 if (!age)
576 rb_erase(&rmap_item->node, &root_unstable_tree);
578 ksm_pages_unshared--;
579 rmap_item->address &= PAGE_MASK;
581 out:
582 cond_resched(); /* we're called from many long loops */
585 static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
586 struct rmap_item **rmap_list)
588 while (*rmap_list) {
589 struct rmap_item *rmap_item = *rmap_list;
590 *rmap_list = rmap_item->rmap_list;
591 remove_rmap_item_from_tree(rmap_item);
592 free_rmap_item(rmap_item);
597 * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather
598 * than check every pte of a given vma, the locking doesn't quite work for
599 * that - an rmap_item is assigned to the stable tree after inserting ksm
600 * page and upping mmap_sem. Nor does it fit with the way we skip dup'ing
601 * rmap_items from parent to child at fork time (so as not to waste time
602 * if exit comes before the next scan reaches it).
604 * Similarly, although we'd like to remove rmap_items (so updating counts
605 * and freeing memory) when unmerging an area, it's easier to leave that
606 * to the next pass of ksmd - consider, for example, how ksmd might be
607 * in cmp_and_merge_page on one of the rmap_items we would be removing.
609 static int unmerge_ksm_pages(struct vm_area_struct *vma,
610 unsigned long start, unsigned long end)
612 unsigned long addr;
613 int err = 0;
615 for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
616 if (ksm_test_exit(vma->vm_mm))
617 break;
618 if (signal_pending(current))
619 err = -ERESTARTSYS;
620 else
621 err = break_ksm(vma, addr);
623 return err;
626 #ifdef CONFIG_SYSFS
628 * Only called through the sysfs control interface:
630 static int unmerge_and_remove_all_rmap_items(void)
632 struct mm_slot *mm_slot;
633 struct mm_struct *mm;
634 struct vm_area_struct *vma;
635 int err = 0;
637 spin_lock(&ksm_mmlist_lock);
638 ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
639 struct mm_slot, mm_list);
640 spin_unlock(&ksm_mmlist_lock);
642 for (mm_slot = ksm_scan.mm_slot;
643 mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
644 mm = mm_slot->mm;
645 down_read(&mm->mmap_sem);
646 for (vma = mm->mmap; vma; vma = vma->vm_next) {
647 if (ksm_test_exit(mm))
648 break;
649 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
650 continue;
651 err = unmerge_ksm_pages(vma,
652 vma->vm_start, vma->vm_end);
653 if (err)
654 goto error;
657 remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
659 spin_lock(&ksm_mmlist_lock);
660 ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
661 struct mm_slot, mm_list);
662 if (ksm_test_exit(mm)) {
663 hlist_del(&mm_slot->link);
664 list_del(&mm_slot->mm_list);
665 spin_unlock(&ksm_mmlist_lock);
667 free_mm_slot(mm_slot);
668 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
669 up_read(&mm->mmap_sem);
670 mmdrop(mm);
671 } else {
672 spin_unlock(&ksm_mmlist_lock);
673 up_read(&mm->mmap_sem);
677 ksm_scan.seqnr = 0;
678 return 0;
680 error:
681 up_read(&mm->mmap_sem);
682 spin_lock(&ksm_mmlist_lock);
683 ksm_scan.mm_slot = &ksm_mm_head;
684 spin_unlock(&ksm_mmlist_lock);
685 return err;
687 #endif /* CONFIG_SYSFS */
689 static u32 calc_checksum(struct page *page)
691 u32 checksum;
692 void *addr = kmap_atomic(page, KM_USER0);
693 checksum = jhash2(addr, PAGE_SIZE / 4, 17);
694 kunmap_atomic(addr, KM_USER0);
695 return checksum;
698 static int memcmp_pages(struct page *page1, struct page *page2)
700 char *addr1, *addr2;
701 int ret;
703 addr1 = kmap_atomic(page1, KM_USER0);
704 addr2 = kmap_atomic(page2, KM_USER1);
705 ret = memcmp(addr1, addr2, PAGE_SIZE);
706 kunmap_atomic(addr2, KM_USER1);
707 kunmap_atomic(addr1, KM_USER0);
708 return ret;
711 static inline int pages_identical(struct page *page1, struct page *page2)
713 return !memcmp_pages(page1, page2);
716 static int write_protect_page(struct vm_area_struct *vma, struct page *page,
717 pte_t *orig_pte)
719 struct mm_struct *mm = vma->vm_mm;
720 unsigned long addr;
721 pte_t *ptep;
722 spinlock_t *ptl;
723 int swapped;
724 int err = -EFAULT;
726 addr = page_address_in_vma(page, vma);
727 if (addr == -EFAULT)
728 goto out;
730 ptep = page_check_address(page, mm, addr, &ptl, 0);
731 if (!ptep)
732 goto out;
734 if (pte_write(*ptep)) {
735 pte_t entry;
737 swapped = PageSwapCache(page);
738 flush_cache_page(vma, addr, page_to_pfn(page));
740 * Ok this is tricky, when get_user_pages_fast() run it doesnt
741 * take any lock, therefore the check that we are going to make
742 * with the pagecount against the mapcount is racey and
743 * O_DIRECT can happen right after the check.
744 * So we clear the pte and flush the tlb before the check
745 * this assure us that no O_DIRECT can happen after the check
746 * or in the middle of the check.
748 entry = ptep_clear_flush(vma, addr, ptep);
750 * Check that no O_DIRECT or similar I/O is in progress on the
751 * page
753 if (page_mapcount(page) + 1 + swapped != page_count(page)) {
754 set_pte_at(mm, addr, ptep, entry);
755 goto out_unlock;
757 entry = pte_wrprotect(entry);
758 set_pte_at_notify(mm, addr, ptep, entry);
760 *orig_pte = *ptep;
761 err = 0;
763 out_unlock:
764 pte_unmap_unlock(ptep, ptl);
765 out:
766 return err;
770 * replace_page - replace page in vma by new ksm page
771 * @vma: vma that holds the pte pointing to page
772 * @page: the page we are replacing by kpage
773 * @kpage: the ksm page we replace page by
774 * @orig_pte: the original value of the pte
776 * Returns 0 on success, -EFAULT on failure.
778 static int replace_page(struct vm_area_struct *vma, struct page *page,
779 struct page *kpage, pte_t orig_pte)
781 struct mm_struct *mm = vma->vm_mm;
782 pgd_t *pgd;
783 pud_t *pud;
784 pmd_t *pmd;
785 pte_t *ptep;
786 spinlock_t *ptl;
787 unsigned long addr;
788 int err = -EFAULT;
790 addr = page_address_in_vma(page, vma);
791 if (addr == -EFAULT)
792 goto out;
794 pgd = pgd_offset(mm, addr);
795 if (!pgd_present(*pgd))
796 goto out;
798 pud = pud_offset(pgd, addr);
799 if (!pud_present(*pud))
800 goto out;
802 pmd = pmd_offset(pud, addr);
803 if (!pmd_present(*pmd))
804 goto out;
806 ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
807 if (!pte_same(*ptep, orig_pte)) {
808 pte_unmap_unlock(ptep, ptl);
809 goto out;
812 get_page(kpage);
813 page_add_anon_rmap(kpage, vma, addr);
815 flush_cache_page(vma, addr, pte_pfn(*ptep));
816 ptep_clear_flush(vma, addr, ptep);
817 set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
819 page_remove_rmap(page);
820 put_page(page);
822 pte_unmap_unlock(ptep, ptl);
823 err = 0;
824 out:
825 return err;
829 * try_to_merge_one_page - take two pages and merge them into one
830 * @vma: the vma that holds the pte pointing to page
831 * @page: the PageAnon page that we want to replace with kpage
832 * @kpage: the PageKsm page that we want to map instead of page,
833 * or NULL the first time when we want to use page as kpage.
835 * This function returns 0 if the pages were merged, -EFAULT otherwise.
837 static int try_to_merge_one_page(struct vm_area_struct *vma,
838 struct page *page, struct page *kpage)
840 pte_t orig_pte = __pte(0);
841 int err = -EFAULT;
843 if (page == kpage) /* ksm page forked */
844 return 0;
846 if (!(vma->vm_flags & VM_MERGEABLE))
847 goto out;
848 if (!PageAnon(page))
849 goto out;
852 * We need the page lock to read a stable PageSwapCache in
853 * write_protect_page(). We use trylock_page() instead of
854 * lock_page() because we don't want to wait here - we
855 * prefer to continue scanning and merging different pages,
856 * then come back to this page when it is unlocked.
858 if (!trylock_page(page))
859 goto out;
861 * If this anonymous page is mapped only here, its pte may need
862 * to be write-protected. If it's mapped elsewhere, all of its
863 * ptes are necessarily already write-protected. But in either
864 * case, we need to lock and check page_count is not raised.
866 if (write_protect_page(vma, page, &orig_pte) == 0) {
867 if (!kpage) {
869 * While we hold page lock, upgrade page from
870 * PageAnon+anon_vma to PageKsm+NULL stable_node:
871 * stable_tree_insert() will update stable_node.
873 set_page_stable_node(page, NULL);
874 mark_page_accessed(page);
875 err = 0;
876 } else if (pages_identical(page, kpage))
877 err = replace_page(vma, page, kpage, orig_pte);
880 if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
881 munlock_vma_page(page);
882 if (!PageMlocked(kpage)) {
883 unlock_page(page);
884 lock_page(kpage);
885 mlock_vma_page(kpage);
886 page = kpage; /* for final unlock */
890 unlock_page(page);
891 out:
892 return err;
896 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
897 * but no new kernel page is allocated: kpage must already be a ksm page.
899 * This function returns 0 if the pages were merged, -EFAULT otherwise.
901 static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
902 struct page *page, struct page *kpage)
904 struct mm_struct *mm = rmap_item->mm;
905 struct vm_area_struct *vma;
906 int err = -EFAULT;
908 down_read(&mm->mmap_sem);
909 if (ksm_test_exit(mm))
910 goto out;
911 vma = find_vma(mm, rmap_item->address);
912 if (!vma || vma->vm_start > rmap_item->address)
913 goto out;
915 err = try_to_merge_one_page(vma, page, kpage);
916 if (err)
917 goto out;
919 /* Must get reference to anon_vma while still holding mmap_sem */
920 hold_anon_vma(rmap_item, vma->anon_vma);
921 out:
922 up_read(&mm->mmap_sem);
923 return err;
927 * try_to_merge_two_pages - take two identical pages and prepare them
928 * to be merged into one page.
930 * This function returns the kpage if we successfully merged two identical
931 * pages into one ksm page, NULL otherwise.
933 * Note that this function upgrades page to ksm page: if one of the pages
934 * is already a ksm page, try_to_merge_with_ksm_page should be used.
936 static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
937 struct page *page,
938 struct rmap_item *tree_rmap_item,
939 struct page *tree_page)
941 int err;
943 err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
944 if (!err) {
945 err = try_to_merge_with_ksm_page(tree_rmap_item,
946 tree_page, page);
948 * If that fails, we have a ksm page with only one pte
949 * pointing to it: so break it.
951 if (err)
952 break_cow(rmap_item);
954 return err ? NULL : page;
958 * stable_tree_search - search for page inside the stable tree
960 * This function checks if there is a page inside the stable tree
961 * with identical content to the page that we are scanning right now.
963 * This function returns the stable tree node of identical content if found,
964 * NULL otherwise.
966 static struct page *stable_tree_search(struct page *page)
968 struct rb_node *node = root_stable_tree.rb_node;
969 struct stable_node *stable_node;
971 stable_node = page_stable_node(page);
972 if (stable_node) { /* ksm page forked */
973 get_page(page);
974 return page;
977 while (node) {
978 struct page *tree_page;
979 int ret;
981 cond_resched();
982 stable_node = rb_entry(node, struct stable_node, node);
983 tree_page = get_ksm_page(stable_node);
984 if (!tree_page)
985 return NULL;
987 ret = memcmp_pages(page, tree_page);
989 if (ret < 0) {
990 put_page(tree_page);
991 node = node->rb_left;
992 } else if (ret > 0) {
993 put_page(tree_page);
994 node = node->rb_right;
995 } else
996 return tree_page;
999 return NULL;
1003 * stable_tree_insert - insert rmap_item pointing to new ksm page
1004 * into the stable tree.
1006 * This function returns the stable tree node just allocated on success,
1007 * NULL otherwise.
1009 static struct stable_node *stable_tree_insert(struct page *kpage)
1011 struct rb_node **new = &root_stable_tree.rb_node;
1012 struct rb_node *parent = NULL;
1013 struct stable_node *stable_node;
1015 while (*new) {
1016 struct page *tree_page;
1017 int ret;
1019 cond_resched();
1020 stable_node = rb_entry(*new, struct stable_node, node);
1021 tree_page = get_ksm_page(stable_node);
1022 if (!tree_page)
1023 return NULL;
1025 ret = memcmp_pages(kpage, tree_page);
1026 put_page(tree_page);
1028 parent = *new;
1029 if (ret < 0)
1030 new = &parent->rb_left;
1031 else if (ret > 0)
1032 new = &parent->rb_right;
1033 else {
1035 * It is not a bug that stable_tree_search() didn't
1036 * find this node: because at that time our page was
1037 * not yet write-protected, so may have changed since.
1039 return NULL;
1043 stable_node = alloc_stable_node();
1044 if (!stable_node)
1045 return NULL;
1047 rb_link_node(&stable_node->node, parent, new);
1048 rb_insert_color(&stable_node->node, &root_stable_tree);
1050 INIT_HLIST_HEAD(&stable_node->hlist);
1052 stable_node->kpfn = page_to_pfn(kpage);
1053 set_page_stable_node(kpage, stable_node);
1055 return stable_node;
1059 * unstable_tree_search_insert - search for identical page,
1060 * else insert rmap_item into the unstable tree.
1062 * This function searches for a page in the unstable tree identical to the
1063 * page currently being scanned; and if no identical page is found in the
1064 * tree, we insert rmap_item as a new object into the unstable tree.
1066 * This function returns pointer to rmap_item found to be identical
1067 * to the currently scanned page, NULL otherwise.
1069 * This function does both searching and inserting, because they share
1070 * the same walking algorithm in an rbtree.
1072 static
1073 struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1074 struct page *page,
1075 struct page **tree_pagep)
1078 struct rb_node **new = &root_unstable_tree.rb_node;
1079 struct rb_node *parent = NULL;
1081 while (*new) {
1082 struct rmap_item *tree_rmap_item;
1083 struct page *tree_page;
1084 int ret;
1086 cond_resched();
1087 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1088 tree_page = get_mergeable_page(tree_rmap_item);
1089 if (IS_ERR_OR_NULL(tree_page))
1090 return NULL;
1093 * Don't substitute a ksm page for a forked page.
1095 if (page == tree_page) {
1096 put_page(tree_page);
1097 return NULL;
1100 ret = memcmp_pages(page, tree_page);
1102 parent = *new;
1103 if (ret < 0) {
1104 put_page(tree_page);
1105 new = &parent->rb_left;
1106 } else if (ret > 0) {
1107 put_page(tree_page);
1108 new = &parent->rb_right;
1109 } else {
1110 *tree_pagep = tree_page;
1111 return tree_rmap_item;
1115 rmap_item->address |= UNSTABLE_FLAG;
1116 rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1117 rb_link_node(&rmap_item->node, parent, new);
1118 rb_insert_color(&rmap_item->node, &root_unstable_tree);
1120 ksm_pages_unshared++;
1121 return NULL;
1125 * stable_tree_append - add another rmap_item to the linked list of
1126 * rmap_items hanging off a given node of the stable tree, all sharing
1127 * the same ksm page.
1129 static void stable_tree_append(struct rmap_item *rmap_item,
1130 struct stable_node *stable_node)
1132 rmap_item->head = stable_node;
1133 rmap_item->address |= STABLE_FLAG;
1134 hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
1136 if (rmap_item->hlist.next)
1137 ksm_pages_sharing++;
1138 else
1139 ksm_pages_shared++;
1143 * cmp_and_merge_page - first see if page can be merged into the stable tree;
1144 * if not, compare checksum to previous and if it's the same, see if page can
1145 * be inserted into the unstable tree, or merged with a page already there and
1146 * both transferred to the stable tree.
1148 * @page: the page that we are searching identical page to.
1149 * @rmap_item: the reverse mapping into the virtual address of this page
1151 static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1153 struct rmap_item *tree_rmap_item;
1154 struct page *tree_page = NULL;
1155 struct stable_node *stable_node;
1156 struct page *kpage;
1157 unsigned int checksum;
1158 int err;
1160 remove_rmap_item_from_tree(rmap_item);
1162 /* We first start with searching the page inside the stable tree */
1163 kpage = stable_tree_search(page);
1164 if (kpage) {
1165 err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
1166 if (!err) {
1168 * The page was successfully merged:
1169 * add its rmap_item to the stable tree.
1171 lock_page(kpage);
1172 stable_tree_append(rmap_item, page_stable_node(kpage));
1173 unlock_page(kpage);
1175 put_page(kpage);
1176 return;
1180 * If the hash value of the page has changed from the last time
1181 * we calculated it, this page is changing frequently: therefore we
1182 * don't want to insert it in the unstable tree, and we don't want
1183 * to waste our time searching for something identical to it there.
1185 checksum = calc_checksum(page);
1186 if (rmap_item->oldchecksum != checksum) {
1187 rmap_item->oldchecksum = checksum;
1188 return;
1191 tree_rmap_item =
1192 unstable_tree_search_insert(rmap_item, page, &tree_page);
1193 if (tree_rmap_item) {
1194 kpage = try_to_merge_two_pages(rmap_item, page,
1195 tree_rmap_item, tree_page);
1196 put_page(tree_page);
1198 * As soon as we merge this page, we want to remove the
1199 * rmap_item of the page we have merged with from the unstable
1200 * tree, and insert it instead as new node in the stable tree.
1202 if (kpage) {
1203 remove_rmap_item_from_tree(tree_rmap_item);
1205 lock_page(kpage);
1206 stable_node = stable_tree_insert(kpage);
1207 if (stable_node) {
1208 stable_tree_append(tree_rmap_item, stable_node);
1209 stable_tree_append(rmap_item, stable_node);
1211 unlock_page(kpage);
1214 * If we fail to insert the page into the stable tree,
1215 * we will have 2 virtual addresses that are pointing
1216 * to a ksm page left outside the stable tree,
1217 * in which case we need to break_cow on both.
1219 if (!stable_node) {
1220 break_cow(tree_rmap_item);
1221 break_cow(rmap_item);
1227 static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
1228 struct rmap_item **rmap_list,
1229 unsigned long addr)
1231 struct rmap_item *rmap_item;
1233 while (*rmap_list) {
1234 rmap_item = *rmap_list;
1235 if ((rmap_item->address & PAGE_MASK) == addr)
1236 return rmap_item;
1237 if (rmap_item->address > addr)
1238 break;
1239 *rmap_list = rmap_item->rmap_list;
1240 remove_rmap_item_from_tree(rmap_item);
1241 free_rmap_item(rmap_item);
1244 rmap_item = alloc_rmap_item();
1245 if (rmap_item) {
1246 /* It has already been zeroed */
1247 rmap_item->mm = mm_slot->mm;
1248 rmap_item->address = addr;
1249 rmap_item->rmap_list = *rmap_list;
1250 *rmap_list = rmap_item;
1252 return rmap_item;
1255 static struct rmap_item *scan_get_next_rmap_item(struct page **page)
1257 struct mm_struct *mm;
1258 struct mm_slot *slot;
1259 struct vm_area_struct *vma;
1260 struct rmap_item *rmap_item;
1262 if (list_empty(&ksm_mm_head.mm_list))
1263 return NULL;
1265 slot = ksm_scan.mm_slot;
1266 if (slot == &ksm_mm_head) {
1267 root_unstable_tree = RB_ROOT;
1269 spin_lock(&ksm_mmlist_lock);
1270 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1271 ksm_scan.mm_slot = slot;
1272 spin_unlock(&ksm_mmlist_lock);
1273 next_mm:
1274 ksm_scan.address = 0;
1275 ksm_scan.rmap_list = &slot->rmap_list;
1278 mm = slot->mm;
1279 down_read(&mm->mmap_sem);
1280 if (ksm_test_exit(mm))
1281 vma = NULL;
1282 else
1283 vma = find_vma(mm, ksm_scan.address);
1285 for (; vma; vma = vma->vm_next) {
1286 if (!(vma->vm_flags & VM_MERGEABLE))
1287 continue;
1288 if (ksm_scan.address < vma->vm_start)
1289 ksm_scan.address = vma->vm_start;
1290 if (!vma->anon_vma)
1291 ksm_scan.address = vma->vm_end;
1293 while (ksm_scan.address < vma->vm_end) {
1294 if (ksm_test_exit(mm))
1295 break;
1296 *page = follow_page(vma, ksm_scan.address, FOLL_GET);
1297 if (!IS_ERR_OR_NULL(*page) && PageAnon(*page)) {
1298 flush_anon_page(vma, *page, ksm_scan.address);
1299 flush_dcache_page(*page);
1300 rmap_item = get_next_rmap_item(slot,
1301 ksm_scan.rmap_list, ksm_scan.address);
1302 if (rmap_item) {
1303 ksm_scan.rmap_list =
1304 &rmap_item->rmap_list;
1305 ksm_scan.address += PAGE_SIZE;
1306 } else
1307 put_page(*page);
1308 up_read(&mm->mmap_sem);
1309 return rmap_item;
1311 if (!IS_ERR_OR_NULL(*page))
1312 put_page(*page);
1313 ksm_scan.address += PAGE_SIZE;
1314 cond_resched();
1318 if (ksm_test_exit(mm)) {
1319 ksm_scan.address = 0;
1320 ksm_scan.rmap_list = &slot->rmap_list;
1323 * Nuke all the rmap_items that are above this current rmap:
1324 * because there were no VM_MERGEABLE vmas with such addresses.
1326 remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
1328 spin_lock(&ksm_mmlist_lock);
1329 ksm_scan.mm_slot = list_entry(slot->mm_list.next,
1330 struct mm_slot, mm_list);
1331 if (ksm_scan.address == 0) {
1333 * We've completed a full scan of all vmas, holding mmap_sem
1334 * throughout, and found no VM_MERGEABLE: so do the same as
1335 * __ksm_exit does to remove this mm from all our lists now.
1336 * This applies either when cleaning up after __ksm_exit
1337 * (but beware: we can reach here even before __ksm_exit),
1338 * or when all VM_MERGEABLE areas have been unmapped (and
1339 * mmap_sem then protects against race with MADV_MERGEABLE).
1341 hlist_del(&slot->link);
1342 list_del(&slot->mm_list);
1343 spin_unlock(&ksm_mmlist_lock);
1345 free_mm_slot(slot);
1346 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1347 up_read(&mm->mmap_sem);
1348 mmdrop(mm);
1349 } else {
1350 spin_unlock(&ksm_mmlist_lock);
1351 up_read(&mm->mmap_sem);
1354 /* Repeat until we've completed scanning the whole list */
1355 slot = ksm_scan.mm_slot;
1356 if (slot != &ksm_mm_head)
1357 goto next_mm;
1359 ksm_scan.seqnr++;
1360 return NULL;
1364 * ksm_do_scan - the ksm scanner main worker function.
1365 * @scan_npages - number of pages we want to scan before we return.
1367 static void ksm_do_scan(unsigned int scan_npages)
1369 struct rmap_item *rmap_item;
1370 struct page *uninitialized_var(page);
1372 while (scan_npages--) {
1373 cond_resched();
1374 rmap_item = scan_get_next_rmap_item(&page);
1375 if (!rmap_item)
1376 return;
1377 if (!PageKsm(page) || !in_stable_tree(rmap_item))
1378 cmp_and_merge_page(page, rmap_item);
1379 put_page(page);
1383 static int ksmd_should_run(void)
1385 return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1388 static int ksm_scan_thread(void *nothing)
1390 set_user_nice(current, 5);
1392 while (!kthread_should_stop()) {
1393 mutex_lock(&ksm_thread_mutex);
1394 if (ksmd_should_run())
1395 ksm_do_scan(ksm_thread_pages_to_scan);
1396 mutex_unlock(&ksm_thread_mutex);
1398 if (ksmd_should_run()) {
1399 schedule_timeout_interruptible(
1400 msecs_to_jiffies(ksm_thread_sleep_millisecs));
1401 } else {
1402 wait_event_interruptible(ksm_thread_wait,
1403 ksmd_should_run() || kthread_should_stop());
1406 return 0;
1409 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1410 unsigned long end, int advice, unsigned long *vm_flags)
1412 struct mm_struct *mm = vma->vm_mm;
1413 int err;
1415 switch (advice) {
1416 case MADV_MERGEABLE:
1418 * Be somewhat over-protective for now!
1420 if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE |
1421 VM_PFNMAP | VM_IO | VM_DONTEXPAND |
1422 VM_RESERVED | VM_HUGETLB | VM_INSERTPAGE |
1423 VM_NONLINEAR | VM_MIXEDMAP | VM_SAO))
1424 return 0; /* just ignore the advice */
1426 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
1427 err = __ksm_enter(mm);
1428 if (err)
1429 return err;
1432 *vm_flags |= VM_MERGEABLE;
1433 break;
1435 case MADV_UNMERGEABLE:
1436 if (!(*vm_flags & VM_MERGEABLE))
1437 return 0; /* just ignore the advice */
1439 if (vma->anon_vma) {
1440 err = unmerge_ksm_pages(vma, start, end);
1441 if (err)
1442 return err;
1445 *vm_flags &= ~VM_MERGEABLE;
1446 break;
1449 return 0;
1452 int __ksm_enter(struct mm_struct *mm)
1454 struct mm_slot *mm_slot;
1455 int needs_wakeup;
1457 mm_slot = alloc_mm_slot();
1458 if (!mm_slot)
1459 return -ENOMEM;
1461 /* Check ksm_run too? Would need tighter locking */
1462 needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1464 spin_lock(&ksm_mmlist_lock);
1465 insert_to_mm_slots_hash(mm, mm_slot);
1467 * Insert just behind the scanning cursor, to let the area settle
1468 * down a little; when fork is followed by immediate exec, we don't
1469 * want ksmd to waste time setting up and tearing down an rmap_list.
1471 list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
1472 spin_unlock(&ksm_mmlist_lock);
1474 set_bit(MMF_VM_MERGEABLE, &mm->flags);
1475 atomic_inc(&mm->mm_count);
1477 if (needs_wakeup)
1478 wake_up_interruptible(&ksm_thread_wait);
1480 return 0;
1483 void __ksm_exit(struct mm_struct *mm)
1485 struct mm_slot *mm_slot;
1486 int easy_to_free = 0;
1489 * This process is exiting: if it's straightforward (as is the
1490 * case when ksmd was never running), free mm_slot immediately.
1491 * But if it's at the cursor or has rmap_items linked to it, use
1492 * mmap_sem to synchronize with any break_cows before pagetables
1493 * are freed, and leave the mm_slot on the list for ksmd to free.
1494 * Beware: ksm may already have noticed it exiting and freed the slot.
1497 spin_lock(&ksm_mmlist_lock);
1498 mm_slot = get_mm_slot(mm);
1499 if (mm_slot && ksm_scan.mm_slot != mm_slot) {
1500 if (!mm_slot->rmap_list) {
1501 hlist_del(&mm_slot->link);
1502 list_del(&mm_slot->mm_list);
1503 easy_to_free = 1;
1504 } else {
1505 list_move(&mm_slot->mm_list,
1506 &ksm_scan.mm_slot->mm_list);
1509 spin_unlock(&ksm_mmlist_lock);
1511 if (easy_to_free) {
1512 free_mm_slot(mm_slot);
1513 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1514 mmdrop(mm);
1515 } else if (mm_slot) {
1516 down_write(&mm->mmap_sem);
1517 up_write(&mm->mmap_sem);
1521 struct page *ksm_does_need_to_copy(struct page *page,
1522 struct vm_area_struct *vma, unsigned long address)
1524 struct page *new_page;
1526 unlock_page(page); /* any racers will COW it, not modify it */
1528 new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
1529 if (new_page) {
1530 copy_user_highpage(new_page, page, address, vma);
1532 SetPageDirty(new_page);
1533 __SetPageUptodate(new_page);
1534 SetPageSwapBacked(new_page);
1535 __set_page_locked(new_page);
1537 if (page_evictable(new_page, vma))
1538 lru_cache_add_lru(new_page, LRU_ACTIVE_ANON);
1539 else
1540 add_page_to_unevictable_list(new_page);
1543 page_cache_release(page);
1544 return new_page;
1547 int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg,
1548 unsigned long *vm_flags)
1550 struct stable_node *stable_node;
1551 struct rmap_item *rmap_item;
1552 struct hlist_node *hlist;
1553 unsigned int mapcount = page_mapcount(page);
1554 int referenced = 0;
1555 int search_new_forks = 0;
1557 VM_BUG_ON(!PageKsm(page));
1558 VM_BUG_ON(!PageLocked(page));
1560 stable_node = page_stable_node(page);
1561 if (!stable_node)
1562 return 0;
1563 again:
1564 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1565 struct anon_vma *anon_vma = rmap_item->anon_vma;
1566 struct anon_vma_chain *vmac;
1567 struct vm_area_struct *vma;
1569 spin_lock(&anon_vma->lock);
1570 list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1571 vma = vmac->vma;
1572 if (rmap_item->address < vma->vm_start ||
1573 rmap_item->address >= vma->vm_end)
1574 continue;
1576 * Initially we examine only the vma which covers this
1577 * rmap_item; but later, if there is still work to do,
1578 * we examine covering vmas in other mms: in case they
1579 * were forked from the original since ksmd passed.
1581 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1582 continue;
1584 if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
1585 continue;
1587 referenced += page_referenced_one(page, vma,
1588 rmap_item->address, &mapcount, vm_flags);
1589 if (!search_new_forks || !mapcount)
1590 break;
1592 spin_unlock(&anon_vma->lock);
1593 if (!mapcount)
1594 goto out;
1596 if (!search_new_forks++)
1597 goto again;
1598 out:
1599 return referenced;
1602 int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
1604 struct stable_node *stable_node;
1605 struct hlist_node *hlist;
1606 struct rmap_item *rmap_item;
1607 int ret = SWAP_AGAIN;
1608 int search_new_forks = 0;
1610 VM_BUG_ON(!PageKsm(page));
1611 VM_BUG_ON(!PageLocked(page));
1613 stable_node = page_stable_node(page);
1614 if (!stable_node)
1615 return SWAP_FAIL;
1616 again:
1617 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1618 struct anon_vma *anon_vma = rmap_item->anon_vma;
1619 struct anon_vma_chain *vmac;
1620 struct vm_area_struct *vma;
1622 spin_lock(&anon_vma->lock);
1623 list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1624 vma = vmac->vma;
1625 if (rmap_item->address < vma->vm_start ||
1626 rmap_item->address >= vma->vm_end)
1627 continue;
1629 * Initially we examine only the vma which covers this
1630 * rmap_item; but later, if there is still work to do,
1631 * we examine covering vmas in other mms: in case they
1632 * were forked from the original since ksmd passed.
1634 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1635 continue;
1637 ret = try_to_unmap_one(page, vma,
1638 rmap_item->address, flags);
1639 if (ret != SWAP_AGAIN || !page_mapped(page)) {
1640 spin_unlock(&anon_vma->lock);
1641 goto out;
1644 spin_unlock(&anon_vma->lock);
1646 if (!search_new_forks++)
1647 goto again;
1648 out:
1649 return ret;
1652 #ifdef CONFIG_MIGRATION
1653 int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *,
1654 struct vm_area_struct *, unsigned long, void *), void *arg)
1656 struct stable_node *stable_node;
1657 struct hlist_node *hlist;
1658 struct rmap_item *rmap_item;
1659 int ret = SWAP_AGAIN;
1660 int search_new_forks = 0;
1662 VM_BUG_ON(!PageKsm(page));
1663 VM_BUG_ON(!PageLocked(page));
1665 stable_node = page_stable_node(page);
1666 if (!stable_node)
1667 return ret;
1668 again:
1669 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1670 struct anon_vma *anon_vma = rmap_item->anon_vma;
1671 struct anon_vma_chain *vmac;
1672 struct vm_area_struct *vma;
1674 spin_lock(&anon_vma->lock);
1675 list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1676 vma = vmac->vma;
1677 if (rmap_item->address < vma->vm_start ||
1678 rmap_item->address >= vma->vm_end)
1679 continue;
1681 * Initially we examine only the vma which covers this
1682 * rmap_item; but later, if there is still work to do,
1683 * we examine covering vmas in other mms: in case they
1684 * were forked from the original since ksmd passed.
1686 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1687 continue;
1689 ret = rmap_one(page, vma, rmap_item->address, arg);
1690 if (ret != SWAP_AGAIN) {
1691 spin_unlock(&anon_vma->lock);
1692 goto out;
1695 spin_unlock(&anon_vma->lock);
1697 if (!search_new_forks++)
1698 goto again;
1699 out:
1700 return ret;
1703 void ksm_migrate_page(struct page *newpage, struct page *oldpage)
1705 struct stable_node *stable_node;
1707 VM_BUG_ON(!PageLocked(oldpage));
1708 VM_BUG_ON(!PageLocked(newpage));
1709 VM_BUG_ON(newpage->mapping != oldpage->mapping);
1711 stable_node = page_stable_node(newpage);
1712 if (stable_node) {
1713 VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage));
1714 stable_node->kpfn = page_to_pfn(newpage);
1717 #endif /* CONFIG_MIGRATION */
1719 #ifdef CONFIG_MEMORY_HOTREMOVE
1720 static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn,
1721 unsigned long end_pfn)
1723 struct rb_node *node;
1725 for (node = rb_first(&root_stable_tree); node; node = rb_next(node)) {
1726 struct stable_node *stable_node;
1728 stable_node = rb_entry(node, struct stable_node, node);
1729 if (stable_node->kpfn >= start_pfn &&
1730 stable_node->kpfn < end_pfn)
1731 return stable_node;
1733 return NULL;
1736 static int ksm_memory_callback(struct notifier_block *self,
1737 unsigned long action, void *arg)
1739 struct memory_notify *mn = arg;
1740 struct stable_node *stable_node;
1742 switch (action) {
1743 case MEM_GOING_OFFLINE:
1745 * Keep it very simple for now: just lock out ksmd and
1746 * MADV_UNMERGEABLE while any memory is going offline.
1748 mutex_lock(&ksm_thread_mutex);
1749 break;
1751 case MEM_OFFLINE:
1753 * Most of the work is done by page migration; but there might
1754 * be a few stable_nodes left over, still pointing to struct
1755 * pages which have been offlined: prune those from the tree.
1757 while ((stable_node = ksm_check_stable_tree(mn->start_pfn,
1758 mn->start_pfn + mn->nr_pages)) != NULL)
1759 remove_node_from_stable_tree(stable_node);
1760 /* fallthrough */
1762 case MEM_CANCEL_OFFLINE:
1763 mutex_unlock(&ksm_thread_mutex);
1764 break;
1766 return NOTIFY_OK;
1768 #endif /* CONFIG_MEMORY_HOTREMOVE */
1770 #ifdef CONFIG_SYSFS
1772 * This all compiles without CONFIG_SYSFS, but is a waste of space.
1775 #define KSM_ATTR_RO(_name) \
1776 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
1777 #define KSM_ATTR(_name) \
1778 static struct kobj_attribute _name##_attr = \
1779 __ATTR(_name, 0644, _name##_show, _name##_store)
1781 static ssize_t sleep_millisecs_show(struct kobject *kobj,
1782 struct kobj_attribute *attr, char *buf)
1784 return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
1787 static ssize_t sleep_millisecs_store(struct kobject *kobj,
1788 struct kobj_attribute *attr,
1789 const char *buf, size_t count)
1791 unsigned long msecs;
1792 int err;
1794 err = strict_strtoul(buf, 10, &msecs);
1795 if (err || msecs > UINT_MAX)
1796 return -EINVAL;
1798 ksm_thread_sleep_millisecs = msecs;
1800 return count;
1802 KSM_ATTR(sleep_millisecs);
1804 static ssize_t pages_to_scan_show(struct kobject *kobj,
1805 struct kobj_attribute *attr, char *buf)
1807 return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
1810 static ssize_t pages_to_scan_store(struct kobject *kobj,
1811 struct kobj_attribute *attr,
1812 const char *buf, size_t count)
1814 int err;
1815 unsigned long nr_pages;
1817 err = strict_strtoul(buf, 10, &nr_pages);
1818 if (err || nr_pages > UINT_MAX)
1819 return -EINVAL;
1821 ksm_thread_pages_to_scan = nr_pages;
1823 return count;
1825 KSM_ATTR(pages_to_scan);
1827 static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
1828 char *buf)
1830 return sprintf(buf, "%u\n", ksm_run);
1833 static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
1834 const char *buf, size_t count)
1836 int err;
1837 unsigned long flags;
1839 err = strict_strtoul(buf, 10, &flags);
1840 if (err || flags > UINT_MAX)
1841 return -EINVAL;
1842 if (flags > KSM_RUN_UNMERGE)
1843 return -EINVAL;
1846 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
1847 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
1848 * breaking COW to free the pages_shared (but leaves mm_slots
1849 * on the list for when ksmd may be set running again).
1852 mutex_lock(&ksm_thread_mutex);
1853 if (ksm_run != flags) {
1854 ksm_run = flags;
1855 if (flags & KSM_RUN_UNMERGE) {
1856 current->flags |= PF_OOM_ORIGIN;
1857 err = unmerge_and_remove_all_rmap_items();
1858 current->flags &= ~PF_OOM_ORIGIN;
1859 if (err) {
1860 ksm_run = KSM_RUN_STOP;
1861 count = err;
1865 mutex_unlock(&ksm_thread_mutex);
1867 if (flags & KSM_RUN_MERGE)
1868 wake_up_interruptible(&ksm_thread_wait);
1870 return count;
1872 KSM_ATTR(run);
1874 static ssize_t pages_shared_show(struct kobject *kobj,
1875 struct kobj_attribute *attr, char *buf)
1877 return sprintf(buf, "%lu\n", ksm_pages_shared);
1879 KSM_ATTR_RO(pages_shared);
1881 static ssize_t pages_sharing_show(struct kobject *kobj,
1882 struct kobj_attribute *attr, char *buf)
1884 return sprintf(buf, "%lu\n", ksm_pages_sharing);
1886 KSM_ATTR_RO(pages_sharing);
1888 static ssize_t pages_unshared_show(struct kobject *kobj,
1889 struct kobj_attribute *attr, char *buf)
1891 return sprintf(buf, "%lu\n", ksm_pages_unshared);
1893 KSM_ATTR_RO(pages_unshared);
1895 static ssize_t pages_volatile_show(struct kobject *kobj,
1896 struct kobj_attribute *attr, char *buf)
1898 long ksm_pages_volatile;
1900 ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
1901 - ksm_pages_sharing - ksm_pages_unshared;
1903 * It was not worth any locking to calculate that statistic,
1904 * but it might therefore sometimes be negative: conceal that.
1906 if (ksm_pages_volatile < 0)
1907 ksm_pages_volatile = 0;
1908 return sprintf(buf, "%ld\n", ksm_pages_volatile);
1910 KSM_ATTR_RO(pages_volatile);
1912 static ssize_t full_scans_show(struct kobject *kobj,
1913 struct kobj_attribute *attr, char *buf)
1915 return sprintf(buf, "%lu\n", ksm_scan.seqnr);
1917 KSM_ATTR_RO(full_scans);
1919 static struct attribute *ksm_attrs[] = {
1920 &sleep_millisecs_attr.attr,
1921 &pages_to_scan_attr.attr,
1922 &run_attr.attr,
1923 &pages_shared_attr.attr,
1924 &pages_sharing_attr.attr,
1925 &pages_unshared_attr.attr,
1926 &pages_volatile_attr.attr,
1927 &full_scans_attr.attr,
1928 NULL,
1931 static struct attribute_group ksm_attr_group = {
1932 .attrs = ksm_attrs,
1933 .name = "ksm",
1935 #endif /* CONFIG_SYSFS */
1937 static int __init ksm_init(void)
1939 struct task_struct *ksm_thread;
1940 int err;
1942 err = ksm_slab_init();
1943 if (err)
1944 goto out;
1946 err = mm_slots_hash_init();
1947 if (err)
1948 goto out_free1;
1950 ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
1951 if (IS_ERR(ksm_thread)) {
1952 printk(KERN_ERR "ksm: creating kthread failed\n");
1953 err = PTR_ERR(ksm_thread);
1954 goto out_free2;
1957 #ifdef CONFIG_SYSFS
1958 err = sysfs_create_group(mm_kobj, &ksm_attr_group);
1959 if (err) {
1960 printk(KERN_ERR "ksm: register sysfs failed\n");
1961 kthread_stop(ksm_thread);
1962 goto out_free2;
1964 #else
1965 ksm_run = KSM_RUN_MERGE; /* no way for user to start it */
1967 #endif /* CONFIG_SYSFS */
1969 #ifdef CONFIG_MEMORY_HOTREMOVE
1971 * Choose a high priority since the callback takes ksm_thread_mutex:
1972 * later callbacks could only be taking locks which nest within that.
1974 hotplug_memory_notifier(ksm_memory_callback, 100);
1975 #endif
1976 return 0;
1978 out_free2:
1979 mm_slots_hash_free();
1980 out_free1:
1981 ksm_slab_free();
1982 out:
1983 return err;
1985 module_init(ksm_init)