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7a338472 | 1 | // SPDX-License-Identifier: GPL-2.0-only |
29f233cf DM |
2 | /* |
3 | * Frontswap frontend | |
4 | * | |
5 | * This code provides the generic "frontend" layer to call a matching | |
6 | * "backend" driver implementation of frontswap. See | |
ad56b738 | 7 | * Documentation/vm/frontswap.rst for more information. |
29f233cf DM |
8 | * |
9 | * Copyright (C) 2009-2012 Oracle Corp. All rights reserved. | |
10 | * Author: Dan Magenheimer | |
29f233cf DM |
11 | */ |
12 | ||
29f233cf DM |
13 | #include <linux/mman.h> |
14 | #include <linux/swap.h> | |
15 | #include <linux/swapops.h> | |
29f233cf | 16 | #include <linux/security.h> |
29f233cf | 17 | #include <linux/module.h> |
29f233cf DM |
18 | #include <linux/debugfs.h> |
19 | #include <linux/frontswap.h> | |
20 | #include <linux/swapfile.h> | |
21 | ||
8ea1d2a1 VB |
22 | DEFINE_STATIC_KEY_FALSE(frontswap_enabled_key); |
23 | ||
29f233cf | 24 | /* |
d1dc6f1b DS |
25 | * frontswap_ops are added by frontswap_register_ops, and provide the |
26 | * frontswap "backend" implementation functions. Multiple implementations | |
27 | * may be registered, but implementations can never deregister. This | |
28 | * is a simple singly-linked list of all registered implementations. | |
29f233cf | 29 | */ |
1e01c968 | 30 | static struct frontswap_ops *frontswap_ops __read_mostly; |
29f233cf | 31 | |
d1dc6f1b DS |
32 | #define for_each_frontswap_ops(ops) \ |
33 | for ((ops) = frontswap_ops; (ops); (ops) = (ops)->next) | |
34 | ||
29f233cf | 35 | /* |
165c8aed | 36 | * If enabled, frontswap_store will return failure even on success. As |
29f233cf DM |
37 | * a result, the swap subsystem will always write the page to swap, in |
38 | * effect converting frontswap into a writethrough cache. In this mode, | |
39 | * there is no direct reduction in swap writes, but a frontswap backend | |
40 | * can unilaterally "reclaim" any pages in use with no data loss, thus | |
41 | * providing increases control over maximum memory usage due to frontswap. | |
42 | */ | |
43 | static bool frontswap_writethrough_enabled __read_mostly; | |
44 | ||
e3483a5f DM |
45 | /* |
46 | * If enabled, the underlying tmem implementation is capable of doing | |
47 | * exclusive gets, so frontswap_load, on a successful tmem_get must | |
48 | * mark the page as no longer in frontswap AND mark it dirty. | |
49 | */ | |
50 | static bool frontswap_tmem_exclusive_gets_enabled __read_mostly; | |
51 | ||
29f233cf DM |
52 | #ifdef CONFIG_DEBUG_FS |
53 | /* | |
54 | * Counters available via /sys/kernel/debug/frontswap (if debugfs is | |
55 | * properly configured). These are for information only so are not protected | |
56 | * against increment races. | |
57 | */ | |
165c8aed KRW |
58 | static u64 frontswap_loads; |
59 | static u64 frontswap_succ_stores; | |
60 | static u64 frontswap_failed_stores; | |
29f233cf DM |
61 | static u64 frontswap_invalidates; |
62 | ||
165c8aed | 63 | static inline void inc_frontswap_loads(void) { |
96bdd2bc | 64 | data_race(frontswap_loads++); |
29f233cf | 65 | } |
165c8aed | 66 | static inline void inc_frontswap_succ_stores(void) { |
96bdd2bc | 67 | data_race(frontswap_succ_stores++); |
29f233cf | 68 | } |
165c8aed | 69 | static inline void inc_frontswap_failed_stores(void) { |
96bdd2bc | 70 | data_race(frontswap_failed_stores++); |
29f233cf DM |
71 | } |
72 | static inline void inc_frontswap_invalidates(void) { | |
96bdd2bc | 73 | data_race(frontswap_invalidates++); |
29f233cf DM |
74 | } |
75 | #else | |
165c8aed KRW |
76 | static inline void inc_frontswap_loads(void) { } |
77 | static inline void inc_frontswap_succ_stores(void) { } | |
78 | static inline void inc_frontswap_failed_stores(void) { } | |
29f233cf DM |
79 | static inline void inc_frontswap_invalidates(void) { } |
80 | #endif | |
905cd0e1 DM |
81 | |
82 | /* | |
83 | * Due to the asynchronous nature of the backends loading potentially | |
84 | * _after_ the swap system has been activated, we have chokepoints | |
85 | * on all frontswap functions to not call the backend until the backend | |
86 | * has registered. | |
87 | * | |
905cd0e1 DM |
88 | * This would not guards us against the user deciding to call swapoff right as |
89 | * we are calling the backend to initialize (so swapon is in action). | |
404f3ecf | 90 | * Fortunately for us, the swapon_mutex has been taken by the callee so we are |
905cd0e1 DM |
91 | * OK. The other scenario where calls to frontswap_store (called via |
92 | * swap_writepage) is racing with frontswap_invalidate_area (called via | |
93 | * swapoff) is again guarded by the swap subsystem. | |
94 | * | |
95 | * While no backend is registered all calls to frontswap_[store|load| | |
96 | * invalidate_area|invalidate_page] are ignored or fail. | |
97 | * | |
98 | * The time between the backend being registered and the swap file system | |
99 | * calling the backend (via the frontswap_* functions) is indeterminate as | |
1e01c968 | 100 | * frontswap_ops is not atomic_t (or a value guarded by a spinlock). |
905cd0e1 DM |
101 | * That is OK as we are comfortable missing some of these calls to the newly |
102 | * registered backend. | |
103 | * | |
104 | * Obviously the opposite (unloading the backend) must be done after all | |
105 | * the frontswap_[store|load|invalidate_area|invalidate_page] start | |
d1dc6f1b DS |
106 | * ignoring or failing the requests. However, there is currently no way |
107 | * to unload a backend once it is registered. | |
905cd0e1 | 108 | */ |
905cd0e1 | 109 | |
29f233cf | 110 | /* |
d1dc6f1b | 111 | * Register operations for frontswap |
29f233cf | 112 | */ |
d1dc6f1b | 113 | void frontswap_register_ops(struct frontswap_ops *ops) |
29f233cf | 114 | { |
d1dc6f1b DS |
115 | DECLARE_BITMAP(a, MAX_SWAPFILES); |
116 | DECLARE_BITMAP(b, MAX_SWAPFILES); | |
117 | struct swap_info_struct *si; | |
118 | unsigned int i; | |
119 | ||
120 | bitmap_zero(a, MAX_SWAPFILES); | |
121 | bitmap_zero(b, MAX_SWAPFILES); | |
122 | ||
123 | spin_lock(&swap_lock); | |
124 | plist_for_each_entry(si, &swap_active_head, list) { | |
125 | if (!WARN_ON(!si->frontswap_map)) | |
126 | set_bit(si->type, a); | |
127 | } | |
128 | spin_unlock(&swap_lock); | |
129 | ||
130 | /* the new ops needs to know the currently active swap devices */ | |
131 | for_each_set_bit(i, a, MAX_SWAPFILES) | |
132 | ops->init(i); | |
133 | ||
134 | /* | |
135 | * Setting frontswap_ops must happen after the ops->init() calls | |
136 | * above; cmpxchg implies smp_mb() which will ensure the init is | |
137 | * complete at this point. | |
138 | */ | |
139 | do { | |
140 | ops->next = frontswap_ops; | |
141 | } while (cmpxchg(&frontswap_ops, ops->next, ops) != ops->next); | |
142 | ||
8ea1d2a1 VB |
143 | static_branch_inc(&frontswap_enabled_key); |
144 | ||
d1dc6f1b DS |
145 | spin_lock(&swap_lock); |
146 | plist_for_each_entry(si, &swap_active_head, list) { | |
147 | if (si->frontswap_map) | |
148 | set_bit(si->type, b); | |
905cd0e1 | 149 | } |
d1dc6f1b DS |
150 | spin_unlock(&swap_lock); |
151 | ||
905cd0e1 | 152 | /* |
d1dc6f1b DS |
153 | * On the very unlikely chance that a swap device was added or |
154 | * removed between setting the "a" list bits and the ops init | |
155 | * calls, we re-check and do init or invalidate for any changed | |
156 | * bits. | |
905cd0e1 | 157 | */ |
d1dc6f1b DS |
158 | if (unlikely(!bitmap_equal(a, b, MAX_SWAPFILES))) { |
159 | for (i = 0; i < MAX_SWAPFILES; i++) { | |
160 | if (!test_bit(i, a) && test_bit(i, b)) | |
161 | ops->init(i); | |
162 | else if (test_bit(i, a) && !test_bit(i, b)) | |
163 | ops->invalidate_area(i); | |
164 | } | |
165 | } | |
29f233cf DM |
166 | } |
167 | EXPORT_SYMBOL(frontswap_register_ops); | |
168 | ||
169 | /* | |
170 | * Enable/disable frontswap writethrough (see above). | |
171 | */ | |
172 | void frontswap_writethrough(bool enable) | |
173 | { | |
174 | frontswap_writethrough_enabled = enable; | |
175 | } | |
176 | EXPORT_SYMBOL(frontswap_writethrough); | |
177 | ||
e3483a5f DM |
178 | /* |
179 | * Enable/disable frontswap exclusive gets (see above). | |
180 | */ | |
181 | void frontswap_tmem_exclusive_gets(bool enable) | |
182 | { | |
183 | frontswap_tmem_exclusive_gets_enabled = enable; | |
184 | } | |
185 | EXPORT_SYMBOL(frontswap_tmem_exclusive_gets); | |
186 | ||
29f233cf DM |
187 | /* |
188 | * Called when a swap device is swapon'd. | |
189 | */ | |
4f89849d | 190 | void __frontswap_init(unsigned type, unsigned long *map) |
29f233cf DM |
191 | { |
192 | struct swap_info_struct *sis = swap_info[type]; | |
d1dc6f1b | 193 | struct frontswap_ops *ops; |
29f233cf | 194 | |
8ea1d2a1 | 195 | VM_BUG_ON(sis == NULL); |
4f89849d MK |
196 | |
197 | /* | |
198 | * p->frontswap is a bitmap that we MUST have to figure out which page | |
199 | * has gone in frontswap. Without it there is no point of continuing. | |
200 | */ | |
201 | if (WARN_ON(!map)) | |
202 | return; | |
203 | /* | |
204 | * Irregardless of whether the frontswap backend has been loaded | |
205 | * before this function or it will be later, we _MUST_ have the | |
206 | * p->frontswap set to something valid to work properly. | |
207 | */ | |
208 | frontswap_map_set(sis, map); | |
d1dc6f1b DS |
209 | |
210 | for_each_frontswap_ops(ops) | |
211 | ops->init(type); | |
29f233cf DM |
212 | } |
213 | EXPORT_SYMBOL(__frontswap_init); | |
214 | ||
f066ea23 BL |
215 | bool __frontswap_test(struct swap_info_struct *sis, |
216 | pgoff_t offset) | |
217 | { | |
d1dc6f1b DS |
218 | if (sis->frontswap_map) |
219 | return test_bit(offset, sis->frontswap_map); | |
220 | return false; | |
f066ea23 BL |
221 | } |
222 | EXPORT_SYMBOL(__frontswap_test); | |
223 | ||
d1dc6f1b DS |
224 | static inline void __frontswap_set(struct swap_info_struct *sis, |
225 | pgoff_t offset) | |
226 | { | |
227 | set_bit(offset, sis->frontswap_map); | |
228 | atomic_inc(&sis->frontswap_pages); | |
229 | } | |
230 | ||
f066ea23 | 231 | static inline void __frontswap_clear(struct swap_info_struct *sis, |
d1dc6f1b | 232 | pgoff_t offset) |
611edfed | 233 | { |
f066ea23 | 234 | clear_bit(offset, sis->frontswap_map); |
611edfed SL |
235 | atomic_dec(&sis->frontswap_pages); |
236 | } | |
237 | ||
29f233cf | 238 | /* |
165c8aed | 239 | * "Store" data from a page to frontswap and associate it with the page's |
29f233cf DM |
240 | * swaptype and offset. Page must be locked and in the swap cache. |
241 | * If frontswap already contains a page with matching swaptype and | |
1d00015e | 242 | * offset, the frontswap implementation may either overwrite the data and |
29f233cf DM |
243 | * return success or invalidate the page from frontswap and return failure. |
244 | */ | |
165c8aed | 245 | int __frontswap_store(struct page *page) |
29f233cf | 246 | { |
d1dc6f1b | 247 | int ret = -1; |
29f233cf DM |
248 | swp_entry_t entry = { .val = page_private(page), }; |
249 | int type = swp_type(entry); | |
250 | struct swap_info_struct *sis = swap_info[type]; | |
251 | pgoff_t offset = swp_offset(entry); | |
d1dc6f1b | 252 | struct frontswap_ops *ops; |
29f233cf | 253 | |
8ea1d2a1 VB |
254 | VM_BUG_ON(!frontswap_ops); |
255 | VM_BUG_ON(!PageLocked(page)); | |
256 | VM_BUG_ON(sis == NULL); | |
d1dc6f1b DS |
257 | |
258 | /* | |
259 | * If a dup, we must remove the old page first; we can't leave the | |
260 | * old page no matter if the store of the new page succeeds or fails, | |
261 | * and we can't rely on the new page replacing the old page as we may | |
262 | * not store to the same implementation that contains the old page. | |
263 | */ | |
264 | if (__frontswap_test(sis, offset)) { | |
265 | __frontswap_clear(sis, offset); | |
266 | for_each_frontswap_ops(ops) | |
267 | ops->invalidate_page(type, offset); | |
268 | } | |
269 | ||
270 | /* Try to store in each implementation, until one succeeds. */ | |
271 | for_each_frontswap_ops(ops) { | |
272 | ret = ops->store(type, offset, page); | |
273 | if (!ret) /* successful store */ | |
274 | break; | |
275 | } | |
29f233cf | 276 | if (ret == 0) { |
d1dc6f1b | 277 | __frontswap_set(sis, offset); |
165c8aed | 278 | inc_frontswap_succ_stores(); |
d9674dda | 279 | } else { |
165c8aed | 280 | inc_frontswap_failed_stores(); |
4bb3e31e | 281 | } |
29f233cf DM |
282 | if (frontswap_writethrough_enabled) |
283 | /* report failure so swap also writes to swap device */ | |
284 | ret = -1; | |
285 | return ret; | |
286 | } | |
165c8aed | 287 | EXPORT_SYMBOL(__frontswap_store); |
29f233cf DM |
288 | |
289 | /* | |
290 | * "Get" data from frontswap associated with swaptype and offset that were | |
291 | * specified when the data was put to frontswap and use it to fill the | |
292 | * specified page with data. Page must be locked and in the swap cache. | |
293 | */ | |
165c8aed | 294 | int __frontswap_load(struct page *page) |
29f233cf DM |
295 | { |
296 | int ret = -1; | |
297 | swp_entry_t entry = { .val = page_private(page), }; | |
298 | int type = swp_type(entry); | |
299 | struct swap_info_struct *sis = swap_info[type]; | |
300 | pgoff_t offset = swp_offset(entry); | |
d1dc6f1b DS |
301 | struct frontswap_ops *ops; |
302 | ||
8ea1d2a1 VB |
303 | VM_BUG_ON(!frontswap_ops); |
304 | VM_BUG_ON(!PageLocked(page)); | |
305 | VM_BUG_ON(sis == NULL); | |
29f233cf | 306 | |
d1dc6f1b DS |
307 | if (!__frontswap_test(sis, offset)) |
308 | return -1; | |
309 | ||
310 | /* Try loading from each implementation, until one succeeds. */ | |
311 | for_each_frontswap_ops(ops) { | |
312 | ret = ops->load(type, offset, page); | |
313 | if (!ret) /* successful load */ | |
314 | break; | |
315 | } | |
e3483a5f | 316 | if (ret == 0) { |
165c8aed | 317 | inc_frontswap_loads(); |
e3483a5f DM |
318 | if (frontswap_tmem_exclusive_gets_enabled) { |
319 | SetPageDirty(page); | |
f066ea23 | 320 | __frontswap_clear(sis, offset); |
e3483a5f DM |
321 | } |
322 | } | |
29f233cf DM |
323 | return ret; |
324 | } | |
165c8aed | 325 | EXPORT_SYMBOL(__frontswap_load); |
29f233cf DM |
326 | |
327 | /* | |
328 | * Invalidate any data from frontswap associated with the specified swaptype | |
329 | * and offset so that a subsequent "get" will fail. | |
330 | */ | |
331 | void __frontswap_invalidate_page(unsigned type, pgoff_t offset) | |
332 | { | |
333 | struct swap_info_struct *sis = swap_info[type]; | |
d1dc6f1b DS |
334 | struct frontswap_ops *ops; |
335 | ||
8ea1d2a1 VB |
336 | VM_BUG_ON(!frontswap_ops); |
337 | VM_BUG_ON(sis == NULL); | |
29f233cf | 338 | |
d1dc6f1b DS |
339 | if (!__frontswap_test(sis, offset)) |
340 | return; | |
341 | ||
342 | for_each_frontswap_ops(ops) | |
343 | ops->invalidate_page(type, offset); | |
344 | __frontswap_clear(sis, offset); | |
345 | inc_frontswap_invalidates(); | |
29f233cf DM |
346 | } |
347 | EXPORT_SYMBOL(__frontswap_invalidate_page); | |
348 | ||
349 | /* | |
350 | * Invalidate all data from frontswap associated with all offsets for the | |
351 | * specified swaptype. | |
352 | */ | |
353 | void __frontswap_invalidate_area(unsigned type) | |
354 | { | |
355 | struct swap_info_struct *sis = swap_info[type]; | |
d1dc6f1b | 356 | struct frontswap_ops *ops; |
29f233cf | 357 | |
8ea1d2a1 VB |
358 | VM_BUG_ON(!frontswap_ops); |
359 | VM_BUG_ON(sis == NULL); | |
d1dc6f1b | 360 | |
d1dc6f1b DS |
361 | if (sis->frontswap_map == NULL) |
362 | return; | |
363 | ||
364 | for_each_frontswap_ops(ops) | |
365 | ops->invalidate_area(type); | |
366 | atomic_set(&sis->frontswap_pages, 0); | |
367 | bitmap_zero(sis->frontswap_map, sis->max); | |
29f233cf DM |
368 | } |
369 | EXPORT_SYMBOL(__frontswap_invalidate_area); | |
370 | ||
96253444 SL |
371 | static unsigned long __frontswap_curr_pages(void) |
372 | { | |
96253444 SL |
373 | unsigned long totalpages = 0; |
374 | struct swap_info_struct *si = NULL; | |
375 | ||
376 | assert_spin_locked(&swap_lock); | |
18ab4d4c | 377 | plist_for_each_entry(si, &swap_active_head, list) |
96253444 | 378 | totalpages += atomic_read(&si->frontswap_pages); |
96253444 SL |
379 | return totalpages; |
380 | } | |
381 | ||
f116695a SL |
382 | static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused, |
383 | int *swapid) | |
384 | { | |
385 | int ret = -EINVAL; | |
386 | struct swap_info_struct *si = NULL; | |
387 | int si_frontswap_pages; | |
388 | unsigned long total_pages_to_unuse = total; | |
389 | unsigned long pages = 0, pages_to_unuse = 0; | |
f116695a SL |
390 | |
391 | assert_spin_locked(&swap_lock); | |
18ab4d4c | 392 | plist_for_each_entry(si, &swap_active_head, list) { |
f116695a SL |
393 | si_frontswap_pages = atomic_read(&si->frontswap_pages); |
394 | if (total_pages_to_unuse < si_frontswap_pages) { | |
395 | pages = pages_to_unuse = total_pages_to_unuse; | |
396 | } else { | |
397 | pages = si_frontswap_pages; | |
398 | pages_to_unuse = 0; /* unuse all */ | |
399 | } | |
400 | /* ensure there is enough RAM to fetch pages from frontswap */ | |
401 | if (security_vm_enough_memory_mm(current->mm, pages)) { | |
402 | ret = -ENOMEM; | |
403 | continue; | |
404 | } | |
405 | vm_unacct_memory(pages); | |
406 | *unused = pages_to_unuse; | |
adfab836 | 407 | *swapid = si->type; |
f116695a SL |
408 | ret = 0; |
409 | break; | |
410 | } | |
411 | ||
412 | return ret; | |
413 | } | |
414 | ||
a00bb1e9 | 415 | /* |
404f3ecf EP |
416 | * Used to check if it's necessary and feasible to unuse pages. |
417 | * Return 1 when nothing to do, 0 when need to shrink pages, | |
a00bb1e9 ZD |
418 | * error code when there is an error. |
419 | */ | |
69217b4c SL |
420 | static int __frontswap_shrink(unsigned long target_pages, |
421 | unsigned long *pages_to_unuse, | |
422 | int *type) | |
423 | { | |
424 | unsigned long total_pages = 0, total_pages_to_unuse; | |
425 | ||
426 | assert_spin_locked(&swap_lock); | |
427 | ||
428 | total_pages = __frontswap_curr_pages(); | |
429 | if (total_pages <= target_pages) { | |
430 | /* Nothing to do */ | |
431 | *pages_to_unuse = 0; | |
a00bb1e9 | 432 | return 1; |
69217b4c SL |
433 | } |
434 | total_pages_to_unuse = total_pages - target_pages; | |
435 | return __frontswap_unuse_pages(total_pages_to_unuse, pages_to_unuse, type); | |
436 | } | |
437 | ||
29f233cf DM |
438 | /* |
439 | * Frontswap, like a true swap device, may unnecessarily retain pages | |
440 | * under certain circumstances; "shrink" frontswap is essentially a | |
441 | * "partial swapoff" and works by calling try_to_unuse to attempt to | |
442 | * unuse enough frontswap pages to attempt to -- subject to memory | |
443 | * constraints -- reduce the number of pages in frontswap to the | |
444 | * number given in the parameter target_pages. | |
445 | */ | |
446 | void frontswap_shrink(unsigned long target_pages) | |
447 | { | |
f116695a | 448 | unsigned long pages_to_unuse = 0; |
3f649ab7 | 449 | int type, ret; |
29f233cf DM |
450 | |
451 | /* | |
452 | * we don't want to hold swap_lock while doing a very | |
453 | * lengthy try_to_unuse, but swap_list may change | |
18ab4d4c | 454 | * so restart scan from swap_active_head each time |
29f233cf DM |
455 | */ |
456 | spin_lock(&swap_lock); | |
69217b4c | 457 | ret = __frontswap_shrink(target_pages, &pages_to_unuse, &type); |
29f233cf | 458 | spin_unlock(&swap_lock); |
a00bb1e9 | 459 | if (ret == 0) |
69217b4c | 460 | try_to_unuse(type, true, pages_to_unuse); |
29f233cf DM |
461 | return; |
462 | } | |
463 | EXPORT_SYMBOL(frontswap_shrink); | |
464 | ||
465 | /* | |
466 | * Count and return the number of frontswap pages across all | |
467 | * swap devices. This is exported so that backend drivers can | |
468 | * determine current usage without reading debugfs. | |
469 | */ | |
470 | unsigned long frontswap_curr_pages(void) | |
471 | { | |
29f233cf | 472 | unsigned long totalpages = 0; |
29f233cf DM |
473 | |
474 | spin_lock(&swap_lock); | |
96253444 | 475 | totalpages = __frontswap_curr_pages(); |
29f233cf | 476 | spin_unlock(&swap_lock); |
96253444 | 477 | |
29f233cf DM |
478 | return totalpages; |
479 | } | |
480 | EXPORT_SYMBOL(frontswap_curr_pages); | |
481 | ||
482 | static int __init init_frontswap(void) | |
483 | { | |
484 | #ifdef CONFIG_DEBUG_FS | |
485 | struct dentry *root = debugfs_create_dir("frontswap", NULL); | |
486 | if (root == NULL) | |
487 | return -ENXIO; | |
0825a6f9 JP |
488 | debugfs_create_u64("loads", 0444, root, &frontswap_loads); |
489 | debugfs_create_u64("succ_stores", 0444, root, &frontswap_succ_stores); | |
490 | debugfs_create_u64("failed_stores", 0444, root, | |
491 | &frontswap_failed_stores); | |
492 | debugfs_create_u64("invalidates", 0444, root, &frontswap_invalidates); | |
29f233cf DM |
493 | #endif |
494 | return 0; | |
495 | } | |
496 | ||
497 | module_init(init_frontswap); |