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/mmu_notifier.h>
33 #include <linux/swap.h>
34 #include <linux/ksm.h>
36 #include <asm/tlbflush.h>
40 * A few notes about the KSM scanning process,
41 * to make it easier to understand the data structures below:
43 * In order to reduce excessive scanning, KSM sorts the memory pages by their
44 * contents into a data structure that holds pointers to the pages' locations.
46 * Since the contents of the pages may change at any moment, KSM cannot just
47 * insert the pages into a normal sorted tree and expect it to find anything.
48 * Therefore KSM uses two data structures - the stable and the unstable tree.
50 * The stable tree holds pointers to all the merged pages (ksm pages), sorted
51 * by their contents. Because each such page is write-protected, searching on
52 * this tree is fully assured to be working (except when pages are unmapped),
53 * and therefore this tree is called the stable tree.
55 * In addition to the stable tree, KSM uses a second data structure called the
56 * unstable tree: this tree holds pointers to pages which have been found to
57 * be "unchanged for a period of time". The unstable tree sorts these pages
58 * by their contents, but since they are not write-protected, KSM cannot rely
59 * upon the unstable tree to work correctly - the unstable tree is liable to
60 * be corrupted as its contents are modified, and so it is called unstable.
62 * KSM solves this problem by several techniques:
64 * 1) The unstable tree is flushed every time KSM completes scanning all
65 * memory areas, and then the tree is rebuilt again from the beginning.
66 * 2) KSM will only insert into the unstable tree, pages whose hash value
67 * has not changed since the previous scan of all memory areas.
68 * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
69 * colors of the nodes and not on their contents, assuring that even when
70 * the tree gets "corrupted" it won't get out of balance, so scanning time
71 * remains the same (also, searching and inserting nodes in an rbtree uses
72 * the same algorithm, so we have no overhead when we flush and rebuild).
73 * 4) KSM never flushes the stable tree, which means that even if it were to
74 * take 10 attempts to find a page in the unstable tree, once it is found,
75 * it is secured in the stable tree. (When we scan a new page, we first
76 * compare it against the stable tree, and then against the unstable tree.)
80 * struct mm_slot - ksm information per mm that is being scanned
81 * @link: link to the mm_slots hash list
82 * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
83 * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
84 * @mm: the mm that this information is valid for
87 struct hlist_node link;
88 struct list_head mm_list;
89 struct rmap_item *rmap_list;
94 * struct ksm_scan - cursor for scanning
95 * @mm_slot: the current mm_slot we are scanning
96 * @address: the next address inside that to be scanned
97 * @rmap_list: link to the next rmap to be scanned in the rmap_list
98 * @seqnr: count of completed full scans (needed when removing unstable node)
100 * There is only the one ksm_scan instance of this cursor structure.
103 struct mm_slot *mm_slot;
104 unsigned long address;
105 struct rmap_item **rmap_list;
110 * struct stable_node - node of the stable rbtree
111 * @page: pointer to struct page of the ksm page
112 * @node: rb node of this ksm page in the stable tree
113 * @hlist: hlist head of rmap_items using this ksm page
118 struct hlist_head hlist;
122 * struct rmap_item - reverse mapping item for virtual addresses
123 * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
124 * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
125 * @mm: the memory structure this rmap_item is pointing into
126 * @address: the virtual address this rmap_item tracks (+ flags in low bits)
127 * @oldchecksum: previous checksum of the page at that virtual address
128 * @node: rb node of this rmap_item in the unstable tree
129 * @head: pointer to stable_node heading this list in the stable tree
130 * @hlist: link into hlist of rmap_items hanging off that stable_node
133 struct rmap_item *rmap_list;
134 struct anon_vma *anon_vma; /* when stable */
135 struct mm_struct *mm;
136 unsigned long address; /* + low bits used for flags below */
137 unsigned int oldchecksum; /* when unstable */
139 struct rb_node node; /* when node of unstable tree */
140 struct { /* when listed from stable tree */
141 struct stable_node *head;
142 struct hlist_node hlist;
147 #define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */
148 #define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */
149 #define STABLE_FLAG 0x200 /* is listed from the stable tree */
151 /* The stable and unstable tree heads */
152 static struct rb_root root_stable_tree = RB_ROOT;
153 static struct rb_root root_unstable_tree = RB_ROOT;
155 #define MM_SLOTS_HASH_HEADS 1024
156 static struct hlist_head *mm_slots_hash;
158 static struct mm_slot ksm_mm_head = {
159 .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
161 static struct ksm_scan ksm_scan = {
162 .mm_slot = &ksm_mm_head,
165 static struct kmem_cache *rmap_item_cache;
166 static struct kmem_cache *stable_node_cache;
167 static struct kmem_cache *mm_slot_cache;
169 /* The number of nodes in the stable tree */
170 static unsigned long ksm_pages_shared;
172 /* The number of page slots additionally sharing those nodes */
173 static unsigned long ksm_pages_sharing;
175 /* The number of nodes in the unstable tree */
176 static unsigned long ksm_pages_unshared;
178 /* The number of rmap_items in use: to calculate pages_volatile */
179 static unsigned long ksm_rmap_items;
181 /* Limit on the number of unswappable pages used */
182 static unsigned long ksm_max_kernel_pages;
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 int __init mm_slots_hash_init(void)
276 mm_slots_hash = kzalloc(MM_SLOTS_HASH_HEADS * sizeof(struct hlist_head),
283 static void __init mm_slots_hash_free(void)
285 kfree(mm_slots_hash);
288 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
290 struct mm_slot *mm_slot;
291 struct hlist_head *bucket;
292 struct hlist_node *node;
294 bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
295 % MM_SLOTS_HASH_HEADS];
296 hlist_for_each_entry(mm_slot, node, bucket, link) {
297 if (mm == mm_slot->mm)
303 static void insert_to_mm_slots_hash(struct mm_struct *mm,
304 struct mm_slot *mm_slot)
306 struct hlist_head *bucket;
308 bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct))
309 % MM_SLOTS_HASH_HEADS];
311 hlist_add_head(&mm_slot->link, bucket);
314 static inline int in_stable_tree(struct rmap_item *rmap_item)
316 return rmap_item->address & STABLE_FLAG;
319 static void hold_anon_vma(struct rmap_item *rmap_item,
320 struct anon_vma *anon_vma)
322 rmap_item->anon_vma = anon_vma;
323 atomic_inc(&anon_vma->ksm_refcount);
326 static void drop_anon_vma(struct rmap_item *rmap_item)
328 struct anon_vma *anon_vma = rmap_item->anon_vma;
330 if (atomic_dec_and_lock(&anon_vma->ksm_refcount, &anon_vma->lock)) {
331 int empty = list_empty(&anon_vma->head);
332 spin_unlock(&anon_vma->lock);
334 anon_vma_free(anon_vma);
339 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
340 * page tables after it has passed through ksm_exit() - which, if necessary,
341 * takes mmap_sem briefly to serialize against them. ksm_exit() does not set
342 * a special flag: they can just back out as soon as mm_users goes to zero.
343 * ksm_test_exit() is used throughout to make this test for exit: in some
344 * places for correctness, in some places just to avoid unnecessary work.
346 static inline bool ksm_test_exit(struct mm_struct *mm)
348 return atomic_read(&mm->mm_users) == 0;
352 * We use break_ksm to break COW on a ksm page: it's a stripped down
354 * if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
357 * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
358 * in case the application has unmapped and remapped mm,addr meanwhile.
359 * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP
360 * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
362 static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
369 page = follow_page(vma, addr, FOLL_GET);
373 ret = handle_mm_fault(vma->vm_mm, vma, addr,
376 ret = VM_FAULT_WRITE;
378 } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM)));
380 * We must loop because handle_mm_fault() may back out if there's
381 * any difficulty e.g. if pte accessed bit gets updated concurrently.
383 * VM_FAULT_WRITE is what we have been hoping for: it indicates that
384 * COW has been broken, even if the vma does not permit VM_WRITE;
385 * but note that a concurrent fault might break PageKsm for us.
387 * VM_FAULT_SIGBUS could occur if we race with truncation of the
388 * backing file, which also invalidates anonymous pages: that's
389 * okay, that truncation will have unmapped the PageKsm for us.
391 * VM_FAULT_OOM: at the time of writing (late July 2009), setting
392 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
393 * current task has TIF_MEMDIE set, and will be OOM killed on return
394 * to user; and ksmd, having no mm, would never be chosen for that.
396 * But if the mm is in a limited mem_cgroup, then the fault may fail
397 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
398 * even ksmd can fail in this way - though it's usually breaking ksm
399 * just to undo a merge it made a moment before, so unlikely to oom.
401 * That's a pity: we might therefore have more kernel pages allocated
402 * than we're counting as nodes in the stable tree; but ksm_do_scan
403 * will retry to break_cow on each pass, so should recover the page
404 * in due course. The important thing is to not let VM_MERGEABLE
405 * be cleared while any such pages might remain in the area.
407 return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
410 static void break_cow(struct rmap_item *rmap_item)
412 struct mm_struct *mm = rmap_item->mm;
413 unsigned long addr = rmap_item->address;
414 struct vm_area_struct *vma;
417 * It is not an accident that whenever we want to break COW
418 * to undo, we also need to drop a reference to the anon_vma.
420 drop_anon_vma(rmap_item);
422 down_read(&mm->mmap_sem);
423 if (ksm_test_exit(mm))
425 vma = find_vma(mm, addr);
426 if (!vma || vma->vm_start > addr)
428 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
430 break_ksm(vma, addr);
432 up_read(&mm->mmap_sem);
435 static struct page *get_mergeable_page(struct rmap_item *rmap_item)
437 struct mm_struct *mm = rmap_item->mm;
438 unsigned long addr = rmap_item->address;
439 struct vm_area_struct *vma;
442 down_read(&mm->mmap_sem);
443 if (ksm_test_exit(mm))
445 vma = find_vma(mm, addr);
446 if (!vma || vma->vm_start > addr)
448 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
451 page = follow_page(vma, addr, FOLL_GET);
454 if (PageAnon(page)) {
455 flush_anon_page(vma, page, addr);
456 flush_dcache_page(page);
461 up_read(&mm->mmap_sem);
465 static void remove_node_from_stable_tree(struct stable_node *stable_node)
467 struct rmap_item *rmap_item;
468 struct hlist_node *hlist;
470 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
471 if (rmap_item->hlist.next)
475 drop_anon_vma(rmap_item);
476 rmap_item->address &= PAGE_MASK;
480 rb_erase(&stable_node->node, &root_stable_tree);
481 free_stable_node(stable_node);
485 * get_ksm_page: checks if the page indicated by the stable node
486 * is still its ksm page, despite having held no reference to it.
487 * In which case we can trust the content of the page, and it
488 * returns the gotten page; but if the page has now been zapped,
489 * remove the stale node from the stable tree and return NULL.
491 * You would expect the stable_node to hold a reference to the ksm page.
492 * But if it increments the page's count, swapping out has to wait for
493 * ksmd to come around again before it can free the page, which may take
494 * seconds or even minutes: much too unresponsive. So instead we use a
495 * "keyhole reference": access to the ksm page from the stable node peeps
496 * out through its keyhole to see if that page still holds the right key,
497 * pointing back to this stable node. This relies on freeing a PageAnon
498 * page to reset its page->mapping to NULL, and relies on no other use of
499 * a page to put something that might look like our key in page->mapping.
501 * include/linux/pagemap.h page_cache_get_speculative() is a good reference,
502 * but this is different - made simpler by ksm_thread_mutex being held, but
503 * interesting for assuming that no other use of the struct page could ever
504 * put our expected_mapping into page->mapping (or a field of the union which
505 * coincides with page->mapping). The RCU calls are not for KSM at all, but
506 * to keep the page_count protocol described with page_cache_get_speculative.
508 * Note: it is possible that get_ksm_page() will return NULL one moment,
509 * then page the next, if the page is in between page_freeze_refs() and
510 * page_unfreeze_refs(): this shouldn't be a problem anywhere, the page
511 * is on its way to being freed; but it is an anomaly to bear in mind.
513 static struct page *get_ksm_page(struct stable_node *stable_node)
516 void *expected_mapping;
518 page = stable_node->page;
519 expected_mapping = (void *)stable_node +
520 (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM);
522 if (page->mapping != expected_mapping)
524 if (!get_page_unless_zero(page))
526 if (page->mapping != expected_mapping) {
534 remove_node_from_stable_tree(stable_node);
539 * Removing rmap_item from stable or unstable tree.
540 * This function will clean the information from the stable/unstable tree.
542 static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
544 if (rmap_item->address & STABLE_FLAG) {
545 struct stable_node *stable_node;
548 stable_node = rmap_item->head;
549 page = get_ksm_page(stable_node);
554 hlist_del(&rmap_item->hlist);
558 if (stable_node->hlist.first)
563 drop_anon_vma(rmap_item);
564 rmap_item->address &= PAGE_MASK;
566 } else if (rmap_item->address & UNSTABLE_FLAG) {
569 * Usually ksmd can and must skip the rb_erase, because
570 * root_unstable_tree was already reset to RB_ROOT.
571 * But be careful when an mm is exiting: do the rb_erase
572 * if this rmap_item was inserted by this scan, rather
573 * than left over from before.
575 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
578 rb_erase(&rmap_item->node, &root_unstable_tree);
580 ksm_pages_unshared--;
581 rmap_item->address &= PAGE_MASK;
584 cond_resched(); /* we're called from many long loops */
587 static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
588 struct rmap_item **rmap_list)
591 struct rmap_item *rmap_item = *rmap_list;
592 *rmap_list = rmap_item->rmap_list;
593 remove_rmap_item_from_tree(rmap_item);
594 free_rmap_item(rmap_item);
599 * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather
600 * than check every pte of a given vma, the locking doesn't quite work for
601 * that - an rmap_item is assigned to the stable tree after inserting ksm
602 * page and upping mmap_sem. Nor does it fit with the way we skip dup'ing
603 * rmap_items from parent to child at fork time (so as not to waste time
604 * if exit comes before the next scan reaches it).
606 * Similarly, although we'd like to remove rmap_items (so updating counts
607 * and freeing memory) when unmerging an area, it's easier to leave that
608 * to the next pass of ksmd - consider, for example, how ksmd might be
609 * in cmp_and_merge_page on one of the rmap_items we would be removing.
611 static int unmerge_ksm_pages(struct vm_area_struct *vma,
612 unsigned long start, unsigned long end)
617 for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
618 if (ksm_test_exit(vma->vm_mm))
620 if (signal_pending(current))
623 err = break_ksm(vma, addr);
630 * Only called through the sysfs control interface:
632 static int unmerge_and_remove_all_rmap_items(void)
634 struct mm_slot *mm_slot;
635 struct mm_struct *mm;
636 struct vm_area_struct *vma;
639 spin_lock(&ksm_mmlist_lock);
640 ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
641 struct mm_slot, mm_list);
642 spin_unlock(&ksm_mmlist_lock);
644 for (mm_slot = ksm_scan.mm_slot;
645 mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
647 down_read(&mm->mmap_sem);
648 for (vma = mm->mmap; vma; vma = vma->vm_next) {
649 if (ksm_test_exit(mm))
651 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
653 err = unmerge_ksm_pages(vma,
654 vma->vm_start, vma->vm_end);
659 remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
661 spin_lock(&ksm_mmlist_lock);
662 ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
663 struct mm_slot, mm_list);
664 if (ksm_test_exit(mm)) {
665 hlist_del(&mm_slot->link);
666 list_del(&mm_slot->mm_list);
667 spin_unlock(&ksm_mmlist_lock);
669 free_mm_slot(mm_slot);
670 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
671 up_read(&mm->mmap_sem);
674 spin_unlock(&ksm_mmlist_lock);
675 up_read(&mm->mmap_sem);
683 up_read(&mm->mmap_sem);
684 spin_lock(&ksm_mmlist_lock);
685 ksm_scan.mm_slot = &ksm_mm_head;
686 spin_unlock(&ksm_mmlist_lock);
689 #endif /* CONFIG_SYSFS */
691 static u32 calc_checksum(struct page *page)
694 void *addr = kmap_atomic(page, KM_USER0);
695 checksum = jhash2(addr, PAGE_SIZE / 4, 17);
696 kunmap_atomic(addr, KM_USER0);
700 static int memcmp_pages(struct page *page1, struct page *page2)
705 addr1 = kmap_atomic(page1, KM_USER0);
706 addr2 = kmap_atomic(page2, KM_USER1);
707 ret = memcmp(addr1, addr2, PAGE_SIZE);
708 kunmap_atomic(addr2, KM_USER1);
709 kunmap_atomic(addr1, KM_USER0);
713 static inline int pages_identical(struct page *page1, struct page *page2)
715 return !memcmp_pages(page1, page2);
718 static int write_protect_page(struct vm_area_struct *vma, struct page *page,
721 struct mm_struct *mm = vma->vm_mm;
728 addr = page_address_in_vma(page, vma);
732 ptep = page_check_address(page, mm, addr, &ptl, 0);
736 if (pte_write(*ptep)) {
739 swapped = PageSwapCache(page);
740 flush_cache_page(vma, addr, page_to_pfn(page));
742 * Ok this is tricky, when get_user_pages_fast() run it doesnt
743 * take any lock, therefore the check that we are going to make
744 * with the pagecount against the mapcount is racey and
745 * O_DIRECT can happen right after the check.
746 * So we clear the pte and flush the tlb before the check
747 * this assure us that no O_DIRECT can happen after the check
748 * or in the middle of the check.
750 entry = ptep_clear_flush(vma, addr, ptep);
752 * Check that no O_DIRECT or similar I/O is in progress on the
755 if (page_mapcount(page) + 1 + swapped != page_count(page)) {
756 set_pte_at_notify(mm, addr, ptep, entry);
759 entry = pte_wrprotect(entry);
760 set_pte_at_notify(mm, addr, ptep, entry);
766 pte_unmap_unlock(ptep, ptl);
772 * replace_page - replace page in vma by new ksm page
773 * @vma: vma that holds the pte pointing to page
774 * @page: the page we are replacing by kpage
775 * @kpage: the ksm page we replace page by
776 * @orig_pte: the original value of the pte
778 * Returns 0 on success, -EFAULT on failure.
780 static int replace_page(struct vm_area_struct *vma, struct page *page,
781 struct page *kpage, pte_t orig_pte)
783 struct mm_struct *mm = vma->vm_mm;
792 addr = page_address_in_vma(page, vma);
796 pgd = pgd_offset(mm, addr);
797 if (!pgd_present(*pgd))
800 pud = pud_offset(pgd, addr);
801 if (!pud_present(*pud))
804 pmd = pmd_offset(pud, addr);
805 if (!pmd_present(*pmd))
808 ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
809 if (!pte_same(*ptep, orig_pte)) {
810 pte_unmap_unlock(ptep, ptl);
815 page_add_anon_rmap(kpage, vma, addr);
817 flush_cache_page(vma, addr, pte_pfn(*ptep));
818 ptep_clear_flush(vma, addr, ptep);
819 set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
821 page_remove_rmap(page);
824 pte_unmap_unlock(ptep, ptl);
831 * try_to_merge_one_page - take two pages and merge them into one
832 * @vma: the vma that holds the pte pointing to page
833 * @page: the PageAnon page that we want to replace with kpage
834 * @kpage: the PageKsm page that we want to map instead of page
836 * This function returns 0 if the pages were merged, -EFAULT otherwise.
838 static int try_to_merge_one_page(struct vm_area_struct *vma,
839 struct page *page, struct page *kpage)
841 pte_t orig_pte = __pte(0);
844 if (page == kpage) /* ksm page forked */
847 if (!(vma->vm_flags & VM_MERGEABLE))
853 * We need the page lock to read a stable PageSwapCache in
854 * write_protect_page(). We use trylock_page() instead of
855 * lock_page() because we don't want to wait here - we
856 * prefer to continue scanning and merging different pages,
857 * then come back to this page when it is unlocked.
859 if (!trylock_page(page))
862 * If this anonymous page is mapped only here, its pte may need
863 * to be write-protected. If it's mapped elsewhere, all of its
864 * ptes are necessarily already write-protected. But in either
865 * case, we need to lock and check page_count is not raised.
867 if (write_protect_page(vma, page, &orig_pte) == 0 &&
868 pages_identical(page, kpage))
869 err = replace_page(vma, page, kpage, orig_pte);
871 if ((vma->vm_flags & VM_LOCKED) && !err) {
872 munlock_vma_page(page);
873 if (!PageMlocked(kpage)) {
877 mlock_vma_page(kpage);
878 page = kpage; /* for final unlock */
888 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
889 * but no new kernel page is allocated: kpage must already be a ksm page.
891 * This function returns 0 if the pages were merged, -EFAULT otherwise.
893 static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
894 struct page *page, struct page *kpage)
896 struct mm_struct *mm = rmap_item->mm;
897 struct vm_area_struct *vma;
900 down_read(&mm->mmap_sem);
901 if (ksm_test_exit(mm))
903 vma = find_vma(mm, rmap_item->address);
904 if (!vma || vma->vm_start > rmap_item->address)
907 err = try_to_merge_one_page(vma, page, kpage);
911 /* Must get reference to anon_vma while still holding mmap_sem */
912 hold_anon_vma(rmap_item, vma->anon_vma);
914 up_read(&mm->mmap_sem);
919 * try_to_merge_two_pages - take two identical pages and prepare them
920 * to be merged into one page.
922 * This function returns the kpage if we successfully merged two identical
923 * pages into one ksm page, NULL otherwise.
925 * Note that this function allocates a new kernel page: if one of the pages
926 * is already a ksm page, try_to_merge_with_ksm_page should be used.
928 static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
930 struct rmap_item *tree_rmap_item,
931 struct page *tree_page)
933 struct mm_struct *mm = rmap_item->mm;
934 struct vm_area_struct *vma;
939 * The number of nodes in the stable tree
940 * is the number of kernel pages that we hold.
942 if (ksm_max_kernel_pages &&
943 ksm_max_kernel_pages <= ksm_pages_shared)
946 kpage = alloc_page(GFP_HIGHUSER);
950 down_read(&mm->mmap_sem);
951 if (ksm_test_exit(mm))
953 vma = find_vma(mm, rmap_item->address);
954 if (!vma || vma->vm_start > rmap_item->address)
957 copy_user_highpage(kpage, page, rmap_item->address, vma);
960 __SetPageUptodate(kpage);
961 SetPageSwapBacked(kpage);
962 set_page_stable_node(kpage, NULL); /* mark it PageKsm */
963 lru_cache_add_lru(kpage, LRU_ACTIVE_ANON);
965 err = try_to_merge_one_page(vma, page, kpage);
969 /* Must get reference to anon_vma while still holding mmap_sem */
970 hold_anon_vma(rmap_item, vma->anon_vma);
972 up_read(&mm->mmap_sem);
975 err = try_to_merge_with_ksm_page(tree_rmap_item,
978 * If that fails, we have a ksm page with only one pte
979 * pointing to it: so break it.
982 break_cow(rmap_item);
992 * stable_tree_search - search for page inside the stable tree
994 * This function checks if there is a page inside the stable tree
995 * with identical content to the page that we are scanning right now.
997 * This function returns the stable tree node of identical content if found,
1000 static struct stable_node *stable_tree_search(struct page *page)
1002 struct rb_node *node = root_stable_tree.rb_node;
1003 struct stable_node *stable_node;
1005 stable_node = page_stable_node(page);
1006 if (stable_node) { /* ksm page forked */
1012 struct page *tree_page;
1016 stable_node = rb_entry(node, struct stable_node, node);
1017 tree_page = get_ksm_page(stable_node);
1021 ret = memcmp_pages(page, tree_page);
1024 put_page(tree_page);
1025 node = node->rb_left;
1026 } else if (ret > 0) {
1027 put_page(tree_page);
1028 node = node->rb_right;
1037 * stable_tree_insert - insert rmap_item pointing to new ksm page
1038 * into the stable tree.
1040 * This function returns the stable tree node just allocated on success,
1043 static struct stable_node *stable_tree_insert(struct page *kpage)
1045 struct rb_node **new = &root_stable_tree.rb_node;
1046 struct rb_node *parent = NULL;
1047 struct stable_node *stable_node;
1050 struct page *tree_page;
1054 stable_node = rb_entry(*new, struct stable_node, node);
1055 tree_page = get_ksm_page(stable_node);
1059 ret = memcmp_pages(kpage, tree_page);
1060 put_page(tree_page);
1064 new = &parent->rb_left;
1066 new = &parent->rb_right;
1069 * It is not a bug that stable_tree_search() didn't
1070 * find this node: because at that time our page was
1071 * not yet write-protected, so may have changed since.
1077 stable_node = alloc_stable_node();
1081 rb_link_node(&stable_node->node, parent, new);
1082 rb_insert_color(&stable_node->node, &root_stable_tree);
1084 INIT_HLIST_HEAD(&stable_node->hlist);
1086 stable_node->page = kpage;
1087 set_page_stable_node(kpage, stable_node);
1093 * unstable_tree_search_insert - search for identical page,
1094 * else insert rmap_item into the unstable tree.
1096 * This function searches for a page in the unstable tree identical to the
1097 * page currently being scanned; and if no identical page is found in the
1098 * tree, we insert rmap_item as a new object into the unstable tree.
1100 * This function returns pointer to rmap_item found to be identical
1101 * to the currently scanned page, NULL otherwise.
1103 * This function does both searching and inserting, because they share
1104 * the same walking algorithm in an rbtree.
1107 struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1109 struct page **tree_pagep)
1112 struct rb_node **new = &root_unstable_tree.rb_node;
1113 struct rb_node *parent = NULL;
1116 struct rmap_item *tree_rmap_item;
1117 struct page *tree_page;
1121 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1122 tree_page = get_mergeable_page(tree_rmap_item);
1127 * Don't substitute a ksm page for a forked page.
1129 if (page == tree_page) {
1130 put_page(tree_page);
1134 ret = memcmp_pages(page, tree_page);
1138 put_page(tree_page);
1139 new = &parent->rb_left;
1140 } else if (ret > 0) {
1141 put_page(tree_page);
1142 new = &parent->rb_right;
1144 *tree_pagep = tree_page;
1145 return tree_rmap_item;
1149 rmap_item->address |= UNSTABLE_FLAG;
1150 rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1151 rb_link_node(&rmap_item->node, parent, new);
1152 rb_insert_color(&rmap_item->node, &root_unstable_tree);
1154 ksm_pages_unshared++;
1159 * stable_tree_append - add another rmap_item to the linked list of
1160 * rmap_items hanging off a given node of the stable tree, all sharing
1161 * the same ksm page.
1163 static void stable_tree_append(struct rmap_item *rmap_item,
1164 struct stable_node *stable_node)
1166 rmap_item->head = stable_node;
1167 rmap_item->address |= STABLE_FLAG;
1168 hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
1170 if (rmap_item->hlist.next)
1171 ksm_pages_sharing++;
1177 * cmp_and_merge_page - first see if page can be merged into the stable tree;
1178 * if not, compare checksum to previous and if it's the same, see if page can
1179 * be inserted into the unstable tree, or merged with a page already there and
1180 * both transferred to the stable tree.
1182 * @page: the page that we are searching identical page to.
1183 * @rmap_item: the reverse mapping into the virtual address of this page
1185 static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1187 struct rmap_item *tree_rmap_item;
1188 struct page *tree_page = NULL;
1189 struct stable_node *stable_node;
1191 unsigned int checksum;
1194 remove_rmap_item_from_tree(rmap_item);
1196 /* We first start with searching the page inside the stable tree */
1197 stable_node = stable_tree_search(page);
1199 kpage = stable_node->page;
1200 err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
1203 * The page was successfully merged:
1204 * add its rmap_item to the stable tree.
1207 stable_tree_append(rmap_item, stable_node);
1215 * If the hash value of the page has changed from the last time
1216 * we calculated it, this page is changing frequently: therefore we
1217 * don't want to insert it in the unstable tree, and we don't want
1218 * to waste our time searching for something identical to it there.
1220 checksum = calc_checksum(page);
1221 if (rmap_item->oldchecksum != checksum) {
1222 rmap_item->oldchecksum = checksum;
1227 unstable_tree_search_insert(rmap_item, page, &tree_page);
1228 if (tree_rmap_item) {
1229 kpage = try_to_merge_two_pages(rmap_item, page,
1230 tree_rmap_item, tree_page);
1231 put_page(tree_page);
1233 * As soon as we merge this page, we want to remove the
1234 * rmap_item of the page we have merged with from the unstable
1235 * tree, and insert it instead as new node in the stable tree.
1238 remove_rmap_item_from_tree(tree_rmap_item);
1241 stable_node = stable_tree_insert(kpage);
1243 stable_tree_append(tree_rmap_item, stable_node);
1244 stable_tree_append(rmap_item, stable_node);
1250 * If we fail to insert the page into the stable tree,
1251 * we will have 2 virtual addresses that are pointing
1252 * to a ksm page left outside the stable tree,
1253 * in which case we need to break_cow on both.
1256 break_cow(tree_rmap_item);
1257 break_cow(rmap_item);
1263 static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
1264 struct rmap_item **rmap_list,
1267 struct rmap_item *rmap_item;
1269 while (*rmap_list) {
1270 rmap_item = *rmap_list;
1271 if ((rmap_item->address & PAGE_MASK) == addr)
1273 if (rmap_item->address > addr)
1275 *rmap_list = rmap_item->rmap_list;
1276 remove_rmap_item_from_tree(rmap_item);
1277 free_rmap_item(rmap_item);
1280 rmap_item = alloc_rmap_item();
1282 /* It has already been zeroed */
1283 rmap_item->mm = mm_slot->mm;
1284 rmap_item->address = addr;
1285 rmap_item->rmap_list = *rmap_list;
1286 *rmap_list = rmap_item;
1291 static struct rmap_item *scan_get_next_rmap_item(struct page **page)
1293 struct mm_struct *mm;
1294 struct mm_slot *slot;
1295 struct vm_area_struct *vma;
1296 struct rmap_item *rmap_item;
1298 if (list_empty(&ksm_mm_head.mm_list))
1301 slot = ksm_scan.mm_slot;
1302 if (slot == &ksm_mm_head) {
1303 root_unstable_tree = RB_ROOT;
1305 spin_lock(&ksm_mmlist_lock);
1306 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1307 ksm_scan.mm_slot = slot;
1308 spin_unlock(&ksm_mmlist_lock);
1310 ksm_scan.address = 0;
1311 ksm_scan.rmap_list = &slot->rmap_list;
1315 down_read(&mm->mmap_sem);
1316 if (ksm_test_exit(mm))
1319 vma = find_vma(mm, ksm_scan.address);
1321 for (; vma; vma = vma->vm_next) {
1322 if (!(vma->vm_flags & VM_MERGEABLE))
1324 if (ksm_scan.address < vma->vm_start)
1325 ksm_scan.address = vma->vm_start;
1327 ksm_scan.address = vma->vm_end;
1329 while (ksm_scan.address < vma->vm_end) {
1330 if (ksm_test_exit(mm))
1332 *page = follow_page(vma, ksm_scan.address, FOLL_GET);
1333 if (*page && PageAnon(*page)) {
1334 flush_anon_page(vma, *page, ksm_scan.address);
1335 flush_dcache_page(*page);
1336 rmap_item = get_next_rmap_item(slot,
1337 ksm_scan.rmap_list, ksm_scan.address);
1339 ksm_scan.rmap_list =
1340 &rmap_item->rmap_list;
1341 ksm_scan.address += PAGE_SIZE;
1344 up_read(&mm->mmap_sem);
1349 ksm_scan.address += PAGE_SIZE;
1354 if (ksm_test_exit(mm)) {
1355 ksm_scan.address = 0;
1356 ksm_scan.rmap_list = &slot->rmap_list;
1359 * Nuke all the rmap_items that are above this current rmap:
1360 * because there were no VM_MERGEABLE vmas with such addresses.
1362 remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
1364 spin_lock(&ksm_mmlist_lock);
1365 ksm_scan.mm_slot = list_entry(slot->mm_list.next,
1366 struct mm_slot, mm_list);
1367 if (ksm_scan.address == 0) {
1369 * We've completed a full scan of all vmas, holding mmap_sem
1370 * throughout, and found no VM_MERGEABLE: so do the same as
1371 * __ksm_exit does to remove this mm from all our lists now.
1372 * This applies either when cleaning up after __ksm_exit
1373 * (but beware: we can reach here even before __ksm_exit),
1374 * or when all VM_MERGEABLE areas have been unmapped (and
1375 * mmap_sem then protects against race with MADV_MERGEABLE).
1377 hlist_del(&slot->link);
1378 list_del(&slot->mm_list);
1379 spin_unlock(&ksm_mmlist_lock);
1382 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1383 up_read(&mm->mmap_sem);
1386 spin_unlock(&ksm_mmlist_lock);
1387 up_read(&mm->mmap_sem);
1390 /* Repeat until we've completed scanning the whole list */
1391 slot = ksm_scan.mm_slot;
1392 if (slot != &ksm_mm_head)
1400 * ksm_do_scan - the ksm scanner main worker function.
1401 * @scan_npages - number of pages we want to scan before we return.
1403 static void ksm_do_scan(unsigned int scan_npages)
1405 struct rmap_item *rmap_item;
1408 while (scan_npages--) {
1410 rmap_item = scan_get_next_rmap_item(&page);
1413 if (!PageKsm(page) || !in_stable_tree(rmap_item))
1414 cmp_and_merge_page(page, rmap_item);
1419 static int ksmd_should_run(void)
1421 return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1424 static int ksm_scan_thread(void *nothing)
1426 set_user_nice(current, 5);
1428 while (!kthread_should_stop()) {
1429 mutex_lock(&ksm_thread_mutex);
1430 if (ksmd_should_run())
1431 ksm_do_scan(ksm_thread_pages_to_scan);
1432 mutex_unlock(&ksm_thread_mutex);
1434 if (ksmd_should_run()) {
1435 schedule_timeout_interruptible(
1436 msecs_to_jiffies(ksm_thread_sleep_millisecs));
1438 wait_event_interruptible(ksm_thread_wait,
1439 ksmd_should_run() || kthread_should_stop());
1445 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1446 unsigned long end, int advice, unsigned long *vm_flags)
1448 struct mm_struct *mm = vma->vm_mm;
1452 case MADV_MERGEABLE:
1454 * Be somewhat over-protective for now!
1456 if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE |
1457 VM_PFNMAP | VM_IO | VM_DONTEXPAND |
1458 VM_RESERVED | VM_HUGETLB | VM_INSERTPAGE |
1459 VM_NONLINEAR | VM_MIXEDMAP | VM_SAO))
1460 return 0; /* just ignore the advice */
1462 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
1463 err = __ksm_enter(mm);
1468 *vm_flags |= VM_MERGEABLE;
1471 case MADV_UNMERGEABLE:
1472 if (!(*vm_flags & VM_MERGEABLE))
1473 return 0; /* just ignore the advice */
1475 if (vma->anon_vma) {
1476 err = unmerge_ksm_pages(vma, start, end);
1481 *vm_flags &= ~VM_MERGEABLE;
1488 int __ksm_enter(struct mm_struct *mm)
1490 struct mm_slot *mm_slot;
1493 mm_slot = alloc_mm_slot();
1497 /* Check ksm_run too? Would need tighter locking */
1498 needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1500 spin_lock(&ksm_mmlist_lock);
1501 insert_to_mm_slots_hash(mm, mm_slot);
1503 * Insert just behind the scanning cursor, to let the area settle
1504 * down a little; when fork is followed by immediate exec, we don't
1505 * want ksmd to waste time setting up and tearing down an rmap_list.
1507 list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
1508 spin_unlock(&ksm_mmlist_lock);
1510 set_bit(MMF_VM_MERGEABLE, &mm->flags);
1511 atomic_inc(&mm->mm_count);
1514 wake_up_interruptible(&ksm_thread_wait);
1519 void __ksm_exit(struct mm_struct *mm)
1521 struct mm_slot *mm_slot;
1522 int easy_to_free = 0;
1525 * This process is exiting: if it's straightforward (as is the
1526 * case when ksmd was never running), free mm_slot immediately.
1527 * But if it's at the cursor or has rmap_items linked to it, use
1528 * mmap_sem to synchronize with any break_cows before pagetables
1529 * are freed, and leave the mm_slot on the list for ksmd to free.
1530 * Beware: ksm may already have noticed it exiting and freed the slot.
1533 spin_lock(&ksm_mmlist_lock);
1534 mm_slot = get_mm_slot(mm);
1535 if (mm_slot && ksm_scan.mm_slot != mm_slot) {
1536 if (!mm_slot->rmap_list) {
1537 hlist_del(&mm_slot->link);
1538 list_del(&mm_slot->mm_list);
1541 list_move(&mm_slot->mm_list,
1542 &ksm_scan.mm_slot->mm_list);
1545 spin_unlock(&ksm_mmlist_lock);
1548 free_mm_slot(mm_slot);
1549 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1551 } else if (mm_slot) {
1552 down_write(&mm->mmap_sem);
1553 up_write(&mm->mmap_sem);
1557 struct page *ksm_does_need_to_copy(struct page *page,
1558 struct vm_area_struct *vma, unsigned long address)
1560 struct page *new_page;
1562 unlock_page(page); /* any racers will COW it, not modify it */
1564 new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
1566 copy_user_highpage(new_page, page, address, vma);
1568 SetPageDirty(new_page);
1569 __SetPageUptodate(new_page);
1570 SetPageSwapBacked(new_page);
1571 __set_page_locked(new_page);
1573 if (page_evictable(new_page, vma))
1574 lru_cache_add_lru(new_page, LRU_ACTIVE_ANON);
1576 add_page_to_unevictable_list(new_page);
1579 page_cache_release(page);
1583 int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg,
1584 unsigned long *vm_flags)
1586 struct stable_node *stable_node;
1587 struct rmap_item *rmap_item;
1588 struct hlist_node *hlist;
1589 unsigned int mapcount = page_mapcount(page);
1591 int search_new_forks = 0;
1593 VM_BUG_ON(!PageKsm(page));
1594 VM_BUG_ON(!PageLocked(page));
1596 stable_node = page_stable_node(page);
1600 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1601 struct anon_vma *anon_vma = rmap_item->anon_vma;
1602 struct vm_area_struct *vma;
1604 spin_lock(&anon_vma->lock);
1605 list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
1606 if (rmap_item->address < vma->vm_start ||
1607 rmap_item->address >= vma->vm_end)
1610 * Initially we examine only the vma which covers this
1611 * rmap_item; but later, if there is still work to do,
1612 * we examine covering vmas in other mms: in case they
1613 * were forked from the original since ksmd passed.
1615 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1618 if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
1621 referenced += page_referenced_one(page, vma,
1622 rmap_item->address, &mapcount, vm_flags);
1623 if (!search_new_forks || !mapcount)
1626 spin_unlock(&anon_vma->lock);
1630 if (!search_new_forks++)
1636 int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
1638 struct stable_node *stable_node;
1639 struct hlist_node *hlist;
1640 struct rmap_item *rmap_item;
1641 int ret = SWAP_AGAIN;
1642 int search_new_forks = 0;
1644 VM_BUG_ON(!PageKsm(page));
1645 VM_BUG_ON(!PageLocked(page));
1647 stable_node = page_stable_node(page);
1651 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1652 struct anon_vma *anon_vma = rmap_item->anon_vma;
1653 struct vm_area_struct *vma;
1655 spin_lock(&anon_vma->lock);
1656 list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
1657 if (rmap_item->address < vma->vm_start ||
1658 rmap_item->address >= vma->vm_end)
1661 * Initially we examine only the vma which covers this
1662 * rmap_item; but later, if there is still work to do,
1663 * we examine covering vmas in other mms: in case they
1664 * were forked from the original since ksmd passed.
1666 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1669 ret = try_to_unmap_one(page, vma,
1670 rmap_item->address, flags);
1671 if (ret != SWAP_AGAIN || !page_mapped(page)) {
1672 spin_unlock(&anon_vma->lock);
1676 spin_unlock(&anon_vma->lock);
1678 if (!search_new_forks++)
1686 * This all compiles without CONFIG_SYSFS, but is a waste of space.
1689 #define KSM_ATTR_RO(_name) \
1690 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
1691 #define KSM_ATTR(_name) \
1692 static struct kobj_attribute _name##_attr = \
1693 __ATTR(_name, 0644, _name##_show, _name##_store)
1695 static ssize_t sleep_millisecs_show(struct kobject *kobj,
1696 struct kobj_attribute *attr, char *buf)
1698 return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
1701 static ssize_t sleep_millisecs_store(struct kobject *kobj,
1702 struct kobj_attribute *attr,
1703 const char *buf, size_t count)
1705 unsigned long msecs;
1708 err = strict_strtoul(buf, 10, &msecs);
1709 if (err || msecs > UINT_MAX)
1712 ksm_thread_sleep_millisecs = msecs;
1716 KSM_ATTR(sleep_millisecs);
1718 static ssize_t pages_to_scan_show(struct kobject *kobj,
1719 struct kobj_attribute *attr, char *buf)
1721 return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
1724 static ssize_t pages_to_scan_store(struct kobject *kobj,
1725 struct kobj_attribute *attr,
1726 const char *buf, size_t count)
1729 unsigned long nr_pages;
1731 err = strict_strtoul(buf, 10, &nr_pages);
1732 if (err || nr_pages > UINT_MAX)
1735 ksm_thread_pages_to_scan = nr_pages;
1739 KSM_ATTR(pages_to_scan);
1741 static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
1744 return sprintf(buf, "%u\n", ksm_run);
1747 static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
1748 const char *buf, size_t count)
1751 unsigned long flags;
1753 err = strict_strtoul(buf, 10, &flags);
1754 if (err || flags > UINT_MAX)
1756 if (flags > KSM_RUN_UNMERGE)
1760 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
1761 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
1762 * breaking COW to free the unswappable pages_shared (but leaves
1763 * mm_slots on the list for when ksmd may be set running again).
1766 mutex_lock(&ksm_thread_mutex);
1767 if (ksm_run != flags) {
1769 if (flags & KSM_RUN_UNMERGE) {
1770 current->flags |= PF_OOM_ORIGIN;
1771 err = unmerge_and_remove_all_rmap_items();
1772 current->flags &= ~PF_OOM_ORIGIN;
1774 ksm_run = KSM_RUN_STOP;
1779 mutex_unlock(&ksm_thread_mutex);
1781 if (flags & KSM_RUN_MERGE)
1782 wake_up_interruptible(&ksm_thread_wait);
1788 static ssize_t max_kernel_pages_store(struct kobject *kobj,
1789 struct kobj_attribute *attr,
1790 const char *buf, size_t count)
1793 unsigned long nr_pages;
1795 err = strict_strtoul(buf, 10, &nr_pages);
1799 ksm_max_kernel_pages = nr_pages;
1804 static ssize_t max_kernel_pages_show(struct kobject *kobj,
1805 struct kobj_attribute *attr, char *buf)
1807 return sprintf(buf, "%lu\n", ksm_max_kernel_pages);
1809 KSM_ATTR(max_kernel_pages);
1811 static ssize_t pages_shared_show(struct kobject *kobj,
1812 struct kobj_attribute *attr, char *buf)
1814 return sprintf(buf, "%lu\n", ksm_pages_shared);
1816 KSM_ATTR_RO(pages_shared);
1818 static ssize_t pages_sharing_show(struct kobject *kobj,
1819 struct kobj_attribute *attr, char *buf)
1821 return sprintf(buf, "%lu\n", ksm_pages_sharing);
1823 KSM_ATTR_RO(pages_sharing);
1825 static ssize_t pages_unshared_show(struct kobject *kobj,
1826 struct kobj_attribute *attr, char *buf)
1828 return sprintf(buf, "%lu\n", ksm_pages_unshared);
1830 KSM_ATTR_RO(pages_unshared);
1832 static ssize_t pages_volatile_show(struct kobject *kobj,
1833 struct kobj_attribute *attr, char *buf)
1835 long ksm_pages_volatile;
1837 ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
1838 - ksm_pages_sharing - ksm_pages_unshared;
1840 * It was not worth any locking to calculate that statistic,
1841 * but it might therefore sometimes be negative: conceal that.
1843 if (ksm_pages_volatile < 0)
1844 ksm_pages_volatile = 0;
1845 return sprintf(buf, "%ld\n", ksm_pages_volatile);
1847 KSM_ATTR_RO(pages_volatile);
1849 static ssize_t full_scans_show(struct kobject *kobj,
1850 struct kobj_attribute *attr, char *buf)
1852 return sprintf(buf, "%lu\n", ksm_scan.seqnr);
1854 KSM_ATTR_RO(full_scans);
1856 static struct attribute *ksm_attrs[] = {
1857 &sleep_millisecs_attr.attr,
1858 &pages_to_scan_attr.attr,
1860 &max_kernel_pages_attr.attr,
1861 &pages_shared_attr.attr,
1862 &pages_sharing_attr.attr,
1863 &pages_unshared_attr.attr,
1864 &pages_volatile_attr.attr,
1865 &full_scans_attr.attr,
1869 static struct attribute_group ksm_attr_group = {
1873 #endif /* CONFIG_SYSFS */
1875 static int __init ksm_init(void)
1877 struct task_struct *ksm_thread;
1880 ksm_max_kernel_pages = totalram_pages / 4;
1882 err = ksm_slab_init();
1886 err = mm_slots_hash_init();
1890 ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
1891 if (IS_ERR(ksm_thread)) {
1892 printk(KERN_ERR "ksm: creating kthread failed\n");
1893 err = PTR_ERR(ksm_thread);
1898 err = sysfs_create_group(mm_kobj, &ksm_attr_group);
1900 printk(KERN_ERR "ksm: register sysfs failed\n");
1901 kthread_stop(ksm_thread);
1905 ksm_run = KSM_RUN_MERGE; /* no way for user to start it */
1907 #endif /* CONFIG_SYSFS */
1912 mm_slots_hash_free();
1918 module_init(ksm_init)