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>
36 #include <linux/hash.h>
38 #include <asm/tlbflush.h>
42 * A few notes about the KSM scanning process,
43 * to make it easier to understand the data structures below:
45 * In order to reduce excessive scanning, KSM sorts the memory pages by their
46 * contents into a data structure that holds pointers to the pages' locations.
48 * Since the contents of the pages may change at any moment, KSM cannot just
49 * insert the pages into a normal sorted tree and expect it to find anything.
50 * Therefore KSM uses two data structures - the stable and the unstable tree.
52 * The stable tree holds pointers to all the merged pages (ksm pages), sorted
53 * by their contents. Because each such page is write-protected, searching on
54 * this tree is fully assured to be working (except when pages are unmapped),
55 * and therefore this tree is called the stable tree.
57 * In addition to the stable tree, KSM uses a second data structure called the
58 * unstable tree: this tree holds pointers to pages which have been found to
59 * be "unchanged for a period of time". The unstable tree sorts these pages
60 * by their contents, but since they are not write-protected, KSM cannot rely
61 * upon the unstable tree to work correctly - the unstable tree is liable to
62 * be corrupted as its contents are modified, and so it is called unstable.
64 * KSM solves this problem by several techniques:
66 * 1) The unstable tree is flushed every time KSM completes scanning all
67 * memory areas, and then the tree is rebuilt again from the beginning.
68 * 2) KSM will only insert into the unstable tree, pages whose hash value
69 * has not changed since the previous scan of all memory areas.
70 * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
71 * colors of the nodes and not on their contents, assuring that even when
72 * the tree gets "corrupted" it won't get out of balance, so scanning time
73 * remains the same (also, searching and inserting nodes in an rbtree uses
74 * the same algorithm, so we have no overhead when we flush and rebuild).
75 * 4) KSM never flushes the stable tree, which means that even if it were to
76 * take 10 attempts to find a page in the unstable tree, once it is found,
77 * it is secured in the stable tree. (When we scan a new page, we first
78 * compare it against the stable tree, and then against the unstable tree.)
82 * struct mm_slot - ksm information per mm that is being scanned
83 * @link: link to the mm_slots hash list
84 * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
85 * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
86 * @mm: the mm that this information is valid for
89 struct hlist_node link;
90 struct list_head mm_list;
91 struct rmap_item *rmap_list;
96 * struct ksm_scan - cursor for scanning
97 * @mm_slot: the current mm_slot we are scanning
98 * @address: the next address inside that to be scanned
99 * @rmap_list: link to the next rmap to be scanned in the rmap_list
100 * @seqnr: count of completed full scans (needed when removing unstable node)
102 * There is only the one ksm_scan instance of this cursor structure.
105 struct mm_slot *mm_slot;
106 unsigned long address;
107 struct rmap_item **rmap_list;
112 * struct stable_node - node of the stable rbtree
113 * @node: rb node of this ksm page in the stable tree
114 * @hlist: hlist head of rmap_items using this ksm page
115 * @kpfn: page frame number of this ksm page
119 struct hlist_head hlist;
124 * struct rmap_item - reverse mapping item for virtual addresses
125 * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
126 * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
127 * @mm: the memory structure this rmap_item is pointing into
128 * @address: the virtual address this rmap_item tracks (+ flags in low bits)
129 * @oldchecksum: previous checksum of the page at that virtual address
130 * @node: rb node of this rmap_item in the unstable tree
131 * @head: pointer to stable_node heading this list in the stable tree
132 * @hlist: link into hlist of rmap_items hanging off that stable_node
135 struct rmap_item *rmap_list;
136 struct anon_vma *anon_vma; /* when stable */
137 struct mm_struct *mm;
138 unsigned long address; /* + low bits used for flags below */
139 unsigned int oldchecksum; /* when unstable */
141 struct rb_node node; /* when node of unstable tree */
142 struct { /* when listed from stable tree */
143 struct stable_node *head;
144 struct hlist_node hlist;
149 #define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */
150 #define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */
151 #define STABLE_FLAG 0x200 /* is listed from the stable tree */
153 /* The stable and unstable tree heads */
154 static struct rb_root root_stable_tree = RB_ROOT;
155 static struct rb_root root_unstable_tree = RB_ROOT;
157 #define MM_SLOTS_HASH_SHIFT 10
158 #define MM_SLOTS_HASH_HEADS (1 << MM_SLOTS_HASH_SHIFT)
159 static struct hlist_head mm_slots_hash[MM_SLOTS_HASH_HEADS];
161 static struct mm_slot ksm_mm_head = {
162 .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
164 static struct ksm_scan ksm_scan = {
165 .mm_slot = &ksm_mm_head,
168 static struct kmem_cache *rmap_item_cache;
169 static struct kmem_cache *stable_node_cache;
170 static struct kmem_cache *mm_slot_cache;
172 /* The number of nodes in the stable tree */
173 static unsigned long ksm_pages_shared;
175 /* The number of page slots additionally sharing those nodes */
176 static unsigned long ksm_pages_sharing;
178 /* The number of nodes in the unstable tree */
179 static unsigned long ksm_pages_unshared;
181 /* The number of rmap_items in use: to calculate pages_volatile */
182 static unsigned long ksm_rmap_items;
184 /* Number of pages ksmd should scan in one batch */
185 static unsigned int ksm_thread_pages_to_scan = 100;
187 /* Milliseconds ksmd should sleep between batches */
188 static unsigned int ksm_thread_sleep_millisecs = 20;
190 #define KSM_RUN_STOP 0
191 #define KSM_RUN_MERGE 1
192 #define KSM_RUN_UNMERGE 2
193 static unsigned int ksm_run = KSM_RUN_STOP;
195 static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
196 static DEFINE_MUTEX(ksm_thread_mutex);
197 static DEFINE_SPINLOCK(ksm_mmlist_lock);
199 #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
200 sizeof(struct __struct), __alignof__(struct __struct),\
203 static int __init ksm_slab_init(void)
205 rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
206 if (!rmap_item_cache)
209 stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
210 if (!stable_node_cache)
213 mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
220 kmem_cache_destroy(stable_node_cache);
222 kmem_cache_destroy(rmap_item_cache);
227 static void __init ksm_slab_free(void)
229 kmem_cache_destroy(mm_slot_cache);
230 kmem_cache_destroy(stable_node_cache);
231 kmem_cache_destroy(rmap_item_cache);
232 mm_slot_cache = NULL;
235 static inline struct rmap_item *alloc_rmap_item(void)
237 struct rmap_item *rmap_item;
239 rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL);
245 static inline void free_rmap_item(struct rmap_item *rmap_item)
248 rmap_item->mm = NULL; /* debug safety */
249 kmem_cache_free(rmap_item_cache, rmap_item);
252 static inline struct stable_node *alloc_stable_node(void)
254 return kmem_cache_alloc(stable_node_cache, GFP_KERNEL);
257 static inline void free_stable_node(struct stable_node *stable_node)
259 kmem_cache_free(stable_node_cache, stable_node);
262 static inline struct mm_slot *alloc_mm_slot(void)
264 if (!mm_slot_cache) /* initialization failed */
266 return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
269 static inline void free_mm_slot(struct mm_slot *mm_slot)
271 kmem_cache_free(mm_slot_cache, mm_slot);
274 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
276 struct mm_slot *mm_slot;
277 struct hlist_head *bucket;
278 struct hlist_node *node;
280 bucket = &mm_slots_hash[hash_ptr(mm, MM_SLOTS_HASH_SHIFT)];
281 hlist_for_each_entry(mm_slot, node, bucket, link) {
282 if (mm == mm_slot->mm)
288 static void insert_to_mm_slots_hash(struct mm_struct *mm,
289 struct mm_slot *mm_slot)
291 struct hlist_head *bucket;
293 bucket = &mm_slots_hash[hash_ptr(mm, MM_SLOTS_HASH_SHIFT)];
295 hlist_add_head(&mm_slot->link, bucket);
298 static inline int in_stable_tree(struct rmap_item *rmap_item)
300 return rmap_item->address & STABLE_FLAG;
303 static void hold_anon_vma(struct rmap_item *rmap_item,
304 struct anon_vma *anon_vma)
306 rmap_item->anon_vma = anon_vma;
307 get_anon_vma(anon_vma);
310 static void ksm_drop_anon_vma(struct rmap_item *rmap_item)
312 struct anon_vma *anon_vma = rmap_item->anon_vma;
314 drop_anon_vma(anon_vma);
318 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
319 * page tables after it has passed through ksm_exit() - which, if necessary,
320 * takes mmap_sem briefly to serialize against them. ksm_exit() does not set
321 * a special flag: they can just back out as soon as mm_users goes to zero.
322 * ksm_test_exit() is used throughout to make this test for exit: in some
323 * places for correctness, in some places just to avoid unnecessary work.
325 static inline bool ksm_test_exit(struct mm_struct *mm)
327 return atomic_read(&mm->mm_users) == 0;
331 * We use break_ksm to break COW on a ksm page: it's a stripped down
333 * if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
336 * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
337 * in case the application has unmapped and remapped mm,addr meanwhile.
338 * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP
339 * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
341 static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
348 page = follow_page(vma, addr, FOLL_GET);
349 if (IS_ERR_OR_NULL(page))
352 ret = handle_mm_fault(vma->vm_mm, vma, addr,
355 ret = VM_FAULT_WRITE;
357 } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM)));
359 * We must loop because handle_mm_fault() may back out if there's
360 * any difficulty e.g. if pte accessed bit gets updated concurrently.
362 * VM_FAULT_WRITE is what we have been hoping for: it indicates that
363 * COW has been broken, even if the vma does not permit VM_WRITE;
364 * but note that a concurrent fault might break PageKsm for us.
366 * VM_FAULT_SIGBUS could occur if we race with truncation of the
367 * backing file, which also invalidates anonymous pages: that's
368 * okay, that truncation will have unmapped the PageKsm for us.
370 * VM_FAULT_OOM: at the time of writing (late July 2009), setting
371 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
372 * current task has TIF_MEMDIE set, and will be OOM killed on return
373 * to user; and ksmd, having no mm, would never be chosen for that.
375 * But if the mm is in a limited mem_cgroup, then the fault may fail
376 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
377 * even ksmd can fail in this way - though it's usually breaking ksm
378 * just to undo a merge it made a moment before, so unlikely to oom.
380 * That's a pity: we might therefore have more kernel pages allocated
381 * than we're counting as nodes in the stable tree; but ksm_do_scan
382 * will retry to break_cow on each pass, so should recover the page
383 * in due course. The important thing is to not let VM_MERGEABLE
384 * be cleared while any such pages might remain in the area.
386 return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
389 static void break_cow(struct rmap_item *rmap_item)
391 struct mm_struct *mm = rmap_item->mm;
392 unsigned long addr = rmap_item->address;
393 struct vm_area_struct *vma;
396 * It is not an accident that whenever we want to break COW
397 * to undo, we also need to drop a reference to the anon_vma.
399 ksm_drop_anon_vma(rmap_item);
401 down_read(&mm->mmap_sem);
402 if (ksm_test_exit(mm))
404 vma = find_vma(mm, addr);
405 if (!vma || vma->vm_start > addr)
407 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
409 break_ksm(vma, addr);
411 up_read(&mm->mmap_sem);
414 static struct page *get_mergeable_page(struct rmap_item *rmap_item)
416 struct mm_struct *mm = rmap_item->mm;
417 unsigned long addr = rmap_item->address;
418 struct vm_area_struct *vma;
421 down_read(&mm->mmap_sem);
422 if (ksm_test_exit(mm))
424 vma = find_vma(mm, addr);
425 if (!vma || vma->vm_start > addr)
427 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
430 page = follow_page(vma, addr, FOLL_GET);
431 if (IS_ERR_OR_NULL(page))
433 if (PageAnon(page) && !PageTransCompound(page)) {
434 flush_anon_page(vma, page, addr);
435 flush_dcache_page(page);
440 up_read(&mm->mmap_sem);
444 static void remove_node_from_stable_tree(struct stable_node *stable_node)
446 struct rmap_item *rmap_item;
447 struct hlist_node *hlist;
449 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
450 if (rmap_item->hlist.next)
454 ksm_drop_anon_vma(rmap_item);
455 rmap_item->address &= PAGE_MASK;
459 rb_erase(&stable_node->node, &root_stable_tree);
460 free_stable_node(stable_node);
464 * get_ksm_page: checks if the page indicated by the stable node
465 * is still its ksm page, despite having held no reference to it.
466 * In which case we can trust the content of the page, and it
467 * returns the gotten page; but if the page has now been zapped,
468 * remove the stale node from the stable tree and return NULL.
470 * You would expect the stable_node to hold a reference to the ksm page.
471 * But if it increments the page's count, swapping out has to wait for
472 * ksmd to come around again before it can free the page, which may take
473 * seconds or even minutes: much too unresponsive. So instead we use a
474 * "keyhole reference": access to the ksm page from the stable node peeps
475 * out through its keyhole to see if that page still holds the right key,
476 * pointing back to this stable node. This relies on freeing a PageAnon
477 * page to reset its page->mapping to NULL, and relies on no other use of
478 * a page to put something that might look like our key in page->mapping.
480 * include/linux/pagemap.h page_cache_get_speculative() is a good reference,
481 * but this is different - made simpler by ksm_thread_mutex being held, but
482 * interesting for assuming that no other use of the struct page could ever
483 * put our expected_mapping into page->mapping (or a field of the union which
484 * coincides with page->mapping). The RCU calls are not for KSM at all, but
485 * to keep the page_count protocol described with page_cache_get_speculative.
487 * Note: it is possible that get_ksm_page() will return NULL one moment,
488 * then page the next, if the page is in between page_freeze_refs() and
489 * page_unfreeze_refs(): this shouldn't be a problem anywhere, the page
490 * is on its way to being freed; but it is an anomaly to bear in mind.
492 static struct page *get_ksm_page(struct stable_node *stable_node)
495 void *expected_mapping;
497 page = pfn_to_page(stable_node->kpfn);
498 expected_mapping = (void *)stable_node +
499 (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
501 if (page->mapping != expected_mapping)
503 if (!get_page_unless_zero(page))
505 if (page->mapping != expected_mapping) {
513 remove_node_from_stable_tree(stable_node);
518 * Removing rmap_item from stable or unstable tree.
519 * This function will clean the information from the stable/unstable tree.
521 static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
523 if (rmap_item->address & STABLE_FLAG) {
524 struct stable_node *stable_node;
527 stable_node = rmap_item->head;
528 page = get_ksm_page(stable_node);
533 hlist_del(&rmap_item->hlist);
537 if (stable_node->hlist.first)
542 ksm_drop_anon_vma(rmap_item);
543 rmap_item->address &= PAGE_MASK;
545 } else if (rmap_item->address & UNSTABLE_FLAG) {
548 * Usually ksmd can and must skip the rb_erase, because
549 * root_unstable_tree was already reset to RB_ROOT.
550 * But be careful when an mm is exiting: do the rb_erase
551 * if this rmap_item was inserted by this scan, rather
552 * than left over from before.
554 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
557 rb_erase(&rmap_item->node, &root_unstable_tree);
559 ksm_pages_unshared--;
560 rmap_item->address &= PAGE_MASK;
563 cond_resched(); /* we're called from many long loops */
566 static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
567 struct rmap_item **rmap_list)
570 struct rmap_item *rmap_item = *rmap_list;
571 *rmap_list = rmap_item->rmap_list;
572 remove_rmap_item_from_tree(rmap_item);
573 free_rmap_item(rmap_item);
578 * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather
579 * than check every pte of a given vma, the locking doesn't quite work for
580 * that - an rmap_item is assigned to the stable tree after inserting ksm
581 * page and upping mmap_sem. Nor does it fit with the way we skip dup'ing
582 * rmap_items from parent to child at fork time (so as not to waste time
583 * if exit comes before the next scan reaches it).
585 * Similarly, although we'd like to remove rmap_items (so updating counts
586 * and freeing memory) when unmerging an area, it's easier to leave that
587 * to the next pass of ksmd - consider, for example, how ksmd might be
588 * in cmp_and_merge_page on one of the rmap_items we would be removing.
590 static int unmerge_ksm_pages(struct vm_area_struct *vma,
591 unsigned long start, unsigned long end)
596 for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
597 if (ksm_test_exit(vma->vm_mm))
599 if (signal_pending(current))
602 err = break_ksm(vma, addr);
609 * Only called through the sysfs control interface:
611 static int unmerge_and_remove_all_rmap_items(void)
613 struct mm_slot *mm_slot;
614 struct mm_struct *mm;
615 struct vm_area_struct *vma;
618 spin_lock(&ksm_mmlist_lock);
619 ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
620 struct mm_slot, mm_list);
621 spin_unlock(&ksm_mmlist_lock);
623 for (mm_slot = ksm_scan.mm_slot;
624 mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
626 down_read(&mm->mmap_sem);
627 for (vma = mm->mmap; vma; vma = vma->vm_next) {
628 if (ksm_test_exit(mm))
630 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
632 err = unmerge_ksm_pages(vma,
633 vma->vm_start, vma->vm_end);
638 remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
640 spin_lock(&ksm_mmlist_lock);
641 ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
642 struct mm_slot, mm_list);
643 if (ksm_test_exit(mm)) {
644 hlist_del(&mm_slot->link);
645 list_del(&mm_slot->mm_list);
646 spin_unlock(&ksm_mmlist_lock);
648 free_mm_slot(mm_slot);
649 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
650 up_read(&mm->mmap_sem);
653 spin_unlock(&ksm_mmlist_lock);
654 up_read(&mm->mmap_sem);
662 up_read(&mm->mmap_sem);
663 spin_lock(&ksm_mmlist_lock);
664 ksm_scan.mm_slot = &ksm_mm_head;
665 spin_unlock(&ksm_mmlist_lock);
668 #endif /* CONFIG_SYSFS */
670 static u32 calc_checksum(struct page *page)
673 void *addr = kmap_atomic(page, KM_USER0);
674 checksum = jhash2(addr, PAGE_SIZE / 4, 17);
675 kunmap_atomic(addr, KM_USER0);
679 static int memcmp_pages(struct page *page1, struct page *page2)
684 addr1 = kmap_atomic(page1, KM_USER0);
685 addr2 = kmap_atomic(page2, KM_USER1);
686 ret = memcmp(addr1, addr2, PAGE_SIZE);
687 kunmap_atomic(addr2, KM_USER1);
688 kunmap_atomic(addr1, KM_USER0);
692 static inline int pages_identical(struct page *page1, struct page *page2)
694 return !memcmp_pages(page1, page2);
697 static int write_protect_page(struct vm_area_struct *vma, struct page *page,
700 struct mm_struct *mm = vma->vm_mm;
707 addr = page_address_in_vma(page, vma);
711 ptep = page_check_address(page, mm, addr, &ptl, 0);
715 if (pte_write(*ptep) || pte_dirty(*ptep)) {
718 swapped = PageSwapCache(page);
719 flush_cache_page(vma, addr, page_to_pfn(page));
721 * Ok this is tricky, when get_user_pages_fast() run it doesnt
722 * take any lock, therefore the check that we are going to make
723 * with the pagecount against the mapcount is racey and
724 * O_DIRECT can happen right after the check.
725 * So we clear the pte and flush the tlb before the check
726 * this assure us that no O_DIRECT can happen after the check
727 * or in the middle of the check.
729 entry = ptep_clear_flush(vma, addr, ptep);
731 * Check that no O_DIRECT or similar I/O is in progress on the
734 if (page_mapcount(page) + 1 + swapped != page_count(page)) {
735 set_pte_at(mm, addr, ptep, entry);
738 if (pte_dirty(entry))
739 set_page_dirty(page);
740 entry = pte_mkclean(pte_wrprotect(entry));
741 set_pte_at_notify(mm, addr, ptep, entry);
747 pte_unmap_unlock(ptep, ptl);
753 * replace_page - replace page in vma by new ksm page
754 * @vma: vma that holds the pte pointing to page
755 * @page: the page we are replacing by kpage
756 * @kpage: the ksm page we replace page by
757 * @orig_pte: the original value of the pte
759 * Returns 0 on success, -EFAULT on failure.
761 static int replace_page(struct vm_area_struct *vma, struct page *page,
762 struct page *kpage, pte_t orig_pte)
764 struct mm_struct *mm = vma->vm_mm;
773 addr = page_address_in_vma(page, vma);
777 pgd = pgd_offset(mm, addr);
778 if (!pgd_present(*pgd))
781 pud = pud_offset(pgd, addr);
782 if (!pud_present(*pud))
785 pmd = pmd_offset(pud, addr);
786 if (!pmd_present(*pmd))
789 ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
790 if (!pte_same(*ptep, orig_pte)) {
791 pte_unmap_unlock(ptep, ptl);
796 page_add_anon_rmap(kpage, vma, addr);
798 flush_cache_page(vma, addr, pte_pfn(*ptep));
799 ptep_clear_flush(vma, addr, ptep);
800 set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
802 page_remove_rmap(page);
803 if (!page_mapped(page))
804 try_to_free_swap(page);
807 pte_unmap_unlock(ptep, ptl);
814 * try_to_merge_one_page - take two pages and merge them into one
815 * @vma: the vma that holds the pte pointing to page
816 * @page: the PageAnon page that we want to replace with kpage
817 * @kpage: the PageKsm page that we want to map instead of page,
818 * or NULL the first time when we want to use page as kpage.
820 * This function returns 0 if the pages were merged, -EFAULT otherwise.
822 static int try_to_merge_one_page(struct vm_area_struct *vma,
823 struct page *page, struct page *kpage)
825 pte_t orig_pte = __pte(0);
828 if (page == kpage) /* ksm page forked */
831 if (!(vma->vm_flags & VM_MERGEABLE))
837 * We need the page lock to read a stable PageSwapCache in
838 * write_protect_page(). We use trylock_page() instead of
839 * lock_page() because we don't want to wait here - we
840 * prefer to continue scanning and merging different pages,
841 * then come back to this page when it is unlocked.
843 if (!trylock_page(page))
846 * If this anonymous page is mapped only here, its pte may need
847 * to be write-protected. If it's mapped elsewhere, all of its
848 * ptes are necessarily already write-protected. But in either
849 * case, we need to lock and check page_count is not raised.
851 if (write_protect_page(vma, page, &orig_pte) == 0) {
854 * While we hold page lock, upgrade page from
855 * PageAnon+anon_vma to PageKsm+NULL stable_node:
856 * stable_tree_insert() will update stable_node.
858 set_page_stable_node(page, NULL);
859 mark_page_accessed(page);
861 } else if (pages_identical(page, kpage))
862 err = replace_page(vma, page, kpage, orig_pte);
865 if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
866 munlock_vma_page(page);
867 if (!PageMlocked(kpage)) {
870 mlock_vma_page(kpage);
871 page = kpage; /* for final unlock */
881 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
882 * but no new kernel page is allocated: kpage must already be a ksm page.
884 * This function returns 0 if the pages were merged, -EFAULT otherwise.
886 static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
887 struct page *page, struct page *kpage)
889 struct mm_struct *mm = rmap_item->mm;
890 struct vm_area_struct *vma;
893 down_read(&mm->mmap_sem);
894 if (ksm_test_exit(mm))
896 vma = find_vma(mm, rmap_item->address);
897 if (!vma || vma->vm_start > rmap_item->address)
900 err = try_to_merge_one_page(vma, page, kpage);
904 /* Must get reference to anon_vma while still holding mmap_sem */
905 hold_anon_vma(rmap_item, vma->anon_vma);
907 up_read(&mm->mmap_sem);
912 * try_to_merge_two_pages - take two identical pages and prepare them
913 * to be merged into one page.
915 * This function returns the kpage if we successfully merged two identical
916 * pages into one ksm page, NULL otherwise.
918 * Note that this function upgrades page to ksm page: if one of the pages
919 * is already a ksm page, try_to_merge_with_ksm_page should be used.
921 static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
923 struct rmap_item *tree_rmap_item,
924 struct page *tree_page)
928 err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
930 err = try_to_merge_with_ksm_page(tree_rmap_item,
933 * If that fails, we have a ksm page with only one pte
934 * pointing to it: so break it.
937 break_cow(rmap_item);
939 return err ? NULL : page;
943 * stable_tree_search - search for page inside the stable tree
945 * This function checks if there is a page inside the stable tree
946 * with identical content to the page that we are scanning right now.
948 * This function returns the stable tree node of identical content if found,
951 static struct page *stable_tree_search(struct page *page)
953 struct rb_node *node = root_stable_tree.rb_node;
954 struct stable_node *stable_node;
956 stable_node = page_stable_node(page);
957 if (stable_node) { /* ksm page forked */
963 struct page *tree_page;
967 stable_node = rb_entry(node, struct stable_node, node);
968 tree_page = get_ksm_page(stable_node);
972 ret = memcmp_pages(page, tree_page);
976 node = node->rb_left;
977 } else if (ret > 0) {
979 node = node->rb_right;
988 * stable_tree_insert - insert rmap_item pointing to new ksm page
989 * into the stable tree.
991 * This function returns the stable tree node just allocated on success,
994 static struct stable_node *stable_tree_insert(struct page *kpage)
996 struct rb_node **new = &root_stable_tree.rb_node;
997 struct rb_node *parent = NULL;
998 struct stable_node *stable_node;
1001 struct page *tree_page;
1005 stable_node = rb_entry(*new, struct stable_node, node);
1006 tree_page = get_ksm_page(stable_node);
1010 ret = memcmp_pages(kpage, tree_page);
1011 put_page(tree_page);
1015 new = &parent->rb_left;
1017 new = &parent->rb_right;
1020 * It is not a bug that stable_tree_search() didn't
1021 * find this node: because at that time our page was
1022 * not yet write-protected, so may have changed since.
1028 stable_node = alloc_stable_node();
1032 rb_link_node(&stable_node->node, parent, new);
1033 rb_insert_color(&stable_node->node, &root_stable_tree);
1035 INIT_HLIST_HEAD(&stable_node->hlist);
1037 stable_node->kpfn = page_to_pfn(kpage);
1038 set_page_stable_node(kpage, stable_node);
1044 * unstable_tree_search_insert - search for identical page,
1045 * else insert rmap_item into the unstable tree.
1047 * This function searches for a page in the unstable tree identical to the
1048 * page currently being scanned; and if no identical page is found in the
1049 * tree, we insert rmap_item as a new object into the unstable tree.
1051 * This function returns pointer to rmap_item found to be identical
1052 * to the currently scanned page, NULL otherwise.
1054 * This function does both searching and inserting, because they share
1055 * the same walking algorithm in an rbtree.
1058 struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1060 struct page **tree_pagep)
1063 struct rb_node **new = &root_unstable_tree.rb_node;
1064 struct rb_node *parent = NULL;
1067 struct rmap_item *tree_rmap_item;
1068 struct page *tree_page;
1072 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1073 tree_page = get_mergeable_page(tree_rmap_item);
1074 if (IS_ERR_OR_NULL(tree_page))
1078 * Don't substitute a ksm page for a forked page.
1080 if (page == tree_page) {
1081 put_page(tree_page);
1085 ret = memcmp_pages(page, tree_page);
1089 put_page(tree_page);
1090 new = &parent->rb_left;
1091 } else if (ret > 0) {
1092 put_page(tree_page);
1093 new = &parent->rb_right;
1095 *tree_pagep = tree_page;
1096 return tree_rmap_item;
1100 rmap_item->address |= UNSTABLE_FLAG;
1101 rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1102 rb_link_node(&rmap_item->node, parent, new);
1103 rb_insert_color(&rmap_item->node, &root_unstable_tree);
1105 ksm_pages_unshared++;
1110 * stable_tree_append - add another rmap_item to the linked list of
1111 * rmap_items hanging off a given node of the stable tree, all sharing
1112 * the same ksm page.
1114 static void stable_tree_append(struct rmap_item *rmap_item,
1115 struct stable_node *stable_node)
1117 rmap_item->head = stable_node;
1118 rmap_item->address |= STABLE_FLAG;
1119 hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
1121 if (rmap_item->hlist.next)
1122 ksm_pages_sharing++;
1128 * cmp_and_merge_page - first see if page can be merged into the stable tree;
1129 * if not, compare checksum to previous and if it's the same, see if page can
1130 * be inserted into the unstable tree, or merged with a page already there and
1131 * both transferred to the stable tree.
1133 * @page: the page that we are searching identical page to.
1134 * @rmap_item: the reverse mapping into the virtual address of this page
1136 static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1138 struct rmap_item *tree_rmap_item;
1139 struct page *tree_page = NULL;
1140 struct stable_node *stable_node;
1142 unsigned int checksum;
1145 remove_rmap_item_from_tree(rmap_item);
1147 /* We first start with searching the page inside the stable tree */
1148 kpage = stable_tree_search(page);
1150 err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
1153 * The page was successfully merged:
1154 * add its rmap_item to the stable tree.
1157 stable_tree_append(rmap_item, page_stable_node(kpage));
1165 * If the hash value of the page has changed from the last time
1166 * we calculated it, this page is changing frequently: therefore we
1167 * don't want to insert it in the unstable tree, and we don't want
1168 * to waste our time searching for something identical to it there.
1170 checksum = calc_checksum(page);
1171 if (rmap_item->oldchecksum != checksum) {
1172 rmap_item->oldchecksum = checksum;
1177 unstable_tree_search_insert(rmap_item, page, &tree_page);
1178 if (tree_rmap_item) {
1179 kpage = try_to_merge_two_pages(rmap_item, page,
1180 tree_rmap_item, tree_page);
1181 put_page(tree_page);
1183 * As soon as we merge this page, we want to remove the
1184 * rmap_item of the page we have merged with from the unstable
1185 * tree, and insert it instead as new node in the stable tree.
1188 remove_rmap_item_from_tree(tree_rmap_item);
1191 stable_node = stable_tree_insert(kpage);
1193 stable_tree_append(tree_rmap_item, stable_node);
1194 stable_tree_append(rmap_item, stable_node);
1199 * If we fail to insert the page into the stable tree,
1200 * we will have 2 virtual addresses that are pointing
1201 * to a ksm page left outside the stable tree,
1202 * in which case we need to break_cow on both.
1205 break_cow(tree_rmap_item);
1206 break_cow(rmap_item);
1212 static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
1213 struct rmap_item **rmap_list,
1216 struct rmap_item *rmap_item;
1218 while (*rmap_list) {
1219 rmap_item = *rmap_list;
1220 if ((rmap_item->address & PAGE_MASK) == addr)
1222 if (rmap_item->address > addr)
1224 *rmap_list = rmap_item->rmap_list;
1225 remove_rmap_item_from_tree(rmap_item);
1226 free_rmap_item(rmap_item);
1229 rmap_item = alloc_rmap_item();
1231 /* It has already been zeroed */
1232 rmap_item->mm = mm_slot->mm;
1233 rmap_item->address = addr;
1234 rmap_item->rmap_list = *rmap_list;
1235 *rmap_list = rmap_item;
1240 static struct rmap_item *scan_get_next_rmap_item(struct page **page)
1242 struct mm_struct *mm;
1243 struct mm_slot *slot;
1244 struct vm_area_struct *vma;
1245 struct rmap_item *rmap_item;
1247 if (list_empty(&ksm_mm_head.mm_list))
1250 slot = ksm_scan.mm_slot;
1251 if (slot == &ksm_mm_head) {
1252 root_unstable_tree = RB_ROOT;
1254 spin_lock(&ksm_mmlist_lock);
1255 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1256 ksm_scan.mm_slot = slot;
1257 spin_unlock(&ksm_mmlist_lock);
1259 ksm_scan.address = 0;
1260 ksm_scan.rmap_list = &slot->rmap_list;
1264 down_read(&mm->mmap_sem);
1265 if (ksm_test_exit(mm))
1268 vma = find_vma(mm, ksm_scan.address);
1270 for (; vma; vma = vma->vm_next) {
1271 if (!(vma->vm_flags & VM_MERGEABLE))
1273 if (ksm_scan.address < vma->vm_start)
1274 ksm_scan.address = vma->vm_start;
1276 ksm_scan.address = vma->vm_end;
1278 while (ksm_scan.address < vma->vm_end) {
1279 if (ksm_test_exit(mm))
1281 *page = follow_page(vma, ksm_scan.address, FOLL_GET);
1282 if (IS_ERR_OR_NULL(*page)) {
1283 ksm_scan.address += PAGE_SIZE;
1287 if (PageTransCompound(*page)) {
1289 ksm_scan.address &= HPAGE_PMD_MASK;
1290 ksm_scan.address += HPAGE_PMD_SIZE;
1294 if (PageAnon(*page)) {
1295 flush_anon_page(vma, *page, ksm_scan.address);
1296 flush_dcache_page(*page);
1297 rmap_item = get_next_rmap_item(slot,
1298 ksm_scan.rmap_list, ksm_scan.address);
1300 ksm_scan.rmap_list =
1301 &rmap_item->rmap_list;
1302 ksm_scan.address += PAGE_SIZE;
1305 up_read(&mm->mmap_sem);
1309 ksm_scan.address += PAGE_SIZE;
1314 if (ksm_test_exit(mm)) {
1315 ksm_scan.address = 0;
1316 ksm_scan.rmap_list = &slot->rmap_list;
1319 * Nuke all the rmap_items that are above this current rmap:
1320 * because there were no VM_MERGEABLE vmas with such addresses.
1322 remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
1324 spin_lock(&ksm_mmlist_lock);
1325 ksm_scan.mm_slot = list_entry(slot->mm_list.next,
1326 struct mm_slot, mm_list);
1327 if (ksm_scan.address == 0) {
1329 * We've completed a full scan of all vmas, holding mmap_sem
1330 * throughout, and found no VM_MERGEABLE: so do the same as
1331 * __ksm_exit does to remove this mm from all our lists now.
1332 * This applies either when cleaning up after __ksm_exit
1333 * (but beware: we can reach here even before __ksm_exit),
1334 * or when all VM_MERGEABLE areas have been unmapped (and
1335 * mmap_sem then protects against race with MADV_MERGEABLE).
1337 hlist_del(&slot->link);
1338 list_del(&slot->mm_list);
1339 spin_unlock(&ksm_mmlist_lock);
1342 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1343 up_read(&mm->mmap_sem);
1346 spin_unlock(&ksm_mmlist_lock);
1347 up_read(&mm->mmap_sem);
1350 /* Repeat until we've completed scanning the whole list */
1351 slot = ksm_scan.mm_slot;
1352 if (slot != &ksm_mm_head)
1360 * ksm_do_scan - the ksm scanner main worker function.
1361 * @scan_npages - number of pages we want to scan before we return.
1363 static void ksm_do_scan(unsigned int scan_npages)
1365 struct rmap_item *rmap_item;
1366 struct page *uninitialized_var(page);
1368 while (scan_npages--) {
1370 rmap_item = scan_get_next_rmap_item(&page);
1373 if (!PageKsm(page) || !in_stable_tree(rmap_item))
1374 cmp_and_merge_page(page, rmap_item);
1379 static int ksmd_should_run(void)
1381 return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1384 static int ksm_scan_thread(void *nothing)
1386 set_user_nice(current, 5);
1388 while (!kthread_should_stop()) {
1389 mutex_lock(&ksm_thread_mutex);
1390 if (ksmd_should_run())
1391 ksm_do_scan(ksm_thread_pages_to_scan);
1392 mutex_unlock(&ksm_thread_mutex);
1394 if (ksmd_should_run()) {
1395 schedule_timeout_interruptible(
1396 msecs_to_jiffies(ksm_thread_sleep_millisecs));
1398 wait_event_interruptible(ksm_thread_wait,
1399 ksmd_should_run() || kthread_should_stop());
1405 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1406 unsigned long end, int advice, unsigned long *vm_flags)
1408 struct mm_struct *mm = vma->vm_mm;
1412 case MADV_MERGEABLE:
1414 * Be somewhat over-protective for now!
1416 if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE |
1417 VM_PFNMAP | VM_IO | VM_DONTEXPAND |
1418 VM_RESERVED | VM_HUGETLB | VM_INSERTPAGE |
1419 VM_NONLINEAR | VM_MIXEDMAP | VM_SAO))
1420 return 0; /* just ignore the advice */
1422 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
1423 err = __ksm_enter(mm);
1428 *vm_flags |= VM_MERGEABLE;
1431 case MADV_UNMERGEABLE:
1432 if (!(*vm_flags & VM_MERGEABLE))
1433 return 0; /* just ignore the advice */
1435 if (vma->anon_vma) {
1436 err = unmerge_ksm_pages(vma, start, end);
1441 *vm_flags &= ~VM_MERGEABLE;
1448 int __ksm_enter(struct mm_struct *mm)
1450 struct mm_slot *mm_slot;
1453 mm_slot = alloc_mm_slot();
1457 /* Check ksm_run too? Would need tighter locking */
1458 needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1460 spin_lock(&ksm_mmlist_lock);
1461 insert_to_mm_slots_hash(mm, mm_slot);
1463 * Insert just behind the scanning cursor, to let the area settle
1464 * down a little; when fork is followed by immediate exec, we don't
1465 * want ksmd to waste time setting up and tearing down an rmap_list.
1467 list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
1468 spin_unlock(&ksm_mmlist_lock);
1470 set_bit(MMF_VM_MERGEABLE, &mm->flags);
1471 atomic_inc(&mm->mm_count);
1474 wake_up_interruptible(&ksm_thread_wait);
1479 void __ksm_exit(struct mm_struct *mm)
1481 struct mm_slot *mm_slot;
1482 int easy_to_free = 0;
1485 * This process is exiting: if it's straightforward (as is the
1486 * case when ksmd was never running), free mm_slot immediately.
1487 * But if it's at the cursor or has rmap_items linked to it, use
1488 * mmap_sem to synchronize with any break_cows before pagetables
1489 * are freed, and leave the mm_slot on the list for ksmd to free.
1490 * Beware: ksm may already have noticed it exiting and freed the slot.
1493 spin_lock(&ksm_mmlist_lock);
1494 mm_slot = get_mm_slot(mm);
1495 if (mm_slot && ksm_scan.mm_slot != mm_slot) {
1496 if (!mm_slot->rmap_list) {
1497 hlist_del(&mm_slot->link);
1498 list_del(&mm_slot->mm_list);
1501 list_move(&mm_slot->mm_list,
1502 &ksm_scan.mm_slot->mm_list);
1505 spin_unlock(&ksm_mmlist_lock);
1508 free_mm_slot(mm_slot);
1509 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1511 } else if (mm_slot) {
1512 down_write(&mm->mmap_sem);
1513 up_write(&mm->mmap_sem);
1517 struct page *ksm_does_need_to_copy(struct page *page,
1518 struct vm_area_struct *vma, unsigned long address)
1520 struct page *new_page;
1522 new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
1524 copy_user_highpage(new_page, page, address, vma);
1526 SetPageDirty(new_page);
1527 __SetPageUptodate(new_page);
1528 SetPageSwapBacked(new_page);
1529 __set_page_locked(new_page);
1531 if (page_evictable(new_page, vma))
1532 lru_cache_add_lru(new_page, LRU_ACTIVE_ANON);
1534 add_page_to_unevictable_list(new_page);
1540 int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg,
1541 unsigned long *vm_flags)
1543 struct stable_node *stable_node;
1544 struct rmap_item *rmap_item;
1545 struct hlist_node *hlist;
1546 unsigned int mapcount = page_mapcount(page);
1548 int search_new_forks = 0;
1550 VM_BUG_ON(!PageKsm(page));
1551 VM_BUG_ON(!PageLocked(page));
1553 stable_node = page_stable_node(page);
1557 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1558 struct anon_vma *anon_vma = rmap_item->anon_vma;
1559 struct anon_vma_chain *vmac;
1560 struct vm_area_struct *vma;
1562 anon_vma_lock(anon_vma);
1563 list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1565 if (rmap_item->address < vma->vm_start ||
1566 rmap_item->address >= vma->vm_end)
1569 * Initially we examine only the vma which covers this
1570 * rmap_item; but later, if there is still work to do,
1571 * we examine covering vmas in other mms: in case they
1572 * were forked from the original since ksmd passed.
1574 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1577 if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
1580 referenced += page_referenced_one(page, vma,
1581 rmap_item->address, &mapcount, vm_flags);
1582 if (!search_new_forks || !mapcount)
1585 anon_vma_unlock(anon_vma);
1589 if (!search_new_forks++)
1595 int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
1597 struct stable_node *stable_node;
1598 struct hlist_node *hlist;
1599 struct rmap_item *rmap_item;
1600 int ret = SWAP_AGAIN;
1601 int search_new_forks = 0;
1603 VM_BUG_ON(!PageKsm(page));
1604 VM_BUG_ON(!PageLocked(page));
1606 stable_node = page_stable_node(page);
1610 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1611 struct anon_vma *anon_vma = rmap_item->anon_vma;
1612 struct anon_vma_chain *vmac;
1613 struct vm_area_struct *vma;
1615 anon_vma_lock(anon_vma);
1616 list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1618 if (rmap_item->address < vma->vm_start ||
1619 rmap_item->address >= vma->vm_end)
1622 * Initially we examine only the vma which covers this
1623 * rmap_item; but later, if there is still work to do,
1624 * we examine covering vmas in other mms: in case they
1625 * were forked from the original since ksmd passed.
1627 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1630 ret = try_to_unmap_one(page, vma,
1631 rmap_item->address, flags);
1632 if (ret != SWAP_AGAIN || !page_mapped(page)) {
1633 anon_vma_unlock(anon_vma);
1637 anon_vma_unlock(anon_vma);
1639 if (!search_new_forks++)
1645 #ifdef CONFIG_MIGRATION
1646 int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *,
1647 struct vm_area_struct *, unsigned long, void *), void *arg)
1649 struct stable_node *stable_node;
1650 struct hlist_node *hlist;
1651 struct rmap_item *rmap_item;
1652 int ret = SWAP_AGAIN;
1653 int search_new_forks = 0;
1655 VM_BUG_ON(!PageKsm(page));
1656 VM_BUG_ON(!PageLocked(page));
1658 stable_node = page_stable_node(page);
1662 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1663 struct anon_vma *anon_vma = rmap_item->anon_vma;
1664 struct anon_vma_chain *vmac;
1665 struct vm_area_struct *vma;
1667 anon_vma_lock(anon_vma);
1668 list_for_each_entry(vmac, &anon_vma->head, same_anon_vma) {
1670 if (rmap_item->address < vma->vm_start ||
1671 rmap_item->address >= vma->vm_end)
1674 * Initially we examine only the vma which covers this
1675 * rmap_item; but later, if there is still work to do,
1676 * we examine covering vmas in other mms: in case they
1677 * were forked from the original since ksmd passed.
1679 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1682 ret = rmap_one(page, vma, rmap_item->address, arg);
1683 if (ret != SWAP_AGAIN) {
1684 anon_vma_unlock(anon_vma);
1688 anon_vma_unlock(anon_vma);
1690 if (!search_new_forks++)
1696 void ksm_migrate_page(struct page *newpage, struct page *oldpage)
1698 struct stable_node *stable_node;
1700 VM_BUG_ON(!PageLocked(oldpage));
1701 VM_BUG_ON(!PageLocked(newpage));
1702 VM_BUG_ON(newpage->mapping != oldpage->mapping);
1704 stable_node = page_stable_node(newpage);
1706 VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage));
1707 stable_node->kpfn = page_to_pfn(newpage);
1710 #endif /* CONFIG_MIGRATION */
1712 #ifdef CONFIG_MEMORY_HOTREMOVE
1713 static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn,
1714 unsigned long end_pfn)
1716 struct rb_node *node;
1718 for (node = rb_first(&root_stable_tree); node; node = rb_next(node)) {
1719 struct stable_node *stable_node;
1721 stable_node = rb_entry(node, struct stable_node, node);
1722 if (stable_node->kpfn >= start_pfn &&
1723 stable_node->kpfn < end_pfn)
1729 static int ksm_memory_callback(struct notifier_block *self,
1730 unsigned long action, void *arg)
1732 struct memory_notify *mn = arg;
1733 struct stable_node *stable_node;
1736 case MEM_GOING_OFFLINE:
1738 * Keep it very simple for now: just lock out ksmd and
1739 * MADV_UNMERGEABLE while any memory is going offline.
1740 * mutex_lock_nested() is necessary because lockdep was alarmed
1741 * that here we take ksm_thread_mutex inside notifier chain
1742 * mutex, and later take notifier chain mutex inside
1743 * ksm_thread_mutex to unlock it. But that's safe because both
1744 * are inside mem_hotplug_mutex.
1746 mutex_lock_nested(&ksm_thread_mutex, SINGLE_DEPTH_NESTING);
1751 * Most of the work is done by page migration; but there might
1752 * be a few stable_nodes left over, still pointing to struct
1753 * pages which have been offlined: prune those from the tree.
1755 while ((stable_node = ksm_check_stable_tree(mn->start_pfn,
1756 mn->start_pfn + mn->nr_pages)) != NULL)
1757 remove_node_from_stable_tree(stable_node);
1760 case MEM_CANCEL_OFFLINE:
1761 mutex_unlock(&ksm_thread_mutex);
1766 #endif /* CONFIG_MEMORY_HOTREMOVE */
1770 * This all compiles without CONFIG_SYSFS, but is a waste of space.
1773 #define KSM_ATTR_RO(_name) \
1774 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
1775 #define KSM_ATTR(_name) \
1776 static struct kobj_attribute _name##_attr = \
1777 __ATTR(_name, 0644, _name##_show, _name##_store)
1779 static ssize_t sleep_millisecs_show(struct kobject *kobj,
1780 struct kobj_attribute *attr, char *buf)
1782 return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
1785 static ssize_t sleep_millisecs_store(struct kobject *kobj,
1786 struct kobj_attribute *attr,
1787 const char *buf, size_t count)
1789 unsigned long msecs;
1792 err = strict_strtoul(buf, 10, &msecs);
1793 if (err || msecs > UINT_MAX)
1796 ksm_thread_sleep_millisecs = msecs;
1800 KSM_ATTR(sleep_millisecs);
1802 static ssize_t pages_to_scan_show(struct kobject *kobj,
1803 struct kobj_attribute *attr, char *buf)
1805 return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
1808 static ssize_t pages_to_scan_store(struct kobject *kobj,
1809 struct kobj_attribute *attr,
1810 const char *buf, size_t count)
1813 unsigned long nr_pages;
1815 err = strict_strtoul(buf, 10, &nr_pages);
1816 if (err || nr_pages > UINT_MAX)
1819 ksm_thread_pages_to_scan = nr_pages;
1823 KSM_ATTR(pages_to_scan);
1825 static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
1828 return sprintf(buf, "%u\n", ksm_run);
1831 static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
1832 const char *buf, size_t count)
1835 unsigned long flags;
1837 err = strict_strtoul(buf, 10, &flags);
1838 if (err || flags > UINT_MAX)
1840 if (flags > KSM_RUN_UNMERGE)
1844 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
1845 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
1846 * breaking COW to free the pages_shared (but leaves mm_slots
1847 * on the list for when ksmd may be set running again).
1850 mutex_lock(&ksm_thread_mutex);
1851 if (ksm_run != flags) {
1853 if (flags & KSM_RUN_UNMERGE) {
1854 current->flags |= PF_OOM_ORIGIN;
1855 err = unmerge_and_remove_all_rmap_items();
1856 current->flags &= ~PF_OOM_ORIGIN;
1858 ksm_run = KSM_RUN_STOP;
1863 mutex_unlock(&ksm_thread_mutex);
1865 if (flags & KSM_RUN_MERGE)
1866 wake_up_interruptible(&ksm_thread_wait);
1872 static ssize_t pages_shared_show(struct kobject *kobj,
1873 struct kobj_attribute *attr, char *buf)
1875 return sprintf(buf, "%lu\n", ksm_pages_shared);
1877 KSM_ATTR_RO(pages_shared);
1879 static ssize_t pages_sharing_show(struct kobject *kobj,
1880 struct kobj_attribute *attr, char *buf)
1882 return sprintf(buf, "%lu\n", ksm_pages_sharing);
1884 KSM_ATTR_RO(pages_sharing);
1886 static ssize_t pages_unshared_show(struct kobject *kobj,
1887 struct kobj_attribute *attr, char *buf)
1889 return sprintf(buf, "%lu\n", ksm_pages_unshared);
1891 KSM_ATTR_RO(pages_unshared);
1893 static ssize_t pages_volatile_show(struct kobject *kobj,
1894 struct kobj_attribute *attr, char *buf)
1896 long ksm_pages_volatile;
1898 ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
1899 - ksm_pages_sharing - ksm_pages_unshared;
1901 * It was not worth any locking to calculate that statistic,
1902 * but it might therefore sometimes be negative: conceal that.
1904 if (ksm_pages_volatile < 0)
1905 ksm_pages_volatile = 0;
1906 return sprintf(buf, "%ld\n", ksm_pages_volatile);
1908 KSM_ATTR_RO(pages_volatile);
1910 static ssize_t full_scans_show(struct kobject *kobj,
1911 struct kobj_attribute *attr, char *buf)
1913 return sprintf(buf, "%lu\n", ksm_scan.seqnr);
1915 KSM_ATTR_RO(full_scans);
1917 static struct attribute *ksm_attrs[] = {
1918 &sleep_millisecs_attr.attr,
1919 &pages_to_scan_attr.attr,
1921 &pages_shared_attr.attr,
1922 &pages_sharing_attr.attr,
1923 &pages_unshared_attr.attr,
1924 &pages_volatile_attr.attr,
1925 &full_scans_attr.attr,
1929 static struct attribute_group ksm_attr_group = {
1933 #endif /* CONFIG_SYSFS */
1935 static int __init ksm_init(void)
1937 struct task_struct *ksm_thread;
1940 err = ksm_slab_init();
1944 ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
1945 if (IS_ERR(ksm_thread)) {
1946 printk(KERN_ERR "ksm: creating kthread failed\n");
1947 err = PTR_ERR(ksm_thread);
1952 err = sysfs_create_group(mm_kobj, &ksm_attr_group);
1954 printk(KERN_ERR "ksm: register sysfs failed\n");
1955 kthread_stop(ksm_thread);
1959 ksm_run = KSM_RUN_MERGE; /* no way for user to start it */
1961 #endif /* CONFIG_SYSFS */
1963 #ifdef CONFIG_MEMORY_HOTREMOVE
1965 * Choose a high priority since the callback takes ksm_thread_mutex:
1966 * later callbacks could only be taking locks which nest within that.
1968 hotplug_memory_notifier(ksm_memory_callback, 100);
1977 module_init(ksm_init)