Commit | Line | Data |
---|---|---|
f8af4da3 | 1 | /* |
31dbd01f IE |
2 | * Memory merging support. |
3 | * | |
4 | * This code enables dynamic sharing of identical pages found in different | |
5 | * memory areas, even if they are not shared by fork() | |
6 | * | |
36b2528d | 7 | * Copyright (C) 2008-2009 Red Hat, Inc. |
31dbd01f IE |
8 | * Authors: |
9 | * Izik Eidus | |
10 | * Andrea Arcangeli | |
11 | * Chris Wright | |
36b2528d | 12 | * Hugh Dickins |
31dbd01f IE |
13 | * |
14 | * This work is licensed under the terms of the GNU GPL, version 2. | |
f8af4da3 HD |
15 | */ |
16 | ||
17 | #include <linux/errno.h> | |
31dbd01f IE |
18 | #include <linux/mm.h> |
19 | #include <linux/fs.h> | |
f8af4da3 | 20 | #include <linux/mman.h> |
31dbd01f IE |
21 | #include <linux/sched.h> |
22 | #include <linux/rwsem.h> | |
23 | #include <linux/pagemap.h> | |
24 | #include <linux/rmap.h> | |
25 | #include <linux/spinlock.h> | |
26 | #include <linux/jhash.h> | |
27 | #include <linux/delay.h> | |
28 | #include <linux/kthread.h> | |
29 | #include <linux/wait.h> | |
30 | #include <linux/slab.h> | |
31 | #include <linux/rbtree.h> | |
62b61f61 | 32 | #include <linux/memory.h> |
31dbd01f | 33 | #include <linux/mmu_notifier.h> |
2c6854fd | 34 | #include <linux/swap.h> |
f8af4da3 HD |
35 | #include <linux/ksm.h> |
36 | ||
31dbd01f | 37 | #include <asm/tlbflush.h> |
73848b46 | 38 | #include "internal.h" |
31dbd01f IE |
39 | |
40 | /* | |
41 | * A few notes about the KSM scanning process, | |
42 | * to make it easier to understand the data structures below: | |
43 | * | |
44 | * In order to reduce excessive scanning, KSM sorts the memory pages by their | |
45 | * contents into a data structure that holds pointers to the pages' locations. | |
46 | * | |
47 | * Since the contents of the pages may change at any moment, KSM cannot just | |
48 | * insert the pages into a normal sorted tree and expect it to find anything. | |
49 | * Therefore KSM uses two data structures - the stable and the unstable tree. | |
50 | * | |
51 | * The stable tree holds pointers to all the merged pages (ksm pages), sorted | |
52 | * by their contents. Because each such page is write-protected, searching on | |
53 | * this tree is fully assured to be working (except when pages are unmapped), | |
54 | * and therefore this tree is called the stable tree. | |
55 | * | |
56 | * In addition to the stable tree, KSM uses a second data structure called the | |
57 | * unstable tree: this tree holds pointers to pages which have been found to | |
58 | * be "unchanged for a period of time". The unstable tree sorts these pages | |
59 | * by their contents, but since they are not write-protected, KSM cannot rely | |
60 | * upon the unstable tree to work correctly - the unstable tree is liable to | |
61 | * be corrupted as its contents are modified, and so it is called unstable. | |
62 | * | |
63 | * KSM solves this problem by several techniques: | |
64 | * | |
65 | * 1) The unstable tree is flushed every time KSM completes scanning all | |
66 | * memory areas, and then the tree is rebuilt again from the beginning. | |
67 | * 2) KSM will only insert into the unstable tree, pages whose hash value | |
68 | * has not changed since the previous scan of all memory areas. | |
69 | * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the | |
70 | * colors of the nodes and not on their contents, assuring that even when | |
71 | * the tree gets "corrupted" it won't get out of balance, so scanning time | |
72 | * remains the same (also, searching and inserting nodes in an rbtree uses | |
73 | * the same algorithm, so we have no overhead when we flush and rebuild). | |
74 | * 4) KSM never flushes the stable tree, which means that even if it were to | |
75 | * take 10 attempts to find a page in the unstable tree, once it is found, | |
76 | * it is secured in the stable tree. (When we scan a new page, we first | |
77 | * compare it against the stable tree, and then against the unstable tree.) | |
78 | */ | |
79 | ||
80 | /** | |
81 | * struct mm_slot - ksm information per mm that is being scanned | |
82 | * @link: link to the mm_slots hash list | |
83 | * @mm_list: link into the mm_slots list, rooted in ksm_mm_head | |
6514d511 | 84 | * @rmap_list: head for this mm_slot's singly-linked list of rmap_items |
31dbd01f IE |
85 | * @mm: the mm that this information is valid for |
86 | */ | |
87 | struct mm_slot { | |
88 | struct hlist_node link; | |
89 | struct list_head mm_list; | |
6514d511 | 90 | struct rmap_item *rmap_list; |
31dbd01f IE |
91 | struct mm_struct *mm; |
92 | }; | |
93 | ||
94 | /** | |
95 | * struct ksm_scan - cursor for scanning | |
96 | * @mm_slot: the current mm_slot we are scanning | |
97 | * @address: the next address inside that to be scanned | |
6514d511 | 98 | * @rmap_list: link to the next rmap to be scanned in the rmap_list |
31dbd01f IE |
99 | * @seqnr: count of completed full scans (needed when removing unstable node) |
100 | * | |
101 | * There is only the one ksm_scan instance of this cursor structure. | |
102 | */ | |
103 | struct ksm_scan { | |
104 | struct mm_slot *mm_slot; | |
105 | unsigned long address; | |
6514d511 | 106 | struct rmap_item **rmap_list; |
31dbd01f IE |
107 | unsigned long seqnr; |
108 | }; | |
109 | ||
7b6ba2c7 HD |
110 | /** |
111 | * struct stable_node - node of the stable rbtree | |
112 | * @node: rb node of this ksm page in the stable tree | |
113 | * @hlist: hlist head of rmap_items using this ksm page | |
62b61f61 | 114 | * @kpfn: page frame number of this ksm page |
7b6ba2c7 HD |
115 | */ |
116 | struct stable_node { | |
117 | struct rb_node node; | |
118 | struct hlist_head hlist; | |
62b61f61 | 119 | unsigned long kpfn; |
7b6ba2c7 HD |
120 | }; |
121 | ||
31dbd01f IE |
122 | /** |
123 | * struct rmap_item - reverse mapping item for virtual addresses | |
6514d511 | 124 | * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list |
db114b83 | 125 | * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree |
31dbd01f IE |
126 | * @mm: the memory structure this rmap_item is pointing into |
127 | * @address: the virtual address this rmap_item tracks (+ flags in low bits) | |
128 | * @oldchecksum: previous checksum of the page at that virtual address | |
7b6ba2c7 HD |
129 | * @node: rb node of this rmap_item in the unstable tree |
130 | * @head: pointer to stable_node heading this list in the stable tree | |
131 | * @hlist: link into hlist of rmap_items hanging off that stable_node | |
31dbd01f IE |
132 | */ |
133 | struct rmap_item { | |
6514d511 | 134 | struct rmap_item *rmap_list; |
db114b83 | 135 | struct anon_vma *anon_vma; /* when stable */ |
31dbd01f IE |
136 | struct mm_struct *mm; |
137 | unsigned long address; /* + low bits used for flags below */ | |
7b6ba2c7 | 138 | unsigned int oldchecksum; /* when unstable */ |
31dbd01f | 139 | union { |
7b6ba2c7 HD |
140 | struct rb_node node; /* when node of unstable tree */ |
141 | struct { /* when listed from stable tree */ | |
142 | struct stable_node *head; | |
143 | struct hlist_node hlist; | |
144 | }; | |
31dbd01f IE |
145 | }; |
146 | }; | |
147 | ||
148 | #define SEQNR_MASK 0x0ff /* low bits of unstable tree seqnr */ | |
7b6ba2c7 HD |
149 | #define UNSTABLE_FLAG 0x100 /* is a node of the unstable tree */ |
150 | #define STABLE_FLAG 0x200 /* is listed from the stable tree */ | |
31dbd01f IE |
151 | |
152 | /* The stable and unstable tree heads */ | |
153 | static struct rb_root root_stable_tree = RB_ROOT; | |
154 | static struct rb_root root_unstable_tree = RB_ROOT; | |
155 | ||
156 | #define MM_SLOTS_HASH_HEADS 1024 | |
157 | static struct hlist_head *mm_slots_hash; | |
158 | ||
159 | static struct mm_slot ksm_mm_head = { | |
160 | .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list), | |
161 | }; | |
162 | static struct ksm_scan ksm_scan = { | |
163 | .mm_slot = &ksm_mm_head, | |
164 | }; | |
165 | ||
166 | static struct kmem_cache *rmap_item_cache; | |
7b6ba2c7 | 167 | static struct kmem_cache *stable_node_cache; |
31dbd01f IE |
168 | static struct kmem_cache *mm_slot_cache; |
169 | ||
170 | /* The number of nodes in the stable tree */ | |
b4028260 | 171 | static unsigned long ksm_pages_shared; |
31dbd01f | 172 | |
e178dfde | 173 | /* The number of page slots additionally sharing those nodes */ |
b4028260 | 174 | static unsigned long ksm_pages_sharing; |
31dbd01f | 175 | |
473b0ce4 HD |
176 | /* The number of nodes in the unstable tree */ |
177 | static unsigned long ksm_pages_unshared; | |
178 | ||
179 | /* The number of rmap_items in use: to calculate pages_volatile */ | |
180 | static unsigned long ksm_rmap_items; | |
181 | ||
31dbd01f | 182 | /* Limit on the number of unswappable pages used */ |
2c6854fd | 183 | static unsigned long ksm_max_kernel_pages; |
31dbd01f IE |
184 | |
185 | /* Number of pages ksmd should scan in one batch */ | |
2c6854fd | 186 | static unsigned int ksm_thread_pages_to_scan = 100; |
31dbd01f IE |
187 | |
188 | /* Milliseconds ksmd should sleep between batches */ | |
2ffd8679 | 189 | static unsigned int ksm_thread_sleep_millisecs = 20; |
31dbd01f IE |
190 | |
191 | #define KSM_RUN_STOP 0 | |
192 | #define KSM_RUN_MERGE 1 | |
193 | #define KSM_RUN_UNMERGE 2 | |
2c6854fd | 194 | static unsigned int ksm_run = KSM_RUN_STOP; |
31dbd01f IE |
195 | |
196 | static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait); | |
197 | static DEFINE_MUTEX(ksm_thread_mutex); | |
198 | static DEFINE_SPINLOCK(ksm_mmlist_lock); | |
199 | ||
200 | #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\ | |
201 | sizeof(struct __struct), __alignof__(struct __struct),\ | |
202 | (__flags), NULL) | |
203 | ||
204 | static int __init ksm_slab_init(void) | |
205 | { | |
206 | rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0); | |
207 | if (!rmap_item_cache) | |
208 | goto out; | |
209 | ||
7b6ba2c7 HD |
210 | stable_node_cache = KSM_KMEM_CACHE(stable_node, 0); |
211 | if (!stable_node_cache) | |
212 | goto out_free1; | |
213 | ||
31dbd01f IE |
214 | mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0); |
215 | if (!mm_slot_cache) | |
7b6ba2c7 | 216 | goto out_free2; |
31dbd01f IE |
217 | |
218 | return 0; | |
219 | ||
7b6ba2c7 HD |
220 | out_free2: |
221 | kmem_cache_destroy(stable_node_cache); | |
222 | out_free1: | |
31dbd01f IE |
223 | kmem_cache_destroy(rmap_item_cache); |
224 | out: | |
225 | return -ENOMEM; | |
226 | } | |
227 | ||
228 | static void __init ksm_slab_free(void) | |
229 | { | |
230 | kmem_cache_destroy(mm_slot_cache); | |
7b6ba2c7 | 231 | kmem_cache_destroy(stable_node_cache); |
31dbd01f IE |
232 | kmem_cache_destroy(rmap_item_cache); |
233 | mm_slot_cache = NULL; | |
234 | } | |
235 | ||
236 | static inline struct rmap_item *alloc_rmap_item(void) | |
237 | { | |
473b0ce4 HD |
238 | struct rmap_item *rmap_item; |
239 | ||
240 | rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL); | |
241 | if (rmap_item) | |
242 | ksm_rmap_items++; | |
243 | return rmap_item; | |
31dbd01f IE |
244 | } |
245 | ||
246 | static inline void free_rmap_item(struct rmap_item *rmap_item) | |
247 | { | |
473b0ce4 | 248 | ksm_rmap_items--; |
31dbd01f IE |
249 | rmap_item->mm = NULL; /* debug safety */ |
250 | kmem_cache_free(rmap_item_cache, rmap_item); | |
251 | } | |
252 | ||
7b6ba2c7 HD |
253 | static inline struct stable_node *alloc_stable_node(void) |
254 | { | |
255 | return kmem_cache_alloc(stable_node_cache, GFP_KERNEL); | |
256 | } | |
257 | ||
258 | static inline void free_stable_node(struct stable_node *stable_node) | |
259 | { | |
260 | kmem_cache_free(stable_node_cache, stable_node); | |
261 | } | |
262 | ||
31dbd01f IE |
263 | static inline struct mm_slot *alloc_mm_slot(void) |
264 | { | |
265 | if (!mm_slot_cache) /* initialization failed */ | |
266 | return NULL; | |
267 | return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL); | |
268 | } | |
269 | ||
270 | static inline void free_mm_slot(struct mm_slot *mm_slot) | |
271 | { | |
272 | kmem_cache_free(mm_slot_cache, mm_slot); | |
273 | } | |
274 | ||
275 | static int __init mm_slots_hash_init(void) | |
276 | { | |
277 | mm_slots_hash = kzalloc(MM_SLOTS_HASH_HEADS * sizeof(struct hlist_head), | |
278 | GFP_KERNEL); | |
279 | if (!mm_slots_hash) | |
280 | return -ENOMEM; | |
281 | return 0; | |
282 | } | |
283 | ||
284 | static void __init mm_slots_hash_free(void) | |
285 | { | |
286 | kfree(mm_slots_hash); | |
287 | } | |
288 | ||
289 | static struct mm_slot *get_mm_slot(struct mm_struct *mm) | |
290 | { | |
291 | struct mm_slot *mm_slot; | |
292 | struct hlist_head *bucket; | |
293 | struct hlist_node *node; | |
294 | ||
295 | bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct)) | |
296 | % MM_SLOTS_HASH_HEADS]; | |
297 | hlist_for_each_entry(mm_slot, node, bucket, link) { | |
298 | if (mm == mm_slot->mm) | |
299 | return mm_slot; | |
300 | } | |
301 | return NULL; | |
302 | } | |
303 | ||
304 | static void insert_to_mm_slots_hash(struct mm_struct *mm, | |
305 | struct mm_slot *mm_slot) | |
306 | { | |
307 | struct hlist_head *bucket; | |
308 | ||
309 | bucket = &mm_slots_hash[((unsigned long)mm / sizeof(struct mm_struct)) | |
310 | % MM_SLOTS_HASH_HEADS]; | |
311 | mm_slot->mm = mm; | |
31dbd01f IE |
312 | hlist_add_head(&mm_slot->link, bucket); |
313 | } | |
314 | ||
315 | static inline int in_stable_tree(struct rmap_item *rmap_item) | |
316 | { | |
317 | return rmap_item->address & STABLE_FLAG; | |
318 | } | |
319 | ||
db114b83 HD |
320 | static void hold_anon_vma(struct rmap_item *rmap_item, |
321 | struct anon_vma *anon_vma) | |
322 | { | |
323 | rmap_item->anon_vma = anon_vma; | |
324 | atomic_inc(&anon_vma->ksm_refcount); | |
325 | } | |
326 | ||
327 | static void drop_anon_vma(struct rmap_item *rmap_item) | |
328 | { | |
329 | struct anon_vma *anon_vma = rmap_item->anon_vma; | |
330 | ||
331 | if (atomic_dec_and_lock(&anon_vma->ksm_refcount, &anon_vma->lock)) { | |
332 | int empty = list_empty(&anon_vma->head); | |
333 | spin_unlock(&anon_vma->lock); | |
334 | if (empty) | |
335 | anon_vma_free(anon_vma); | |
336 | } | |
337 | } | |
338 | ||
a913e182 HD |
339 | /* |
340 | * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's | |
341 | * page tables after it has passed through ksm_exit() - which, if necessary, | |
342 | * takes mmap_sem briefly to serialize against them. ksm_exit() does not set | |
343 | * a special flag: they can just back out as soon as mm_users goes to zero. | |
344 | * ksm_test_exit() is used throughout to make this test for exit: in some | |
345 | * places for correctness, in some places just to avoid unnecessary work. | |
346 | */ | |
347 | static inline bool ksm_test_exit(struct mm_struct *mm) | |
348 | { | |
349 | return atomic_read(&mm->mm_users) == 0; | |
350 | } | |
351 | ||
31dbd01f IE |
352 | /* |
353 | * We use break_ksm to break COW on a ksm page: it's a stripped down | |
354 | * | |
355 | * if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1) | |
356 | * put_page(page); | |
357 | * | |
358 | * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma, | |
359 | * in case the application has unmapped and remapped mm,addr meanwhile. | |
360 | * Could a ksm page appear anywhere else? Actually yes, in a VM_PFNMAP | |
361 | * mmap of /dev/mem or /dev/kmem, where we would not want to touch it. | |
362 | */ | |
d952b791 | 363 | static int break_ksm(struct vm_area_struct *vma, unsigned long addr) |
31dbd01f IE |
364 | { |
365 | struct page *page; | |
d952b791 | 366 | int ret = 0; |
31dbd01f IE |
367 | |
368 | do { | |
369 | cond_resched(); | |
370 | page = follow_page(vma, addr, FOLL_GET); | |
371 | if (!page) | |
372 | break; | |
373 | if (PageKsm(page)) | |
374 | ret = handle_mm_fault(vma->vm_mm, vma, addr, | |
375 | FAULT_FLAG_WRITE); | |
376 | else | |
377 | ret = VM_FAULT_WRITE; | |
378 | put_page(page); | |
d952b791 HD |
379 | } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_OOM))); |
380 | /* | |
381 | * We must loop because handle_mm_fault() may back out if there's | |
382 | * any difficulty e.g. if pte accessed bit gets updated concurrently. | |
383 | * | |
384 | * VM_FAULT_WRITE is what we have been hoping for: it indicates that | |
385 | * COW has been broken, even if the vma does not permit VM_WRITE; | |
386 | * but note that a concurrent fault might break PageKsm for us. | |
387 | * | |
388 | * VM_FAULT_SIGBUS could occur if we race with truncation of the | |
389 | * backing file, which also invalidates anonymous pages: that's | |
390 | * okay, that truncation will have unmapped the PageKsm for us. | |
391 | * | |
392 | * VM_FAULT_OOM: at the time of writing (late July 2009), setting | |
393 | * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the | |
394 | * current task has TIF_MEMDIE set, and will be OOM killed on return | |
395 | * to user; and ksmd, having no mm, would never be chosen for that. | |
396 | * | |
397 | * But if the mm is in a limited mem_cgroup, then the fault may fail | |
398 | * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and | |
399 | * even ksmd can fail in this way - though it's usually breaking ksm | |
400 | * just to undo a merge it made a moment before, so unlikely to oom. | |
401 | * | |
402 | * That's a pity: we might therefore have more kernel pages allocated | |
403 | * than we're counting as nodes in the stable tree; but ksm_do_scan | |
404 | * will retry to break_cow on each pass, so should recover the page | |
405 | * in due course. The important thing is to not let VM_MERGEABLE | |
406 | * be cleared while any such pages might remain in the area. | |
407 | */ | |
408 | return (ret & VM_FAULT_OOM) ? -ENOMEM : 0; | |
31dbd01f IE |
409 | } |
410 | ||
8dd3557a | 411 | static void break_cow(struct rmap_item *rmap_item) |
31dbd01f | 412 | { |
8dd3557a HD |
413 | struct mm_struct *mm = rmap_item->mm; |
414 | unsigned long addr = rmap_item->address; | |
31dbd01f IE |
415 | struct vm_area_struct *vma; |
416 | ||
4035c07a HD |
417 | /* |
418 | * It is not an accident that whenever we want to break COW | |
419 | * to undo, we also need to drop a reference to the anon_vma. | |
420 | */ | |
421 | drop_anon_vma(rmap_item); | |
422 | ||
81464e30 | 423 | down_read(&mm->mmap_sem); |
9ba69294 HD |
424 | if (ksm_test_exit(mm)) |
425 | goto out; | |
31dbd01f IE |
426 | vma = find_vma(mm, addr); |
427 | if (!vma || vma->vm_start > addr) | |
81464e30 | 428 | goto out; |
31dbd01f | 429 | if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) |
81464e30 | 430 | goto out; |
31dbd01f | 431 | break_ksm(vma, addr); |
81464e30 | 432 | out: |
31dbd01f IE |
433 | up_read(&mm->mmap_sem); |
434 | } | |
435 | ||
436 | static struct page *get_mergeable_page(struct rmap_item *rmap_item) | |
437 | { | |
438 | struct mm_struct *mm = rmap_item->mm; | |
439 | unsigned long addr = rmap_item->address; | |
440 | struct vm_area_struct *vma; | |
441 | struct page *page; | |
442 | ||
443 | down_read(&mm->mmap_sem); | |
9ba69294 HD |
444 | if (ksm_test_exit(mm)) |
445 | goto out; | |
31dbd01f IE |
446 | vma = find_vma(mm, addr); |
447 | if (!vma || vma->vm_start > addr) | |
448 | goto out; | |
449 | if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) | |
450 | goto out; | |
451 | ||
452 | page = follow_page(vma, addr, FOLL_GET); | |
453 | if (!page) | |
454 | goto out; | |
455 | if (PageAnon(page)) { | |
456 | flush_anon_page(vma, page, addr); | |
457 | flush_dcache_page(page); | |
458 | } else { | |
459 | put_page(page); | |
460 | out: page = NULL; | |
461 | } | |
462 | up_read(&mm->mmap_sem); | |
463 | return page; | |
464 | } | |
465 | ||
4035c07a HD |
466 | static void remove_node_from_stable_tree(struct stable_node *stable_node) |
467 | { | |
468 | struct rmap_item *rmap_item; | |
469 | struct hlist_node *hlist; | |
470 | ||
471 | hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) { | |
472 | if (rmap_item->hlist.next) | |
473 | ksm_pages_sharing--; | |
474 | else | |
475 | ksm_pages_shared--; | |
476 | drop_anon_vma(rmap_item); | |
477 | rmap_item->address &= PAGE_MASK; | |
478 | cond_resched(); | |
479 | } | |
480 | ||
481 | rb_erase(&stable_node->node, &root_stable_tree); | |
482 | free_stable_node(stable_node); | |
483 | } | |
484 | ||
485 | /* | |
486 | * get_ksm_page: checks if the page indicated by the stable node | |
487 | * is still its ksm page, despite having held no reference to it. | |
488 | * In which case we can trust the content of the page, and it | |
489 | * returns the gotten page; but if the page has now been zapped, | |
490 | * remove the stale node from the stable tree and return NULL. | |
491 | * | |
492 | * You would expect the stable_node to hold a reference to the ksm page. | |
493 | * But if it increments the page's count, swapping out has to wait for | |
494 | * ksmd to come around again before it can free the page, which may take | |
495 | * seconds or even minutes: much too unresponsive. So instead we use a | |
496 | * "keyhole reference": access to the ksm page from the stable node peeps | |
497 | * out through its keyhole to see if that page still holds the right key, | |
498 | * pointing back to this stable node. This relies on freeing a PageAnon | |
499 | * page to reset its page->mapping to NULL, and relies on no other use of | |
500 | * a page to put something that might look like our key in page->mapping. | |
501 | * | |
502 | * include/linux/pagemap.h page_cache_get_speculative() is a good reference, | |
503 | * but this is different - made simpler by ksm_thread_mutex being held, but | |
504 | * interesting for assuming that no other use of the struct page could ever | |
505 | * put our expected_mapping into page->mapping (or a field of the union which | |
506 | * coincides with page->mapping). The RCU calls are not for KSM at all, but | |
507 | * to keep the page_count protocol described with page_cache_get_speculative. | |
508 | * | |
509 | * Note: it is possible that get_ksm_page() will return NULL one moment, | |
510 | * then page the next, if the page is in between page_freeze_refs() and | |
511 | * page_unfreeze_refs(): this shouldn't be a problem anywhere, the page | |
512 | * is on its way to being freed; but it is an anomaly to bear in mind. | |
513 | */ | |
514 | static struct page *get_ksm_page(struct stable_node *stable_node) | |
515 | { | |
516 | struct page *page; | |
517 | void *expected_mapping; | |
518 | ||
62b61f61 | 519 | page = pfn_to_page(stable_node->kpfn); |
4035c07a HD |
520 | expected_mapping = (void *)stable_node + |
521 | (PAGE_MAPPING_ANON | PAGE_MAPPING_KSM); | |
522 | rcu_read_lock(); | |
523 | if (page->mapping != expected_mapping) | |
524 | goto stale; | |
525 | if (!get_page_unless_zero(page)) | |
526 | goto stale; | |
527 | if (page->mapping != expected_mapping) { | |
528 | put_page(page); | |
529 | goto stale; | |
530 | } | |
531 | rcu_read_unlock(); | |
532 | return page; | |
533 | stale: | |
534 | rcu_read_unlock(); | |
535 | remove_node_from_stable_tree(stable_node); | |
536 | return NULL; | |
537 | } | |
538 | ||
31dbd01f IE |
539 | /* |
540 | * Removing rmap_item from stable or unstable tree. | |
541 | * This function will clean the information from the stable/unstable tree. | |
542 | */ | |
543 | static void remove_rmap_item_from_tree(struct rmap_item *rmap_item) | |
544 | { | |
7b6ba2c7 HD |
545 | if (rmap_item->address & STABLE_FLAG) { |
546 | struct stable_node *stable_node; | |
5ad64688 | 547 | struct page *page; |
31dbd01f | 548 | |
7b6ba2c7 | 549 | stable_node = rmap_item->head; |
4035c07a HD |
550 | page = get_ksm_page(stable_node); |
551 | if (!page) | |
552 | goto out; | |
5ad64688 | 553 | |
4035c07a | 554 | lock_page(page); |
7b6ba2c7 | 555 | hlist_del(&rmap_item->hlist); |
4035c07a HD |
556 | unlock_page(page); |
557 | put_page(page); | |
08beca44 | 558 | |
4035c07a HD |
559 | if (stable_node->hlist.first) |
560 | ksm_pages_sharing--; | |
561 | else | |
7b6ba2c7 | 562 | ksm_pages_shared--; |
31dbd01f | 563 | |
db114b83 | 564 | drop_anon_vma(rmap_item); |
93d17715 | 565 | rmap_item->address &= PAGE_MASK; |
31dbd01f | 566 | |
7b6ba2c7 | 567 | } else if (rmap_item->address & UNSTABLE_FLAG) { |
31dbd01f IE |
568 | unsigned char age; |
569 | /* | |
9ba69294 | 570 | * Usually ksmd can and must skip the rb_erase, because |
31dbd01f | 571 | * root_unstable_tree was already reset to RB_ROOT. |
9ba69294 HD |
572 | * But be careful when an mm is exiting: do the rb_erase |
573 | * if this rmap_item was inserted by this scan, rather | |
574 | * than left over from before. | |
31dbd01f IE |
575 | */ |
576 | age = (unsigned char)(ksm_scan.seqnr - rmap_item->address); | |
cd551f97 | 577 | BUG_ON(age > 1); |
31dbd01f IE |
578 | if (!age) |
579 | rb_erase(&rmap_item->node, &root_unstable_tree); | |
93d17715 | 580 | |
473b0ce4 | 581 | ksm_pages_unshared--; |
93d17715 | 582 | rmap_item->address &= PAGE_MASK; |
31dbd01f | 583 | } |
4035c07a | 584 | out: |
31dbd01f IE |
585 | cond_resched(); /* we're called from many long loops */ |
586 | } | |
587 | ||
31dbd01f | 588 | static void remove_trailing_rmap_items(struct mm_slot *mm_slot, |
6514d511 | 589 | struct rmap_item **rmap_list) |
31dbd01f | 590 | { |
6514d511 HD |
591 | while (*rmap_list) { |
592 | struct rmap_item *rmap_item = *rmap_list; | |
593 | *rmap_list = rmap_item->rmap_list; | |
31dbd01f | 594 | remove_rmap_item_from_tree(rmap_item); |
31dbd01f IE |
595 | free_rmap_item(rmap_item); |
596 | } | |
597 | } | |
598 | ||
599 | /* | |
600 | * Though it's very tempting to unmerge in_stable_tree(rmap_item)s rather | |
601 | * than check every pte of a given vma, the locking doesn't quite work for | |
602 | * that - an rmap_item is assigned to the stable tree after inserting ksm | |
603 | * page and upping mmap_sem. Nor does it fit with the way we skip dup'ing | |
604 | * rmap_items from parent to child at fork time (so as not to waste time | |
605 | * if exit comes before the next scan reaches it). | |
81464e30 HD |
606 | * |
607 | * Similarly, although we'd like to remove rmap_items (so updating counts | |
608 | * and freeing memory) when unmerging an area, it's easier to leave that | |
609 | * to the next pass of ksmd - consider, for example, how ksmd might be | |
610 | * in cmp_and_merge_page on one of the rmap_items we would be removing. | |
31dbd01f | 611 | */ |
d952b791 HD |
612 | static int unmerge_ksm_pages(struct vm_area_struct *vma, |
613 | unsigned long start, unsigned long end) | |
31dbd01f IE |
614 | { |
615 | unsigned long addr; | |
d952b791 | 616 | int err = 0; |
31dbd01f | 617 | |
d952b791 | 618 | for (addr = start; addr < end && !err; addr += PAGE_SIZE) { |
9ba69294 HD |
619 | if (ksm_test_exit(vma->vm_mm)) |
620 | break; | |
d952b791 HD |
621 | if (signal_pending(current)) |
622 | err = -ERESTARTSYS; | |
623 | else | |
624 | err = break_ksm(vma, addr); | |
625 | } | |
626 | return err; | |
31dbd01f IE |
627 | } |
628 | ||
2ffd8679 HD |
629 | #ifdef CONFIG_SYSFS |
630 | /* | |
631 | * Only called through the sysfs control interface: | |
632 | */ | |
d952b791 | 633 | static int unmerge_and_remove_all_rmap_items(void) |
31dbd01f IE |
634 | { |
635 | struct mm_slot *mm_slot; | |
636 | struct mm_struct *mm; | |
637 | struct vm_area_struct *vma; | |
d952b791 HD |
638 | int err = 0; |
639 | ||
640 | spin_lock(&ksm_mmlist_lock); | |
9ba69294 | 641 | ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next, |
d952b791 HD |
642 | struct mm_slot, mm_list); |
643 | spin_unlock(&ksm_mmlist_lock); | |
31dbd01f | 644 | |
9ba69294 HD |
645 | for (mm_slot = ksm_scan.mm_slot; |
646 | mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) { | |
31dbd01f IE |
647 | mm = mm_slot->mm; |
648 | down_read(&mm->mmap_sem); | |
649 | for (vma = mm->mmap; vma; vma = vma->vm_next) { | |
9ba69294 HD |
650 | if (ksm_test_exit(mm)) |
651 | break; | |
31dbd01f IE |
652 | if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma) |
653 | continue; | |
d952b791 HD |
654 | err = unmerge_ksm_pages(vma, |
655 | vma->vm_start, vma->vm_end); | |
9ba69294 HD |
656 | if (err) |
657 | goto error; | |
31dbd01f | 658 | } |
9ba69294 | 659 | |
6514d511 | 660 | remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list); |
d952b791 HD |
661 | |
662 | spin_lock(&ksm_mmlist_lock); | |
9ba69294 | 663 | ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next, |
d952b791 | 664 | struct mm_slot, mm_list); |
9ba69294 HD |
665 | if (ksm_test_exit(mm)) { |
666 | hlist_del(&mm_slot->link); | |
667 | list_del(&mm_slot->mm_list); | |
668 | spin_unlock(&ksm_mmlist_lock); | |
669 | ||
670 | free_mm_slot(mm_slot); | |
671 | clear_bit(MMF_VM_MERGEABLE, &mm->flags); | |
672 | up_read(&mm->mmap_sem); | |
673 | mmdrop(mm); | |
674 | } else { | |
675 | spin_unlock(&ksm_mmlist_lock); | |
676 | up_read(&mm->mmap_sem); | |
677 | } | |
31dbd01f IE |
678 | } |
679 | ||
d952b791 | 680 | ksm_scan.seqnr = 0; |
9ba69294 HD |
681 | return 0; |
682 | ||
683 | error: | |
684 | up_read(&mm->mmap_sem); | |
31dbd01f | 685 | spin_lock(&ksm_mmlist_lock); |
d952b791 | 686 | ksm_scan.mm_slot = &ksm_mm_head; |
31dbd01f | 687 | spin_unlock(&ksm_mmlist_lock); |
d952b791 | 688 | return err; |
31dbd01f | 689 | } |
2ffd8679 | 690 | #endif /* CONFIG_SYSFS */ |
31dbd01f | 691 | |
31dbd01f IE |
692 | static u32 calc_checksum(struct page *page) |
693 | { | |
694 | u32 checksum; | |
695 | void *addr = kmap_atomic(page, KM_USER0); | |
696 | checksum = jhash2(addr, PAGE_SIZE / 4, 17); | |
697 | kunmap_atomic(addr, KM_USER0); | |
698 | return checksum; | |
699 | } | |
700 | ||
701 | static int memcmp_pages(struct page *page1, struct page *page2) | |
702 | { | |
703 | char *addr1, *addr2; | |
704 | int ret; | |
705 | ||
706 | addr1 = kmap_atomic(page1, KM_USER0); | |
707 | addr2 = kmap_atomic(page2, KM_USER1); | |
708 | ret = memcmp(addr1, addr2, PAGE_SIZE); | |
709 | kunmap_atomic(addr2, KM_USER1); | |
710 | kunmap_atomic(addr1, KM_USER0); | |
711 | return ret; | |
712 | } | |
713 | ||
714 | static inline int pages_identical(struct page *page1, struct page *page2) | |
715 | { | |
716 | return !memcmp_pages(page1, page2); | |
717 | } | |
718 | ||
719 | static int write_protect_page(struct vm_area_struct *vma, struct page *page, | |
720 | pte_t *orig_pte) | |
721 | { | |
722 | struct mm_struct *mm = vma->vm_mm; | |
723 | unsigned long addr; | |
724 | pte_t *ptep; | |
725 | spinlock_t *ptl; | |
726 | int swapped; | |
727 | int err = -EFAULT; | |
728 | ||
729 | addr = page_address_in_vma(page, vma); | |
730 | if (addr == -EFAULT) | |
731 | goto out; | |
732 | ||
733 | ptep = page_check_address(page, mm, addr, &ptl, 0); | |
734 | if (!ptep) | |
735 | goto out; | |
736 | ||
737 | if (pte_write(*ptep)) { | |
738 | pte_t entry; | |
739 | ||
740 | swapped = PageSwapCache(page); | |
741 | flush_cache_page(vma, addr, page_to_pfn(page)); | |
742 | /* | |
743 | * Ok this is tricky, when get_user_pages_fast() run it doesnt | |
744 | * take any lock, therefore the check that we are going to make | |
745 | * with the pagecount against the mapcount is racey and | |
746 | * O_DIRECT can happen right after the check. | |
747 | * So we clear the pte and flush the tlb before the check | |
748 | * this assure us that no O_DIRECT can happen after the check | |
749 | * or in the middle of the check. | |
750 | */ | |
751 | entry = ptep_clear_flush(vma, addr, ptep); | |
752 | /* | |
753 | * Check that no O_DIRECT or similar I/O is in progress on the | |
754 | * page | |
755 | */ | |
31e855ea | 756 | if (page_mapcount(page) + 1 + swapped != page_count(page)) { |
31dbd01f IE |
757 | set_pte_at_notify(mm, addr, ptep, entry); |
758 | goto out_unlock; | |
759 | } | |
760 | entry = pte_wrprotect(entry); | |
761 | set_pte_at_notify(mm, addr, ptep, entry); | |
762 | } | |
763 | *orig_pte = *ptep; | |
764 | err = 0; | |
765 | ||
766 | out_unlock: | |
767 | pte_unmap_unlock(ptep, ptl); | |
768 | out: | |
769 | return err; | |
770 | } | |
771 | ||
772 | /** | |
773 | * replace_page - replace page in vma by new ksm page | |
8dd3557a HD |
774 | * @vma: vma that holds the pte pointing to page |
775 | * @page: the page we are replacing by kpage | |
776 | * @kpage: the ksm page we replace page by | |
31dbd01f IE |
777 | * @orig_pte: the original value of the pte |
778 | * | |
779 | * Returns 0 on success, -EFAULT on failure. | |
780 | */ | |
8dd3557a HD |
781 | static int replace_page(struct vm_area_struct *vma, struct page *page, |
782 | struct page *kpage, pte_t orig_pte) | |
31dbd01f IE |
783 | { |
784 | struct mm_struct *mm = vma->vm_mm; | |
785 | pgd_t *pgd; | |
786 | pud_t *pud; | |
787 | pmd_t *pmd; | |
788 | pte_t *ptep; | |
789 | spinlock_t *ptl; | |
790 | unsigned long addr; | |
31dbd01f IE |
791 | int err = -EFAULT; |
792 | ||
8dd3557a | 793 | addr = page_address_in_vma(page, vma); |
31dbd01f IE |
794 | if (addr == -EFAULT) |
795 | goto out; | |
796 | ||
797 | pgd = pgd_offset(mm, addr); | |
798 | if (!pgd_present(*pgd)) | |
799 | goto out; | |
800 | ||
801 | pud = pud_offset(pgd, addr); | |
802 | if (!pud_present(*pud)) | |
803 | goto out; | |
804 | ||
805 | pmd = pmd_offset(pud, addr); | |
806 | if (!pmd_present(*pmd)) | |
807 | goto out; | |
808 | ||
809 | ptep = pte_offset_map_lock(mm, pmd, addr, &ptl); | |
810 | if (!pte_same(*ptep, orig_pte)) { | |
811 | pte_unmap_unlock(ptep, ptl); | |
812 | goto out; | |
813 | } | |
814 | ||
8dd3557a | 815 | get_page(kpage); |
5ad64688 | 816 | page_add_anon_rmap(kpage, vma, addr); |
31dbd01f IE |
817 | |
818 | flush_cache_page(vma, addr, pte_pfn(*ptep)); | |
819 | ptep_clear_flush(vma, addr, ptep); | |
8dd3557a | 820 | set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot)); |
31dbd01f | 821 | |
8dd3557a HD |
822 | page_remove_rmap(page); |
823 | put_page(page); | |
31dbd01f IE |
824 | |
825 | pte_unmap_unlock(ptep, ptl); | |
826 | err = 0; | |
827 | out: | |
828 | return err; | |
829 | } | |
830 | ||
831 | /* | |
832 | * try_to_merge_one_page - take two pages and merge them into one | |
8dd3557a HD |
833 | * @vma: the vma that holds the pte pointing to page |
834 | * @page: the PageAnon page that we want to replace with kpage | |
80e14822 HD |
835 | * @kpage: the PageKsm page that we want to map instead of page, |
836 | * or NULL the first time when we want to use page as kpage. | |
31dbd01f IE |
837 | * |
838 | * This function returns 0 if the pages were merged, -EFAULT otherwise. | |
839 | */ | |
840 | static int try_to_merge_one_page(struct vm_area_struct *vma, | |
8dd3557a | 841 | struct page *page, struct page *kpage) |
31dbd01f IE |
842 | { |
843 | pte_t orig_pte = __pte(0); | |
844 | int err = -EFAULT; | |
845 | ||
db114b83 HD |
846 | if (page == kpage) /* ksm page forked */ |
847 | return 0; | |
848 | ||
31dbd01f IE |
849 | if (!(vma->vm_flags & VM_MERGEABLE)) |
850 | goto out; | |
8dd3557a | 851 | if (!PageAnon(page)) |
31dbd01f IE |
852 | goto out; |
853 | ||
31dbd01f IE |
854 | /* |
855 | * We need the page lock to read a stable PageSwapCache in | |
856 | * write_protect_page(). We use trylock_page() instead of | |
857 | * lock_page() because we don't want to wait here - we | |
858 | * prefer to continue scanning and merging different pages, | |
859 | * then come back to this page when it is unlocked. | |
860 | */ | |
8dd3557a | 861 | if (!trylock_page(page)) |
31e855ea | 862 | goto out; |
31dbd01f IE |
863 | /* |
864 | * If this anonymous page is mapped only here, its pte may need | |
865 | * to be write-protected. If it's mapped elsewhere, all of its | |
866 | * ptes are necessarily already write-protected. But in either | |
867 | * case, we need to lock and check page_count is not raised. | |
868 | */ | |
80e14822 HD |
869 | if (write_protect_page(vma, page, &orig_pte) == 0) { |
870 | if (!kpage) { | |
871 | /* | |
872 | * While we hold page lock, upgrade page from | |
873 | * PageAnon+anon_vma to PageKsm+NULL stable_node: | |
874 | * stable_tree_insert() will update stable_node. | |
875 | */ | |
876 | set_page_stable_node(page, NULL); | |
877 | mark_page_accessed(page); | |
878 | err = 0; | |
879 | } else if (pages_identical(page, kpage)) | |
880 | err = replace_page(vma, page, kpage, orig_pte); | |
881 | } | |
31dbd01f | 882 | |
80e14822 | 883 | if ((vma->vm_flags & VM_LOCKED) && kpage && !err) { |
73848b46 | 884 | munlock_vma_page(page); |
5ad64688 HD |
885 | if (!PageMlocked(kpage)) { |
886 | unlock_page(page); | |
5ad64688 HD |
887 | lock_page(kpage); |
888 | mlock_vma_page(kpage); | |
889 | page = kpage; /* for final unlock */ | |
890 | } | |
891 | } | |
73848b46 | 892 | |
8dd3557a | 893 | unlock_page(page); |
31dbd01f IE |
894 | out: |
895 | return err; | |
896 | } | |
897 | ||
81464e30 HD |
898 | /* |
899 | * try_to_merge_with_ksm_page - like try_to_merge_two_pages, | |
900 | * but no new kernel page is allocated: kpage must already be a ksm page. | |
8dd3557a HD |
901 | * |
902 | * This function returns 0 if the pages were merged, -EFAULT otherwise. | |
81464e30 | 903 | */ |
8dd3557a HD |
904 | static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item, |
905 | struct page *page, struct page *kpage) | |
81464e30 | 906 | { |
8dd3557a | 907 | struct mm_struct *mm = rmap_item->mm; |
81464e30 HD |
908 | struct vm_area_struct *vma; |
909 | int err = -EFAULT; | |
910 | ||
8dd3557a HD |
911 | down_read(&mm->mmap_sem); |
912 | if (ksm_test_exit(mm)) | |
9ba69294 | 913 | goto out; |
8dd3557a HD |
914 | vma = find_vma(mm, rmap_item->address); |
915 | if (!vma || vma->vm_start > rmap_item->address) | |
81464e30 HD |
916 | goto out; |
917 | ||
8dd3557a | 918 | err = try_to_merge_one_page(vma, page, kpage); |
db114b83 HD |
919 | if (err) |
920 | goto out; | |
921 | ||
922 | /* Must get reference to anon_vma while still holding mmap_sem */ | |
923 | hold_anon_vma(rmap_item, vma->anon_vma); | |
81464e30 | 924 | out: |
8dd3557a | 925 | up_read(&mm->mmap_sem); |
81464e30 HD |
926 | return err; |
927 | } | |
928 | ||
31dbd01f IE |
929 | /* |
930 | * try_to_merge_two_pages - take two identical pages and prepare them | |
931 | * to be merged into one page. | |
932 | * | |
8dd3557a HD |
933 | * This function returns the kpage if we successfully merged two identical |
934 | * pages into one ksm page, NULL otherwise. | |
31dbd01f | 935 | * |
80e14822 | 936 | * Note that this function upgrades page to ksm page: if one of the pages |
31dbd01f IE |
937 | * is already a ksm page, try_to_merge_with_ksm_page should be used. |
938 | */ | |
8dd3557a HD |
939 | static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item, |
940 | struct page *page, | |
941 | struct rmap_item *tree_rmap_item, | |
942 | struct page *tree_page) | |
31dbd01f | 943 | { |
80e14822 | 944 | int err; |
31dbd01f IE |
945 | |
946 | /* | |
947 | * The number of nodes in the stable tree | |
948 | * is the number of kernel pages that we hold. | |
949 | */ | |
950 | if (ksm_max_kernel_pages && | |
b4028260 | 951 | ksm_max_kernel_pages <= ksm_pages_shared) |
8dd3557a | 952 | return NULL; |
31dbd01f | 953 | |
80e14822 | 954 | err = try_to_merge_with_ksm_page(rmap_item, page, NULL); |
31dbd01f | 955 | if (!err) { |
8dd3557a | 956 | err = try_to_merge_with_ksm_page(tree_rmap_item, |
80e14822 | 957 | tree_page, page); |
31dbd01f | 958 | /* |
81464e30 HD |
959 | * If that fails, we have a ksm page with only one pte |
960 | * pointing to it: so break it. | |
31dbd01f | 961 | */ |
4035c07a | 962 | if (err) |
8dd3557a | 963 | break_cow(rmap_item); |
31dbd01f | 964 | } |
80e14822 | 965 | return err ? NULL : page; |
31dbd01f IE |
966 | } |
967 | ||
31dbd01f | 968 | /* |
8dd3557a | 969 | * stable_tree_search - search for page inside the stable tree |
31dbd01f IE |
970 | * |
971 | * This function checks if there is a page inside the stable tree | |
972 | * with identical content to the page that we are scanning right now. | |
973 | * | |
7b6ba2c7 | 974 | * This function returns the stable tree node of identical content if found, |
31dbd01f IE |
975 | * NULL otherwise. |
976 | */ | |
62b61f61 | 977 | static struct page *stable_tree_search(struct page *page) |
31dbd01f IE |
978 | { |
979 | struct rb_node *node = root_stable_tree.rb_node; | |
7b6ba2c7 | 980 | struct stable_node *stable_node; |
31dbd01f | 981 | |
08beca44 HD |
982 | stable_node = page_stable_node(page); |
983 | if (stable_node) { /* ksm page forked */ | |
984 | get_page(page); | |
62b61f61 | 985 | return page; |
08beca44 HD |
986 | } |
987 | ||
31dbd01f | 988 | while (node) { |
4035c07a | 989 | struct page *tree_page; |
31dbd01f IE |
990 | int ret; |
991 | ||
08beca44 | 992 | cond_resched(); |
7b6ba2c7 | 993 | stable_node = rb_entry(node, struct stable_node, node); |
4035c07a HD |
994 | tree_page = get_ksm_page(stable_node); |
995 | if (!tree_page) | |
996 | return NULL; | |
31dbd01f | 997 | |
4035c07a | 998 | ret = memcmp_pages(page, tree_page); |
31dbd01f | 999 | |
4035c07a HD |
1000 | if (ret < 0) { |
1001 | put_page(tree_page); | |
31dbd01f | 1002 | node = node->rb_left; |
4035c07a HD |
1003 | } else if (ret > 0) { |
1004 | put_page(tree_page); | |
31dbd01f | 1005 | node = node->rb_right; |
4035c07a | 1006 | } else |
62b61f61 | 1007 | return tree_page; |
31dbd01f IE |
1008 | } |
1009 | ||
1010 | return NULL; | |
1011 | } | |
1012 | ||
1013 | /* | |
1014 | * stable_tree_insert - insert rmap_item pointing to new ksm page | |
1015 | * into the stable tree. | |
1016 | * | |
7b6ba2c7 HD |
1017 | * This function returns the stable tree node just allocated on success, |
1018 | * NULL otherwise. | |
31dbd01f | 1019 | */ |
7b6ba2c7 | 1020 | static struct stable_node *stable_tree_insert(struct page *kpage) |
31dbd01f IE |
1021 | { |
1022 | struct rb_node **new = &root_stable_tree.rb_node; | |
1023 | struct rb_node *parent = NULL; | |
7b6ba2c7 | 1024 | struct stable_node *stable_node; |
31dbd01f IE |
1025 | |
1026 | while (*new) { | |
4035c07a | 1027 | struct page *tree_page; |
31dbd01f IE |
1028 | int ret; |
1029 | ||
08beca44 | 1030 | cond_resched(); |
7b6ba2c7 | 1031 | stable_node = rb_entry(*new, struct stable_node, node); |
4035c07a HD |
1032 | tree_page = get_ksm_page(stable_node); |
1033 | if (!tree_page) | |
1034 | return NULL; | |
31dbd01f | 1035 | |
4035c07a HD |
1036 | ret = memcmp_pages(kpage, tree_page); |
1037 | put_page(tree_page); | |
31dbd01f IE |
1038 | |
1039 | parent = *new; | |
1040 | if (ret < 0) | |
1041 | new = &parent->rb_left; | |
1042 | else if (ret > 0) | |
1043 | new = &parent->rb_right; | |
1044 | else { | |
1045 | /* | |
1046 | * It is not a bug that stable_tree_search() didn't | |
1047 | * find this node: because at that time our page was | |
1048 | * not yet write-protected, so may have changed since. | |
1049 | */ | |
1050 | return NULL; | |
1051 | } | |
1052 | } | |
1053 | ||
7b6ba2c7 HD |
1054 | stable_node = alloc_stable_node(); |
1055 | if (!stable_node) | |
1056 | return NULL; | |
31dbd01f | 1057 | |
7b6ba2c7 HD |
1058 | rb_link_node(&stable_node->node, parent, new); |
1059 | rb_insert_color(&stable_node->node, &root_stable_tree); | |
1060 | ||
1061 | INIT_HLIST_HEAD(&stable_node->hlist); | |
1062 | ||
62b61f61 | 1063 | stable_node->kpfn = page_to_pfn(kpage); |
08beca44 HD |
1064 | set_page_stable_node(kpage, stable_node); |
1065 | ||
7b6ba2c7 | 1066 | return stable_node; |
31dbd01f IE |
1067 | } |
1068 | ||
1069 | /* | |
8dd3557a HD |
1070 | * unstable_tree_search_insert - search for identical page, |
1071 | * else insert rmap_item into the unstable tree. | |
31dbd01f IE |
1072 | * |
1073 | * This function searches for a page in the unstable tree identical to the | |
1074 | * page currently being scanned; and if no identical page is found in the | |
1075 | * tree, we insert rmap_item as a new object into the unstable tree. | |
1076 | * | |
1077 | * This function returns pointer to rmap_item found to be identical | |
1078 | * to the currently scanned page, NULL otherwise. | |
1079 | * | |
1080 | * This function does both searching and inserting, because they share | |
1081 | * the same walking algorithm in an rbtree. | |
1082 | */ | |
8dd3557a HD |
1083 | static |
1084 | struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item, | |
1085 | struct page *page, | |
1086 | struct page **tree_pagep) | |
1087 | ||
31dbd01f IE |
1088 | { |
1089 | struct rb_node **new = &root_unstable_tree.rb_node; | |
1090 | struct rb_node *parent = NULL; | |
1091 | ||
1092 | while (*new) { | |
1093 | struct rmap_item *tree_rmap_item; | |
8dd3557a | 1094 | struct page *tree_page; |
31dbd01f IE |
1095 | int ret; |
1096 | ||
d178f27f | 1097 | cond_resched(); |
31dbd01f | 1098 | tree_rmap_item = rb_entry(*new, struct rmap_item, node); |
8dd3557a HD |
1099 | tree_page = get_mergeable_page(tree_rmap_item); |
1100 | if (!tree_page) | |
31dbd01f IE |
1101 | return NULL; |
1102 | ||
1103 | /* | |
8dd3557a | 1104 | * Don't substitute a ksm page for a forked page. |
31dbd01f | 1105 | */ |
8dd3557a HD |
1106 | if (page == tree_page) { |
1107 | put_page(tree_page); | |
31dbd01f IE |
1108 | return NULL; |
1109 | } | |
1110 | ||
8dd3557a | 1111 | ret = memcmp_pages(page, tree_page); |
31dbd01f IE |
1112 | |
1113 | parent = *new; | |
1114 | if (ret < 0) { | |
8dd3557a | 1115 | put_page(tree_page); |
31dbd01f IE |
1116 | new = &parent->rb_left; |
1117 | } else if (ret > 0) { | |
8dd3557a | 1118 | put_page(tree_page); |
31dbd01f IE |
1119 | new = &parent->rb_right; |
1120 | } else { | |
8dd3557a | 1121 | *tree_pagep = tree_page; |
31dbd01f IE |
1122 | return tree_rmap_item; |
1123 | } | |
1124 | } | |
1125 | ||
7b6ba2c7 | 1126 | rmap_item->address |= UNSTABLE_FLAG; |
31dbd01f IE |
1127 | rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK); |
1128 | rb_link_node(&rmap_item->node, parent, new); | |
1129 | rb_insert_color(&rmap_item->node, &root_unstable_tree); | |
1130 | ||
473b0ce4 | 1131 | ksm_pages_unshared++; |
31dbd01f IE |
1132 | return NULL; |
1133 | } | |
1134 | ||
1135 | /* | |
1136 | * stable_tree_append - add another rmap_item to the linked list of | |
1137 | * rmap_items hanging off a given node of the stable tree, all sharing | |
1138 | * the same ksm page. | |
1139 | */ | |
1140 | static void stable_tree_append(struct rmap_item *rmap_item, | |
7b6ba2c7 | 1141 | struct stable_node *stable_node) |
31dbd01f | 1142 | { |
7b6ba2c7 | 1143 | rmap_item->head = stable_node; |
31dbd01f | 1144 | rmap_item->address |= STABLE_FLAG; |
7b6ba2c7 | 1145 | hlist_add_head(&rmap_item->hlist, &stable_node->hlist); |
e178dfde | 1146 | |
7b6ba2c7 HD |
1147 | if (rmap_item->hlist.next) |
1148 | ksm_pages_sharing++; | |
1149 | else | |
1150 | ksm_pages_shared++; | |
31dbd01f IE |
1151 | } |
1152 | ||
1153 | /* | |
81464e30 HD |
1154 | * cmp_and_merge_page - first see if page can be merged into the stable tree; |
1155 | * if not, compare checksum to previous and if it's the same, see if page can | |
1156 | * be inserted into the unstable tree, or merged with a page already there and | |
1157 | * both transferred to the stable tree. | |
31dbd01f IE |
1158 | * |
1159 | * @page: the page that we are searching identical page to. | |
1160 | * @rmap_item: the reverse mapping into the virtual address of this page | |
1161 | */ | |
1162 | static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item) | |
1163 | { | |
31dbd01f | 1164 | struct rmap_item *tree_rmap_item; |
8dd3557a | 1165 | struct page *tree_page = NULL; |
7b6ba2c7 | 1166 | struct stable_node *stable_node; |
8dd3557a | 1167 | struct page *kpage; |
31dbd01f IE |
1168 | unsigned int checksum; |
1169 | int err; | |
1170 | ||
93d17715 | 1171 | remove_rmap_item_from_tree(rmap_item); |
31dbd01f IE |
1172 | |
1173 | /* We first start with searching the page inside the stable tree */ | |
62b61f61 HD |
1174 | kpage = stable_tree_search(page); |
1175 | if (kpage) { | |
08beca44 | 1176 | err = try_to_merge_with_ksm_page(rmap_item, page, kpage); |
31dbd01f IE |
1177 | if (!err) { |
1178 | /* | |
1179 | * The page was successfully merged: | |
1180 | * add its rmap_item to the stable tree. | |
1181 | */ | |
5ad64688 | 1182 | lock_page(kpage); |
62b61f61 | 1183 | stable_tree_append(rmap_item, page_stable_node(kpage)); |
5ad64688 | 1184 | unlock_page(kpage); |
31dbd01f | 1185 | } |
8dd3557a | 1186 | put_page(kpage); |
31dbd01f IE |
1187 | return; |
1188 | } | |
1189 | ||
1190 | /* | |
4035c07a HD |
1191 | * If the hash value of the page has changed from the last time |
1192 | * we calculated it, this page is changing frequently: therefore we | |
1193 | * don't want to insert it in the unstable tree, and we don't want | |
1194 | * to waste our time searching for something identical to it there. | |
31dbd01f IE |
1195 | */ |
1196 | checksum = calc_checksum(page); | |
1197 | if (rmap_item->oldchecksum != checksum) { | |
1198 | rmap_item->oldchecksum = checksum; | |
1199 | return; | |
1200 | } | |
1201 | ||
8dd3557a HD |
1202 | tree_rmap_item = |
1203 | unstable_tree_search_insert(rmap_item, page, &tree_page); | |
31dbd01f | 1204 | if (tree_rmap_item) { |
8dd3557a HD |
1205 | kpage = try_to_merge_two_pages(rmap_item, page, |
1206 | tree_rmap_item, tree_page); | |
1207 | put_page(tree_page); | |
31dbd01f IE |
1208 | /* |
1209 | * As soon as we merge this page, we want to remove the | |
1210 | * rmap_item of the page we have merged with from the unstable | |
1211 | * tree, and insert it instead as new node in the stable tree. | |
1212 | */ | |
8dd3557a | 1213 | if (kpage) { |
93d17715 | 1214 | remove_rmap_item_from_tree(tree_rmap_item); |
473b0ce4 | 1215 | |
5ad64688 | 1216 | lock_page(kpage); |
7b6ba2c7 HD |
1217 | stable_node = stable_tree_insert(kpage); |
1218 | if (stable_node) { | |
1219 | stable_tree_append(tree_rmap_item, stable_node); | |
1220 | stable_tree_append(rmap_item, stable_node); | |
1221 | } | |
5ad64688 | 1222 | unlock_page(kpage); |
7b6ba2c7 | 1223 | |
31dbd01f IE |
1224 | /* |
1225 | * If we fail to insert the page into the stable tree, | |
1226 | * we will have 2 virtual addresses that are pointing | |
1227 | * to a ksm page left outside the stable tree, | |
1228 | * in which case we need to break_cow on both. | |
1229 | */ | |
7b6ba2c7 | 1230 | if (!stable_node) { |
8dd3557a HD |
1231 | break_cow(tree_rmap_item); |
1232 | break_cow(rmap_item); | |
31dbd01f IE |
1233 | } |
1234 | } | |
31dbd01f IE |
1235 | } |
1236 | } | |
1237 | ||
1238 | static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot, | |
6514d511 | 1239 | struct rmap_item **rmap_list, |
31dbd01f IE |
1240 | unsigned long addr) |
1241 | { | |
1242 | struct rmap_item *rmap_item; | |
1243 | ||
6514d511 HD |
1244 | while (*rmap_list) { |
1245 | rmap_item = *rmap_list; | |
93d17715 | 1246 | if ((rmap_item->address & PAGE_MASK) == addr) |
31dbd01f | 1247 | return rmap_item; |
31dbd01f IE |
1248 | if (rmap_item->address > addr) |
1249 | break; | |
6514d511 | 1250 | *rmap_list = rmap_item->rmap_list; |
31dbd01f | 1251 | remove_rmap_item_from_tree(rmap_item); |
31dbd01f IE |
1252 | free_rmap_item(rmap_item); |
1253 | } | |
1254 | ||
1255 | rmap_item = alloc_rmap_item(); | |
1256 | if (rmap_item) { | |
1257 | /* It has already been zeroed */ | |
1258 | rmap_item->mm = mm_slot->mm; | |
1259 | rmap_item->address = addr; | |
6514d511 HD |
1260 | rmap_item->rmap_list = *rmap_list; |
1261 | *rmap_list = rmap_item; | |
31dbd01f IE |
1262 | } |
1263 | return rmap_item; | |
1264 | } | |
1265 | ||
1266 | static struct rmap_item *scan_get_next_rmap_item(struct page **page) | |
1267 | { | |
1268 | struct mm_struct *mm; | |
1269 | struct mm_slot *slot; | |
1270 | struct vm_area_struct *vma; | |
1271 | struct rmap_item *rmap_item; | |
1272 | ||
1273 | if (list_empty(&ksm_mm_head.mm_list)) | |
1274 | return NULL; | |
1275 | ||
1276 | slot = ksm_scan.mm_slot; | |
1277 | if (slot == &ksm_mm_head) { | |
1278 | root_unstable_tree = RB_ROOT; | |
1279 | ||
1280 | spin_lock(&ksm_mmlist_lock); | |
1281 | slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list); | |
1282 | ksm_scan.mm_slot = slot; | |
1283 | spin_unlock(&ksm_mmlist_lock); | |
1284 | next_mm: | |
1285 | ksm_scan.address = 0; | |
6514d511 | 1286 | ksm_scan.rmap_list = &slot->rmap_list; |
31dbd01f IE |
1287 | } |
1288 | ||
1289 | mm = slot->mm; | |
1290 | down_read(&mm->mmap_sem); | |
9ba69294 HD |
1291 | if (ksm_test_exit(mm)) |
1292 | vma = NULL; | |
1293 | else | |
1294 | vma = find_vma(mm, ksm_scan.address); | |
1295 | ||
1296 | for (; vma; vma = vma->vm_next) { | |
31dbd01f IE |
1297 | if (!(vma->vm_flags & VM_MERGEABLE)) |
1298 | continue; | |
1299 | if (ksm_scan.address < vma->vm_start) | |
1300 | ksm_scan.address = vma->vm_start; | |
1301 | if (!vma->anon_vma) | |
1302 | ksm_scan.address = vma->vm_end; | |
1303 | ||
1304 | while (ksm_scan.address < vma->vm_end) { | |
9ba69294 HD |
1305 | if (ksm_test_exit(mm)) |
1306 | break; | |
31dbd01f IE |
1307 | *page = follow_page(vma, ksm_scan.address, FOLL_GET); |
1308 | if (*page && PageAnon(*page)) { | |
1309 | flush_anon_page(vma, *page, ksm_scan.address); | |
1310 | flush_dcache_page(*page); | |
1311 | rmap_item = get_next_rmap_item(slot, | |
6514d511 | 1312 | ksm_scan.rmap_list, ksm_scan.address); |
31dbd01f | 1313 | if (rmap_item) { |
6514d511 HD |
1314 | ksm_scan.rmap_list = |
1315 | &rmap_item->rmap_list; | |
31dbd01f IE |
1316 | ksm_scan.address += PAGE_SIZE; |
1317 | } else | |
1318 | put_page(*page); | |
1319 | up_read(&mm->mmap_sem); | |
1320 | return rmap_item; | |
1321 | } | |
1322 | if (*page) | |
1323 | put_page(*page); | |
1324 | ksm_scan.address += PAGE_SIZE; | |
1325 | cond_resched(); | |
1326 | } | |
1327 | } | |
1328 | ||
9ba69294 HD |
1329 | if (ksm_test_exit(mm)) { |
1330 | ksm_scan.address = 0; | |
6514d511 | 1331 | ksm_scan.rmap_list = &slot->rmap_list; |
9ba69294 | 1332 | } |
31dbd01f IE |
1333 | /* |
1334 | * Nuke all the rmap_items that are above this current rmap: | |
1335 | * because there were no VM_MERGEABLE vmas with such addresses. | |
1336 | */ | |
6514d511 | 1337 | remove_trailing_rmap_items(slot, ksm_scan.rmap_list); |
31dbd01f IE |
1338 | |
1339 | spin_lock(&ksm_mmlist_lock); | |
cd551f97 HD |
1340 | ksm_scan.mm_slot = list_entry(slot->mm_list.next, |
1341 | struct mm_slot, mm_list); | |
1342 | if (ksm_scan.address == 0) { | |
1343 | /* | |
1344 | * We've completed a full scan of all vmas, holding mmap_sem | |
1345 | * throughout, and found no VM_MERGEABLE: so do the same as | |
1346 | * __ksm_exit does to remove this mm from all our lists now. | |
9ba69294 HD |
1347 | * This applies either when cleaning up after __ksm_exit |
1348 | * (but beware: we can reach here even before __ksm_exit), | |
1349 | * or when all VM_MERGEABLE areas have been unmapped (and | |
1350 | * mmap_sem then protects against race with MADV_MERGEABLE). | |
cd551f97 HD |
1351 | */ |
1352 | hlist_del(&slot->link); | |
1353 | list_del(&slot->mm_list); | |
9ba69294 HD |
1354 | spin_unlock(&ksm_mmlist_lock); |
1355 | ||
cd551f97 HD |
1356 | free_mm_slot(slot); |
1357 | clear_bit(MMF_VM_MERGEABLE, &mm->flags); | |
9ba69294 HD |
1358 | up_read(&mm->mmap_sem); |
1359 | mmdrop(mm); | |
1360 | } else { | |
1361 | spin_unlock(&ksm_mmlist_lock); | |
1362 | up_read(&mm->mmap_sem); | |
cd551f97 | 1363 | } |
31dbd01f IE |
1364 | |
1365 | /* Repeat until we've completed scanning the whole list */ | |
cd551f97 | 1366 | slot = ksm_scan.mm_slot; |
31dbd01f IE |
1367 | if (slot != &ksm_mm_head) |
1368 | goto next_mm; | |
1369 | ||
31dbd01f IE |
1370 | ksm_scan.seqnr++; |
1371 | return NULL; | |
1372 | } | |
1373 | ||
1374 | /** | |
1375 | * ksm_do_scan - the ksm scanner main worker function. | |
1376 | * @scan_npages - number of pages we want to scan before we return. | |
1377 | */ | |
1378 | static void ksm_do_scan(unsigned int scan_npages) | |
1379 | { | |
1380 | struct rmap_item *rmap_item; | |
1381 | struct page *page; | |
1382 | ||
1383 | while (scan_npages--) { | |
1384 | cond_resched(); | |
1385 | rmap_item = scan_get_next_rmap_item(&page); | |
1386 | if (!rmap_item) | |
1387 | return; | |
1388 | if (!PageKsm(page) || !in_stable_tree(rmap_item)) | |
1389 | cmp_and_merge_page(page, rmap_item); | |
1390 | put_page(page); | |
1391 | } | |
1392 | } | |
1393 | ||
6e158384 HD |
1394 | static int ksmd_should_run(void) |
1395 | { | |
1396 | return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list); | |
1397 | } | |
1398 | ||
31dbd01f IE |
1399 | static int ksm_scan_thread(void *nothing) |
1400 | { | |
339aa624 | 1401 | set_user_nice(current, 5); |
31dbd01f IE |
1402 | |
1403 | while (!kthread_should_stop()) { | |
6e158384 HD |
1404 | mutex_lock(&ksm_thread_mutex); |
1405 | if (ksmd_should_run()) | |
31dbd01f | 1406 | ksm_do_scan(ksm_thread_pages_to_scan); |
6e158384 HD |
1407 | mutex_unlock(&ksm_thread_mutex); |
1408 | ||
1409 | if (ksmd_should_run()) { | |
31dbd01f IE |
1410 | schedule_timeout_interruptible( |
1411 | msecs_to_jiffies(ksm_thread_sleep_millisecs)); | |
1412 | } else { | |
1413 | wait_event_interruptible(ksm_thread_wait, | |
6e158384 | 1414 | ksmd_should_run() || kthread_should_stop()); |
31dbd01f IE |
1415 | } |
1416 | } | |
1417 | return 0; | |
1418 | } | |
1419 | ||
f8af4da3 HD |
1420 | int ksm_madvise(struct vm_area_struct *vma, unsigned long start, |
1421 | unsigned long end, int advice, unsigned long *vm_flags) | |
1422 | { | |
1423 | struct mm_struct *mm = vma->vm_mm; | |
d952b791 | 1424 | int err; |
f8af4da3 HD |
1425 | |
1426 | switch (advice) { | |
1427 | case MADV_MERGEABLE: | |
1428 | /* | |
1429 | * Be somewhat over-protective for now! | |
1430 | */ | |
1431 | if (*vm_flags & (VM_MERGEABLE | VM_SHARED | VM_MAYSHARE | | |
1432 | VM_PFNMAP | VM_IO | VM_DONTEXPAND | | |
1433 | VM_RESERVED | VM_HUGETLB | VM_INSERTPAGE | | |
5ad64688 | 1434 | VM_NONLINEAR | VM_MIXEDMAP | VM_SAO)) |
f8af4da3 HD |
1435 | return 0; /* just ignore the advice */ |
1436 | ||
d952b791 HD |
1437 | if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) { |
1438 | err = __ksm_enter(mm); | |
1439 | if (err) | |
1440 | return err; | |
1441 | } | |
f8af4da3 HD |
1442 | |
1443 | *vm_flags |= VM_MERGEABLE; | |
1444 | break; | |
1445 | ||
1446 | case MADV_UNMERGEABLE: | |
1447 | if (!(*vm_flags & VM_MERGEABLE)) | |
1448 | return 0; /* just ignore the advice */ | |
1449 | ||
d952b791 HD |
1450 | if (vma->anon_vma) { |
1451 | err = unmerge_ksm_pages(vma, start, end); | |
1452 | if (err) | |
1453 | return err; | |
1454 | } | |
f8af4da3 HD |
1455 | |
1456 | *vm_flags &= ~VM_MERGEABLE; | |
1457 | break; | |
1458 | } | |
1459 | ||
1460 | return 0; | |
1461 | } | |
1462 | ||
1463 | int __ksm_enter(struct mm_struct *mm) | |
1464 | { | |
6e158384 HD |
1465 | struct mm_slot *mm_slot; |
1466 | int needs_wakeup; | |
1467 | ||
1468 | mm_slot = alloc_mm_slot(); | |
31dbd01f IE |
1469 | if (!mm_slot) |
1470 | return -ENOMEM; | |
1471 | ||
6e158384 HD |
1472 | /* Check ksm_run too? Would need tighter locking */ |
1473 | needs_wakeup = list_empty(&ksm_mm_head.mm_list); | |
1474 | ||
31dbd01f IE |
1475 | spin_lock(&ksm_mmlist_lock); |
1476 | insert_to_mm_slots_hash(mm, mm_slot); | |
1477 | /* | |
1478 | * Insert just behind the scanning cursor, to let the area settle | |
1479 | * down a little; when fork is followed by immediate exec, we don't | |
1480 | * want ksmd to waste time setting up and tearing down an rmap_list. | |
1481 | */ | |
1482 | list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list); | |
1483 | spin_unlock(&ksm_mmlist_lock); | |
1484 | ||
f8af4da3 | 1485 | set_bit(MMF_VM_MERGEABLE, &mm->flags); |
9ba69294 | 1486 | atomic_inc(&mm->mm_count); |
6e158384 HD |
1487 | |
1488 | if (needs_wakeup) | |
1489 | wake_up_interruptible(&ksm_thread_wait); | |
1490 | ||
f8af4da3 HD |
1491 | return 0; |
1492 | } | |
1493 | ||
1c2fb7a4 | 1494 | void __ksm_exit(struct mm_struct *mm) |
f8af4da3 | 1495 | { |
cd551f97 | 1496 | struct mm_slot *mm_slot; |
9ba69294 | 1497 | int easy_to_free = 0; |
cd551f97 | 1498 | |
31dbd01f | 1499 | /* |
9ba69294 HD |
1500 | * This process is exiting: if it's straightforward (as is the |
1501 | * case when ksmd was never running), free mm_slot immediately. | |
1502 | * But if it's at the cursor or has rmap_items linked to it, use | |
1503 | * mmap_sem to synchronize with any break_cows before pagetables | |
1504 | * are freed, and leave the mm_slot on the list for ksmd to free. | |
1505 | * Beware: ksm may already have noticed it exiting and freed the slot. | |
31dbd01f | 1506 | */ |
9ba69294 | 1507 | |
cd551f97 HD |
1508 | spin_lock(&ksm_mmlist_lock); |
1509 | mm_slot = get_mm_slot(mm); | |
9ba69294 | 1510 | if (mm_slot && ksm_scan.mm_slot != mm_slot) { |
6514d511 | 1511 | if (!mm_slot->rmap_list) { |
9ba69294 HD |
1512 | hlist_del(&mm_slot->link); |
1513 | list_del(&mm_slot->mm_list); | |
1514 | easy_to_free = 1; | |
1515 | } else { | |
1516 | list_move(&mm_slot->mm_list, | |
1517 | &ksm_scan.mm_slot->mm_list); | |
1518 | } | |
cd551f97 | 1519 | } |
cd551f97 HD |
1520 | spin_unlock(&ksm_mmlist_lock); |
1521 | ||
9ba69294 HD |
1522 | if (easy_to_free) { |
1523 | free_mm_slot(mm_slot); | |
1524 | clear_bit(MMF_VM_MERGEABLE, &mm->flags); | |
1525 | mmdrop(mm); | |
1526 | } else if (mm_slot) { | |
9ba69294 HD |
1527 | down_write(&mm->mmap_sem); |
1528 | up_write(&mm->mmap_sem); | |
9ba69294 | 1529 | } |
31dbd01f IE |
1530 | } |
1531 | ||
5ad64688 HD |
1532 | struct page *ksm_does_need_to_copy(struct page *page, |
1533 | struct vm_area_struct *vma, unsigned long address) | |
1534 | { | |
1535 | struct page *new_page; | |
1536 | ||
1537 | unlock_page(page); /* any racers will COW it, not modify it */ | |
1538 | ||
1539 | new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address); | |
1540 | if (new_page) { | |
1541 | copy_user_highpage(new_page, page, address, vma); | |
1542 | ||
1543 | SetPageDirty(new_page); | |
1544 | __SetPageUptodate(new_page); | |
1545 | SetPageSwapBacked(new_page); | |
1546 | __set_page_locked(new_page); | |
1547 | ||
1548 | if (page_evictable(new_page, vma)) | |
1549 | lru_cache_add_lru(new_page, LRU_ACTIVE_ANON); | |
1550 | else | |
1551 | add_page_to_unevictable_list(new_page); | |
1552 | } | |
1553 | ||
1554 | page_cache_release(page); | |
1555 | return new_page; | |
1556 | } | |
1557 | ||
1558 | int page_referenced_ksm(struct page *page, struct mem_cgroup *memcg, | |
1559 | unsigned long *vm_flags) | |
1560 | { | |
1561 | struct stable_node *stable_node; | |
1562 | struct rmap_item *rmap_item; | |
1563 | struct hlist_node *hlist; | |
1564 | unsigned int mapcount = page_mapcount(page); | |
1565 | int referenced = 0; | |
db114b83 | 1566 | int search_new_forks = 0; |
5ad64688 HD |
1567 | |
1568 | VM_BUG_ON(!PageKsm(page)); | |
1569 | VM_BUG_ON(!PageLocked(page)); | |
1570 | ||
1571 | stable_node = page_stable_node(page); | |
1572 | if (!stable_node) | |
1573 | return 0; | |
db114b83 | 1574 | again: |
5ad64688 | 1575 | hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) { |
db114b83 HD |
1576 | struct anon_vma *anon_vma = rmap_item->anon_vma; |
1577 | struct vm_area_struct *vma; | |
5ad64688 | 1578 | |
db114b83 HD |
1579 | spin_lock(&anon_vma->lock); |
1580 | list_for_each_entry(vma, &anon_vma->head, anon_vma_node) { | |
1581 | if (rmap_item->address < vma->vm_start || | |
1582 | rmap_item->address >= vma->vm_end) | |
1583 | continue; | |
1584 | /* | |
1585 | * Initially we examine only the vma which covers this | |
1586 | * rmap_item; but later, if there is still work to do, | |
1587 | * we examine covering vmas in other mms: in case they | |
1588 | * were forked from the original since ksmd passed. | |
1589 | */ | |
1590 | if ((rmap_item->mm == vma->vm_mm) == search_new_forks) | |
1591 | continue; | |
1592 | ||
1593 | if (memcg && !mm_match_cgroup(vma->vm_mm, memcg)) | |
1594 | continue; | |
5ad64688 | 1595 | |
db114b83 | 1596 | referenced += page_referenced_one(page, vma, |
5ad64688 | 1597 | rmap_item->address, &mapcount, vm_flags); |
db114b83 HD |
1598 | if (!search_new_forks || !mapcount) |
1599 | break; | |
1600 | } | |
1601 | spin_unlock(&anon_vma->lock); | |
5ad64688 HD |
1602 | if (!mapcount) |
1603 | goto out; | |
1604 | } | |
db114b83 HD |
1605 | if (!search_new_forks++) |
1606 | goto again; | |
5ad64688 | 1607 | out: |
5ad64688 HD |
1608 | return referenced; |
1609 | } | |
1610 | ||
1611 | int try_to_unmap_ksm(struct page *page, enum ttu_flags flags) | |
1612 | { | |
1613 | struct stable_node *stable_node; | |
1614 | struct hlist_node *hlist; | |
1615 | struct rmap_item *rmap_item; | |
1616 | int ret = SWAP_AGAIN; | |
db114b83 | 1617 | int search_new_forks = 0; |
5ad64688 HD |
1618 | |
1619 | VM_BUG_ON(!PageKsm(page)); | |
1620 | VM_BUG_ON(!PageLocked(page)); | |
1621 | ||
1622 | stable_node = page_stable_node(page); | |
1623 | if (!stable_node) | |
1624 | return SWAP_FAIL; | |
db114b83 | 1625 | again: |
5ad64688 | 1626 | hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) { |
db114b83 HD |
1627 | struct anon_vma *anon_vma = rmap_item->anon_vma; |
1628 | struct vm_area_struct *vma; | |
5ad64688 | 1629 | |
db114b83 HD |
1630 | spin_lock(&anon_vma->lock); |
1631 | list_for_each_entry(vma, &anon_vma->head, anon_vma_node) { | |
1632 | if (rmap_item->address < vma->vm_start || | |
1633 | rmap_item->address >= vma->vm_end) | |
1634 | continue; | |
1635 | /* | |
1636 | * Initially we examine only the vma which covers this | |
1637 | * rmap_item; but later, if there is still work to do, | |
1638 | * we examine covering vmas in other mms: in case they | |
1639 | * were forked from the original since ksmd passed. | |
1640 | */ | |
1641 | if ((rmap_item->mm == vma->vm_mm) == search_new_forks) | |
1642 | continue; | |
1643 | ||
1644 | ret = try_to_unmap_one(page, vma, | |
1645 | rmap_item->address, flags); | |
1646 | if (ret != SWAP_AGAIN || !page_mapped(page)) { | |
1647 | spin_unlock(&anon_vma->lock); | |
1648 | goto out; | |
1649 | } | |
1650 | } | |
1651 | spin_unlock(&anon_vma->lock); | |
5ad64688 | 1652 | } |
db114b83 HD |
1653 | if (!search_new_forks++) |
1654 | goto again; | |
5ad64688 | 1655 | out: |
5ad64688 HD |
1656 | return ret; |
1657 | } | |
1658 | ||
e9995ef9 HD |
1659 | #ifdef CONFIG_MIGRATION |
1660 | int rmap_walk_ksm(struct page *page, int (*rmap_one)(struct page *, | |
1661 | struct vm_area_struct *, unsigned long, void *), void *arg) | |
1662 | { | |
1663 | struct stable_node *stable_node; | |
1664 | struct hlist_node *hlist; | |
1665 | struct rmap_item *rmap_item; | |
1666 | int ret = SWAP_AGAIN; | |
1667 | int search_new_forks = 0; | |
1668 | ||
1669 | VM_BUG_ON(!PageKsm(page)); | |
1670 | VM_BUG_ON(!PageLocked(page)); | |
1671 | ||
1672 | stable_node = page_stable_node(page); | |
1673 | if (!stable_node) | |
1674 | return ret; | |
1675 | again: | |
1676 | hlist_for_each_entry(rmap_item, hlist, &stable_node->hlist, hlist) { | |
1677 | struct anon_vma *anon_vma = rmap_item->anon_vma; | |
1678 | struct vm_area_struct *vma; | |
1679 | ||
1680 | spin_lock(&anon_vma->lock); | |
1681 | list_for_each_entry(vma, &anon_vma->head, anon_vma_node) { | |
1682 | if (rmap_item->address < vma->vm_start || | |
1683 | rmap_item->address >= vma->vm_end) | |
1684 | continue; | |
1685 | /* | |
1686 | * Initially we examine only the vma which covers this | |
1687 | * rmap_item; but later, if there is still work to do, | |
1688 | * we examine covering vmas in other mms: in case they | |
1689 | * were forked from the original since ksmd passed. | |
1690 | */ | |
1691 | if ((rmap_item->mm == vma->vm_mm) == search_new_forks) | |
1692 | continue; | |
1693 | ||
1694 | ret = rmap_one(page, vma, rmap_item->address, arg); | |
1695 | if (ret != SWAP_AGAIN) { | |
1696 | spin_unlock(&anon_vma->lock); | |
1697 | goto out; | |
1698 | } | |
1699 | } | |
1700 | spin_unlock(&anon_vma->lock); | |
1701 | } | |
1702 | if (!search_new_forks++) | |
1703 | goto again; | |
1704 | out: | |
1705 | return ret; | |
1706 | } | |
1707 | ||
1708 | void ksm_migrate_page(struct page *newpage, struct page *oldpage) | |
1709 | { | |
1710 | struct stable_node *stable_node; | |
1711 | ||
1712 | VM_BUG_ON(!PageLocked(oldpage)); | |
1713 | VM_BUG_ON(!PageLocked(newpage)); | |
1714 | VM_BUG_ON(newpage->mapping != oldpage->mapping); | |
1715 | ||
1716 | stable_node = page_stable_node(newpage); | |
1717 | if (stable_node) { | |
62b61f61 HD |
1718 | VM_BUG_ON(stable_node->kpfn != page_to_pfn(oldpage)); |
1719 | stable_node->kpfn = page_to_pfn(newpage); | |
e9995ef9 HD |
1720 | } |
1721 | } | |
1722 | #endif /* CONFIG_MIGRATION */ | |
1723 | ||
62b61f61 HD |
1724 | #ifdef CONFIG_MEMORY_HOTREMOVE |
1725 | static struct stable_node *ksm_check_stable_tree(unsigned long start_pfn, | |
1726 | unsigned long end_pfn) | |
1727 | { | |
1728 | struct rb_node *node; | |
1729 | ||
1730 | for (node = rb_first(&root_stable_tree); node; node = rb_next(node)) { | |
1731 | struct stable_node *stable_node; | |
1732 | ||
1733 | stable_node = rb_entry(node, struct stable_node, node); | |
1734 | if (stable_node->kpfn >= start_pfn && | |
1735 | stable_node->kpfn < end_pfn) | |
1736 | return stable_node; | |
1737 | } | |
1738 | return NULL; | |
1739 | } | |
1740 | ||
1741 | static int ksm_memory_callback(struct notifier_block *self, | |
1742 | unsigned long action, void *arg) | |
1743 | { | |
1744 | struct memory_notify *mn = arg; | |
1745 | struct stable_node *stable_node; | |
1746 | ||
1747 | switch (action) { | |
1748 | case MEM_GOING_OFFLINE: | |
1749 | /* | |
1750 | * Keep it very simple for now: just lock out ksmd and | |
1751 | * MADV_UNMERGEABLE while any memory is going offline. | |
1752 | */ | |
1753 | mutex_lock(&ksm_thread_mutex); | |
1754 | break; | |
1755 | ||
1756 | case MEM_OFFLINE: | |
1757 | /* | |
1758 | * Most of the work is done by page migration; but there might | |
1759 | * be a few stable_nodes left over, still pointing to struct | |
1760 | * pages which have been offlined: prune those from the tree. | |
1761 | */ | |
1762 | while ((stable_node = ksm_check_stable_tree(mn->start_pfn, | |
1763 | mn->start_pfn + mn->nr_pages)) != NULL) | |
1764 | remove_node_from_stable_tree(stable_node); | |
1765 | /* fallthrough */ | |
1766 | ||
1767 | case MEM_CANCEL_OFFLINE: | |
1768 | mutex_unlock(&ksm_thread_mutex); | |
1769 | break; | |
1770 | } | |
1771 | return NOTIFY_OK; | |
1772 | } | |
1773 | #endif /* CONFIG_MEMORY_HOTREMOVE */ | |
1774 | ||
2ffd8679 HD |
1775 | #ifdef CONFIG_SYSFS |
1776 | /* | |
1777 | * This all compiles without CONFIG_SYSFS, but is a waste of space. | |
1778 | */ | |
1779 | ||
31dbd01f IE |
1780 | #define KSM_ATTR_RO(_name) \ |
1781 | static struct kobj_attribute _name##_attr = __ATTR_RO(_name) | |
1782 | #define KSM_ATTR(_name) \ | |
1783 | static struct kobj_attribute _name##_attr = \ | |
1784 | __ATTR(_name, 0644, _name##_show, _name##_store) | |
1785 | ||
1786 | static ssize_t sleep_millisecs_show(struct kobject *kobj, | |
1787 | struct kobj_attribute *attr, char *buf) | |
1788 | { | |
1789 | return sprintf(buf, "%u\n", ksm_thread_sleep_millisecs); | |
1790 | } | |
1791 | ||
1792 | static ssize_t sleep_millisecs_store(struct kobject *kobj, | |
1793 | struct kobj_attribute *attr, | |
1794 | const char *buf, size_t count) | |
1795 | { | |
1796 | unsigned long msecs; | |
1797 | int err; | |
1798 | ||
1799 | err = strict_strtoul(buf, 10, &msecs); | |
1800 | if (err || msecs > UINT_MAX) | |
1801 | return -EINVAL; | |
1802 | ||
1803 | ksm_thread_sleep_millisecs = msecs; | |
1804 | ||
1805 | return count; | |
1806 | } | |
1807 | KSM_ATTR(sleep_millisecs); | |
1808 | ||
1809 | static ssize_t pages_to_scan_show(struct kobject *kobj, | |
1810 | struct kobj_attribute *attr, char *buf) | |
1811 | { | |
1812 | return sprintf(buf, "%u\n", ksm_thread_pages_to_scan); | |
1813 | } | |
1814 | ||
1815 | static ssize_t pages_to_scan_store(struct kobject *kobj, | |
1816 | struct kobj_attribute *attr, | |
1817 | const char *buf, size_t count) | |
1818 | { | |
1819 | int err; | |
1820 | unsigned long nr_pages; | |
1821 | ||
1822 | err = strict_strtoul(buf, 10, &nr_pages); | |
1823 | if (err || nr_pages > UINT_MAX) | |
1824 | return -EINVAL; | |
1825 | ||
1826 | ksm_thread_pages_to_scan = nr_pages; | |
1827 | ||
1828 | return count; | |
1829 | } | |
1830 | KSM_ATTR(pages_to_scan); | |
1831 | ||
1832 | static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr, | |
1833 | char *buf) | |
1834 | { | |
1835 | return sprintf(buf, "%u\n", ksm_run); | |
1836 | } | |
1837 | ||
1838 | static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr, | |
1839 | const char *buf, size_t count) | |
1840 | { | |
1841 | int err; | |
1842 | unsigned long flags; | |
1843 | ||
1844 | err = strict_strtoul(buf, 10, &flags); | |
1845 | if (err || flags > UINT_MAX) | |
1846 | return -EINVAL; | |
1847 | if (flags > KSM_RUN_UNMERGE) | |
1848 | return -EINVAL; | |
1849 | ||
1850 | /* | |
1851 | * KSM_RUN_MERGE sets ksmd running, and 0 stops it running. | |
1852 | * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items, | |
b4028260 | 1853 | * breaking COW to free the unswappable pages_shared (but leaves |
31dbd01f IE |
1854 | * mm_slots on the list for when ksmd may be set running again). |
1855 | */ | |
1856 | ||
1857 | mutex_lock(&ksm_thread_mutex); | |
1858 | if (ksm_run != flags) { | |
1859 | ksm_run = flags; | |
d952b791 | 1860 | if (flags & KSM_RUN_UNMERGE) { |
35451bee | 1861 | current->flags |= PF_OOM_ORIGIN; |
d952b791 | 1862 | err = unmerge_and_remove_all_rmap_items(); |
35451bee | 1863 | current->flags &= ~PF_OOM_ORIGIN; |
d952b791 HD |
1864 | if (err) { |
1865 | ksm_run = KSM_RUN_STOP; | |
1866 | count = err; | |
1867 | } | |
1868 | } | |
31dbd01f IE |
1869 | } |
1870 | mutex_unlock(&ksm_thread_mutex); | |
1871 | ||
1872 | if (flags & KSM_RUN_MERGE) | |
1873 | wake_up_interruptible(&ksm_thread_wait); | |
1874 | ||
1875 | return count; | |
1876 | } | |
1877 | KSM_ATTR(run); | |
1878 | ||
31dbd01f IE |
1879 | static ssize_t max_kernel_pages_store(struct kobject *kobj, |
1880 | struct kobj_attribute *attr, | |
1881 | const char *buf, size_t count) | |
1882 | { | |
1883 | int err; | |
1884 | unsigned long nr_pages; | |
1885 | ||
1886 | err = strict_strtoul(buf, 10, &nr_pages); | |
1887 | if (err) | |
1888 | return -EINVAL; | |
1889 | ||
1890 | ksm_max_kernel_pages = nr_pages; | |
1891 | ||
1892 | return count; | |
1893 | } | |
1894 | ||
1895 | static ssize_t max_kernel_pages_show(struct kobject *kobj, | |
1896 | struct kobj_attribute *attr, char *buf) | |
1897 | { | |
1898 | return sprintf(buf, "%lu\n", ksm_max_kernel_pages); | |
1899 | } | |
1900 | KSM_ATTR(max_kernel_pages); | |
1901 | ||
b4028260 HD |
1902 | static ssize_t pages_shared_show(struct kobject *kobj, |
1903 | struct kobj_attribute *attr, char *buf) | |
1904 | { | |
1905 | return sprintf(buf, "%lu\n", ksm_pages_shared); | |
1906 | } | |
1907 | KSM_ATTR_RO(pages_shared); | |
1908 | ||
1909 | static ssize_t pages_sharing_show(struct kobject *kobj, | |
1910 | struct kobj_attribute *attr, char *buf) | |
1911 | { | |
e178dfde | 1912 | return sprintf(buf, "%lu\n", ksm_pages_sharing); |
b4028260 HD |
1913 | } |
1914 | KSM_ATTR_RO(pages_sharing); | |
1915 | ||
473b0ce4 HD |
1916 | static ssize_t pages_unshared_show(struct kobject *kobj, |
1917 | struct kobj_attribute *attr, char *buf) | |
1918 | { | |
1919 | return sprintf(buf, "%lu\n", ksm_pages_unshared); | |
1920 | } | |
1921 | KSM_ATTR_RO(pages_unshared); | |
1922 | ||
1923 | static ssize_t pages_volatile_show(struct kobject *kobj, | |
1924 | struct kobj_attribute *attr, char *buf) | |
1925 | { | |
1926 | long ksm_pages_volatile; | |
1927 | ||
1928 | ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared | |
1929 | - ksm_pages_sharing - ksm_pages_unshared; | |
1930 | /* | |
1931 | * It was not worth any locking to calculate that statistic, | |
1932 | * but it might therefore sometimes be negative: conceal that. | |
1933 | */ | |
1934 | if (ksm_pages_volatile < 0) | |
1935 | ksm_pages_volatile = 0; | |
1936 | return sprintf(buf, "%ld\n", ksm_pages_volatile); | |
1937 | } | |
1938 | KSM_ATTR_RO(pages_volatile); | |
1939 | ||
1940 | static ssize_t full_scans_show(struct kobject *kobj, | |
1941 | struct kobj_attribute *attr, char *buf) | |
1942 | { | |
1943 | return sprintf(buf, "%lu\n", ksm_scan.seqnr); | |
1944 | } | |
1945 | KSM_ATTR_RO(full_scans); | |
1946 | ||
31dbd01f IE |
1947 | static struct attribute *ksm_attrs[] = { |
1948 | &sleep_millisecs_attr.attr, | |
1949 | &pages_to_scan_attr.attr, | |
1950 | &run_attr.attr, | |
31dbd01f | 1951 | &max_kernel_pages_attr.attr, |
b4028260 HD |
1952 | &pages_shared_attr.attr, |
1953 | &pages_sharing_attr.attr, | |
473b0ce4 HD |
1954 | &pages_unshared_attr.attr, |
1955 | &pages_volatile_attr.attr, | |
1956 | &full_scans_attr.attr, | |
31dbd01f IE |
1957 | NULL, |
1958 | }; | |
1959 | ||
1960 | static struct attribute_group ksm_attr_group = { | |
1961 | .attrs = ksm_attrs, | |
1962 | .name = "ksm", | |
1963 | }; | |
2ffd8679 | 1964 | #endif /* CONFIG_SYSFS */ |
31dbd01f IE |
1965 | |
1966 | static int __init ksm_init(void) | |
1967 | { | |
1968 | struct task_struct *ksm_thread; | |
1969 | int err; | |
1970 | ||
c73602ad | 1971 | ksm_max_kernel_pages = totalram_pages / 4; |
2c6854fd | 1972 | |
31dbd01f IE |
1973 | err = ksm_slab_init(); |
1974 | if (err) | |
1975 | goto out; | |
1976 | ||
1977 | err = mm_slots_hash_init(); | |
1978 | if (err) | |
1979 | goto out_free1; | |
1980 | ||
1981 | ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd"); | |
1982 | if (IS_ERR(ksm_thread)) { | |
1983 | printk(KERN_ERR "ksm: creating kthread failed\n"); | |
1984 | err = PTR_ERR(ksm_thread); | |
1985 | goto out_free2; | |
1986 | } | |
1987 | ||
2ffd8679 | 1988 | #ifdef CONFIG_SYSFS |
31dbd01f IE |
1989 | err = sysfs_create_group(mm_kobj, &ksm_attr_group); |
1990 | if (err) { | |
1991 | printk(KERN_ERR "ksm: register sysfs failed\n"); | |
2ffd8679 HD |
1992 | kthread_stop(ksm_thread); |
1993 | goto out_free2; | |
31dbd01f | 1994 | } |
c73602ad HD |
1995 | #else |
1996 | ksm_run = KSM_RUN_MERGE; /* no way for user to start it */ | |
1997 | ||
2ffd8679 | 1998 | #endif /* CONFIG_SYSFS */ |
31dbd01f | 1999 | |
62b61f61 HD |
2000 | #ifdef CONFIG_MEMORY_HOTREMOVE |
2001 | /* | |
2002 | * Choose a high priority since the callback takes ksm_thread_mutex: | |
2003 | * later callbacks could only be taking locks which nest within that. | |
2004 | */ | |
2005 | hotplug_memory_notifier(ksm_memory_callback, 100); | |
2006 | #endif | |
31dbd01f IE |
2007 | return 0; |
2008 | ||
31dbd01f IE |
2009 | out_free2: |
2010 | mm_slots_hash_free(); | |
2011 | out_free1: | |
2012 | ksm_slab_free(); | |
2013 | out: | |
2014 | return err; | |
f8af4da3 | 2015 | } |
31dbd01f | 2016 | module_init(ksm_init) |