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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 | /* | |
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 | * This global enablement flag reduces overhead on systems where frontswap_ops | |
31 | * has not been registered, so is preferred to the slower alternative: a | |
32 | * function call that checks a non-global. | |
33 | */ | |
34 | bool frontswap_enabled __read_mostly; | |
35 | EXPORT_SYMBOL(frontswap_enabled); | |
36 | ||
37 | /* | |
165c8aed | 38 | * If enabled, frontswap_store will return failure even on success. As |
29f233cf DM |
39 | * a result, the swap subsystem will always write the page to swap, in |
40 | * effect converting frontswap into a writethrough cache. In this mode, | |
41 | * there is no direct reduction in swap writes, but a frontswap backend | |
42 | * can unilaterally "reclaim" any pages in use with no data loss, thus | |
43 | * providing increases control over maximum memory usage due to frontswap. | |
44 | */ | |
45 | static bool frontswap_writethrough_enabled __read_mostly; | |
46 | ||
e3483a5f DM |
47 | /* |
48 | * If enabled, the underlying tmem implementation is capable of doing | |
49 | * exclusive gets, so frontswap_load, on a successful tmem_get must | |
50 | * mark the page as no longer in frontswap AND mark it dirty. | |
51 | */ | |
52 | static bool frontswap_tmem_exclusive_gets_enabled __read_mostly; | |
53 | ||
29f233cf DM |
54 | #ifdef CONFIG_DEBUG_FS |
55 | /* | |
56 | * Counters available via /sys/kernel/debug/frontswap (if debugfs is | |
57 | * properly configured). These are for information only so are not protected | |
58 | * against increment races. | |
59 | */ | |
165c8aed KRW |
60 | static u64 frontswap_loads; |
61 | static u64 frontswap_succ_stores; | |
62 | static u64 frontswap_failed_stores; | |
29f233cf DM |
63 | static u64 frontswap_invalidates; |
64 | ||
165c8aed KRW |
65 | static inline void inc_frontswap_loads(void) { |
66 | frontswap_loads++; | |
29f233cf | 67 | } |
165c8aed KRW |
68 | static inline void inc_frontswap_succ_stores(void) { |
69 | frontswap_succ_stores++; | |
29f233cf | 70 | } |
165c8aed KRW |
71 | static inline void inc_frontswap_failed_stores(void) { |
72 | frontswap_failed_stores++; | |
29f233cf DM |
73 | } |
74 | static inline void inc_frontswap_invalidates(void) { | |
75 | frontswap_invalidates++; | |
76 | } | |
77 | #else | |
165c8aed KRW |
78 | static inline void inc_frontswap_loads(void) { } |
79 | static inline void inc_frontswap_succ_stores(void) { } | |
80 | static inline void inc_frontswap_failed_stores(void) { } | |
29f233cf DM |
81 | static inline void inc_frontswap_invalidates(void) { } |
82 | #endif | |
905cd0e1 DM |
83 | |
84 | /* | |
85 | * Due to the asynchronous nature of the backends loading potentially | |
86 | * _after_ the swap system has been activated, we have chokepoints | |
87 | * on all frontswap functions to not call the backend until the backend | |
88 | * has registered. | |
89 | * | |
90 | * Specifically when no backend is registered (nobody called | |
91 | * frontswap_register_ops) all calls to frontswap_init (which is done via | |
92 | * swapon -> enable_swap_info -> frontswap_init) are registered and remembered | |
93 | * (via the setting of need_init bitmap) but fail to create tmem_pools. When a | |
94 | * backend registers with frontswap at some later point the previous | |
95 | * calls to frontswap_init are executed (by iterating over the need_init | |
96 | * bitmap) to create tmem_pools and set the respective poolids. All of that is | |
97 | * guarded by us using atomic bit operations on the 'need_init' bitmap. | |
98 | * | |
99 | * This would not guards us against the user deciding to call swapoff right as | |
100 | * we are calling the backend to initialize (so swapon is in action). | |
101 | * Fortunatly for us, the swapon_mutex has been taked by the callee so we are | |
102 | * OK. The other scenario where calls to frontswap_store (called via | |
103 | * swap_writepage) is racing with frontswap_invalidate_area (called via | |
104 | * swapoff) is again guarded by the swap subsystem. | |
105 | * | |
106 | * While no backend is registered all calls to frontswap_[store|load| | |
107 | * invalidate_area|invalidate_page] are ignored or fail. | |
108 | * | |
109 | * The time between the backend being registered and the swap file system | |
110 | * calling the backend (via the frontswap_* functions) is indeterminate as | |
111 | * backend_registered is not atomic_t (or a value guarded by a spinlock). | |
112 | * That is OK as we are comfortable missing some of these calls to the newly | |
113 | * registered backend. | |
114 | * | |
115 | * Obviously the opposite (unloading the backend) must be done after all | |
116 | * the frontswap_[store|load|invalidate_area|invalidate_page] start | |
117 | * ignorning or failing the requests - at which point backend_registered | |
118 | * would have to be made in some fashion atomic. | |
119 | */ | |
120 | static DECLARE_BITMAP(need_init, MAX_SWAPFILES); | |
121 | static bool backend_registered __read_mostly; | |
122 | ||
29f233cf DM |
123 | /* |
124 | * Register operations for frontswap, returning previous thus allowing | |
125 | * detection of multiple backends and possible nesting. | |
126 | */ | |
127 | struct frontswap_ops frontswap_register_ops(struct frontswap_ops *ops) | |
128 | { | |
129 | struct frontswap_ops old = frontswap_ops; | |
905cd0e1 | 130 | int i; |
29f233cf DM |
131 | |
132 | frontswap_ops = *ops; | |
133 | frontswap_enabled = true; | |
905cd0e1 DM |
134 | |
135 | for (i = 0; i < MAX_SWAPFILES; i++) { | |
136 | if (test_and_clear_bit(i, need_init)) | |
137 | (*frontswap_ops.init)(i); | |
138 | } | |
139 | /* | |
140 | * We MUST have backend_registered set _after_ the frontswap_init's | |
141 | * have been called. Otherwise __frontswap_store might fail. Hence | |
142 | * the barrier to make sure compiler does not re-order us. | |
143 | */ | |
144 | barrier(); | |
145 | backend_registered = true; | |
29f233cf DM |
146 | return old; |
147 | } | |
148 | EXPORT_SYMBOL(frontswap_register_ops); | |
149 | ||
150 | /* | |
151 | * Enable/disable frontswap writethrough (see above). | |
152 | */ | |
153 | void frontswap_writethrough(bool enable) | |
154 | { | |
155 | frontswap_writethrough_enabled = enable; | |
156 | } | |
157 | EXPORT_SYMBOL(frontswap_writethrough); | |
158 | ||
e3483a5f DM |
159 | /* |
160 | * Enable/disable frontswap exclusive gets (see above). | |
161 | */ | |
162 | void frontswap_tmem_exclusive_gets(bool enable) | |
163 | { | |
164 | frontswap_tmem_exclusive_gets_enabled = enable; | |
165 | } | |
166 | EXPORT_SYMBOL(frontswap_tmem_exclusive_gets); | |
167 | ||
29f233cf DM |
168 | /* |
169 | * Called when a swap device is swapon'd. | |
170 | */ | |
171 | void __frontswap_init(unsigned type) | |
172 | { | |
173 | struct swap_info_struct *sis = swap_info[type]; | |
174 | ||
905cd0e1 DM |
175 | if (backend_registered) { |
176 | BUG_ON(sis == NULL); | |
177 | if (sis->frontswap_map == NULL) | |
178 | return; | |
179 | (*frontswap_ops.init)(type); | |
180 | } else { | |
181 | BUG_ON(type > MAX_SWAPFILES); | |
182 | set_bit(type, need_init); | |
183 | } | |
184 | ||
29f233cf DM |
185 | } |
186 | EXPORT_SYMBOL(__frontswap_init); | |
187 | ||
611edfed SL |
188 | static inline void __frontswap_clear(struct swap_info_struct *sis, pgoff_t offset) |
189 | { | |
190 | frontswap_clear(sis, offset); | |
191 | atomic_dec(&sis->frontswap_pages); | |
192 | } | |
193 | ||
29f233cf | 194 | /* |
165c8aed | 195 | * "Store" data from a page to frontswap and associate it with the page's |
29f233cf DM |
196 | * swaptype and offset. Page must be locked and in the swap cache. |
197 | * If frontswap already contains a page with matching swaptype and | |
1d00015e | 198 | * offset, the frontswap implementation may either overwrite the data and |
29f233cf DM |
199 | * return success or invalidate the page from frontswap and return failure. |
200 | */ | |
165c8aed | 201 | int __frontswap_store(struct page *page) |
29f233cf DM |
202 | { |
203 | int ret = -1, dup = 0; | |
204 | swp_entry_t entry = { .val = page_private(page), }; | |
205 | int type = swp_type(entry); | |
206 | struct swap_info_struct *sis = swap_info[type]; | |
207 | pgoff_t offset = swp_offset(entry); | |
208 | ||
905cd0e1 DM |
209 | if (!backend_registered) { |
210 | inc_frontswap_failed_stores(); | |
211 | return ret; | |
212 | } | |
213 | ||
29f233cf DM |
214 | BUG_ON(!PageLocked(page)); |
215 | BUG_ON(sis == NULL); | |
216 | if (frontswap_test(sis, offset)) | |
217 | dup = 1; | |
ef383597 | 218 | ret = frontswap_ops.store(type, offset, page); |
29f233cf DM |
219 | if (ret == 0) { |
220 | frontswap_set(sis, offset); | |
165c8aed | 221 | inc_frontswap_succ_stores(); |
29f233cf DM |
222 | if (!dup) |
223 | atomic_inc(&sis->frontswap_pages); | |
d9674dda | 224 | } else { |
29f233cf DM |
225 | /* |
226 | failed dup always results in automatic invalidate of | |
227 | the (older) page from frontswap | |
228 | */ | |
165c8aed | 229 | inc_frontswap_failed_stores(); |
611edfed SL |
230 | if (dup) |
231 | __frontswap_clear(sis, offset); | |
4bb3e31e | 232 | } |
29f233cf DM |
233 | if (frontswap_writethrough_enabled) |
234 | /* report failure so swap also writes to swap device */ | |
235 | ret = -1; | |
236 | return ret; | |
237 | } | |
165c8aed | 238 | EXPORT_SYMBOL(__frontswap_store); |
29f233cf DM |
239 | |
240 | /* | |
241 | * "Get" data from frontswap associated with swaptype and offset that were | |
242 | * specified when the data was put to frontswap and use it to fill the | |
243 | * specified page with data. Page must be locked and in the swap cache. | |
244 | */ | |
165c8aed | 245 | int __frontswap_load(struct page *page) |
29f233cf DM |
246 | { |
247 | int ret = -1; | |
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); | |
252 | ||
905cd0e1 DM |
253 | if (!backend_registered) |
254 | return ret; | |
255 | ||
29f233cf DM |
256 | BUG_ON(!PageLocked(page)); |
257 | BUG_ON(sis == NULL); | |
258 | if (frontswap_test(sis, offset)) | |
ef383597 | 259 | ret = frontswap_ops.load(type, offset, page); |
e3483a5f | 260 | if (ret == 0) { |
165c8aed | 261 | inc_frontswap_loads(); |
e3483a5f DM |
262 | if (frontswap_tmem_exclusive_gets_enabled) { |
263 | SetPageDirty(page); | |
264 | frontswap_clear(sis, offset); | |
265 | } | |
266 | } | |
29f233cf DM |
267 | return ret; |
268 | } | |
165c8aed | 269 | EXPORT_SYMBOL(__frontswap_load); |
29f233cf DM |
270 | |
271 | /* | |
272 | * Invalidate any data from frontswap associated with the specified swaptype | |
273 | * and offset so that a subsequent "get" will fail. | |
274 | */ | |
275 | void __frontswap_invalidate_page(unsigned type, pgoff_t offset) | |
276 | { | |
277 | struct swap_info_struct *sis = swap_info[type]; | |
278 | ||
905cd0e1 DM |
279 | if (!backend_registered) |
280 | return; | |
281 | ||
29f233cf DM |
282 | BUG_ON(sis == NULL); |
283 | if (frontswap_test(sis, offset)) { | |
ef383597 | 284 | frontswap_ops.invalidate_page(type, offset); |
611edfed | 285 | __frontswap_clear(sis, offset); |
29f233cf DM |
286 | inc_frontswap_invalidates(); |
287 | } | |
288 | } | |
289 | EXPORT_SYMBOL(__frontswap_invalidate_page); | |
290 | ||
291 | /* | |
292 | * Invalidate all data from frontswap associated with all offsets for the | |
293 | * specified swaptype. | |
294 | */ | |
295 | void __frontswap_invalidate_area(unsigned type) | |
296 | { | |
297 | struct swap_info_struct *sis = swap_info[type]; | |
298 | ||
905cd0e1 DM |
299 | if (backend_registered) { |
300 | BUG_ON(sis == NULL); | |
301 | if (sis->frontswap_map == NULL) | |
302 | return; | |
303 | (*frontswap_ops.invalidate_area)(type); | |
304 | atomic_set(&sis->frontswap_pages, 0); | |
305 | memset(sis->frontswap_map, 0, sis->max / sizeof(long)); | |
306 | } | |
307 | clear_bit(type, need_init); | |
29f233cf DM |
308 | } |
309 | EXPORT_SYMBOL(__frontswap_invalidate_area); | |
310 | ||
96253444 SL |
311 | static unsigned long __frontswap_curr_pages(void) |
312 | { | |
313 | int type; | |
314 | unsigned long totalpages = 0; | |
315 | struct swap_info_struct *si = NULL; | |
316 | ||
317 | assert_spin_locked(&swap_lock); | |
318 | for (type = swap_list.head; type >= 0; type = si->next) { | |
319 | si = swap_info[type]; | |
320 | totalpages += atomic_read(&si->frontswap_pages); | |
321 | } | |
322 | return totalpages; | |
323 | } | |
324 | ||
f116695a SL |
325 | static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused, |
326 | int *swapid) | |
327 | { | |
328 | int ret = -EINVAL; | |
329 | struct swap_info_struct *si = NULL; | |
330 | int si_frontswap_pages; | |
331 | unsigned long total_pages_to_unuse = total; | |
332 | unsigned long pages = 0, pages_to_unuse = 0; | |
333 | int type; | |
334 | ||
335 | assert_spin_locked(&swap_lock); | |
336 | for (type = swap_list.head; type >= 0; type = si->next) { | |
337 | si = swap_info[type]; | |
338 | si_frontswap_pages = atomic_read(&si->frontswap_pages); | |
339 | if (total_pages_to_unuse < si_frontswap_pages) { | |
340 | pages = pages_to_unuse = total_pages_to_unuse; | |
341 | } else { | |
342 | pages = si_frontswap_pages; | |
343 | pages_to_unuse = 0; /* unuse all */ | |
344 | } | |
345 | /* ensure there is enough RAM to fetch pages from frontswap */ | |
346 | if (security_vm_enough_memory_mm(current->mm, pages)) { | |
347 | ret = -ENOMEM; | |
348 | continue; | |
349 | } | |
350 | vm_unacct_memory(pages); | |
351 | *unused = pages_to_unuse; | |
352 | *swapid = type; | |
353 | ret = 0; | |
354 | break; | |
355 | } | |
356 | ||
357 | return ret; | |
358 | } | |
359 | ||
a00bb1e9 ZD |
360 | /* |
361 | * Used to check if it's necessory and feasible to unuse pages. | |
362 | * Return 1 when nothing to do, 0 when need to shink pages, | |
363 | * error code when there is an error. | |
364 | */ | |
69217b4c SL |
365 | static int __frontswap_shrink(unsigned long target_pages, |
366 | unsigned long *pages_to_unuse, | |
367 | int *type) | |
368 | { | |
369 | unsigned long total_pages = 0, total_pages_to_unuse; | |
370 | ||
371 | assert_spin_locked(&swap_lock); | |
372 | ||
373 | total_pages = __frontswap_curr_pages(); | |
374 | if (total_pages <= target_pages) { | |
375 | /* Nothing to do */ | |
376 | *pages_to_unuse = 0; | |
a00bb1e9 | 377 | return 1; |
69217b4c SL |
378 | } |
379 | total_pages_to_unuse = total_pages - target_pages; | |
380 | return __frontswap_unuse_pages(total_pages_to_unuse, pages_to_unuse, type); | |
381 | } | |
382 | ||
29f233cf DM |
383 | /* |
384 | * Frontswap, like a true swap device, may unnecessarily retain pages | |
385 | * under certain circumstances; "shrink" frontswap is essentially a | |
386 | * "partial swapoff" and works by calling try_to_unuse to attempt to | |
387 | * unuse enough frontswap pages to attempt to -- subject to memory | |
388 | * constraints -- reduce the number of pages in frontswap to the | |
389 | * number given in the parameter target_pages. | |
390 | */ | |
391 | void frontswap_shrink(unsigned long target_pages) | |
392 | { | |
f116695a | 393 | unsigned long pages_to_unuse = 0; |
6b982fcf | 394 | int uninitialized_var(type), ret; |
29f233cf DM |
395 | |
396 | /* | |
397 | * we don't want to hold swap_lock while doing a very | |
398 | * lengthy try_to_unuse, but swap_list may change | |
399 | * so restart scan from swap_list.head each time | |
400 | */ | |
401 | spin_lock(&swap_lock); | |
69217b4c | 402 | ret = __frontswap_shrink(target_pages, &pages_to_unuse, &type); |
29f233cf | 403 | spin_unlock(&swap_lock); |
a00bb1e9 | 404 | if (ret == 0) |
69217b4c | 405 | try_to_unuse(type, true, pages_to_unuse); |
29f233cf DM |
406 | return; |
407 | } | |
408 | EXPORT_SYMBOL(frontswap_shrink); | |
409 | ||
410 | /* | |
411 | * Count and return the number of frontswap pages across all | |
412 | * swap devices. This is exported so that backend drivers can | |
413 | * determine current usage without reading debugfs. | |
414 | */ | |
415 | unsigned long frontswap_curr_pages(void) | |
416 | { | |
29f233cf | 417 | unsigned long totalpages = 0; |
29f233cf DM |
418 | |
419 | spin_lock(&swap_lock); | |
96253444 | 420 | totalpages = __frontswap_curr_pages(); |
29f233cf | 421 | spin_unlock(&swap_lock); |
96253444 | 422 | |
29f233cf DM |
423 | return totalpages; |
424 | } | |
425 | EXPORT_SYMBOL(frontswap_curr_pages); | |
426 | ||
427 | static int __init init_frontswap(void) | |
428 | { | |
429 | #ifdef CONFIG_DEBUG_FS | |
430 | struct dentry *root = debugfs_create_dir("frontswap", NULL); | |
431 | if (root == NULL) | |
432 | return -ENXIO; | |
165c8aed KRW |
433 | debugfs_create_u64("loads", S_IRUGO, root, &frontswap_loads); |
434 | debugfs_create_u64("succ_stores", S_IRUGO, root, &frontswap_succ_stores); | |
435 | debugfs_create_u64("failed_stores", S_IRUGO, root, | |
436 | &frontswap_failed_stores); | |
29f233cf DM |
437 | debugfs_create_u64("invalidates", S_IRUGO, |
438 | root, &frontswap_invalidates); | |
439 | #endif | |
905cd0e1 | 440 | frontswap_enabled = 1; |
29f233cf DM |
441 | return 0; |
442 | } | |
443 | ||
444 | module_init(init_frontswap); |