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;
416 down_read(&mm->mmap_sem);
417 if (ksm_test_exit(mm))
419 vma = find_vma(mm, addr);
420 if (!vma || vma->vm_start > addr)
422 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
424 break_ksm(vma, addr);
426 up_read(&mm->mmap_sem);
429 static struct page *get_mergeable_page(struct rmap_item *rmap_item)
431 struct mm_struct *mm = rmap_item->mm;
432 unsigned long addr = rmap_item->address;
433 struct vm_area_struct *vma;
436 down_read(&mm->mmap_sem);
437 if (ksm_test_exit(mm))
439 vma = find_vma(mm, addr);
440 if (!vma || vma->vm_start > addr)
442 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
445 page = follow_page(vma, addr, FOLL_GET);
448 if (PageAnon(page)) {
449 flush_anon_page(vma, page, addr);
450 flush_dcache_page(page);
455 up_read(&mm->mmap_sem);
460 * Removing rmap_item from stable or unstable tree.
461 * This function will clean the information from the stable/unstable tree.
463 static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
465 if (rmap_item->address & STABLE_FLAG) {
466 struct stable_node *stable_node;
469 stable_node = rmap_item->head;
470 page = stable_node->page;
473 hlist_del(&rmap_item->hlist);
474 if (stable_node->hlist.first) {
478 set_page_stable_node(page, NULL);
482 rb_erase(&stable_node->node, &root_stable_tree);
483 free_stable_node(stable_node);
487 drop_anon_vma(rmap_item);
488 rmap_item->address &= PAGE_MASK;
490 } else if (rmap_item->address & UNSTABLE_FLAG) {
493 * Usually ksmd can and must skip the rb_erase, because
494 * root_unstable_tree was already reset to RB_ROOT.
495 * But be careful when an mm is exiting: do the rb_erase
496 * if this rmap_item was inserted by this scan, rather
497 * than left over from before.
499 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
502 rb_erase(&rmap_item->node, &root_unstable_tree);
504 ksm_pages_unshared--;
505 rmap_item->address &= PAGE_MASK;
508 cond_resched(); /* we're called from many long loops */
511 static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
512 struct rmap_item **rmap_list)
515 struct rmap_item *rmap_item = *rmap_list;
516 *rmap_list = rmap_item->rmap_list;
517 remove_rmap_item_from_tree(rmap_item);
518 free_rmap_item(rmap_item);
523 * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather
524 * than check every pte of a given vma, the locking doesn't quite work for
525 * that - an rmap_item is assigned to the stable tree after inserting ksm
526 * page and upping mmap_sem. Nor does it fit with the way we skip dup'ing
527 * rmap_items from parent to child at fork time (so as not to waste time
528 * if exit comes before the next scan reaches it).
530 * Similarly, although we'd like to remove rmap_items (so updating counts
531 * and freeing memory) when unmerging an area, it's easier to leave that
532 * to the next pass of ksmd - consider, for example, how ksmd might be
533 * in cmp_and_merge_page on one of the rmap_items we would be removing.
535 static int unmerge_ksm_pages(struct vm_area_struct *vma,
536 unsigned long start, unsigned long end)
541 for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
542 if (ksm_test_exit(vma->vm_mm))
544 if (signal_pending(current))
547 err = break_ksm(vma, addr);
554 * Only called through the sysfs control interface:
556 static int unmerge_and_remove_all_rmap_items(void)
558 struct mm_slot *mm_slot;
559 struct mm_struct *mm;
560 struct vm_area_struct *vma;
563 spin_lock(&ksm_mmlist_lock);
564 ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
565 struct mm_slot, mm_list);
566 spin_unlock(&ksm_mmlist_lock);
568 for (mm_slot = ksm_scan.mm_slot;
569 mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
571 down_read(&mm->mmap_sem);
572 for (vma = mm->mmap; vma; vma = vma->vm_next) {
573 if (ksm_test_exit(mm))
575 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
577 err = unmerge_ksm_pages(vma,
578 vma->vm_start, vma->vm_end);
583 remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
585 spin_lock(&ksm_mmlist_lock);
586 ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
587 struct mm_slot, mm_list);
588 if (ksm_test_exit(mm)) {
589 hlist_del(&mm_slot->link);
590 list_del(&mm_slot->mm_list);
591 spin_unlock(&ksm_mmlist_lock);
593 free_mm_slot(mm_slot);
594 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
595 up_read(&mm->mmap_sem);
598 spin_unlock(&ksm_mmlist_lock);
599 up_read(&mm->mmap_sem);
607 up_read(&mm->mmap_sem);
608 spin_lock(&ksm_mmlist_lock);
609 ksm_scan.mm_slot = &ksm_mm_head;
610 spin_unlock(&ksm_mmlist_lock);
613 #endif /* CONFIG_SYSFS */
615 static u32 calc_checksum(struct page *page)
618 void *addr = kmap_atomic(page, KM_USER0);
619 checksum = jhash2(addr, PAGE_SIZE / 4, 17);
620 kunmap_atomic(addr, KM_USER0);
624 static int memcmp_pages(struct page *page1, struct page *page2)
629 addr1 = kmap_atomic(page1, KM_USER0);
630 addr2 = kmap_atomic(page2, KM_USER1);
631 ret = memcmp(addr1, addr2, PAGE_SIZE);
632 kunmap_atomic(addr2, KM_USER1);
633 kunmap_atomic(addr1, KM_USER0);
637 static inline int pages_identical(struct page *page1, struct page *page2)
639 return !memcmp_pages(page1, page2);
642 static int write_protect_page(struct vm_area_struct *vma, struct page *page,
645 struct mm_struct *mm = vma->vm_mm;
652 addr = page_address_in_vma(page, vma);
656 ptep = page_check_address(page, mm, addr, &ptl, 0);
660 if (pte_write(*ptep)) {
663 swapped = PageSwapCache(page);
664 flush_cache_page(vma, addr, page_to_pfn(page));
666 * Ok this is tricky, when get_user_pages_fast() run it doesnt
667 * take any lock, therefore the check that we are going to make
668 * with the pagecount against the mapcount is racey and
669 * O_DIRECT can happen right after the check.
670 * So we clear the pte and flush the tlb before the check
671 * this assure us that no O_DIRECT can happen after the check
672 * or in the middle of the check.
674 entry = ptep_clear_flush(vma, addr, ptep);
676 * Check that no O_DIRECT or similar I/O is in progress on the
679 if (page_mapcount(page) + 1 + swapped != page_count(page)) {
680 set_pte_at_notify(mm, addr, ptep, entry);
683 entry = pte_wrprotect(entry);
684 set_pte_at_notify(mm, addr, ptep, entry);
690 pte_unmap_unlock(ptep, ptl);
696 * replace_page - replace page in vma by new ksm page
697 * @vma: vma that holds the pte pointing to page
698 * @page: the page we are replacing by kpage
699 * @kpage: the ksm page we replace page by
700 * @orig_pte: the original value of the pte
702 * Returns 0 on success, -EFAULT on failure.
704 static int replace_page(struct vm_area_struct *vma, struct page *page,
705 struct page *kpage, pte_t orig_pte)
707 struct mm_struct *mm = vma->vm_mm;
716 addr = page_address_in_vma(page, vma);
720 pgd = pgd_offset(mm, addr);
721 if (!pgd_present(*pgd))
724 pud = pud_offset(pgd, addr);
725 if (!pud_present(*pud))
728 pmd = pmd_offset(pud, addr);
729 if (!pmd_present(*pmd))
732 ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
733 if (!pte_same(*ptep, orig_pte)) {
734 pte_unmap_unlock(ptep, ptl);
739 page_add_anon_rmap(kpage, vma, addr);
741 flush_cache_page(vma, addr, pte_pfn(*ptep));
742 ptep_clear_flush(vma, addr, ptep);
743 set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
745 page_remove_rmap(page);
748 pte_unmap_unlock(ptep, ptl);
755 * try_to_merge_one_page - take two pages and merge them into one
756 * @vma: the vma that holds the pte pointing to page
757 * @page: the PageAnon page that we want to replace with kpage
758 * @kpage: the PageKsm page that we want to map instead of page
760 * This function returns 0 if the pages were merged, -EFAULT otherwise.
762 static int try_to_merge_one_page(struct vm_area_struct *vma,
763 struct page *page, struct page *kpage)
765 pte_t orig_pte = __pte(0);
768 if (page == kpage) /* ksm page forked */
771 if (!(vma->vm_flags & VM_MERGEABLE))
777 * We need the page lock to read a stable PageSwapCache in
778 * write_protect_page(). We use trylock_page() instead of
779 * lock_page() because we don't want to wait here - we
780 * prefer to continue scanning and merging different pages,
781 * then come back to this page when it is unlocked.
783 if (!trylock_page(page))
786 * If this anonymous page is mapped only here, its pte may need
787 * to be write-protected. If it's mapped elsewhere, all of its
788 * ptes are necessarily already write-protected. But in either
789 * case, we need to lock and check page_count is not raised.
791 if (write_protect_page(vma, page, &orig_pte) == 0 &&
792 pages_identical(page, kpage))
793 err = replace_page(vma, page, kpage, orig_pte);
795 if ((vma->vm_flags & VM_LOCKED) && !err) {
796 munlock_vma_page(page);
797 if (!PageMlocked(kpage)) {
801 mlock_vma_page(kpage);
802 page = kpage; /* for final unlock */
812 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
813 * but no new kernel page is allocated: kpage must already be a ksm page.
815 * This function returns 0 if the pages were merged, -EFAULT otherwise.
817 static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
818 struct page *page, struct page *kpage)
820 struct mm_struct *mm = rmap_item->mm;
821 struct vm_area_struct *vma;
824 down_read(&mm->mmap_sem);
825 if (ksm_test_exit(mm))
827 vma = find_vma(mm, rmap_item->address);
828 if (!vma || vma->vm_start > rmap_item->address)
831 err = try_to_merge_one_page(vma, page, kpage);
835 /* Must get reference to anon_vma while still holding mmap_sem */
836 hold_anon_vma(rmap_item, vma->anon_vma);
838 up_read(&mm->mmap_sem);
843 * try_to_merge_two_pages - take two identical pages and prepare them
844 * to be merged into one page.
846 * This function returns the kpage if we successfully merged two identical
847 * pages into one ksm page, NULL otherwise.
849 * Note that this function allocates a new kernel page: if one of the pages
850 * is already a ksm page, try_to_merge_with_ksm_page should be used.
852 static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
854 struct rmap_item *tree_rmap_item,
855 struct page *tree_page)
857 struct mm_struct *mm = rmap_item->mm;
858 struct vm_area_struct *vma;
863 * The number of nodes in the stable tree
864 * is the number of kernel pages that we hold.
866 if (ksm_max_kernel_pages &&
867 ksm_max_kernel_pages <= ksm_pages_shared)
870 kpage = alloc_page(GFP_HIGHUSER);
874 down_read(&mm->mmap_sem);
875 if (ksm_test_exit(mm))
877 vma = find_vma(mm, rmap_item->address);
878 if (!vma || vma->vm_start > rmap_item->address)
881 copy_user_highpage(kpage, page, rmap_item->address, vma);
884 __SetPageUptodate(kpage);
885 SetPageSwapBacked(kpage);
886 set_page_stable_node(kpage, NULL); /* mark it PageKsm */
887 lru_cache_add_lru(kpage, LRU_ACTIVE_ANON);
889 err = try_to_merge_one_page(vma, page, kpage);
893 /* Must get reference to anon_vma while still holding mmap_sem */
894 hold_anon_vma(rmap_item, vma->anon_vma);
896 up_read(&mm->mmap_sem);
899 err = try_to_merge_with_ksm_page(tree_rmap_item,
902 * If that fails, we have a ksm page with only one pte
903 * pointing to it: so break it.
906 drop_anon_vma(rmap_item);
907 break_cow(rmap_item);
918 * stable_tree_search - search for page inside the stable tree
920 * This function checks if there is a page inside the stable tree
921 * with identical content to the page that we are scanning right now.
923 * This function returns the stable tree node of identical content if found,
926 static struct stable_node *stable_tree_search(struct page *page)
928 struct rb_node *node = root_stable_tree.rb_node;
929 struct stable_node *stable_node;
931 stable_node = page_stable_node(page);
932 if (stable_node) { /* ksm page forked */
941 stable_node = rb_entry(node, struct stable_node, node);
943 ret = memcmp_pages(page, stable_node->page);
946 node = node->rb_left;
948 node = node->rb_right;
950 get_page(stable_node->page);
959 * stable_tree_insert - insert rmap_item pointing to new ksm page
960 * into the stable tree.
962 * This function returns the stable tree node just allocated on success,
965 static struct stable_node *stable_tree_insert(struct page *kpage)
967 struct rb_node **new = &root_stable_tree.rb_node;
968 struct rb_node *parent = NULL;
969 struct stable_node *stable_node;
975 stable_node = rb_entry(*new, struct stable_node, node);
977 ret = memcmp_pages(kpage, stable_node->page);
981 new = &parent->rb_left;
983 new = &parent->rb_right;
986 * It is not a bug that stable_tree_search() didn't
987 * find this node: because at that time our page was
988 * not yet write-protected, so may have changed since.
994 stable_node = alloc_stable_node();
998 rb_link_node(&stable_node->node, parent, new);
999 rb_insert_color(&stable_node->node, &root_stable_tree);
1001 INIT_HLIST_HEAD(&stable_node->hlist);
1004 stable_node->page = kpage;
1005 set_page_stable_node(kpage, stable_node);
1011 * unstable_tree_search_insert - search for identical page,
1012 * else insert rmap_item into the unstable tree.
1014 * This function searches for a page in the unstable tree identical to the
1015 * page currently being scanned; and if no identical page is found in the
1016 * tree, we insert rmap_item as a new object into the unstable tree.
1018 * This function returns pointer to rmap_item found to be identical
1019 * to the currently scanned page, NULL otherwise.
1021 * This function does both searching and inserting, because they share
1022 * the same walking algorithm in an rbtree.
1025 struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1027 struct page **tree_pagep)
1030 struct rb_node **new = &root_unstable_tree.rb_node;
1031 struct rb_node *parent = NULL;
1034 struct rmap_item *tree_rmap_item;
1035 struct page *tree_page;
1039 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1040 tree_page = get_mergeable_page(tree_rmap_item);
1045 * Don't substitute a ksm page for a forked page.
1047 if (page == tree_page) {
1048 put_page(tree_page);
1052 ret = memcmp_pages(page, tree_page);
1056 put_page(tree_page);
1057 new = &parent->rb_left;
1058 } else if (ret > 0) {
1059 put_page(tree_page);
1060 new = &parent->rb_right;
1062 *tree_pagep = tree_page;
1063 return tree_rmap_item;
1067 rmap_item->address |= UNSTABLE_FLAG;
1068 rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1069 rb_link_node(&rmap_item->node, parent, new);
1070 rb_insert_color(&rmap_item->node, &root_unstable_tree);
1072 ksm_pages_unshared++;
1077 * stable_tree_append - add another rmap_item to the linked list of
1078 * rmap_items hanging off a given node of the stable tree, all sharing
1079 * the same ksm page.
1081 static void stable_tree_append(struct rmap_item *rmap_item,
1082 struct stable_node *stable_node)
1084 rmap_item->head = stable_node;
1085 rmap_item->address |= STABLE_FLAG;
1086 hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
1088 if (rmap_item->hlist.next)
1089 ksm_pages_sharing++;
1095 * cmp_and_merge_page - first see if page can be merged into the stable tree;
1096 * if not, compare checksum to previous and if it's the same, see if page can
1097 * be inserted into the unstable tree, or merged with a page already there and
1098 * both transferred to the stable tree.
1100 * @page: the page that we are searching identical page to.
1101 * @rmap_item: the reverse mapping into the virtual address of this page
1103 static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
1105 struct rmap_item *tree_rmap_item;
1106 struct page *tree_page = NULL;
1107 struct stable_node *stable_node;
1109 unsigned int checksum;
1112 remove_rmap_item_from_tree(rmap_item);
1114 /* We first start with searching the page inside the stable tree */
1115 stable_node = stable_tree_search(page);
1117 kpage = stable_node->page;
1118 err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
1121 * The page was successfully merged:
1122 * add its rmap_item to the stable tree.
1125 stable_tree_append(rmap_item, stable_node);
1133 * A ksm page might have got here by fork, but its other
1134 * references have already been removed from the stable tree.
1135 * Or it might be left over from a break_ksm which failed
1136 * when the mem_cgroup had reached its limit: try again now.
1139 break_cow(rmap_item);
1142 * In case the hash value of the page was changed from the last time we
1143 * have calculated it, this page to be changed frequely, therefore we
1144 * don't want to insert it to the unstable tree, and we don't want to
1145 * waste our time to search if there is something identical to it there.
1147 checksum = calc_checksum(page);
1148 if (rmap_item->oldchecksum != checksum) {
1149 rmap_item->oldchecksum = checksum;
1154 unstable_tree_search_insert(rmap_item, page, &tree_page);
1155 if (tree_rmap_item) {
1156 kpage = try_to_merge_two_pages(rmap_item, page,
1157 tree_rmap_item, tree_page);
1158 put_page(tree_page);
1160 * As soon as we merge this page, we want to remove the
1161 * rmap_item of the page we have merged with from the unstable
1162 * tree, and insert it instead as new node in the stable tree.
1165 remove_rmap_item_from_tree(tree_rmap_item);
1168 stable_node = stable_tree_insert(kpage);
1170 stable_tree_append(tree_rmap_item, stable_node);
1171 stable_tree_append(rmap_item, stable_node);
1177 * If we fail to insert the page into the stable tree,
1178 * we will have 2 virtual addresses that are pointing
1179 * to a ksm page left outside the stable tree,
1180 * in which case we need to break_cow on both.
1183 drop_anon_vma(tree_rmap_item);
1184 break_cow(tree_rmap_item);
1185 drop_anon_vma(rmap_item);
1186 break_cow(rmap_item);
1192 static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
1193 struct rmap_item **rmap_list,
1196 struct rmap_item *rmap_item;
1198 while (*rmap_list) {
1199 rmap_item = *rmap_list;
1200 if ((rmap_item->address & PAGE_MASK) == addr)
1202 if (rmap_item->address > addr)
1204 *rmap_list = rmap_item->rmap_list;
1205 remove_rmap_item_from_tree(rmap_item);
1206 free_rmap_item(rmap_item);
1209 rmap_item = alloc_rmap_item();
1211 /* It has already been zeroed */
1212 rmap_item->mm = mm_slot->mm;
1213 rmap_item->address = addr;
1214 rmap_item->rmap_list = *rmap_list;
1215 *rmap_list = rmap_item;
1220 static struct rmap_item *scan_get_next_rmap_item(struct page **page)
1222 struct mm_struct *mm;
1223 struct mm_slot *slot;
1224 struct vm_area_struct *vma;
1225 struct rmap_item *rmap_item;
1227 if (list_empty(&ksm_mm_head.mm_list))
1230 slot = ksm_scan.mm_slot;
1231 if (slot == &ksm_mm_head) {
1232 root_unstable_tree = RB_ROOT;
1234 spin_lock(&ksm_mmlist_lock);
1235 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
1236 ksm_scan.mm_slot = slot;
1237 spin_unlock(&ksm_mmlist_lock);
1239 ksm_scan.address = 0;
1240 ksm_scan.rmap_list = &slot->rmap_list;
1244 down_read(&mm->mmap_sem);
1245 if (ksm_test_exit(mm))
1248 vma = find_vma(mm, ksm_scan.address);
1250 for (; vma; vma = vma->vm_next) {
1251 if (!(vma->vm_flags & VM_MERGEABLE))
1253 if (ksm_scan.address < vma->vm_start)
1254 ksm_scan.address = vma->vm_start;
1256 ksm_scan.address = vma->vm_end;
1258 while (ksm_scan.address < vma->vm_end) {
1259 if (ksm_test_exit(mm))
1261 *page = follow_page(vma, ksm_scan.address, FOLL_GET);
1262 if (*page && PageAnon(*page)) {
1263 flush_anon_page(vma, *page, ksm_scan.address);
1264 flush_dcache_page(*page);
1265 rmap_item = get_next_rmap_item(slot,
1266 ksm_scan.rmap_list, ksm_scan.address);
1268 ksm_scan.rmap_list =
1269 &rmap_item->rmap_list;
1270 ksm_scan.address += PAGE_SIZE;
1273 up_read(&mm->mmap_sem);
1278 ksm_scan.address += PAGE_SIZE;
1283 if (ksm_test_exit(mm)) {
1284 ksm_scan.address = 0;
1285 ksm_scan.rmap_list = &slot->rmap_list;
1288 * Nuke all the rmap_items that are above this current rmap:
1289 * because there were no VM_MERGEABLE vmas with such addresses.
1291 remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
1293 spin_lock(&ksm_mmlist_lock);
1294 ksm_scan.mm_slot = list_entry(slot->mm_list.next,
1295 struct mm_slot, mm_list);
1296 if (ksm_scan.address == 0) {
1298 * We've completed a full scan of all vmas, holding mmap_sem
1299 * throughout, and found no VM_MERGEABLE: so do the same as
1300 * __ksm_exit does to remove this mm from all our lists now.
1301 * This applies either when cleaning up after __ksm_exit
1302 * (but beware: we can reach here even before __ksm_exit),
1303 * or when all VM_MERGEABLE areas have been unmapped (and
1304 * mmap_sem then protects against race with MADV_MERGEABLE).
1306 hlist_del(&slot->link);
1307 list_del(&slot->mm_list);
1308 spin_unlock(&ksm_mmlist_lock);
1311 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1312 up_read(&mm->mmap_sem);
1315 spin_unlock(&ksm_mmlist_lock);
1316 up_read(&mm->mmap_sem);
1319 /* Repeat until we've completed scanning the whole list */
1320 slot = ksm_scan.mm_slot;
1321 if (slot != &ksm_mm_head)
1329 * ksm_do_scan - the ksm scanner main worker function.
1330 * @scan_npages - number of pages we want to scan before we return.
1332 static void ksm_do_scan(unsigned int scan_npages)
1334 struct rmap_item *rmap_item;
1337 while (scan_npages--) {
1339 rmap_item = scan_get_next_rmap_item(&page);
1342 if (!PageKsm(page) || !in_stable_tree(rmap_item))
1343 cmp_and_merge_page(page, rmap_item);
1348 static int ksmd_should_run(void)
1350 return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
1353 static int ksm_scan_thread(void *nothing)
1355 set_user_nice(current, 5);
1357 while (!kthread_should_stop()) {
1358 mutex_lock(&ksm_thread_mutex);
1359 if (ksmd_should_run())
1360 ksm_do_scan(ksm_thread_pages_to_scan);
1361 mutex_unlock(&ksm_thread_mutex);
1363 if (ksmd_should_run()) {
1364 schedule_timeout_interruptible(
1365 msecs_to_jiffies(ksm_thread_sleep_millisecs));
1367 wait_event_interruptible(ksm_thread_wait,
1368 ksmd_should_run() || kthread_should_stop());
1374 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
1375 unsigned long end, int advice, unsigned long *vm_flags)
1377 struct mm_struct *mm = vma->vm_mm;
1381 case MADV_MERGEABLE:
1383 * Be somewhat over-protective for now!
1385 if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE |
1386 VM_PFNMAP | VM_IO | VM_DONTEXPAND |
1387 VM_RESERVED | VM_HUGETLB | VM_INSERTPAGE |
1388 VM_NONLINEAR | VM_MIXEDMAP | VM_SAO))
1389 return 0; /* just ignore the advice */
1391 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
1392 err = __ksm_enter(mm);
1397 *vm_flags |= VM_MERGEABLE;
1400 case MADV_UNMERGEABLE:
1401 if (!(*vm_flags & VM_MERGEABLE))
1402 return 0; /* just ignore the advice */
1404 if (vma->anon_vma) {
1405 err = unmerge_ksm_pages(vma, start, end);
1410 *vm_flags &= ~VM_MERGEABLE;
1417 int __ksm_enter(struct mm_struct *mm)
1419 struct mm_slot *mm_slot;
1422 mm_slot = alloc_mm_slot();
1426 /* Check ksm_run too? Would need tighter locking */
1427 needs_wakeup = list_empty(&ksm_mm_head.mm_list);
1429 spin_lock(&ksm_mmlist_lock);
1430 insert_to_mm_slots_hash(mm, mm_slot);
1432 * Insert just behind the scanning cursor, to let the area settle
1433 * down a little; when fork is followed by immediate exec, we don't
1434 * want ksmd to waste time setting up and tearing down an rmap_list.
1436 list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
1437 spin_unlock(&ksm_mmlist_lock);
1439 set_bit(MMF_VM_MERGEABLE, &mm->flags);
1440 atomic_inc(&mm->mm_count);
1443 wake_up_interruptible(&ksm_thread_wait);
1448 void __ksm_exit(struct mm_struct *mm)
1450 struct mm_slot *mm_slot;
1451 int easy_to_free = 0;
1454 * This process is exiting: if it's straightforward (as is the
1455 * case when ksmd was never running), free mm_slot immediately.
1456 * But if it's at the cursor or has rmap_items linked to it, use
1457 * mmap_sem to synchronize with any break_cows before pagetables
1458 * are freed, and leave the mm_slot on the list for ksmd to free.
1459 * Beware: ksm may already have noticed it exiting and freed the slot.
1462 spin_lock(&ksm_mmlist_lock);
1463 mm_slot = get_mm_slot(mm);
1464 if (mm_slot && ksm_scan.mm_slot != mm_slot) {
1465 if (!mm_slot->rmap_list) {
1466 hlist_del(&mm_slot->link);
1467 list_del(&mm_slot->mm_list);
1470 list_move(&mm_slot->mm_list,
1471 &ksm_scan.mm_slot->mm_list);
1474 spin_unlock(&ksm_mmlist_lock);
1477 free_mm_slot(mm_slot);
1478 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1480 } else if (mm_slot) {
1481 down_write(&mm->mmap_sem);
1482 up_write(&mm->mmap_sem);
1486 struct page *ksm_does_need_to_copy(struct page *page,
1487 struct vm_area_struct *vma, unsigned long address)
1489 struct page *new_page;
1491 unlock_page(page); /* any racers will COW it, not modify it */
1493 new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
1495 copy_user_highpage(new_page, page, address, vma);
1497 SetPageDirty(new_page);
1498 __SetPageUptodate(new_page);
1499 SetPageSwapBacked(new_page);
1500 __set_page_locked(new_page);
1502 if (page_evictable(new_page, vma))
1503 lru_cache_add_lru(new_page, LRU_ACTIVE_ANON);
1505 add_page_to_unevictable_list(new_page);
1508 page_cache_release(page);
1512 int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg,
1513 unsigned long *vm_flags)
1515 struct stable_node *stable_node;
1516 struct rmap_item *rmap_item;
1517 struct hlist_node *hlist;
1518 unsigned int mapcount = page_mapcount(page);
1520 int search_new_forks = 0;
1522 VM_BUG_ON(!PageKsm(page));
1523 VM_BUG_ON(!PageLocked(page));
1525 stable_node = page_stable_node(page);
1529 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1530 struct anon_vma *anon_vma = rmap_item->anon_vma;
1531 struct vm_area_struct *vma;
1533 spin_lock(&anon_vma->lock);
1534 list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
1535 if (rmap_item->address < vma->vm_start ||
1536 rmap_item->address >= vma->vm_end)
1539 * Initially we examine only the vma which covers this
1540 * rmap_item; but later, if there is still work to do,
1541 * we examine covering vmas in other mms: in case they
1542 * were forked from the original since ksmd passed.
1544 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1547 if (memcg && !mm_match_cgroup(vma->vm_mm, memcg))
1550 referenced += page_referenced_one(page, vma,
1551 rmap_item->address, &mapcount, vm_flags);
1552 if (!search_new_forks || !mapcount)
1555 spin_unlock(&anon_vma->lock);
1559 if (!search_new_forks++)
1565 int try_to_unmap_ksm(struct page *page, enum ttu_flags flags)
1567 struct stable_node *stable_node;
1568 struct hlist_node *hlist;
1569 struct rmap_item *rmap_item;
1570 int ret = SWAP_AGAIN;
1571 int search_new_forks = 0;
1573 VM_BUG_ON(!PageKsm(page));
1574 VM_BUG_ON(!PageLocked(page));
1576 stable_node = page_stable_node(page);
1580 hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) {
1581 struct anon_vma *anon_vma = rmap_item->anon_vma;
1582 struct vm_area_struct *vma;
1584 spin_lock(&anon_vma->lock);
1585 list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
1586 if (rmap_item->address < vma->vm_start ||
1587 rmap_item->address >= vma->vm_end)
1590 * Initially we examine only the vma which covers this
1591 * rmap_item; but later, if there is still work to do,
1592 * we examine covering vmas in other mms: in case they
1593 * were forked from the original since ksmd passed.
1595 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
1598 ret = try_to_unmap_one(page, vma,
1599 rmap_item->address, flags);
1600 if (ret != SWAP_AGAIN || !page_mapped(page)) {
1601 spin_unlock(&anon_vma->lock);
1605 spin_unlock(&anon_vma->lock);
1607 if (!search_new_forks++)
1615 * This all compiles without CONFIG_SYSFS, but is a waste of space.
1618 #define KSM_ATTR_RO(_name) \
1619 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
1620 #define KSM_ATTR(_name) \
1621 static struct kobj_attribute _name##_attr = \
1622 __ATTR(_name, 0644, _name##_show, _name##_store)
1624 static ssize_t sleep_millisecs_show(struct kobject *kobj,
1625 struct kobj_attribute *attr, char *buf)
1627 return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
1630 static ssize_t sleep_millisecs_store(struct kobject *kobj,
1631 struct kobj_attribute *attr,
1632 const char *buf, size_t count)
1634 unsigned long msecs;
1637 err = strict_strtoul(buf, 10, &msecs);
1638 if (err || msecs > UINT_MAX)
1641 ksm_thread_sleep_millisecs = msecs;
1645 KSM_ATTR(sleep_millisecs);
1647 static ssize_t pages_to_scan_show(struct kobject *kobj,
1648 struct kobj_attribute *attr, char *buf)
1650 return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
1653 static ssize_t pages_to_scan_store(struct kobject *kobj,
1654 struct kobj_attribute *attr,
1655 const char *buf, size_t count)
1658 unsigned long nr_pages;
1660 err = strict_strtoul(buf, 10, &nr_pages);
1661 if (err || nr_pages > UINT_MAX)
1664 ksm_thread_pages_to_scan = nr_pages;
1668 KSM_ATTR(pages_to_scan);
1670 static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
1673 return sprintf(buf, "%u\n", ksm_run);
1676 static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
1677 const char *buf, size_t count)
1680 unsigned long flags;
1682 err = strict_strtoul(buf, 10, &flags);
1683 if (err || flags > UINT_MAX)
1685 if (flags > KSM_RUN_UNMERGE)
1689 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
1690 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
1691 * breaking COW to free the unswappable pages_shared (but leaves
1692 * mm_slots on the list for when ksmd may be set running again).
1695 mutex_lock(&ksm_thread_mutex);
1696 if (ksm_run != flags) {
1698 if (flags & KSM_RUN_UNMERGE) {
1699 current->flags |= PF_OOM_ORIGIN;
1700 err = unmerge_and_remove_all_rmap_items();
1701 current->flags &= ~PF_OOM_ORIGIN;
1703 ksm_run = KSM_RUN_STOP;
1708 mutex_unlock(&ksm_thread_mutex);
1710 if (flags & KSM_RUN_MERGE)
1711 wake_up_interruptible(&ksm_thread_wait);
1717 static ssize_t max_kernel_pages_store(struct kobject *kobj,
1718 struct kobj_attribute *attr,
1719 const char *buf, size_t count)
1722 unsigned long nr_pages;
1724 err = strict_strtoul(buf, 10, &nr_pages);
1728 ksm_max_kernel_pages = nr_pages;
1733 static ssize_t max_kernel_pages_show(struct kobject *kobj,
1734 struct kobj_attribute *attr, char *buf)
1736 return sprintf(buf, "%lu\n", ksm_max_kernel_pages);
1738 KSM_ATTR(max_kernel_pages);
1740 static ssize_t pages_shared_show(struct kobject *kobj,
1741 struct kobj_attribute *attr, char *buf)
1743 return sprintf(buf, "%lu\n", ksm_pages_shared);
1745 KSM_ATTR_RO(pages_shared);
1747 static ssize_t pages_sharing_show(struct kobject *kobj,
1748 struct kobj_attribute *attr, char *buf)
1750 return sprintf(buf, "%lu\n", ksm_pages_sharing);
1752 KSM_ATTR_RO(pages_sharing);
1754 static ssize_t pages_unshared_show(struct kobject *kobj,
1755 struct kobj_attribute *attr, char *buf)
1757 return sprintf(buf, "%lu\n", ksm_pages_unshared);
1759 KSM_ATTR_RO(pages_unshared);
1761 static ssize_t pages_volatile_show(struct kobject *kobj,
1762 struct kobj_attribute *attr, char *buf)
1764 long ksm_pages_volatile;
1766 ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
1767 - ksm_pages_sharing - ksm_pages_unshared;
1769 * It was not worth any locking to calculate that statistic,
1770 * but it might therefore sometimes be negative: conceal that.
1772 if (ksm_pages_volatile < 0)
1773 ksm_pages_volatile = 0;
1774 return sprintf(buf, "%ld\n", ksm_pages_volatile);
1776 KSM_ATTR_RO(pages_volatile);
1778 static ssize_t full_scans_show(struct kobject *kobj,
1779 struct kobj_attribute *attr, char *buf)
1781 return sprintf(buf, "%lu\n", ksm_scan.seqnr);
1783 KSM_ATTR_RO(full_scans);
1785 static struct attribute *ksm_attrs[] = {
1786 &sleep_millisecs_attr.attr,
1787 &pages_to_scan_attr.attr,
1789 &max_kernel_pages_attr.attr,
1790 &pages_shared_attr.attr,
1791 &pages_sharing_attr.attr,
1792 &pages_unshared_attr.attr,
1793 &pages_volatile_attr.attr,
1794 &full_scans_attr.attr,
1798 static struct attribute_group ksm_attr_group = {
1802 #endif /* CONFIG_SYSFS */
1804 static int __init ksm_init(void)
1806 struct task_struct *ksm_thread;
1809 ksm_max_kernel_pages = totalram_pages / 4;
1811 err = ksm_slab_init();
1815 err = mm_slots_hash_init();
1819 ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
1820 if (IS_ERR(ksm_thread)) {
1821 printk(KERN_ERR "ksm: creating kthread failed\n");
1822 err = PTR_ERR(ksm_thread);
1827 err = sysfs_create_group(mm_kobj, &ksm_attr_group);
1829 printk(KERN_ERR "ksm: register sysfs failed\n");
1830 kthread_stop(ksm_thread);
1834 ksm_run = KSM_RUN_MERGE; /* no way for user to start it */
1836 #endif /* CONFIG_SYSFS */
1841 mm_slots_hash_free();
1847 module_init(ksm_init)