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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 | ||
68d68ff6 ZD |
63 | static inline void inc_frontswap_loads(void) |
64 | { | |
96bdd2bc | 65 | data_race(frontswap_loads++); |
29f233cf | 66 | } |
68d68ff6 ZD |
67 | static inline void inc_frontswap_succ_stores(void) |
68 | { | |
96bdd2bc | 69 | data_race(frontswap_succ_stores++); |
29f233cf | 70 | } |
68d68ff6 ZD |
71 | static inline void inc_frontswap_failed_stores(void) |
72 | { | |
96bdd2bc | 73 | data_race(frontswap_failed_stores++); |
29f233cf | 74 | } |
68d68ff6 ZD |
75 | static inline void inc_frontswap_invalidates(void) |
76 | { | |
96bdd2bc | 77 | data_race(frontswap_invalidates++); |
29f233cf DM |
78 | } |
79 | #else | |
165c8aed KRW |
80 | static inline void inc_frontswap_loads(void) { } |
81 | static inline void inc_frontswap_succ_stores(void) { } | |
82 | static inline void inc_frontswap_failed_stores(void) { } | |
29f233cf DM |
83 | static inline void inc_frontswap_invalidates(void) { } |
84 | #endif | |
905cd0e1 DM |
85 | |
86 | /* | |
87 | * Due to the asynchronous nature of the backends loading potentially | |
88 | * _after_ the swap system has been activated, we have chokepoints | |
89 | * on all frontswap functions to not call the backend until the backend | |
90 | * has registered. | |
91 | * | |
905cd0e1 DM |
92 | * This would not guards us against the user deciding to call swapoff right as |
93 | * we are calling the backend to initialize (so swapon is in action). | |
404f3ecf | 94 | * Fortunately for us, the swapon_mutex has been taken by the callee so we are |
905cd0e1 DM |
95 | * OK. The other scenario where calls to frontswap_store (called via |
96 | * swap_writepage) is racing with frontswap_invalidate_area (called via | |
97 | * swapoff) is again guarded by the swap subsystem. | |
98 | * | |
99 | * While no backend is registered all calls to frontswap_[store|load| | |
100 | * invalidate_area|invalidate_page] are ignored or fail. | |
101 | * | |
102 | * The time between the backend being registered and the swap file system | |
103 | * calling the backend (via the frontswap_* functions) is indeterminate as | |
1e01c968 | 104 | * frontswap_ops is not atomic_t (or a value guarded by a spinlock). |
905cd0e1 DM |
105 | * That is OK as we are comfortable missing some of these calls to the newly |
106 | * registered backend. | |
107 | * | |
108 | * Obviously the opposite (unloading the backend) must be done after all | |
109 | * the frontswap_[store|load|invalidate_area|invalidate_page] start | |
d1dc6f1b DS |
110 | * ignoring or failing the requests. However, there is currently no way |
111 | * to unload a backend once it is registered. | |
905cd0e1 | 112 | */ |
905cd0e1 | 113 | |
29f233cf | 114 | /* |
d1dc6f1b | 115 | * Register operations for frontswap |
29f233cf | 116 | */ |
d1dc6f1b | 117 | void frontswap_register_ops(struct frontswap_ops *ops) |
29f233cf | 118 | { |
d1dc6f1b DS |
119 | DECLARE_BITMAP(a, MAX_SWAPFILES); |
120 | DECLARE_BITMAP(b, MAX_SWAPFILES); | |
121 | struct swap_info_struct *si; | |
122 | unsigned int i; | |
123 | ||
124 | bitmap_zero(a, MAX_SWAPFILES); | |
125 | bitmap_zero(b, MAX_SWAPFILES); | |
126 | ||
127 | spin_lock(&swap_lock); | |
128 | plist_for_each_entry(si, &swap_active_head, list) { | |
129 | if (!WARN_ON(!si->frontswap_map)) | |
130 | set_bit(si->type, a); | |
131 | } | |
132 | spin_unlock(&swap_lock); | |
133 | ||
134 | /* the new ops needs to know the currently active swap devices */ | |
135 | for_each_set_bit(i, a, MAX_SWAPFILES) | |
136 | ops->init(i); | |
137 | ||
138 | /* | |
139 | * Setting frontswap_ops must happen after the ops->init() calls | |
140 | * above; cmpxchg implies smp_mb() which will ensure the init is | |
141 | * complete at this point. | |
142 | */ | |
143 | do { | |
144 | ops->next = frontswap_ops; | |
145 | } while (cmpxchg(&frontswap_ops, ops->next, ops) != ops->next); | |
146 | ||
8ea1d2a1 VB |
147 | static_branch_inc(&frontswap_enabled_key); |
148 | ||
d1dc6f1b DS |
149 | spin_lock(&swap_lock); |
150 | plist_for_each_entry(si, &swap_active_head, list) { | |
151 | if (si->frontswap_map) | |
152 | set_bit(si->type, b); | |
905cd0e1 | 153 | } |
d1dc6f1b DS |
154 | spin_unlock(&swap_lock); |
155 | ||
905cd0e1 | 156 | /* |
d1dc6f1b DS |
157 | * On the very unlikely chance that a swap device was added or |
158 | * removed between setting the "a" list bits and the ops init | |
159 | * calls, we re-check and do init or invalidate for any changed | |
160 | * bits. | |
905cd0e1 | 161 | */ |
d1dc6f1b DS |
162 | if (unlikely(!bitmap_equal(a, b, MAX_SWAPFILES))) { |
163 | for (i = 0; i < MAX_SWAPFILES; i++) { | |
164 | if (!test_bit(i, a) && test_bit(i, b)) | |
165 | ops->init(i); | |
166 | else if (test_bit(i, a) && !test_bit(i, b)) | |
167 | ops->invalidate_area(i); | |
168 | } | |
169 | } | |
29f233cf DM |
170 | } |
171 | EXPORT_SYMBOL(frontswap_register_ops); | |
172 | ||
173 | /* | |
174 | * Enable/disable frontswap writethrough (see above). | |
175 | */ | |
176 | void frontswap_writethrough(bool enable) | |
177 | { | |
178 | frontswap_writethrough_enabled = enable; | |
179 | } | |
180 | EXPORT_SYMBOL(frontswap_writethrough); | |
181 | ||
e3483a5f DM |
182 | /* |
183 | * Enable/disable frontswap exclusive gets (see above). | |
184 | */ | |
185 | void frontswap_tmem_exclusive_gets(bool enable) | |
186 | { | |
187 | frontswap_tmem_exclusive_gets_enabled = enable; | |
188 | } | |
189 | EXPORT_SYMBOL(frontswap_tmem_exclusive_gets); | |
190 | ||
29f233cf DM |
191 | /* |
192 | * Called when a swap device is swapon'd. | |
193 | */ | |
4f89849d | 194 | void __frontswap_init(unsigned type, unsigned long *map) |
29f233cf DM |
195 | { |
196 | struct swap_info_struct *sis = swap_info[type]; | |
d1dc6f1b | 197 | struct frontswap_ops *ops; |
29f233cf | 198 | |
8ea1d2a1 | 199 | VM_BUG_ON(sis == NULL); |
4f89849d MK |
200 | |
201 | /* | |
202 | * p->frontswap is a bitmap that we MUST have to figure out which page | |
203 | * has gone in frontswap. Without it there is no point of continuing. | |
204 | */ | |
205 | if (WARN_ON(!map)) | |
206 | return; | |
207 | /* | |
208 | * Irregardless of whether the frontswap backend has been loaded | |
209 | * before this function or it will be later, we _MUST_ have the | |
210 | * p->frontswap set to something valid to work properly. | |
211 | */ | |
212 | frontswap_map_set(sis, map); | |
d1dc6f1b DS |
213 | |
214 | for_each_frontswap_ops(ops) | |
215 | ops->init(type); | |
29f233cf DM |
216 | } |
217 | EXPORT_SYMBOL(__frontswap_init); | |
218 | ||
f066ea23 BL |
219 | bool __frontswap_test(struct swap_info_struct *sis, |
220 | pgoff_t offset) | |
221 | { | |
d1dc6f1b DS |
222 | if (sis->frontswap_map) |
223 | return test_bit(offset, sis->frontswap_map); | |
224 | return false; | |
f066ea23 BL |
225 | } |
226 | EXPORT_SYMBOL(__frontswap_test); | |
227 | ||
d1dc6f1b DS |
228 | static inline void __frontswap_set(struct swap_info_struct *sis, |
229 | pgoff_t offset) | |
230 | { | |
231 | set_bit(offset, sis->frontswap_map); | |
232 | atomic_inc(&sis->frontswap_pages); | |
233 | } | |
234 | ||
f066ea23 | 235 | static inline void __frontswap_clear(struct swap_info_struct *sis, |
d1dc6f1b | 236 | pgoff_t offset) |
611edfed | 237 | { |
f066ea23 | 238 | clear_bit(offset, sis->frontswap_map); |
611edfed SL |
239 | atomic_dec(&sis->frontswap_pages); |
240 | } | |
241 | ||
29f233cf | 242 | /* |
165c8aed | 243 | * "Store" data from a page to frontswap and associate it with the page's |
29f233cf DM |
244 | * swaptype and offset. Page must be locked and in the swap cache. |
245 | * If frontswap already contains a page with matching swaptype and | |
1d00015e | 246 | * offset, the frontswap implementation may either overwrite the data and |
29f233cf DM |
247 | * return success or invalidate the page from frontswap and return failure. |
248 | */ | |
165c8aed | 249 | int __frontswap_store(struct page *page) |
29f233cf | 250 | { |
d1dc6f1b | 251 | int ret = -1; |
29f233cf DM |
252 | swp_entry_t entry = { .val = page_private(page), }; |
253 | int type = swp_type(entry); | |
254 | struct swap_info_struct *sis = swap_info[type]; | |
255 | pgoff_t offset = swp_offset(entry); | |
d1dc6f1b | 256 | struct frontswap_ops *ops; |
29f233cf | 257 | |
8ea1d2a1 VB |
258 | VM_BUG_ON(!frontswap_ops); |
259 | VM_BUG_ON(!PageLocked(page)); | |
260 | VM_BUG_ON(sis == NULL); | |
d1dc6f1b DS |
261 | |
262 | /* | |
263 | * If a dup, we must remove the old page first; we can't leave the | |
264 | * old page no matter if the store of the new page succeeds or fails, | |
265 | * and we can't rely on the new page replacing the old page as we may | |
266 | * not store to the same implementation that contains the old page. | |
267 | */ | |
268 | if (__frontswap_test(sis, offset)) { | |
269 | __frontswap_clear(sis, offset); | |
270 | for_each_frontswap_ops(ops) | |
271 | ops->invalidate_page(type, offset); | |
272 | } | |
273 | ||
274 | /* Try to store in each implementation, until one succeeds. */ | |
275 | for_each_frontswap_ops(ops) { | |
276 | ret = ops->store(type, offset, page); | |
277 | if (!ret) /* successful store */ | |
278 | break; | |
279 | } | |
29f233cf | 280 | if (ret == 0) { |
d1dc6f1b | 281 | __frontswap_set(sis, offset); |
165c8aed | 282 | inc_frontswap_succ_stores(); |
d9674dda | 283 | } else { |
165c8aed | 284 | inc_frontswap_failed_stores(); |
4bb3e31e | 285 | } |
29f233cf DM |
286 | if (frontswap_writethrough_enabled) |
287 | /* report failure so swap also writes to swap device */ | |
288 | ret = -1; | |
289 | return ret; | |
290 | } | |
165c8aed | 291 | EXPORT_SYMBOL(__frontswap_store); |
29f233cf DM |
292 | |
293 | /* | |
294 | * "Get" data from frontswap associated with swaptype and offset that were | |
295 | * specified when the data was put to frontswap and use it to fill the | |
296 | * specified page with data. Page must be locked and in the swap cache. | |
297 | */ | |
165c8aed | 298 | int __frontswap_load(struct page *page) |
29f233cf DM |
299 | { |
300 | int ret = -1; | |
301 | swp_entry_t entry = { .val = page_private(page), }; | |
302 | int type = swp_type(entry); | |
303 | struct swap_info_struct *sis = swap_info[type]; | |
304 | pgoff_t offset = swp_offset(entry); | |
d1dc6f1b DS |
305 | struct frontswap_ops *ops; |
306 | ||
8ea1d2a1 VB |
307 | VM_BUG_ON(!frontswap_ops); |
308 | VM_BUG_ON(!PageLocked(page)); | |
309 | VM_BUG_ON(sis == NULL); | |
29f233cf | 310 | |
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 | ||
8ea1d2a1 VB |
340 | VM_BUG_ON(!frontswap_ops); |
341 | VM_BUG_ON(sis == NULL); | |
29f233cf | 342 | |
d1dc6f1b DS |
343 | if (!__frontswap_test(sis, offset)) |
344 | return; | |
345 | ||
346 | for_each_frontswap_ops(ops) | |
347 | ops->invalidate_page(type, offset); | |
348 | __frontswap_clear(sis, offset); | |
349 | inc_frontswap_invalidates(); | |
29f233cf DM |
350 | } |
351 | EXPORT_SYMBOL(__frontswap_invalidate_page); | |
352 | ||
353 | /* | |
354 | * Invalidate all data from frontswap associated with all offsets for the | |
355 | * specified swaptype. | |
356 | */ | |
357 | void __frontswap_invalidate_area(unsigned type) | |
358 | { | |
359 | struct swap_info_struct *sis = swap_info[type]; | |
d1dc6f1b | 360 | struct frontswap_ops *ops; |
29f233cf | 361 | |
8ea1d2a1 VB |
362 | VM_BUG_ON(!frontswap_ops); |
363 | VM_BUG_ON(sis == NULL); | |
d1dc6f1b | 364 | |
d1dc6f1b DS |
365 | if (sis->frontswap_map == NULL) |
366 | return; | |
367 | ||
368 | for_each_frontswap_ops(ops) | |
369 | ops->invalidate_area(type); | |
370 | atomic_set(&sis->frontswap_pages, 0); | |
371 | bitmap_zero(sis->frontswap_map, sis->max); | |
29f233cf DM |
372 | } |
373 | EXPORT_SYMBOL(__frontswap_invalidate_area); | |
374 | ||
96253444 SL |
375 | static unsigned long __frontswap_curr_pages(void) |
376 | { | |
96253444 SL |
377 | unsigned long totalpages = 0; |
378 | struct swap_info_struct *si = NULL; | |
379 | ||
380 | assert_spin_locked(&swap_lock); | |
18ab4d4c | 381 | plist_for_each_entry(si, &swap_active_head, list) |
96253444 | 382 | totalpages += atomic_read(&si->frontswap_pages); |
96253444 SL |
383 | return totalpages; |
384 | } | |
385 | ||
f116695a SL |
386 | static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused, |
387 | int *swapid) | |
388 | { | |
389 | int ret = -EINVAL; | |
390 | struct swap_info_struct *si = NULL; | |
391 | int si_frontswap_pages; | |
392 | unsigned long total_pages_to_unuse = total; | |
393 | unsigned long pages = 0, pages_to_unuse = 0; | |
f116695a SL |
394 | |
395 | assert_spin_locked(&swap_lock); | |
18ab4d4c | 396 | plist_for_each_entry(si, &swap_active_head, list) { |
f116695a SL |
397 | si_frontswap_pages = atomic_read(&si->frontswap_pages); |
398 | if (total_pages_to_unuse < si_frontswap_pages) { | |
399 | pages = pages_to_unuse = total_pages_to_unuse; | |
400 | } else { | |
401 | pages = si_frontswap_pages; | |
402 | pages_to_unuse = 0; /* unuse all */ | |
403 | } | |
404 | /* ensure there is enough RAM to fetch pages from frontswap */ | |
405 | if (security_vm_enough_memory_mm(current->mm, pages)) { | |
406 | ret = -ENOMEM; | |
407 | continue; | |
408 | } | |
409 | vm_unacct_memory(pages); | |
410 | *unused = pages_to_unuse; | |
adfab836 | 411 | *swapid = si->type; |
f116695a SL |
412 | ret = 0; |
413 | break; | |
414 | } | |
415 | ||
416 | return ret; | |
417 | } | |
418 | ||
a00bb1e9 | 419 | /* |
404f3ecf EP |
420 | * Used to check if it's necessary and feasible to unuse pages. |
421 | * Return 1 when nothing to do, 0 when need to shrink pages, | |
a00bb1e9 ZD |
422 | * error code when there is an error. |
423 | */ | |
69217b4c SL |
424 | static int __frontswap_shrink(unsigned long target_pages, |
425 | unsigned long *pages_to_unuse, | |
426 | int *type) | |
427 | { | |
428 | unsigned long total_pages = 0, total_pages_to_unuse; | |
429 | ||
430 | assert_spin_locked(&swap_lock); | |
431 | ||
432 | total_pages = __frontswap_curr_pages(); | |
433 | if (total_pages <= target_pages) { | |
434 | /* Nothing to do */ | |
435 | *pages_to_unuse = 0; | |
a00bb1e9 | 436 | return 1; |
69217b4c SL |
437 | } |
438 | total_pages_to_unuse = total_pages - target_pages; | |
439 | return __frontswap_unuse_pages(total_pages_to_unuse, pages_to_unuse, type); | |
440 | } | |
441 | ||
29f233cf DM |
442 | /* |
443 | * Frontswap, like a true swap device, may unnecessarily retain pages | |
444 | * under certain circumstances; "shrink" frontswap is essentially a | |
445 | * "partial swapoff" and works by calling try_to_unuse to attempt to | |
446 | * unuse enough frontswap pages to attempt to -- subject to memory | |
447 | * constraints -- reduce the number of pages in frontswap to the | |
448 | * number given in the parameter target_pages. | |
449 | */ | |
450 | void frontswap_shrink(unsigned long target_pages) | |
451 | { | |
f116695a | 452 | unsigned long pages_to_unuse = 0; |
3f649ab7 | 453 | int type, ret; |
29f233cf DM |
454 | |
455 | /* | |
456 | * we don't want to hold swap_lock while doing a very | |
457 | * lengthy try_to_unuse, but swap_list may change | |
18ab4d4c | 458 | * so restart scan from swap_active_head each time |
29f233cf DM |
459 | */ |
460 | spin_lock(&swap_lock); | |
69217b4c | 461 | ret = __frontswap_shrink(target_pages, &pages_to_unuse, &type); |
29f233cf | 462 | spin_unlock(&swap_lock); |
a00bb1e9 | 463 | if (ret == 0) |
69217b4c | 464 | try_to_unuse(type, true, pages_to_unuse); |
29f233cf DM |
465 | return; |
466 | } | |
467 | EXPORT_SYMBOL(frontswap_shrink); | |
468 | ||
469 | /* | |
470 | * Count and return the number of frontswap pages across all | |
471 | * swap devices. This is exported so that backend drivers can | |
472 | * determine current usage without reading debugfs. | |
473 | */ | |
474 | unsigned long frontswap_curr_pages(void) | |
475 | { | |
29f233cf | 476 | unsigned long totalpages = 0; |
29f233cf DM |
477 | |
478 | spin_lock(&swap_lock); | |
96253444 | 479 | totalpages = __frontswap_curr_pages(); |
29f233cf | 480 | spin_unlock(&swap_lock); |
96253444 | 481 | |
29f233cf DM |
482 | return totalpages; |
483 | } | |
484 | EXPORT_SYMBOL(frontswap_curr_pages); | |
485 | ||
486 | static int __init init_frontswap(void) | |
487 | { | |
488 | #ifdef CONFIG_DEBUG_FS | |
489 | struct dentry *root = debugfs_create_dir("frontswap", NULL); | |
490 | if (root == NULL) | |
491 | return -ENXIO; | |
0825a6f9 JP |
492 | debugfs_create_u64("loads", 0444, root, &frontswap_loads); |
493 | debugfs_create_u64("succ_stores", 0444, root, &frontswap_succ_stores); | |
494 | debugfs_create_u64("failed_stores", 0444, root, | |
495 | &frontswap_failed_stores); | |
496 | debugfs_create_u64("invalidates", 0444, root, &frontswap_invalidates); | |
29f233cf DM |
497 | #endif |
498 | return 0; | |
499 | } | |
500 | ||
501 | module_init(init_frontswap); |