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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 | * 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 | /* |
38 | * If enabled, frontswap_store will return failure even on success. As |
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 | |
47 | #ifdef CONFIG_DEBUG_FS |
48 | /* |
49 | * Counters available via /sys/kernel/debug/frontswap (if debugfs is |
50 | * properly configured). These are for information only so are not protected |
51 | * against increment races. |
52 | */ |
53 | static u64 frontswap_loads; |
54 | static u64 frontswap_succ_stores; |
55 | static u64 frontswap_failed_stores; |
56 | static u64 frontswap_invalidates; |
57 | |
58 | static inline void inc_frontswap_loads(void) { |
59 | frontswap_loads++; |
60 | } |
61 | static inline void inc_frontswap_succ_stores(void) { |
62 | frontswap_succ_stores++; |
63 | } |
64 | static inline void inc_frontswap_failed_stores(void) { |
65 | frontswap_failed_stores++; |
66 | } |
67 | static inline void inc_frontswap_invalidates(void) { |
68 | frontswap_invalidates++; |
69 | } |
70 | #else |
71 | static inline void inc_frontswap_loads(void) { } |
72 | static inline void inc_frontswap_succ_stores(void) { } |
73 | static inline void inc_frontswap_failed_stores(void) { } |
74 | static inline void inc_frontswap_invalidates(void) { } |
75 | #endif |
76 | /* |
77 | * Register operations for frontswap, returning previous thus allowing |
78 | * detection of multiple backends and possible nesting. |
79 | */ |
80 | struct frontswap_ops frontswap_register_ops(struct frontswap_ops *ops) |
81 | { |
82 | struct frontswap_ops old = frontswap_ops; |
83 | |
84 | frontswap_ops = *ops; |
85 | frontswap_enabled = true; |
86 | return old; |
87 | } |
88 | EXPORT_SYMBOL(frontswap_register_ops); |
89 | |
90 | /* |
91 | * Enable/disable frontswap writethrough (see above). |
92 | */ |
93 | void frontswap_writethrough(bool enable) |
94 | { |
95 | frontswap_writethrough_enabled = enable; |
96 | } |
97 | EXPORT_SYMBOL(frontswap_writethrough); |
98 | |
99 | /* |
100 | * Called when a swap device is swapon'd. |
101 | */ |
102 | void __frontswap_init(unsigned type) |
103 | { |
104 | struct swap_info_struct *sis = swap_info[type]; |
105 | |
106 | BUG_ON(sis == NULL); |
107 | if (sis->frontswap_map == NULL) |
108 | return; |
109 | frontswap_ops.init(type); |
110 | } |
111 | EXPORT_SYMBOL(__frontswap_init); |
112 | |
113 | static inline void __frontswap_clear(struct swap_info_struct *sis, pgoff_t offset) |
114 | { |
115 | frontswap_clear(sis, offset); |
116 | atomic_dec(&sis->frontswap_pages); |
117 | } |
118 | |
119 | /* |
120 | * "Store" data from a page to frontswap and associate it with the page's |
121 | * swaptype and offset. Page must be locked and in the swap cache. |
122 | * If frontswap already contains a page with matching swaptype and |
123 | * offset, the frontswap implementation may either overwrite the data and |
124 | * return success or invalidate the page from frontswap and return failure. |
125 | */ |
126 | int __frontswap_store(struct page *page) |
127 | { |
128 | int ret = -1, dup = 0; |
129 | swp_entry_t entry = { .val = page_private(page), }; |
130 | int type = swp_type(entry); |
131 | struct swap_info_struct *sis = swap_info[type]; |
132 | pgoff_t offset = swp_offset(entry); |
133 | |
134 | BUG_ON(!PageLocked(page)); |
135 | BUG_ON(sis == NULL); |
136 | if (frontswap_test(sis, offset)) |
137 | dup = 1; |
138 | ret = frontswap_ops.store(type, offset, page); |
139 | if (ret == 0) { |
140 | frontswap_set(sis, offset); |
141 | inc_frontswap_succ_stores(); |
142 | if (!dup) |
143 | atomic_inc(&sis->frontswap_pages); |
144 | } else { |
145 | /* |
146 | failed dup always results in automatic invalidate of |
147 | the (older) page from frontswap |
148 | */ |
149 | inc_frontswap_failed_stores(); |
150 | if (dup) |
151 | __frontswap_clear(sis, offset); |
152 | } |
153 | if (frontswap_writethrough_enabled) |
154 | /* report failure so swap also writes to swap device */ |
155 | ret = -1; |
156 | return ret; |
157 | } |
158 | EXPORT_SYMBOL(__frontswap_store); |
159 | |
160 | /* |
161 | * "Get" data from frontswap associated with swaptype and offset that were |
162 | * specified when the data was put to frontswap and use it to fill the |
163 | * specified page with data. Page must be locked and in the swap cache. |
164 | */ |
165 | int __frontswap_load(struct page *page) |
166 | { |
167 | int ret = -1; |
168 | swp_entry_t entry = { .val = page_private(page), }; |
169 | int type = swp_type(entry); |
170 | struct swap_info_struct *sis = swap_info[type]; |
171 | pgoff_t offset = swp_offset(entry); |
172 | |
173 | BUG_ON(!PageLocked(page)); |
174 | BUG_ON(sis == NULL); |
175 | if (frontswap_test(sis, offset)) |
176 | ret = frontswap_ops.load(type, offset, page); |
177 | if (ret == 0) |
178 | inc_frontswap_loads(); |
179 | return ret; |
180 | } |
181 | EXPORT_SYMBOL(__frontswap_load); |
182 | |
183 | /* |
184 | * Invalidate any data from frontswap associated with the specified swaptype |
185 | * and offset so that a subsequent "get" will fail. |
186 | */ |
187 | void __frontswap_invalidate_page(unsigned type, pgoff_t offset) |
188 | { |
189 | struct swap_info_struct *sis = swap_info[type]; |
190 | |
191 | BUG_ON(sis == NULL); |
192 | if (frontswap_test(sis, offset)) { |
193 | frontswap_ops.invalidate_page(type, offset); |
194 | __frontswap_clear(sis, offset); |
195 | inc_frontswap_invalidates(); |
196 | } |
197 | } |
198 | EXPORT_SYMBOL(__frontswap_invalidate_page); |
199 | |
200 | /* |
201 | * Invalidate all data from frontswap associated with all offsets for the |
202 | * specified swaptype. |
203 | */ |
204 | void __frontswap_invalidate_area(unsigned type) |
205 | { |
206 | struct swap_info_struct *sis = swap_info[type]; |
207 | |
208 | BUG_ON(sis == NULL); |
209 | if (sis->frontswap_map == NULL) |
210 | return; |
211 | frontswap_ops.invalidate_area(type); |
212 | atomic_set(&sis->frontswap_pages, 0); |
213 | memset(sis->frontswap_map, 0, sis->max / sizeof(long)); |
214 | } |
215 | EXPORT_SYMBOL(__frontswap_invalidate_area); |
216 | |
217 | static unsigned long __frontswap_curr_pages(void) |
218 | { |
219 | int type; |
220 | unsigned long totalpages = 0; |
221 | struct swap_info_struct *si = NULL; |
222 | |
223 | assert_spin_locked(&swap_lock); |
224 | for (type = swap_list.head; type >= 0; type = si->next) { |
225 | si = swap_info[type]; |
226 | totalpages += atomic_read(&si->frontswap_pages); |
227 | } |
228 | return totalpages; |
229 | } |
230 | |
231 | static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused, |
232 | int *swapid) |
233 | { |
234 | int ret = -EINVAL; |
235 | struct swap_info_struct *si = NULL; |
236 | int si_frontswap_pages; |
237 | unsigned long total_pages_to_unuse = total; |
238 | unsigned long pages = 0, pages_to_unuse = 0; |
239 | int type; |
240 | |
241 | assert_spin_locked(&swap_lock); |
242 | for (type = swap_list.head; type >= 0; type = si->next) { |
243 | si = swap_info[type]; |
244 | si_frontswap_pages = atomic_read(&si->frontswap_pages); |
245 | if (total_pages_to_unuse < si_frontswap_pages) { |
246 | pages = pages_to_unuse = total_pages_to_unuse; |
247 | } else { |
248 | pages = si_frontswap_pages; |
249 | pages_to_unuse = 0; /* unuse all */ |
250 | } |
251 | /* ensure there is enough RAM to fetch pages from frontswap */ |
252 | if (security_vm_enough_memory_mm(current->mm, pages)) { |
253 | ret = -ENOMEM; |
254 | continue; |
255 | } |
256 | vm_unacct_memory(pages); |
257 | *unused = pages_to_unuse; |
258 | *swapid = type; |
259 | ret = 0; |
260 | break; |
261 | } |
262 | |
263 | return ret; |
264 | } |
265 | |
266 | static int __frontswap_shrink(unsigned long target_pages, |
267 | unsigned long *pages_to_unuse, |
268 | int *type) |
269 | { |
270 | unsigned long total_pages = 0, total_pages_to_unuse; |
271 | |
272 | assert_spin_locked(&swap_lock); |
273 | |
274 | total_pages = __frontswap_curr_pages(); |
275 | if (total_pages <= target_pages) { |
276 | /* Nothing to do */ |
277 | *pages_to_unuse = 0; |
278 | return 0; |
279 | } |
280 | total_pages_to_unuse = total_pages - target_pages; |
281 | return __frontswap_unuse_pages(total_pages_to_unuse, pages_to_unuse, type); |
282 | } |
283 | |
284 | /* |
285 | * Frontswap, like a true swap device, may unnecessarily retain pages |
286 | * under certain circumstances; "shrink" frontswap is essentially a |
287 | * "partial swapoff" and works by calling try_to_unuse to attempt to |
288 | * unuse enough frontswap pages to attempt to -- subject to memory |
289 | * constraints -- reduce the number of pages in frontswap to the |
290 | * number given in the parameter target_pages. |
291 | */ |
292 | void frontswap_shrink(unsigned long target_pages) |
293 | { |
294 | unsigned long pages_to_unuse = 0; |
295 | int type, ret; |
296 | |
297 | /* |
298 | * we don't want to hold swap_lock while doing a very |
299 | * lengthy try_to_unuse, but swap_list may change |
300 | * so restart scan from swap_list.head each time |
301 | */ |
302 | spin_lock(&swap_lock); |
303 | ret = __frontswap_shrink(target_pages, &pages_to_unuse, &type); |
304 | spin_unlock(&swap_lock); |
305 | if (ret == 0 && pages_to_unuse) |
306 | try_to_unuse(type, true, pages_to_unuse); |
307 | return; |
308 | } |
309 | EXPORT_SYMBOL(frontswap_shrink); |
310 | |
311 | /* |
312 | * Count and return the number of frontswap pages across all |
313 | * swap devices. This is exported so that backend drivers can |
314 | * determine current usage without reading debugfs. |
315 | */ |
316 | unsigned long frontswap_curr_pages(void) |
317 | { |
318 | unsigned long totalpages = 0; |
319 | |
320 | spin_lock(&swap_lock); |
321 | totalpages = __frontswap_curr_pages(); |
322 | spin_unlock(&swap_lock); |
323 | |
324 | return totalpages; |
325 | } |
326 | EXPORT_SYMBOL(frontswap_curr_pages); |
327 | |
328 | static int __init init_frontswap(void) |
329 | { |
330 | #ifdef CONFIG_DEBUG_FS |
331 | struct dentry *root = debugfs_create_dir("frontswap", NULL); |
332 | if (root == NULL) |
333 | return -ENXIO; |
334 | debugfs_create_u64("loads", S_IRUGO, root, &frontswap_loads); |
335 | debugfs_create_u64("succ_stores", S_IRUGO, root, &frontswap_succ_stores); |
336 | debugfs_create_u64("failed_stores", S_IRUGO, root, |
337 | &frontswap_failed_stores); |
338 | debugfs_create_u64("invalidates", S_IRUGO, |
339 | root, &frontswap_invalidates); |
340 | #endif |
341 | return 0; |
342 | } |
343 | |
344 | module_init(init_frontswap); |
345 |
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