1 // SPDX-License-Identifier: GPL-2.0-only
3 * Memory merging support.
5 * This code enables dynamic sharing of identical pages found in different
6 * memory areas, even if they are not shared by fork()
8 * Copyright (C) 2008-2009 Red Hat, Inc.
16 #include <linux/errno.h>
19 #include <linux/mman.h>
20 #include <linux/sched.h>
21 #include <linux/sched/mm.h>
22 #include <linux/sched/coredump.h>
23 #include <linux/rwsem.h>
24 #include <linux/pagemap.h>
25 #include <linux/rmap.h>
26 #include <linux/spinlock.h>
27 #include <linux/xxhash.h>
28 #include <linux/delay.h>
29 #include <linux/kthread.h>
30 #include <linux/wait.h>
31 #include <linux/slab.h>
32 #include <linux/rbtree.h>
33 #include <linux/memory.h>
34 #include <linux/mmu_notifier.h>
35 #include <linux/swap.h>
36 #include <linux/ksm.h>
37 #include <linux/hashtable.h>
38 #include <linux/freezer.h>
39 #include <linux/oom.h>
40 #include <linux/numa.h>
42 #include <asm/tlbflush.h>
47 #define DO_NUMA(x) do { (x); } while (0)
50 #define DO_NUMA(x) do { } while (0)
56 * A few notes about the KSM scanning process,
57 * to make it easier to understand the data structures below:
59 * In order to reduce excessive scanning, KSM sorts the memory pages by their
60 * contents into a data structure that holds pointers to the pages' locations.
62 * Since the contents of the pages may change at any moment, KSM cannot just
63 * insert the pages into a normal sorted tree and expect it to find anything.
64 * Therefore KSM uses two data structures - the stable and the unstable tree.
66 * The stable tree holds pointers to all the merged pages (ksm pages), sorted
67 * by their contents. Because each such page is write-protected, searching on
68 * this tree is fully assured to be working (except when pages are unmapped),
69 * and therefore this tree is called the stable tree.
71 * The stable tree node includes information required for reverse
72 * mapping from a KSM page to virtual addresses that map this page.
74 * In order to avoid large latencies of the rmap walks on KSM pages,
75 * KSM maintains two types of nodes in the stable tree:
77 * * the regular nodes that keep the reverse mapping structures in a
79 * * the "chains" that link nodes ("dups") that represent the same
80 * write protected memory content, but each "dup" corresponds to a
81 * different KSM page copy of that content
83 * Internally, the regular nodes, "dups" and "chains" are represented
84 * using the same :c:type:`struct stable_node` structure.
86 * In addition to the stable tree, KSM uses a second data structure called the
87 * unstable tree: this tree holds pointers to pages which have been found to
88 * be "unchanged for a period of time". The unstable tree sorts these pages
89 * by their contents, but since they are not write-protected, KSM cannot rely
90 * upon the unstable tree to work correctly - the unstable tree is liable to
91 * be corrupted as its contents are modified, and so it is called unstable.
93 * KSM solves this problem by several techniques:
95 * 1) The unstable tree is flushed every time KSM completes scanning all
96 * memory areas, and then the tree is rebuilt again from the beginning.
97 * 2) KSM will only insert into the unstable tree, pages whose hash value
98 * has not changed since the previous scan of all memory areas.
99 * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
100 * colors of the nodes and not on their contents, assuring that even when
101 * the tree gets "corrupted" it won't get out of balance, so scanning time
102 * remains the same (also, searching and inserting nodes in an rbtree uses
103 * the same algorithm, so we have no overhead when we flush and rebuild).
104 * 4) KSM never flushes the stable tree, which means that even if it were to
105 * take 10 attempts to find a page in the unstable tree, once it is found,
106 * it is secured in the stable tree. (When we scan a new page, we first
107 * compare it against the stable tree, and then against the unstable tree.)
109 * If the merge_across_nodes tunable is unset, then KSM maintains multiple
110 * stable trees and multiple unstable trees: one of each for each NUMA node.
114 * struct mm_slot - ksm information per mm that is being scanned
115 * @link: link to the mm_slots hash list
116 * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
117 * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
118 * @mm: the mm that this information is valid for
121 struct hlist_node link;
122 struct list_head mm_list;
123 struct rmap_item *rmap_list;
124 struct mm_struct *mm;
128 * struct ksm_scan - cursor for scanning
129 * @mm_slot: the current mm_slot we are scanning
130 * @address: the next address inside that to be scanned
131 * @rmap_list: link to the next rmap to be scanned in the rmap_list
132 * @seqnr: count of completed full scans (needed when removing unstable node)
134 * There is only the one ksm_scan instance of this cursor structure.
137 struct mm_slot *mm_slot;
138 unsigned long address;
139 struct rmap_item **rmap_list;
144 * struct stable_node - node of the stable rbtree
145 * @node: rb node of this ksm page in the stable tree
146 * @head: (overlaying parent) &migrate_nodes indicates temporarily on that list
147 * @hlist_dup: linked into the stable_node->hlist with a stable_node chain
148 * @list: linked into migrate_nodes, pending placement in the proper node tree
149 * @hlist: hlist head of rmap_items using this ksm page
150 * @kpfn: page frame number of this ksm page (perhaps temporarily on wrong nid)
151 * @chain_prune_time: time of the last full garbage collection
152 * @rmap_hlist_len: number of rmap_item entries in hlist or STABLE_NODE_CHAIN
153 * @nid: NUMA node id of stable tree in which linked (may not match kpfn)
157 struct rb_node node; /* when node of stable tree */
158 struct { /* when listed for migration */
159 struct list_head *head;
161 struct hlist_node hlist_dup;
162 struct list_head list;
166 struct hlist_head hlist;
169 unsigned long chain_prune_time;
172 * STABLE_NODE_CHAIN can be any negative number in
173 * rmap_hlist_len negative range, but better not -1 to be able
174 * to reliably detect underflows.
176 #define STABLE_NODE_CHAIN -1024
184 * struct rmap_item - reverse mapping item for virtual addresses
185 * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
186 * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
187 * @nid: NUMA node id of unstable tree in which linked (may not match page)
188 * @mm: the memory structure this rmap_item is pointing into
189 * @address: the virtual address this rmap_item tracks (+ flags in low bits)
190 * @oldchecksum: previous checksum of the page at that virtual address
191 * @node: rb node of this rmap_item in the unstable tree
192 * @head: pointer to stable_node heading this list in the stable tree
193 * @hlist: link into hlist of rmap_items hanging off that stable_node
196 struct rmap_item *rmap_list;
198 struct anon_vma *anon_vma; /* when stable */
200 int nid; /* when node of unstable tree */
203 struct mm_struct *mm;
204 unsigned long address; /* + low bits used for flags below */
205 unsigned int oldchecksum; /* when unstable */
207 struct rb_node node; /* when node of unstable tree */
208 struct { /* when listed from stable tree */
209 struct stable_node *head;
210 struct hlist_node hlist;
215 #define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */
216 #define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */
217 #define STABLE_FLAG 0x200 /* is listed from the stable tree */
218 #define KSM_FLAG_MASK (SEQNR_MASK|UNSTABLE_FLAG|STABLE_FLAG)
219 /* to mask all the flags */
221 /* The stable and unstable tree heads */
222 static struct rb_root one_stable_tree[1] = { RB_ROOT };
223 static struct rb_root one_unstable_tree[1] = { RB_ROOT };
224 static struct rb_root *root_stable_tree = one_stable_tree;
225 static struct rb_root *root_unstable_tree = one_unstable_tree;
227 /* Recently migrated nodes of stable tree, pending proper placement */
228 static LIST_HEAD(migrate_nodes);
229 #define STABLE_NODE_DUP_HEAD ((struct list_head *)&migrate_nodes.prev)
231 #define MM_SLOTS_HASH_BITS 10
232 static DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
234 static struct mm_slot ksm_mm_head = {
235 .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
237 static struct ksm_scan ksm_scan = {
238 .mm_slot = &ksm_mm_head,
241 static struct kmem_cache *rmap_item_cache;
242 static struct kmem_cache *stable_node_cache;
243 static struct kmem_cache *mm_slot_cache;
245 /* The number of nodes in the stable tree */
246 static unsigned long ksm_pages_shared;
248 /* The number of page slots additionally sharing those nodes */
249 static unsigned long ksm_pages_sharing;
251 /* The number of nodes in the unstable tree */
252 static unsigned long ksm_pages_unshared;
254 /* The number of rmap_items in use: to calculate pages_volatile */
255 static unsigned long ksm_rmap_items;
257 /* The number of stable_node chains */
258 static unsigned long ksm_stable_node_chains;
260 /* The number of stable_node dups linked to the stable_node chains */
261 static unsigned long ksm_stable_node_dups;
263 /* Delay in pruning stale stable_node_dups in the stable_node_chains */
264 static int ksm_stable_node_chains_prune_millisecs = 2000;
266 /* Maximum number of page slots sharing a stable node */
267 static int ksm_max_page_sharing = 256;
269 /* Number of pages ksmd should scan in one batch */
270 static unsigned int ksm_thread_pages_to_scan = 100;
272 /* Milliseconds ksmd should sleep between batches */
273 static unsigned int ksm_thread_sleep_millisecs = 20;
275 /* Checksum of an empty (zeroed) page */
276 static unsigned int zero_checksum __read_mostly;
278 /* Whether to merge empty (zeroed) pages with actual zero pages */
279 static bool ksm_use_zero_pages __read_mostly;
282 /* Zeroed when merging across nodes is not allowed */
283 static unsigned int ksm_merge_across_nodes = 1;
284 static int ksm_nr_node_ids = 1;
286 #define ksm_merge_across_nodes 1U
287 #define ksm_nr_node_ids 1
290 #define KSM_RUN_STOP 0
291 #define KSM_RUN_MERGE 1
292 #define KSM_RUN_UNMERGE 2
293 #define KSM_RUN_OFFLINE 4
294 static unsigned long ksm_run = KSM_RUN_STOP;
295 static void wait_while_offlining(void);
297 static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
298 static DECLARE_WAIT_QUEUE_HEAD(ksm_iter_wait);
299 static DEFINE_MUTEX(ksm_thread_mutex);
300 static DEFINE_SPINLOCK(ksm_mmlist_lock);
302 #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
303 sizeof(struct __struct), __alignof__(struct __struct),\
306 static int __init ksm_slab_init(void)
308 rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
309 if (!rmap_item_cache)
312 stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
313 if (!stable_node_cache)
316 mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
323 kmem_cache_destroy(stable_node_cache);
325 kmem_cache_destroy(rmap_item_cache);
330 static void __init ksm_slab_free(void)
332 kmem_cache_destroy(mm_slot_cache);
333 kmem_cache_destroy(stable_node_cache);
334 kmem_cache_destroy(rmap_item_cache);
335 mm_slot_cache = NULL;
338 static __always_inline bool is_stable_node_chain(struct stable_node *chain)
340 return chain->rmap_hlist_len == STABLE_NODE_CHAIN;
343 static __always_inline bool is_stable_node_dup(struct stable_node *dup)
345 return dup->head == STABLE_NODE_DUP_HEAD;
348 static inline void stable_node_chain_add_dup(struct stable_node *dup,
349 struct stable_node *chain)
351 VM_BUG_ON(is_stable_node_dup(dup));
352 dup->head = STABLE_NODE_DUP_HEAD;
353 VM_BUG_ON(!is_stable_node_chain(chain));
354 hlist_add_head(&dup->hlist_dup, &chain->hlist);
355 ksm_stable_node_dups++;
358 static inline void __stable_node_dup_del(struct stable_node *dup)
360 VM_BUG_ON(!is_stable_node_dup(dup));
361 hlist_del(&dup->hlist_dup);
362 ksm_stable_node_dups--;
365 static inline void stable_node_dup_del(struct stable_node *dup)
367 VM_BUG_ON(is_stable_node_chain(dup));
368 if (is_stable_node_dup(dup))
369 __stable_node_dup_del(dup);
371 rb_erase(&dup->node, root_stable_tree + NUMA(dup->nid));
372 #ifdef CONFIG_DEBUG_VM
377 static inline struct rmap_item *alloc_rmap_item(void)
379 struct rmap_item *rmap_item;
381 rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL |
382 __GFP_NORETRY | __GFP_NOWARN);
388 static inline void free_rmap_item(struct rmap_item *rmap_item)
391 rmap_item->mm = NULL; /* debug safety */
392 kmem_cache_free(rmap_item_cache, rmap_item);
395 static inline struct stable_node *alloc_stable_node(void)
398 * The allocation can take too long with GFP_KERNEL when memory is under
399 * pressure, which may lead to hung task warnings. Adding __GFP_HIGH
400 * grants access to memory reserves, helping to avoid this problem.
402 return kmem_cache_alloc(stable_node_cache, GFP_KERNEL | __GFP_HIGH);
405 static inline void free_stable_node(struct stable_node *stable_node)
407 VM_BUG_ON(stable_node->rmap_hlist_len &&
408 !is_stable_node_chain(stable_node));
409 kmem_cache_free(stable_node_cache, stable_node);
412 static inline struct mm_slot *alloc_mm_slot(void)
414 if (!mm_slot_cache) /* initialization failed */
416 return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
419 static inline void free_mm_slot(struct mm_slot *mm_slot)
421 kmem_cache_free(mm_slot_cache, mm_slot);
424 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
426 struct mm_slot *slot;
428 hash_for_each_possible(mm_slots_hash, slot, link, (unsigned long)mm)
435 static void insert_to_mm_slots_hash(struct mm_struct *mm,
436 struct mm_slot *mm_slot)
439 hash_add(mm_slots_hash, &mm_slot->link, (unsigned long)mm);
443 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
444 * page tables after it has passed through ksm_exit() - which, if necessary,
445 * takes mmap_sem briefly to serialize against them. ksm_exit() does not set
446 * a special flag: they can just back out as soon as mm_users goes to zero.
447 * ksm_test_exit() is used throughout to make this test for exit: in some
448 * places for correctness, in some places just to avoid unnecessary work.
450 static inline bool ksm_test_exit(struct mm_struct *mm)
452 return atomic_read(&mm->mm_users) == 0;
456 * We use break_ksm to break COW on a ksm page: it's a stripped down
458 * if (get_user_pages(addr, 1, 1, 1, &page, NULL) == 1)
461 * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
462 * in case the application has unmapped and remapped mm,addr meanwhile.
463 * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP
464 * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
466 * FAULT_FLAG/FOLL_REMOTE are because we do this outside the context
467 * of the process that owns 'vma'. We also do not want to enforce
468 * protection keys here anyway.
470 static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
477 page = follow_page(vma, addr,
478 FOLL_GET | FOLL_MIGRATION | FOLL_REMOTE);
479 if (IS_ERR_OR_NULL(page))
482 ret = handle_mm_fault(vma, addr,
483 FAULT_FLAG_WRITE | FAULT_FLAG_REMOTE);
485 ret = VM_FAULT_WRITE;
487 } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | VM_FAULT_OOM)));
489 * We must loop because handle_mm_fault() may back out if there's
490 * any difficulty e.g. if pte accessed bit gets updated concurrently.
492 * VM_FAULT_WRITE is what we have been hoping for: it indicates that
493 * COW has been broken, even if the vma does not permit VM_WRITE;
494 * but note that a concurrent fault might break PageKsm for us.
496 * VM_FAULT_SIGBUS could occur if we race with truncation of the
497 * backing file, which also invalidates anonymous pages: that's
498 * okay, that truncation will have unmapped the PageKsm for us.
500 * VM_FAULT_OOM: at the time of writing (late July 2009), setting
501 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
502 * current task has TIF_MEMDIE set, and will be OOM killed on return
503 * to user; and ksmd, having no mm, would never be chosen for that.
505 * But if the mm is in a limited mem_cgroup, then the fault may fail
506 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
507 * even ksmd can fail in this way - though it's usually breaking ksm
508 * just to undo a merge it made a moment before, so unlikely to oom.
510 * That's a pity: we might therefore have more kernel pages allocated
511 * than we're counting as nodes in the stable tree; but ksm_do_scan
512 * will retry to break_cow on each pass, so should recover the page
513 * in due course. The important thing is to not let VM_MERGEABLE
514 * be cleared while any such pages might remain in the area.
516 return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
519 static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
522 struct vm_area_struct *vma;
523 if (ksm_test_exit(mm))
525 vma = find_vma(mm, addr);
526 if (!vma || vma->vm_start > addr)
528 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
533 static void break_cow(struct rmap_item *rmap_item)
535 struct mm_struct *mm = rmap_item->mm;
536 unsigned long addr = rmap_item->address;
537 struct vm_area_struct *vma;
540 * It is not an accident that whenever we want to break COW
541 * to undo, we also need to drop a reference to the anon_vma.
543 put_anon_vma(rmap_item->anon_vma);
545 down_read(&mm->mmap_sem);
546 vma = find_mergeable_vma(mm, addr);
548 break_ksm(vma, addr);
549 up_read(&mm->mmap_sem);
552 static struct page *get_mergeable_page(struct rmap_item *rmap_item)
554 struct mm_struct *mm = rmap_item->mm;
555 unsigned long addr = rmap_item->address;
556 struct vm_area_struct *vma;
559 down_read(&mm->mmap_sem);
560 vma = find_mergeable_vma(mm, addr);
564 page = follow_page(vma, addr, FOLL_GET);
565 if (IS_ERR_OR_NULL(page))
567 if (PageAnon(page)) {
568 flush_anon_page(vma, page, addr);
569 flush_dcache_page(page);
575 up_read(&mm->mmap_sem);
580 * This helper is used for getting right index into array of tree roots.
581 * When merge_across_nodes knob is set to 1, there are only two rb-trees for
582 * stable and unstable pages from all nodes with roots in index 0. Otherwise,
583 * every node has its own stable and unstable tree.
585 static inline int get_kpfn_nid(unsigned long kpfn)
587 return ksm_merge_across_nodes ? 0 : NUMA(pfn_to_nid(kpfn));
590 static struct stable_node *alloc_stable_node_chain(struct stable_node *dup,
591 struct rb_root *root)
593 struct stable_node *chain = alloc_stable_node();
594 VM_BUG_ON(is_stable_node_chain(dup));
596 INIT_HLIST_HEAD(&chain->hlist);
597 chain->chain_prune_time = jiffies;
598 chain->rmap_hlist_len = STABLE_NODE_CHAIN;
599 #if defined (CONFIG_DEBUG_VM) && defined(CONFIG_NUMA)
600 chain->nid = NUMA_NO_NODE; /* debug */
602 ksm_stable_node_chains++;
605 * Put the stable node chain in the first dimension of
606 * the stable tree and at the same time remove the old
609 rb_replace_node(&dup->node, &chain->node, root);
612 * Move the old stable node to the second dimension
613 * queued in the hlist_dup. The invariant is that all
614 * dup stable_nodes in the chain->hlist point to pages
615 * that are wrprotected and have the exact same
618 stable_node_chain_add_dup(dup, chain);
623 static inline void free_stable_node_chain(struct stable_node *chain,
624 struct rb_root *root)
626 rb_erase(&chain->node, root);
627 free_stable_node(chain);
628 ksm_stable_node_chains--;
631 static void remove_node_from_stable_tree(struct stable_node *stable_node)
633 struct rmap_item *rmap_item;
635 /* check it's not STABLE_NODE_CHAIN or negative */
636 BUG_ON(stable_node->rmap_hlist_len < 0);
638 hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
639 if (rmap_item->hlist.next)
643 VM_BUG_ON(stable_node->rmap_hlist_len <= 0);
644 stable_node->rmap_hlist_len--;
645 put_anon_vma(rmap_item->anon_vma);
646 rmap_item->address &= PAGE_MASK;
651 * We need the second aligned pointer of the migrate_nodes
652 * list_head to stay clear from the rb_parent_color union
653 * (aligned and different than any node) and also different
654 * from &migrate_nodes. This will verify that future list.h changes
655 * don't break STABLE_NODE_DUP_HEAD. Only recent gcc can handle it.
657 #if defined(GCC_VERSION) && GCC_VERSION >= 40903
658 BUILD_BUG_ON(STABLE_NODE_DUP_HEAD <= &migrate_nodes);
659 BUILD_BUG_ON(STABLE_NODE_DUP_HEAD >= &migrate_nodes + 1);
662 if (stable_node->head == &migrate_nodes)
663 list_del(&stable_node->list);
665 stable_node_dup_del(stable_node);
666 free_stable_node(stable_node);
669 enum get_ksm_page_flags {
676 * get_ksm_page: checks if the page indicated by the stable node
677 * is still its ksm page, despite having held no reference to it.
678 * In which case we can trust the content of the page, and it
679 * returns the gotten page; but if the page has now been zapped,
680 * remove the stale node from the stable tree and return NULL.
681 * But beware, the stable node's page might be being migrated.
683 * You would expect the stable_node to hold a reference to the ksm page.
684 * But if it increments the page's count, swapping out has to wait for
685 * ksmd to come around again before it can free the page, which may take
686 * seconds or even minutes: much too unresponsive. So instead we use a
687 * "keyhole reference": access to the ksm page from the stable node peeps
688 * out through its keyhole to see if that page still holds the right key,
689 * pointing back to this stable node. This relies on freeing a PageAnon
690 * page to reset its page->mapping to NULL, and relies on no other use of
691 * a page to put something that might look like our key in page->mapping.
692 * is on its way to being freed; but it is an anomaly to bear in mind.
694 static struct page *get_ksm_page(struct stable_node *stable_node,
695 enum get_ksm_page_flags flags)
698 void *expected_mapping;
701 expected_mapping = (void *)((unsigned long)stable_node |
704 kpfn = READ_ONCE(stable_node->kpfn); /* Address dependency. */
705 page = pfn_to_page(kpfn);
706 if (READ_ONCE(page->mapping) != expected_mapping)
710 * We cannot do anything with the page while its refcount is 0.
711 * Usually 0 means free, or tail of a higher-order page: in which
712 * case this node is no longer referenced, and should be freed;
713 * however, it might mean that the page is under page_ref_freeze().
714 * The __remove_mapping() case is easy, again the node is now stale;
715 * the same is in reuse_ksm_page() case; but if page is swapcache
716 * in migrate_page_move_mapping(), it might still be our page,
717 * in which case it's essential to keep the node.
719 while (!get_page_unless_zero(page)) {
721 * Another check for page->mapping != expected_mapping would
722 * work here too. We have chosen the !PageSwapCache test to
723 * optimize the common case, when the page is or is about to
724 * be freed: PageSwapCache is cleared (under spin_lock_irq)
725 * in the ref_freeze section of __remove_mapping(); but Anon
726 * page->mapping reset to NULL later, in free_pages_prepare().
728 if (!PageSwapCache(page))
733 if (READ_ONCE(page->mapping) != expected_mapping) {
738 if (flags == GET_KSM_PAGE_TRYLOCK) {
739 if (!trylock_page(page)) {
741 return ERR_PTR(-EBUSY);
743 } else if (flags == GET_KSM_PAGE_LOCK)
746 if (flags != GET_KSM_PAGE_NOLOCK) {
747 if (READ_ONCE(page->mapping) != expected_mapping) {
757 * We come here from above when page->mapping or !PageSwapCache
758 * suggests that the node is stale; but it might be under migration.
759 * We need smp_rmb(), matching the smp_wmb() in ksm_migrate_page(),
760 * before checking whether node->kpfn has been changed.
763 if (READ_ONCE(stable_node->kpfn) != kpfn)
765 remove_node_from_stable_tree(stable_node);
770 * Removing rmap_item from stable or unstable tree.
771 * This function will clean the information from the stable/unstable tree.
773 static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
775 if (rmap_item->address & STABLE_FLAG) {
776 struct stable_node *stable_node;
779 stable_node = rmap_item->head;
780 page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
784 hlist_del(&rmap_item->hlist);
788 if (!hlist_empty(&stable_node->hlist))
792 VM_BUG_ON(stable_node->rmap_hlist_len <= 0);
793 stable_node->rmap_hlist_len--;
795 put_anon_vma(rmap_item->anon_vma);
796 rmap_item->address &= PAGE_MASK;
798 } else if (rmap_item->address & UNSTABLE_FLAG) {
801 * Usually ksmd can and must skip the rb_erase, because
802 * root_unstable_tree was already reset to RB_ROOT.
803 * But be careful when an mm is exiting: do the rb_erase
804 * if this rmap_item was inserted by this scan, rather
805 * than left over from before.
807 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
810 rb_erase(&rmap_item->node,
811 root_unstable_tree + NUMA(rmap_item->nid));
812 ksm_pages_unshared--;
813 rmap_item->address &= PAGE_MASK;
816 cond_resched(); /* we're called from many long loops */
819 static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
820 struct rmap_item **rmap_list)
823 struct rmap_item *rmap_item = *rmap_list;
824 *rmap_list = rmap_item->rmap_list;
825 remove_rmap_item_from_tree(rmap_item);
826 free_rmap_item(rmap_item);
831 * Though it's very tempting to unmerge rmap_items from stable tree rather
832 * than check every pte of a given vma, the locking doesn't quite work for
833 * that - an rmap_item is assigned to the stable tree after inserting ksm
834 * page and upping mmap_sem. Nor does it fit with the way we skip dup'ing
835 * rmap_items from parent to child at fork time (so as not to waste time
836 * if exit comes before the next scan reaches it).
838 * Similarly, although we'd like to remove rmap_items (so updating counts
839 * and freeing memory) when unmerging an area, it's easier to leave that
840 * to the next pass of ksmd - consider, for example, how ksmd might be
841 * in cmp_and_merge_page on one of the rmap_items we would be removing.
843 static int unmerge_ksm_pages(struct vm_area_struct *vma,
844 unsigned long start, unsigned long end)
849 for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
850 if (ksm_test_exit(vma->vm_mm))
852 if (signal_pending(current))
855 err = break_ksm(vma, addr);
860 static inline struct stable_node *page_stable_node(struct page *page)
862 return PageKsm(page) ? page_rmapping(page) : NULL;
865 static inline void set_page_stable_node(struct page *page,
866 struct stable_node *stable_node)
868 page->mapping = (void *)((unsigned long)stable_node | PAGE_MAPPING_KSM);
873 * Only called through the sysfs control interface:
875 static int remove_stable_node(struct stable_node *stable_node)
880 page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
883 * get_ksm_page did remove_node_from_stable_tree itself.
889 * Page could be still mapped if this races with __mmput() running in
890 * between ksm_exit() and exit_mmap(). Just refuse to let
891 * merge_across_nodes/max_page_sharing be switched.
894 if (!page_mapped(page)) {
896 * The stable node did not yet appear stale to get_ksm_page(),
897 * since that allows for an unmapped ksm page to be recognized
898 * right up until it is freed; but the node is safe to remove.
899 * This page might be in a pagevec waiting to be freed,
900 * or it might be PageSwapCache (perhaps under writeback),
901 * or it might have been removed from swapcache a moment ago.
903 set_page_stable_node(page, NULL);
904 remove_node_from_stable_tree(stable_node);
913 static int remove_stable_node_chain(struct stable_node *stable_node,
914 struct rb_root *root)
916 struct stable_node *dup;
917 struct hlist_node *hlist_safe;
919 if (!is_stable_node_chain(stable_node)) {
920 VM_BUG_ON(is_stable_node_dup(stable_node));
921 if (remove_stable_node(stable_node))
927 hlist_for_each_entry_safe(dup, hlist_safe,
928 &stable_node->hlist, hlist_dup) {
929 VM_BUG_ON(!is_stable_node_dup(dup));
930 if (remove_stable_node(dup))
933 BUG_ON(!hlist_empty(&stable_node->hlist));
934 free_stable_node_chain(stable_node, root);
938 static int remove_all_stable_nodes(void)
940 struct stable_node *stable_node, *next;
944 for (nid = 0; nid < ksm_nr_node_ids; nid++) {
945 while (root_stable_tree[nid].rb_node) {
946 stable_node = rb_entry(root_stable_tree[nid].rb_node,
947 struct stable_node, node);
948 if (remove_stable_node_chain(stable_node,
949 root_stable_tree + nid)) {
951 break; /* proceed to next nid */
956 list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
957 if (remove_stable_node(stable_node))
964 static int unmerge_and_remove_all_rmap_items(void)
966 struct mm_slot *mm_slot;
967 struct mm_struct *mm;
968 struct vm_area_struct *vma;
971 spin_lock(&ksm_mmlist_lock);
972 ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
973 struct mm_slot, mm_list);
974 spin_unlock(&ksm_mmlist_lock);
976 for (mm_slot = ksm_scan.mm_slot;
977 mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
979 down_read(&mm->mmap_sem);
980 for (vma = mm->mmap; vma; vma = vma->vm_next) {
981 if (ksm_test_exit(mm))
983 if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
985 err = unmerge_ksm_pages(vma,
986 vma->vm_start, vma->vm_end);
991 remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
992 up_read(&mm->mmap_sem);
994 spin_lock(&ksm_mmlist_lock);
995 ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
996 struct mm_slot, mm_list);
997 if (ksm_test_exit(mm)) {
998 hash_del(&mm_slot->link);
999 list_del(&mm_slot->mm_list);
1000 spin_unlock(&ksm_mmlist_lock);
1002 free_mm_slot(mm_slot);
1003 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1006 spin_unlock(&ksm_mmlist_lock);
1009 /* Clean up stable nodes, but don't worry if some are still busy */
1010 remove_all_stable_nodes();
1015 up_read(&mm->mmap_sem);
1016 spin_lock(&ksm_mmlist_lock);
1017 ksm_scan.mm_slot = &ksm_mm_head;
1018 spin_unlock(&ksm_mmlist_lock);
1021 #endif /* CONFIG_SYSFS */
1023 static u32 calc_checksum(struct page *page)
1026 void *addr = kmap_atomic(page);
1027 checksum = xxhash(addr, PAGE_SIZE, 0);
1028 kunmap_atomic(addr);
1032 static int write_protect_page(struct vm_area_struct *vma, struct page *page,
1035 struct mm_struct *mm = vma->vm_mm;
1036 struct page_vma_mapped_walk pvmw = {
1042 struct mmu_notifier_range range;
1044 pvmw.address = page_address_in_vma(page, vma);
1045 if (pvmw.address == -EFAULT)
1048 BUG_ON(PageTransCompound(page));
1050 mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm,
1052 pvmw.address + PAGE_SIZE);
1053 mmu_notifier_invalidate_range_start(&range);
1055 if (!page_vma_mapped_walk(&pvmw))
1057 if (WARN_ONCE(!pvmw.pte, "Unexpected PMD mapping?"))
1060 if (pte_write(*pvmw.pte) || pte_dirty(*pvmw.pte) ||
1061 (pte_protnone(*pvmw.pte) && pte_savedwrite(*pvmw.pte)) ||
1062 mm_tlb_flush_pending(mm)) {
1065 swapped = PageSwapCache(page);
1066 flush_cache_page(vma, pvmw.address, page_to_pfn(page));
1068 * Ok this is tricky, when get_user_pages_fast() run it doesn't
1069 * take any lock, therefore the check that we are going to make
1070 * with the pagecount against the mapcount is racey and
1071 * O_DIRECT can happen right after the check.
1072 * So we clear the pte and flush the tlb before the check
1073 * this assure us that no O_DIRECT can happen after the check
1074 * or in the middle of the check.
1076 * No need to notify as we are downgrading page table to read
1077 * only not changing it to point to a new page.
1079 * See Documentation/vm/mmu_notifier.rst
1081 entry = ptep_clear_flush(vma, pvmw.address, pvmw.pte);
1083 * Check that no O_DIRECT or similar I/O is in progress on the
1086 if (page_mapcount(page) + 1 + swapped != page_count(page)) {
1087 set_pte_at(mm, pvmw.address, pvmw.pte, entry);
1090 if (pte_dirty(entry))
1091 set_page_dirty(page);
1093 if (pte_protnone(entry))
1094 entry = pte_mkclean(pte_clear_savedwrite(entry));
1096 entry = pte_mkclean(pte_wrprotect(entry));
1097 set_pte_at_notify(mm, pvmw.address, pvmw.pte, entry);
1099 *orig_pte = *pvmw.pte;
1103 page_vma_mapped_walk_done(&pvmw);
1105 mmu_notifier_invalidate_range_end(&range);
1111 * replace_page - replace page in vma by new ksm page
1112 * @vma: vma that holds the pte pointing to page
1113 * @page: the page we are replacing by kpage
1114 * @kpage: the ksm page we replace page by
1115 * @orig_pte: the original value of the pte
1117 * Returns 0 on success, -EFAULT on failure.
1119 static int replace_page(struct vm_area_struct *vma, struct page *page,
1120 struct page *kpage, pte_t orig_pte)
1122 struct mm_struct *mm = vma->vm_mm;
1129 struct mmu_notifier_range range;
1131 addr = page_address_in_vma(page, vma);
1132 if (addr == -EFAULT)
1135 pmd = mm_find_pmd(mm, addr);
1139 mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm, addr,
1141 mmu_notifier_invalidate_range_start(&range);
1143 ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
1144 if (!pte_same(*ptep, orig_pte)) {
1145 pte_unmap_unlock(ptep, ptl);
1150 * No need to check ksm_use_zero_pages here: we can only have a
1151 * zero_page here if ksm_use_zero_pages was enabled alreaady.
1153 if (!is_zero_pfn(page_to_pfn(kpage))) {
1155 page_add_anon_rmap(kpage, vma, addr, false);
1156 newpte = mk_pte(kpage, vma->vm_page_prot);
1158 newpte = pte_mkspecial(pfn_pte(page_to_pfn(kpage),
1159 vma->vm_page_prot));
1161 * We're replacing an anonymous page with a zero page, which is
1162 * not anonymous. We need to do proper accounting otherwise we
1163 * will get wrong values in /proc, and a BUG message in dmesg
1164 * when tearing down the mm.
1166 dec_mm_counter(mm, MM_ANONPAGES);
1169 flush_cache_page(vma, addr, pte_pfn(*ptep));
1171 * No need to notify as we are replacing a read only page with another
1172 * read only page with the same content.
1174 * See Documentation/vm/mmu_notifier.rst
1176 ptep_clear_flush(vma, addr, ptep);
1177 set_pte_at_notify(mm, addr, ptep, newpte);
1179 page_remove_rmap(page, false);
1180 if (!page_mapped(page))
1181 try_to_free_swap(page);
1184 pte_unmap_unlock(ptep, ptl);
1187 mmu_notifier_invalidate_range_end(&range);
1193 * try_to_merge_one_page - take two pages and merge them into one
1194 * @vma: the vma that holds the pte pointing to page
1195 * @page: the PageAnon page that we want to replace with kpage
1196 * @kpage: the PageKsm page that we want to map instead of page,
1197 * or NULL the first time when we want to use page as kpage.
1199 * This function returns 0 if the pages were merged, -EFAULT otherwise.
1201 static int try_to_merge_one_page(struct vm_area_struct *vma,
1202 struct page *page, struct page *kpage)
1204 pte_t orig_pte = __pte(0);
1207 if (page == kpage) /* ksm page forked */
1210 if (!PageAnon(page))
1214 * We need the page lock to read a stable PageSwapCache in
1215 * write_protect_page(). We use trylock_page() instead of
1216 * lock_page() because we don't want to wait here - we
1217 * prefer to continue scanning and merging different pages,
1218 * then come back to this page when it is unlocked.
1220 if (!trylock_page(page))
1223 if (PageTransCompound(page)) {
1224 if (split_huge_page(page))
1229 * If this anonymous page is mapped only here, its pte may need
1230 * to be write-protected. If it's mapped elsewhere, all of its
1231 * ptes are necessarily already write-protected. But in either
1232 * case, we need to lock and check page_count is not raised.
1234 if (write_protect_page(vma, page, &orig_pte) == 0) {
1237 * While we hold page lock, upgrade page from
1238 * PageAnon+anon_vma to PageKsm+NULL stable_node:
1239 * stable_tree_insert() will update stable_node.
1241 set_page_stable_node(page, NULL);
1242 mark_page_accessed(page);
1244 * Page reclaim just frees a clean page with no dirty
1245 * ptes: make sure that the ksm page would be swapped.
1247 if (!PageDirty(page))
1250 } else if (pages_identical(page, kpage))
1251 err = replace_page(vma, page, kpage, orig_pte);
1254 if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
1255 munlock_vma_page(page);
1256 if (!PageMlocked(kpage)) {
1259 mlock_vma_page(kpage);
1260 page = kpage; /* for final unlock */
1271 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
1272 * but no new kernel page is allocated: kpage must already be a ksm page.
1274 * This function returns 0 if the pages were merged, -EFAULT otherwise.
1276 static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
1277 struct page *page, struct page *kpage)
1279 struct mm_struct *mm = rmap_item->mm;
1280 struct vm_area_struct *vma;
1283 down_read(&mm->mmap_sem);
1284 vma = find_mergeable_vma(mm, rmap_item->address);
1288 err = try_to_merge_one_page(vma, page, kpage);
1292 /* Unstable nid is in union with stable anon_vma: remove first */
1293 remove_rmap_item_from_tree(rmap_item);
1295 /* Must get reference to anon_vma while still holding mmap_sem */
1296 rmap_item->anon_vma = vma->anon_vma;
1297 get_anon_vma(vma->anon_vma);
1299 up_read(&mm->mmap_sem);
1304 * try_to_merge_two_pages - take two identical pages and prepare them
1305 * to be merged into one page.
1307 * This function returns the kpage if we successfully merged two identical
1308 * pages into one ksm page, NULL otherwise.
1310 * Note that this function upgrades page to ksm page: if one of the pages
1311 * is already a ksm page, try_to_merge_with_ksm_page should be used.
1313 static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
1315 struct rmap_item *tree_rmap_item,
1316 struct page *tree_page)
1320 err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
1322 err = try_to_merge_with_ksm_page(tree_rmap_item,
1325 * If that fails, we have a ksm page with only one pte
1326 * pointing to it: so break it.
1329 break_cow(rmap_item);
1331 return err ? NULL : page;
1334 static __always_inline
1335 bool __is_page_sharing_candidate(struct stable_node *stable_node, int offset)
1337 VM_BUG_ON(stable_node->rmap_hlist_len < 0);
1339 * Check that at least one mapping still exists, otherwise
1340 * there's no much point to merge and share with this
1341 * stable_node, as the underlying tree_page of the other
1342 * sharer is going to be freed soon.
1344 return stable_node->rmap_hlist_len &&
1345 stable_node->rmap_hlist_len + offset < ksm_max_page_sharing;
1348 static __always_inline
1349 bool is_page_sharing_candidate(struct stable_node *stable_node)
1351 return __is_page_sharing_candidate(stable_node, 0);
1354 static struct page *stable_node_dup(struct stable_node **_stable_node_dup,
1355 struct stable_node **_stable_node,
1356 struct rb_root *root,
1357 bool prune_stale_stable_nodes)
1359 struct stable_node *dup, *found = NULL, *stable_node = *_stable_node;
1360 struct hlist_node *hlist_safe;
1361 struct page *_tree_page, *tree_page = NULL;
1363 int found_rmap_hlist_len;
1365 if (!prune_stale_stable_nodes ||
1366 time_before(jiffies, stable_node->chain_prune_time +
1368 ksm_stable_node_chains_prune_millisecs)))
1369 prune_stale_stable_nodes = false;
1371 stable_node->chain_prune_time = jiffies;
1373 hlist_for_each_entry_safe(dup, hlist_safe,
1374 &stable_node->hlist, hlist_dup) {
1377 * We must walk all stable_node_dup to prune the stale
1378 * stable nodes during lookup.
1380 * get_ksm_page can drop the nodes from the
1381 * stable_node->hlist if they point to freed pages
1382 * (that's why we do a _safe walk). The "dup"
1383 * stable_node parameter itself will be freed from
1384 * under us if it returns NULL.
1386 _tree_page = get_ksm_page(dup, GET_KSM_PAGE_NOLOCK);
1390 if (is_page_sharing_candidate(dup)) {
1392 dup->rmap_hlist_len > found_rmap_hlist_len) {
1394 put_page(tree_page);
1396 found_rmap_hlist_len = found->rmap_hlist_len;
1397 tree_page = _tree_page;
1399 /* skip put_page for found dup */
1400 if (!prune_stale_stable_nodes)
1405 put_page(_tree_page);
1410 * nr is counting all dups in the chain only if
1411 * prune_stale_stable_nodes is true, otherwise we may
1412 * break the loop at nr == 1 even if there are
1415 if (prune_stale_stable_nodes && nr == 1) {
1417 * If there's not just one entry it would
1418 * corrupt memory, better BUG_ON. In KSM
1419 * context with no lock held it's not even
1422 BUG_ON(stable_node->hlist.first->next);
1425 * There's just one entry and it is below the
1426 * deduplication limit so drop the chain.
1428 rb_replace_node(&stable_node->node, &found->node,
1430 free_stable_node(stable_node);
1431 ksm_stable_node_chains--;
1432 ksm_stable_node_dups--;
1434 * NOTE: the caller depends on the stable_node
1435 * to be equal to stable_node_dup if the chain
1438 *_stable_node = found;
1440 * Just for robustneess as stable_node is
1441 * otherwise left as a stable pointer, the
1442 * compiler shall optimize it away at build
1446 } else if (stable_node->hlist.first != &found->hlist_dup &&
1447 __is_page_sharing_candidate(found, 1)) {
1449 * If the found stable_node dup can accept one
1450 * more future merge (in addition to the one
1451 * that is underway) and is not at the head of
1452 * the chain, put it there so next search will
1453 * be quicker in the !prune_stale_stable_nodes
1456 * NOTE: it would be inaccurate to use nr > 1
1457 * instead of checking the hlist.first pointer
1458 * directly, because in the
1459 * prune_stale_stable_nodes case "nr" isn't
1460 * the position of the found dup in the chain,
1461 * but the total number of dups in the chain.
1463 hlist_del(&found->hlist_dup);
1464 hlist_add_head(&found->hlist_dup,
1465 &stable_node->hlist);
1469 *_stable_node_dup = found;
1473 static struct stable_node *stable_node_dup_any(struct stable_node *stable_node,
1474 struct rb_root *root)
1476 if (!is_stable_node_chain(stable_node))
1478 if (hlist_empty(&stable_node->hlist)) {
1479 free_stable_node_chain(stable_node, root);
1482 return hlist_entry(stable_node->hlist.first,
1483 typeof(*stable_node), hlist_dup);
1487 * Like for get_ksm_page, this function can free the *_stable_node and
1488 * *_stable_node_dup if the returned tree_page is NULL.
1490 * It can also free and overwrite *_stable_node with the found
1491 * stable_node_dup if the chain is collapsed (in which case
1492 * *_stable_node will be equal to *_stable_node_dup like if the chain
1493 * never existed). It's up to the caller to verify tree_page is not
1494 * NULL before dereferencing *_stable_node or *_stable_node_dup.
1496 * *_stable_node_dup is really a second output parameter of this
1497 * function and will be overwritten in all cases, the caller doesn't
1498 * need to initialize it.
1500 static struct page *__stable_node_chain(struct stable_node **_stable_node_dup,
1501 struct stable_node **_stable_node,
1502 struct rb_root *root,
1503 bool prune_stale_stable_nodes)
1505 struct stable_node *stable_node = *_stable_node;
1506 if (!is_stable_node_chain(stable_node)) {
1507 if (is_page_sharing_candidate(stable_node)) {
1508 *_stable_node_dup = stable_node;
1509 return get_ksm_page(stable_node, GET_KSM_PAGE_NOLOCK);
1512 * _stable_node_dup set to NULL means the stable_node
1513 * reached the ksm_max_page_sharing limit.
1515 *_stable_node_dup = NULL;
1518 return stable_node_dup(_stable_node_dup, _stable_node, root,
1519 prune_stale_stable_nodes);
1522 static __always_inline struct page *chain_prune(struct stable_node **s_n_d,
1523 struct stable_node **s_n,
1524 struct rb_root *root)
1526 return __stable_node_chain(s_n_d, s_n, root, true);
1529 static __always_inline struct page *chain(struct stable_node **s_n_d,
1530 struct stable_node *s_n,
1531 struct rb_root *root)
1533 struct stable_node *old_stable_node = s_n;
1534 struct page *tree_page;
1536 tree_page = __stable_node_chain(s_n_d, &s_n, root, false);
1537 /* not pruning dups so s_n cannot have changed */
1538 VM_BUG_ON(s_n != old_stable_node);
1543 * stable_tree_search - search for page inside the stable tree
1545 * This function checks if there is a page inside the stable tree
1546 * with identical content to the page that we are scanning right now.
1548 * This function returns the stable tree node of identical content if found,
1551 static struct page *stable_tree_search(struct page *page)
1554 struct rb_root *root;
1555 struct rb_node **new;
1556 struct rb_node *parent;
1557 struct stable_node *stable_node, *stable_node_dup, *stable_node_any;
1558 struct stable_node *page_node;
1560 page_node = page_stable_node(page);
1561 if (page_node && page_node->head != &migrate_nodes) {
1562 /* ksm page forked */
1567 nid = get_kpfn_nid(page_to_pfn(page));
1568 root = root_stable_tree + nid;
1570 new = &root->rb_node;
1574 struct page *tree_page;
1578 stable_node = rb_entry(*new, struct stable_node, node);
1579 stable_node_any = NULL;
1580 tree_page = chain_prune(&stable_node_dup, &stable_node, root);
1582 * NOTE: stable_node may have been freed by
1583 * chain_prune() if the returned stable_node_dup is
1584 * not NULL. stable_node_dup may have been inserted in
1585 * the rbtree instead as a regular stable_node (in
1586 * order to collapse the stable_node chain if a single
1587 * stable_node dup was found in it). In such case the
1588 * stable_node is overwritten by the calleee to point
1589 * to the stable_node_dup that was collapsed in the
1590 * stable rbtree and stable_node will be equal to
1591 * stable_node_dup like if the chain never existed.
1593 if (!stable_node_dup) {
1595 * Either all stable_node dups were full in
1596 * this stable_node chain, or this chain was
1597 * empty and should be rb_erased.
1599 stable_node_any = stable_node_dup_any(stable_node,
1601 if (!stable_node_any) {
1602 /* rb_erase just run */
1606 * Take any of the stable_node dups page of
1607 * this stable_node chain to let the tree walk
1608 * continue. All KSM pages belonging to the
1609 * stable_node dups in a stable_node chain
1610 * have the same content and they're
1611 * wrprotected at all times. Any will work
1612 * fine to continue the walk.
1614 tree_page = get_ksm_page(stable_node_any,
1615 GET_KSM_PAGE_NOLOCK);
1617 VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
1620 * If we walked over a stale stable_node,
1621 * get_ksm_page() will call rb_erase() and it
1622 * may rebalance the tree from under us. So
1623 * restart the search from scratch. Returning
1624 * NULL would be safe too, but we'd generate
1625 * false negative insertions just because some
1626 * stable_node was stale.
1631 ret = memcmp_pages(page, tree_page);
1632 put_page(tree_page);
1636 new = &parent->rb_left;
1638 new = &parent->rb_right;
1641 VM_BUG_ON(page_node->head != &migrate_nodes);
1643 * Test if the migrated page should be merged
1644 * into a stable node dup. If the mapcount is
1645 * 1 we can migrate it with another KSM page
1646 * without adding it to the chain.
1648 if (page_mapcount(page) > 1)
1652 if (!stable_node_dup) {
1654 * If the stable_node is a chain and
1655 * we got a payload match in memcmp
1656 * but we cannot merge the scanned
1657 * page in any of the existing
1658 * stable_node dups because they're
1659 * all full, we need to wait the
1660 * scanned page to find itself a match
1661 * in the unstable tree to create a
1662 * brand new KSM page to add later to
1663 * the dups of this stable_node.
1669 * Lock and unlock the stable_node's page (which
1670 * might already have been migrated) so that page
1671 * migration is sure to notice its raised count.
1672 * It would be more elegant to return stable_node
1673 * than kpage, but that involves more changes.
1675 tree_page = get_ksm_page(stable_node_dup,
1676 GET_KSM_PAGE_TRYLOCK);
1678 if (PTR_ERR(tree_page) == -EBUSY)
1679 return ERR_PTR(-EBUSY);
1681 if (unlikely(!tree_page))
1683 * The tree may have been rebalanced,
1684 * so re-evaluate parent and new.
1687 unlock_page(tree_page);
1689 if (get_kpfn_nid(stable_node_dup->kpfn) !=
1690 NUMA(stable_node_dup->nid)) {
1691 put_page(tree_page);
1701 list_del(&page_node->list);
1702 DO_NUMA(page_node->nid = nid);
1703 rb_link_node(&page_node->node, parent, new);
1704 rb_insert_color(&page_node->node, root);
1706 if (is_page_sharing_candidate(page_node)) {
1714 * If stable_node was a chain and chain_prune collapsed it,
1715 * stable_node has been updated to be the new regular
1716 * stable_node. A collapse of the chain is indistinguishable
1717 * from the case there was no chain in the stable
1718 * rbtree. Otherwise stable_node is the chain and
1719 * stable_node_dup is the dup to replace.
1721 if (stable_node_dup == stable_node) {
1722 VM_BUG_ON(is_stable_node_chain(stable_node_dup));
1723 VM_BUG_ON(is_stable_node_dup(stable_node_dup));
1724 /* there is no chain */
1726 VM_BUG_ON(page_node->head != &migrate_nodes);
1727 list_del(&page_node->list);
1728 DO_NUMA(page_node->nid = nid);
1729 rb_replace_node(&stable_node_dup->node,
1732 if (is_page_sharing_candidate(page_node))
1737 rb_erase(&stable_node_dup->node, root);
1741 VM_BUG_ON(!is_stable_node_chain(stable_node));
1742 __stable_node_dup_del(stable_node_dup);
1744 VM_BUG_ON(page_node->head != &migrate_nodes);
1745 list_del(&page_node->list);
1746 DO_NUMA(page_node->nid = nid);
1747 stable_node_chain_add_dup(page_node, stable_node);
1748 if (is_page_sharing_candidate(page_node))
1756 stable_node_dup->head = &migrate_nodes;
1757 list_add(&stable_node_dup->list, stable_node_dup->head);
1761 /* stable_node_dup could be null if it reached the limit */
1762 if (!stable_node_dup)
1763 stable_node_dup = stable_node_any;
1765 * If stable_node was a chain and chain_prune collapsed it,
1766 * stable_node has been updated to be the new regular
1767 * stable_node. A collapse of the chain is indistinguishable
1768 * from the case there was no chain in the stable
1769 * rbtree. Otherwise stable_node is the chain and
1770 * stable_node_dup is the dup to replace.
1772 if (stable_node_dup == stable_node) {
1773 VM_BUG_ON(is_stable_node_chain(stable_node_dup));
1774 VM_BUG_ON(is_stable_node_dup(stable_node_dup));
1775 /* chain is missing so create it */
1776 stable_node = alloc_stable_node_chain(stable_node_dup,
1782 * Add this stable_node dup that was
1783 * migrated to the stable_node chain
1784 * of the current nid for this page
1787 VM_BUG_ON(!is_stable_node_chain(stable_node));
1788 VM_BUG_ON(!is_stable_node_dup(stable_node_dup));
1789 VM_BUG_ON(page_node->head != &migrate_nodes);
1790 list_del(&page_node->list);
1791 DO_NUMA(page_node->nid = nid);
1792 stable_node_chain_add_dup(page_node, stable_node);
1797 * stable_tree_insert - insert stable tree node pointing to new ksm page
1798 * into the stable tree.
1800 * This function returns the stable tree node just allocated on success,
1803 static struct stable_node *stable_tree_insert(struct page *kpage)
1807 struct rb_root *root;
1808 struct rb_node **new;
1809 struct rb_node *parent;
1810 struct stable_node *stable_node, *stable_node_dup, *stable_node_any;
1811 bool need_chain = false;
1813 kpfn = page_to_pfn(kpage);
1814 nid = get_kpfn_nid(kpfn);
1815 root = root_stable_tree + nid;
1818 new = &root->rb_node;
1821 struct page *tree_page;
1825 stable_node = rb_entry(*new, struct stable_node, node);
1826 stable_node_any = NULL;
1827 tree_page = chain(&stable_node_dup, stable_node, root);
1828 if (!stable_node_dup) {
1830 * Either all stable_node dups were full in
1831 * this stable_node chain, or this chain was
1832 * empty and should be rb_erased.
1834 stable_node_any = stable_node_dup_any(stable_node,
1836 if (!stable_node_any) {
1837 /* rb_erase just run */
1841 * Take any of the stable_node dups page of
1842 * this stable_node chain to let the tree walk
1843 * continue. All KSM pages belonging to the
1844 * stable_node dups in a stable_node chain
1845 * have the same content and they're
1846 * wrprotected at all times. Any will work
1847 * fine to continue the walk.
1849 tree_page = get_ksm_page(stable_node_any,
1850 GET_KSM_PAGE_NOLOCK);
1852 VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
1855 * If we walked over a stale stable_node,
1856 * get_ksm_page() will call rb_erase() and it
1857 * may rebalance the tree from under us. So
1858 * restart the search from scratch. Returning
1859 * NULL would be safe too, but we'd generate
1860 * false negative insertions just because some
1861 * stable_node was stale.
1866 ret = memcmp_pages(kpage, tree_page);
1867 put_page(tree_page);
1871 new = &parent->rb_left;
1873 new = &parent->rb_right;
1880 stable_node_dup = alloc_stable_node();
1881 if (!stable_node_dup)
1884 INIT_HLIST_HEAD(&stable_node_dup->hlist);
1885 stable_node_dup->kpfn = kpfn;
1886 set_page_stable_node(kpage, stable_node_dup);
1887 stable_node_dup->rmap_hlist_len = 0;
1888 DO_NUMA(stable_node_dup->nid = nid);
1890 rb_link_node(&stable_node_dup->node, parent, new);
1891 rb_insert_color(&stable_node_dup->node, root);
1893 if (!is_stable_node_chain(stable_node)) {
1894 struct stable_node *orig = stable_node;
1895 /* chain is missing so create it */
1896 stable_node = alloc_stable_node_chain(orig, root);
1898 free_stable_node(stable_node_dup);
1902 stable_node_chain_add_dup(stable_node_dup, stable_node);
1905 return stable_node_dup;
1909 * unstable_tree_search_insert - search for identical page,
1910 * else insert rmap_item into the unstable tree.
1912 * This function searches for a page in the unstable tree identical to the
1913 * page currently being scanned; and if no identical page is found in the
1914 * tree, we insert rmap_item as a new object into the unstable tree.
1916 * This function returns pointer to rmap_item found to be identical
1917 * to the currently scanned page, NULL otherwise.
1919 * This function does both searching and inserting, because they share
1920 * the same walking algorithm in an rbtree.
1923 struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1925 struct page **tree_pagep)
1927 struct rb_node **new;
1928 struct rb_root *root;
1929 struct rb_node *parent = NULL;
1932 nid = get_kpfn_nid(page_to_pfn(page));
1933 root = root_unstable_tree + nid;
1934 new = &root->rb_node;
1937 struct rmap_item *tree_rmap_item;
1938 struct page *tree_page;
1942 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1943 tree_page = get_mergeable_page(tree_rmap_item);
1948 * Don't substitute a ksm page for a forked page.
1950 if (page == tree_page) {
1951 put_page(tree_page);
1955 ret = memcmp_pages(page, tree_page);
1959 put_page(tree_page);
1960 new = &parent->rb_left;
1961 } else if (ret > 0) {
1962 put_page(tree_page);
1963 new = &parent->rb_right;
1964 } else if (!ksm_merge_across_nodes &&
1965 page_to_nid(tree_page) != nid) {
1967 * If tree_page has been migrated to another NUMA node,
1968 * it will be flushed out and put in the right unstable
1969 * tree next time: only merge with it when across_nodes.
1971 put_page(tree_page);
1974 *tree_pagep = tree_page;
1975 return tree_rmap_item;
1979 rmap_item->address |= UNSTABLE_FLAG;
1980 rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1981 DO_NUMA(rmap_item->nid = nid);
1982 rb_link_node(&rmap_item->node, parent, new);
1983 rb_insert_color(&rmap_item->node, root);
1985 ksm_pages_unshared++;
1990 * stable_tree_append - add another rmap_item to the linked list of
1991 * rmap_items hanging off a given node of the stable tree, all sharing
1992 * the same ksm page.
1994 static void stable_tree_append(struct rmap_item *rmap_item,
1995 struct stable_node *stable_node,
1996 bool max_page_sharing_bypass)
1999 * rmap won't find this mapping if we don't insert the
2000 * rmap_item in the right stable_node
2001 * duplicate. page_migration could break later if rmap breaks,
2002 * so we can as well crash here. We really need to check for
2003 * rmap_hlist_len == STABLE_NODE_CHAIN, but we can as well check
2004 * for other negative values as an undeflow if detected here
2005 * for the first time (and not when decreasing rmap_hlist_len)
2006 * would be sign of memory corruption in the stable_node.
2008 BUG_ON(stable_node->rmap_hlist_len < 0);
2010 stable_node->rmap_hlist_len++;
2011 if (!max_page_sharing_bypass)
2012 /* possibly non fatal but unexpected overflow, only warn */
2013 WARN_ON_ONCE(stable_node->rmap_hlist_len >
2014 ksm_max_page_sharing);
2016 rmap_item->head = stable_node;
2017 rmap_item->address |= STABLE_FLAG;
2018 hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
2020 if (rmap_item->hlist.next)
2021 ksm_pages_sharing++;
2027 * cmp_and_merge_page - first see if page can be merged into the stable tree;
2028 * if not, compare checksum to previous and if it's the same, see if page can
2029 * be inserted into the unstable tree, or merged with a page already there and
2030 * both transferred to the stable tree.
2032 * @page: the page that we are searching identical page to.
2033 * @rmap_item: the reverse mapping into the virtual address of this page
2035 static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
2037 struct mm_struct *mm = rmap_item->mm;
2038 struct rmap_item *tree_rmap_item;
2039 struct page *tree_page = NULL;
2040 struct stable_node *stable_node;
2042 unsigned int checksum;
2044 bool max_page_sharing_bypass = false;
2046 stable_node = page_stable_node(page);
2048 if (stable_node->head != &migrate_nodes &&
2049 get_kpfn_nid(READ_ONCE(stable_node->kpfn)) !=
2050 NUMA(stable_node->nid)) {
2051 stable_node_dup_del(stable_node);
2052 stable_node->head = &migrate_nodes;
2053 list_add(&stable_node->list, stable_node->head);
2055 if (stable_node->head != &migrate_nodes &&
2056 rmap_item->head == stable_node)
2059 * If it's a KSM fork, allow it to go over the sharing limit
2062 if (!is_page_sharing_candidate(stable_node))
2063 max_page_sharing_bypass = true;
2066 /* We first start with searching the page inside the stable tree */
2067 kpage = stable_tree_search(page);
2068 if (kpage == page && rmap_item->head == stable_node) {
2073 remove_rmap_item_from_tree(rmap_item);
2076 if (PTR_ERR(kpage) == -EBUSY)
2079 err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
2082 * The page was successfully merged:
2083 * add its rmap_item to the stable tree.
2086 stable_tree_append(rmap_item, page_stable_node(kpage),
2087 max_page_sharing_bypass);
2095 * If the hash value of the page has changed from the last time
2096 * we calculated it, this page is changing frequently: therefore we
2097 * don't want to insert it in the unstable tree, and we don't want
2098 * to waste our time searching for something identical to it there.
2100 checksum = calc_checksum(page);
2101 if (rmap_item->oldchecksum != checksum) {
2102 rmap_item->oldchecksum = checksum;
2107 * Same checksum as an empty page. We attempt to merge it with the
2108 * appropriate zero page if the user enabled this via sysfs.
2110 if (ksm_use_zero_pages && (checksum == zero_checksum)) {
2111 struct vm_area_struct *vma;
2113 down_read(&mm->mmap_sem);
2114 vma = find_mergeable_vma(mm, rmap_item->address);
2115 err = try_to_merge_one_page(vma, page,
2116 ZERO_PAGE(rmap_item->address));
2117 up_read(&mm->mmap_sem);
2119 * In case of failure, the page was not really empty, so we
2120 * need to continue. Otherwise we're done.
2126 unstable_tree_search_insert(rmap_item, page, &tree_page);
2127 if (tree_rmap_item) {
2130 kpage = try_to_merge_two_pages(rmap_item, page,
2131 tree_rmap_item, tree_page);
2133 * If both pages we tried to merge belong to the same compound
2134 * page, then we actually ended up increasing the reference
2135 * count of the same compound page twice, and split_huge_page
2137 * Here we set a flag if that happened, and we use it later to
2138 * try split_huge_page again. Since we call put_page right
2139 * afterwards, the reference count will be correct and
2140 * split_huge_page should succeed.
2142 split = PageTransCompound(page)
2143 && compound_head(page) == compound_head(tree_page);
2144 put_page(tree_page);
2147 * The pages were successfully merged: insert new
2148 * node in the stable tree and add both rmap_items.
2151 stable_node = stable_tree_insert(kpage);
2153 stable_tree_append(tree_rmap_item, stable_node,
2155 stable_tree_append(rmap_item, stable_node,
2161 * If we fail to insert the page into the stable tree,
2162 * we will have 2 virtual addresses that are pointing
2163 * to a ksm page left outside the stable tree,
2164 * in which case we need to break_cow on both.
2167 break_cow(tree_rmap_item);
2168 break_cow(rmap_item);
2172 * We are here if we tried to merge two pages and
2173 * failed because they both belonged to the same
2174 * compound page. We will split the page now, but no
2175 * merging will take place.
2176 * We do not want to add the cost of a full lock; if
2177 * the page is locked, it is better to skip it and
2178 * perhaps try again later.
2180 if (!trylock_page(page))
2182 split_huge_page(page);
2188 static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
2189 struct rmap_item **rmap_list,
2192 struct rmap_item *rmap_item;
2194 while (*rmap_list) {
2195 rmap_item = *rmap_list;
2196 if ((rmap_item->address & PAGE_MASK) == addr)
2198 if (rmap_item->address > addr)
2200 *rmap_list = rmap_item->rmap_list;
2201 remove_rmap_item_from_tree(rmap_item);
2202 free_rmap_item(rmap_item);
2205 rmap_item = alloc_rmap_item();
2207 /* It has already been zeroed */
2208 rmap_item->mm = mm_slot->mm;
2209 rmap_item->address = addr;
2210 rmap_item->rmap_list = *rmap_list;
2211 *rmap_list = rmap_item;
2216 static struct rmap_item *scan_get_next_rmap_item(struct page **page)
2218 struct mm_struct *mm;
2219 struct mm_slot *slot;
2220 struct vm_area_struct *vma;
2221 struct rmap_item *rmap_item;
2224 if (list_empty(&ksm_mm_head.mm_list))
2227 slot = ksm_scan.mm_slot;
2228 if (slot == &ksm_mm_head) {
2230 * A number of pages can hang around indefinitely on per-cpu
2231 * pagevecs, raised page count preventing write_protect_page
2232 * from merging them. Though it doesn't really matter much,
2233 * it is puzzling to see some stuck in pages_volatile until
2234 * other activity jostles them out, and they also prevented
2235 * LTP's KSM test from succeeding deterministically; so drain
2236 * them here (here rather than on entry to ksm_do_scan(),
2237 * so we don't IPI too often when pages_to_scan is set low).
2239 lru_add_drain_all();
2242 * Whereas stale stable_nodes on the stable_tree itself
2243 * get pruned in the regular course of stable_tree_search(),
2244 * those moved out to the migrate_nodes list can accumulate:
2245 * so prune them once before each full scan.
2247 if (!ksm_merge_across_nodes) {
2248 struct stable_node *stable_node, *next;
2251 list_for_each_entry_safe(stable_node, next,
2252 &migrate_nodes, list) {
2253 page = get_ksm_page(stable_node,
2254 GET_KSM_PAGE_NOLOCK);
2261 for (nid = 0; nid < ksm_nr_node_ids; nid++)
2262 root_unstable_tree[nid] = RB_ROOT;
2264 spin_lock(&ksm_mmlist_lock);
2265 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
2266 ksm_scan.mm_slot = slot;
2267 spin_unlock(&ksm_mmlist_lock);
2269 * Although we tested list_empty() above, a racing __ksm_exit
2270 * of the last mm on the list may have removed it since then.
2272 if (slot == &ksm_mm_head)
2275 ksm_scan.address = 0;
2276 ksm_scan.rmap_list = &slot->rmap_list;
2280 down_read(&mm->mmap_sem);
2281 if (ksm_test_exit(mm))
2284 vma = find_vma(mm, ksm_scan.address);
2286 for (; vma; vma = vma->vm_next) {
2287 if (!(vma->vm_flags & VM_MERGEABLE))
2289 if (ksm_scan.address < vma->vm_start)
2290 ksm_scan.address = vma->vm_start;
2292 ksm_scan.address = vma->vm_end;
2294 while (ksm_scan.address < vma->vm_end) {
2295 if (ksm_test_exit(mm))
2297 *page = follow_page(vma, ksm_scan.address, FOLL_GET);
2298 if (IS_ERR_OR_NULL(*page)) {
2299 ksm_scan.address += PAGE_SIZE;
2303 if (PageAnon(*page)) {
2304 flush_anon_page(vma, *page, ksm_scan.address);
2305 flush_dcache_page(*page);
2306 rmap_item = get_next_rmap_item(slot,
2307 ksm_scan.rmap_list, ksm_scan.address);
2309 ksm_scan.rmap_list =
2310 &rmap_item->rmap_list;
2311 ksm_scan.address += PAGE_SIZE;
2314 up_read(&mm->mmap_sem);
2318 ksm_scan.address += PAGE_SIZE;
2323 if (ksm_test_exit(mm)) {
2324 ksm_scan.address = 0;
2325 ksm_scan.rmap_list = &slot->rmap_list;
2328 * Nuke all the rmap_items that are above this current rmap:
2329 * because there were no VM_MERGEABLE vmas with such addresses.
2331 remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
2333 spin_lock(&ksm_mmlist_lock);
2334 ksm_scan.mm_slot = list_entry(slot->mm_list.next,
2335 struct mm_slot, mm_list);
2336 if (ksm_scan.address == 0) {
2338 * We've completed a full scan of all vmas, holding mmap_sem
2339 * throughout, and found no VM_MERGEABLE: so do the same as
2340 * __ksm_exit does to remove this mm from all our lists now.
2341 * This applies either when cleaning up after __ksm_exit
2342 * (but beware: we can reach here even before __ksm_exit),
2343 * or when all VM_MERGEABLE areas have been unmapped (and
2344 * mmap_sem then protects against race with MADV_MERGEABLE).
2346 hash_del(&slot->link);
2347 list_del(&slot->mm_list);
2348 spin_unlock(&ksm_mmlist_lock);
2351 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
2352 up_read(&mm->mmap_sem);
2355 up_read(&mm->mmap_sem);
2357 * up_read(&mm->mmap_sem) first because after
2358 * spin_unlock(&ksm_mmlist_lock) run, the "mm" may
2359 * already have been freed under us by __ksm_exit()
2360 * because the "mm_slot" is still hashed and
2361 * ksm_scan.mm_slot doesn't point to it anymore.
2363 spin_unlock(&ksm_mmlist_lock);
2366 /* Repeat until we've completed scanning the whole list */
2367 slot = ksm_scan.mm_slot;
2368 if (slot != &ksm_mm_head)
2376 * ksm_do_scan - the ksm scanner main worker function.
2377 * @scan_npages: number of pages we want to scan before we return.
2379 static void ksm_do_scan(unsigned int scan_npages)
2381 struct rmap_item *rmap_item;
2382 struct page *uninitialized_var(page);
2384 while (scan_npages-- && likely(!freezing(current))) {
2386 rmap_item = scan_get_next_rmap_item(&page);
2389 cmp_and_merge_page(page, rmap_item);
2394 static int ksmd_should_run(void)
2396 return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
2399 static int ksm_scan_thread(void *nothing)
2401 unsigned int sleep_ms;
2404 set_user_nice(current, 5);
2406 while (!kthread_should_stop()) {
2407 mutex_lock(&ksm_thread_mutex);
2408 wait_while_offlining();
2409 if (ksmd_should_run())
2410 ksm_do_scan(ksm_thread_pages_to_scan);
2411 mutex_unlock(&ksm_thread_mutex);
2415 if (ksmd_should_run()) {
2416 sleep_ms = READ_ONCE(ksm_thread_sleep_millisecs);
2417 wait_event_interruptible_timeout(ksm_iter_wait,
2418 sleep_ms != READ_ONCE(ksm_thread_sleep_millisecs),
2419 msecs_to_jiffies(sleep_ms));
2421 wait_event_freezable(ksm_thread_wait,
2422 ksmd_should_run() || kthread_should_stop());
2428 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
2429 unsigned long end, int advice, unsigned long *vm_flags)
2431 struct mm_struct *mm = vma->vm_mm;
2435 case MADV_MERGEABLE:
2437 * Be somewhat over-protective for now!
2439 if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE |
2440 VM_PFNMAP | VM_IO | VM_DONTEXPAND |
2441 VM_HUGETLB | VM_MIXEDMAP))
2442 return 0; /* just ignore the advice */
2444 if (vma_is_dax(vma))
2448 if (*vm_flags & VM_SAO)
2452 if (*vm_flags & VM_SPARC_ADI)
2456 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
2457 err = __ksm_enter(mm);
2462 *vm_flags |= VM_MERGEABLE;
2465 case MADV_UNMERGEABLE:
2466 if (!(*vm_flags & VM_MERGEABLE))
2467 return 0; /* just ignore the advice */
2469 if (vma->anon_vma) {
2470 err = unmerge_ksm_pages(vma, start, end);
2475 *vm_flags &= ~VM_MERGEABLE;
2481 EXPORT_SYMBOL_GPL(ksm_madvise);
2483 int __ksm_enter(struct mm_struct *mm)
2485 struct mm_slot *mm_slot;
2488 mm_slot = alloc_mm_slot();
2492 /* Check ksm_run too? Would need tighter locking */
2493 needs_wakeup = list_empty(&ksm_mm_head.mm_list);
2495 spin_lock(&ksm_mmlist_lock);
2496 insert_to_mm_slots_hash(mm, mm_slot);
2498 * When KSM_RUN_MERGE (or KSM_RUN_STOP),
2499 * insert just behind the scanning cursor, to let the area settle
2500 * down a little; when fork is followed by immediate exec, we don't
2501 * want ksmd to waste time setting up and tearing down an rmap_list.
2503 * But when KSM_RUN_UNMERGE, it's important to insert ahead of its
2504 * scanning cursor, otherwise KSM pages in newly forked mms will be
2505 * missed: then we might as well insert at the end of the list.
2507 if (ksm_run & KSM_RUN_UNMERGE)
2508 list_add_tail(&mm_slot->mm_list, &ksm_mm_head.mm_list);
2510 list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
2511 spin_unlock(&ksm_mmlist_lock);
2513 set_bit(MMF_VM_MERGEABLE, &mm->flags);
2517 wake_up_interruptible(&ksm_thread_wait);
2522 void __ksm_exit(struct mm_struct *mm)
2524 struct mm_slot *mm_slot;
2525 int easy_to_free = 0;
2528 * This process is exiting: if it's straightforward (as is the
2529 * case when ksmd was never running), free mm_slot immediately.
2530 * But if it's at the cursor or has rmap_items linked to it, use
2531 * mmap_sem to synchronize with any break_cows before pagetables
2532 * are freed, and leave the mm_slot on the list for ksmd to free.
2533 * Beware: ksm may already have noticed it exiting and freed the slot.
2536 spin_lock(&ksm_mmlist_lock);
2537 mm_slot = get_mm_slot(mm);
2538 if (mm_slot && ksm_scan.mm_slot != mm_slot) {
2539 if (!mm_slot->rmap_list) {
2540 hash_del(&mm_slot->link);
2541 list_del(&mm_slot->mm_list);
2544 list_move(&mm_slot->mm_list,
2545 &ksm_scan.mm_slot->mm_list);
2548 spin_unlock(&ksm_mmlist_lock);
2551 free_mm_slot(mm_slot);
2552 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
2554 } else if (mm_slot) {
2555 down_write(&mm->mmap_sem);
2556 up_write(&mm->mmap_sem);
2560 struct page *ksm_might_need_to_copy(struct page *page,
2561 struct vm_area_struct *vma, unsigned long address)
2563 struct anon_vma *anon_vma = page_anon_vma(page);
2564 struct page *new_page;
2566 if (PageKsm(page)) {
2567 if (page_stable_node(page) &&
2568 !(ksm_run & KSM_RUN_UNMERGE))
2569 return page; /* no need to copy it */
2570 } else if (!anon_vma) {
2571 return page; /* no need to copy it */
2572 } else if (anon_vma->root == vma->anon_vma->root &&
2573 page->index == linear_page_index(vma, address)) {
2574 return page; /* still no need to copy it */
2576 if (!PageUptodate(page))
2577 return page; /* let do_swap_page report the error */
2579 new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
2581 copy_user_highpage(new_page, page, address, vma);
2583 SetPageDirty(new_page);
2584 __SetPageUptodate(new_page);
2585 __SetPageLocked(new_page);
2591 void rmap_walk_ksm(struct page *page, struct rmap_walk_control *rwc)
2593 struct stable_node *stable_node;
2594 struct rmap_item *rmap_item;
2595 int search_new_forks = 0;
2597 VM_BUG_ON_PAGE(!PageKsm(page), page);
2600 * Rely on the page lock to protect against concurrent modifications
2601 * to that page's node of the stable tree.
2603 VM_BUG_ON_PAGE(!PageLocked(page), page);
2605 stable_node = page_stable_node(page);
2609 hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
2610 struct anon_vma *anon_vma = rmap_item->anon_vma;
2611 struct anon_vma_chain *vmac;
2612 struct vm_area_struct *vma;
2615 anon_vma_lock_read(anon_vma);
2616 anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
2623 /* Ignore the stable/unstable/sqnr flags */
2624 addr = rmap_item->address & ~KSM_FLAG_MASK;
2626 if (addr < vma->vm_start || addr >= vma->vm_end)
2629 * Initially we examine only the vma which covers this
2630 * rmap_item; but later, if there is still work to do,
2631 * we examine covering vmas in other mms: in case they
2632 * were forked from the original since ksmd passed.
2634 if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
2637 if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
2640 if (!rwc->rmap_one(page, vma, addr, rwc->arg)) {
2641 anon_vma_unlock_read(anon_vma);
2644 if (rwc->done && rwc->done(page)) {
2645 anon_vma_unlock_read(anon_vma);
2649 anon_vma_unlock_read(anon_vma);
2651 if (!search_new_forks++)
2655 bool reuse_ksm_page(struct page *page,
2656 struct vm_area_struct *vma,
2657 unsigned long address)
2659 #ifdef CONFIG_DEBUG_VM
2660 if (WARN_ON(is_zero_pfn(page_to_pfn(page))) ||
2661 WARN_ON(!page_mapped(page)) ||
2662 WARN_ON(!PageLocked(page))) {
2663 dump_page(page, "reuse_ksm_page");
2668 if (PageSwapCache(page) || !page_stable_node(page))
2670 /* Prohibit parallel get_ksm_page() */
2671 if (!page_ref_freeze(page, 1))
2674 page_move_anon_rmap(page, vma);
2675 page->index = linear_page_index(vma, address);
2676 page_ref_unfreeze(page, 1);
2680 #ifdef CONFIG_MIGRATION
2681 void ksm_migrate_page(struct page *newpage, struct page *oldpage)
2683 struct stable_node *stable_node;
2685 VM_BUG_ON_PAGE(!PageLocked(oldpage), oldpage);
2686 VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
2687 VM_BUG_ON_PAGE(newpage->mapping != oldpage->mapping, newpage);
2689 stable_node = page_stable_node(newpage);
2691 VM_BUG_ON_PAGE(stable_node->kpfn != page_to_pfn(oldpage), oldpage);
2692 stable_node->kpfn = page_to_pfn(newpage);
2694 * newpage->mapping was set in advance; now we need smp_wmb()
2695 * to make sure that the new stable_node->kpfn is visible
2696 * to get_ksm_page() before it can see that oldpage->mapping
2697 * has gone stale (or that PageSwapCache has been cleared).
2700 set_page_stable_node(oldpage, NULL);
2703 #endif /* CONFIG_MIGRATION */
2705 #ifdef CONFIG_MEMORY_HOTREMOVE
2706 static void wait_while_offlining(void)
2708 while (ksm_run & KSM_RUN_OFFLINE) {
2709 mutex_unlock(&ksm_thread_mutex);
2710 wait_on_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE),
2711 TASK_UNINTERRUPTIBLE);
2712 mutex_lock(&ksm_thread_mutex);
2716 static bool stable_node_dup_remove_range(struct stable_node *stable_node,
2717 unsigned long start_pfn,
2718 unsigned long end_pfn)
2720 if (stable_node->kpfn >= start_pfn &&
2721 stable_node->kpfn < end_pfn) {
2723 * Don't get_ksm_page, page has already gone:
2724 * which is why we keep kpfn instead of page*
2726 remove_node_from_stable_tree(stable_node);
2732 static bool stable_node_chain_remove_range(struct stable_node *stable_node,
2733 unsigned long start_pfn,
2734 unsigned long end_pfn,
2735 struct rb_root *root)
2737 struct stable_node *dup;
2738 struct hlist_node *hlist_safe;
2740 if (!is_stable_node_chain(stable_node)) {
2741 VM_BUG_ON(is_stable_node_dup(stable_node));
2742 return stable_node_dup_remove_range(stable_node, start_pfn,
2746 hlist_for_each_entry_safe(dup, hlist_safe,
2747 &stable_node->hlist, hlist_dup) {
2748 VM_BUG_ON(!is_stable_node_dup(dup));
2749 stable_node_dup_remove_range(dup, start_pfn, end_pfn);
2751 if (hlist_empty(&stable_node->hlist)) {
2752 free_stable_node_chain(stable_node, root);
2753 return true; /* notify caller that tree was rebalanced */
2758 static void ksm_check_stable_tree(unsigned long start_pfn,
2759 unsigned long end_pfn)
2761 struct stable_node *stable_node, *next;
2762 struct rb_node *node;
2765 for (nid = 0; nid < ksm_nr_node_ids; nid++) {
2766 node = rb_first(root_stable_tree + nid);
2768 stable_node = rb_entry(node, struct stable_node, node);
2769 if (stable_node_chain_remove_range(stable_node,
2773 node = rb_first(root_stable_tree + nid);
2775 node = rb_next(node);
2779 list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
2780 if (stable_node->kpfn >= start_pfn &&
2781 stable_node->kpfn < end_pfn)
2782 remove_node_from_stable_tree(stable_node);
2787 static int ksm_memory_callback(struct notifier_block *self,
2788 unsigned long action, void *arg)
2790 struct memory_notify *mn = arg;
2793 case MEM_GOING_OFFLINE:
2795 * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
2796 * and remove_all_stable_nodes() while memory is going offline:
2797 * it is unsafe for them to touch the stable tree at this time.
2798 * But unmerge_ksm_pages(), rmap lookups and other entry points
2799 * which do not need the ksm_thread_mutex are all safe.
2801 mutex_lock(&ksm_thread_mutex);
2802 ksm_run |= KSM_RUN_OFFLINE;
2803 mutex_unlock(&ksm_thread_mutex);
2808 * Most of the work is done by page migration; but there might
2809 * be a few stable_nodes left over, still pointing to struct
2810 * pages which have been offlined: prune those from the tree,
2811 * otherwise get_ksm_page() might later try to access a
2812 * non-existent struct page.
2814 ksm_check_stable_tree(mn->start_pfn,
2815 mn->start_pfn + mn->nr_pages);
2818 case MEM_CANCEL_OFFLINE:
2819 mutex_lock(&ksm_thread_mutex);
2820 ksm_run &= ~KSM_RUN_OFFLINE;
2821 mutex_unlock(&ksm_thread_mutex);
2823 smp_mb(); /* wake_up_bit advises this */
2824 wake_up_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE));
2830 static void wait_while_offlining(void)
2833 #endif /* CONFIG_MEMORY_HOTREMOVE */
2837 * This all compiles without CONFIG_SYSFS, but is a waste of space.
2840 #define KSM_ATTR_RO(_name) \
2841 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
2842 #define KSM_ATTR(_name) \
2843 static struct kobj_attribute _name##_attr = \
2844 __ATTR(_name, 0644, _name##_show, _name##_store)
2846 static ssize_t sleep_millisecs_show(struct kobject *kobj,
2847 struct kobj_attribute *attr, char *buf)
2849 return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs);
2852 static ssize_t sleep_millisecs_store(struct kobject *kobj,
2853 struct kobj_attribute *attr,
2854 const char *buf, size_t count)
2856 unsigned long msecs;
2859 err = kstrtoul(buf, 10, &msecs);
2860 if (err || msecs > UINT_MAX)
2863 ksm_thread_sleep_millisecs = msecs;
2864 wake_up_interruptible(&ksm_iter_wait);
2868 KSM_ATTR(sleep_millisecs);
2870 static ssize_t pages_to_scan_show(struct kobject *kobj,
2871 struct kobj_attribute *attr, char *buf)
2873 return sprintf(buf, "%u\n", ksm_thread_pages_to_scan);
2876 static ssize_t pages_to_scan_store(struct kobject *kobj,
2877 struct kobj_attribute *attr,
2878 const char *buf, size_t count)
2881 unsigned long nr_pages;
2883 err = kstrtoul(buf, 10, &nr_pages);
2884 if (err || nr_pages > UINT_MAX)
2887 ksm_thread_pages_to_scan = nr_pages;
2891 KSM_ATTR(pages_to_scan);
2893 static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
2896 return sprintf(buf, "%lu\n", ksm_run);
2899 static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
2900 const char *buf, size_t count)
2903 unsigned long flags;
2905 err = kstrtoul(buf, 10, &flags);
2906 if (err || flags > UINT_MAX)
2908 if (flags > KSM_RUN_UNMERGE)
2912 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
2913 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
2914 * breaking COW to free the pages_shared (but leaves mm_slots
2915 * on the list for when ksmd may be set running again).
2918 mutex_lock(&ksm_thread_mutex);
2919 wait_while_offlining();
2920 if (ksm_run != flags) {
2922 if (flags & KSM_RUN_UNMERGE) {
2923 set_current_oom_origin();
2924 err = unmerge_and_remove_all_rmap_items();
2925 clear_current_oom_origin();
2927 ksm_run = KSM_RUN_STOP;
2932 mutex_unlock(&ksm_thread_mutex);
2934 if (flags & KSM_RUN_MERGE)
2935 wake_up_interruptible(&ksm_thread_wait);
2942 static ssize_t merge_across_nodes_show(struct kobject *kobj,
2943 struct kobj_attribute *attr, char *buf)
2945 return sprintf(buf, "%u\n", ksm_merge_across_nodes);
2948 static ssize_t merge_across_nodes_store(struct kobject *kobj,
2949 struct kobj_attribute *attr,
2950 const char *buf, size_t count)
2955 err = kstrtoul(buf, 10, &knob);
2961 mutex_lock(&ksm_thread_mutex);
2962 wait_while_offlining();
2963 if (ksm_merge_across_nodes != knob) {
2964 if (ksm_pages_shared || remove_all_stable_nodes())
2966 else if (root_stable_tree == one_stable_tree) {
2967 struct rb_root *buf;
2969 * This is the first time that we switch away from the
2970 * default of merging across nodes: must now allocate
2971 * a buffer to hold as many roots as may be needed.
2972 * Allocate stable and unstable together:
2973 * MAXSMP NODES_SHIFT 10 will use 16kB.
2975 buf = kcalloc(nr_node_ids + nr_node_ids, sizeof(*buf),
2977 /* Let us assume that RB_ROOT is NULL is zero */
2981 root_stable_tree = buf;
2982 root_unstable_tree = buf + nr_node_ids;
2983 /* Stable tree is empty but not the unstable */
2984 root_unstable_tree[0] = one_unstable_tree[0];
2988 ksm_merge_across_nodes = knob;
2989 ksm_nr_node_ids = knob ? 1 : nr_node_ids;
2992 mutex_unlock(&ksm_thread_mutex);
2994 return err ? err : count;
2996 KSM_ATTR(merge_across_nodes);
2999 static ssize_t use_zero_pages_show(struct kobject *kobj,
3000 struct kobj_attribute *attr, char *buf)
3002 return sprintf(buf, "%u\n", ksm_use_zero_pages);
3004 static ssize_t use_zero_pages_store(struct kobject *kobj,
3005 struct kobj_attribute *attr,
3006 const char *buf, size_t count)
3011 err = kstrtobool(buf, &value);
3015 ksm_use_zero_pages = value;
3019 KSM_ATTR(use_zero_pages);
3021 static ssize_t max_page_sharing_show(struct kobject *kobj,
3022 struct kobj_attribute *attr, char *buf)
3024 return sprintf(buf, "%u\n", ksm_max_page_sharing);
3027 static ssize_t max_page_sharing_store(struct kobject *kobj,
3028 struct kobj_attribute *attr,
3029 const char *buf, size_t count)
3034 err = kstrtoint(buf, 10, &knob);
3038 * When a KSM page is created it is shared by 2 mappings. This
3039 * being a signed comparison, it implicitly verifies it's not
3045 if (READ_ONCE(ksm_max_page_sharing) == knob)
3048 mutex_lock(&ksm_thread_mutex);
3049 wait_while_offlining();
3050 if (ksm_max_page_sharing != knob) {
3051 if (ksm_pages_shared || remove_all_stable_nodes())
3054 ksm_max_page_sharing = knob;
3056 mutex_unlock(&ksm_thread_mutex);
3058 return err ? err : count;
3060 KSM_ATTR(max_page_sharing);
3062 static ssize_t pages_shared_show(struct kobject *kobj,
3063 struct kobj_attribute *attr, char *buf)
3065 return sprintf(buf, "%lu\n", ksm_pages_shared);
3067 KSM_ATTR_RO(pages_shared);
3069 static ssize_t pages_sharing_show(struct kobject *kobj,
3070 struct kobj_attribute *attr, char *buf)
3072 return sprintf(buf, "%lu\n", ksm_pages_sharing);
3074 KSM_ATTR_RO(pages_sharing);
3076 static ssize_t pages_unshared_show(struct kobject *kobj,
3077 struct kobj_attribute *attr, char *buf)
3079 return sprintf(buf, "%lu\n", ksm_pages_unshared);
3081 KSM_ATTR_RO(pages_unshared);
3083 static ssize_t pages_volatile_show(struct kobject *kobj,
3084 struct kobj_attribute *attr, char *buf)
3086 long ksm_pages_volatile;
3088 ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
3089 - ksm_pages_sharing - ksm_pages_unshared;
3091 * It was not worth any locking to calculate that statistic,
3092 * but it might therefore sometimes be negative: conceal that.
3094 if (ksm_pages_volatile < 0)
3095 ksm_pages_volatile = 0;
3096 return sprintf(buf, "%ld\n", ksm_pages_volatile);
3098 KSM_ATTR_RO(pages_volatile);
3100 static ssize_t stable_node_dups_show(struct kobject *kobj,
3101 struct kobj_attribute *attr, char *buf)
3103 return sprintf(buf, "%lu\n", ksm_stable_node_dups);
3105 KSM_ATTR_RO(stable_node_dups);
3107 static ssize_t stable_node_chains_show(struct kobject *kobj,
3108 struct kobj_attribute *attr, char *buf)
3110 return sprintf(buf, "%lu\n", ksm_stable_node_chains);
3112 KSM_ATTR_RO(stable_node_chains);
3115 stable_node_chains_prune_millisecs_show(struct kobject *kobj,
3116 struct kobj_attribute *attr,
3119 return sprintf(buf, "%u\n", ksm_stable_node_chains_prune_millisecs);
3123 stable_node_chains_prune_millisecs_store(struct kobject *kobj,
3124 struct kobj_attribute *attr,
3125 const char *buf, size_t count)
3127 unsigned long msecs;
3130 err = kstrtoul(buf, 10, &msecs);
3131 if (err || msecs > UINT_MAX)
3134 ksm_stable_node_chains_prune_millisecs = msecs;
3138 KSM_ATTR(stable_node_chains_prune_millisecs);
3140 static ssize_t full_scans_show(struct kobject *kobj,
3141 struct kobj_attribute *attr, char *buf)
3143 return sprintf(buf, "%lu\n", ksm_scan.seqnr);
3145 KSM_ATTR_RO(full_scans);
3147 static struct attribute *ksm_attrs[] = {
3148 &sleep_millisecs_attr.attr,
3149 &pages_to_scan_attr.attr,
3151 &pages_shared_attr.attr,
3152 &pages_sharing_attr.attr,
3153 &pages_unshared_attr.attr,
3154 &pages_volatile_attr.attr,
3155 &full_scans_attr.attr,
3157 &merge_across_nodes_attr.attr,
3159 &max_page_sharing_attr.attr,
3160 &stable_node_chains_attr.attr,
3161 &stable_node_dups_attr.attr,
3162 &stable_node_chains_prune_millisecs_attr.attr,
3163 &use_zero_pages_attr.attr,
3167 static const struct attribute_group ksm_attr_group = {
3171 #endif /* CONFIG_SYSFS */
3173 static int __init ksm_init(void)
3175 struct task_struct *ksm_thread;
3178 /* The correct value depends on page size and endianness */
3179 zero_checksum = calc_checksum(ZERO_PAGE(0));
3180 /* Default to false for backwards compatibility */
3181 ksm_use_zero_pages = false;
3183 err = ksm_slab_init();
3187 ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
3188 if (IS_ERR(ksm_thread)) {
3189 pr_err("ksm: creating kthread failed\n");
3190 err = PTR_ERR(ksm_thread);
3195 err = sysfs_create_group(mm_kobj, &ksm_attr_group);
3197 pr_err("ksm: register sysfs failed\n");
3198 kthread_stop(ksm_thread);
3202 ksm_run = KSM_RUN_MERGE; /* no way for user to start it */
3204 #endif /* CONFIG_SYSFS */
3206 #ifdef CONFIG_MEMORY_HOTREMOVE
3207 /* There is no significance to this priority 100 */
3208 hotplug_memory_notifier(ksm_memory_callback, 100);
3217 subsys_initcall(ksm_init);