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1 | // SPDX-License-Identifier: GPL-2.0-only | |
2 | /* | |
3 | * Memory merging support. | |
4 | * | |
5 | * This code enables dynamic sharing of identical pages found in different | |
6 | * memory areas, even if they are not shared by fork() | |
7 | * | |
8 | * Copyright (C) 2008-2009 Red Hat, Inc. | |
9 | * Authors: | |
10 | * Izik Eidus | |
11 | * Andrea Arcangeli | |
12 | * Chris Wright | |
13 | * Hugh Dickins | |
14 | */ | |
15 | ||
16 | #include <linux/errno.h> | |
17 | #include <linux/mm.h> | |
18 | #include <linux/fs.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> | |
41 | ||
42 | #include <asm/tlbflush.h> | |
43 | #include "internal.h" | |
44 | ||
45 | #ifdef CONFIG_NUMA | |
46 | #define NUMA(x) (x) | |
47 | #define DO_NUMA(x) do { (x); } while (0) | |
48 | #else | |
49 | #define NUMA(x) (0) | |
50 | #define DO_NUMA(x) do { } while (0) | |
51 | #endif | |
52 | ||
53 | /** | |
54 | * DOC: Overview | |
55 | * | |
56 | * A few notes about the KSM scanning process, | |
57 | * to make it easier to understand the data structures below: | |
58 | * | |
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. | |
61 | * | |
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. | |
65 | * | |
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. | |
70 | * | |
71 | * The stable tree node includes information required for reverse | |
72 | * mapping from a KSM page to virtual addresses that map this page. | |
73 | * | |
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: | |
76 | * | |
77 | * * the regular nodes that keep the reverse mapping structures in a | |
78 | * linked list | |
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 | |
82 | * | |
83 | * Internally, the regular nodes, "dups" and "chains" are represented | |
84 | * using the same struct stable_node structure. | |
85 | * | |
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. | |
92 | * | |
93 | * KSM solves this problem by several techniques: | |
94 | * | |
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.) | |
108 | * | |
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. | |
111 | */ | |
112 | ||
113 | /** | |
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 | |
119 | */ | |
120 | struct mm_slot { | |
121 | struct hlist_node link; | |
122 | struct list_head mm_list; | |
123 | struct rmap_item *rmap_list; | |
124 | struct mm_struct *mm; | |
125 | }; | |
126 | ||
127 | /** | |
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) | |
133 | * | |
134 | * There is only the one ksm_scan instance of this cursor structure. | |
135 | */ | |
136 | struct ksm_scan { | |
137 | struct mm_slot *mm_slot; | |
138 | unsigned long address; | |
139 | struct rmap_item **rmap_list; | |
140 | unsigned long seqnr; | |
141 | }; | |
142 | ||
143 | /** | |
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) | |
154 | */ | |
155 | struct stable_node { | |
156 | union { | |
157 | struct rb_node node; /* when node of stable tree */ | |
158 | struct { /* when listed for migration */ | |
159 | struct list_head *head; | |
160 | struct { | |
161 | struct hlist_node hlist_dup; | |
162 | struct list_head list; | |
163 | }; | |
164 | }; | |
165 | }; | |
166 | struct hlist_head hlist; | |
167 | union { | |
168 | unsigned long kpfn; | |
169 | unsigned long chain_prune_time; | |
170 | }; | |
171 | /* | |
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. | |
175 | */ | |
176 | #define STABLE_NODE_CHAIN -1024 | |
177 | int rmap_hlist_len; | |
178 | #ifdef CONFIG_NUMA | |
179 | int nid; | |
180 | #endif | |
181 | }; | |
182 | ||
183 | /** | |
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 | |
194 | */ | |
195 | struct rmap_item { | |
196 | struct rmap_item *rmap_list; | |
197 | union { | |
198 | struct anon_vma *anon_vma; /* when stable */ | |
199 | #ifdef CONFIG_NUMA | |
200 | int nid; /* when node of unstable tree */ | |
201 | #endif | |
202 | }; | |
203 | struct mm_struct *mm; | |
204 | unsigned long address; /* + low bits used for flags below */ | |
205 | unsigned int oldchecksum; /* when unstable */ | |
206 | union { | |
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; | |
211 | }; | |
212 | }; | |
213 | }; | |
214 | ||
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 */ | |
220 | ||
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; | |
226 | ||
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) | |
230 | ||
231 | #define MM_SLOTS_HASH_BITS 10 | |
232 | static DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS); | |
233 | ||
234 | static struct mm_slot ksm_mm_head = { | |
235 | .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list), | |
236 | }; | |
237 | static struct ksm_scan ksm_scan = { | |
238 | .mm_slot = &ksm_mm_head, | |
239 | }; | |
240 | ||
241 | static struct kmem_cache *rmap_item_cache; | |
242 | static struct kmem_cache *stable_node_cache; | |
243 | static struct kmem_cache *mm_slot_cache; | |
244 | ||
245 | /* The number of nodes in the stable tree */ | |
246 | static unsigned long ksm_pages_shared; | |
247 | ||
248 | /* The number of page slots additionally sharing those nodes */ | |
249 | static unsigned long ksm_pages_sharing; | |
250 | ||
251 | /* The number of nodes in the unstable tree */ | |
252 | static unsigned long ksm_pages_unshared; | |
253 | ||
254 | /* The number of rmap_items in use: to calculate pages_volatile */ | |
255 | static unsigned long ksm_rmap_items; | |
256 | ||
257 | /* The number of stable_node chains */ | |
258 | static unsigned long ksm_stable_node_chains; | |
259 | ||
260 | /* The number of stable_node dups linked to the stable_node chains */ | |
261 | static unsigned long ksm_stable_node_dups; | |
262 | ||
263 | /* Delay in pruning stale stable_node_dups in the stable_node_chains */ | |
264 | static int ksm_stable_node_chains_prune_millisecs = 2000; | |
265 | ||
266 | /* Maximum number of page slots sharing a stable node */ | |
267 | static int ksm_max_page_sharing = 256; | |
268 | ||
269 | /* Number of pages ksmd should scan in one batch */ | |
270 | static unsigned int ksm_thread_pages_to_scan = 100; | |
271 | ||
272 | /* Milliseconds ksmd should sleep between batches */ | |
273 | static unsigned int ksm_thread_sleep_millisecs = 20; | |
274 | ||
275 | /* Checksum of an empty (zeroed) page */ | |
276 | static unsigned int zero_checksum __read_mostly; | |
277 | ||
278 | /* Whether to merge empty (zeroed) pages with actual zero pages */ | |
279 | static bool ksm_use_zero_pages __read_mostly; | |
280 | ||
281 | #ifdef CONFIG_NUMA | |
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; | |
285 | #else | |
286 | #define ksm_merge_across_nodes 1U | |
287 | #define ksm_nr_node_ids 1 | |
288 | #endif | |
289 | ||
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); | |
296 | ||
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); | |
301 | ||
302 | #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\ | |
303 | sizeof(struct __struct), __alignof__(struct __struct),\ | |
304 | (__flags), NULL) | |
305 | ||
306 | static int __init ksm_slab_init(void) | |
307 | { | |
308 | rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0); | |
309 | if (!rmap_item_cache) | |
310 | goto out; | |
311 | ||
312 | stable_node_cache = KSM_KMEM_CACHE(stable_node, 0); | |
313 | if (!stable_node_cache) | |
314 | goto out_free1; | |
315 | ||
316 | mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0); | |
317 | if (!mm_slot_cache) | |
318 | goto out_free2; | |
319 | ||
320 | return 0; | |
321 | ||
322 | out_free2: | |
323 | kmem_cache_destroy(stable_node_cache); | |
324 | out_free1: | |
325 | kmem_cache_destroy(rmap_item_cache); | |
326 | out: | |
327 | return -ENOMEM; | |
328 | } | |
329 | ||
330 | static void __init ksm_slab_free(void) | |
331 | { | |
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; | |
336 | } | |
337 | ||
338 | static __always_inline bool is_stable_node_chain(struct stable_node *chain) | |
339 | { | |
340 | return chain->rmap_hlist_len == STABLE_NODE_CHAIN; | |
341 | } | |
342 | ||
343 | static __always_inline bool is_stable_node_dup(struct stable_node *dup) | |
344 | { | |
345 | return dup->head == STABLE_NODE_DUP_HEAD; | |
346 | } | |
347 | ||
348 | static inline void stable_node_chain_add_dup(struct stable_node *dup, | |
349 | struct stable_node *chain) | |
350 | { | |
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++; | |
356 | } | |
357 | ||
358 | static inline void __stable_node_dup_del(struct stable_node *dup) | |
359 | { | |
360 | VM_BUG_ON(!is_stable_node_dup(dup)); | |
361 | hlist_del(&dup->hlist_dup); | |
362 | ksm_stable_node_dups--; | |
363 | } | |
364 | ||
365 | static inline void stable_node_dup_del(struct stable_node *dup) | |
366 | { | |
367 | VM_BUG_ON(is_stable_node_chain(dup)); | |
368 | if (is_stable_node_dup(dup)) | |
369 | __stable_node_dup_del(dup); | |
370 | else | |
371 | rb_erase(&dup->node, root_stable_tree + NUMA(dup->nid)); | |
372 | #ifdef CONFIG_DEBUG_VM | |
373 | dup->head = NULL; | |
374 | #endif | |
375 | } | |
376 | ||
377 | static inline struct rmap_item *alloc_rmap_item(void) | |
378 | { | |
379 | struct rmap_item *rmap_item; | |
380 | ||
381 | rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL | | |
382 | __GFP_NORETRY | __GFP_NOWARN); | |
383 | if (rmap_item) | |
384 | ksm_rmap_items++; | |
385 | return rmap_item; | |
386 | } | |
387 | ||
388 | static inline void free_rmap_item(struct rmap_item *rmap_item) | |
389 | { | |
390 | ksm_rmap_items--; | |
391 | rmap_item->mm = NULL; /* debug safety */ | |
392 | kmem_cache_free(rmap_item_cache, rmap_item); | |
393 | } | |
394 | ||
395 | static inline struct stable_node *alloc_stable_node(void) | |
396 | { | |
397 | /* | |
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. | |
401 | */ | |
402 | return kmem_cache_alloc(stable_node_cache, GFP_KERNEL | __GFP_HIGH); | |
403 | } | |
404 | ||
405 | static inline void free_stable_node(struct stable_node *stable_node) | |
406 | { | |
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); | |
410 | } | |
411 | ||
412 | static inline struct mm_slot *alloc_mm_slot(void) | |
413 | { | |
414 | if (!mm_slot_cache) /* initialization failed */ | |
415 | return NULL; | |
416 | return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL); | |
417 | } | |
418 | ||
419 | static inline void free_mm_slot(struct mm_slot *mm_slot) | |
420 | { | |
421 | kmem_cache_free(mm_slot_cache, mm_slot); | |
422 | } | |
423 | ||
424 | static struct mm_slot *get_mm_slot(struct mm_struct *mm) | |
425 | { | |
426 | struct mm_slot *slot; | |
427 | ||
428 | hash_for_each_possible(mm_slots_hash, slot, link, (unsigned long)mm) | |
429 | if (slot->mm == mm) | |
430 | return slot; | |
431 | ||
432 | return NULL; | |
433 | } | |
434 | ||
435 | static void insert_to_mm_slots_hash(struct mm_struct *mm, | |
436 | struct mm_slot *mm_slot) | |
437 | { | |
438 | mm_slot->mm = mm; | |
439 | hash_add(mm_slots_hash, &mm_slot->link, (unsigned long)mm); | |
440 | } | |
441 | ||
442 | /* | |
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_lock 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. | |
449 | */ | |
450 | static inline bool ksm_test_exit(struct mm_struct *mm) | |
451 | { | |
452 | return atomic_read(&mm->mm_users) == 0; | |
453 | } | |
454 | ||
455 | /* | |
456 | * We use break_ksm to break COW on a ksm page: it's a stripped down | |
457 | * | |
458 | * if (get_user_pages(addr, 1, FOLL_WRITE, &page, NULL) == 1) | |
459 | * put_page(page); | |
460 | * | |
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. | |
465 | * | |
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. | |
469 | */ | |
470 | static int break_ksm(struct vm_area_struct *vma, unsigned long addr) | |
471 | { | |
472 | struct page *page; | |
473 | vm_fault_t ret = 0; | |
474 | ||
475 | do { | |
476 | cond_resched(); | |
477 | page = follow_page(vma, addr, | |
478 | FOLL_GET | FOLL_MIGRATION | FOLL_REMOTE); | |
479 | if (IS_ERR_OR_NULL(page)) | |
480 | break; | |
481 | if (PageKsm(page)) | |
482 | ret = handle_mm_fault(vma, addr, | |
483 | FAULT_FLAG_WRITE | FAULT_FLAG_REMOTE, | |
484 | NULL); | |
485 | else | |
486 | ret = VM_FAULT_WRITE; | |
487 | put_page(page); | |
488 | } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | VM_FAULT_OOM))); | |
489 | /* | |
490 | * We must loop because handle_mm_fault() may back out if there's | |
491 | * any difficulty e.g. if pte accessed bit gets updated concurrently. | |
492 | * | |
493 | * VM_FAULT_WRITE is what we have been hoping for: it indicates that | |
494 | * COW has been broken, even if the vma does not permit VM_WRITE; | |
495 | * but note that a concurrent fault might break PageKsm for us. | |
496 | * | |
497 | * VM_FAULT_SIGBUS could occur if we race with truncation of the | |
498 | * backing file, which also invalidates anonymous pages: that's | |
499 | * okay, that truncation will have unmapped the PageKsm for us. | |
500 | * | |
501 | * VM_FAULT_OOM: at the time of writing (late July 2009), setting | |
502 | * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the | |
503 | * current task has TIF_MEMDIE set, and will be OOM killed on return | |
504 | * to user; and ksmd, having no mm, would never be chosen for that. | |
505 | * | |
506 | * But if the mm is in a limited mem_cgroup, then the fault may fail | |
507 | * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and | |
508 | * even ksmd can fail in this way - though it's usually breaking ksm | |
509 | * just to undo a merge it made a moment before, so unlikely to oom. | |
510 | * | |
511 | * That's a pity: we might therefore have more kernel pages allocated | |
512 | * than we're counting as nodes in the stable tree; but ksm_do_scan | |
513 | * will retry to break_cow on each pass, so should recover the page | |
514 | * in due course. The important thing is to not let VM_MERGEABLE | |
515 | * be cleared while any such pages might remain in the area. | |
516 | */ | |
517 | return (ret & VM_FAULT_OOM) ? -ENOMEM : 0; | |
518 | } | |
519 | ||
520 | static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm, | |
521 | unsigned long addr) | |
522 | { | |
523 | struct vm_area_struct *vma; | |
524 | if (ksm_test_exit(mm)) | |
525 | return NULL; | |
526 | vma = find_vma(mm, addr); | |
527 | if (!vma || vma->vm_start > addr) | |
528 | return NULL; | |
529 | if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) | |
530 | return NULL; | |
531 | return vma; | |
532 | } | |
533 | ||
534 | static void break_cow(struct rmap_item *rmap_item) | |
535 | { | |
536 | struct mm_struct *mm = rmap_item->mm; | |
537 | unsigned long addr = rmap_item->address; | |
538 | struct vm_area_struct *vma; | |
539 | ||
540 | /* | |
541 | * It is not an accident that whenever we want to break COW | |
542 | * to undo, we also need to drop a reference to the anon_vma. | |
543 | */ | |
544 | put_anon_vma(rmap_item->anon_vma); | |
545 | ||
546 | mmap_read_lock(mm); | |
547 | vma = find_mergeable_vma(mm, addr); | |
548 | if (vma) | |
549 | break_ksm(vma, addr); | |
550 | mmap_read_unlock(mm); | |
551 | } | |
552 | ||
553 | static struct page *get_mergeable_page(struct rmap_item *rmap_item) | |
554 | { | |
555 | struct mm_struct *mm = rmap_item->mm; | |
556 | unsigned long addr = rmap_item->address; | |
557 | struct vm_area_struct *vma; | |
558 | struct page *page; | |
559 | ||
560 | mmap_read_lock(mm); | |
561 | vma = find_mergeable_vma(mm, addr); | |
562 | if (!vma) | |
563 | goto out; | |
564 | ||
565 | page = follow_page(vma, addr, FOLL_GET); | |
566 | if (IS_ERR_OR_NULL(page)) | |
567 | goto out; | |
568 | if (PageAnon(page)) { | |
569 | flush_anon_page(vma, page, addr); | |
570 | flush_dcache_page(page); | |
571 | } else { | |
572 | put_page(page); | |
573 | out: | |
574 | page = NULL; | |
575 | } | |
576 | mmap_read_unlock(mm); | |
577 | return page; | |
578 | } | |
579 | ||
580 | /* | |
581 | * This helper is used for getting right index into array of tree roots. | |
582 | * When merge_across_nodes knob is set to 1, there are only two rb-trees for | |
583 | * stable and unstable pages from all nodes with roots in index 0. Otherwise, | |
584 | * every node has its own stable and unstable tree. | |
585 | */ | |
586 | static inline int get_kpfn_nid(unsigned long kpfn) | |
587 | { | |
588 | return ksm_merge_across_nodes ? 0 : NUMA(pfn_to_nid(kpfn)); | |
589 | } | |
590 | ||
591 | static struct stable_node *alloc_stable_node_chain(struct stable_node *dup, | |
592 | struct rb_root *root) | |
593 | { | |
594 | struct stable_node *chain = alloc_stable_node(); | |
595 | VM_BUG_ON(is_stable_node_chain(dup)); | |
596 | if (likely(chain)) { | |
597 | INIT_HLIST_HEAD(&chain->hlist); | |
598 | chain->chain_prune_time = jiffies; | |
599 | chain->rmap_hlist_len = STABLE_NODE_CHAIN; | |
600 | #if defined (CONFIG_DEBUG_VM) && defined(CONFIG_NUMA) | |
601 | chain->nid = NUMA_NO_NODE; /* debug */ | |
602 | #endif | |
603 | ksm_stable_node_chains++; | |
604 | ||
605 | /* | |
606 | * Put the stable node chain in the first dimension of | |
607 | * the stable tree and at the same time remove the old | |
608 | * stable node. | |
609 | */ | |
610 | rb_replace_node(&dup->node, &chain->node, root); | |
611 | ||
612 | /* | |
613 | * Move the old stable node to the second dimension | |
614 | * queued in the hlist_dup. The invariant is that all | |
615 | * dup stable_nodes in the chain->hlist point to pages | |
616 | * that are write protected and have the exact same | |
617 | * content. | |
618 | */ | |
619 | stable_node_chain_add_dup(dup, chain); | |
620 | } | |
621 | return chain; | |
622 | } | |
623 | ||
624 | static inline void free_stable_node_chain(struct stable_node *chain, | |
625 | struct rb_root *root) | |
626 | { | |
627 | rb_erase(&chain->node, root); | |
628 | free_stable_node(chain); | |
629 | ksm_stable_node_chains--; | |
630 | } | |
631 | ||
632 | static void remove_node_from_stable_tree(struct stable_node *stable_node) | |
633 | { | |
634 | struct rmap_item *rmap_item; | |
635 | ||
636 | /* check it's not STABLE_NODE_CHAIN or negative */ | |
637 | BUG_ON(stable_node->rmap_hlist_len < 0); | |
638 | ||
639 | hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) { | |
640 | if (rmap_item->hlist.next) | |
641 | ksm_pages_sharing--; | |
642 | else | |
643 | ksm_pages_shared--; | |
644 | VM_BUG_ON(stable_node->rmap_hlist_len <= 0); | |
645 | stable_node->rmap_hlist_len--; | |
646 | put_anon_vma(rmap_item->anon_vma); | |
647 | rmap_item->address &= PAGE_MASK; | |
648 | cond_resched(); | |
649 | } | |
650 | ||
651 | /* | |
652 | * We need the second aligned pointer of the migrate_nodes | |
653 | * list_head to stay clear from the rb_parent_color union | |
654 | * (aligned and different than any node) and also different | |
655 | * from &migrate_nodes. This will verify that future list.h changes | |
656 | * don't break STABLE_NODE_DUP_HEAD. Only recent gcc can handle it. | |
657 | */ | |
658 | #if defined(GCC_VERSION) && GCC_VERSION >= 40903 | |
659 | BUILD_BUG_ON(STABLE_NODE_DUP_HEAD <= &migrate_nodes); | |
660 | BUILD_BUG_ON(STABLE_NODE_DUP_HEAD >= &migrate_nodes + 1); | |
661 | #endif | |
662 | ||
663 | if (stable_node->head == &migrate_nodes) | |
664 | list_del(&stable_node->list); | |
665 | else | |
666 | stable_node_dup_del(stable_node); | |
667 | free_stable_node(stable_node); | |
668 | } | |
669 | ||
670 | enum get_ksm_page_flags { | |
671 | GET_KSM_PAGE_NOLOCK, | |
672 | GET_KSM_PAGE_LOCK, | |
673 | GET_KSM_PAGE_TRYLOCK | |
674 | }; | |
675 | ||
676 | /* | |
677 | * get_ksm_page: checks if the page indicated by the stable node | |
678 | * is still its ksm page, despite having held no reference to it. | |
679 | * In which case we can trust the content of the page, and it | |
680 | * returns the gotten page; but if the page has now been zapped, | |
681 | * remove the stale node from the stable tree and return NULL. | |
682 | * But beware, the stable node's page might be being migrated. | |
683 | * | |
684 | * You would expect the stable_node to hold a reference to the ksm page. | |
685 | * But if it increments the page's count, swapping out has to wait for | |
686 | * ksmd to come around again before it can free the page, which may take | |
687 | * seconds or even minutes: much too unresponsive. So instead we use a | |
688 | * "keyhole reference": access to the ksm page from the stable node peeps | |
689 | * out through its keyhole to see if that page still holds the right key, | |
690 | * pointing back to this stable node. This relies on freeing a PageAnon | |
691 | * page to reset its page->mapping to NULL, and relies on no other use of | |
692 | * a page to put something that might look like our key in page->mapping. | |
693 | * is on its way to being freed; but it is an anomaly to bear in mind. | |
694 | */ | |
695 | static struct page *get_ksm_page(struct stable_node *stable_node, | |
696 | enum get_ksm_page_flags flags) | |
697 | { | |
698 | struct page *page; | |
699 | void *expected_mapping; | |
700 | unsigned long kpfn; | |
701 | ||
702 | expected_mapping = (void *)((unsigned long)stable_node | | |
703 | PAGE_MAPPING_KSM); | |
704 | again: | |
705 | kpfn = READ_ONCE(stable_node->kpfn); /* Address dependency. */ | |
706 | page = pfn_to_page(kpfn); | |
707 | if (READ_ONCE(page->mapping) != expected_mapping) | |
708 | goto stale; | |
709 | ||
710 | /* | |
711 | * We cannot do anything with the page while its refcount is 0. | |
712 | * Usually 0 means free, or tail of a higher-order page: in which | |
713 | * case this node is no longer referenced, and should be freed; | |
714 | * however, it might mean that the page is under page_ref_freeze(). | |
715 | * The __remove_mapping() case is easy, again the node is now stale; | |
716 | * the same is in reuse_ksm_page() case; but if page is swapcache | |
717 | * in migrate_page_move_mapping(), it might still be our page, | |
718 | * in which case it's essential to keep the node. | |
719 | */ | |
720 | while (!get_page_unless_zero(page)) { | |
721 | /* | |
722 | * Another check for page->mapping != expected_mapping would | |
723 | * work here too. We have chosen the !PageSwapCache test to | |
724 | * optimize the common case, when the page is or is about to | |
725 | * be freed: PageSwapCache is cleared (under spin_lock_irq) | |
726 | * in the ref_freeze section of __remove_mapping(); but Anon | |
727 | * page->mapping reset to NULL later, in free_pages_prepare(). | |
728 | */ | |
729 | if (!PageSwapCache(page)) | |
730 | goto stale; | |
731 | cpu_relax(); | |
732 | } | |
733 | ||
734 | if (READ_ONCE(page->mapping) != expected_mapping) { | |
735 | put_page(page); | |
736 | goto stale; | |
737 | } | |
738 | ||
739 | if (flags == GET_KSM_PAGE_TRYLOCK) { | |
740 | if (!trylock_page(page)) { | |
741 | put_page(page); | |
742 | return ERR_PTR(-EBUSY); | |
743 | } | |
744 | } else if (flags == GET_KSM_PAGE_LOCK) | |
745 | lock_page(page); | |
746 | ||
747 | if (flags != GET_KSM_PAGE_NOLOCK) { | |
748 | if (READ_ONCE(page->mapping) != expected_mapping) { | |
749 | unlock_page(page); | |
750 | put_page(page); | |
751 | goto stale; | |
752 | } | |
753 | } | |
754 | return page; | |
755 | ||
756 | stale: | |
757 | /* | |
758 | * We come here from above when page->mapping or !PageSwapCache | |
759 | * suggests that the node is stale; but it might be under migration. | |
760 | * We need smp_rmb(), matching the smp_wmb() in ksm_migrate_page(), | |
761 | * before checking whether node->kpfn has been changed. | |
762 | */ | |
763 | smp_rmb(); | |
764 | if (READ_ONCE(stable_node->kpfn) != kpfn) | |
765 | goto again; | |
766 | remove_node_from_stable_tree(stable_node); | |
767 | return NULL; | |
768 | } | |
769 | ||
770 | /* | |
771 | * Removing rmap_item from stable or unstable tree. | |
772 | * This function will clean the information from the stable/unstable tree. | |
773 | */ | |
774 | static void remove_rmap_item_from_tree(struct rmap_item *rmap_item) | |
775 | { | |
776 | if (rmap_item->address & STABLE_FLAG) { | |
777 | struct stable_node *stable_node; | |
778 | struct page *page; | |
779 | ||
780 | stable_node = rmap_item->head; | |
781 | page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK); | |
782 | if (!page) | |
783 | goto out; | |
784 | ||
785 | hlist_del(&rmap_item->hlist); | |
786 | unlock_page(page); | |
787 | put_page(page); | |
788 | ||
789 | if (!hlist_empty(&stable_node->hlist)) | |
790 | ksm_pages_sharing--; | |
791 | else | |
792 | ksm_pages_shared--; | |
793 | VM_BUG_ON(stable_node->rmap_hlist_len <= 0); | |
794 | stable_node->rmap_hlist_len--; | |
795 | ||
796 | put_anon_vma(rmap_item->anon_vma); | |
797 | rmap_item->address &= PAGE_MASK; | |
798 | ||
799 | } else if (rmap_item->address & UNSTABLE_FLAG) { | |
800 | unsigned char age; | |
801 | /* | |
802 | * Usually ksmd can and must skip the rb_erase, because | |
803 | * root_unstable_tree was already reset to RB_ROOT. | |
804 | * But be careful when an mm is exiting: do the rb_erase | |
805 | * if this rmap_item was inserted by this scan, rather | |
806 | * than left over from before. | |
807 | */ | |
808 | age = (unsigned char)(ksm_scan.seqnr - rmap_item->address); | |
809 | BUG_ON(age > 1); | |
810 | if (!age) | |
811 | rb_erase(&rmap_item->node, | |
812 | root_unstable_tree + NUMA(rmap_item->nid)); | |
813 | ksm_pages_unshared--; | |
814 | rmap_item->address &= PAGE_MASK; | |
815 | } | |
816 | out: | |
817 | cond_resched(); /* we're called from many long loops */ | |
818 | } | |
819 | ||
820 | static void remove_trailing_rmap_items(struct mm_slot *mm_slot, | |
821 | struct rmap_item **rmap_list) | |
822 | { | |
823 | while (*rmap_list) { | |
824 | struct rmap_item *rmap_item = *rmap_list; | |
825 | *rmap_list = rmap_item->rmap_list; | |
826 | remove_rmap_item_from_tree(rmap_item); | |
827 | free_rmap_item(rmap_item); | |
828 | } | |
829 | } | |
830 | ||
831 | /* | |
832 | * Though it's very tempting to unmerge rmap_items from stable tree rather | |
833 | * than check every pte of a given vma, the locking doesn't quite work for | |
834 | * that - an rmap_item is assigned to the stable tree after inserting ksm | |
835 | * page and upping mmap_lock. Nor does it fit with the way we skip dup'ing | |
836 | * rmap_items from parent to child at fork time (so as not to waste time | |
837 | * if exit comes before the next scan reaches it). | |
838 | * | |
839 | * Similarly, although we'd like to remove rmap_items (so updating counts | |
840 | * and freeing memory) when unmerging an area, it's easier to leave that | |
841 | * to the next pass of ksmd - consider, for example, how ksmd might be | |
842 | * in cmp_and_merge_page on one of the rmap_items we would be removing. | |
843 | */ | |
844 | static int unmerge_ksm_pages(struct vm_area_struct *vma, | |
845 | unsigned long start, unsigned long end) | |
846 | { | |
847 | unsigned long addr; | |
848 | int err = 0; | |
849 | ||
850 | for (addr = start; addr < end && !err; addr += PAGE_SIZE) { | |
851 | if (ksm_test_exit(vma->vm_mm)) | |
852 | break; | |
853 | if (signal_pending(current)) | |
854 | err = -ERESTARTSYS; | |
855 | else | |
856 | err = break_ksm(vma, addr); | |
857 | } | |
858 | return err; | |
859 | } | |
860 | ||
861 | static inline struct stable_node *page_stable_node(struct page *page) | |
862 | { | |
863 | return PageKsm(page) ? page_rmapping(page) : NULL; | |
864 | } | |
865 | ||
866 | static inline void set_page_stable_node(struct page *page, | |
867 | struct stable_node *stable_node) | |
868 | { | |
869 | page->mapping = (void *)((unsigned long)stable_node | PAGE_MAPPING_KSM); | |
870 | } | |
871 | ||
872 | #ifdef CONFIG_SYSFS | |
873 | /* | |
874 | * Only called through the sysfs control interface: | |
875 | */ | |
876 | static int remove_stable_node(struct stable_node *stable_node) | |
877 | { | |
878 | struct page *page; | |
879 | int err; | |
880 | ||
881 | page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK); | |
882 | if (!page) { | |
883 | /* | |
884 | * get_ksm_page did remove_node_from_stable_tree itself. | |
885 | */ | |
886 | return 0; | |
887 | } | |
888 | ||
889 | /* | |
890 | * Page could be still mapped if this races with __mmput() running in | |
891 | * between ksm_exit() and exit_mmap(). Just refuse to let | |
892 | * merge_across_nodes/max_page_sharing be switched. | |
893 | */ | |
894 | err = -EBUSY; | |
895 | if (!page_mapped(page)) { | |
896 | /* | |
897 | * The stable node did not yet appear stale to get_ksm_page(), | |
898 | * since that allows for an unmapped ksm page to be recognized | |
899 | * right up until it is freed; but the node is safe to remove. | |
900 | * This page might be in a pagevec waiting to be freed, | |
901 | * or it might be PageSwapCache (perhaps under writeback), | |
902 | * or it might have been removed from swapcache a moment ago. | |
903 | */ | |
904 | set_page_stable_node(page, NULL); | |
905 | remove_node_from_stable_tree(stable_node); | |
906 | err = 0; | |
907 | } | |
908 | ||
909 | unlock_page(page); | |
910 | put_page(page); | |
911 | return err; | |
912 | } | |
913 | ||
914 | static int remove_stable_node_chain(struct stable_node *stable_node, | |
915 | struct rb_root *root) | |
916 | { | |
917 | struct stable_node *dup; | |
918 | struct hlist_node *hlist_safe; | |
919 | ||
920 | if (!is_stable_node_chain(stable_node)) { | |
921 | VM_BUG_ON(is_stable_node_dup(stable_node)); | |
922 | if (remove_stable_node(stable_node)) | |
923 | return true; | |
924 | else | |
925 | return false; | |
926 | } | |
927 | ||
928 | hlist_for_each_entry_safe(dup, hlist_safe, | |
929 | &stable_node->hlist, hlist_dup) { | |
930 | VM_BUG_ON(!is_stable_node_dup(dup)); | |
931 | if (remove_stable_node(dup)) | |
932 | return true; | |
933 | } | |
934 | BUG_ON(!hlist_empty(&stable_node->hlist)); | |
935 | free_stable_node_chain(stable_node, root); | |
936 | return false; | |
937 | } | |
938 | ||
939 | static int remove_all_stable_nodes(void) | |
940 | { | |
941 | struct stable_node *stable_node, *next; | |
942 | int nid; | |
943 | int err = 0; | |
944 | ||
945 | for (nid = 0; nid < ksm_nr_node_ids; nid++) { | |
946 | while (root_stable_tree[nid].rb_node) { | |
947 | stable_node = rb_entry(root_stable_tree[nid].rb_node, | |
948 | struct stable_node, node); | |
949 | if (remove_stable_node_chain(stable_node, | |
950 | root_stable_tree + nid)) { | |
951 | err = -EBUSY; | |
952 | break; /* proceed to next nid */ | |
953 | } | |
954 | cond_resched(); | |
955 | } | |
956 | } | |
957 | list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) { | |
958 | if (remove_stable_node(stable_node)) | |
959 | err = -EBUSY; | |
960 | cond_resched(); | |
961 | } | |
962 | return err; | |
963 | } | |
964 | ||
965 | static int unmerge_and_remove_all_rmap_items(void) | |
966 | { | |
967 | struct mm_slot *mm_slot; | |
968 | struct mm_struct *mm; | |
969 | struct vm_area_struct *vma; | |
970 | int err = 0; | |
971 | ||
972 | spin_lock(&ksm_mmlist_lock); | |
973 | ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next, | |
974 | struct mm_slot, mm_list); | |
975 | spin_unlock(&ksm_mmlist_lock); | |
976 | ||
977 | for (mm_slot = ksm_scan.mm_slot; | |
978 | mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) { | |
979 | mm = mm_slot->mm; | |
980 | mmap_read_lock(mm); | |
981 | for (vma = mm->mmap; vma; vma = vma->vm_next) { | |
982 | if (ksm_test_exit(mm)) | |
983 | break; | |
984 | if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) | |
985 | continue; | |
986 | err = unmerge_ksm_pages(vma, | |
987 | vma->vm_start, vma->vm_end); | |
988 | if (err) | |
989 | goto error; | |
990 | } | |
991 | ||
992 | remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list); | |
993 | mmap_read_unlock(mm); | |
994 | ||
995 | spin_lock(&ksm_mmlist_lock); | |
996 | ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next, | |
997 | struct mm_slot, mm_list); | |
998 | if (ksm_test_exit(mm)) { | |
999 | hash_del(&mm_slot->link); | |
1000 | list_del(&mm_slot->mm_list); | |
1001 | spin_unlock(&ksm_mmlist_lock); | |
1002 | ||
1003 | free_mm_slot(mm_slot); | |
1004 | clear_bit(MMF_VM_MERGEABLE, &mm->flags); | |
1005 | mmdrop(mm); | |
1006 | } else | |
1007 | spin_unlock(&ksm_mmlist_lock); | |
1008 | } | |
1009 | ||
1010 | /* Clean up stable nodes, but don't worry if some are still busy */ | |
1011 | remove_all_stable_nodes(); | |
1012 | ksm_scan.seqnr = 0; | |
1013 | return 0; | |
1014 | ||
1015 | error: | |
1016 | mmap_read_unlock(mm); | |
1017 | spin_lock(&ksm_mmlist_lock); | |
1018 | ksm_scan.mm_slot = &ksm_mm_head; | |
1019 | spin_unlock(&ksm_mmlist_lock); | |
1020 | return err; | |
1021 | } | |
1022 | #endif /* CONFIG_SYSFS */ | |
1023 | ||
1024 | static u32 calc_checksum(struct page *page) | |
1025 | { | |
1026 | u32 checksum; | |
1027 | void *addr = kmap_atomic(page); | |
1028 | checksum = xxhash(addr, PAGE_SIZE, 0); | |
1029 | kunmap_atomic(addr); | |
1030 | return checksum; | |
1031 | } | |
1032 | ||
1033 | static int write_protect_page(struct vm_area_struct *vma, struct page *page, | |
1034 | pte_t *orig_pte) | |
1035 | { | |
1036 | struct mm_struct *mm = vma->vm_mm; | |
1037 | struct page_vma_mapped_walk pvmw = { | |
1038 | .page = page, | |
1039 | .vma = vma, | |
1040 | }; | |
1041 | int swapped; | |
1042 | int err = -EFAULT; | |
1043 | struct mmu_notifier_range range; | |
1044 | ||
1045 | pvmw.address = page_address_in_vma(page, vma); | |
1046 | if (pvmw.address == -EFAULT) | |
1047 | goto out; | |
1048 | ||
1049 | BUG_ON(PageTransCompound(page)); | |
1050 | ||
1051 | mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm, | |
1052 | pvmw.address, | |
1053 | pvmw.address + PAGE_SIZE); | |
1054 | mmu_notifier_invalidate_range_start(&range); | |
1055 | ||
1056 | if (!page_vma_mapped_walk(&pvmw)) | |
1057 | goto out_mn; | |
1058 | if (WARN_ONCE(!pvmw.pte, "Unexpected PMD mapping?")) | |
1059 | goto out_unlock; | |
1060 | ||
1061 | if (pte_write(*pvmw.pte) || pte_dirty(*pvmw.pte) || | |
1062 | (pte_protnone(*pvmw.pte) && pte_savedwrite(*pvmw.pte)) || | |
1063 | mm_tlb_flush_pending(mm)) { | |
1064 | pte_t entry; | |
1065 | ||
1066 | swapped = PageSwapCache(page); | |
1067 | flush_cache_page(vma, pvmw.address, page_to_pfn(page)); | |
1068 | /* | |
1069 | * Ok this is tricky, when get_user_pages_fast() run it doesn't | |
1070 | * take any lock, therefore the check that we are going to make | |
1071 | * with the pagecount against the mapcount is racey and | |
1072 | * O_DIRECT can happen right after the check. | |
1073 | * So we clear the pte and flush the tlb before the check | |
1074 | * this assure us that no O_DIRECT can happen after the check | |
1075 | * or in the middle of the check. | |
1076 | * | |
1077 | * No need to notify as we are downgrading page table to read | |
1078 | * only not changing it to point to a new page. | |
1079 | * | |
1080 | * See Documentation/vm/mmu_notifier.rst | |
1081 | */ | |
1082 | entry = ptep_clear_flush(vma, pvmw.address, pvmw.pte); | |
1083 | /* | |
1084 | * Check that no O_DIRECT or similar I/O is in progress on the | |
1085 | * page | |
1086 | */ | |
1087 | if (page_mapcount(page) + 1 + swapped != page_count(page)) { | |
1088 | set_pte_at(mm, pvmw.address, pvmw.pte, entry); | |
1089 | goto out_unlock; | |
1090 | } | |
1091 | if (pte_dirty(entry)) | |
1092 | set_page_dirty(page); | |
1093 | ||
1094 | if (pte_protnone(entry)) | |
1095 | entry = pte_mkclean(pte_clear_savedwrite(entry)); | |
1096 | else | |
1097 | entry = pte_mkclean(pte_wrprotect(entry)); | |
1098 | set_pte_at_notify(mm, pvmw.address, pvmw.pte, entry); | |
1099 | } | |
1100 | *orig_pte = *pvmw.pte; | |
1101 | err = 0; | |
1102 | ||
1103 | out_unlock: | |
1104 | page_vma_mapped_walk_done(&pvmw); | |
1105 | out_mn: | |
1106 | mmu_notifier_invalidate_range_end(&range); | |
1107 | out: | |
1108 | return err; | |
1109 | } | |
1110 | ||
1111 | /** | |
1112 | * replace_page - replace page in vma by new ksm page | |
1113 | * @vma: vma that holds the pte pointing to page | |
1114 | * @page: the page we are replacing by kpage | |
1115 | * @kpage: the ksm page we replace page by | |
1116 | * @orig_pte: the original value of the pte | |
1117 | * | |
1118 | * Returns 0 on success, -EFAULT on failure. | |
1119 | */ | |
1120 | static int replace_page(struct vm_area_struct *vma, struct page *page, | |
1121 | struct page *kpage, pte_t orig_pte) | |
1122 | { | |
1123 | struct mm_struct *mm = vma->vm_mm; | |
1124 | pmd_t *pmd; | |
1125 | pte_t *ptep; | |
1126 | pte_t newpte; | |
1127 | spinlock_t *ptl; | |
1128 | unsigned long addr; | |
1129 | int err = -EFAULT; | |
1130 | struct mmu_notifier_range range; | |
1131 | ||
1132 | addr = page_address_in_vma(page, vma); | |
1133 | if (addr == -EFAULT) | |
1134 | goto out; | |
1135 | ||
1136 | pmd = mm_find_pmd(mm, addr); | |
1137 | if (!pmd) | |
1138 | goto out; | |
1139 | ||
1140 | mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm, addr, | |
1141 | addr + PAGE_SIZE); | |
1142 | mmu_notifier_invalidate_range_start(&range); | |
1143 | ||
1144 | ptep = pte_offset_map_lock(mm, pmd, addr, &ptl); | |
1145 | if (!pte_same(*ptep, orig_pte)) { | |
1146 | pte_unmap_unlock(ptep, ptl); | |
1147 | goto out_mn; | |
1148 | } | |
1149 | ||
1150 | /* | |
1151 | * No need to check ksm_use_zero_pages here: we can only have a | |
1152 | * zero_page here if ksm_use_zero_pages was enabled already. | |
1153 | */ | |
1154 | if (!is_zero_pfn(page_to_pfn(kpage))) { | |
1155 | get_page(kpage); | |
1156 | page_add_anon_rmap(kpage, vma, addr, false); | |
1157 | newpte = mk_pte(kpage, vma->vm_page_prot); | |
1158 | } else { | |
1159 | newpte = pte_mkspecial(pfn_pte(page_to_pfn(kpage), | |
1160 | vma->vm_page_prot)); | |
1161 | /* | |
1162 | * We're replacing an anonymous page with a zero page, which is | |
1163 | * not anonymous. We need to do proper accounting otherwise we | |
1164 | * will get wrong values in /proc, and a BUG message in dmesg | |
1165 | * when tearing down the mm. | |
1166 | */ | |
1167 | dec_mm_counter(mm, MM_ANONPAGES); | |
1168 | } | |
1169 | ||
1170 | flush_cache_page(vma, addr, pte_pfn(*ptep)); | |
1171 | /* | |
1172 | * No need to notify as we are replacing a read only page with another | |
1173 | * read only page with the same content. | |
1174 | * | |
1175 | * See Documentation/vm/mmu_notifier.rst | |
1176 | */ | |
1177 | ptep_clear_flush(vma, addr, ptep); | |
1178 | set_pte_at_notify(mm, addr, ptep, newpte); | |
1179 | ||
1180 | page_remove_rmap(page, false); | |
1181 | if (!page_mapped(page)) | |
1182 | try_to_free_swap(page); | |
1183 | put_page(page); | |
1184 | ||
1185 | pte_unmap_unlock(ptep, ptl); | |
1186 | err = 0; | |
1187 | out_mn: | |
1188 | mmu_notifier_invalidate_range_end(&range); | |
1189 | out: | |
1190 | return err; | |
1191 | } | |
1192 | ||
1193 | /* | |
1194 | * try_to_merge_one_page - take two pages and merge them into one | |
1195 | * @vma: the vma that holds the pte pointing to page | |
1196 | * @page: the PageAnon page that we want to replace with kpage | |
1197 | * @kpage: the PageKsm page that we want to map instead of page, | |
1198 | * or NULL the first time when we want to use page as kpage. | |
1199 | * | |
1200 | * This function returns 0 if the pages were merged, -EFAULT otherwise. | |
1201 | */ | |
1202 | static int try_to_merge_one_page(struct vm_area_struct *vma, | |
1203 | struct page *page, struct page *kpage) | |
1204 | { | |
1205 | pte_t orig_pte = __pte(0); | |
1206 | int err = -EFAULT; | |
1207 | ||
1208 | if (page == kpage) /* ksm page forked */ | |
1209 | return 0; | |
1210 | ||
1211 | if (!PageAnon(page)) | |
1212 | goto out; | |
1213 | ||
1214 | /* | |
1215 | * We need the page lock to read a stable PageSwapCache in | |
1216 | * write_protect_page(). We use trylock_page() instead of | |
1217 | * lock_page() because we don't want to wait here - we | |
1218 | * prefer to continue scanning and merging different pages, | |
1219 | * then come back to this page when it is unlocked. | |
1220 | */ | |
1221 | if (!trylock_page(page)) | |
1222 | goto out; | |
1223 | ||
1224 | if (PageTransCompound(page)) { | |
1225 | if (split_huge_page(page)) | |
1226 | goto out_unlock; | |
1227 | } | |
1228 | ||
1229 | /* | |
1230 | * If this anonymous page is mapped only here, its pte may need | |
1231 | * to be write-protected. If it's mapped elsewhere, all of its | |
1232 | * ptes are necessarily already write-protected. But in either | |
1233 | * case, we need to lock and check page_count is not raised. | |
1234 | */ | |
1235 | if (write_protect_page(vma, page, &orig_pte) == 0) { | |
1236 | if (!kpage) { | |
1237 | /* | |
1238 | * While we hold page lock, upgrade page from | |
1239 | * PageAnon+anon_vma to PageKsm+NULL stable_node: | |
1240 | * stable_tree_insert() will update stable_node. | |
1241 | */ | |
1242 | set_page_stable_node(page, NULL); | |
1243 | mark_page_accessed(page); | |
1244 | /* | |
1245 | * Page reclaim just frees a clean page with no dirty | |
1246 | * ptes: make sure that the ksm page would be swapped. | |
1247 | */ | |
1248 | if (!PageDirty(page)) | |
1249 | SetPageDirty(page); | |
1250 | err = 0; | |
1251 | } else if (pages_identical(page, kpage)) | |
1252 | err = replace_page(vma, page, kpage, orig_pte); | |
1253 | } | |
1254 | ||
1255 | if ((vma->vm_flags & VM_LOCKED) && kpage && !err) { | |
1256 | munlock_vma_page(page); | |
1257 | if (!PageMlocked(kpage)) { | |
1258 | unlock_page(page); | |
1259 | lock_page(kpage); | |
1260 | mlock_vma_page(kpage); | |
1261 | page = kpage; /* for final unlock */ | |
1262 | } | |
1263 | } | |
1264 | ||
1265 | out_unlock: | |
1266 | unlock_page(page); | |
1267 | out: | |
1268 | return err; | |
1269 | } | |
1270 | ||
1271 | /* | |
1272 | * try_to_merge_with_ksm_page - like try_to_merge_two_pages, | |
1273 | * but no new kernel page is allocated: kpage must already be a ksm page. | |
1274 | * | |
1275 | * This function returns 0 if the pages were merged, -EFAULT otherwise. | |
1276 | */ | |
1277 | static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item, | |
1278 | struct page *page, struct page *kpage) | |
1279 | { | |
1280 | struct mm_struct *mm = rmap_item->mm; | |
1281 | struct vm_area_struct *vma; | |
1282 | int err = -EFAULT; | |
1283 | ||
1284 | mmap_read_lock(mm); | |
1285 | vma = find_mergeable_vma(mm, rmap_item->address); | |
1286 | if (!vma) | |
1287 | goto out; | |
1288 | ||
1289 | err = try_to_merge_one_page(vma, page, kpage); | |
1290 | if (err) | |
1291 | goto out; | |
1292 | ||
1293 | /* Unstable nid is in union with stable anon_vma: remove first */ | |
1294 | remove_rmap_item_from_tree(rmap_item); | |
1295 | ||
1296 | /* Must get reference to anon_vma while still holding mmap_lock */ | |
1297 | rmap_item->anon_vma = vma->anon_vma; | |
1298 | get_anon_vma(vma->anon_vma); | |
1299 | out: | |
1300 | mmap_read_unlock(mm); | |
1301 | return err; | |
1302 | } | |
1303 | ||
1304 | /* | |
1305 | * try_to_merge_two_pages - take two identical pages and prepare them | |
1306 | * to be merged into one page. | |
1307 | * | |
1308 | * This function returns the kpage if we successfully merged two identical | |
1309 | * pages into one ksm page, NULL otherwise. | |
1310 | * | |
1311 | * Note that this function upgrades page to ksm page: if one of the pages | |
1312 | * is already a ksm page, try_to_merge_with_ksm_page should be used. | |
1313 | */ | |
1314 | static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item, | |
1315 | struct page *page, | |
1316 | struct rmap_item *tree_rmap_item, | |
1317 | struct page *tree_page) | |
1318 | { | |
1319 | int err; | |
1320 | ||
1321 | err = try_to_merge_with_ksm_page(rmap_item, page, NULL); | |
1322 | if (!err) { | |
1323 | err = try_to_merge_with_ksm_page(tree_rmap_item, | |
1324 | tree_page, page); | |
1325 | /* | |
1326 | * If that fails, we have a ksm page with only one pte | |
1327 | * pointing to it: so break it. | |
1328 | */ | |
1329 | if (err) | |
1330 | break_cow(rmap_item); | |
1331 | } | |
1332 | return err ? NULL : page; | |
1333 | } | |
1334 | ||
1335 | static __always_inline | |
1336 | bool __is_page_sharing_candidate(struct stable_node *stable_node, int offset) | |
1337 | { | |
1338 | VM_BUG_ON(stable_node->rmap_hlist_len < 0); | |
1339 | /* | |
1340 | * Check that at least one mapping still exists, otherwise | |
1341 | * there's no much point to merge and share with this | |
1342 | * stable_node, as the underlying tree_page of the other | |
1343 | * sharer is going to be freed soon. | |
1344 | */ | |
1345 | return stable_node->rmap_hlist_len && | |
1346 | stable_node->rmap_hlist_len + offset < ksm_max_page_sharing; | |
1347 | } | |
1348 | ||
1349 | static __always_inline | |
1350 | bool is_page_sharing_candidate(struct stable_node *stable_node) | |
1351 | { | |
1352 | return __is_page_sharing_candidate(stable_node, 0); | |
1353 | } | |
1354 | ||
1355 | static struct page *stable_node_dup(struct stable_node **_stable_node_dup, | |
1356 | struct stable_node **_stable_node, | |
1357 | struct rb_root *root, | |
1358 | bool prune_stale_stable_nodes) | |
1359 | { | |
1360 | struct stable_node *dup, *found = NULL, *stable_node = *_stable_node; | |
1361 | struct hlist_node *hlist_safe; | |
1362 | struct page *_tree_page, *tree_page = NULL; | |
1363 | int nr = 0; | |
1364 | int found_rmap_hlist_len; | |
1365 | ||
1366 | if (!prune_stale_stable_nodes || | |
1367 | time_before(jiffies, stable_node->chain_prune_time + | |
1368 | msecs_to_jiffies( | |
1369 | ksm_stable_node_chains_prune_millisecs))) | |
1370 | prune_stale_stable_nodes = false; | |
1371 | else | |
1372 | stable_node->chain_prune_time = jiffies; | |
1373 | ||
1374 | hlist_for_each_entry_safe(dup, hlist_safe, | |
1375 | &stable_node->hlist, hlist_dup) { | |
1376 | cond_resched(); | |
1377 | /* | |
1378 | * We must walk all stable_node_dup to prune the stale | |
1379 | * stable nodes during lookup. | |
1380 | * | |
1381 | * get_ksm_page can drop the nodes from the | |
1382 | * stable_node->hlist if they point to freed pages | |
1383 | * (that's why we do a _safe walk). The "dup" | |
1384 | * stable_node parameter itself will be freed from | |
1385 | * under us if it returns NULL. | |
1386 | */ | |
1387 | _tree_page = get_ksm_page(dup, GET_KSM_PAGE_NOLOCK); | |
1388 | if (!_tree_page) | |
1389 | continue; | |
1390 | nr += 1; | |
1391 | if (is_page_sharing_candidate(dup)) { | |
1392 | if (!found || | |
1393 | dup->rmap_hlist_len > found_rmap_hlist_len) { | |
1394 | if (found) | |
1395 | put_page(tree_page); | |
1396 | found = dup; | |
1397 | found_rmap_hlist_len = found->rmap_hlist_len; | |
1398 | tree_page = _tree_page; | |
1399 | ||
1400 | /* skip put_page for found dup */ | |
1401 | if (!prune_stale_stable_nodes) | |
1402 | break; | |
1403 | continue; | |
1404 | } | |
1405 | } | |
1406 | put_page(_tree_page); | |
1407 | } | |
1408 | ||
1409 | if (found) { | |
1410 | /* | |
1411 | * nr is counting all dups in the chain only if | |
1412 | * prune_stale_stable_nodes is true, otherwise we may | |
1413 | * break the loop at nr == 1 even if there are | |
1414 | * multiple entries. | |
1415 | */ | |
1416 | if (prune_stale_stable_nodes && nr == 1) { | |
1417 | /* | |
1418 | * If there's not just one entry it would | |
1419 | * corrupt memory, better BUG_ON. In KSM | |
1420 | * context with no lock held it's not even | |
1421 | * fatal. | |
1422 | */ | |
1423 | BUG_ON(stable_node->hlist.first->next); | |
1424 | ||
1425 | /* | |
1426 | * There's just one entry and it is below the | |
1427 | * deduplication limit so drop the chain. | |
1428 | */ | |
1429 | rb_replace_node(&stable_node->node, &found->node, | |
1430 | root); | |
1431 | free_stable_node(stable_node); | |
1432 | ksm_stable_node_chains--; | |
1433 | ksm_stable_node_dups--; | |
1434 | /* | |
1435 | * NOTE: the caller depends on the stable_node | |
1436 | * to be equal to stable_node_dup if the chain | |
1437 | * was collapsed. | |
1438 | */ | |
1439 | *_stable_node = found; | |
1440 | /* | |
1441 | * Just for robustneess as stable_node is | |
1442 | * otherwise left as a stable pointer, the | |
1443 | * compiler shall optimize it away at build | |
1444 | * time. | |
1445 | */ | |
1446 | stable_node = NULL; | |
1447 | } else if (stable_node->hlist.first != &found->hlist_dup && | |
1448 | __is_page_sharing_candidate(found, 1)) { | |
1449 | /* | |
1450 | * If the found stable_node dup can accept one | |
1451 | * more future merge (in addition to the one | |
1452 | * that is underway) and is not at the head of | |
1453 | * the chain, put it there so next search will | |
1454 | * be quicker in the !prune_stale_stable_nodes | |
1455 | * case. | |
1456 | * | |
1457 | * NOTE: it would be inaccurate to use nr > 1 | |
1458 | * instead of checking the hlist.first pointer | |
1459 | * directly, because in the | |
1460 | * prune_stale_stable_nodes case "nr" isn't | |
1461 | * the position of the found dup in the chain, | |
1462 | * but the total number of dups in the chain. | |
1463 | */ | |
1464 | hlist_del(&found->hlist_dup); | |
1465 | hlist_add_head(&found->hlist_dup, | |
1466 | &stable_node->hlist); | |
1467 | } | |
1468 | } | |
1469 | ||
1470 | *_stable_node_dup = found; | |
1471 | return tree_page; | |
1472 | } | |
1473 | ||
1474 | static struct stable_node *stable_node_dup_any(struct stable_node *stable_node, | |
1475 | struct rb_root *root) | |
1476 | { | |
1477 | if (!is_stable_node_chain(stable_node)) | |
1478 | return stable_node; | |
1479 | if (hlist_empty(&stable_node->hlist)) { | |
1480 | free_stable_node_chain(stable_node, root); | |
1481 | return NULL; | |
1482 | } | |
1483 | return hlist_entry(stable_node->hlist.first, | |
1484 | typeof(*stable_node), hlist_dup); | |
1485 | } | |
1486 | ||
1487 | /* | |
1488 | * Like for get_ksm_page, this function can free the *_stable_node and | |
1489 | * *_stable_node_dup if the returned tree_page is NULL. | |
1490 | * | |
1491 | * It can also free and overwrite *_stable_node with the found | |
1492 | * stable_node_dup if the chain is collapsed (in which case | |
1493 | * *_stable_node will be equal to *_stable_node_dup like if the chain | |
1494 | * never existed). It's up to the caller to verify tree_page is not | |
1495 | * NULL before dereferencing *_stable_node or *_stable_node_dup. | |
1496 | * | |
1497 | * *_stable_node_dup is really a second output parameter of this | |
1498 | * function and will be overwritten in all cases, the caller doesn't | |
1499 | * need to initialize it. | |
1500 | */ | |
1501 | static struct page *__stable_node_chain(struct stable_node **_stable_node_dup, | |
1502 | struct stable_node **_stable_node, | |
1503 | struct rb_root *root, | |
1504 | bool prune_stale_stable_nodes) | |
1505 | { | |
1506 | struct stable_node *stable_node = *_stable_node; | |
1507 | if (!is_stable_node_chain(stable_node)) { | |
1508 | if (is_page_sharing_candidate(stable_node)) { | |
1509 | *_stable_node_dup = stable_node; | |
1510 | return get_ksm_page(stable_node, GET_KSM_PAGE_NOLOCK); | |
1511 | } | |
1512 | /* | |
1513 | * _stable_node_dup set to NULL means the stable_node | |
1514 | * reached the ksm_max_page_sharing limit. | |
1515 | */ | |
1516 | *_stable_node_dup = NULL; | |
1517 | return NULL; | |
1518 | } | |
1519 | return stable_node_dup(_stable_node_dup, _stable_node, root, | |
1520 | prune_stale_stable_nodes); | |
1521 | } | |
1522 | ||
1523 | static __always_inline struct page *chain_prune(struct stable_node **s_n_d, | |
1524 | struct stable_node **s_n, | |
1525 | struct rb_root *root) | |
1526 | { | |
1527 | return __stable_node_chain(s_n_d, s_n, root, true); | |
1528 | } | |
1529 | ||
1530 | static __always_inline struct page *chain(struct stable_node **s_n_d, | |
1531 | struct stable_node *s_n, | |
1532 | struct rb_root *root) | |
1533 | { | |
1534 | struct stable_node *old_stable_node = s_n; | |
1535 | struct page *tree_page; | |
1536 | ||
1537 | tree_page = __stable_node_chain(s_n_d, &s_n, root, false); | |
1538 | /* not pruning dups so s_n cannot have changed */ | |
1539 | VM_BUG_ON(s_n != old_stable_node); | |
1540 | return tree_page; | |
1541 | } | |
1542 | ||
1543 | /* | |
1544 | * stable_tree_search - search for page inside the stable tree | |
1545 | * | |
1546 | * This function checks if there is a page inside the stable tree | |
1547 | * with identical content to the page that we are scanning right now. | |
1548 | * | |
1549 | * This function returns the stable tree node of identical content if found, | |
1550 | * NULL otherwise. | |
1551 | */ | |
1552 | static struct page *stable_tree_search(struct page *page) | |
1553 | { | |
1554 | int nid; | |
1555 | struct rb_root *root; | |
1556 | struct rb_node **new; | |
1557 | struct rb_node *parent; | |
1558 | struct stable_node *stable_node, *stable_node_dup, *stable_node_any; | |
1559 | struct stable_node *page_node; | |
1560 | ||
1561 | page_node = page_stable_node(page); | |
1562 | if (page_node && page_node->head != &migrate_nodes) { | |
1563 | /* ksm page forked */ | |
1564 | get_page(page); | |
1565 | return page; | |
1566 | } | |
1567 | ||
1568 | nid = get_kpfn_nid(page_to_pfn(page)); | |
1569 | root = root_stable_tree + nid; | |
1570 | again: | |
1571 | new = &root->rb_node; | |
1572 | parent = NULL; | |
1573 | ||
1574 | while (*new) { | |
1575 | struct page *tree_page; | |
1576 | int ret; | |
1577 | ||
1578 | cond_resched(); | |
1579 | stable_node = rb_entry(*new, struct stable_node, node); | |
1580 | stable_node_any = NULL; | |
1581 | tree_page = chain_prune(&stable_node_dup, &stable_node, root); | |
1582 | /* | |
1583 | * NOTE: stable_node may have been freed by | |
1584 | * chain_prune() if the returned stable_node_dup is | |
1585 | * not NULL. stable_node_dup may have been inserted in | |
1586 | * the rbtree instead as a regular stable_node (in | |
1587 | * order to collapse the stable_node chain if a single | |
1588 | * stable_node dup was found in it). In such case the | |
1589 | * stable_node is overwritten by the calleee to point | |
1590 | * to the stable_node_dup that was collapsed in the | |
1591 | * stable rbtree and stable_node will be equal to | |
1592 | * stable_node_dup like if the chain never existed. | |
1593 | */ | |
1594 | if (!stable_node_dup) { | |
1595 | /* | |
1596 | * Either all stable_node dups were full in | |
1597 | * this stable_node chain, or this chain was | |
1598 | * empty and should be rb_erased. | |
1599 | */ | |
1600 | stable_node_any = stable_node_dup_any(stable_node, | |
1601 | root); | |
1602 | if (!stable_node_any) { | |
1603 | /* rb_erase just run */ | |
1604 | goto again; | |
1605 | } | |
1606 | /* | |
1607 | * Take any of the stable_node dups page of | |
1608 | * this stable_node chain to let the tree walk | |
1609 | * continue. All KSM pages belonging to the | |
1610 | * stable_node dups in a stable_node chain | |
1611 | * have the same content and they're | |
1612 | * write protected at all times. Any will work | |
1613 | * fine to continue the walk. | |
1614 | */ | |
1615 | tree_page = get_ksm_page(stable_node_any, | |
1616 | GET_KSM_PAGE_NOLOCK); | |
1617 | } | |
1618 | VM_BUG_ON(!stable_node_dup ^ !!stable_node_any); | |
1619 | if (!tree_page) { | |
1620 | /* | |
1621 | * If we walked over a stale stable_node, | |
1622 | * get_ksm_page() will call rb_erase() and it | |
1623 | * may rebalance the tree from under us. So | |
1624 | * restart the search from scratch. Returning | |
1625 | * NULL would be safe too, but we'd generate | |
1626 | * false negative insertions just because some | |
1627 | * stable_node was stale. | |
1628 | */ | |
1629 | goto again; | |
1630 | } | |
1631 | ||
1632 | ret = memcmp_pages(page, tree_page); | |
1633 | put_page(tree_page); | |
1634 | ||
1635 | parent = *new; | |
1636 | if (ret < 0) | |
1637 | new = &parent->rb_left; | |
1638 | else if (ret > 0) | |
1639 | new = &parent->rb_right; | |
1640 | else { | |
1641 | if (page_node) { | |
1642 | VM_BUG_ON(page_node->head != &migrate_nodes); | |
1643 | /* | |
1644 | * Test if the migrated page should be merged | |
1645 | * into a stable node dup. If the mapcount is | |
1646 | * 1 we can migrate it with another KSM page | |
1647 | * without adding it to the chain. | |
1648 | */ | |
1649 | if (page_mapcount(page) > 1) | |
1650 | goto chain_append; | |
1651 | } | |
1652 | ||
1653 | if (!stable_node_dup) { | |
1654 | /* | |
1655 | * If the stable_node is a chain and | |
1656 | * we got a payload match in memcmp | |
1657 | * but we cannot merge the scanned | |
1658 | * page in any of the existing | |
1659 | * stable_node dups because they're | |
1660 | * all full, we need to wait the | |
1661 | * scanned page to find itself a match | |
1662 | * in the unstable tree to create a | |
1663 | * brand new KSM page to add later to | |
1664 | * the dups of this stable_node. | |
1665 | */ | |
1666 | return NULL; | |
1667 | } | |
1668 | ||
1669 | /* | |
1670 | * Lock and unlock the stable_node's page (which | |
1671 | * might already have been migrated) so that page | |
1672 | * migration is sure to notice its raised count. | |
1673 | * It would be more elegant to return stable_node | |
1674 | * than kpage, but that involves more changes. | |
1675 | */ | |
1676 | tree_page = get_ksm_page(stable_node_dup, | |
1677 | GET_KSM_PAGE_TRYLOCK); | |
1678 | ||
1679 | if (PTR_ERR(tree_page) == -EBUSY) | |
1680 | return ERR_PTR(-EBUSY); | |
1681 | ||
1682 | if (unlikely(!tree_page)) | |
1683 | /* | |
1684 | * The tree may have been rebalanced, | |
1685 | * so re-evaluate parent and new. | |
1686 | */ | |
1687 | goto again; | |
1688 | unlock_page(tree_page); | |
1689 | ||
1690 | if (get_kpfn_nid(stable_node_dup->kpfn) != | |
1691 | NUMA(stable_node_dup->nid)) { | |
1692 | put_page(tree_page); | |
1693 | goto replace; | |
1694 | } | |
1695 | return tree_page; | |
1696 | } | |
1697 | } | |
1698 | ||
1699 | if (!page_node) | |
1700 | return NULL; | |
1701 | ||
1702 | list_del(&page_node->list); | |
1703 | DO_NUMA(page_node->nid = nid); | |
1704 | rb_link_node(&page_node->node, parent, new); | |
1705 | rb_insert_color(&page_node->node, root); | |
1706 | out: | |
1707 | if (is_page_sharing_candidate(page_node)) { | |
1708 | get_page(page); | |
1709 | return page; | |
1710 | } else | |
1711 | return NULL; | |
1712 | ||
1713 | replace: | |
1714 | /* | |
1715 | * If stable_node was a chain and chain_prune collapsed it, | |
1716 | * stable_node has been updated to be the new regular | |
1717 | * stable_node. A collapse of the chain is indistinguishable | |
1718 | * from the case there was no chain in the stable | |
1719 | * rbtree. Otherwise stable_node is the chain and | |
1720 | * stable_node_dup is the dup to replace. | |
1721 | */ | |
1722 | if (stable_node_dup == stable_node) { | |
1723 | VM_BUG_ON(is_stable_node_chain(stable_node_dup)); | |
1724 | VM_BUG_ON(is_stable_node_dup(stable_node_dup)); | |
1725 | /* there is no chain */ | |
1726 | if (page_node) { | |
1727 | VM_BUG_ON(page_node->head != &migrate_nodes); | |
1728 | list_del(&page_node->list); | |
1729 | DO_NUMA(page_node->nid = nid); | |
1730 | rb_replace_node(&stable_node_dup->node, | |
1731 | &page_node->node, | |
1732 | root); | |
1733 | if (is_page_sharing_candidate(page_node)) | |
1734 | get_page(page); | |
1735 | else | |
1736 | page = NULL; | |
1737 | } else { | |
1738 | rb_erase(&stable_node_dup->node, root); | |
1739 | page = NULL; | |
1740 | } | |
1741 | } else { | |
1742 | VM_BUG_ON(!is_stable_node_chain(stable_node)); | |
1743 | __stable_node_dup_del(stable_node_dup); | |
1744 | if (page_node) { | |
1745 | VM_BUG_ON(page_node->head != &migrate_nodes); | |
1746 | list_del(&page_node->list); | |
1747 | DO_NUMA(page_node->nid = nid); | |
1748 | stable_node_chain_add_dup(page_node, stable_node); | |
1749 | if (is_page_sharing_candidate(page_node)) | |
1750 | get_page(page); | |
1751 | else | |
1752 | page = NULL; | |
1753 | } else { | |
1754 | page = NULL; | |
1755 | } | |
1756 | } | |
1757 | stable_node_dup->head = &migrate_nodes; | |
1758 | list_add(&stable_node_dup->list, stable_node_dup->head); | |
1759 | return page; | |
1760 | ||
1761 | chain_append: | |
1762 | /* stable_node_dup could be null if it reached the limit */ | |
1763 | if (!stable_node_dup) | |
1764 | stable_node_dup = stable_node_any; | |
1765 | /* | |
1766 | * If stable_node was a chain and chain_prune collapsed it, | |
1767 | * stable_node has been updated to be the new regular | |
1768 | * stable_node. A collapse of the chain is indistinguishable | |
1769 | * from the case there was no chain in the stable | |
1770 | * rbtree. Otherwise stable_node is the chain and | |
1771 | * stable_node_dup is the dup to replace. | |
1772 | */ | |
1773 | if (stable_node_dup == stable_node) { | |
1774 | VM_BUG_ON(is_stable_node_chain(stable_node_dup)); | |
1775 | VM_BUG_ON(is_stable_node_dup(stable_node_dup)); | |
1776 | /* chain is missing so create it */ | |
1777 | stable_node = alloc_stable_node_chain(stable_node_dup, | |
1778 | root); | |
1779 | if (!stable_node) | |
1780 | return NULL; | |
1781 | } | |
1782 | /* | |
1783 | * Add this stable_node dup that was | |
1784 | * migrated to the stable_node chain | |
1785 | * of the current nid for this page | |
1786 | * content. | |
1787 | */ | |
1788 | VM_BUG_ON(!is_stable_node_chain(stable_node)); | |
1789 | VM_BUG_ON(!is_stable_node_dup(stable_node_dup)); | |
1790 | VM_BUG_ON(page_node->head != &migrate_nodes); | |
1791 | list_del(&page_node->list); | |
1792 | DO_NUMA(page_node->nid = nid); | |
1793 | stable_node_chain_add_dup(page_node, stable_node); | |
1794 | goto out; | |
1795 | } | |
1796 | ||
1797 | /* | |
1798 | * stable_tree_insert - insert stable tree node pointing to new ksm page | |
1799 | * into the stable tree. | |
1800 | * | |
1801 | * This function returns the stable tree node just allocated on success, | |
1802 | * NULL otherwise. | |
1803 | */ | |
1804 | static struct stable_node *stable_tree_insert(struct page *kpage) | |
1805 | { | |
1806 | int nid; | |
1807 | unsigned long kpfn; | |
1808 | struct rb_root *root; | |
1809 | struct rb_node **new; | |
1810 | struct rb_node *parent; | |
1811 | struct stable_node *stable_node, *stable_node_dup, *stable_node_any; | |
1812 | bool need_chain = false; | |
1813 | ||
1814 | kpfn = page_to_pfn(kpage); | |
1815 | nid = get_kpfn_nid(kpfn); | |
1816 | root = root_stable_tree + nid; | |
1817 | again: | |
1818 | parent = NULL; | |
1819 | new = &root->rb_node; | |
1820 | ||
1821 | while (*new) { | |
1822 | struct page *tree_page; | |
1823 | int ret; | |
1824 | ||
1825 | cond_resched(); | |
1826 | stable_node = rb_entry(*new, struct stable_node, node); | |
1827 | stable_node_any = NULL; | |
1828 | tree_page = chain(&stable_node_dup, stable_node, root); | |
1829 | if (!stable_node_dup) { | |
1830 | /* | |
1831 | * Either all stable_node dups were full in | |
1832 | * this stable_node chain, or this chain was | |
1833 | * empty and should be rb_erased. | |
1834 | */ | |
1835 | stable_node_any = stable_node_dup_any(stable_node, | |
1836 | root); | |
1837 | if (!stable_node_any) { | |
1838 | /* rb_erase just run */ | |
1839 | goto again; | |
1840 | } | |
1841 | /* | |
1842 | * Take any of the stable_node dups page of | |
1843 | * this stable_node chain to let the tree walk | |
1844 | * continue. All KSM pages belonging to the | |
1845 | * stable_node dups in a stable_node chain | |
1846 | * have the same content and they're | |
1847 | * write protected at all times. Any will work | |
1848 | * fine to continue the walk. | |
1849 | */ | |
1850 | tree_page = get_ksm_page(stable_node_any, | |
1851 | GET_KSM_PAGE_NOLOCK); | |
1852 | } | |
1853 | VM_BUG_ON(!stable_node_dup ^ !!stable_node_any); | |
1854 | if (!tree_page) { | |
1855 | /* | |
1856 | * If we walked over a stale stable_node, | |
1857 | * get_ksm_page() will call rb_erase() and it | |
1858 | * may rebalance the tree from under us. So | |
1859 | * restart the search from scratch. Returning | |
1860 | * NULL would be safe too, but we'd generate | |
1861 | * false negative insertions just because some | |
1862 | * stable_node was stale. | |
1863 | */ | |
1864 | goto again; | |
1865 | } | |
1866 | ||
1867 | ret = memcmp_pages(kpage, tree_page); | |
1868 | put_page(tree_page); | |
1869 | ||
1870 | parent = *new; | |
1871 | if (ret < 0) | |
1872 | new = &parent->rb_left; | |
1873 | else if (ret > 0) | |
1874 | new = &parent->rb_right; | |
1875 | else { | |
1876 | need_chain = true; | |
1877 | break; | |
1878 | } | |
1879 | } | |
1880 | ||
1881 | stable_node_dup = alloc_stable_node(); | |
1882 | if (!stable_node_dup) | |
1883 | return NULL; | |
1884 | ||
1885 | INIT_HLIST_HEAD(&stable_node_dup->hlist); | |
1886 | stable_node_dup->kpfn = kpfn; | |
1887 | set_page_stable_node(kpage, stable_node_dup); | |
1888 | stable_node_dup->rmap_hlist_len = 0; | |
1889 | DO_NUMA(stable_node_dup->nid = nid); | |
1890 | if (!need_chain) { | |
1891 | rb_link_node(&stable_node_dup->node, parent, new); | |
1892 | rb_insert_color(&stable_node_dup->node, root); | |
1893 | } else { | |
1894 | if (!is_stable_node_chain(stable_node)) { | |
1895 | struct stable_node *orig = stable_node; | |
1896 | /* chain is missing so create it */ | |
1897 | stable_node = alloc_stable_node_chain(orig, root); | |
1898 | if (!stable_node) { | |
1899 | free_stable_node(stable_node_dup); | |
1900 | return NULL; | |
1901 | } | |
1902 | } | |
1903 | stable_node_chain_add_dup(stable_node_dup, stable_node); | |
1904 | } | |
1905 | ||
1906 | return stable_node_dup; | |
1907 | } | |
1908 | ||
1909 | /* | |
1910 | * unstable_tree_search_insert - search for identical page, | |
1911 | * else insert rmap_item into the unstable tree. | |
1912 | * | |
1913 | * This function searches for a page in the unstable tree identical to the | |
1914 | * page currently being scanned; and if no identical page is found in the | |
1915 | * tree, we insert rmap_item as a new object into the unstable tree. | |
1916 | * | |
1917 | * This function returns pointer to rmap_item found to be identical | |
1918 | * to the currently scanned page, NULL otherwise. | |
1919 | * | |
1920 | * This function does both searching and inserting, because they share | |
1921 | * the same walking algorithm in an rbtree. | |
1922 | */ | |
1923 | static | |
1924 | struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item, | |
1925 | struct page *page, | |
1926 | struct page **tree_pagep) | |
1927 | { | |
1928 | struct rb_node **new; | |
1929 | struct rb_root *root; | |
1930 | struct rb_node *parent = NULL; | |
1931 | int nid; | |
1932 | ||
1933 | nid = get_kpfn_nid(page_to_pfn(page)); | |
1934 | root = root_unstable_tree + nid; | |
1935 | new = &root->rb_node; | |
1936 | ||
1937 | while (*new) { | |
1938 | struct rmap_item *tree_rmap_item; | |
1939 | struct page *tree_page; | |
1940 | int ret; | |
1941 | ||
1942 | cond_resched(); | |
1943 | tree_rmap_item = rb_entry(*new, struct rmap_item, node); | |
1944 | tree_page = get_mergeable_page(tree_rmap_item); | |
1945 | if (!tree_page) | |
1946 | return NULL; | |
1947 | ||
1948 | /* | |
1949 | * Don't substitute a ksm page for a forked page. | |
1950 | */ | |
1951 | if (page == tree_page) { | |
1952 | put_page(tree_page); | |
1953 | return NULL; | |
1954 | } | |
1955 | ||
1956 | ret = memcmp_pages(page, tree_page); | |
1957 | ||
1958 | parent = *new; | |
1959 | if (ret < 0) { | |
1960 | put_page(tree_page); | |
1961 | new = &parent->rb_left; | |
1962 | } else if (ret > 0) { | |
1963 | put_page(tree_page); | |
1964 | new = &parent->rb_right; | |
1965 | } else if (!ksm_merge_across_nodes && | |
1966 | page_to_nid(tree_page) != nid) { | |
1967 | /* | |
1968 | * If tree_page has been migrated to another NUMA node, | |
1969 | * it will be flushed out and put in the right unstable | |
1970 | * tree next time: only merge with it when across_nodes. | |
1971 | */ | |
1972 | put_page(tree_page); | |
1973 | return NULL; | |
1974 | } else { | |
1975 | *tree_pagep = tree_page; | |
1976 | return tree_rmap_item; | |
1977 | } | |
1978 | } | |
1979 | ||
1980 | rmap_item->address |= UNSTABLE_FLAG; | |
1981 | rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK); | |
1982 | DO_NUMA(rmap_item->nid = nid); | |
1983 | rb_link_node(&rmap_item->node, parent, new); | |
1984 | rb_insert_color(&rmap_item->node, root); | |
1985 | ||
1986 | ksm_pages_unshared++; | |
1987 | return NULL; | |
1988 | } | |
1989 | ||
1990 | /* | |
1991 | * stable_tree_append - add another rmap_item to the linked list of | |
1992 | * rmap_items hanging off a given node of the stable tree, all sharing | |
1993 | * the same ksm page. | |
1994 | */ | |
1995 | static void stable_tree_append(struct rmap_item *rmap_item, | |
1996 | struct stable_node *stable_node, | |
1997 | bool max_page_sharing_bypass) | |
1998 | { | |
1999 | /* | |
2000 | * rmap won't find this mapping if we don't insert the | |
2001 | * rmap_item in the right stable_node | |
2002 | * duplicate. page_migration could break later if rmap breaks, | |
2003 | * so we can as well crash here. We really need to check for | |
2004 | * rmap_hlist_len == STABLE_NODE_CHAIN, but we can as well check | |
2005 | * for other negative values as an underflow if detected here | |
2006 | * for the first time (and not when decreasing rmap_hlist_len) | |
2007 | * would be sign of memory corruption in the stable_node. | |
2008 | */ | |
2009 | BUG_ON(stable_node->rmap_hlist_len < 0); | |
2010 | ||
2011 | stable_node->rmap_hlist_len++; | |
2012 | if (!max_page_sharing_bypass) | |
2013 | /* possibly non fatal but unexpected overflow, only warn */ | |
2014 | WARN_ON_ONCE(stable_node->rmap_hlist_len > | |
2015 | ksm_max_page_sharing); | |
2016 | ||
2017 | rmap_item->head = stable_node; | |
2018 | rmap_item->address |= STABLE_FLAG; | |
2019 | hlist_add_head(&rmap_item->hlist, &stable_node->hlist); | |
2020 | ||
2021 | if (rmap_item->hlist.next) | |
2022 | ksm_pages_sharing++; | |
2023 | else | |
2024 | ksm_pages_shared++; | |
2025 | } | |
2026 | ||
2027 | /* | |
2028 | * cmp_and_merge_page - first see if page can be merged into the stable tree; | |
2029 | * if not, compare checksum to previous and if it's the same, see if page can | |
2030 | * be inserted into the unstable tree, or merged with a page already there and | |
2031 | * both transferred to the stable tree. | |
2032 | * | |
2033 | * @page: the page that we are searching identical page to. | |
2034 | * @rmap_item: the reverse mapping into the virtual address of this page | |
2035 | */ | |
2036 | static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item) | |
2037 | { | |
2038 | struct mm_struct *mm = rmap_item->mm; | |
2039 | struct rmap_item *tree_rmap_item; | |
2040 | struct page *tree_page = NULL; | |
2041 | struct stable_node *stable_node; | |
2042 | struct page *kpage; | |
2043 | unsigned int checksum; | |
2044 | int err; | |
2045 | bool max_page_sharing_bypass = false; | |
2046 | ||
2047 | stable_node = page_stable_node(page); | |
2048 | if (stable_node) { | |
2049 | if (stable_node->head != &migrate_nodes && | |
2050 | get_kpfn_nid(READ_ONCE(stable_node->kpfn)) != | |
2051 | NUMA(stable_node->nid)) { | |
2052 | stable_node_dup_del(stable_node); | |
2053 | stable_node->head = &migrate_nodes; | |
2054 | list_add(&stable_node->list, stable_node->head); | |
2055 | } | |
2056 | if (stable_node->head != &migrate_nodes && | |
2057 | rmap_item->head == stable_node) | |
2058 | return; | |
2059 | /* | |
2060 | * If it's a KSM fork, allow it to go over the sharing limit | |
2061 | * without warnings. | |
2062 | */ | |
2063 | if (!is_page_sharing_candidate(stable_node)) | |
2064 | max_page_sharing_bypass = true; | |
2065 | } | |
2066 | ||
2067 | /* We first start with searching the page inside the stable tree */ | |
2068 | kpage = stable_tree_search(page); | |
2069 | if (kpage == page && rmap_item->head == stable_node) { | |
2070 | put_page(kpage); | |
2071 | return; | |
2072 | } | |
2073 | ||
2074 | remove_rmap_item_from_tree(rmap_item); | |
2075 | ||
2076 | if (kpage) { | |
2077 | if (PTR_ERR(kpage) == -EBUSY) | |
2078 | return; | |
2079 | ||
2080 | err = try_to_merge_with_ksm_page(rmap_item, page, kpage); | |
2081 | if (!err) { | |
2082 | /* | |
2083 | * The page was successfully merged: | |
2084 | * add its rmap_item to the stable tree. | |
2085 | */ | |
2086 | lock_page(kpage); | |
2087 | stable_tree_append(rmap_item, page_stable_node(kpage), | |
2088 | max_page_sharing_bypass); | |
2089 | unlock_page(kpage); | |
2090 | } | |
2091 | put_page(kpage); | |
2092 | return; | |
2093 | } | |
2094 | ||
2095 | /* | |
2096 | * If the hash value of the page has changed from the last time | |
2097 | * we calculated it, this page is changing frequently: therefore we | |
2098 | * don't want to insert it in the unstable tree, and we don't want | |
2099 | * to waste our time searching for something identical to it there. | |
2100 | */ | |
2101 | checksum = calc_checksum(page); | |
2102 | if (rmap_item->oldchecksum != checksum) { | |
2103 | rmap_item->oldchecksum = checksum; | |
2104 | return; | |
2105 | } | |
2106 | ||
2107 | /* | |
2108 | * Same checksum as an empty page. We attempt to merge it with the | |
2109 | * appropriate zero page if the user enabled this via sysfs. | |
2110 | */ | |
2111 | if (ksm_use_zero_pages && (checksum == zero_checksum)) { | |
2112 | struct vm_area_struct *vma; | |
2113 | ||
2114 | mmap_read_lock(mm); | |
2115 | vma = find_mergeable_vma(mm, rmap_item->address); | |
2116 | if (vma) { | |
2117 | err = try_to_merge_one_page(vma, page, | |
2118 | ZERO_PAGE(rmap_item->address)); | |
2119 | } else { | |
2120 | /* | |
2121 | * If the vma is out of date, we do not need to | |
2122 | * continue. | |
2123 | */ | |
2124 | err = 0; | |
2125 | } | |
2126 | mmap_read_unlock(mm); | |
2127 | /* | |
2128 | * In case of failure, the page was not really empty, so we | |
2129 | * need to continue. Otherwise we're done. | |
2130 | */ | |
2131 | if (!err) | |
2132 | return; | |
2133 | } | |
2134 | tree_rmap_item = | |
2135 | unstable_tree_search_insert(rmap_item, page, &tree_page); | |
2136 | if (tree_rmap_item) { | |
2137 | bool split; | |
2138 | ||
2139 | kpage = try_to_merge_two_pages(rmap_item, page, | |
2140 | tree_rmap_item, tree_page); | |
2141 | /* | |
2142 | * If both pages we tried to merge belong to the same compound | |
2143 | * page, then we actually ended up increasing the reference | |
2144 | * count of the same compound page twice, and split_huge_page | |
2145 | * failed. | |
2146 | * Here we set a flag if that happened, and we use it later to | |
2147 | * try split_huge_page again. Since we call put_page right | |
2148 | * afterwards, the reference count will be correct and | |
2149 | * split_huge_page should succeed. | |
2150 | */ | |
2151 | split = PageTransCompound(page) | |
2152 | && compound_head(page) == compound_head(tree_page); | |
2153 | put_page(tree_page); | |
2154 | if (kpage) { | |
2155 | /* | |
2156 | * The pages were successfully merged: insert new | |
2157 | * node in the stable tree and add both rmap_items. | |
2158 | */ | |
2159 | lock_page(kpage); | |
2160 | stable_node = stable_tree_insert(kpage); | |
2161 | if (stable_node) { | |
2162 | stable_tree_append(tree_rmap_item, stable_node, | |
2163 | false); | |
2164 | stable_tree_append(rmap_item, stable_node, | |
2165 | false); | |
2166 | } | |
2167 | unlock_page(kpage); | |
2168 | ||
2169 | /* | |
2170 | * If we fail to insert the page into the stable tree, | |
2171 | * we will have 2 virtual addresses that are pointing | |
2172 | * to a ksm page left outside the stable tree, | |
2173 | * in which case we need to break_cow on both. | |
2174 | */ | |
2175 | if (!stable_node) { | |
2176 | break_cow(tree_rmap_item); | |
2177 | break_cow(rmap_item); | |
2178 | } | |
2179 | } else if (split) { | |
2180 | /* | |
2181 | * We are here if we tried to merge two pages and | |
2182 | * failed because they both belonged to the same | |
2183 | * compound page. We will split the page now, but no | |
2184 | * merging will take place. | |
2185 | * We do not want to add the cost of a full lock; if | |
2186 | * the page is locked, it is better to skip it and | |
2187 | * perhaps try again later. | |
2188 | */ | |
2189 | if (!trylock_page(page)) | |
2190 | return; | |
2191 | split_huge_page(page); | |
2192 | unlock_page(page); | |
2193 | } | |
2194 | } | |
2195 | } | |
2196 | ||
2197 | static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot, | |
2198 | struct rmap_item **rmap_list, | |
2199 | unsigned long addr) | |
2200 | { | |
2201 | struct rmap_item *rmap_item; | |
2202 | ||
2203 | while (*rmap_list) { | |
2204 | rmap_item = *rmap_list; | |
2205 | if ((rmap_item->address & PAGE_MASK) == addr) | |
2206 | return rmap_item; | |
2207 | if (rmap_item->address > addr) | |
2208 | break; | |
2209 | *rmap_list = rmap_item->rmap_list; | |
2210 | remove_rmap_item_from_tree(rmap_item); | |
2211 | free_rmap_item(rmap_item); | |
2212 | } | |
2213 | ||
2214 | rmap_item = alloc_rmap_item(); | |
2215 | if (rmap_item) { | |
2216 | /* It has already been zeroed */ | |
2217 | rmap_item->mm = mm_slot->mm; | |
2218 | rmap_item->address = addr; | |
2219 | rmap_item->rmap_list = *rmap_list; | |
2220 | *rmap_list = rmap_item; | |
2221 | } | |
2222 | return rmap_item; | |
2223 | } | |
2224 | ||
2225 | static struct rmap_item *scan_get_next_rmap_item(struct page **page) | |
2226 | { | |
2227 | struct mm_struct *mm; | |
2228 | struct mm_slot *slot; | |
2229 | struct vm_area_struct *vma; | |
2230 | struct rmap_item *rmap_item; | |
2231 | int nid; | |
2232 | ||
2233 | if (list_empty(&ksm_mm_head.mm_list)) | |
2234 | return NULL; | |
2235 | ||
2236 | slot = ksm_scan.mm_slot; | |
2237 | if (slot == &ksm_mm_head) { | |
2238 | /* | |
2239 | * A number of pages can hang around indefinitely on per-cpu | |
2240 | * pagevecs, raised page count preventing write_protect_page | |
2241 | * from merging them. Though it doesn't really matter much, | |
2242 | * it is puzzling to see some stuck in pages_volatile until | |
2243 | * other activity jostles them out, and they also prevented | |
2244 | * LTP's KSM test from succeeding deterministically; so drain | |
2245 | * them here (here rather than on entry to ksm_do_scan(), | |
2246 | * so we don't IPI too often when pages_to_scan is set low). | |
2247 | */ | |
2248 | lru_add_drain_all(); | |
2249 | ||
2250 | /* | |
2251 | * Whereas stale stable_nodes on the stable_tree itself | |
2252 | * get pruned in the regular course of stable_tree_search(), | |
2253 | * those moved out to the migrate_nodes list can accumulate: | |
2254 | * so prune them once before each full scan. | |
2255 | */ | |
2256 | if (!ksm_merge_across_nodes) { | |
2257 | struct stable_node *stable_node, *next; | |
2258 | struct page *page; | |
2259 | ||
2260 | list_for_each_entry_safe(stable_node, next, | |
2261 | &migrate_nodes, list) { | |
2262 | page = get_ksm_page(stable_node, | |
2263 | GET_KSM_PAGE_NOLOCK); | |
2264 | if (page) | |
2265 | put_page(page); | |
2266 | cond_resched(); | |
2267 | } | |
2268 | } | |
2269 | ||
2270 | for (nid = 0; nid < ksm_nr_node_ids; nid++) | |
2271 | root_unstable_tree[nid] = RB_ROOT; | |
2272 | ||
2273 | spin_lock(&ksm_mmlist_lock); | |
2274 | slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list); | |
2275 | ksm_scan.mm_slot = slot; | |
2276 | spin_unlock(&ksm_mmlist_lock); | |
2277 | /* | |
2278 | * Although we tested list_empty() above, a racing __ksm_exit | |
2279 | * of the last mm on the list may have removed it since then. | |
2280 | */ | |
2281 | if (slot == &ksm_mm_head) | |
2282 | return NULL; | |
2283 | next_mm: | |
2284 | ksm_scan.address = 0; | |
2285 | ksm_scan.rmap_list = &slot->rmap_list; | |
2286 | } | |
2287 | ||
2288 | mm = slot->mm; | |
2289 | mmap_read_lock(mm); | |
2290 | if (ksm_test_exit(mm)) | |
2291 | vma = NULL; | |
2292 | else | |
2293 | vma = find_vma(mm, ksm_scan.address); | |
2294 | ||
2295 | for (; vma; vma = vma->vm_next) { | |
2296 | if (!(vma->vm_flags & VM_MERGEABLE)) | |
2297 | continue; | |
2298 | if (ksm_scan.address < vma->vm_start) | |
2299 | ksm_scan.address = vma->vm_start; | |
2300 | if (!vma->anon_vma) | |
2301 | ksm_scan.address = vma->vm_end; | |
2302 | ||
2303 | while (ksm_scan.address < vma->vm_end) { | |
2304 | if (ksm_test_exit(mm)) | |
2305 | break; | |
2306 | *page = follow_page(vma, ksm_scan.address, FOLL_GET); | |
2307 | if (IS_ERR_OR_NULL(*page)) { | |
2308 | ksm_scan.address += PAGE_SIZE; | |
2309 | cond_resched(); | |
2310 | continue; | |
2311 | } | |
2312 | if (PageAnon(*page)) { | |
2313 | flush_anon_page(vma, *page, ksm_scan.address); | |
2314 | flush_dcache_page(*page); | |
2315 | rmap_item = get_next_rmap_item(slot, | |
2316 | ksm_scan.rmap_list, ksm_scan.address); | |
2317 | if (rmap_item) { | |
2318 | ksm_scan.rmap_list = | |
2319 | &rmap_item->rmap_list; | |
2320 | ksm_scan.address += PAGE_SIZE; | |
2321 | } else | |
2322 | put_page(*page); | |
2323 | mmap_read_unlock(mm); | |
2324 | return rmap_item; | |
2325 | } | |
2326 | put_page(*page); | |
2327 | ksm_scan.address += PAGE_SIZE; | |
2328 | cond_resched(); | |
2329 | } | |
2330 | } | |
2331 | ||
2332 | if (ksm_test_exit(mm)) { | |
2333 | ksm_scan.address = 0; | |
2334 | ksm_scan.rmap_list = &slot->rmap_list; | |
2335 | } | |
2336 | /* | |
2337 | * Nuke all the rmap_items that are above this current rmap: | |
2338 | * because there were no VM_MERGEABLE vmas with such addresses. | |
2339 | */ | |
2340 | remove_trailing_rmap_items(slot, ksm_scan.rmap_list); | |
2341 | ||
2342 | spin_lock(&ksm_mmlist_lock); | |
2343 | ksm_scan.mm_slot = list_entry(slot->mm_list.next, | |
2344 | struct mm_slot, mm_list); | |
2345 | if (ksm_scan.address == 0) { | |
2346 | /* | |
2347 | * We've completed a full scan of all vmas, holding mmap_lock | |
2348 | * throughout, and found no VM_MERGEABLE: so do the same as | |
2349 | * __ksm_exit does to remove this mm from all our lists now. | |
2350 | * This applies either when cleaning up after __ksm_exit | |
2351 | * (but beware: we can reach here even before __ksm_exit), | |
2352 | * or when all VM_MERGEABLE areas have been unmapped (and | |
2353 | * mmap_lock then protects against race with MADV_MERGEABLE). | |
2354 | */ | |
2355 | hash_del(&slot->link); | |
2356 | list_del(&slot->mm_list); | |
2357 | spin_unlock(&ksm_mmlist_lock); | |
2358 | ||
2359 | free_mm_slot(slot); | |
2360 | clear_bit(MMF_VM_MERGEABLE, &mm->flags); | |
2361 | mmap_read_unlock(mm); | |
2362 | mmdrop(mm); | |
2363 | } else { | |
2364 | mmap_read_unlock(mm); | |
2365 | /* | |
2366 | * mmap_read_unlock(mm) first because after | |
2367 | * spin_unlock(&ksm_mmlist_lock) run, the "mm" may | |
2368 | * already have been freed under us by __ksm_exit() | |
2369 | * because the "mm_slot" is still hashed and | |
2370 | * ksm_scan.mm_slot doesn't point to it anymore. | |
2371 | */ | |
2372 | spin_unlock(&ksm_mmlist_lock); | |
2373 | } | |
2374 | ||
2375 | /* Repeat until we've completed scanning the whole list */ | |
2376 | slot = ksm_scan.mm_slot; | |
2377 | if (slot != &ksm_mm_head) | |
2378 | goto next_mm; | |
2379 | ||
2380 | ksm_scan.seqnr++; | |
2381 | return NULL; | |
2382 | } | |
2383 | ||
2384 | /** | |
2385 | * ksm_do_scan - the ksm scanner main worker function. | |
2386 | * @scan_npages: number of pages we want to scan before we return. | |
2387 | */ | |
2388 | static void ksm_do_scan(unsigned int scan_npages) | |
2389 | { | |
2390 | struct rmap_item *rmap_item; | |
2391 | struct page *page; | |
2392 | ||
2393 | while (scan_npages-- && likely(!freezing(current))) { | |
2394 | cond_resched(); | |
2395 | rmap_item = scan_get_next_rmap_item(&page); | |
2396 | if (!rmap_item) | |
2397 | return; | |
2398 | cmp_and_merge_page(page, rmap_item); | |
2399 | put_page(page); | |
2400 | } | |
2401 | } | |
2402 | ||
2403 | static int ksmd_should_run(void) | |
2404 | { | |
2405 | return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list); | |
2406 | } | |
2407 | ||
2408 | static int ksm_scan_thread(void *nothing) | |
2409 | { | |
2410 | unsigned int sleep_ms; | |
2411 | ||
2412 | set_freezable(); | |
2413 | set_user_nice(current, 5); | |
2414 | ||
2415 | while (!kthread_should_stop()) { | |
2416 | mutex_lock(&ksm_thread_mutex); | |
2417 | wait_while_offlining(); | |
2418 | if (ksmd_should_run()) | |
2419 | ksm_do_scan(ksm_thread_pages_to_scan); | |
2420 | mutex_unlock(&ksm_thread_mutex); | |
2421 | ||
2422 | try_to_freeze(); | |
2423 | ||
2424 | if (ksmd_should_run()) { | |
2425 | sleep_ms = READ_ONCE(ksm_thread_sleep_millisecs); | |
2426 | if (sleep_ms >= 1000) | |
2427 | wait_event_interruptible_timeout(ksm_iter_wait, | |
2428 | sleep_ms != READ_ONCE(ksm_thread_sleep_millisecs), | |
2429 | msecs_to_jiffies(round_jiffies_relative(sleep_ms))); | |
2430 | else | |
2431 | wait_event_interruptible_timeout(ksm_iter_wait, | |
2432 | sleep_ms != READ_ONCE(ksm_thread_sleep_millisecs), | |
2433 | msecs_to_jiffies(sleep_ms)); | |
2434 | } else { | |
2435 | wait_event_freezable(ksm_thread_wait, | |
2436 | ksmd_should_run() || kthread_should_stop()); | |
2437 | } | |
2438 | } | |
2439 | return 0; | |
2440 | } | |
2441 | ||
2442 | int ksm_madvise(struct vm_area_struct *vma, unsigned long start, | |
2443 | unsigned long end, int advice, unsigned long *vm_flags) | |
2444 | { | |
2445 | struct mm_struct *mm = vma->vm_mm; | |
2446 | int err; | |
2447 | ||
2448 | switch (advice) { | |
2449 | case MADV_MERGEABLE: | |
2450 | /* | |
2451 | * Be somewhat over-protective for now! | |
2452 | */ | |
2453 | if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE | | |
2454 | VM_PFNMAP | VM_IO | VM_DONTEXPAND | | |
2455 | VM_HUGETLB | VM_MIXEDMAP)) | |
2456 | return 0; /* just ignore the advice */ | |
2457 | ||
2458 | if (vma_is_dax(vma)) | |
2459 | return 0; | |
2460 | ||
2461 | #ifdef VM_SAO | |
2462 | if (*vm_flags & VM_SAO) | |
2463 | return 0; | |
2464 | #endif | |
2465 | #ifdef VM_SPARC_ADI | |
2466 | if (*vm_flags & VM_SPARC_ADI) | |
2467 | return 0; | |
2468 | #endif | |
2469 | ||
2470 | if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) { | |
2471 | err = __ksm_enter(mm); | |
2472 | if (err) | |
2473 | return err; | |
2474 | } | |
2475 | ||
2476 | *vm_flags |= VM_MERGEABLE; | |
2477 | break; | |
2478 | ||
2479 | case MADV_UNMERGEABLE: | |
2480 | if (!(*vm_flags & VM_MERGEABLE)) | |
2481 | return 0; /* just ignore the advice */ | |
2482 | ||
2483 | if (vma->anon_vma) { | |
2484 | err = unmerge_ksm_pages(vma, start, end); | |
2485 | if (err) | |
2486 | return err; | |
2487 | } | |
2488 | ||
2489 | *vm_flags &= ~VM_MERGEABLE; | |
2490 | break; | |
2491 | } | |
2492 | ||
2493 | return 0; | |
2494 | } | |
2495 | EXPORT_SYMBOL_GPL(ksm_madvise); | |
2496 | ||
2497 | int __ksm_enter(struct mm_struct *mm) | |
2498 | { | |
2499 | struct mm_slot *mm_slot; | |
2500 | int needs_wakeup; | |
2501 | ||
2502 | mm_slot = alloc_mm_slot(); | |
2503 | if (!mm_slot) | |
2504 | return -ENOMEM; | |
2505 | ||
2506 | /* Check ksm_run too? Would need tighter locking */ | |
2507 | needs_wakeup = list_empty(&ksm_mm_head.mm_list); | |
2508 | ||
2509 | spin_lock(&ksm_mmlist_lock); | |
2510 | insert_to_mm_slots_hash(mm, mm_slot); | |
2511 | /* | |
2512 | * When KSM_RUN_MERGE (or KSM_RUN_STOP), | |
2513 | * insert just behind the scanning cursor, to let the area settle | |
2514 | * down a little; when fork is followed by immediate exec, we don't | |
2515 | * want ksmd to waste time setting up and tearing down an rmap_list. | |
2516 | * | |
2517 | * But when KSM_RUN_UNMERGE, it's important to insert ahead of its | |
2518 | * scanning cursor, otherwise KSM pages in newly forked mms will be | |
2519 | * missed: then we might as well insert at the end of the list. | |
2520 | */ | |
2521 | if (ksm_run & KSM_RUN_UNMERGE) | |
2522 | list_add_tail(&mm_slot->mm_list, &ksm_mm_head.mm_list); | |
2523 | else | |
2524 | list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list); | |
2525 | spin_unlock(&ksm_mmlist_lock); | |
2526 | ||
2527 | set_bit(MMF_VM_MERGEABLE, &mm->flags); | |
2528 | mmgrab(mm); | |
2529 | ||
2530 | if (needs_wakeup) | |
2531 | wake_up_interruptible(&ksm_thread_wait); | |
2532 | ||
2533 | return 0; | |
2534 | } | |
2535 | ||
2536 | void __ksm_exit(struct mm_struct *mm) | |
2537 | { | |
2538 | struct mm_slot *mm_slot; | |
2539 | int easy_to_free = 0; | |
2540 | ||
2541 | /* | |
2542 | * This process is exiting: if it's straightforward (as is the | |
2543 | * case when ksmd was never running), free mm_slot immediately. | |
2544 | * But if it's at the cursor or has rmap_items linked to it, use | |
2545 | * mmap_lock to synchronize with any break_cows before pagetables | |
2546 | * are freed, and leave the mm_slot on the list for ksmd to free. | |
2547 | * Beware: ksm may already have noticed it exiting and freed the slot. | |
2548 | */ | |
2549 | ||
2550 | spin_lock(&ksm_mmlist_lock); | |
2551 | mm_slot = get_mm_slot(mm); | |
2552 | if (mm_slot && ksm_scan.mm_slot != mm_slot) { | |
2553 | if (!mm_slot->rmap_list) { | |
2554 | hash_del(&mm_slot->link); | |
2555 | list_del(&mm_slot->mm_list); | |
2556 | easy_to_free = 1; | |
2557 | } else { | |
2558 | list_move(&mm_slot->mm_list, | |
2559 | &ksm_scan.mm_slot->mm_list); | |
2560 | } | |
2561 | } | |
2562 | spin_unlock(&ksm_mmlist_lock); | |
2563 | ||
2564 | if (easy_to_free) { | |
2565 | free_mm_slot(mm_slot); | |
2566 | clear_bit(MMF_VM_MERGEABLE, &mm->flags); | |
2567 | mmdrop(mm); | |
2568 | } else if (mm_slot) { | |
2569 | mmap_write_lock(mm); | |
2570 | mmap_write_unlock(mm); | |
2571 | } | |
2572 | } | |
2573 | ||
2574 | struct page *ksm_might_need_to_copy(struct page *page, | |
2575 | struct vm_area_struct *vma, unsigned long address) | |
2576 | { | |
2577 | struct anon_vma *anon_vma = page_anon_vma(page); | |
2578 | struct page *new_page; | |
2579 | ||
2580 | if (PageKsm(page)) { | |
2581 | if (page_stable_node(page) && | |
2582 | !(ksm_run & KSM_RUN_UNMERGE)) | |
2583 | return page; /* no need to copy it */ | |
2584 | } else if (!anon_vma) { | |
2585 | return page; /* no need to copy it */ | |
2586 | } else if (anon_vma->root == vma->anon_vma->root && | |
2587 | page->index == linear_page_index(vma, address)) { | |
2588 | return page; /* still no need to copy it */ | |
2589 | } | |
2590 | if (!PageUptodate(page)) | |
2591 | return page; /* let do_swap_page report the error */ | |
2592 | ||
2593 | new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address); | |
2594 | if (new_page && mem_cgroup_charge(new_page, vma->vm_mm, GFP_KERNEL)) { | |
2595 | put_page(new_page); | |
2596 | new_page = NULL; | |
2597 | } | |
2598 | if (new_page) { | |
2599 | copy_user_highpage(new_page, page, address, vma); | |
2600 | ||
2601 | SetPageDirty(new_page); | |
2602 | __SetPageUptodate(new_page); | |
2603 | __SetPageLocked(new_page); | |
2604 | } | |
2605 | ||
2606 | return new_page; | |
2607 | } | |
2608 | ||
2609 | void rmap_walk_ksm(struct page *page, struct rmap_walk_control *rwc) | |
2610 | { | |
2611 | struct stable_node *stable_node; | |
2612 | struct rmap_item *rmap_item; | |
2613 | int search_new_forks = 0; | |
2614 | ||
2615 | VM_BUG_ON_PAGE(!PageKsm(page), page); | |
2616 | ||
2617 | /* | |
2618 | * Rely on the page lock to protect against concurrent modifications | |
2619 | * to that page's node of the stable tree. | |
2620 | */ | |
2621 | VM_BUG_ON_PAGE(!PageLocked(page), page); | |
2622 | ||
2623 | stable_node = page_stable_node(page); | |
2624 | if (!stable_node) | |
2625 | return; | |
2626 | again: | |
2627 | hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) { | |
2628 | struct anon_vma *anon_vma = rmap_item->anon_vma; | |
2629 | struct anon_vma_chain *vmac; | |
2630 | struct vm_area_struct *vma; | |
2631 | ||
2632 | cond_resched(); | |
2633 | anon_vma_lock_read(anon_vma); | |
2634 | anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root, | |
2635 | 0, ULONG_MAX) { | |
2636 | unsigned long addr; | |
2637 | ||
2638 | cond_resched(); | |
2639 | vma = vmac->vma; | |
2640 | ||
2641 | /* Ignore the stable/unstable/sqnr flags */ | |
2642 | addr = rmap_item->address & ~KSM_FLAG_MASK; | |
2643 | ||
2644 | if (addr < vma->vm_start || addr >= vma->vm_end) | |
2645 | continue; | |
2646 | /* | |
2647 | * Initially we examine only the vma which covers this | |
2648 | * rmap_item; but later, if there is still work to do, | |
2649 | * we examine covering vmas in other mms: in case they | |
2650 | * were forked from the original since ksmd passed. | |
2651 | */ | |
2652 | if ((rmap_item->mm == vma->vm_mm) == search_new_forks) | |
2653 | continue; | |
2654 | ||
2655 | if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg)) | |
2656 | continue; | |
2657 | ||
2658 | if (!rwc->rmap_one(page, vma, addr, rwc->arg)) { | |
2659 | anon_vma_unlock_read(anon_vma); | |
2660 | return; | |
2661 | } | |
2662 | if (rwc->done && rwc->done(page)) { | |
2663 | anon_vma_unlock_read(anon_vma); | |
2664 | return; | |
2665 | } | |
2666 | } | |
2667 | anon_vma_unlock_read(anon_vma); | |
2668 | } | |
2669 | if (!search_new_forks++) | |
2670 | goto again; | |
2671 | } | |
2672 | ||
2673 | #ifdef CONFIG_MIGRATION | |
2674 | void ksm_migrate_page(struct page *newpage, struct page *oldpage) | |
2675 | { | |
2676 | struct stable_node *stable_node; | |
2677 | ||
2678 | VM_BUG_ON_PAGE(!PageLocked(oldpage), oldpage); | |
2679 | VM_BUG_ON_PAGE(!PageLocked(newpage), newpage); | |
2680 | VM_BUG_ON_PAGE(newpage->mapping != oldpage->mapping, newpage); | |
2681 | ||
2682 | stable_node = page_stable_node(newpage); | |
2683 | if (stable_node) { | |
2684 | VM_BUG_ON_PAGE(stable_node->kpfn != page_to_pfn(oldpage), oldpage); | |
2685 | stable_node->kpfn = page_to_pfn(newpage); | |
2686 | /* | |
2687 | * newpage->mapping was set in advance; now we need smp_wmb() | |
2688 | * to make sure that the new stable_node->kpfn is visible | |
2689 | * to get_ksm_page() before it can see that oldpage->mapping | |
2690 | * has gone stale (or that PageSwapCache has been cleared). | |
2691 | */ | |
2692 | smp_wmb(); | |
2693 | set_page_stable_node(oldpage, NULL); | |
2694 | } | |
2695 | } | |
2696 | #endif /* CONFIG_MIGRATION */ | |
2697 | ||
2698 | #ifdef CONFIG_MEMORY_HOTREMOVE | |
2699 | static void wait_while_offlining(void) | |
2700 | { | |
2701 | while (ksm_run & KSM_RUN_OFFLINE) { | |
2702 | mutex_unlock(&ksm_thread_mutex); | |
2703 | wait_on_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE), | |
2704 | TASK_UNINTERRUPTIBLE); | |
2705 | mutex_lock(&ksm_thread_mutex); | |
2706 | } | |
2707 | } | |
2708 | ||
2709 | static bool stable_node_dup_remove_range(struct stable_node *stable_node, | |
2710 | unsigned long start_pfn, | |
2711 | unsigned long end_pfn) | |
2712 | { | |
2713 | if (stable_node->kpfn >= start_pfn && | |
2714 | stable_node->kpfn < end_pfn) { | |
2715 | /* | |
2716 | * Don't get_ksm_page, page has already gone: | |
2717 | * which is why we keep kpfn instead of page* | |
2718 | */ | |
2719 | remove_node_from_stable_tree(stable_node); | |
2720 | return true; | |
2721 | } | |
2722 | return false; | |
2723 | } | |
2724 | ||
2725 | static bool stable_node_chain_remove_range(struct stable_node *stable_node, | |
2726 | unsigned long start_pfn, | |
2727 | unsigned long end_pfn, | |
2728 | struct rb_root *root) | |
2729 | { | |
2730 | struct stable_node *dup; | |
2731 | struct hlist_node *hlist_safe; | |
2732 | ||
2733 | if (!is_stable_node_chain(stable_node)) { | |
2734 | VM_BUG_ON(is_stable_node_dup(stable_node)); | |
2735 | return stable_node_dup_remove_range(stable_node, start_pfn, | |
2736 | end_pfn); | |
2737 | } | |
2738 | ||
2739 | hlist_for_each_entry_safe(dup, hlist_safe, | |
2740 | &stable_node->hlist, hlist_dup) { | |
2741 | VM_BUG_ON(!is_stable_node_dup(dup)); | |
2742 | stable_node_dup_remove_range(dup, start_pfn, end_pfn); | |
2743 | } | |
2744 | if (hlist_empty(&stable_node->hlist)) { | |
2745 | free_stable_node_chain(stable_node, root); | |
2746 | return true; /* notify caller that tree was rebalanced */ | |
2747 | } else | |
2748 | return false; | |
2749 | } | |
2750 | ||
2751 | static void ksm_check_stable_tree(unsigned long start_pfn, | |
2752 | unsigned long end_pfn) | |
2753 | { | |
2754 | struct stable_node *stable_node, *next; | |
2755 | struct rb_node *node; | |
2756 | int nid; | |
2757 | ||
2758 | for (nid = 0; nid < ksm_nr_node_ids; nid++) { | |
2759 | node = rb_first(root_stable_tree + nid); | |
2760 | while (node) { | |
2761 | stable_node = rb_entry(node, struct stable_node, node); | |
2762 | if (stable_node_chain_remove_range(stable_node, | |
2763 | start_pfn, end_pfn, | |
2764 | root_stable_tree + | |
2765 | nid)) | |
2766 | node = rb_first(root_stable_tree + nid); | |
2767 | else | |
2768 | node = rb_next(node); | |
2769 | cond_resched(); | |
2770 | } | |
2771 | } | |
2772 | list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) { | |
2773 | if (stable_node->kpfn >= start_pfn && | |
2774 | stable_node->kpfn < end_pfn) | |
2775 | remove_node_from_stable_tree(stable_node); | |
2776 | cond_resched(); | |
2777 | } | |
2778 | } | |
2779 | ||
2780 | static int ksm_memory_callback(struct notifier_block *self, | |
2781 | unsigned long action, void *arg) | |
2782 | { | |
2783 | struct memory_notify *mn = arg; | |
2784 | ||
2785 | switch (action) { | |
2786 | case MEM_GOING_OFFLINE: | |
2787 | /* | |
2788 | * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items() | |
2789 | * and remove_all_stable_nodes() while memory is going offline: | |
2790 | * it is unsafe for them to touch the stable tree at this time. | |
2791 | * But unmerge_ksm_pages(), rmap lookups and other entry points | |
2792 | * which do not need the ksm_thread_mutex are all safe. | |
2793 | */ | |
2794 | mutex_lock(&ksm_thread_mutex); | |
2795 | ksm_run |= KSM_RUN_OFFLINE; | |
2796 | mutex_unlock(&ksm_thread_mutex); | |
2797 | break; | |
2798 | ||
2799 | case MEM_OFFLINE: | |
2800 | /* | |
2801 | * Most of the work is done by page migration; but there might | |
2802 | * be a few stable_nodes left over, still pointing to struct | |
2803 | * pages which have been offlined: prune those from the tree, | |
2804 | * otherwise get_ksm_page() might later try to access a | |
2805 | * non-existent struct page. | |
2806 | */ | |
2807 | ksm_check_stable_tree(mn->start_pfn, | |
2808 | mn->start_pfn + mn->nr_pages); | |
2809 | fallthrough; | |
2810 | case MEM_CANCEL_OFFLINE: | |
2811 | mutex_lock(&ksm_thread_mutex); | |
2812 | ksm_run &= ~KSM_RUN_OFFLINE; | |
2813 | mutex_unlock(&ksm_thread_mutex); | |
2814 | ||
2815 | smp_mb(); /* wake_up_bit advises this */ | |
2816 | wake_up_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE)); | |
2817 | break; | |
2818 | } | |
2819 | return NOTIFY_OK; | |
2820 | } | |
2821 | #else | |
2822 | static void wait_while_offlining(void) | |
2823 | { | |
2824 | } | |
2825 | #endif /* CONFIG_MEMORY_HOTREMOVE */ | |
2826 | ||
2827 | #ifdef CONFIG_SYSFS | |
2828 | /* | |
2829 | * This all compiles without CONFIG_SYSFS, but is a waste of space. | |
2830 | */ | |
2831 | ||
2832 | #define KSM_ATTR_RO(_name) \ | |
2833 | static struct kobj_attribute _name##_attr = __ATTR_RO(_name) | |
2834 | #define KSM_ATTR(_name) \ | |
2835 | static struct kobj_attribute _name##_attr = \ | |
2836 | __ATTR(_name, 0644, _name##_show, _name##_store) | |
2837 | ||
2838 | static ssize_t sleep_millisecs_show(struct kobject *kobj, | |
2839 | struct kobj_attribute *attr, char *buf) | |
2840 | { | |
2841 | return sysfs_emit(buf, "%u\n", ksm_thread_sleep_millisecs); | |
2842 | } | |
2843 | ||
2844 | static ssize_t sleep_millisecs_store(struct kobject *kobj, | |
2845 | struct kobj_attribute *attr, | |
2846 | const char *buf, size_t count) | |
2847 | { | |
2848 | unsigned int msecs; | |
2849 | int err; | |
2850 | ||
2851 | err = kstrtouint(buf, 10, &msecs); | |
2852 | if (err) | |
2853 | return -EINVAL; | |
2854 | ||
2855 | ksm_thread_sleep_millisecs = msecs; | |
2856 | wake_up_interruptible(&ksm_iter_wait); | |
2857 | ||
2858 | return count; | |
2859 | } | |
2860 | KSM_ATTR(sleep_millisecs); | |
2861 | ||
2862 | static ssize_t pages_to_scan_show(struct kobject *kobj, | |
2863 | struct kobj_attribute *attr, char *buf) | |
2864 | { | |
2865 | return sysfs_emit(buf, "%u\n", ksm_thread_pages_to_scan); | |
2866 | } | |
2867 | ||
2868 | static ssize_t pages_to_scan_store(struct kobject *kobj, | |
2869 | struct kobj_attribute *attr, | |
2870 | const char *buf, size_t count) | |
2871 | { | |
2872 | unsigned int nr_pages; | |
2873 | int err; | |
2874 | ||
2875 | err = kstrtouint(buf, 10, &nr_pages); | |
2876 | if (err) | |
2877 | return -EINVAL; | |
2878 | ||
2879 | ksm_thread_pages_to_scan = nr_pages; | |
2880 | ||
2881 | return count; | |
2882 | } | |
2883 | KSM_ATTR(pages_to_scan); | |
2884 | ||
2885 | static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr, | |
2886 | char *buf) | |
2887 | { | |
2888 | return sysfs_emit(buf, "%lu\n", ksm_run); | |
2889 | } | |
2890 | ||
2891 | static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr, | |
2892 | const char *buf, size_t count) | |
2893 | { | |
2894 | unsigned int flags; | |
2895 | int err; | |
2896 | ||
2897 | err = kstrtouint(buf, 10, &flags); | |
2898 | if (err) | |
2899 | return -EINVAL; | |
2900 | if (flags > KSM_RUN_UNMERGE) | |
2901 | return -EINVAL; | |
2902 | ||
2903 | /* | |
2904 | * KSM_RUN_MERGE sets ksmd running, and 0 stops it running. | |
2905 | * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items, | |
2906 | * breaking COW to free the pages_shared (but leaves mm_slots | |
2907 | * on the list for when ksmd may be set running again). | |
2908 | */ | |
2909 | ||
2910 | mutex_lock(&ksm_thread_mutex); | |
2911 | wait_while_offlining(); | |
2912 | if (ksm_run != flags) { | |
2913 | ksm_run = flags; | |
2914 | if (flags & KSM_RUN_UNMERGE) { | |
2915 | set_current_oom_origin(); | |
2916 | err = unmerge_and_remove_all_rmap_items(); | |
2917 | clear_current_oom_origin(); | |
2918 | if (err) { | |
2919 | ksm_run = KSM_RUN_STOP; | |
2920 | count = err; | |
2921 | } | |
2922 | } | |
2923 | } | |
2924 | mutex_unlock(&ksm_thread_mutex); | |
2925 | ||
2926 | if (flags & KSM_RUN_MERGE) | |
2927 | wake_up_interruptible(&ksm_thread_wait); | |
2928 | ||
2929 | return count; | |
2930 | } | |
2931 | KSM_ATTR(run); | |
2932 | ||
2933 | #ifdef CONFIG_NUMA | |
2934 | static ssize_t merge_across_nodes_show(struct kobject *kobj, | |
2935 | struct kobj_attribute *attr, char *buf) | |
2936 | { | |
2937 | return sysfs_emit(buf, "%u\n", ksm_merge_across_nodes); | |
2938 | } | |
2939 | ||
2940 | static ssize_t merge_across_nodes_store(struct kobject *kobj, | |
2941 | struct kobj_attribute *attr, | |
2942 | const char *buf, size_t count) | |
2943 | { | |
2944 | int err; | |
2945 | unsigned long knob; | |
2946 | ||
2947 | err = kstrtoul(buf, 10, &knob); | |
2948 | if (err) | |
2949 | return err; | |
2950 | if (knob > 1) | |
2951 | return -EINVAL; | |
2952 | ||
2953 | mutex_lock(&ksm_thread_mutex); | |
2954 | wait_while_offlining(); | |
2955 | if (ksm_merge_across_nodes != knob) { | |
2956 | if (ksm_pages_shared || remove_all_stable_nodes()) | |
2957 | err = -EBUSY; | |
2958 | else if (root_stable_tree == one_stable_tree) { | |
2959 | struct rb_root *buf; | |
2960 | /* | |
2961 | * This is the first time that we switch away from the | |
2962 | * default of merging across nodes: must now allocate | |
2963 | * a buffer to hold as many roots as may be needed. | |
2964 | * Allocate stable and unstable together: | |
2965 | * MAXSMP NODES_SHIFT 10 will use 16kB. | |
2966 | */ | |
2967 | buf = kcalloc(nr_node_ids + nr_node_ids, sizeof(*buf), | |
2968 | GFP_KERNEL); | |
2969 | /* Let us assume that RB_ROOT is NULL is zero */ | |
2970 | if (!buf) | |
2971 | err = -ENOMEM; | |
2972 | else { | |
2973 | root_stable_tree = buf; | |
2974 | root_unstable_tree = buf + nr_node_ids; | |
2975 | /* Stable tree is empty but not the unstable */ | |
2976 | root_unstable_tree[0] = one_unstable_tree[0]; | |
2977 | } | |
2978 | } | |
2979 | if (!err) { | |
2980 | ksm_merge_across_nodes = knob; | |
2981 | ksm_nr_node_ids = knob ? 1 : nr_node_ids; | |
2982 | } | |
2983 | } | |
2984 | mutex_unlock(&ksm_thread_mutex); | |
2985 | ||
2986 | return err ? err : count; | |
2987 | } | |
2988 | KSM_ATTR(merge_across_nodes); | |
2989 | #endif | |
2990 | ||
2991 | static ssize_t use_zero_pages_show(struct kobject *kobj, | |
2992 | struct kobj_attribute *attr, char *buf) | |
2993 | { | |
2994 | return sysfs_emit(buf, "%u\n", ksm_use_zero_pages); | |
2995 | } | |
2996 | static ssize_t use_zero_pages_store(struct kobject *kobj, | |
2997 | struct kobj_attribute *attr, | |
2998 | const char *buf, size_t count) | |
2999 | { | |
3000 | int err; | |
3001 | bool value; | |
3002 | ||
3003 | err = kstrtobool(buf, &value); | |
3004 | if (err) | |
3005 | return -EINVAL; | |
3006 | ||
3007 | ksm_use_zero_pages = value; | |
3008 | ||
3009 | return count; | |
3010 | } | |
3011 | KSM_ATTR(use_zero_pages); | |
3012 | ||
3013 | static ssize_t max_page_sharing_show(struct kobject *kobj, | |
3014 | struct kobj_attribute *attr, char *buf) | |
3015 | { | |
3016 | return sysfs_emit(buf, "%u\n", ksm_max_page_sharing); | |
3017 | } | |
3018 | ||
3019 | static ssize_t max_page_sharing_store(struct kobject *kobj, | |
3020 | struct kobj_attribute *attr, | |
3021 | const char *buf, size_t count) | |
3022 | { | |
3023 | int err; | |
3024 | int knob; | |
3025 | ||
3026 | err = kstrtoint(buf, 10, &knob); | |
3027 | if (err) | |
3028 | return err; | |
3029 | /* | |
3030 | * When a KSM page is created it is shared by 2 mappings. This | |
3031 | * being a signed comparison, it implicitly verifies it's not | |
3032 | * negative. | |
3033 | */ | |
3034 | if (knob < 2) | |
3035 | return -EINVAL; | |
3036 | ||
3037 | if (READ_ONCE(ksm_max_page_sharing) == knob) | |
3038 | return count; | |
3039 | ||
3040 | mutex_lock(&ksm_thread_mutex); | |
3041 | wait_while_offlining(); | |
3042 | if (ksm_max_page_sharing != knob) { | |
3043 | if (ksm_pages_shared || remove_all_stable_nodes()) | |
3044 | err = -EBUSY; | |
3045 | else | |
3046 | ksm_max_page_sharing = knob; | |
3047 | } | |
3048 | mutex_unlock(&ksm_thread_mutex); | |
3049 | ||
3050 | return err ? err : count; | |
3051 | } | |
3052 | KSM_ATTR(max_page_sharing); | |
3053 | ||
3054 | static ssize_t pages_shared_show(struct kobject *kobj, | |
3055 | struct kobj_attribute *attr, char *buf) | |
3056 | { | |
3057 | return sysfs_emit(buf, "%lu\n", ksm_pages_shared); | |
3058 | } | |
3059 | KSM_ATTR_RO(pages_shared); | |
3060 | ||
3061 | static ssize_t pages_sharing_show(struct kobject *kobj, | |
3062 | struct kobj_attribute *attr, char *buf) | |
3063 | { | |
3064 | return sysfs_emit(buf, "%lu\n", ksm_pages_sharing); | |
3065 | } | |
3066 | KSM_ATTR_RO(pages_sharing); | |
3067 | ||
3068 | static ssize_t pages_unshared_show(struct kobject *kobj, | |
3069 | struct kobj_attribute *attr, char *buf) | |
3070 | { | |
3071 | return sysfs_emit(buf, "%lu\n", ksm_pages_unshared); | |
3072 | } | |
3073 | KSM_ATTR_RO(pages_unshared); | |
3074 | ||
3075 | static ssize_t pages_volatile_show(struct kobject *kobj, | |
3076 | struct kobj_attribute *attr, char *buf) | |
3077 | { | |
3078 | long ksm_pages_volatile; | |
3079 | ||
3080 | ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared | |
3081 | - ksm_pages_sharing - ksm_pages_unshared; | |
3082 | /* | |
3083 | * It was not worth any locking to calculate that statistic, | |
3084 | * but it might therefore sometimes be negative: conceal that. | |
3085 | */ | |
3086 | if (ksm_pages_volatile < 0) | |
3087 | ksm_pages_volatile = 0; | |
3088 | return sysfs_emit(buf, "%ld\n", ksm_pages_volatile); | |
3089 | } | |
3090 | KSM_ATTR_RO(pages_volatile); | |
3091 | ||
3092 | static ssize_t stable_node_dups_show(struct kobject *kobj, | |
3093 | struct kobj_attribute *attr, char *buf) | |
3094 | { | |
3095 | return sysfs_emit(buf, "%lu\n", ksm_stable_node_dups); | |
3096 | } | |
3097 | KSM_ATTR_RO(stable_node_dups); | |
3098 | ||
3099 | static ssize_t stable_node_chains_show(struct kobject *kobj, | |
3100 | struct kobj_attribute *attr, char *buf) | |
3101 | { | |
3102 | return sysfs_emit(buf, "%lu\n", ksm_stable_node_chains); | |
3103 | } | |
3104 | KSM_ATTR_RO(stable_node_chains); | |
3105 | ||
3106 | static ssize_t | |
3107 | stable_node_chains_prune_millisecs_show(struct kobject *kobj, | |
3108 | struct kobj_attribute *attr, | |
3109 | char *buf) | |
3110 | { | |
3111 | return sysfs_emit(buf, "%u\n", ksm_stable_node_chains_prune_millisecs); | |
3112 | } | |
3113 | ||
3114 | static ssize_t | |
3115 | stable_node_chains_prune_millisecs_store(struct kobject *kobj, | |
3116 | struct kobj_attribute *attr, | |
3117 | const char *buf, size_t count) | |
3118 | { | |
3119 | unsigned long msecs; | |
3120 | int err; | |
3121 | ||
3122 | err = kstrtoul(buf, 10, &msecs); | |
3123 | if (err || msecs > UINT_MAX) | |
3124 | return -EINVAL; | |
3125 | ||
3126 | ksm_stable_node_chains_prune_millisecs = msecs; | |
3127 | ||
3128 | return count; | |
3129 | } | |
3130 | KSM_ATTR(stable_node_chains_prune_millisecs); | |
3131 | ||
3132 | static ssize_t full_scans_show(struct kobject *kobj, | |
3133 | struct kobj_attribute *attr, char *buf) | |
3134 | { | |
3135 | return sysfs_emit(buf, "%lu\n", ksm_scan.seqnr); | |
3136 | } | |
3137 | KSM_ATTR_RO(full_scans); | |
3138 | ||
3139 | static struct attribute *ksm_attrs[] = { | |
3140 | &sleep_millisecs_attr.attr, | |
3141 | &pages_to_scan_attr.attr, | |
3142 | &run_attr.attr, | |
3143 | &pages_shared_attr.attr, | |
3144 | &pages_sharing_attr.attr, | |
3145 | &pages_unshared_attr.attr, | |
3146 | &pages_volatile_attr.attr, | |
3147 | &full_scans_attr.attr, | |
3148 | #ifdef CONFIG_NUMA | |
3149 | &merge_across_nodes_attr.attr, | |
3150 | #endif | |
3151 | &max_page_sharing_attr.attr, | |
3152 | &stable_node_chains_attr.attr, | |
3153 | &stable_node_dups_attr.attr, | |
3154 | &stable_node_chains_prune_millisecs_attr.attr, | |
3155 | &use_zero_pages_attr.attr, | |
3156 | NULL, | |
3157 | }; | |
3158 | ||
3159 | static const struct attribute_group ksm_attr_group = { | |
3160 | .attrs = ksm_attrs, | |
3161 | .name = "ksm", | |
3162 | }; | |
3163 | #endif /* CONFIG_SYSFS */ | |
3164 | ||
3165 | static int __init ksm_init(void) | |
3166 | { | |
3167 | struct task_struct *ksm_thread; | |
3168 | int err; | |
3169 | ||
3170 | /* The correct value depends on page size and endianness */ | |
3171 | zero_checksum = calc_checksum(ZERO_PAGE(0)); | |
3172 | /* Default to false for backwards compatibility */ | |
3173 | ksm_use_zero_pages = false; | |
3174 | ||
3175 | err = ksm_slab_init(); | |
3176 | if (err) | |
3177 | goto out; | |
3178 | ||
3179 | ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd"); | |
3180 | if (IS_ERR(ksm_thread)) { | |
3181 | pr_err("ksm: creating kthread failed\n"); | |
3182 | err = PTR_ERR(ksm_thread); | |
3183 | goto out_free; | |
3184 | } | |
3185 | ||
3186 | #ifdef CONFIG_SYSFS | |
3187 | err = sysfs_create_group(mm_kobj, &ksm_attr_group); | |
3188 | if (err) { | |
3189 | pr_err("ksm: register sysfs failed\n"); | |
3190 | kthread_stop(ksm_thread); | |
3191 | goto out_free; | |
3192 | } | |
3193 | #else | |
3194 | ksm_run = KSM_RUN_MERGE; /* no way for user to start it */ | |
3195 | ||
3196 | #endif /* CONFIG_SYSFS */ | |
3197 | ||
3198 | #ifdef CONFIG_MEMORY_HOTREMOVE | |
3199 | /* There is no significance to this priority 100 */ | |
3200 | hotplug_memory_notifier(ksm_memory_callback, 100); | |
3201 | #endif | |
3202 | return 0; | |
3203 | ||
3204 | out_free: | |
3205 | ksm_slab_free(); | |
3206 | out: | |
3207 | return err; | |
3208 | } | |
3209 | subsys_initcall(ksm_init); |