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 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 */
219 /* The stable and unstable tree heads */
220 static struct rb_root one_stable_tree
[1] = { RB_ROOT
};
221 static struct rb_root one_unstable_tree
[1] = { RB_ROOT
};
222 static struct rb_root
*root_stable_tree
= one_stable_tree
;
223 static struct rb_root
*root_unstable_tree
= one_unstable_tree
;
225 /* Recently migrated nodes of stable tree, pending proper placement */
226 static LIST_HEAD(migrate_nodes
);
227 #define STABLE_NODE_DUP_HEAD ((struct list_head *)&migrate_nodes.prev)
229 #define MM_SLOTS_HASH_BITS 10
230 static DEFINE_HASHTABLE(mm_slots_hash
, MM_SLOTS_HASH_BITS
);
232 static struct mm_slot ksm_mm_head
= {
233 .mm_list
= LIST_HEAD_INIT(ksm_mm_head
.mm_list
),
235 static struct ksm_scan ksm_scan
= {
236 .mm_slot
= &ksm_mm_head
,
239 static struct kmem_cache
*rmap_item_cache
;
240 static struct kmem_cache
*stable_node_cache
;
241 static struct kmem_cache
*mm_slot_cache
;
243 /* The number of nodes in the stable tree */
244 static unsigned long ksm_pages_shared
;
246 /* The number of page slots additionally sharing those nodes */
247 static unsigned long ksm_pages_sharing
;
249 /* The number of nodes in the unstable tree */
250 static unsigned long ksm_pages_unshared
;
252 /* The number of rmap_items in use: to calculate pages_volatile */
253 static unsigned long ksm_rmap_items
;
255 /* The number of stable_node chains */
256 static unsigned long ksm_stable_node_chains
;
258 /* The number of stable_node dups linked to the stable_node chains */
259 static unsigned long ksm_stable_node_dups
;
261 /* Delay in pruning stale stable_node_dups in the stable_node_chains */
262 static int ksm_stable_node_chains_prune_millisecs
= 2000;
264 /* Maximum number of page slots sharing a stable node */
265 static int ksm_max_page_sharing
= 256;
267 /* Number of pages ksmd should scan in one batch */
268 static unsigned int ksm_thread_pages_to_scan
= 100;
270 /* Milliseconds ksmd should sleep between batches */
271 static unsigned int ksm_thread_sleep_millisecs
= 20;
273 /* Checksum of an empty (zeroed) page */
274 static unsigned int zero_checksum __read_mostly
;
276 /* Whether to merge empty (zeroed) pages with actual zero pages */
277 static bool ksm_use_zero_pages __read_mostly
;
280 /* Zeroed when merging across nodes is not allowed */
281 static unsigned int ksm_merge_across_nodes
= 1;
282 static int ksm_nr_node_ids
= 1;
284 #define ksm_merge_across_nodes 1U
285 #define ksm_nr_node_ids 1
288 #define KSM_RUN_STOP 0
289 #define KSM_RUN_MERGE 1
290 #define KSM_RUN_UNMERGE 2
291 #define KSM_RUN_OFFLINE 4
292 static unsigned long ksm_run
= KSM_RUN_STOP
;
293 static void wait_while_offlining(void);
295 static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait
);
296 static DECLARE_WAIT_QUEUE_HEAD(ksm_iter_wait
);
297 static DEFINE_MUTEX(ksm_thread_mutex
);
298 static DEFINE_SPINLOCK(ksm_mmlist_lock
);
300 #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
301 sizeof(struct __struct), __alignof__(struct __struct),\
304 static int __init
ksm_slab_init(void)
306 rmap_item_cache
= KSM_KMEM_CACHE(rmap_item
, 0);
307 if (!rmap_item_cache
)
310 stable_node_cache
= KSM_KMEM_CACHE(stable_node
, 0);
311 if (!stable_node_cache
)
314 mm_slot_cache
= KSM_KMEM_CACHE(mm_slot
, 0);
321 kmem_cache_destroy(stable_node_cache
);
323 kmem_cache_destroy(rmap_item_cache
);
328 static void __init
ksm_slab_free(void)
330 kmem_cache_destroy(mm_slot_cache
);
331 kmem_cache_destroy(stable_node_cache
);
332 kmem_cache_destroy(rmap_item_cache
);
333 mm_slot_cache
= NULL
;
336 static __always_inline
bool is_stable_node_chain(struct stable_node
*chain
)
338 return chain
->rmap_hlist_len
== STABLE_NODE_CHAIN
;
341 static __always_inline
bool is_stable_node_dup(struct stable_node
*dup
)
343 return dup
->head
== STABLE_NODE_DUP_HEAD
;
346 static inline void stable_node_chain_add_dup(struct stable_node
*dup
,
347 struct stable_node
*chain
)
349 VM_BUG_ON(is_stable_node_dup(dup
));
350 dup
->head
= STABLE_NODE_DUP_HEAD
;
351 VM_BUG_ON(!is_stable_node_chain(chain
));
352 hlist_add_head(&dup
->hlist_dup
, &chain
->hlist
);
353 ksm_stable_node_dups
++;
356 static inline void __stable_node_dup_del(struct stable_node
*dup
)
358 VM_BUG_ON(!is_stable_node_dup(dup
));
359 hlist_del(&dup
->hlist_dup
);
360 ksm_stable_node_dups
--;
363 static inline void stable_node_dup_del(struct stable_node
*dup
)
365 VM_BUG_ON(is_stable_node_chain(dup
));
366 if (is_stable_node_dup(dup
))
367 __stable_node_dup_del(dup
);
369 rb_erase(&dup
->node
, root_stable_tree
+ NUMA(dup
->nid
));
370 #ifdef CONFIG_DEBUG_VM
375 static inline struct rmap_item
*alloc_rmap_item(void)
377 struct rmap_item
*rmap_item
;
379 rmap_item
= kmem_cache_zalloc(rmap_item_cache
, GFP_KERNEL
|
380 __GFP_NORETRY
| __GFP_NOWARN
);
386 static inline void free_rmap_item(struct rmap_item
*rmap_item
)
389 rmap_item
->mm
= NULL
; /* debug safety */
390 kmem_cache_free(rmap_item_cache
, rmap_item
);
393 static inline struct stable_node
*alloc_stable_node(void)
396 * The allocation can take too long with GFP_KERNEL when memory is under
397 * pressure, which may lead to hung task warnings. Adding __GFP_HIGH
398 * grants access to memory reserves, helping to avoid this problem.
400 return kmem_cache_alloc(stable_node_cache
, GFP_KERNEL
| __GFP_HIGH
);
403 static inline void free_stable_node(struct stable_node
*stable_node
)
405 VM_BUG_ON(stable_node
->rmap_hlist_len
&&
406 !is_stable_node_chain(stable_node
));
407 kmem_cache_free(stable_node_cache
, stable_node
);
410 static inline struct mm_slot
*alloc_mm_slot(void)
412 if (!mm_slot_cache
) /* initialization failed */
414 return kmem_cache_zalloc(mm_slot_cache
, GFP_KERNEL
);
417 static inline void free_mm_slot(struct mm_slot
*mm_slot
)
419 kmem_cache_free(mm_slot_cache
, mm_slot
);
422 static struct mm_slot
*get_mm_slot(struct mm_struct
*mm
)
424 struct mm_slot
*slot
;
426 hash_for_each_possible(mm_slots_hash
, slot
, link
, (unsigned long)mm
)
433 static void insert_to_mm_slots_hash(struct mm_struct
*mm
,
434 struct mm_slot
*mm_slot
)
437 hash_add(mm_slots_hash
, &mm_slot
->link
, (unsigned long)mm
);
441 * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
442 * page tables after it has passed through ksm_exit() - which, if necessary,
443 * takes mmap_lock briefly to serialize against them. ksm_exit() does not set
444 * a special flag: they can just back out as soon as mm_users goes to zero.
445 * ksm_test_exit() is used throughout to make this test for exit: in some
446 * places for correctness, in some places just to avoid unnecessary work.
448 static inline bool ksm_test_exit(struct mm_struct
*mm
)
450 return atomic_read(&mm
->mm_users
) == 0;
454 * We use break_ksm to break COW on a ksm page: it's a stripped down
456 * if (get_user_pages(addr, 1, FOLL_WRITE, &page, NULL) == 1)
459 * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
460 * in case the application has unmapped and remapped mm,addr meanwhile.
461 * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP
462 * mmap of /dev/mem, where we would not want to touch it.
464 * FAULT_FLAG/FOLL_REMOTE are because we do this outside the context
465 * of the process that owns 'vma'. We also do not want to enforce
466 * protection keys here anyway.
468 static int break_ksm(struct vm_area_struct
*vma
, unsigned long addr
)
475 page
= follow_page(vma
, addr
,
476 FOLL_GET
| FOLL_MIGRATION
| FOLL_REMOTE
);
477 if (IS_ERR_OR_NULL(page
))
480 ret
= handle_mm_fault(vma
, addr
,
481 FAULT_FLAG_WRITE
| FAULT_FLAG_REMOTE
,
484 ret
= VM_FAULT_WRITE
;
486 } while (!(ret
& (VM_FAULT_WRITE
| VM_FAULT_SIGBUS
| VM_FAULT_SIGSEGV
| VM_FAULT_OOM
)));
488 * We must loop because handle_mm_fault() may back out if there's
489 * any difficulty e.g. if pte accessed bit gets updated concurrently.
491 * VM_FAULT_WRITE is what we have been hoping for: it indicates that
492 * COW has been broken, even if the vma does not permit VM_WRITE;
493 * but note that a concurrent fault might break PageKsm for us.
495 * VM_FAULT_SIGBUS could occur if we race with truncation of the
496 * backing file, which also invalidates anonymous pages: that's
497 * okay, that truncation will have unmapped the PageKsm for us.
499 * VM_FAULT_OOM: at the time of writing (late July 2009), setting
500 * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
501 * current task has TIF_MEMDIE set, and will be OOM killed on return
502 * to user; and ksmd, having no mm, would never be chosen for that.
504 * But if the mm is in a limited mem_cgroup, then the fault may fail
505 * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
506 * even ksmd can fail in this way - though it's usually breaking ksm
507 * just to undo a merge it made a moment before, so unlikely to oom.
509 * That's a pity: we might therefore have more kernel pages allocated
510 * than we're counting as nodes in the stable tree; but ksm_do_scan
511 * will retry to break_cow on each pass, so should recover the page
512 * in due course. The important thing is to not let VM_MERGEABLE
513 * be cleared while any such pages might remain in the area.
515 return (ret
& VM_FAULT_OOM
) ? -ENOMEM
: 0;
518 static struct vm_area_struct
*find_mergeable_vma(struct mm_struct
*mm
,
521 struct vm_area_struct
*vma
;
522 if (ksm_test_exit(mm
))
524 vma
= vma_lookup(mm
, addr
);
525 if (!vma
|| !(vma
->vm_flags
& VM_MERGEABLE
) || !vma
->anon_vma
)
530 static void break_cow(struct rmap_item
*rmap_item
)
532 struct mm_struct
*mm
= rmap_item
->mm
;
533 unsigned long addr
= rmap_item
->address
;
534 struct vm_area_struct
*vma
;
537 * It is not an accident that whenever we want to break COW
538 * to undo, we also need to drop a reference to the anon_vma.
540 put_anon_vma(rmap_item
->anon_vma
);
543 vma
= find_mergeable_vma(mm
, addr
);
545 break_ksm(vma
, addr
);
546 mmap_read_unlock(mm
);
549 static struct page
*get_mergeable_page(struct rmap_item
*rmap_item
)
551 struct mm_struct
*mm
= rmap_item
->mm
;
552 unsigned long addr
= rmap_item
->address
;
553 struct vm_area_struct
*vma
;
557 vma
= find_mergeable_vma(mm
, addr
);
561 page
= follow_page(vma
, addr
, FOLL_GET
);
562 if (IS_ERR_OR_NULL(page
))
564 if (PageAnon(page
)) {
565 flush_anon_page(vma
, page
, addr
);
566 flush_dcache_page(page
);
572 mmap_read_unlock(mm
);
577 * This helper is used for getting right index into array of tree roots.
578 * When merge_across_nodes knob is set to 1, there are only two rb-trees for
579 * stable and unstable pages from all nodes with roots in index 0. Otherwise,
580 * every node has its own stable and unstable tree.
582 static inline int get_kpfn_nid(unsigned long kpfn
)
584 return ksm_merge_across_nodes
? 0 : NUMA(pfn_to_nid(kpfn
));
587 static struct stable_node
*alloc_stable_node_chain(struct stable_node
*dup
,
588 struct rb_root
*root
)
590 struct stable_node
*chain
= alloc_stable_node();
591 VM_BUG_ON(is_stable_node_chain(dup
));
593 INIT_HLIST_HEAD(&chain
->hlist
);
594 chain
->chain_prune_time
= jiffies
;
595 chain
->rmap_hlist_len
= STABLE_NODE_CHAIN
;
596 #if defined (CONFIG_DEBUG_VM) && defined(CONFIG_NUMA)
597 chain
->nid
= NUMA_NO_NODE
; /* debug */
599 ksm_stable_node_chains
++;
602 * Put the stable node chain in the first dimension of
603 * the stable tree and at the same time remove the old
606 rb_replace_node(&dup
->node
, &chain
->node
, root
);
609 * Move the old stable node to the second dimension
610 * queued in the hlist_dup. The invariant is that all
611 * dup stable_nodes in the chain->hlist point to pages
612 * that are write protected and have the exact same
615 stable_node_chain_add_dup(dup
, chain
);
620 static inline void free_stable_node_chain(struct stable_node
*chain
,
621 struct rb_root
*root
)
623 rb_erase(&chain
->node
, root
);
624 free_stable_node(chain
);
625 ksm_stable_node_chains
--;
628 static void remove_node_from_stable_tree(struct stable_node
*stable_node
)
630 struct rmap_item
*rmap_item
;
632 /* check it's not STABLE_NODE_CHAIN or negative */
633 BUG_ON(stable_node
->rmap_hlist_len
< 0);
635 hlist_for_each_entry(rmap_item
, &stable_node
->hlist
, hlist
) {
636 if (rmap_item
->hlist
.next
)
640 VM_BUG_ON(stable_node
->rmap_hlist_len
<= 0);
641 stable_node
->rmap_hlist_len
--;
642 put_anon_vma(rmap_item
->anon_vma
);
643 rmap_item
->address
&= PAGE_MASK
;
648 * We need the second aligned pointer of the migrate_nodes
649 * list_head to stay clear from the rb_parent_color union
650 * (aligned and different than any node) and also different
651 * from &migrate_nodes. This will verify that future list.h changes
652 * don't break STABLE_NODE_DUP_HEAD. Only recent gcc can handle it.
654 #if defined(GCC_VERSION) && GCC_VERSION >= 40903
655 BUILD_BUG_ON(STABLE_NODE_DUP_HEAD
<= &migrate_nodes
);
656 BUILD_BUG_ON(STABLE_NODE_DUP_HEAD
>= &migrate_nodes
+ 1);
659 if (stable_node
->head
== &migrate_nodes
)
660 list_del(&stable_node
->list
);
662 stable_node_dup_del(stable_node
);
663 free_stable_node(stable_node
);
666 enum get_ksm_page_flags
{
673 * get_ksm_page: checks if the page indicated by the stable node
674 * is still its ksm page, despite having held no reference to it.
675 * In which case we can trust the content of the page, and it
676 * returns the gotten page; but if the page has now been zapped,
677 * remove the stale node from the stable tree and return NULL.
678 * But beware, the stable node's page might be being migrated.
680 * You would expect the stable_node to hold a reference to the ksm page.
681 * But if it increments the page's count, swapping out has to wait for
682 * ksmd to come around again before it can free the page, which may take
683 * seconds or even minutes: much too unresponsive. So instead we use a
684 * "keyhole reference": access to the ksm page from the stable node peeps
685 * out through its keyhole to see if that page still holds the right key,
686 * pointing back to this stable node. This relies on freeing a PageAnon
687 * page to reset its page->mapping to NULL, and relies on no other use of
688 * a page to put something that might look like our key in page->mapping.
689 * is on its way to being freed; but it is an anomaly to bear in mind.
691 static struct page
*get_ksm_page(struct stable_node
*stable_node
,
692 enum get_ksm_page_flags flags
)
695 void *expected_mapping
;
698 expected_mapping
= (void *)((unsigned long)stable_node
|
701 kpfn
= READ_ONCE(stable_node
->kpfn
); /* Address dependency. */
702 page
= pfn_to_page(kpfn
);
703 if (READ_ONCE(page
->mapping
) != expected_mapping
)
707 * We cannot do anything with the page while its refcount is 0.
708 * Usually 0 means free, or tail of a higher-order page: in which
709 * case this node is no longer referenced, and should be freed;
710 * however, it might mean that the page is under page_ref_freeze().
711 * The __remove_mapping() case is easy, again the node is now stale;
712 * the same is in reuse_ksm_page() case; but if page is swapcache
713 * in migrate_page_move_mapping(), it might still be our page,
714 * in which case it's essential to keep the node.
716 while (!get_page_unless_zero(page
)) {
718 * Another check for page->mapping != expected_mapping would
719 * work here too. We have chosen the !PageSwapCache test to
720 * optimize the common case, when the page is or is about to
721 * be freed: PageSwapCache is cleared (under spin_lock_irq)
722 * in the ref_freeze section of __remove_mapping(); but Anon
723 * page->mapping reset to NULL later, in free_pages_prepare().
725 if (!PageSwapCache(page
))
730 if (READ_ONCE(page
->mapping
) != expected_mapping
) {
735 if (flags
== GET_KSM_PAGE_TRYLOCK
) {
736 if (!trylock_page(page
)) {
738 return ERR_PTR(-EBUSY
);
740 } else if (flags
== GET_KSM_PAGE_LOCK
)
743 if (flags
!= GET_KSM_PAGE_NOLOCK
) {
744 if (READ_ONCE(page
->mapping
) != expected_mapping
) {
754 * We come here from above when page->mapping or !PageSwapCache
755 * suggests that the node is stale; but it might be under migration.
756 * We need smp_rmb(), matching the smp_wmb() in ksm_migrate_page(),
757 * before checking whether node->kpfn has been changed.
760 if (READ_ONCE(stable_node
->kpfn
) != kpfn
)
762 remove_node_from_stable_tree(stable_node
);
767 * Removing rmap_item from stable or unstable tree.
768 * This function will clean the information from the stable/unstable tree.
770 static void remove_rmap_item_from_tree(struct rmap_item
*rmap_item
)
772 if (rmap_item
->address
& STABLE_FLAG
) {
773 struct stable_node
*stable_node
;
776 stable_node
= rmap_item
->head
;
777 page
= get_ksm_page(stable_node
, GET_KSM_PAGE_LOCK
);
781 hlist_del(&rmap_item
->hlist
);
785 if (!hlist_empty(&stable_node
->hlist
))
789 VM_BUG_ON(stable_node
->rmap_hlist_len
<= 0);
790 stable_node
->rmap_hlist_len
--;
792 put_anon_vma(rmap_item
->anon_vma
);
793 rmap_item
->head
= NULL
;
794 rmap_item
->address
&= PAGE_MASK
;
796 } else if (rmap_item
->address
& UNSTABLE_FLAG
) {
799 * Usually ksmd can and must skip the rb_erase, because
800 * root_unstable_tree was already reset to RB_ROOT.
801 * But be careful when an mm is exiting: do the rb_erase
802 * if this rmap_item was inserted by this scan, rather
803 * than left over from before.
805 age
= (unsigned char)(ksm_scan
.seqnr
- rmap_item
->address
);
808 rb_erase(&rmap_item
->node
,
809 root_unstable_tree
+ NUMA(rmap_item
->nid
));
810 ksm_pages_unshared
--;
811 rmap_item
->address
&= PAGE_MASK
;
814 cond_resched(); /* we're called from many long loops */
817 static void remove_trailing_rmap_items(struct rmap_item
**rmap_list
)
820 struct rmap_item
*rmap_item
= *rmap_list
;
821 *rmap_list
= rmap_item
->rmap_list
;
822 remove_rmap_item_from_tree(rmap_item
);
823 free_rmap_item(rmap_item
);
828 * Though it's very tempting to unmerge rmap_items from stable tree rather
829 * than check every pte of a given vma, the locking doesn't quite work for
830 * that - an rmap_item is assigned to the stable tree after inserting ksm
831 * page and upping mmap_lock. Nor does it fit with the way we skip dup'ing
832 * rmap_items from parent to child at fork time (so as not to waste time
833 * if exit comes before the next scan reaches it).
835 * Similarly, although we'd like to remove rmap_items (so updating counts
836 * and freeing memory) when unmerging an area, it's easier to leave that
837 * to the next pass of ksmd - consider, for example, how ksmd might be
838 * in cmp_and_merge_page on one of the rmap_items we would be removing.
840 static int unmerge_ksm_pages(struct vm_area_struct
*vma
,
841 unsigned long start
, unsigned long end
)
846 for (addr
= start
; addr
< end
&& !err
; addr
+= PAGE_SIZE
) {
847 if (ksm_test_exit(vma
->vm_mm
))
849 if (signal_pending(current
))
852 err
= break_ksm(vma
, addr
);
857 static inline struct stable_node
*page_stable_node(struct page
*page
)
859 return PageKsm(page
) ? page_rmapping(page
) : NULL
;
862 static inline void set_page_stable_node(struct page
*page
,
863 struct stable_node
*stable_node
)
865 page
->mapping
= (void *)((unsigned long)stable_node
| PAGE_MAPPING_KSM
);
870 * Only called through the sysfs control interface:
872 static int remove_stable_node(struct stable_node
*stable_node
)
877 page
= get_ksm_page(stable_node
, GET_KSM_PAGE_LOCK
);
880 * get_ksm_page did remove_node_from_stable_tree itself.
886 * Page could be still mapped if this races with __mmput() running in
887 * between ksm_exit() and exit_mmap(). Just refuse to let
888 * merge_across_nodes/max_page_sharing be switched.
891 if (!page_mapped(page
)) {
893 * The stable node did not yet appear stale to get_ksm_page(),
894 * since that allows for an unmapped ksm page to be recognized
895 * right up until it is freed; but the node is safe to remove.
896 * This page might be in a pagevec waiting to be freed,
897 * or it might be PageSwapCache (perhaps under writeback),
898 * or it might have been removed from swapcache a moment ago.
900 set_page_stable_node(page
, NULL
);
901 remove_node_from_stable_tree(stable_node
);
910 static int remove_stable_node_chain(struct stable_node
*stable_node
,
911 struct rb_root
*root
)
913 struct stable_node
*dup
;
914 struct hlist_node
*hlist_safe
;
916 if (!is_stable_node_chain(stable_node
)) {
917 VM_BUG_ON(is_stable_node_dup(stable_node
));
918 if (remove_stable_node(stable_node
))
924 hlist_for_each_entry_safe(dup
, hlist_safe
,
925 &stable_node
->hlist
, hlist_dup
) {
926 VM_BUG_ON(!is_stable_node_dup(dup
));
927 if (remove_stable_node(dup
))
930 BUG_ON(!hlist_empty(&stable_node
->hlist
));
931 free_stable_node_chain(stable_node
, root
);
935 static int remove_all_stable_nodes(void)
937 struct stable_node
*stable_node
, *next
;
941 for (nid
= 0; nid
< ksm_nr_node_ids
; nid
++) {
942 while (root_stable_tree
[nid
].rb_node
) {
943 stable_node
= rb_entry(root_stable_tree
[nid
].rb_node
,
944 struct stable_node
, node
);
945 if (remove_stable_node_chain(stable_node
,
946 root_stable_tree
+ nid
)) {
948 break; /* proceed to next nid */
953 list_for_each_entry_safe(stable_node
, next
, &migrate_nodes
, list
) {
954 if (remove_stable_node(stable_node
))
961 static int unmerge_and_remove_all_rmap_items(void)
963 struct mm_slot
*mm_slot
;
964 struct mm_struct
*mm
;
965 struct vm_area_struct
*vma
;
968 spin_lock(&ksm_mmlist_lock
);
969 ksm_scan
.mm_slot
= list_entry(ksm_mm_head
.mm_list
.next
,
970 struct mm_slot
, mm_list
);
971 spin_unlock(&ksm_mmlist_lock
);
973 for (mm_slot
= ksm_scan
.mm_slot
;
974 mm_slot
!= &ksm_mm_head
; mm_slot
= ksm_scan
.mm_slot
) {
977 for (vma
= mm
->mmap
; vma
; vma
= vma
->vm_next
) {
978 if (ksm_test_exit(mm
))
980 if (!(vma
->vm_flags
& VM_MERGEABLE
) || !vma
->anon_vma
)
982 err
= unmerge_ksm_pages(vma
,
983 vma
->vm_start
, vma
->vm_end
);
988 remove_trailing_rmap_items(&mm_slot
->rmap_list
);
989 mmap_read_unlock(mm
);
991 spin_lock(&ksm_mmlist_lock
);
992 ksm_scan
.mm_slot
= list_entry(mm_slot
->mm_list
.next
,
993 struct mm_slot
, mm_list
);
994 if (ksm_test_exit(mm
)) {
995 hash_del(&mm_slot
->link
);
996 list_del(&mm_slot
->mm_list
);
997 spin_unlock(&ksm_mmlist_lock
);
999 free_mm_slot(mm_slot
);
1000 clear_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
1003 spin_unlock(&ksm_mmlist_lock
);
1006 /* Clean up stable nodes, but don't worry if some are still busy */
1007 remove_all_stable_nodes();
1012 mmap_read_unlock(mm
);
1013 spin_lock(&ksm_mmlist_lock
);
1014 ksm_scan
.mm_slot
= &ksm_mm_head
;
1015 spin_unlock(&ksm_mmlist_lock
);
1018 #endif /* CONFIG_SYSFS */
1020 static u32
calc_checksum(struct page
*page
)
1023 void *addr
= kmap_atomic(page
);
1024 checksum
= xxhash(addr
, PAGE_SIZE
, 0);
1025 kunmap_atomic(addr
);
1029 static int write_protect_page(struct vm_area_struct
*vma
, struct page
*page
,
1032 struct mm_struct
*mm
= vma
->vm_mm
;
1033 struct page_vma_mapped_walk pvmw
= {
1039 struct mmu_notifier_range range
;
1041 pvmw
.address
= page_address_in_vma(page
, vma
);
1042 if (pvmw
.address
== -EFAULT
)
1045 BUG_ON(PageTransCompound(page
));
1047 mmu_notifier_range_init(&range
, MMU_NOTIFY_CLEAR
, 0, vma
, mm
,
1049 pvmw
.address
+ PAGE_SIZE
);
1050 mmu_notifier_invalidate_range_start(&range
);
1052 if (!page_vma_mapped_walk(&pvmw
))
1054 if (WARN_ONCE(!pvmw
.pte
, "Unexpected PMD mapping?"))
1057 if (pte_write(*pvmw
.pte
) || pte_dirty(*pvmw
.pte
) ||
1058 (pte_protnone(*pvmw
.pte
) && pte_savedwrite(*pvmw
.pte
)) ||
1059 mm_tlb_flush_pending(mm
)) {
1062 swapped
= PageSwapCache(page
);
1063 flush_cache_page(vma
, pvmw
.address
, page_to_pfn(page
));
1065 * Ok this is tricky, when get_user_pages_fast() run it doesn't
1066 * take any lock, therefore the check that we are going to make
1067 * with the pagecount against the mapcount is racy and
1068 * O_DIRECT can happen right after the check.
1069 * So we clear the pte and flush the tlb before the check
1070 * this assure us that no O_DIRECT can happen after the check
1071 * or in the middle of the check.
1073 * No need to notify as we are downgrading page table to read
1074 * only not changing it to point to a new page.
1076 * See Documentation/vm/mmu_notifier.rst
1078 entry
= ptep_clear_flush(vma
, pvmw
.address
, pvmw
.pte
);
1080 * Check that no O_DIRECT or similar I/O is in progress on the
1083 if (page_mapcount(page
) + 1 + swapped
!= page_count(page
)) {
1084 set_pte_at(mm
, pvmw
.address
, pvmw
.pte
, entry
);
1087 if (pte_dirty(entry
))
1088 set_page_dirty(page
);
1090 if (pte_protnone(entry
))
1091 entry
= pte_mkclean(pte_clear_savedwrite(entry
));
1093 entry
= pte_mkclean(pte_wrprotect(entry
));
1094 set_pte_at_notify(mm
, pvmw
.address
, pvmw
.pte
, entry
);
1096 *orig_pte
= *pvmw
.pte
;
1100 page_vma_mapped_walk_done(&pvmw
);
1102 mmu_notifier_invalidate_range_end(&range
);
1108 * replace_page - replace page in vma by new ksm page
1109 * @vma: vma that holds the pte pointing to page
1110 * @page: the page we are replacing by kpage
1111 * @kpage: the ksm page we replace page by
1112 * @orig_pte: the original value of the pte
1114 * Returns 0 on success, -EFAULT on failure.
1116 static int replace_page(struct vm_area_struct
*vma
, struct page
*page
,
1117 struct page
*kpage
, pte_t orig_pte
)
1119 struct mm_struct
*mm
= vma
->vm_mm
;
1126 struct mmu_notifier_range range
;
1128 addr
= page_address_in_vma(page
, vma
);
1129 if (addr
== -EFAULT
)
1132 pmd
= mm_find_pmd(mm
, addr
);
1136 mmu_notifier_range_init(&range
, MMU_NOTIFY_CLEAR
, 0, vma
, mm
, addr
,
1138 mmu_notifier_invalidate_range_start(&range
);
1140 ptep
= pte_offset_map_lock(mm
, pmd
, addr
, &ptl
);
1141 if (!pte_same(*ptep
, orig_pte
)) {
1142 pte_unmap_unlock(ptep
, ptl
);
1147 * No need to check ksm_use_zero_pages here: we can only have a
1148 * zero_page here if ksm_use_zero_pages was enabled already.
1150 if (!is_zero_pfn(page_to_pfn(kpage
))) {
1152 page_add_anon_rmap(kpage
, vma
, addr
, false);
1153 newpte
= mk_pte(kpage
, vma
->vm_page_prot
);
1155 newpte
= pte_mkspecial(pfn_pte(page_to_pfn(kpage
),
1156 vma
->vm_page_prot
));
1158 * We're replacing an anonymous page with a zero page, which is
1159 * not anonymous. We need to do proper accounting otherwise we
1160 * will get wrong values in /proc, and a BUG message in dmesg
1161 * when tearing down the mm.
1163 dec_mm_counter(mm
, MM_ANONPAGES
);
1166 flush_cache_page(vma
, addr
, pte_pfn(*ptep
));
1168 * No need to notify as we are replacing a read only page with another
1169 * read only page with the same content.
1171 * See Documentation/vm/mmu_notifier.rst
1173 ptep_clear_flush(vma
, addr
, ptep
);
1174 set_pte_at_notify(mm
, addr
, ptep
, newpte
);
1176 page_remove_rmap(page
, false);
1177 if (!page_mapped(page
))
1178 try_to_free_swap(page
);
1181 pte_unmap_unlock(ptep
, ptl
);
1184 mmu_notifier_invalidate_range_end(&range
);
1190 * try_to_merge_one_page - take two pages and merge them into one
1191 * @vma: the vma that holds the pte pointing to page
1192 * @page: the PageAnon page that we want to replace with kpage
1193 * @kpage: the PageKsm page that we want to map instead of page,
1194 * or NULL the first time when we want to use page as kpage.
1196 * This function returns 0 if the pages were merged, -EFAULT otherwise.
1198 static int try_to_merge_one_page(struct vm_area_struct
*vma
,
1199 struct page
*page
, struct page
*kpage
)
1201 pte_t orig_pte
= __pte(0);
1204 if (page
== kpage
) /* ksm page forked */
1207 if (!PageAnon(page
))
1211 * We need the page lock to read a stable PageSwapCache in
1212 * write_protect_page(). We use trylock_page() instead of
1213 * lock_page() because we don't want to wait here - we
1214 * prefer to continue scanning and merging different pages,
1215 * then come back to this page when it is unlocked.
1217 if (!trylock_page(page
))
1220 if (PageTransCompound(page
)) {
1221 if (split_huge_page(page
))
1226 * If this anonymous page is mapped only here, its pte may need
1227 * to be write-protected. If it's mapped elsewhere, all of its
1228 * ptes are necessarily already write-protected. But in either
1229 * case, we need to lock and check page_count is not raised.
1231 if (write_protect_page(vma
, page
, &orig_pte
) == 0) {
1234 * While we hold page lock, upgrade page from
1235 * PageAnon+anon_vma to PageKsm+NULL stable_node:
1236 * stable_tree_insert() will update stable_node.
1238 set_page_stable_node(page
, NULL
);
1239 mark_page_accessed(page
);
1241 * Page reclaim just frees a clean page with no dirty
1242 * ptes: make sure that the ksm page would be swapped.
1244 if (!PageDirty(page
))
1247 } else if (pages_identical(page
, kpage
))
1248 err
= replace_page(vma
, page
, kpage
, orig_pte
);
1251 if ((vma
->vm_flags
& VM_LOCKED
) && kpage
&& !err
) {
1252 munlock_vma_page(page
);
1253 if (!PageMlocked(kpage
)) {
1256 mlock_vma_page(kpage
);
1257 page
= kpage
; /* for final unlock */
1268 * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
1269 * but no new kernel page is allocated: kpage must already be a ksm page.
1271 * This function returns 0 if the pages were merged, -EFAULT otherwise.
1273 static int try_to_merge_with_ksm_page(struct rmap_item
*rmap_item
,
1274 struct page
*page
, struct page
*kpage
)
1276 struct mm_struct
*mm
= rmap_item
->mm
;
1277 struct vm_area_struct
*vma
;
1281 vma
= find_mergeable_vma(mm
, rmap_item
->address
);
1285 err
= try_to_merge_one_page(vma
, page
, kpage
);
1289 /* Unstable nid is in union with stable anon_vma: remove first */
1290 remove_rmap_item_from_tree(rmap_item
);
1292 /* Must get reference to anon_vma while still holding mmap_lock */
1293 rmap_item
->anon_vma
= vma
->anon_vma
;
1294 get_anon_vma(vma
->anon_vma
);
1296 mmap_read_unlock(mm
);
1301 * try_to_merge_two_pages - take two identical pages and prepare them
1302 * to be merged into one page.
1304 * This function returns the kpage if we successfully merged two identical
1305 * pages into one ksm page, NULL otherwise.
1307 * Note that this function upgrades page to ksm page: if one of the pages
1308 * is already a ksm page, try_to_merge_with_ksm_page should be used.
1310 static struct page
*try_to_merge_two_pages(struct rmap_item
*rmap_item
,
1312 struct rmap_item
*tree_rmap_item
,
1313 struct page
*tree_page
)
1317 err
= try_to_merge_with_ksm_page(rmap_item
, page
, NULL
);
1319 err
= try_to_merge_with_ksm_page(tree_rmap_item
,
1322 * If that fails, we have a ksm page with only one pte
1323 * pointing to it: so break it.
1326 break_cow(rmap_item
);
1328 return err
? NULL
: page
;
1331 static __always_inline
1332 bool __is_page_sharing_candidate(struct stable_node
*stable_node
, int offset
)
1334 VM_BUG_ON(stable_node
->rmap_hlist_len
< 0);
1336 * Check that at least one mapping still exists, otherwise
1337 * there's no much point to merge and share with this
1338 * stable_node, as the underlying tree_page of the other
1339 * sharer is going to be freed soon.
1341 return stable_node
->rmap_hlist_len
&&
1342 stable_node
->rmap_hlist_len
+ offset
< ksm_max_page_sharing
;
1345 static __always_inline
1346 bool is_page_sharing_candidate(struct stable_node
*stable_node
)
1348 return __is_page_sharing_candidate(stable_node
, 0);
1351 static struct page
*stable_node_dup(struct stable_node
**_stable_node_dup
,
1352 struct stable_node
**_stable_node
,
1353 struct rb_root
*root
,
1354 bool prune_stale_stable_nodes
)
1356 struct stable_node
*dup
, *found
= NULL
, *stable_node
= *_stable_node
;
1357 struct hlist_node
*hlist_safe
;
1358 struct page
*_tree_page
, *tree_page
= NULL
;
1360 int found_rmap_hlist_len
;
1362 if (!prune_stale_stable_nodes
||
1363 time_before(jiffies
, stable_node
->chain_prune_time
+
1365 ksm_stable_node_chains_prune_millisecs
)))
1366 prune_stale_stable_nodes
= false;
1368 stable_node
->chain_prune_time
= jiffies
;
1370 hlist_for_each_entry_safe(dup
, hlist_safe
,
1371 &stable_node
->hlist
, hlist_dup
) {
1374 * We must walk all stable_node_dup to prune the stale
1375 * stable nodes during lookup.
1377 * get_ksm_page can drop the nodes from the
1378 * stable_node->hlist if they point to freed pages
1379 * (that's why we do a _safe walk). The "dup"
1380 * stable_node parameter itself will be freed from
1381 * under us if it returns NULL.
1383 _tree_page
= get_ksm_page(dup
, GET_KSM_PAGE_NOLOCK
);
1387 if (is_page_sharing_candidate(dup
)) {
1389 dup
->rmap_hlist_len
> found_rmap_hlist_len
) {
1391 put_page(tree_page
);
1393 found_rmap_hlist_len
= found
->rmap_hlist_len
;
1394 tree_page
= _tree_page
;
1396 /* skip put_page for found dup */
1397 if (!prune_stale_stable_nodes
)
1402 put_page(_tree_page
);
1407 * nr is counting all dups in the chain only if
1408 * prune_stale_stable_nodes is true, otherwise we may
1409 * break the loop at nr == 1 even if there are
1412 if (prune_stale_stable_nodes
&& nr
== 1) {
1414 * If there's not just one entry it would
1415 * corrupt memory, better BUG_ON. In KSM
1416 * context with no lock held it's not even
1419 BUG_ON(stable_node
->hlist
.first
->next
);
1422 * There's just one entry and it is below the
1423 * deduplication limit so drop the chain.
1425 rb_replace_node(&stable_node
->node
, &found
->node
,
1427 free_stable_node(stable_node
);
1428 ksm_stable_node_chains
--;
1429 ksm_stable_node_dups
--;
1431 * NOTE: the caller depends on the stable_node
1432 * to be equal to stable_node_dup if the chain
1435 *_stable_node
= found
;
1437 * Just for robustness, as stable_node is
1438 * otherwise left as a stable pointer, the
1439 * compiler shall optimize it away at build
1443 } else if (stable_node
->hlist
.first
!= &found
->hlist_dup
&&
1444 __is_page_sharing_candidate(found
, 1)) {
1446 * If the found stable_node dup can accept one
1447 * more future merge (in addition to the one
1448 * that is underway) and is not at the head of
1449 * the chain, put it there so next search will
1450 * be quicker in the !prune_stale_stable_nodes
1453 * NOTE: it would be inaccurate to use nr > 1
1454 * instead of checking the hlist.first pointer
1455 * directly, because in the
1456 * prune_stale_stable_nodes case "nr" isn't
1457 * the position of the found dup in the chain,
1458 * but the total number of dups in the chain.
1460 hlist_del(&found
->hlist_dup
);
1461 hlist_add_head(&found
->hlist_dup
,
1462 &stable_node
->hlist
);
1466 *_stable_node_dup
= found
;
1470 static struct stable_node
*stable_node_dup_any(struct stable_node
*stable_node
,
1471 struct rb_root
*root
)
1473 if (!is_stable_node_chain(stable_node
))
1475 if (hlist_empty(&stable_node
->hlist
)) {
1476 free_stable_node_chain(stable_node
, root
);
1479 return hlist_entry(stable_node
->hlist
.first
,
1480 typeof(*stable_node
), hlist_dup
);
1484 * Like for get_ksm_page, this function can free the *_stable_node and
1485 * *_stable_node_dup if the returned tree_page is NULL.
1487 * It can also free and overwrite *_stable_node with the found
1488 * stable_node_dup if the chain is collapsed (in which case
1489 * *_stable_node will be equal to *_stable_node_dup like if the chain
1490 * never existed). It's up to the caller to verify tree_page is not
1491 * NULL before dereferencing *_stable_node or *_stable_node_dup.
1493 * *_stable_node_dup is really a second output parameter of this
1494 * function and will be overwritten in all cases, the caller doesn't
1495 * need to initialize it.
1497 static struct page
*__stable_node_chain(struct stable_node
**_stable_node_dup
,
1498 struct stable_node
**_stable_node
,
1499 struct rb_root
*root
,
1500 bool prune_stale_stable_nodes
)
1502 struct stable_node
*stable_node
= *_stable_node
;
1503 if (!is_stable_node_chain(stable_node
)) {
1504 if (is_page_sharing_candidate(stable_node
)) {
1505 *_stable_node_dup
= stable_node
;
1506 return get_ksm_page(stable_node
, GET_KSM_PAGE_NOLOCK
);
1509 * _stable_node_dup set to NULL means the stable_node
1510 * reached the ksm_max_page_sharing limit.
1512 *_stable_node_dup
= NULL
;
1515 return stable_node_dup(_stable_node_dup
, _stable_node
, root
,
1516 prune_stale_stable_nodes
);
1519 static __always_inline
struct page
*chain_prune(struct stable_node
**s_n_d
,
1520 struct stable_node
**s_n
,
1521 struct rb_root
*root
)
1523 return __stable_node_chain(s_n_d
, s_n
, root
, true);
1526 static __always_inline
struct page
*chain(struct stable_node
**s_n_d
,
1527 struct stable_node
*s_n
,
1528 struct rb_root
*root
)
1530 struct stable_node
*old_stable_node
= s_n
;
1531 struct page
*tree_page
;
1533 tree_page
= __stable_node_chain(s_n_d
, &s_n
, root
, false);
1534 /* not pruning dups so s_n cannot have changed */
1535 VM_BUG_ON(s_n
!= old_stable_node
);
1540 * stable_tree_search - search for page inside the stable tree
1542 * This function checks if there is a page inside the stable tree
1543 * with identical content to the page that we are scanning right now.
1545 * This function returns the stable tree node of identical content if found,
1548 static struct page
*stable_tree_search(struct page
*page
)
1551 struct rb_root
*root
;
1552 struct rb_node
**new;
1553 struct rb_node
*parent
;
1554 struct stable_node
*stable_node
, *stable_node_dup
, *stable_node_any
;
1555 struct stable_node
*page_node
;
1557 page_node
= page_stable_node(page
);
1558 if (page_node
&& page_node
->head
!= &migrate_nodes
) {
1559 /* ksm page forked */
1564 nid
= get_kpfn_nid(page_to_pfn(page
));
1565 root
= root_stable_tree
+ nid
;
1567 new = &root
->rb_node
;
1571 struct page
*tree_page
;
1575 stable_node
= rb_entry(*new, struct stable_node
, node
);
1576 stable_node_any
= NULL
;
1577 tree_page
= chain_prune(&stable_node_dup
, &stable_node
, root
);
1579 * NOTE: stable_node may have been freed by
1580 * chain_prune() if the returned stable_node_dup is
1581 * not NULL. stable_node_dup may have been inserted in
1582 * the rbtree instead as a regular stable_node (in
1583 * order to collapse the stable_node chain if a single
1584 * stable_node dup was found in it). In such case the
1585 * stable_node is overwritten by the calleee to point
1586 * to the stable_node_dup that was collapsed in the
1587 * stable rbtree and stable_node will be equal to
1588 * stable_node_dup like if the chain never existed.
1590 if (!stable_node_dup
) {
1592 * Either all stable_node dups were full in
1593 * this stable_node chain, or this chain was
1594 * empty and should be rb_erased.
1596 stable_node_any
= stable_node_dup_any(stable_node
,
1598 if (!stable_node_any
) {
1599 /* rb_erase just run */
1603 * Take any of the stable_node dups page of
1604 * this stable_node chain to let the tree walk
1605 * continue. All KSM pages belonging to the
1606 * stable_node dups in a stable_node chain
1607 * have the same content and they're
1608 * write protected at all times. Any will work
1609 * fine to continue the walk.
1611 tree_page
= get_ksm_page(stable_node_any
,
1612 GET_KSM_PAGE_NOLOCK
);
1614 VM_BUG_ON(!stable_node_dup
^ !!stable_node_any
);
1617 * If we walked over a stale stable_node,
1618 * get_ksm_page() will call rb_erase() and it
1619 * may rebalance the tree from under us. So
1620 * restart the search from scratch. Returning
1621 * NULL would be safe too, but we'd generate
1622 * false negative insertions just because some
1623 * stable_node was stale.
1628 ret
= memcmp_pages(page
, tree_page
);
1629 put_page(tree_page
);
1633 new = &parent
->rb_left
;
1635 new = &parent
->rb_right
;
1638 VM_BUG_ON(page_node
->head
!= &migrate_nodes
);
1640 * Test if the migrated page should be merged
1641 * into a stable node dup. If the mapcount is
1642 * 1 we can migrate it with another KSM page
1643 * without adding it to the chain.
1645 if (page_mapcount(page
) > 1)
1649 if (!stable_node_dup
) {
1651 * If the stable_node is a chain and
1652 * we got a payload match in memcmp
1653 * but we cannot merge the scanned
1654 * page in any of the existing
1655 * stable_node dups because they're
1656 * all full, we need to wait the
1657 * scanned page to find itself a match
1658 * in the unstable tree to create a
1659 * brand new KSM page to add later to
1660 * the dups of this stable_node.
1666 * Lock and unlock the stable_node's page (which
1667 * might already have been migrated) so that page
1668 * migration is sure to notice its raised count.
1669 * It would be more elegant to return stable_node
1670 * than kpage, but that involves more changes.
1672 tree_page
= get_ksm_page(stable_node_dup
,
1673 GET_KSM_PAGE_TRYLOCK
);
1675 if (PTR_ERR(tree_page
) == -EBUSY
)
1676 return ERR_PTR(-EBUSY
);
1678 if (unlikely(!tree_page
))
1680 * The tree may have been rebalanced,
1681 * so re-evaluate parent and new.
1684 unlock_page(tree_page
);
1686 if (get_kpfn_nid(stable_node_dup
->kpfn
) !=
1687 NUMA(stable_node_dup
->nid
)) {
1688 put_page(tree_page
);
1698 list_del(&page_node
->list
);
1699 DO_NUMA(page_node
->nid
= nid
);
1700 rb_link_node(&page_node
->node
, parent
, new);
1701 rb_insert_color(&page_node
->node
, root
);
1703 if (is_page_sharing_candidate(page_node
)) {
1711 * If stable_node was a chain and chain_prune collapsed it,
1712 * stable_node has been updated to be the new regular
1713 * stable_node. A collapse of the chain is indistinguishable
1714 * from the case there was no chain in the stable
1715 * rbtree. Otherwise stable_node is the chain and
1716 * stable_node_dup is the dup to replace.
1718 if (stable_node_dup
== stable_node
) {
1719 VM_BUG_ON(is_stable_node_chain(stable_node_dup
));
1720 VM_BUG_ON(is_stable_node_dup(stable_node_dup
));
1721 /* there is no chain */
1723 VM_BUG_ON(page_node
->head
!= &migrate_nodes
);
1724 list_del(&page_node
->list
);
1725 DO_NUMA(page_node
->nid
= nid
);
1726 rb_replace_node(&stable_node_dup
->node
,
1729 if (is_page_sharing_candidate(page_node
))
1734 rb_erase(&stable_node_dup
->node
, root
);
1738 VM_BUG_ON(!is_stable_node_chain(stable_node
));
1739 __stable_node_dup_del(stable_node_dup
);
1741 VM_BUG_ON(page_node
->head
!= &migrate_nodes
);
1742 list_del(&page_node
->list
);
1743 DO_NUMA(page_node
->nid
= nid
);
1744 stable_node_chain_add_dup(page_node
, stable_node
);
1745 if (is_page_sharing_candidate(page_node
))
1753 stable_node_dup
->head
= &migrate_nodes
;
1754 list_add(&stable_node_dup
->list
, stable_node_dup
->head
);
1758 /* stable_node_dup could be null if it reached the limit */
1759 if (!stable_node_dup
)
1760 stable_node_dup
= stable_node_any
;
1762 * If stable_node was a chain and chain_prune collapsed it,
1763 * stable_node has been updated to be the new regular
1764 * stable_node. A collapse of the chain is indistinguishable
1765 * from the case there was no chain in the stable
1766 * rbtree. Otherwise stable_node is the chain and
1767 * stable_node_dup is the dup to replace.
1769 if (stable_node_dup
== stable_node
) {
1770 VM_BUG_ON(is_stable_node_dup(stable_node_dup
));
1771 /* chain is missing so create it */
1772 stable_node
= alloc_stable_node_chain(stable_node_dup
,
1778 * Add this stable_node dup that was
1779 * migrated to the stable_node chain
1780 * of the current nid for this page
1783 VM_BUG_ON(!is_stable_node_dup(stable_node_dup
));
1784 VM_BUG_ON(page_node
->head
!= &migrate_nodes
);
1785 list_del(&page_node
->list
);
1786 DO_NUMA(page_node
->nid
= nid
);
1787 stable_node_chain_add_dup(page_node
, stable_node
);
1792 * stable_tree_insert - insert stable tree node pointing to new ksm page
1793 * into the stable tree.
1795 * This function returns the stable tree node just allocated on success,
1798 static struct stable_node
*stable_tree_insert(struct page
*kpage
)
1802 struct rb_root
*root
;
1803 struct rb_node
**new;
1804 struct rb_node
*parent
;
1805 struct stable_node
*stable_node
, *stable_node_dup
, *stable_node_any
;
1806 bool need_chain
= false;
1808 kpfn
= page_to_pfn(kpage
);
1809 nid
= get_kpfn_nid(kpfn
);
1810 root
= root_stable_tree
+ nid
;
1813 new = &root
->rb_node
;
1816 struct page
*tree_page
;
1820 stable_node
= rb_entry(*new, struct stable_node
, node
);
1821 stable_node_any
= NULL
;
1822 tree_page
= chain(&stable_node_dup
, stable_node
, root
);
1823 if (!stable_node_dup
) {
1825 * Either all stable_node dups were full in
1826 * this stable_node chain, or this chain was
1827 * empty and should be rb_erased.
1829 stable_node_any
= stable_node_dup_any(stable_node
,
1831 if (!stable_node_any
) {
1832 /* rb_erase just run */
1836 * Take any of the stable_node dups page of
1837 * this stable_node chain to let the tree walk
1838 * continue. All KSM pages belonging to the
1839 * stable_node dups in a stable_node chain
1840 * have the same content and they're
1841 * write protected at all times. Any will work
1842 * fine to continue the walk.
1844 tree_page
= get_ksm_page(stable_node_any
,
1845 GET_KSM_PAGE_NOLOCK
);
1847 VM_BUG_ON(!stable_node_dup
^ !!stable_node_any
);
1850 * If we walked over a stale stable_node,
1851 * get_ksm_page() will call rb_erase() and it
1852 * may rebalance the tree from under us. So
1853 * restart the search from scratch. Returning
1854 * NULL would be safe too, but we'd generate
1855 * false negative insertions just because some
1856 * stable_node was stale.
1861 ret
= memcmp_pages(kpage
, tree_page
);
1862 put_page(tree_page
);
1866 new = &parent
->rb_left
;
1868 new = &parent
->rb_right
;
1875 stable_node_dup
= alloc_stable_node();
1876 if (!stable_node_dup
)
1879 INIT_HLIST_HEAD(&stable_node_dup
->hlist
);
1880 stable_node_dup
->kpfn
= kpfn
;
1881 set_page_stable_node(kpage
, stable_node_dup
);
1882 stable_node_dup
->rmap_hlist_len
= 0;
1883 DO_NUMA(stable_node_dup
->nid
= nid
);
1885 rb_link_node(&stable_node_dup
->node
, parent
, new);
1886 rb_insert_color(&stable_node_dup
->node
, root
);
1888 if (!is_stable_node_chain(stable_node
)) {
1889 struct stable_node
*orig
= stable_node
;
1890 /* chain is missing so create it */
1891 stable_node
= alloc_stable_node_chain(orig
, root
);
1893 free_stable_node(stable_node_dup
);
1897 stable_node_chain_add_dup(stable_node_dup
, stable_node
);
1900 return stable_node_dup
;
1904 * unstable_tree_search_insert - search for identical page,
1905 * else insert rmap_item into the unstable tree.
1907 * This function searches for a page in the unstable tree identical to the
1908 * page currently being scanned; and if no identical page is found in the
1909 * tree, we insert rmap_item as a new object into the unstable tree.
1911 * This function returns pointer to rmap_item found to be identical
1912 * to the currently scanned page, NULL otherwise.
1914 * This function does both searching and inserting, because they share
1915 * the same walking algorithm in an rbtree.
1918 struct rmap_item
*unstable_tree_search_insert(struct rmap_item
*rmap_item
,
1920 struct page
**tree_pagep
)
1922 struct rb_node
**new;
1923 struct rb_root
*root
;
1924 struct rb_node
*parent
= NULL
;
1927 nid
= get_kpfn_nid(page_to_pfn(page
));
1928 root
= root_unstable_tree
+ nid
;
1929 new = &root
->rb_node
;
1932 struct rmap_item
*tree_rmap_item
;
1933 struct page
*tree_page
;
1937 tree_rmap_item
= rb_entry(*new, struct rmap_item
, node
);
1938 tree_page
= get_mergeable_page(tree_rmap_item
);
1943 * Don't substitute a ksm page for a forked page.
1945 if (page
== tree_page
) {
1946 put_page(tree_page
);
1950 ret
= memcmp_pages(page
, tree_page
);
1954 put_page(tree_page
);
1955 new = &parent
->rb_left
;
1956 } else if (ret
> 0) {
1957 put_page(tree_page
);
1958 new = &parent
->rb_right
;
1959 } else if (!ksm_merge_across_nodes
&&
1960 page_to_nid(tree_page
) != nid
) {
1962 * If tree_page has been migrated to another NUMA node,
1963 * it will be flushed out and put in the right unstable
1964 * tree next time: only merge with it when across_nodes.
1966 put_page(tree_page
);
1969 *tree_pagep
= tree_page
;
1970 return tree_rmap_item
;
1974 rmap_item
->address
|= UNSTABLE_FLAG
;
1975 rmap_item
->address
|= (ksm_scan
.seqnr
& SEQNR_MASK
);
1976 DO_NUMA(rmap_item
->nid
= nid
);
1977 rb_link_node(&rmap_item
->node
, parent
, new);
1978 rb_insert_color(&rmap_item
->node
, root
);
1980 ksm_pages_unshared
++;
1985 * stable_tree_append - add another rmap_item to the linked list of
1986 * rmap_items hanging off a given node of the stable tree, all sharing
1987 * the same ksm page.
1989 static void stable_tree_append(struct rmap_item
*rmap_item
,
1990 struct stable_node
*stable_node
,
1991 bool max_page_sharing_bypass
)
1994 * rmap won't find this mapping if we don't insert the
1995 * rmap_item in the right stable_node
1996 * duplicate. page_migration could break later if rmap breaks,
1997 * so we can as well crash here. We really need to check for
1998 * rmap_hlist_len == STABLE_NODE_CHAIN, but we can as well check
1999 * for other negative values as an underflow if detected here
2000 * for the first time (and not when decreasing rmap_hlist_len)
2001 * would be sign of memory corruption in the stable_node.
2003 BUG_ON(stable_node
->rmap_hlist_len
< 0);
2005 stable_node
->rmap_hlist_len
++;
2006 if (!max_page_sharing_bypass
)
2007 /* possibly non fatal but unexpected overflow, only warn */
2008 WARN_ON_ONCE(stable_node
->rmap_hlist_len
>
2009 ksm_max_page_sharing
);
2011 rmap_item
->head
= stable_node
;
2012 rmap_item
->address
|= STABLE_FLAG
;
2013 hlist_add_head(&rmap_item
->hlist
, &stable_node
->hlist
);
2015 if (rmap_item
->hlist
.next
)
2016 ksm_pages_sharing
++;
2022 * cmp_and_merge_page - first see if page can be merged into the stable tree;
2023 * if not, compare checksum to previous and if it's the same, see if page can
2024 * be inserted into the unstable tree, or merged with a page already there and
2025 * both transferred to the stable tree.
2027 * @page: the page that we are searching identical page to.
2028 * @rmap_item: the reverse mapping into the virtual address of this page
2030 static void cmp_and_merge_page(struct page
*page
, struct rmap_item
*rmap_item
)
2032 struct mm_struct
*mm
= rmap_item
->mm
;
2033 struct rmap_item
*tree_rmap_item
;
2034 struct page
*tree_page
= NULL
;
2035 struct stable_node
*stable_node
;
2037 unsigned int checksum
;
2039 bool max_page_sharing_bypass
= false;
2041 stable_node
= page_stable_node(page
);
2043 if (stable_node
->head
!= &migrate_nodes
&&
2044 get_kpfn_nid(READ_ONCE(stable_node
->kpfn
)) !=
2045 NUMA(stable_node
->nid
)) {
2046 stable_node_dup_del(stable_node
);
2047 stable_node
->head
= &migrate_nodes
;
2048 list_add(&stable_node
->list
, stable_node
->head
);
2050 if (stable_node
->head
!= &migrate_nodes
&&
2051 rmap_item
->head
== stable_node
)
2054 * If it's a KSM fork, allow it to go over the sharing limit
2057 if (!is_page_sharing_candidate(stable_node
))
2058 max_page_sharing_bypass
= true;
2061 /* We first start with searching the page inside the stable tree */
2062 kpage
= stable_tree_search(page
);
2063 if (kpage
== page
&& rmap_item
->head
== stable_node
) {
2068 remove_rmap_item_from_tree(rmap_item
);
2071 if (PTR_ERR(kpage
) == -EBUSY
)
2074 err
= try_to_merge_with_ksm_page(rmap_item
, page
, kpage
);
2077 * The page was successfully merged:
2078 * add its rmap_item to the stable tree.
2081 stable_tree_append(rmap_item
, page_stable_node(kpage
),
2082 max_page_sharing_bypass
);
2090 * If the hash value of the page has changed from the last time
2091 * we calculated it, this page is changing frequently: therefore we
2092 * don't want to insert it in the unstable tree, and we don't want
2093 * to waste our time searching for something identical to it there.
2095 checksum
= calc_checksum(page
);
2096 if (rmap_item
->oldchecksum
!= checksum
) {
2097 rmap_item
->oldchecksum
= checksum
;
2102 * Same checksum as an empty page. We attempt to merge it with the
2103 * appropriate zero page if the user enabled this via sysfs.
2105 if (ksm_use_zero_pages
&& (checksum
== zero_checksum
)) {
2106 struct vm_area_struct
*vma
;
2109 vma
= find_mergeable_vma(mm
, rmap_item
->address
);
2111 err
= try_to_merge_one_page(vma
, page
,
2112 ZERO_PAGE(rmap_item
->address
));
2115 * If the vma is out of date, we do not need to
2120 mmap_read_unlock(mm
);
2122 * In case of failure, the page was not really empty, so we
2123 * need to continue. Otherwise we're done.
2129 unstable_tree_search_insert(rmap_item
, page
, &tree_page
);
2130 if (tree_rmap_item
) {
2133 kpage
= try_to_merge_two_pages(rmap_item
, page
,
2134 tree_rmap_item
, tree_page
);
2136 * If both pages we tried to merge belong to the same compound
2137 * page, then we actually ended up increasing the reference
2138 * count of the same compound page twice, and split_huge_page
2140 * Here we set a flag if that happened, and we use it later to
2141 * try split_huge_page again. Since we call put_page right
2142 * afterwards, the reference count will be correct and
2143 * split_huge_page should succeed.
2145 split
= PageTransCompound(page
)
2146 && compound_head(page
) == compound_head(tree_page
);
2147 put_page(tree_page
);
2150 * The pages were successfully merged: insert new
2151 * node in the stable tree and add both rmap_items.
2154 stable_node
= stable_tree_insert(kpage
);
2156 stable_tree_append(tree_rmap_item
, stable_node
,
2158 stable_tree_append(rmap_item
, stable_node
,
2164 * If we fail to insert the page into the stable tree,
2165 * we will have 2 virtual addresses that are pointing
2166 * to a ksm page left outside the stable tree,
2167 * in which case we need to break_cow on both.
2170 break_cow(tree_rmap_item
);
2171 break_cow(rmap_item
);
2175 * We are here if we tried to merge two pages and
2176 * failed because they both belonged to the same
2177 * compound page. We will split the page now, but no
2178 * merging will take place.
2179 * We do not want to add the cost of a full lock; if
2180 * the page is locked, it is better to skip it and
2181 * perhaps try again later.
2183 if (!trylock_page(page
))
2185 split_huge_page(page
);
2191 static struct rmap_item
*get_next_rmap_item(struct mm_slot
*mm_slot
,
2192 struct rmap_item
**rmap_list
,
2195 struct rmap_item
*rmap_item
;
2197 while (*rmap_list
) {
2198 rmap_item
= *rmap_list
;
2199 if ((rmap_item
->address
& PAGE_MASK
) == addr
)
2201 if (rmap_item
->address
> addr
)
2203 *rmap_list
= rmap_item
->rmap_list
;
2204 remove_rmap_item_from_tree(rmap_item
);
2205 free_rmap_item(rmap_item
);
2208 rmap_item
= alloc_rmap_item();
2210 /* It has already been zeroed */
2211 rmap_item
->mm
= mm_slot
->mm
;
2212 rmap_item
->address
= addr
;
2213 rmap_item
->rmap_list
= *rmap_list
;
2214 *rmap_list
= rmap_item
;
2219 static struct rmap_item
*scan_get_next_rmap_item(struct page
**page
)
2221 struct mm_struct
*mm
;
2222 struct mm_slot
*slot
;
2223 struct vm_area_struct
*vma
;
2224 struct rmap_item
*rmap_item
;
2227 if (list_empty(&ksm_mm_head
.mm_list
))
2230 slot
= ksm_scan
.mm_slot
;
2231 if (slot
== &ksm_mm_head
) {
2233 * A number of pages can hang around indefinitely on per-cpu
2234 * pagevecs, raised page count preventing write_protect_page
2235 * from merging them. Though it doesn't really matter much,
2236 * it is puzzling to see some stuck in pages_volatile until
2237 * other activity jostles them out, and they also prevented
2238 * LTP's KSM test from succeeding deterministically; so drain
2239 * them here (here rather than on entry to ksm_do_scan(),
2240 * so we don't IPI too often when pages_to_scan is set low).
2242 lru_add_drain_all();
2245 * Whereas stale stable_nodes on the stable_tree itself
2246 * get pruned in the regular course of stable_tree_search(),
2247 * those moved out to the migrate_nodes list can accumulate:
2248 * so prune them once before each full scan.
2250 if (!ksm_merge_across_nodes
) {
2251 struct stable_node
*stable_node
, *next
;
2254 list_for_each_entry_safe(stable_node
, next
,
2255 &migrate_nodes
, list
) {
2256 page
= get_ksm_page(stable_node
,
2257 GET_KSM_PAGE_NOLOCK
);
2264 for (nid
= 0; nid
< ksm_nr_node_ids
; nid
++)
2265 root_unstable_tree
[nid
] = RB_ROOT
;
2267 spin_lock(&ksm_mmlist_lock
);
2268 slot
= list_entry(slot
->mm_list
.next
, struct mm_slot
, mm_list
);
2269 ksm_scan
.mm_slot
= slot
;
2270 spin_unlock(&ksm_mmlist_lock
);
2272 * Although we tested list_empty() above, a racing __ksm_exit
2273 * of the last mm on the list may have removed it since then.
2275 if (slot
== &ksm_mm_head
)
2278 ksm_scan
.address
= 0;
2279 ksm_scan
.rmap_list
= &slot
->rmap_list
;
2284 if (ksm_test_exit(mm
))
2287 vma
= find_vma(mm
, ksm_scan
.address
);
2289 for (; vma
; vma
= vma
->vm_next
) {
2290 if (!(vma
->vm_flags
& VM_MERGEABLE
))
2292 if (ksm_scan
.address
< vma
->vm_start
)
2293 ksm_scan
.address
= vma
->vm_start
;
2295 ksm_scan
.address
= vma
->vm_end
;
2297 while (ksm_scan
.address
< vma
->vm_end
) {
2298 if (ksm_test_exit(mm
))
2300 *page
= follow_page(vma
, ksm_scan
.address
, FOLL_GET
);
2301 if (IS_ERR_OR_NULL(*page
)) {
2302 ksm_scan
.address
+= PAGE_SIZE
;
2306 if (PageAnon(*page
)) {
2307 flush_anon_page(vma
, *page
, ksm_scan
.address
);
2308 flush_dcache_page(*page
);
2309 rmap_item
= get_next_rmap_item(slot
,
2310 ksm_scan
.rmap_list
, ksm_scan
.address
);
2312 ksm_scan
.rmap_list
=
2313 &rmap_item
->rmap_list
;
2314 ksm_scan
.address
+= PAGE_SIZE
;
2317 mmap_read_unlock(mm
);
2321 ksm_scan
.address
+= PAGE_SIZE
;
2326 if (ksm_test_exit(mm
)) {
2327 ksm_scan
.address
= 0;
2328 ksm_scan
.rmap_list
= &slot
->rmap_list
;
2331 * Nuke all the rmap_items that are above this current rmap:
2332 * because there were no VM_MERGEABLE vmas with such addresses.
2334 remove_trailing_rmap_items(ksm_scan
.rmap_list
);
2336 spin_lock(&ksm_mmlist_lock
);
2337 ksm_scan
.mm_slot
= list_entry(slot
->mm_list
.next
,
2338 struct mm_slot
, mm_list
);
2339 if (ksm_scan
.address
== 0) {
2341 * We've completed a full scan of all vmas, holding mmap_lock
2342 * throughout, and found no VM_MERGEABLE: so do the same as
2343 * __ksm_exit does to remove this mm from all our lists now.
2344 * This applies either when cleaning up after __ksm_exit
2345 * (but beware: we can reach here even before __ksm_exit),
2346 * or when all VM_MERGEABLE areas have been unmapped (and
2347 * mmap_lock then protects against race with MADV_MERGEABLE).
2349 hash_del(&slot
->link
);
2350 list_del(&slot
->mm_list
);
2351 spin_unlock(&ksm_mmlist_lock
);
2354 clear_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
2355 mmap_read_unlock(mm
);
2358 mmap_read_unlock(mm
);
2360 * mmap_read_unlock(mm) first because after
2361 * spin_unlock(&ksm_mmlist_lock) run, the "mm" may
2362 * already have been freed under us by __ksm_exit()
2363 * because the "mm_slot" is still hashed and
2364 * ksm_scan.mm_slot doesn't point to it anymore.
2366 spin_unlock(&ksm_mmlist_lock
);
2369 /* Repeat until we've completed scanning the whole list */
2370 slot
= ksm_scan
.mm_slot
;
2371 if (slot
!= &ksm_mm_head
)
2379 * ksm_do_scan - the ksm scanner main worker function.
2380 * @scan_npages: number of pages we want to scan before we return.
2382 static void ksm_do_scan(unsigned int scan_npages
)
2384 struct rmap_item
*rmap_item
;
2387 while (scan_npages
-- && likely(!freezing(current
))) {
2389 rmap_item
= scan_get_next_rmap_item(&page
);
2392 cmp_and_merge_page(page
, rmap_item
);
2397 static int ksmd_should_run(void)
2399 return (ksm_run
& KSM_RUN_MERGE
) && !list_empty(&ksm_mm_head
.mm_list
);
2402 static int ksm_scan_thread(void *nothing
)
2404 unsigned int sleep_ms
;
2407 set_user_nice(current
, 5);
2409 while (!kthread_should_stop()) {
2410 mutex_lock(&ksm_thread_mutex
);
2411 wait_while_offlining();
2412 if (ksmd_should_run())
2413 ksm_do_scan(ksm_thread_pages_to_scan
);
2414 mutex_unlock(&ksm_thread_mutex
);
2418 if (ksmd_should_run()) {
2419 sleep_ms
= READ_ONCE(ksm_thread_sleep_millisecs
);
2420 wait_event_interruptible_timeout(ksm_iter_wait
,
2421 sleep_ms
!= READ_ONCE(ksm_thread_sleep_millisecs
),
2422 msecs_to_jiffies(sleep_ms
));
2424 wait_event_freezable(ksm_thread_wait
,
2425 ksmd_should_run() || kthread_should_stop());
2431 int ksm_madvise(struct vm_area_struct
*vma
, unsigned long start
,
2432 unsigned long end
, int advice
, unsigned long *vm_flags
)
2434 struct mm_struct
*mm
= vma
->vm_mm
;
2438 case MADV_MERGEABLE
:
2440 * Be somewhat over-protective for now!
2442 if (*vm_flags
& (VM_MERGEABLE
| VM_SHARED
| VM_MAYSHARE
|
2443 VM_PFNMAP
| VM_IO
| VM_DONTEXPAND
|
2444 VM_HUGETLB
| VM_MIXEDMAP
))
2445 return 0; /* just ignore the advice */
2447 if (vma_is_dax(vma
))
2451 if (*vm_flags
& VM_SAO
)
2455 if (*vm_flags
& VM_SPARC_ADI
)
2459 if (!test_bit(MMF_VM_MERGEABLE
, &mm
->flags
)) {
2460 err
= __ksm_enter(mm
);
2465 *vm_flags
|= VM_MERGEABLE
;
2468 case MADV_UNMERGEABLE
:
2469 if (!(*vm_flags
& VM_MERGEABLE
))
2470 return 0; /* just ignore the advice */
2472 if (vma
->anon_vma
) {
2473 err
= unmerge_ksm_pages(vma
, start
, end
);
2478 *vm_flags
&= ~VM_MERGEABLE
;
2484 EXPORT_SYMBOL_GPL(ksm_madvise
);
2486 int __ksm_enter(struct mm_struct
*mm
)
2488 struct mm_slot
*mm_slot
;
2491 mm_slot
= alloc_mm_slot();
2495 /* Check ksm_run too? Would need tighter locking */
2496 needs_wakeup
= list_empty(&ksm_mm_head
.mm_list
);
2498 spin_lock(&ksm_mmlist_lock
);
2499 insert_to_mm_slots_hash(mm
, mm_slot
);
2501 * When KSM_RUN_MERGE (or KSM_RUN_STOP),
2502 * insert just behind the scanning cursor, to let the area settle
2503 * down a little; when fork is followed by immediate exec, we don't
2504 * want ksmd to waste time setting up and tearing down an rmap_list.
2506 * But when KSM_RUN_UNMERGE, it's important to insert ahead of its
2507 * scanning cursor, otherwise KSM pages in newly forked mms will be
2508 * missed: then we might as well insert at the end of the list.
2510 if (ksm_run
& KSM_RUN_UNMERGE
)
2511 list_add_tail(&mm_slot
->mm_list
, &ksm_mm_head
.mm_list
);
2513 list_add_tail(&mm_slot
->mm_list
, &ksm_scan
.mm_slot
->mm_list
);
2514 spin_unlock(&ksm_mmlist_lock
);
2516 set_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
2520 wake_up_interruptible(&ksm_thread_wait
);
2525 void __ksm_exit(struct mm_struct
*mm
)
2527 struct mm_slot
*mm_slot
;
2528 int easy_to_free
= 0;
2531 * This process is exiting: if it's straightforward (as is the
2532 * case when ksmd was never running), free mm_slot immediately.
2533 * But if it's at the cursor or has rmap_items linked to it, use
2534 * mmap_lock to synchronize with any break_cows before pagetables
2535 * are freed, and leave the mm_slot on the list for ksmd to free.
2536 * Beware: ksm may already have noticed it exiting and freed the slot.
2539 spin_lock(&ksm_mmlist_lock
);
2540 mm_slot
= get_mm_slot(mm
);
2541 if (mm_slot
&& ksm_scan
.mm_slot
!= mm_slot
) {
2542 if (!mm_slot
->rmap_list
) {
2543 hash_del(&mm_slot
->link
);
2544 list_del(&mm_slot
->mm_list
);
2547 list_move(&mm_slot
->mm_list
,
2548 &ksm_scan
.mm_slot
->mm_list
);
2551 spin_unlock(&ksm_mmlist_lock
);
2554 free_mm_slot(mm_slot
);
2555 clear_bit(MMF_VM_MERGEABLE
, &mm
->flags
);
2557 } else if (mm_slot
) {
2558 mmap_write_lock(mm
);
2559 mmap_write_unlock(mm
);
2563 struct page
*ksm_might_need_to_copy(struct page
*page
,
2564 struct vm_area_struct
*vma
, unsigned long address
)
2566 struct anon_vma
*anon_vma
= page_anon_vma(page
);
2567 struct page
*new_page
;
2569 if (PageKsm(page
)) {
2570 if (page_stable_node(page
) &&
2571 !(ksm_run
& KSM_RUN_UNMERGE
))
2572 return page
; /* no need to copy it */
2573 } else if (!anon_vma
) {
2574 return page
; /* no need to copy it */
2575 } else if (anon_vma
->root
== vma
->anon_vma
->root
&&
2576 page
->index
== linear_page_index(vma
, address
)) {
2577 return page
; /* still no need to copy it */
2579 if (!PageUptodate(page
))
2580 return page
; /* let do_swap_page report the error */
2582 new_page
= alloc_page_vma(GFP_HIGHUSER_MOVABLE
, vma
, address
);
2583 if (new_page
&& mem_cgroup_charge(new_page
, vma
->vm_mm
, GFP_KERNEL
)) {
2588 copy_user_highpage(new_page
, page
, address
, vma
);
2590 SetPageDirty(new_page
);
2591 __SetPageUptodate(new_page
);
2592 __SetPageLocked(new_page
);
2598 void rmap_walk_ksm(struct page
*page
, struct rmap_walk_control
*rwc
)
2600 struct stable_node
*stable_node
;
2601 struct rmap_item
*rmap_item
;
2602 int search_new_forks
= 0;
2604 VM_BUG_ON_PAGE(!PageKsm(page
), page
);
2607 * Rely on the page lock to protect against concurrent modifications
2608 * to that page's node of the stable tree.
2610 VM_BUG_ON_PAGE(!PageLocked(page
), page
);
2612 stable_node
= page_stable_node(page
);
2616 hlist_for_each_entry(rmap_item
, &stable_node
->hlist
, hlist
) {
2617 struct anon_vma
*anon_vma
= rmap_item
->anon_vma
;
2618 struct anon_vma_chain
*vmac
;
2619 struct vm_area_struct
*vma
;
2622 anon_vma_lock_read(anon_vma
);
2623 anon_vma_interval_tree_foreach(vmac
, &anon_vma
->rb_root
,
2630 /* Ignore the stable/unstable/sqnr flags */
2631 addr
= rmap_item
->address
& PAGE_MASK
;
2633 if (addr
< vma
->vm_start
|| addr
>= vma
->vm_end
)
2636 * Initially we examine only the vma which covers this
2637 * rmap_item; but later, if there is still work to do,
2638 * we examine covering vmas in other mms: in case they
2639 * were forked from the original since ksmd passed.
2641 if ((rmap_item
->mm
== vma
->vm_mm
) == search_new_forks
)
2644 if (rwc
->invalid_vma
&& rwc
->invalid_vma(vma
, rwc
->arg
))
2647 if (!rwc
->rmap_one(page
, vma
, addr
, rwc
->arg
)) {
2648 anon_vma_unlock_read(anon_vma
);
2651 if (rwc
->done
&& rwc
->done(page
)) {
2652 anon_vma_unlock_read(anon_vma
);
2656 anon_vma_unlock_read(anon_vma
);
2658 if (!search_new_forks
++)
2662 #ifdef CONFIG_MIGRATION
2663 void ksm_migrate_page(struct page
*newpage
, struct page
*oldpage
)
2665 struct stable_node
*stable_node
;
2667 VM_BUG_ON_PAGE(!PageLocked(oldpage
), oldpage
);
2668 VM_BUG_ON_PAGE(!PageLocked(newpage
), newpage
);
2669 VM_BUG_ON_PAGE(newpage
->mapping
!= oldpage
->mapping
, newpage
);
2671 stable_node
= page_stable_node(newpage
);
2673 VM_BUG_ON_PAGE(stable_node
->kpfn
!= page_to_pfn(oldpage
), oldpage
);
2674 stable_node
->kpfn
= page_to_pfn(newpage
);
2676 * newpage->mapping was set in advance; now we need smp_wmb()
2677 * to make sure that the new stable_node->kpfn is visible
2678 * to get_ksm_page() before it can see that oldpage->mapping
2679 * has gone stale (or that PageSwapCache has been cleared).
2682 set_page_stable_node(oldpage
, NULL
);
2685 #endif /* CONFIG_MIGRATION */
2687 #ifdef CONFIG_MEMORY_HOTREMOVE
2688 static void wait_while_offlining(void)
2690 while (ksm_run
& KSM_RUN_OFFLINE
) {
2691 mutex_unlock(&ksm_thread_mutex
);
2692 wait_on_bit(&ksm_run
, ilog2(KSM_RUN_OFFLINE
),
2693 TASK_UNINTERRUPTIBLE
);
2694 mutex_lock(&ksm_thread_mutex
);
2698 static bool stable_node_dup_remove_range(struct stable_node
*stable_node
,
2699 unsigned long start_pfn
,
2700 unsigned long end_pfn
)
2702 if (stable_node
->kpfn
>= start_pfn
&&
2703 stable_node
->kpfn
< end_pfn
) {
2705 * Don't get_ksm_page, page has already gone:
2706 * which is why we keep kpfn instead of page*
2708 remove_node_from_stable_tree(stable_node
);
2714 static bool stable_node_chain_remove_range(struct stable_node
*stable_node
,
2715 unsigned long start_pfn
,
2716 unsigned long end_pfn
,
2717 struct rb_root
*root
)
2719 struct stable_node
*dup
;
2720 struct hlist_node
*hlist_safe
;
2722 if (!is_stable_node_chain(stable_node
)) {
2723 VM_BUG_ON(is_stable_node_dup(stable_node
));
2724 return stable_node_dup_remove_range(stable_node
, start_pfn
,
2728 hlist_for_each_entry_safe(dup
, hlist_safe
,
2729 &stable_node
->hlist
, hlist_dup
) {
2730 VM_BUG_ON(!is_stable_node_dup(dup
));
2731 stable_node_dup_remove_range(dup
, start_pfn
, end_pfn
);
2733 if (hlist_empty(&stable_node
->hlist
)) {
2734 free_stable_node_chain(stable_node
, root
);
2735 return true; /* notify caller that tree was rebalanced */
2740 static void ksm_check_stable_tree(unsigned long start_pfn
,
2741 unsigned long end_pfn
)
2743 struct stable_node
*stable_node
, *next
;
2744 struct rb_node
*node
;
2747 for (nid
= 0; nid
< ksm_nr_node_ids
; nid
++) {
2748 node
= rb_first(root_stable_tree
+ nid
);
2750 stable_node
= rb_entry(node
, struct stable_node
, node
);
2751 if (stable_node_chain_remove_range(stable_node
,
2755 node
= rb_first(root_stable_tree
+ nid
);
2757 node
= rb_next(node
);
2761 list_for_each_entry_safe(stable_node
, next
, &migrate_nodes
, list
) {
2762 if (stable_node
->kpfn
>= start_pfn
&&
2763 stable_node
->kpfn
< end_pfn
)
2764 remove_node_from_stable_tree(stable_node
);
2769 static int ksm_memory_callback(struct notifier_block
*self
,
2770 unsigned long action
, void *arg
)
2772 struct memory_notify
*mn
= arg
;
2775 case MEM_GOING_OFFLINE
:
2777 * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
2778 * and remove_all_stable_nodes() while memory is going offline:
2779 * it is unsafe for them to touch the stable tree at this time.
2780 * But unmerge_ksm_pages(), rmap lookups and other entry points
2781 * which do not need the ksm_thread_mutex are all safe.
2783 mutex_lock(&ksm_thread_mutex
);
2784 ksm_run
|= KSM_RUN_OFFLINE
;
2785 mutex_unlock(&ksm_thread_mutex
);
2790 * Most of the work is done by page migration; but there might
2791 * be a few stable_nodes left over, still pointing to struct
2792 * pages which have been offlined: prune those from the tree,
2793 * otherwise get_ksm_page() might later try to access a
2794 * non-existent struct page.
2796 ksm_check_stable_tree(mn
->start_pfn
,
2797 mn
->start_pfn
+ mn
->nr_pages
);
2799 case MEM_CANCEL_OFFLINE
:
2800 mutex_lock(&ksm_thread_mutex
);
2801 ksm_run
&= ~KSM_RUN_OFFLINE
;
2802 mutex_unlock(&ksm_thread_mutex
);
2804 smp_mb(); /* wake_up_bit advises this */
2805 wake_up_bit(&ksm_run
, ilog2(KSM_RUN_OFFLINE
));
2811 static void wait_while_offlining(void)
2814 #endif /* CONFIG_MEMORY_HOTREMOVE */
2818 * This all compiles without CONFIG_SYSFS, but is a waste of space.
2821 #define KSM_ATTR_RO(_name) \
2822 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
2823 #define KSM_ATTR(_name) \
2824 static struct kobj_attribute _name##_attr = \
2825 __ATTR(_name, 0644, _name##_show, _name##_store)
2827 static ssize_t
sleep_millisecs_show(struct kobject
*kobj
,
2828 struct kobj_attribute
*attr
, char *buf
)
2830 return sysfs_emit(buf
, "%u\n", ksm_thread_sleep_millisecs
);
2833 static ssize_t
sleep_millisecs_store(struct kobject
*kobj
,
2834 struct kobj_attribute
*attr
,
2835 const char *buf
, size_t count
)
2840 err
= kstrtouint(buf
, 10, &msecs
);
2844 ksm_thread_sleep_millisecs
= msecs
;
2845 wake_up_interruptible(&ksm_iter_wait
);
2849 KSM_ATTR(sleep_millisecs
);
2851 static ssize_t
pages_to_scan_show(struct kobject
*kobj
,
2852 struct kobj_attribute
*attr
, char *buf
)
2854 return sysfs_emit(buf
, "%u\n", ksm_thread_pages_to_scan
);
2857 static ssize_t
pages_to_scan_store(struct kobject
*kobj
,
2858 struct kobj_attribute
*attr
,
2859 const char *buf
, size_t count
)
2861 unsigned int nr_pages
;
2864 err
= kstrtouint(buf
, 10, &nr_pages
);
2868 ksm_thread_pages_to_scan
= nr_pages
;
2872 KSM_ATTR(pages_to_scan
);
2874 static ssize_t
run_show(struct kobject
*kobj
, struct kobj_attribute
*attr
,
2877 return sysfs_emit(buf
, "%lu\n", ksm_run
);
2880 static ssize_t
run_store(struct kobject
*kobj
, struct kobj_attribute
*attr
,
2881 const char *buf
, size_t count
)
2886 err
= kstrtouint(buf
, 10, &flags
);
2889 if (flags
> KSM_RUN_UNMERGE
)
2893 * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
2894 * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
2895 * breaking COW to free the pages_shared (but leaves mm_slots
2896 * on the list for when ksmd may be set running again).
2899 mutex_lock(&ksm_thread_mutex
);
2900 wait_while_offlining();
2901 if (ksm_run
!= flags
) {
2903 if (flags
& KSM_RUN_UNMERGE
) {
2904 set_current_oom_origin();
2905 err
= unmerge_and_remove_all_rmap_items();
2906 clear_current_oom_origin();
2908 ksm_run
= KSM_RUN_STOP
;
2913 mutex_unlock(&ksm_thread_mutex
);
2915 if (flags
& KSM_RUN_MERGE
)
2916 wake_up_interruptible(&ksm_thread_wait
);
2923 static ssize_t
merge_across_nodes_show(struct kobject
*kobj
,
2924 struct kobj_attribute
*attr
, char *buf
)
2926 return sysfs_emit(buf
, "%u\n", ksm_merge_across_nodes
);
2929 static ssize_t
merge_across_nodes_store(struct kobject
*kobj
,
2930 struct kobj_attribute
*attr
,
2931 const char *buf
, size_t count
)
2936 err
= kstrtoul(buf
, 10, &knob
);
2942 mutex_lock(&ksm_thread_mutex
);
2943 wait_while_offlining();
2944 if (ksm_merge_across_nodes
!= knob
) {
2945 if (ksm_pages_shared
|| remove_all_stable_nodes())
2947 else if (root_stable_tree
== one_stable_tree
) {
2948 struct rb_root
*buf
;
2950 * This is the first time that we switch away from the
2951 * default of merging across nodes: must now allocate
2952 * a buffer to hold as many roots as may be needed.
2953 * Allocate stable and unstable together:
2954 * MAXSMP NODES_SHIFT 10 will use 16kB.
2956 buf
= kcalloc(nr_node_ids
+ nr_node_ids
, sizeof(*buf
),
2958 /* Let us assume that RB_ROOT is NULL is zero */
2962 root_stable_tree
= buf
;
2963 root_unstable_tree
= buf
+ nr_node_ids
;
2964 /* Stable tree is empty but not the unstable */
2965 root_unstable_tree
[0] = one_unstable_tree
[0];
2969 ksm_merge_across_nodes
= knob
;
2970 ksm_nr_node_ids
= knob
? 1 : nr_node_ids
;
2973 mutex_unlock(&ksm_thread_mutex
);
2975 return err
? err
: count
;
2977 KSM_ATTR(merge_across_nodes
);
2980 static ssize_t
use_zero_pages_show(struct kobject
*kobj
,
2981 struct kobj_attribute
*attr
, char *buf
)
2983 return sysfs_emit(buf
, "%u\n", ksm_use_zero_pages
);
2985 static ssize_t
use_zero_pages_store(struct kobject
*kobj
,
2986 struct kobj_attribute
*attr
,
2987 const char *buf
, size_t count
)
2992 err
= kstrtobool(buf
, &value
);
2996 ksm_use_zero_pages
= value
;
3000 KSM_ATTR(use_zero_pages
);
3002 static ssize_t
max_page_sharing_show(struct kobject
*kobj
,
3003 struct kobj_attribute
*attr
, char *buf
)
3005 return sysfs_emit(buf
, "%u\n", ksm_max_page_sharing
);
3008 static ssize_t
max_page_sharing_store(struct kobject
*kobj
,
3009 struct kobj_attribute
*attr
,
3010 const char *buf
, size_t count
)
3015 err
= kstrtoint(buf
, 10, &knob
);
3019 * When a KSM page is created it is shared by 2 mappings. This
3020 * being a signed comparison, it implicitly verifies it's not
3026 if (READ_ONCE(ksm_max_page_sharing
) == knob
)
3029 mutex_lock(&ksm_thread_mutex
);
3030 wait_while_offlining();
3031 if (ksm_max_page_sharing
!= knob
) {
3032 if (ksm_pages_shared
|| remove_all_stable_nodes())
3035 ksm_max_page_sharing
= knob
;
3037 mutex_unlock(&ksm_thread_mutex
);
3039 return err
? err
: count
;
3041 KSM_ATTR(max_page_sharing
);
3043 static ssize_t
pages_shared_show(struct kobject
*kobj
,
3044 struct kobj_attribute
*attr
, char *buf
)
3046 return sysfs_emit(buf
, "%lu\n", ksm_pages_shared
);
3048 KSM_ATTR_RO(pages_shared
);
3050 static ssize_t
pages_sharing_show(struct kobject
*kobj
,
3051 struct kobj_attribute
*attr
, char *buf
)
3053 return sysfs_emit(buf
, "%lu\n", ksm_pages_sharing
);
3055 KSM_ATTR_RO(pages_sharing
);
3057 static ssize_t
pages_unshared_show(struct kobject
*kobj
,
3058 struct kobj_attribute
*attr
, char *buf
)
3060 return sysfs_emit(buf
, "%lu\n", ksm_pages_unshared
);
3062 KSM_ATTR_RO(pages_unshared
);
3064 static ssize_t
pages_volatile_show(struct kobject
*kobj
,
3065 struct kobj_attribute
*attr
, char *buf
)
3067 long ksm_pages_volatile
;
3069 ksm_pages_volatile
= ksm_rmap_items
- ksm_pages_shared
3070 - ksm_pages_sharing
- ksm_pages_unshared
;
3072 * It was not worth any locking to calculate that statistic,
3073 * but it might therefore sometimes be negative: conceal that.
3075 if (ksm_pages_volatile
< 0)
3076 ksm_pages_volatile
= 0;
3077 return sysfs_emit(buf
, "%ld\n", ksm_pages_volatile
);
3079 KSM_ATTR_RO(pages_volatile
);
3081 static ssize_t
stable_node_dups_show(struct kobject
*kobj
,
3082 struct kobj_attribute
*attr
, char *buf
)
3084 return sysfs_emit(buf
, "%lu\n", ksm_stable_node_dups
);
3086 KSM_ATTR_RO(stable_node_dups
);
3088 static ssize_t
stable_node_chains_show(struct kobject
*kobj
,
3089 struct kobj_attribute
*attr
, char *buf
)
3091 return sysfs_emit(buf
, "%lu\n", ksm_stable_node_chains
);
3093 KSM_ATTR_RO(stable_node_chains
);
3096 stable_node_chains_prune_millisecs_show(struct kobject
*kobj
,
3097 struct kobj_attribute
*attr
,
3100 return sysfs_emit(buf
, "%u\n", ksm_stable_node_chains_prune_millisecs
);
3104 stable_node_chains_prune_millisecs_store(struct kobject
*kobj
,
3105 struct kobj_attribute
*attr
,
3106 const char *buf
, size_t count
)
3108 unsigned long msecs
;
3111 err
= kstrtoul(buf
, 10, &msecs
);
3112 if (err
|| msecs
> UINT_MAX
)
3115 ksm_stable_node_chains_prune_millisecs
= msecs
;
3119 KSM_ATTR(stable_node_chains_prune_millisecs
);
3121 static ssize_t
full_scans_show(struct kobject
*kobj
,
3122 struct kobj_attribute
*attr
, char *buf
)
3124 return sysfs_emit(buf
, "%lu\n", ksm_scan
.seqnr
);
3126 KSM_ATTR_RO(full_scans
);
3128 static struct attribute
*ksm_attrs
[] = {
3129 &sleep_millisecs_attr
.attr
,
3130 &pages_to_scan_attr
.attr
,
3132 &pages_shared_attr
.attr
,
3133 &pages_sharing_attr
.attr
,
3134 &pages_unshared_attr
.attr
,
3135 &pages_volatile_attr
.attr
,
3136 &full_scans_attr
.attr
,
3138 &merge_across_nodes_attr
.attr
,
3140 &max_page_sharing_attr
.attr
,
3141 &stable_node_chains_attr
.attr
,
3142 &stable_node_dups_attr
.attr
,
3143 &stable_node_chains_prune_millisecs_attr
.attr
,
3144 &use_zero_pages_attr
.attr
,
3148 static const struct attribute_group ksm_attr_group
= {
3152 #endif /* CONFIG_SYSFS */
3154 static int __init
ksm_init(void)
3156 struct task_struct
*ksm_thread
;
3159 /* The correct value depends on page size and endianness */
3160 zero_checksum
= calc_checksum(ZERO_PAGE(0));
3161 /* Default to false for backwards compatibility */
3162 ksm_use_zero_pages
= false;
3164 err
= ksm_slab_init();
3168 ksm_thread
= kthread_run(ksm_scan_thread
, NULL
, "ksmd");
3169 if (IS_ERR(ksm_thread
)) {
3170 pr_err("ksm: creating kthread failed\n");
3171 err
= PTR_ERR(ksm_thread
);
3176 err
= sysfs_create_group(mm_kobj
, &ksm_attr_group
);
3178 pr_err("ksm: register sysfs failed\n");
3179 kthread_stop(ksm_thread
);
3183 ksm_run
= KSM_RUN_MERGE
; /* no way for user to start it */
3185 #endif /* CONFIG_SYSFS */
3187 #ifdef CONFIG_MEMORY_HOTREMOVE
3188 /* There is no significance to this priority 100 */
3189 hotplug_memory_notifier(ksm_memory_callback
, 100);
3198 subsys_initcall(ksm_init
);