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.
14 * This work is licensed under the terms of the GNU GPL, version 2.
17 #include <linux/errno.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>
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.)
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
88 struct hlist_node link;
89 struct list_head mm_list;
90 struct rmap_item *rmap_list;
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.
104 struct mm_slot *mm_slot;
105 unsigned long address;
106 struct rmap_item **rmap_list;
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
118 struct hlist_head hlist;
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
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 */
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 /* Limit on the number of unswappable pages used */
183 static unsigned long ksm_max_kernel_pages;
185 /* Number of pages ksmd should scan in one batch */
186 static unsigned int ksm_thread_pages_to_scan = 100;
188 /* Milliseconds ksmd should sleep between batches */
189 static unsigned int ksm_thread_sleep_millisecs = 20;
191 #define KSM_RUN_STOP 0
192 #define KSM_RUN_MERGE 1
193 #define KSM_RUN_UNMERGE 2
194 static unsigned int ksm_run = KSM_RUN_STOP;
196 static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
197 static DEFINE_MUTEX(ksm_thread_mutex);
198 static DEFINE_SPINLOCK(ksm_mmlist_lock);
200 #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
201 sizeof(struct __struct), __alignof__(struct __struct),\
204 static int __init ksm_slab_init(void)
206 rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
207 if (!rmap_item_cache)
210 stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
211 if (!stable_node_cache)
214 mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
221 kmem_cache_destroy(stable_node_cache);
223 kmem_cache_destroy(rmap_item_cache);
228 static void __init ksm_slab_free(void)
230 kmem_cache_destroy(mm_slot_cache);
231 kmem_cache_destroy(stable_node_cache);
232 kmem_cache_destroy(rmap_item_cache);
233 mm_slot_cache = NULL;
236 static inline struct rmap_item *alloc_rmap_item(void)
238 struct rmap_item *rmap_item;
240 rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
246 static inline void free_rmap_item(struct rmap_item *rmap_item)
249 rmap_item->mm = NULL; /* debug safety */
250 kmem_cache_free(rmap_item_cache, rmap_item);
253 static inline struct stable_node *alloc_stable_node(void)
255 return kmem_cache_alloc(stable_node_cache, GFP_KERNEL);
258 static inline void free_stable_node(struct stable_node *stable_node)
260 kmem_cache_free(stable_node_cache, stable_node);
263 static inline struct mm_slot *alloc_mm_slot(void)
265 if (!mm_slot_cache) /* initialization failed */
267 return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
270 static inline void free_mm_slot(struct mm_slot *mm_slot)
272 kmem_cache_free(mm_slot_cache, mm_slot);
275 static int __init mm_slots_hash_init(void)
277 mm_slots_hash = kzalloc(MM_SLOTS_HASH_HEADS * sizeof(struct hlist_head),
284 static void __init mm_slots_hash_free(void)
286 kfree(mm_slots_hash);
289 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
291 struct mm_slot *mm_slot;
292 struct hlist_head *bucket;
293 struct hlist_node *node;
295 bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
296 % MM_SLOTS_HASH_HEADS];
297 hlist_for_each_entry(mm_slot, node, bucket, link) {
298 if (mm == mm_slot->mm)
304 static void insert_to_mm_slots_hash(struct mm_struct *mm,
305 struct mm_slot *mm_slot)
307 struct hlist_head *bucket;
309 bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
310 % MM_SLOTS_HASH_HEADS];
312 hlist_add_head(&mm_slot->link, bucket);
315 static inline int in_stable_tree(struct rmap_item *rmap_item)
317 return rmap_item->address & STABLE_FLAG;
320 static void hold_anon_vma(struct rmap_item *rmap_item,
321 struct anon_vma *anon_vma)
323 rmap_item->anon_vma = anon_vma;
324 atomic_inc(&anon_vma->ksm_refcount);
327 static void drop_anon_vma(struct rmap_item *rmap_item)
329 struct anon_vma *anon_vma = rmap_item->anon_vma;
331 if (atomic_dec_and_lock(&anon_vma->ksm_refcount, &anon_vma->lock)) {
332 int empty = list_empty(&anon_vma->head);
333 spin_unlock(&anon_vma->lock);
335 anon_vma_free(anon_vma);
340 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
341 * page tables after it has passed through ksm_exit() - which, if necessary,
342 * takes mmap_sem briefly to serialize against them. ksm_exit() does not set
343 * a special flag: they can just back out as soon as mm_users goes to zero.
344 * ksm_test_exit() is used throughout to make this test for exit: in some
345 * places for correctness, in some places just to avoid unnecessary work.
347 static inline bool ksm_test_exit(struct mm_struct *mm)
349 return atomic_read(&mm->mm_users) == 0;
353 * We use break_ksm to break COW on a ksm page: it's a stripped down
355 * if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
358 * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
359 * in case the application has unmapped and remapped mm,addr meanwhile.
360 * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP
361 * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
363 static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
370 page = follow_page(vma, addr, FOLL_GET);
374 ret = handle_mm_fault(vma->vm_mm, vma, addr,
377 ret = VM_FAULT_WRITE;
379 } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM)));
381 * We must loop because handle_mm_fault() may back out if there's
382 * any difficulty e.g. if pte accessed bit gets updated concurrently.
384 * VM_FAULT_WRITE is what we have been hoping for: it indicates that
385 * COW has been broken, even if the vma does not permit VM_WRITE;
386 * but note that a concurrent fault might break PageKsm for us.
388 * VM_FAULT_SIGBUS could occur if we race with truncation of the
389 * backing file, which also invalidates anonymous pages: that's
390 * okay, that truncation will have unmapped the PageKsm for us.
392 * VM_FAULT_OOM: at the time of writing (late July 2009), setting
393 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
394 * current task has TIF_MEMDIE set, and will be OOM killed on return
395 * to user; and ksmd, having no mm, would never be chosen for that.
397 * But if the mm is in a limited mem_cgroup, then the fault may fail
398 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
399 * even ksmd can fail in this way - though it's usually breaking ksm
400 * just to undo a merge it made a moment before, so unlikely to oom.
402 * That's a pity: we might therefore have more kernel pages allocated
403 * than we're counting as nodes in the stable tree; but ksm_do_scan
404 * will retry to break_cow on each pass, so should recover the page
405 * in due course. The important thing is to not let VM_MERGEABLE
406 * be cleared while any such pages might remain in the area.
408 return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
411 static void break_cow(struct rmap_item *rmap_item)
413 struct mm_struct *mm = rmap_item->mm;
414 unsigned long addr = rmap_item->address;
415 struct vm_area_struct *vma;
418 * It is not an accident that whenever we want to break COW
419 * to undo, we also need to drop a reference to the anon_vma.
421 drop_anon_vma(rmap_item);
423 down_read(&mm->mmap_sem);
424 if (ksm_test_exit(mm))
426 vma = find_vma(mm, addr);
427 if (!vma || vma->vm_start > addr)
429 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
431 break_ksm(vma, addr);
433 up_read(&mm->mmap_sem);
436 static struct page *get_mergeable_page(struct rmap_item *rmap_item)
438 struct mm_struct *mm = rmap_item->mm;
439 unsigned long addr = rmap_item->address;
440 struct vm_area_struct *vma;
443 down_read(&mm->mmap_sem);
444 if (ksm_test_exit(mm))
446 vma = find_vma(mm, addr);
447 if (!vma || vma->vm_start > addr)
449 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
452 page = follow_page(vma, addr, FOLL_GET);
455 if (PageAnon(page)) {
456 flush_anon_page(vma, page, addr);
457 flush_dcache_page(page);
462 up_read(&mm->mmap_sem);
466 static void remove_node_from_stable_tree(struct stable_node *stable_node)
468 struct rmap_item *rmap_item;
469 struct hlist_node *hlist;
471 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
472 if (rmap_item->hlist.next)
476 drop_anon_vma(rmap_item);
477 rmap_item->address &= PAGE_MASK;
481 rb_erase(&stable_node->node, &root_stable_tree);
482 free_stable_node(stable_node);
486 * get_ksm_page: checks if the page indicated by the stable node
487 * is still its ksm page, despite having held no reference to it.
488 * In which case we can trust the content of the page, and it
489 * returns the gotten page; but if the page has now been zapped,
490 * remove the stale node from the stable tree and return NULL.
492 * You would expect the stable_node to hold a reference to the ksm page.
493 * But if it increments the page's count, swapping out has to wait for
494 * ksmd to come around again before it can free the page, which may take
495 * seconds or even minutes: much too unresponsive. So instead we use a
496 * "keyhole reference": access to the ksm page from the stable node peeps
497 * out through its keyhole to see if that page still holds the right key,
498 * pointing back to this stable node. This relies on freeing a PageAnon
499 * page to reset its page->mapping to NULL, and relies on no other use of
500 * a page to put something that might look like our key in page->mapping.
502 * include/linux/pagemap.h page_cache_get_speculative() is a good reference,
503 * but this is different - made simpler by ksm_thread_mutex being held, but
504 * interesting for assuming that no other use of the struct page could ever
505 * put our expected_mapping into page->mapping (or a field of the union which
506 * coincides with page->mapping). The RCU calls are not for KSM at all, but
507 * to keep the page_count protocol described with page_cache_get_speculative.
509 * Note: it is possible that get_ksm_page() will return NULL one moment,
510 * then page the next, if the page is in between page_freeze_refs() and
511 * page_unfreeze_refs(): this shouldn't be a problem anywhere, the page
512 * is on its way to being freed; but it is an anomaly to bear in mind.
514 static struct page *get_ksm_page(struct stable_node *stable_node)
517 void *expected_mapping;
519 page = pfn_to_page(stable_node->kpfn);
520 expected_mapping = (void *)stable_node +
521 (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
523 if (page->mapping != expected_mapping)
525 if (!get_page_unless_zero(page))
527 if (page->mapping != expected_mapping) {
535 remove_node_from_stable_tree(stable_node);
540 * Removing rmap_item from stable or unstable tree.
541 * This function will clean the information from the stable/unstable tree.
543 static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
545 if (rmap_item->address & STABLE_FLAG) {
546 struct stable_node *stable_node;
549 stable_node = rmap_item->head;
550 page = get_ksm_page(stable_node);
555 hlist_del(&rmap_item->hlist);
559 if (stable_node->hlist.first)
564 drop_anon_vma(rmap_item);
565 rmap_item->address &= PAGE_MASK;
567 } else if (rmap_item->address & UNSTABLE_FLAG) {
570 * Usually ksmd can and must skip the rb_erase, because
571 * root_unstable_tree was already reset to RB_ROOT.
572 * But be careful when an mm is exiting: do the rb_erase
573 * if this rmap_item was inserted by this scan, rather
574 * than left over from before.
576 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
579 rb_erase(&rmap_item->node, &root_unstable_tree);
581 ksm_pages_unshared--;
582 rmap_item->address &= PAGE_MASK;
585 cond_resched(); /* we're called from many long loops */
588 static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
589 struct rmap_item **rmap_list)
592 struct rmap_item *rmap_item = *rmap_list;
593 *rmap_list = rmap_item->rmap_list;
594 remove_rmap_item_from_tree(rmap_item);
595 free_rmap_item(rmap_item);
600 * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather
601 * than check every pte of a given vma, the locking doesn't quite work for
602 * that - an rmap_item is assigned to the stable tree after inserting ksm
603 * page and upping mmap_sem. Nor does it fit with the way we skip dup'ing
604 * rmap_items from parent to child at fork time (so as not to waste time
605 * if exit comes before the next scan reaches it).
607 * Similarly, although we'd like to remove rmap_items (so updating counts
608 * and freeing memory) when unmerging an area, it's easier to leave that
609 * to the next pass of ksmd - consider, for example, how ksmd might be
610 * in cmp_and_merge_page on one of the rmap_items we would be removing.
612 static int unmerge_ksm_pages(struct vm_area_struct *vma,
613 unsigned long start, unsigned long end)
618 for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
619 if (ksm_test_exit(vma->vm_mm))
621 if (signal_pending(current))
624 err = break_ksm(vma, addr);
631 * Only called through the sysfs control interface:
633 static int unmerge_and_remove_all_rmap_items(void)
635 struct mm_slot *mm_slot;
636 struct mm_struct *mm;
637 struct vm_area_struct *vma;
640 spin_lock(&ksm_mmlist_lock);
641 ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
642 struct mm_slot, mm_list);
643 spin_unlock(&ksm_mmlist_lock);
645 for (mm_slot = ksm_scan.mm_slot;
646 mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
648 down_read(&mm->mmap_sem);
649 for (vma = mm->mmap; vma; vma = vma->vm_next) {
650 if (ksm_test_exit(mm))
652 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
654 err = unmerge_ksm_pages(vma,
655 vma->vm_start, vma->vm_end);
660 remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
662 spin_lock(&ksm_mmlist_lock);
663 ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
664 struct mm_slot, mm_list);
665 if (ksm_test_exit(mm)) {
666 hlist_del(&mm_slot->link);
667 list_del(&mm_slot->mm_list);
668 spin_unlock(&ksm_mmlist_lock);
670 free_mm_slot(mm_slot);
671 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
672 up_read(&mm->mmap_sem);
675 spin_unlock(&ksm_mmlist_lock);
676 up_read(&mm->mmap_sem);
684 up_read(&mm->mmap_sem);
685 spin_lock(&ksm_mmlist_lock);
686 ksm_scan.mm_slot = &ksm_mm_head;
687 spin_unlock(&ksm_mmlist_lock);
690 #endif /* CONFIG_SYSFS */
692 static u32 calc_checksum(struct page *page)
695 void *addr = kmap_atomic(page, KM_USER0);
696 checksum = jhash2(addr, PAGE_SIZE / 4, 17);
697 kunmap_atomic(addr, KM_USER0);
701 static int memcmp_pages(struct page *page1, struct page *page2)
706 addr1 = kmap_atomic(page1, KM_USER0);
707 addr2 = kmap_atomic(page2, KM_USER1);
708 ret = memcmp(addr1, addr2, PAGE_SIZE);
709 kunmap_atomic(addr2, KM_USER1);
710 kunmap_atomic(addr1, KM_USER0);
714 static inline int pages_identical(struct page *page1, struct page *page2)
716 return !memcmp_pages(page1, page2);
719 static int write_protect_page(struct vm_area_struct *vma, struct page *page,
722 struct mm_struct *mm = vma->vm_mm;
729 addr = page_address_in_vma(page, vma);
733 ptep = page_check_address(page, mm, addr, &ptl, 0);
737 if (pte_write(*ptep)) {
740 swapped = PageSwapCache(page);
741 flush_cache_page(vma, addr, page_to_pfn(page));
743 * Ok this is tricky, when get_user_pages_fast() run it doesnt
744 * take any lock, therefore the check that we are going to make
745 * with the pagecount against the mapcount is racey and
746 * O_DIRECT can happen right after the check.
747 * So we clear the pte and flush the tlb before the check
748 * this assure us that no O_DIRECT can happen after the check
749 * or in the middle of the check.
751 entry = ptep_clear_flush(vma, addr, ptep);
753 * Check that no O_DIRECT or similar I/O is in progress on the
756 if (page_mapcount(page) + 1 + swapped != page_count(page)) {
757 set_pte_at_notify(mm, addr, ptep, entry);
760 entry = pte_wrprotect(entry);
761 set_pte_at_notify(mm, addr, ptep, entry);
767 pte_unmap_unlock(ptep, ptl);
773 * replace_page - replace page in vma by new ksm page
774 * @vma: vma that holds the pte pointing to page
775 * @page: the page we are replacing by kpage
776 * @kpage: the ksm page we replace page by
777 * @orig_pte: the original value of the pte
779 * Returns 0 on success, -EFAULT on failure.
781 static int replace_page(struct vm_area_struct *vma, struct page *page,
782 struct page *kpage, pte_t orig_pte)
784 struct mm_struct *mm = vma->vm_mm;
793 addr = page_address_in_vma(page, vma);
797 pgd = pgd_offset(mm, addr);
798 if (!pgd_present(*pgd))
801 pud = pud_offset(pgd, addr);
802 if (!pud_present(*pud))
805 pmd = pmd_offset(pud, addr);
806 if (!pmd_present(*pmd))
809 ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
810 if (!pte_same(*ptep, orig_pte)) {
811 pte_unmap_unlock(ptep, ptl);
816 page_add_anon_rmap(kpage, vma, addr);
818 flush_cache_page(vma, addr, pte_pfn(*ptep));
819 ptep_clear_flush(vma, addr, ptep);
820 set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
822 page_remove_rmap(page);
825 pte_unmap_unlock(ptep, ptl);
832 * try_to_merge_one_page - take two pages and merge them into one
833 * @vma: the vma that holds the pte pointing to page
834 * @page: the PageAnon page that we want to replace with kpage
835 * @kpage: the PageKsm page that we want to map instead of page,
836 * or NULL the first time when we want to use page as kpage.
838 * This function returns 0 if the pages were merged, -EFAULT otherwise.
840 static int try_to_merge_one_page(struct vm_area_struct *vma,
841 struct page *page, struct page *kpage)
843 pte_t orig_pte = __pte(0);
846 if (page == kpage) /* ksm page forked */
849 if (!(vma->vm_flags & VM_MERGEABLE))
855 * We need the page lock to read a stable PageSwapCache in
856 * write_protect_page(). We use trylock_page() instead of
857 * lock_page() because we don't want to wait here - we
858 * prefer to continue scanning and merging different pages,
859 * then come back to this page when it is unlocked.
861 if (!trylock_page(page))
864 * If this anonymous page is mapped only here, its pte may need
865 * to be write-protected. If it's mapped elsewhere, all of its
866 * ptes are necessarily already write-protected. But in either
867 * case, we need to lock and check page_count is not raised.
869 if (write_protect_page(vma, page, &orig_pte) == 0) {
872 * While we hold page lock, upgrade page from
873 * PageAnon+anon_vma to PageKsm+NULL stable_node:
874 * stable_tree_insert() will update stable_node.
876 set_page_stable_node(page, NULL);
877 mark_page_accessed(page);
879 } else if (pages_identical(page, kpage))
880 err = replace_page(vma, page, kpage, orig_pte);
883 if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
884 munlock_vma_page(page);
885 if (!PageMlocked(kpage)) {
888 mlock_vma_page(kpage);
889 page = kpage; /* for final unlock */
899 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
900 * but no new kernel page is allocated: kpage must already be a ksm page.
902 * This function returns 0 if the pages were merged, -EFAULT otherwise.
904 static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
905 struct page *page, struct page *kpage)
907 struct mm_struct *mm = rmap_item->mm;
908 struct vm_area_struct *vma;
911 down_read(&mm->mmap_sem);
912 if (ksm_test_exit(mm))
914 vma = find_vma(mm, rmap_item->address);
915 if (!vma || vma->vm_start > rmap_item->address)
918 err = try_to_merge_one_page(vma, page, kpage);
922 /* Must get reference to anon_vma while still holding mmap_sem */
923 hold_anon_vma(rmap_item, vma->anon_vma);
925 up_read(&mm->mmap_sem);
930 * try_to_merge_two_pages - take two identical pages and prepare them
931 * to be merged into one page.
933 * This function returns the kpage if we successfully merged two identical
934 * pages into one ksm page, NULL otherwise.
936 * Note that this function upgrades page to ksm page: if one of the pages
937 * is already a ksm page, try_to_merge_with_ksm_page should be used.
939 static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
941 struct rmap_item *tree_rmap_item,
942 struct page *tree_page)
947 * The number of nodes in the stable tree
948 * is the number of kernel pages that we hold.
950 if (ksm_max_kernel_pages &&
951 ksm_max_kernel_pages <= ksm_pages_shared)
954 err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
956 err = try_to_merge_with_ksm_page(tree_rmap_item,
959 * If that fails, we have a ksm page with only one pte
960 * pointing to it: so break it.
963 break_cow(rmap_item);
965 return err ? NULL : page;
969 * stable_tree_search - search for page inside the stable tree
971 * This function checks if there is a page inside the stable tree
972 * with identical content to the page that we are scanning right now.
974 * This function returns the stable tree node of identical content if found,
977 static struct page *stable_tree_search(struct page *page)
979 struct rb_node *node = root_stable_tree.rb_node;
980 struct stable_node *stable_node;
982 stable_node = page_stable_node(page);
983 if (stable_node) { /* ksm page forked */
989 struct page *tree_page;
993 stable_node = rb_entry(node, struct stable_node, node);
994 tree_page = get_ksm_page(stable_node);
998 ret = memcmp_pages(page, tree_page);
1001 put_page(tree_page);
1002 node = node->rb_left;
1003 } else if (ret > 0) {
1004 put_page(tree_page);
1005 node = node->rb_right;
1014 * stable_tree_insert - insert rmap_item pointing to new ksm page
1015 * into the stable tree.
1017 * This function returns the stable tree node just allocated on success,
1020 static struct stable_node *stable_tree_insert(struct page *kpage)
1022 struct rb_node **new = &root_stable_tree.rb_node;
1023 struct rb_node *parent = NULL;
1024 struct stable_node *stable_node;
1027 struct page *tree_page;
1031 stable_node = rb_entry(*new, struct stable_node, node);
1032 tree_page = get_ksm_page(stable_node);
1036 ret = memcmp_pages(kpage, tree_page);
1037 put_page(tree_page);
1041 new = &parent->rb_left;
1043 new = &parent->rb_right;
1046 * It is not a bug that stable_tree_search() didn't
1047 * find this node: because at that time our page was
1048 * not yet write-protected, so may have changed since.
1054 stable_node = alloc_stable_node();
1058 rb_link_node(&stable_node->node, parent, new);
1059 rb_insert_color(&stable_node->node, &root_stable_tree);
1061 INIT_HLIST_HEAD(&stable_node->hlist);
1063 stable_node->kpfn = page_to_pfn(kpage);
1064 set_page_stable_node(kpage, stable_node);
1070 * unstable_tree_search_insert - search for identical page,
1071 * else insert rmap_item into the unstable tree.
1073 * This function searches for a page in the unstable tree identical to the
1074 * page currently being scanned; and if no identical page is found in the
1075 * tree, we insert rmap_item as a new object into the unstable tree.
1077 * This function returns pointer to rmap_item found to be identical
1078 * to the currently scanned page, NULL otherwise.
1080 * This function does both searching and inserting, because they share
1081 * the same walking algorithm in an rbtree.
1084 struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1086 struct page **tree_pagep)
1089 struct rb_node **new = &root_unstable_tree.rb_node;
1090 struct rb_node *parent = NULL;
1093 struct rmap_item *tree_rmap_item;
1094 struct page *tree_page;
1098 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1099 tree_page = get_mergeable_page(tree_rmap_item);
1104 * Don't substitute a ksm page for a forked page.
1106 if (page == tree_page) {
1107 put_page(tree_page);
1111 ret = memcmp_pages(page, tree_page);
1115 put_page(tree_page);
1116 new = &parent->rb_left;
1117 } else if (ret > 0) {
1118 put_page(tree_page);
1119 new = &parent->rb_right;
1121 *tree_pagep = tree_page;
1122 return tree_rmap_item;
1126 rmap_item->address |= UNSTABLE_FLAG;
1127 rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1128 rb_link_node(&rmap_item->node, parent, new);
1129 rb_insert_color(&rmap_item->node, &root_unstable_tree);
1131 ksm_pages_unshared++;
1136 * stable_tree_append - add another rmap_item to the linked list of
1137 * rmap_items hanging off a given node of the stable tree, all sharing
1138 * the same ksm page.
1140 static void stable_tree_append(struct rmap_item *rmap_item,
1141 struct stable_node *stable_node)
1143 rmap_item->head = stable_node;
1144 rmap_item->address |= STABLE_FLAG;
1145 hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
1147 if (rmap_item->hlist.next)
1148 ksm_pages_sharing++;
1154 * cmp_and_merge_page - first see if page can be merged into the stable tree;
1155 * if not, compare checksum to previous and if it's the same, see if page can
1156 * be inserted into the unstable tree, or merged with a page already there and
1157 * both transferred to the stable tree.
1159 * @page: the page that we are searching identical page to.
1160 * @rmap_item: the reverse mapping into the virtual address of this page
1162 static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1164 struct rmap_item *tree_rmap_item;
1165 struct page *tree_page = NULL;
1166 struct stable_node *stable_node;
1168 unsigned int checksum;
1171 remove_rmap_item_from_tree(rmap_item);
1173 /* We first start with searching the page inside the stable tree */
1174 kpage = stable_tree_search(page);
1176 err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
1179 * The page was successfully merged:
1180 * add its rmap_item to the stable tree.
1183 stable_tree_append(rmap_item, page_stable_node(kpage));
1191 * If the hash value of the page has changed from the last time
1192 * we calculated it, this page is changing frequently: therefore we
1193 * don't want to insert it in the unstable tree, and we don't want
1194 * to waste our time searching for something identical to it there.
1196 checksum = calc_checksum(page);
1197 if (rmap_item->oldchecksum != checksum) {
1198 rmap_item->oldchecksum = checksum;
1203 unstable_tree_search_insert(rmap_item, page, &tree_page);
1204 if (tree_rmap_item) {
1205 kpage = try_to_merge_two_pages(rmap_item, page,
1206 tree_rmap_item, tree_page);
1207 put_page(tree_page);
1209 * As soon as we merge this page, we want to remove the
1210 * rmap_item of the page we have merged with from the unstable
1211 * tree, and insert it instead as new node in the stable tree.
1214 remove_rmap_item_from_tree(tree_rmap_item);
1217 stable_node = stable_tree_insert(kpage);
1219 stable_tree_append(tree_rmap_item, stable_node);
1220 stable_tree_append(rmap_item, stable_node);
1225 * If we fail to insert the page into the stable tree,
1226 * we will have 2 virtual addresses that are pointing
1227 * to a ksm page left outside the stable tree,
1228 * in which case we need to break_cow on both.
1231 break_cow(tree_rmap_item);
1232 break_cow(rmap_item);
1238 static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
1239 struct rmap_item **rmap_list,
1242 struct rmap_item *rmap_item;
1244 while (*rmap_list) {
1245 rmap_item = *rmap_list;
1246 if ((rmap_item->address & PAGE_MASK) == addr)
1248 if (rmap_item->address > addr)
1250 *rmap_list = rmap_item->rmap_list;
1251 remove_rmap_item_from_tree(rmap_item);
1252 free_rmap_item(rmap_item);
1255 rmap_item = alloc_rmap_item();
1257 /* It has already been zeroed */
1258 rmap_item->mm = mm_slot->mm;
1259 rmap_item->address = addr;
1260 rmap_item->rmap_list = *rmap_list;
1261 *rmap_list = rmap_item;
1266 static struct rmap_item *scan_get_next_rmap_item(struct page **page)
1268 struct mm_struct *mm;
1269 struct mm_slot *slot;
1270 struct vm_area_struct *vma;
1271 struct rmap_item *rmap_item;
1273 if (list_empty(&ksm_mm_head.mm_list))
1276 slot = ksm_scan.mm_slot;
1277 if (slot == &ksm_mm_head) {
1278 root_unstable_tree = RB_ROOT;
1280 spin_lock(&ksm_mmlist_lock);
1281 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1282 ksm_scan.mm_slot = slot;
1283 spin_unlock(&ksm_mmlist_lock);
1285 ksm_scan.address = 0;
1286 ksm_scan.rmap_list = &slot->rmap_list;
1290 down_read(&mm->mmap_sem);
1291 if (ksm_test_exit(mm))
1294 vma = find_vma(mm, ksm_scan.address);
1296 for (; vma; vma = vma->vm_next) {
1297 if (!(vma->vm_flags & VM_MERGEABLE))
1299 if (ksm_scan.address < vma->vm_start)
1300 ksm_scan.address = vma->vm_start;
1302 ksm_scan.address = vma->vm_end;
1304 while (ksm_scan.address < vma->vm_end) {
1305 if (ksm_test_exit(mm))
1307 *page = follow_page(vma, ksm_scan.address, FOLL_GET);
1308 if (*page && PageAnon(*page)) {
1309 flush_anon_page(vma, *page, ksm_scan.address);
1310 flush_dcache_page(*page);
1311 rmap_item = get_next_rmap_item(slot,
1312 ksm_scan.rmap_list, ksm_scan.address);
1314 ksm_scan.rmap_list =
1315 &rmap_item->rmap_list;
1316 ksm_scan.address += PAGE_SIZE;
1319 up_read(&mm->mmap_sem);
1324 ksm_scan.address += PAGE_SIZE;
1329 if (ksm_test_exit(mm)) {
1330 ksm_scan.address = 0;
1331 ksm_scan.rmap_list = &slot->rmap_list;
1334 * Nuke all the rmap_items that are above this current rmap:
1335 * because there were no VM_MERGEABLE vmas with such addresses.
1337 remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
1339 spin_lock(&ksm_mmlist_lock);
1340 ksm_scan.mm_slot = list_entry(slot->mm_list.next,
1341 struct mm_slot, mm_list);
1342 if (ksm_scan.address == 0) {
1344 * We've completed a full scan of all vmas, holding mmap_sem
1345 * throughout, and found no VM_MERGEABLE: so do the same as
1346 * __ksm_exit does to remove this mm from all our lists now.
1347 * This applies either when cleaning up after __ksm_exit
1348 * (but beware: we can reach here even before __ksm_exit),
1349 * or when all VM_MERGEABLE areas have been unmapped (and
1350 * mmap_sem then protects against race with MADV_MERGEABLE).
1352 hlist_del(&slot->link);
1353 list_del(&slot->mm_list);
1354 spin_unlock(&ksm_mmlist_lock);
1357 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1358 up_read(&mm->mmap_sem);
1361 spin_unlock(&ksm_mmlist_lock);
1362 up_read(&mm->mmap_sem);
1365 /* Repeat until we've completed scanning the whole list */
1366 slot = ksm_scan.mm_slot;
1367 if (slot != &ksm_mm_head)
1375 * ksm_do_scan - the ksm scanner main worker function.
1376 * @scan_npages - number of pages we want to scan before we return.
1378 static void ksm_do_scan(unsigned int scan_npages)
1380 struct rmap_item *rmap_item;
1383 while (scan_npages--) {
1385 rmap_item = scan_get_next_rmap_item(&page);
1388 if (!PageKsm(page) || !in_stable_tree(rmap_item))
1389 cmp_and_merge_page(page, rmap_item);
1394 static int ksmd_should_run(void)
1396 return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1399 static int ksm_scan_thread(void *nothing)
1401 set_user_nice(current, 5);
1403 while (!kthread_should_stop()) {
1404 mutex_lock(&ksm_thread_mutex);
1405 if (ksmd_should_run())
1406 ksm_do_scan(ksm_thread_pages_to_scan);
1407 mutex_unlock(&ksm_thread_mutex);
1409 if (ksmd_should_run()) {
1410 schedule_timeout_interruptible(
1411 msecs_to_jiffies(ksm_thread_sleep_millisecs));
1413 wait_event_interruptible(ksm_thread_wait,
1414 ksmd_should_run() || kthread_should_stop());
1420 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1421 unsigned long end, int advice, unsigned long *vm_flags)
1423 struct mm_struct *mm = vma->vm_mm;
1427 case MADV_MERGEABLE:
1429 * Be somewhat over-protective for now!
1431 if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE |
1432 VM_PFNMAP | VM_IO | VM_DONTEXPAND |
1433 VM_RESERVED | VM_HUGETLB | VM_INSERTPAGE |
1434 VM_NONLINEAR | VM_MIXEDMAP | VM_SAO))
1435 return 0; /* just ignore the advice */
1437 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
1438 err = __ksm_enter(mm);
1443 *vm_flags |= VM_MERGEABLE;
1446 case MADV_UNMERGEABLE:
1447 if (!(*vm_flags & VM_MERGEABLE))
1448 return 0; /* just ignore the advice */
1450 if (vma->anon_vma) {
1451 err = unmerge_ksm_pages(vma, start, end);
1456 *vm_flags &= ~VM_MERGEABLE;
1463 int __ksm_enter(struct mm_struct *mm)
1465 struct mm_slot *mm_slot;
1468 mm_slot = alloc_mm_slot();
1472 /* Check ksm_run too? Would need tighter locking */
1473 needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1475 spin_lock(&ksm_mmlist_lock);
1476 insert_to_mm_slots_hash(mm, mm_slot);
1478 * Insert just behind the scanning cursor, to let the area settle
1479 * down a little; when fork is followed by immediate exec, we don't
1480 * want ksmd to waste time setting up and tearing down an rmap_list.
1482 list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
1483 spin_unlock(&ksm_mmlist_lock);
1485 set_bit(MMF_VM_MERGEABLE, &mm->flags);
1486 atomic_inc(&mm->mm_count);
1489 wake_up_interruptible(&ksm_thread_wait);
1494 void __ksm_exit(struct mm_struct *mm)
1496 struct mm_slot *mm_slot;
1497 int easy_to_free = 0;
1500 * This process is exiting: if it's straightforward (as is the
1501 * case when ksmd was never running), free mm_slot immediately.
1502 * But if it's at the cursor or has rmap_items linked to it, use
1503 * mmap_sem to synchronize with any break_cows before pagetables
1504 * are freed, and leave the mm_slot on the list for ksmd to free.
1505 * Beware: ksm may already have noticed it exiting and freed the slot.
1508 spin_lock(&ksm_mmlist_lock);
1509 mm_slot = get_mm_slot(mm);
1510 if (mm_slot && ksm_scan.mm_slot != mm_slot) {
1511 if (!mm_slot->rmap_list) {
1512 hlist_del(&mm_slot->link);
1513 list_del(&mm_slot->mm_list);
1516 list_move(&mm_slot->mm_list,
1517 &ksm_scan.mm_slot->mm_list);
1520 spin_unlock(&ksm_mmlist_lock);
1523 free_mm_slot(mm_slot);
1524 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1526 } else if (mm_slot) {
1527 down_write(&mm->mmap_sem);
1528 up_write(&mm->mmap_sem);
1532 struct page *ksm_does_need_to_copy(struct page *page,
1533 struct vm_area_struct *vma, unsigned long address)
1535 struct page *new_page;
1537 unlock_page(page); /* any racers will COW it, not modify it */
1539 new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
1541 copy_user_highpage(new_page, page, address, vma);
1543 SetPageDirty(new_page);
1544 __SetPageUptodate(new_page);
1545 SetPageSwapBacked(new_page);
1546 __set_page_locked(new_page);
1548 if (page_evictable(new_page, vma))
1549 lru_cache_add_lru(new_page, LRU_ACTIVE_ANON);
1551 add_page_to_unevictable_list(new_page);
1554 page_cache_release(page);
1558 int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg,
1559 unsigned long *vm_flags)
1561 struct stable_node *stable_node;
1562 struct rmap_item *rmap_item;
1563 struct hlist_node *hlist;
1564 unsigned int mapcount = page_mapcount(page);
1566 int search_new_forks = 0;
1568 VM_BUG_ON(!PageKsm(page));
1569 VM_BUG_ON(!PageLocked(page));
1571 stable_node = page_stable_node(page);
1575 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1576 struct anon_vma *anon_vma = rmap_item->anon_vma;
1577 struct vm_area_struct *vma;
1579 spin_lock(&anon_vma->lock);
1580 list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
1581 if (rmap_item->address < vma->vm_start ||
1582 rmap_item->address >= vma->vm_end)
1585 * Initially we examine only the vma which covers this
1586 * rmap_item; but later, if there is still work to do,
1587 * we examine covering vmas in other mms: in case they
1588 * were forked from the original since ksmd passed.
1590 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1593 if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
1596 referenced += page_referenced_one(page, vma,
1597 rmap_item->address, &mapcount, vm_flags);
1598 if (!search_new_forks || !mapcount)
1601 spin_unlock(&anon_vma->lock);
1605 if (!search_new_forks++)
1611 int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
1613 struct stable_node *stable_node;
1614 struct hlist_node *hlist;
1615 struct rmap_item *rmap_item;
1616 int ret = SWAP_AGAIN;
1617 int search_new_forks = 0;
1619 VM_BUG_ON(!PageKsm(page));
1620 VM_BUG_ON(!PageLocked(page));
1622 stable_node = page_stable_node(page);
1626 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1627 struct anon_vma *anon_vma = rmap_item->anon_vma;
1628 struct vm_area_struct *vma;
1630 spin_lock(&anon_vma->lock);
1631 list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
1632 if (rmap_item->address < vma->vm_start ||
1633 rmap_item->address >= vma->vm_end)
1636 * Initially we examine only the vma which covers this
1637 * rmap_item; but later, if there is still work to do,
1638 * we examine covering vmas in other mms: in case they
1639 * were forked from the original since ksmd passed.
1641 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1644 ret = try_to_unmap_one(page, vma,
1645 rmap_item->address, flags);
1646 if (ret != SWAP_AGAIN || !page_mapped(page)) {
1647 spin_unlock(&anon_vma->lock);
1651 spin_unlock(&anon_vma->lock);
1653 if (!search_new_forks++)
1659 #ifdef CONFIG_MIGRATION
1660 int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *,
1661 struct vm_area_struct *, unsigned long, void *), void *arg)
1663 struct stable_node *stable_node;
1664 struct hlist_node *hlist;
1665 struct rmap_item *rmap_item;
1666 int ret = SWAP_AGAIN;
1667 int search_new_forks = 0;
1669 VM_BUG_ON(!PageKsm(page));
1670 VM_BUG_ON(!PageLocked(page));
1672 stable_node = page_stable_node(page);
1676 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1677 struct anon_vma *anon_vma = rmap_item->anon_vma;
1678 struct vm_area_struct *vma;
1680 spin_lock(&anon_vma->lock);
1681 list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
1682 if (rmap_item->address < vma->vm_start ||
1683 rmap_item->address >= vma->vm_end)
1686 * Initially we examine only the vma which covers this
1687 * rmap_item; but later, if there is still work to do,
1688 * we examine covering vmas in other mms: in case they
1689 * were forked from the original since ksmd passed.
1691 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1694 ret = rmap_one(page, vma, rmap_item->address, arg);
1695 if (ret != SWAP_AGAIN) {
1696 spin_unlock(&anon_vma->lock);
1700 spin_unlock(&anon_vma->lock);
1702 if (!search_new_forks++)
1708 void ksm_migrate_page(struct page *newpage, struct page *oldpage)
1710 struct stable_node *stable_node;
1712 VM_BUG_ON(!PageLocked(oldpage));
1713 VM_BUG_ON(!PageLocked(newpage));
1714 VM_BUG_ON(newpage->mapping != oldpage->mapping);
1716 stable_node = page_stable_node(newpage);
1718 VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage));
1719 stable_node->kpfn = page_to_pfn(newpage);
1722 #endif /* CONFIG_MIGRATION */
1724 #ifdef CONFIG_MEMORY_HOTREMOVE
1725 static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn,
1726 unsigned long end_pfn)
1728 struct rb_node *node;
1730 for (node = rb_first(&root_stable_tree); node; node = rb_next(node)) {
1731 struct stable_node *stable_node;
1733 stable_node = rb_entry(node, struct stable_node, node);
1734 if (stable_node->kpfn >= start_pfn &&
1735 stable_node->kpfn < end_pfn)
1741 static int ksm_memory_callback(struct notifier_block *self,
1742 unsigned long action, void *arg)
1744 struct memory_notify *mn = arg;
1745 struct stable_node *stable_node;
1748 case MEM_GOING_OFFLINE:
1750 * Keep it very simple for now: just lock out ksmd and
1751 * MADV_UNMERGEABLE while any memory is going offline.
1753 mutex_lock(&ksm_thread_mutex);
1758 * Most of the work is done by page migration; but there might
1759 * be a few stable_nodes left over, still pointing to struct
1760 * pages which have been offlined: prune those from the tree.
1762 while ((stable_node = ksm_check_stable_tree(mn->start_pfn,
1763 mn->start_pfn + mn->nr_pages)) != NULL)
1764 remove_node_from_stable_tree(stable_node);
1767 case MEM_CANCEL_OFFLINE:
1768 mutex_unlock(&ksm_thread_mutex);
1773 #endif /* CONFIG_MEMORY_HOTREMOVE */
1777 * This all compiles without CONFIG_SYSFS, but is a waste of space.
1780 #define KSM_ATTR_RO(_name) \
1781 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
1782 #define KSM_ATTR(_name) \
1783 static struct kobj_attribute _name##_attr = \
1784 __ATTR(_name, 0644, _name##_show, _name##_store)
1786 static ssize_t sleep_millisecs_show(struct kobject *kobj,
1787 struct kobj_attribute *attr, char *buf)
1789 return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
1792 static ssize_t sleep_millisecs_store(struct kobject *kobj,
1793 struct kobj_attribute *attr,
1794 const char *buf, size_t count)
1796 unsigned long msecs;
1799 err = strict_strtoul(buf, 10, &msecs);
1800 if (err || msecs > UINT_MAX)
1803 ksm_thread_sleep_millisecs = msecs;
1807 KSM_ATTR(sleep_millisecs);
1809 static ssize_t pages_to_scan_show(struct kobject *kobj,
1810 struct kobj_attribute *attr, char *buf)
1812 return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
1815 static ssize_t pages_to_scan_store(struct kobject *kobj,
1816 struct kobj_attribute *attr,
1817 const char *buf, size_t count)
1820 unsigned long nr_pages;
1822 err = strict_strtoul(buf, 10, &nr_pages);
1823 if (err || nr_pages > UINT_MAX)
1826 ksm_thread_pages_to_scan = nr_pages;
1830 KSM_ATTR(pages_to_scan);
1832 static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
1835 return sprintf(buf, "%u\n", ksm_run);
1838 static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
1839 const char *buf, size_t count)
1842 unsigned long flags;
1844 err = strict_strtoul(buf, 10, &flags);
1845 if (err || flags > UINT_MAX)
1847 if (flags > KSM_RUN_UNMERGE)
1851 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
1852 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
1853 * breaking COW to free the unswappable pages_shared (but leaves
1854 * mm_slots on the list for when ksmd may be set running again).
1857 mutex_lock(&ksm_thread_mutex);
1858 if (ksm_run != flags) {
1860 if (flags & KSM_RUN_UNMERGE) {
1861 current->flags |= PF_OOM_ORIGIN;
1862 err = unmerge_and_remove_all_rmap_items();
1863 current->flags &= ~PF_OOM_ORIGIN;
1865 ksm_run = KSM_RUN_STOP;
1870 mutex_unlock(&ksm_thread_mutex);
1872 if (flags & KSM_RUN_MERGE)
1873 wake_up_interruptible(&ksm_thread_wait);
1879 static ssize_t max_kernel_pages_store(struct kobject *kobj,
1880 struct kobj_attribute *attr,
1881 const char *buf, size_t count)
1884 unsigned long nr_pages;
1886 err = strict_strtoul(buf, 10, &nr_pages);
1890 ksm_max_kernel_pages = nr_pages;
1895 static ssize_t max_kernel_pages_show(struct kobject *kobj,
1896 struct kobj_attribute *attr, char *buf)
1898 return sprintf(buf, "%lu\n", ksm_max_kernel_pages);
1900 KSM_ATTR(max_kernel_pages);
1902 static ssize_t pages_shared_show(struct kobject *kobj,
1903 struct kobj_attribute *attr, char *buf)
1905 return sprintf(buf, "%lu\n", ksm_pages_shared);
1907 KSM_ATTR_RO(pages_shared);
1909 static ssize_t pages_sharing_show(struct kobject *kobj,
1910 struct kobj_attribute *attr, char *buf)
1912 return sprintf(buf, "%lu\n", ksm_pages_sharing);
1914 KSM_ATTR_RO(pages_sharing);
1916 static ssize_t pages_unshared_show(struct kobject *kobj,
1917 struct kobj_attribute *attr, char *buf)
1919 return sprintf(buf, "%lu\n", ksm_pages_unshared);
1921 KSM_ATTR_RO(pages_unshared);
1923 static ssize_t pages_volatile_show(struct kobject *kobj,
1924 struct kobj_attribute *attr, char *buf)
1926 long ksm_pages_volatile;
1928 ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
1929 - ksm_pages_sharing - ksm_pages_unshared;
1931 * It was not worth any locking to calculate that statistic,
1932 * but it might therefore sometimes be negative: conceal that.
1934 if (ksm_pages_volatile < 0)
1935 ksm_pages_volatile = 0;
1936 return sprintf(buf, "%ld\n", ksm_pages_volatile);
1938 KSM_ATTR_RO(pages_volatile);
1940 static ssize_t full_scans_show(struct kobject *kobj,
1941 struct kobj_attribute *attr, char *buf)
1943 return sprintf(buf, "%lu\n", ksm_scan.seqnr);
1945 KSM_ATTR_RO(full_scans);
1947 static struct attribute *ksm_attrs[] = {
1948 &sleep_millisecs_attr.attr,
1949 &pages_to_scan_attr.attr,
1951 &max_kernel_pages_attr.attr,
1952 &pages_shared_attr.attr,
1953 &pages_sharing_attr.attr,
1954 &pages_unshared_attr.attr,
1955 &pages_volatile_attr.attr,
1956 &full_scans_attr.attr,
1960 static struct attribute_group ksm_attr_group = {
1964 #endif /* CONFIG_SYSFS */
1966 static int __init ksm_init(void)
1968 struct task_struct *ksm_thread;
1971 ksm_max_kernel_pages = totalram_pages / 4;
1973 err = ksm_slab_init();
1977 err = mm_slots_hash_init();
1981 ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
1982 if (IS_ERR(ksm_thread)) {
1983 printk(KERN_ERR "ksm: creating kthread failed\n");
1984 err = PTR_ERR(ksm_thread);
1989 err = sysfs_create_group(mm_kobj, &ksm_attr_group);
1991 printk(KERN_ERR "ksm: register sysfs failed\n");
1992 kthread_stop(ksm_thread);
1996 ksm_run = KSM_RUN_MERGE; /* no way for user to start it */
1998 #endif /* CONFIG_SYSFS */
2000 #ifdef CONFIG_MEMORY_HOTREMOVE
2002 * Choose a high priority since the callback takes ksm_thread_mutex:
2003 * later callbacks could only be taking locks which nest within that.
2005 hotplug_memory_notifier(ksm_memory_callback, 100);
2010 mm_slots_hash_free();
2016 module_init(ksm_init)