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