Commit | Line | Data |
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29f233cf DM |
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 | ||
29f233cf DM |
14 | #include <linux/mman.h> |
15 | #include <linux/swap.h> | |
16 | #include <linux/swapops.h> | |
29f233cf | 17 | #include <linux/security.h> |
29f233cf | 18 | #include <linux/module.h> |
29f233cf DM |
19 | #include <linux/debugfs.h> |
20 | #include <linux/frontswap.h> | |
21 | #include <linux/swapfile.h> | |
22 | ||
23 | /* | |
d1dc6f1b DS |
24 | * frontswap_ops are added by frontswap_register_ops, and provide the |
25 | * frontswap "backend" implementation functions. Multiple implementations | |
26 | * may be registered, but implementations can never deregister. This | |
27 | * is a simple singly-linked list of all registered implementations. | |
29f233cf | 28 | */ |
1e01c968 | 29 | static struct frontswap_ops *frontswap_ops __read_mostly; |
29f233cf | 30 | |
d1dc6f1b DS |
31 | #define for_each_frontswap_ops(ops) \ |
32 | for ((ops) = frontswap_ops; (ops); (ops) = (ops)->next) | |
33 | ||
29f233cf | 34 | /* |
165c8aed | 35 | * If enabled, frontswap_store will return failure even on success. As |
29f233cf DM |
36 | * a result, the swap subsystem will always write the page to swap, in |
37 | * effect converting frontswap into a writethrough cache. In this mode, | |
38 | * there is no direct reduction in swap writes, but a frontswap backend | |
39 | * can unilaterally "reclaim" any pages in use with no data loss, thus | |
40 | * providing increases control over maximum memory usage due to frontswap. | |
41 | */ | |
42 | static bool frontswap_writethrough_enabled __read_mostly; | |
43 | ||
e3483a5f DM |
44 | /* |
45 | * If enabled, the underlying tmem implementation is capable of doing | |
46 | * exclusive gets, so frontswap_load, on a successful tmem_get must | |
47 | * mark the page as no longer in frontswap AND mark it dirty. | |
48 | */ | |
49 | static bool frontswap_tmem_exclusive_gets_enabled __read_mostly; | |
50 | ||
29f233cf DM |
51 | #ifdef CONFIG_DEBUG_FS |
52 | /* | |
53 | * Counters available via /sys/kernel/debug/frontswap (if debugfs is | |
54 | * properly configured). These are for information only so are not protected | |
55 | * against increment races. | |
56 | */ | |
165c8aed KRW |
57 | static u64 frontswap_loads; |
58 | static u64 frontswap_succ_stores; | |
59 | static u64 frontswap_failed_stores; | |
29f233cf DM |
60 | static u64 frontswap_invalidates; |
61 | ||
165c8aed KRW |
62 | static inline void inc_frontswap_loads(void) { |
63 | frontswap_loads++; | |
29f233cf | 64 | } |
165c8aed KRW |
65 | static inline void inc_frontswap_succ_stores(void) { |
66 | frontswap_succ_stores++; | |
29f233cf | 67 | } |
165c8aed KRW |
68 | static inline void inc_frontswap_failed_stores(void) { |
69 | frontswap_failed_stores++; | |
29f233cf DM |
70 | } |
71 | static inline void inc_frontswap_invalidates(void) { | |
72 | frontswap_invalidates++; | |
73 | } | |
74 | #else | |
165c8aed KRW |
75 | static inline void inc_frontswap_loads(void) { } |
76 | static inline void inc_frontswap_succ_stores(void) { } | |
77 | static inline void inc_frontswap_failed_stores(void) { } | |
29f233cf DM |
78 | static inline void inc_frontswap_invalidates(void) { } |
79 | #endif | |
905cd0e1 DM |
80 | |
81 | /* | |
82 | * Due to the asynchronous nature of the backends loading potentially | |
83 | * _after_ the swap system has been activated, we have chokepoints | |
84 | * on all frontswap functions to not call the backend until the backend | |
85 | * has registered. | |
86 | * | |
905cd0e1 DM |
87 | * This would not guards us against the user deciding to call swapoff right as |
88 | * we are calling the backend to initialize (so swapon is in action). | |
89 | * Fortunatly for us, the swapon_mutex has been taked by the callee so we are | |
90 | * OK. The other scenario where calls to frontswap_store (called via | |
91 | * swap_writepage) is racing with frontswap_invalidate_area (called via | |
92 | * swapoff) is again guarded by the swap subsystem. | |
93 | * | |
94 | * While no backend is registered all calls to frontswap_[store|load| | |
95 | * invalidate_area|invalidate_page] are ignored or fail. | |
96 | * | |
97 | * The time between the backend being registered and the swap file system | |
98 | * calling the backend (via the frontswap_* functions) is indeterminate as | |
1e01c968 | 99 | * frontswap_ops is not atomic_t (or a value guarded by a spinlock). |
905cd0e1 DM |
100 | * That is OK as we are comfortable missing some of these calls to the newly |
101 | * registered backend. | |
102 | * | |
103 | * Obviously the opposite (unloading the backend) must be done after all | |
104 | * the frontswap_[store|load|invalidate_area|invalidate_page] start | |
d1dc6f1b DS |
105 | * ignoring or failing the requests. However, there is currently no way |
106 | * to unload a backend once it is registered. | |
905cd0e1 | 107 | */ |
905cd0e1 | 108 | |
29f233cf | 109 | /* |
d1dc6f1b | 110 | * Register operations for frontswap |
29f233cf | 111 | */ |
d1dc6f1b | 112 | void frontswap_register_ops(struct frontswap_ops *ops) |
29f233cf | 113 | { |
d1dc6f1b DS |
114 | DECLARE_BITMAP(a, MAX_SWAPFILES); |
115 | DECLARE_BITMAP(b, MAX_SWAPFILES); | |
116 | struct swap_info_struct *si; | |
117 | unsigned int i; | |
118 | ||
119 | bitmap_zero(a, MAX_SWAPFILES); | |
120 | bitmap_zero(b, MAX_SWAPFILES); | |
121 | ||
122 | spin_lock(&swap_lock); | |
123 | plist_for_each_entry(si, &swap_active_head, list) { | |
124 | if (!WARN_ON(!si->frontswap_map)) | |
125 | set_bit(si->type, a); | |
126 | } | |
127 | spin_unlock(&swap_lock); | |
128 | ||
129 | /* the new ops needs to know the currently active swap devices */ | |
130 | for_each_set_bit(i, a, MAX_SWAPFILES) | |
131 | ops->init(i); | |
132 | ||
133 | /* | |
134 | * Setting frontswap_ops must happen after the ops->init() calls | |
135 | * above; cmpxchg implies smp_mb() which will ensure the init is | |
136 | * complete at this point. | |
137 | */ | |
138 | do { | |
139 | ops->next = frontswap_ops; | |
140 | } while (cmpxchg(&frontswap_ops, ops->next, ops) != ops->next); | |
141 | ||
142 | spin_lock(&swap_lock); | |
143 | plist_for_each_entry(si, &swap_active_head, list) { | |
144 | if (si->frontswap_map) | |
145 | set_bit(si->type, b); | |
905cd0e1 | 146 | } |
d1dc6f1b DS |
147 | spin_unlock(&swap_lock); |
148 | ||
905cd0e1 | 149 | /* |
d1dc6f1b DS |
150 | * On the very unlikely chance that a swap device was added or |
151 | * removed between setting the "a" list bits and the ops init | |
152 | * calls, we re-check and do init or invalidate for any changed | |
153 | * bits. | |
905cd0e1 | 154 | */ |
d1dc6f1b DS |
155 | if (unlikely(!bitmap_equal(a, b, MAX_SWAPFILES))) { |
156 | for (i = 0; i < MAX_SWAPFILES; i++) { | |
157 | if (!test_bit(i, a) && test_bit(i, b)) | |
158 | ops->init(i); | |
159 | else if (test_bit(i, a) && !test_bit(i, b)) | |
160 | ops->invalidate_area(i); | |
161 | } | |
162 | } | |
29f233cf DM |
163 | } |
164 | EXPORT_SYMBOL(frontswap_register_ops); | |
165 | ||
166 | /* | |
167 | * Enable/disable frontswap writethrough (see above). | |
168 | */ | |
169 | void frontswap_writethrough(bool enable) | |
170 | { | |
171 | frontswap_writethrough_enabled = enable; | |
172 | } | |
173 | EXPORT_SYMBOL(frontswap_writethrough); | |
174 | ||
e3483a5f DM |
175 | /* |
176 | * Enable/disable frontswap exclusive gets (see above). | |
177 | */ | |
178 | void frontswap_tmem_exclusive_gets(bool enable) | |
179 | { | |
180 | frontswap_tmem_exclusive_gets_enabled = enable; | |
181 | } | |
182 | EXPORT_SYMBOL(frontswap_tmem_exclusive_gets); | |
183 | ||
29f233cf DM |
184 | /* |
185 | * Called when a swap device is swapon'd. | |
186 | */ | |
4f89849d | 187 | void __frontswap_init(unsigned type, unsigned long *map) |
29f233cf DM |
188 | { |
189 | struct swap_info_struct *sis = swap_info[type]; | |
d1dc6f1b | 190 | struct frontswap_ops *ops; |
29f233cf | 191 | |
4f89849d MK |
192 | BUG_ON(sis == NULL); |
193 | ||
194 | /* | |
195 | * p->frontswap is a bitmap that we MUST have to figure out which page | |
196 | * has gone in frontswap. Without it there is no point of continuing. | |
197 | */ | |
198 | if (WARN_ON(!map)) | |
199 | return; | |
200 | /* | |
201 | * Irregardless of whether the frontswap backend has been loaded | |
202 | * before this function or it will be later, we _MUST_ have the | |
203 | * p->frontswap set to something valid to work properly. | |
204 | */ | |
205 | frontswap_map_set(sis, map); | |
d1dc6f1b DS |
206 | |
207 | for_each_frontswap_ops(ops) | |
208 | ops->init(type); | |
29f233cf DM |
209 | } |
210 | EXPORT_SYMBOL(__frontswap_init); | |
211 | ||
f066ea23 BL |
212 | bool __frontswap_test(struct swap_info_struct *sis, |
213 | pgoff_t offset) | |
214 | { | |
d1dc6f1b DS |
215 | if (sis->frontswap_map) |
216 | return test_bit(offset, sis->frontswap_map); | |
217 | return false; | |
f066ea23 BL |
218 | } |
219 | EXPORT_SYMBOL(__frontswap_test); | |
220 | ||
d1dc6f1b DS |
221 | static inline void __frontswap_set(struct swap_info_struct *sis, |
222 | pgoff_t offset) | |
223 | { | |
224 | set_bit(offset, sis->frontswap_map); | |
225 | atomic_inc(&sis->frontswap_pages); | |
226 | } | |
227 | ||
f066ea23 | 228 | static inline void __frontswap_clear(struct swap_info_struct *sis, |
d1dc6f1b | 229 | pgoff_t offset) |
611edfed | 230 | { |
f066ea23 | 231 | clear_bit(offset, sis->frontswap_map); |
611edfed SL |
232 | atomic_dec(&sis->frontswap_pages); |
233 | } | |
234 | ||
29f233cf | 235 | /* |
165c8aed | 236 | * "Store" data from a page to frontswap and associate it with the page's |
29f233cf DM |
237 | * swaptype and offset. Page must be locked and in the swap cache. |
238 | * If frontswap already contains a page with matching swaptype and | |
1d00015e | 239 | * offset, the frontswap implementation may either overwrite the data and |
29f233cf DM |
240 | * return success or invalidate the page from frontswap and return failure. |
241 | */ | |
165c8aed | 242 | int __frontswap_store(struct page *page) |
29f233cf | 243 | { |
d1dc6f1b | 244 | int ret = -1; |
29f233cf DM |
245 | swp_entry_t entry = { .val = page_private(page), }; |
246 | int type = swp_type(entry); | |
247 | struct swap_info_struct *sis = swap_info[type]; | |
248 | pgoff_t offset = swp_offset(entry); | |
d1dc6f1b | 249 | struct frontswap_ops *ops; |
29f233cf | 250 | |
f066ea23 BL |
251 | /* |
252 | * Return if no backend registed. | |
253 | * Don't need to inc frontswap_failed_stores here. | |
254 | */ | |
255 | if (!frontswap_ops) | |
d1dc6f1b | 256 | return -1; |
905cd0e1 | 257 | |
29f233cf DM |
258 | BUG_ON(!PageLocked(page)); |
259 | BUG_ON(sis == NULL); | |
d1dc6f1b DS |
260 | |
261 | /* | |
262 | * If a dup, we must remove the old page first; we can't leave the | |
263 | * old page no matter if the store of the new page succeeds or fails, | |
264 | * and we can't rely on the new page replacing the old page as we may | |
265 | * not store to the same implementation that contains the old page. | |
266 | */ | |
267 | if (__frontswap_test(sis, offset)) { | |
268 | __frontswap_clear(sis, offset); | |
269 | for_each_frontswap_ops(ops) | |
270 | ops->invalidate_page(type, offset); | |
271 | } | |
272 | ||
273 | /* Try to store in each implementation, until one succeeds. */ | |
274 | for_each_frontswap_ops(ops) { | |
275 | ret = ops->store(type, offset, page); | |
276 | if (!ret) /* successful store */ | |
277 | break; | |
278 | } | |
29f233cf | 279 | if (ret == 0) { |
d1dc6f1b | 280 | __frontswap_set(sis, offset); |
165c8aed | 281 | inc_frontswap_succ_stores(); |
d9674dda | 282 | } else { |
165c8aed | 283 | inc_frontswap_failed_stores(); |
4bb3e31e | 284 | } |
29f233cf DM |
285 | if (frontswap_writethrough_enabled) |
286 | /* report failure so swap also writes to swap device */ | |
287 | ret = -1; | |
288 | return ret; | |
289 | } | |
165c8aed | 290 | EXPORT_SYMBOL(__frontswap_store); |
29f233cf DM |
291 | |
292 | /* | |
293 | * "Get" data from frontswap associated with swaptype and offset that were | |
294 | * specified when the data was put to frontswap and use it to fill the | |
295 | * specified page with data. Page must be locked and in the swap cache. | |
296 | */ | |
165c8aed | 297 | int __frontswap_load(struct page *page) |
29f233cf DM |
298 | { |
299 | int ret = -1; | |
300 | swp_entry_t entry = { .val = page_private(page), }; | |
301 | int type = swp_type(entry); | |
302 | struct swap_info_struct *sis = swap_info[type]; | |
303 | pgoff_t offset = swp_offset(entry); | |
d1dc6f1b DS |
304 | struct frontswap_ops *ops; |
305 | ||
306 | if (!frontswap_ops) | |
307 | return -1; | |
29f233cf DM |
308 | |
309 | BUG_ON(!PageLocked(page)); | |
310 | BUG_ON(sis == NULL); | |
d1dc6f1b DS |
311 | if (!__frontswap_test(sis, offset)) |
312 | return -1; | |
313 | ||
314 | /* Try loading from each implementation, until one succeeds. */ | |
315 | for_each_frontswap_ops(ops) { | |
316 | ret = ops->load(type, offset, page); | |
317 | if (!ret) /* successful load */ | |
318 | break; | |
319 | } | |
e3483a5f | 320 | if (ret == 0) { |
165c8aed | 321 | inc_frontswap_loads(); |
e3483a5f DM |
322 | if (frontswap_tmem_exclusive_gets_enabled) { |
323 | SetPageDirty(page); | |
f066ea23 | 324 | __frontswap_clear(sis, offset); |
e3483a5f DM |
325 | } |
326 | } | |
29f233cf DM |
327 | return ret; |
328 | } | |
165c8aed | 329 | EXPORT_SYMBOL(__frontswap_load); |
29f233cf DM |
330 | |
331 | /* | |
332 | * Invalidate any data from frontswap associated with the specified swaptype | |
333 | * and offset so that a subsequent "get" will fail. | |
334 | */ | |
335 | void __frontswap_invalidate_page(unsigned type, pgoff_t offset) | |
336 | { | |
337 | struct swap_info_struct *sis = swap_info[type]; | |
d1dc6f1b DS |
338 | struct frontswap_ops *ops; |
339 | ||
340 | if (!frontswap_ops) | |
341 | return; | |
29f233cf DM |
342 | |
343 | BUG_ON(sis == NULL); | |
d1dc6f1b DS |
344 | if (!__frontswap_test(sis, offset)) |
345 | return; | |
346 | ||
347 | for_each_frontswap_ops(ops) | |
348 | ops->invalidate_page(type, offset); | |
349 | __frontswap_clear(sis, offset); | |
350 | inc_frontswap_invalidates(); | |
29f233cf DM |
351 | } |
352 | EXPORT_SYMBOL(__frontswap_invalidate_page); | |
353 | ||
354 | /* | |
355 | * Invalidate all data from frontswap associated with all offsets for the | |
356 | * specified swaptype. | |
357 | */ | |
358 | void __frontswap_invalidate_area(unsigned type) | |
359 | { | |
360 | struct swap_info_struct *sis = swap_info[type]; | |
d1dc6f1b | 361 | struct frontswap_ops *ops; |
29f233cf | 362 | |
d1dc6f1b DS |
363 | if (!frontswap_ops) |
364 | return; | |
365 | ||
366 | BUG_ON(sis == NULL); | |
367 | if (sis->frontswap_map == NULL) | |
368 | return; | |
369 | ||
370 | for_each_frontswap_ops(ops) | |
371 | ops->invalidate_area(type); | |
372 | atomic_set(&sis->frontswap_pages, 0); | |
373 | bitmap_zero(sis->frontswap_map, sis->max); | |
29f233cf DM |
374 | } |
375 | EXPORT_SYMBOL(__frontswap_invalidate_area); | |
376 | ||
96253444 SL |
377 | static unsigned long __frontswap_curr_pages(void) |
378 | { | |
96253444 SL |
379 | unsigned long totalpages = 0; |
380 | struct swap_info_struct *si = NULL; | |
381 | ||
382 | assert_spin_locked(&swap_lock); | |
18ab4d4c | 383 | plist_for_each_entry(si, &swap_active_head, list) |
96253444 | 384 | totalpages += atomic_read(&si->frontswap_pages); |
96253444 SL |
385 | return totalpages; |
386 | } | |
387 | ||
f116695a SL |
388 | static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused, |
389 | int *swapid) | |
390 | { | |
391 | int ret = -EINVAL; | |
392 | struct swap_info_struct *si = NULL; | |
393 | int si_frontswap_pages; | |
394 | unsigned long total_pages_to_unuse = total; | |
395 | unsigned long pages = 0, pages_to_unuse = 0; | |
f116695a SL |
396 | |
397 | assert_spin_locked(&swap_lock); | |
18ab4d4c | 398 | plist_for_each_entry(si, &swap_active_head, list) { |
f116695a SL |
399 | si_frontswap_pages = atomic_read(&si->frontswap_pages); |
400 | if (total_pages_to_unuse < si_frontswap_pages) { | |
401 | pages = pages_to_unuse = total_pages_to_unuse; | |
402 | } else { | |
403 | pages = si_frontswap_pages; | |
404 | pages_to_unuse = 0; /* unuse all */ | |
405 | } | |
406 | /* ensure there is enough RAM to fetch pages from frontswap */ | |
407 | if (security_vm_enough_memory_mm(current->mm, pages)) { | |
408 | ret = -ENOMEM; | |
409 | continue; | |
410 | } | |
411 | vm_unacct_memory(pages); | |
412 | *unused = pages_to_unuse; | |
adfab836 | 413 | *swapid = si->type; |
f116695a SL |
414 | ret = 0; |
415 | break; | |
416 | } | |
417 | ||
418 | return ret; | |
419 | } | |
420 | ||
a00bb1e9 ZD |
421 | /* |
422 | * Used to check if it's necessory and feasible to unuse pages. | |
423 | * Return 1 when nothing to do, 0 when need to shink pages, | |
424 | * error code when there is an error. | |
425 | */ | |
69217b4c SL |
426 | static int __frontswap_shrink(unsigned long target_pages, |
427 | unsigned long *pages_to_unuse, | |
428 | int *type) | |
429 | { | |
430 | unsigned long total_pages = 0, total_pages_to_unuse; | |
431 | ||
432 | assert_spin_locked(&swap_lock); | |
433 | ||
434 | total_pages = __frontswap_curr_pages(); | |
435 | if (total_pages <= target_pages) { | |
436 | /* Nothing to do */ | |
437 | *pages_to_unuse = 0; | |
a00bb1e9 | 438 | return 1; |
69217b4c SL |
439 | } |
440 | total_pages_to_unuse = total_pages - target_pages; | |
441 | return __frontswap_unuse_pages(total_pages_to_unuse, pages_to_unuse, type); | |
442 | } | |
443 | ||
29f233cf DM |
444 | /* |
445 | * Frontswap, like a true swap device, may unnecessarily retain pages | |
446 | * under certain circumstances; "shrink" frontswap is essentially a | |
447 | * "partial swapoff" and works by calling try_to_unuse to attempt to | |
448 | * unuse enough frontswap pages to attempt to -- subject to memory | |
449 | * constraints -- reduce the number of pages in frontswap to the | |
450 | * number given in the parameter target_pages. | |
451 | */ | |
452 | void frontswap_shrink(unsigned long target_pages) | |
453 | { | |
f116695a | 454 | unsigned long pages_to_unuse = 0; |
6b982fcf | 455 | int uninitialized_var(type), ret; |
29f233cf DM |
456 | |
457 | /* | |
458 | * we don't want to hold swap_lock while doing a very | |
459 | * lengthy try_to_unuse, but swap_list may change | |
18ab4d4c | 460 | * so restart scan from swap_active_head each time |
29f233cf DM |
461 | */ |
462 | spin_lock(&swap_lock); | |
69217b4c | 463 | ret = __frontswap_shrink(target_pages, &pages_to_unuse, &type); |
29f233cf | 464 | spin_unlock(&swap_lock); |
a00bb1e9 | 465 | if (ret == 0) |
69217b4c | 466 | try_to_unuse(type, true, pages_to_unuse); |
29f233cf DM |
467 | return; |
468 | } | |
469 | EXPORT_SYMBOL(frontswap_shrink); | |
470 | ||
471 | /* | |
472 | * Count and return the number of frontswap pages across all | |
473 | * swap devices. This is exported so that backend drivers can | |
474 | * determine current usage without reading debugfs. | |
475 | */ | |
476 | unsigned long frontswap_curr_pages(void) | |
477 | { | |
29f233cf | 478 | unsigned long totalpages = 0; |
29f233cf DM |
479 | |
480 | spin_lock(&swap_lock); | |
96253444 | 481 | totalpages = __frontswap_curr_pages(); |
29f233cf | 482 | spin_unlock(&swap_lock); |
96253444 | 483 | |
29f233cf DM |
484 | return totalpages; |
485 | } | |
486 | EXPORT_SYMBOL(frontswap_curr_pages); | |
487 | ||
488 | static int __init init_frontswap(void) | |
489 | { | |
490 | #ifdef CONFIG_DEBUG_FS | |
491 | struct dentry *root = debugfs_create_dir("frontswap", NULL); | |
492 | if (root == NULL) | |
493 | return -ENXIO; | |
165c8aed KRW |
494 | debugfs_create_u64("loads", S_IRUGO, root, &frontswap_loads); |
495 | debugfs_create_u64("succ_stores", S_IRUGO, root, &frontswap_succ_stores); | |
496 | debugfs_create_u64("failed_stores", S_IRUGO, root, | |
497 | &frontswap_failed_stores); | |
29f233cf DM |
498 | debugfs_create_u64("invalidates", S_IRUGO, |
499 | root, &frontswap_invalidates); | |
500 | #endif | |
501 | return 0; | |
502 | } | |
503 | ||
504 | module_init(init_frontswap); |