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1 | /* | |
2 | * Frontswap frontend | |
3 | * | |
4 | * This code provides the generic "frontend" layer to call a matching | |
5 | * "backend" driver implementation of frontswap. See | |
6 | * Documentation/vm/frontswap.txt for more information. | |
7 | * | |
8 | * Copyright (C) 2009-2012 Oracle Corp. All rights reserved. | |
9 | * Author: Dan Magenheimer | |
10 | * | |
11 | * This work is licensed under the terms of the GNU GPL, version 2. | |
12 | */ | |
13 | ||
14 | #include <linux/mman.h> | |
15 | #include <linux/swap.h> | |
16 | #include <linux/swapops.h> | |
17 | #include <linux/security.h> | |
18 | #include <linux/module.h> | |
19 | #include <linux/debugfs.h> | |
20 | #include <linux/frontswap.h> | |
21 | #include <linux/swapfile.h> | |
22 | ||
23 | DEFINE_STATIC_KEY_FALSE(frontswap_enabled_key); | |
24 | ||
25 | /* | |
26 | * frontswap_ops are added by frontswap_register_ops, and provide the | |
27 | * frontswap "backend" implementation functions. Multiple implementations | |
28 | * may be registered, but implementations can never deregister. This | |
29 | * is a simple singly-linked list of all registered implementations. | |
30 | */ | |
31 | static struct frontswap_ops *frontswap_ops __read_mostly; | |
32 | ||
33 | #define for_each_frontswap_ops(ops) \ | |
34 | for ((ops) = frontswap_ops; (ops); (ops) = (ops)->next) | |
35 | ||
36 | /* | |
37 | * If enabled, frontswap_store will return failure even on success. As | |
38 | * a result, the swap subsystem will always write the page to swap, in | |
39 | * effect converting frontswap into a writethrough cache. In this mode, | |
40 | * there is no direct reduction in swap writes, but a frontswap backend | |
41 | * can unilaterally "reclaim" any pages in use with no data loss, thus | |
42 | * providing increases control over maximum memory usage due to frontswap. | |
43 | */ | |
44 | static bool frontswap_writethrough_enabled __read_mostly; | |
45 | ||
46 | /* | |
47 | * If enabled, the underlying tmem implementation is capable of doing | |
48 | * exclusive gets, so frontswap_load, on a successful tmem_get must | |
49 | * mark the page as no longer in frontswap AND mark it dirty. | |
50 | */ | |
51 | static bool frontswap_tmem_exclusive_gets_enabled __read_mostly; | |
52 | ||
53 | #ifdef CONFIG_DEBUG_FS | |
54 | /* | |
55 | * Counters available via /sys/kernel/debug/frontswap (if debugfs is | |
56 | * properly configured). These are for information only so are not protected | |
57 | * against increment races. | |
58 | */ | |
59 | static u64 frontswap_loads; | |
60 | static u64 frontswap_succ_stores; | |
61 | static u64 frontswap_failed_stores; | |
62 | static u64 frontswap_invalidates; | |
63 | ||
64 | static inline void inc_frontswap_loads(void) { | |
65 | frontswap_loads++; | |
66 | } | |
67 | static inline void inc_frontswap_succ_stores(void) { | |
68 | frontswap_succ_stores++; | |
69 | } | |
70 | static inline void inc_frontswap_failed_stores(void) { | |
71 | frontswap_failed_stores++; | |
72 | } | |
73 | static inline void inc_frontswap_invalidates(void) { | |
74 | frontswap_invalidates++; | |
75 | } | |
76 | #else | |
77 | static inline void inc_frontswap_loads(void) { } | |
78 | static inline void inc_frontswap_succ_stores(void) { } | |
79 | static inline void inc_frontswap_failed_stores(void) { } | |
80 | static inline void inc_frontswap_invalidates(void) { } | |
81 | #endif | |
82 | ||
83 | /* | |
84 | * Due to the asynchronous nature of the backends loading potentially | |
85 | * _after_ the swap system has been activated, we have chokepoints | |
86 | * on all frontswap functions to not call the backend until the backend | |
87 | * has registered. | |
88 | * | |
89 | * This would not guards us against the user deciding to call swapoff right as | |
90 | * we are calling the backend to initialize (so swapon is in action). | |
91 | * Fortunatly for us, the swapon_mutex has been taked by the callee so we are | |
92 | * OK. The other scenario where calls to frontswap_store (called via | |
93 | * swap_writepage) is racing with frontswap_invalidate_area (called via | |
94 | * swapoff) is again guarded by the swap subsystem. | |
95 | * | |
96 | * While no backend is registered all calls to frontswap_[store|load| | |
97 | * invalidate_area|invalidate_page] are ignored or fail. | |
98 | * | |
99 | * The time between the backend being registered and the swap file system | |
100 | * calling the backend (via the frontswap_* functions) is indeterminate as | |
101 | * frontswap_ops is not atomic_t (or a value guarded by a spinlock). | |
102 | * That is OK as we are comfortable missing some of these calls to the newly | |
103 | * registered backend. | |
104 | * | |
105 | * Obviously the opposite (unloading the backend) must be done after all | |
106 | * the frontswap_[store|load|invalidate_area|invalidate_page] start | |
107 | * ignoring or failing the requests. However, there is currently no way | |
108 | * to unload a backend once it is registered. | |
109 | */ | |
110 | ||
111 | /* | |
112 | * Register operations for frontswap | |
113 | */ | |
114 | void frontswap_register_ops(struct frontswap_ops *ops) | |
115 | { | |
116 | DECLARE_BITMAP(a, MAX_SWAPFILES); | |
117 | DECLARE_BITMAP(b, MAX_SWAPFILES); | |
118 | struct swap_info_struct *si; | |
119 | unsigned int i; | |
120 | ||
121 | bitmap_zero(a, MAX_SWAPFILES); | |
122 | bitmap_zero(b, MAX_SWAPFILES); | |
123 | ||
124 | spin_lock(&swap_lock); | |
125 | plist_for_each_entry(si, &swap_active_head, list) { | |
126 | if (!WARN_ON(!si->frontswap_map)) | |
127 | set_bit(si->type, a); | |
128 | } | |
129 | spin_unlock(&swap_lock); | |
130 | ||
131 | /* the new ops needs to know the currently active swap devices */ | |
132 | for_each_set_bit(i, a, MAX_SWAPFILES) | |
133 | ops->init(i); | |
134 | ||
135 | /* | |
136 | * Setting frontswap_ops must happen after the ops->init() calls | |
137 | * above; cmpxchg implies smp_mb() which will ensure the init is | |
138 | * complete at this point. | |
139 | */ | |
140 | do { | |
141 | ops->next = frontswap_ops; | |
142 | } while (cmpxchg(&frontswap_ops, ops->next, ops) != ops->next); | |
143 | ||
144 | static_branch_inc(&frontswap_enabled_key); | |
145 | ||
146 | spin_lock(&swap_lock); | |
147 | plist_for_each_entry(si, &swap_active_head, list) { | |
148 | if (si->frontswap_map) | |
149 | set_bit(si->type, b); | |
150 | } | |
151 | spin_unlock(&swap_lock); | |
152 | ||
153 | /* | |
154 | * On the very unlikely chance that a swap device was added or | |
155 | * removed between setting the "a" list bits and the ops init | |
156 | * calls, we re-check and do init or invalidate for any changed | |
157 | * bits. | |
158 | */ | |
159 | if (unlikely(!bitmap_equal(a, b, MAX_SWAPFILES))) { | |
160 | for (i = 0; i < MAX_SWAPFILES; i++) { | |
161 | if (!test_bit(i, a) && test_bit(i, b)) | |
162 | ops->init(i); | |
163 | else if (test_bit(i, a) && !test_bit(i, b)) | |
164 | ops->invalidate_area(i); | |
165 | } | |
166 | } | |
167 | } | |
168 | EXPORT_SYMBOL(frontswap_register_ops); | |
169 | ||
170 | /* | |
171 | * Enable/disable frontswap writethrough (see above). | |
172 | */ | |
173 | void frontswap_writethrough(bool enable) | |
174 | { | |
175 | frontswap_writethrough_enabled = enable; | |
176 | } | |
177 | EXPORT_SYMBOL(frontswap_writethrough); | |
178 | ||
179 | /* | |
180 | * Enable/disable frontswap exclusive gets (see above). | |
181 | */ | |
182 | void frontswap_tmem_exclusive_gets(bool enable) | |
183 | { | |
184 | frontswap_tmem_exclusive_gets_enabled = enable; | |
185 | } | |
186 | EXPORT_SYMBOL(frontswap_tmem_exclusive_gets); | |
187 | ||
188 | /* | |
189 | * Called when a swap device is swapon'd. | |
190 | */ | |
191 | void __frontswap_init(unsigned type, unsigned long *map) | |
192 | { | |
193 | struct swap_info_struct *sis = swap_info[type]; | |
194 | struct frontswap_ops *ops; | |
195 | ||
196 | VM_BUG_ON(sis == NULL); | |
197 | ||
198 | /* | |
199 | * p->frontswap is a bitmap that we MUST have to figure out which page | |
200 | * has gone in frontswap. Without it there is no point of continuing. | |
201 | */ | |
202 | if (WARN_ON(!map)) | |
203 | return; | |
204 | /* | |
205 | * Irregardless of whether the frontswap backend has been loaded | |
206 | * before this function or it will be later, we _MUST_ have the | |
207 | * p->frontswap set to something valid to work properly. | |
208 | */ | |
209 | frontswap_map_set(sis, map); | |
210 | ||
211 | for_each_frontswap_ops(ops) | |
212 | ops->init(type); | |
213 | } | |
214 | EXPORT_SYMBOL(__frontswap_init); | |
215 | ||
216 | bool __frontswap_test(struct swap_info_struct *sis, | |
217 | pgoff_t offset) | |
218 | { | |
219 | if (sis->frontswap_map) | |
220 | return test_bit(offset, sis->frontswap_map); | |
221 | return false; | |
222 | } | |
223 | EXPORT_SYMBOL(__frontswap_test); | |
224 | ||
225 | static inline void __frontswap_set(struct swap_info_struct *sis, | |
226 | pgoff_t offset) | |
227 | { | |
228 | set_bit(offset, sis->frontswap_map); | |
229 | atomic_inc(&sis->frontswap_pages); | |
230 | } | |
231 | ||
232 | static inline void __frontswap_clear(struct swap_info_struct *sis, | |
233 | pgoff_t offset) | |
234 | { | |
235 | clear_bit(offset, sis->frontswap_map); | |
236 | atomic_dec(&sis->frontswap_pages); | |
237 | } | |
238 | ||
239 | /* | |
240 | * "Store" data from a page to frontswap and associate it with the page's | |
241 | * swaptype and offset. Page must be locked and in the swap cache. | |
242 | * If frontswap already contains a page with matching swaptype and | |
243 | * offset, the frontswap implementation may either overwrite the data and | |
244 | * return success or invalidate the page from frontswap and return failure. | |
245 | */ | |
246 | int __frontswap_store(struct page *page) | |
247 | { | |
248 | int ret = -1; | |
249 | swp_entry_t entry = { .val = page_private(page), }; | |
250 | int type = swp_type(entry); | |
251 | struct swap_info_struct *sis = swap_info[type]; | |
252 | pgoff_t offset = swp_offset(entry); | |
253 | struct frontswap_ops *ops; | |
254 | ||
255 | VM_BUG_ON(!frontswap_ops); | |
256 | VM_BUG_ON(!PageLocked(page)); | |
257 | VM_BUG_ON(sis == NULL); | |
258 | ||
259 | /* | |
260 | * If a dup, we must remove the old page first; we can't leave the | |
261 | * old page no matter if the store of the new page succeeds or fails, | |
262 | * and we can't rely on the new page replacing the old page as we may | |
263 | * not store to the same implementation that contains the old page. | |
264 | */ | |
265 | if (__frontswap_test(sis, offset)) { | |
266 | __frontswap_clear(sis, offset); | |
267 | for_each_frontswap_ops(ops) | |
268 | ops->invalidate_page(type, offset); | |
269 | } | |
270 | ||
271 | /* Try to store in each implementation, until one succeeds. */ | |
272 | for_each_frontswap_ops(ops) { | |
273 | ret = ops->store(type, offset, page); | |
274 | if (!ret) /* successful store */ | |
275 | break; | |
276 | } | |
277 | if (ret == 0) { | |
278 | __frontswap_set(sis, offset); | |
279 | inc_frontswap_succ_stores(); | |
280 | } else { | |
281 | inc_frontswap_failed_stores(); | |
282 | } | |
283 | if (frontswap_writethrough_enabled) | |
284 | /* report failure so swap also writes to swap device */ | |
285 | ret = -1; | |
286 | return ret; | |
287 | } | |
288 | EXPORT_SYMBOL(__frontswap_store); | |
289 | ||
290 | /* | |
291 | * "Get" data from frontswap associated with swaptype and offset that were | |
292 | * specified when the data was put to frontswap and use it to fill the | |
293 | * specified page with data. Page must be locked and in the swap cache. | |
294 | */ | |
295 | int __frontswap_load(struct page *page) | |
296 | { | |
297 | int ret = -1; | |
298 | swp_entry_t entry = { .val = page_private(page), }; | |
299 | int type = swp_type(entry); | |
300 | struct swap_info_struct *sis = swap_info[type]; | |
301 | pgoff_t offset = swp_offset(entry); | |
302 | struct frontswap_ops *ops; | |
303 | ||
304 | VM_BUG_ON(!frontswap_ops); | |
305 | VM_BUG_ON(!PageLocked(page)); | |
306 | VM_BUG_ON(sis == NULL); | |
307 | ||
308 | if (!__frontswap_test(sis, offset)) | |
309 | return -1; | |
310 | ||
311 | /* Try loading from each implementation, until one succeeds. */ | |
312 | for_each_frontswap_ops(ops) { | |
313 | ret = ops->load(type, offset, page); | |
314 | if (!ret) /* successful load */ | |
315 | break; | |
316 | } | |
317 | if (ret == 0) { | |
318 | inc_frontswap_loads(); | |
319 | if (frontswap_tmem_exclusive_gets_enabled) { | |
320 | SetPageDirty(page); | |
321 | __frontswap_clear(sis, offset); | |
322 | } | |
323 | } | |
324 | return ret; | |
325 | } | |
326 | EXPORT_SYMBOL(__frontswap_load); | |
327 | ||
328 | /* | |
329 | * Invalidate any data from frontswap associated with the specified swaptype | |
330 | * and offset so that a subsequent "get" will fail. | |
331 | */ | |
332 | void __frontswap_invalidate_page(unsigned type, pgoff_t offset) | |
333 | { | |
334 | struct swap_info_struct *sis = swap_info[type]; | |
335 | struct frontswap_ops *ops; | |
336 | ||
337 | VM_BUG_ON(!frontswap_ops); | |
338 | VM_BUG_ON(sis == NULL); | |
339 | ||
340 | if (!__frontswap_test(sis, offset)) | |
341 | return; | |
342 | ||
343 | for_each_frontswap_ops(ops) | |
344 | ops->invalidate_page(type, offset); | |
345 | __frontswap_clear(sis, offset); | |
346 | inc_frontswap_invalidates(); | |
347 | } | |
348 | EXPORT_SYMBOL(__frontswap_invalidate_page); | |
349 | ||
350 | /* | |
351 | * Invalidate all data from frontswap associated with all offsets for the | |
352 | * specified swaptype. | |
353 | */ | |
354 | void __frontswap_invalidate_area(unsigned type) | |
355 | { | |
356 | struct swap_info_struct *sis = swap_info[type]; | |
357 | struct frontswap_ops *ops; | |
358 | ||
359 | VM_BUG_ON(!frontswap_ops); | |
360 | VM_BUG_ON(sis == NULL); | |
361 | ||
362 | if (sis->frontswap_map == NULL) | |
363 | return; | |
364 | ||
365 | for_each_frontswap_ops(ops) | |
366 | ops->invalidate_area(type); | |
367 | atomic_set(&sis->frontswap_pages, 0); | |
368 | bitmap_zero(sis->frontswap_map, sis->max); | |
369 | } | |
370 | EXPORT_SYMBOL(__frontswap_invalidate_area); | |
371 | ||
372 | static unsigned long __frontswap_curr_pages(void) | |
373 | { | |
374 | unsigned long totalpages = 0; | |
375 | struct swap_info_struct *si = NULL; | |
376 | ||
377 | assert_spin_locked(&swap_lock); | |
378 | plist_for_each_entry(si, &swap_active_head, list) | |
379 | totalpages += atomic_read(&si->frontswap_pages); | |
380 | return totalpages; | |
381 | } | |
382 | ||
383 | static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused, | |
384 | int *swapid) | |
385 | { | |
386 | int ret = -EINVAL; | |
387 | struct swap_info_struct *si = NULL; | |
388 | int si_frontswap_pages; | |
389 | unsigned long total_pages_to_unuse = total; | |
390 | unsigned long pages = 0, pages_to_unuse = 0; | |
391 | ||
392 | assert_spin_locked(&swap_lock); | |
393 | plist_for_each_entry(si, &swap_active_head, list) { | |
394 | si_frontswap_pages = atomic_read(&si->frontswap_pages); | |
395 | if (total_pages_to_unuse < si_frontswap_pages) { | |
396 | pages = pages_to_unuse = total_pages_to_unuse; | |
397 | } else { | |
398 | pages = si_frontswap_pages; | |
399 | pages_to_unuse = 0; /* unuse all */ | |
400 | } | |
401 | /* ensure there is enough RAM to fetch pages from frontswap */ | |
402 | if (security_vm_enough_memory_mm(current->mm, pages)) { | |
403 | ret = -ENOMEM; | |
404 | continue; | |
405 | } | |
406 | vm_unacct_memory(pages); | |
407 | *unused = pages_to_unuse; | |
408 | *swapid = si->type; | |
409 | ret = 0; | |
410 | break; | |
411 | } | |
412 | ||
413 | return ret; | |
414 | } | |
415 | ||
416 | /* | |
417 | * Used to check if it's necessory and feasible to unuse pages. | |
418 | * Return 1 when nothing to do, 0 when need to shink pages, | |
419 | * error code when there is an error. | |
420 | */ | |
421 | static int __frontswap_shrink(unsigned long target_pages, | |
422 | unsigned long *pages_to_unuse, | |
423 | int *type) | |
424 | { | |
425 | unsigned long total_pages = 0, total_pages_to_unuse; | |
426 | ||
427 | assert_spin_locked(&swap_lock); | |
428 | ||
429 | total_pages = __frontswap_curr_pages(); | |
430 | if (total_pages <= target_pages) { | |
431 | /* Nothing to do */ | |
432 | *pages_to_unuse = 0; | |
433 | return 1; | |
434 | } | |
435 | total_pages_to_unuse = total_pages - target_pages; | |
436 | return __frontswap_unuse_pages(total_pages_to_unuse, pages_to_unuse, type); | |
437 | } | |
438 | ||
439 | /* | |
440 | * Frontswap, like a true swap device, may unnecessarily retain pages | |
441 | * under certain circumstances; "shrink" frontswap is essentially a | |
442 | * "partial swapoff" and works by calling try_to_unuse to attempt to | |
443 | * unuse enough frontswap pages to attempt to -- subject to memory | |
444 | * constraints -- reduce the number of pages in frontswap to the | |
445 | * number given in the parameter target_pages. | |
446 | */ | |
447 | void frontswap_shrink(unsigned long target_pages) | |
448 | { | |
449 | unsigned long pages_to_unuse = 0; | |
450 | int uninitialized_var(type), ret; | |
451 | ||
452 | /* | |
453 | * we don't want to hold swap_lock while doing a very | |
454 | * lengthy try_to_unuse, but swap_list may change | |
455 | * so restart scan from swap_active_head each time | |
456 | */ | |
457 | spin_lock(&swap_lock); | |
458 | ret = __frontswap_shrink(target_pages, &pages_to_unuse, &type); | |
459 | spin_unlock(&swap_lock); | |
460 | if (ret == 0) | |
461 | try_to_unuse(type, true, pages_to_unuse); | |
462 | return; | |
463 | } | |
464 | EXPORT_SYMBOL(frontswap_shrink); | |
465 | ||
466 | /* | |
467 | * Count and return the number of frontswap pages across all | |
468 | * swap devices. This is exported so that backend drivers can | |
469 | * determine current usage without reading debugfs. | |
470 | */ | |
471 | unsigned long frontswap_curr_pages(void) | |
472 | { | |
473 | unsigned long totalpages = 0; | |
474 | ||
475 | spin_lock(&swap_lock); | |
476 | totalpages = __frontswap_curr_pages(); | |
477 | spin_unlock(&swap_lock); | |
478 | ||
479 | return totalpages; | |
480 | } | |
481 | EXPORT_SYMBOL(frontswap_curr_pages); | |
482 | ||
483 | static int __init init_frontswap(void) | |
484 | { | |
485 | #ifdef CONFIG_DEBUG_FS | |
486 | struct dentry *root = debugfs_create_dir("frontswap", NULL); | |
487 | if (root == NULL) | |
488 | return -ENXIO; | |
489 | debugfs_create_u64("loads", S_IRUGO, root, &frontswap_loads); | |
490 | debugfs_create_u64("succ_stores", S_IRUGO, root, &frontswap_succ_stores); | |
491 | debugfs_create_u64("failed_stores", S_IRUGO, root, | |
492 | &frontswap_failed_stores); | |
493 | debugfs_create_u64("invalidates", S_IRUGO, | |
494 | root, &frontswap_invalidates); | |
495 | #endif | |
496 | return 0; | |
497 | } | |
498 | ||
499 | module_init(init_frontswap); |