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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 | ||
14 | #include <linux/mm.h> | |
15 | #include <linux/mman.h> | |
16 | #include <linux/swap.h> | |
17 | #include <linux/swapops.h> | |
18 | #include <linux/proc_fs.h> | |
19 | #include <linux/security.h> | |
20 | #include <linux/capability.h> | |
21 | #include <linux/module.h> | |
22 | #include <linux/uaccess.h> | |
23 | #include <linux/debugfs.h> | |
24 | #include <linux/frontswap.h> | |
25 | #include <linux/swapfile.h> | |
26 | ||
27 | /* | |
28 | * frontswap_ops is set by frontswap_register_ops to contain the pointers | |
29 | * to the frontswap "backend" implementation functions. | |
30 | */ | |
31 | static struct frontswap_ops frontswap_ops __read_mostly; | |
32 | ||
33 | /* | |
34 | * This global enablement flag reduces overhead on systems where frontswap_ops | |
35 | * has not been registered, so is preferred to the slower alternative: a | |
36 | * function call that checks a non-global. | |
37 | */ | |
38 | bool frontswap_enabled __read_mostly; | |
39 | EXPORT_SYMBOL(frontswap_enabled); | |
40 | ||
41 | /* | |
165c8aed | 42 | * If enabled, frontswap_store will return failure even on success. As |
29f233cf DM |
43 | * a result, the swap subsystem will always write the page to swap, in |
44 | * effect converting frontswap into a writethrough cache. In this mode, | |
45 | * there is no direct reduction in swap writes, but a frontswap backend | |
46 | * can unilaterally "reclaim" any pages in use with no data loss, thus | |
47 | * providing increases control over maximum memory usage due to frontswap. | |
48 | */ | |
49 | static bool frontswap_writethrough_enabled __read_mostly; | |
50 | ||
51 | #ifdef CONFIG_DEBUG_FS | |
52 | /* | |
53 | * Counters available via /sys/kernel/debug/frontswap (if debugfs is | |
54 | * properly configured). These are for information only so are not protected | |
55 | * against increment races. | |
56 | */ | |
165c8aed KRW |
57 | static u64 frontswap_loads; |
58 | static u64 frontswap_succ_stores; | |
59 | static u64 frontswap_failed_stores; | |
29f233cf DM |
60 | static u64 frontswap_invalidates; |
61 | ||
165c8aed KRW |
62 | static inline void inc_frontswap_loads(void) { |
63 | frontswap_loads++; | |
29f233cf | 64 | } |
165c8aed KRW |
65 | static inline void inc_frontswap_succ_stores(void) { |
66 | frontswap_succ_stores++; | |
29f233cf | 67 | } |
165c8aed KRW |
68 | static inline void inc_frontswap_failed_stores(void) { |
69 | frontswap_failed_stores++; | |
29f233cf DM |
70 | } |
71 | static inline void inc_frontswap_invalidates(void) { | |
72 | frontswap_invalidates++; | |
73 | } | |
74 | #else | |
165c8aed KRW |
75 | static inline void inc_frontswap_loads(void) { } |
76 | static inline void inc_frontswap_succ_stores(void) { } | |
77 | static inline void inc_frontswap_failed_stores(void) { } | |
29f233cf DM |
78 | static inline void inc_frontswap_invalidates(void) { } |
79 | #endif | |
80 | /* | |
81 | * Register operations for frontswap, returning previous thus allowing | |
82 | * detection of multiple backends and possible nesting. | |
83 | */ | |
84 | struct frontswap_ops frontswap_register_ops(struct frontswap_ops *ops) | |
85 | { | |
86 | struct frontswap_ops old = frontswap_ops; | |
87 | ||
88 | frontswap_ops = *ops; | |
89 | frontswap_enabled = true; | |
90 | return old; | |
91 | } | |
92 | EXPORT_SYMBOL(frontswap_register_ops); | |
93 | ||
94 | /* | |
95 | * Enable/disable frontswap writethrough (see above). | |
96 | */ | |
97 | void frontswap_writethrough(bool enable) | |
98 | { | |
99 | frontswap_writethrough_enabled = enable; | |
100 | } | |
101 | EXPORT_SYMBOL(frontswap_writethrough); | |
102 | ||
103 | /* | |
104 | * Called when a swap device is swapon'd. | |
105 | */ | |
106 | void __frontswap_init(unsigned type) | |
107 | { | |
108 | struct swap_info_struct *sis = swap_info[type]; | |
109 | ||
110 | BUG_ON(sis == NULL); | |
111 | if (sis->frontswap_map == NULL) | |
112 | return; | |
113 | if (frontswap_enabled) | |
114 | (*frontswap_ops.init)(type); | |
115 | } | |
116 | EXPORT_SYMBOL(__frontswap_init); | |
117 | ||
118 | /* | |
165c8aed | 119 | * "Store" data from a page to frontswap and associate it with the page's |
29f233cf DM |
120 | * swaptype and offset. Page must be locked and in the swap cache. |
121 | * If frontswap already contains a page with matching swaptype and | |
122 | * offset, the frontswap implmentation may either overwrite the data and | |
123 | * return success or invalidate the page from frontswap and return failure. | |
124 | */ | |
165c8aed | 125 | int __frontswap_store(struct page *page) |
29f233cf DM |
126 | { |
127 | int ret = -1, dup = 0; | |
128 | swp_entry_t entry = { .val = page_private(page), }; | |
129 | int type = swp_type(entry); | |
130 | struct swap_info_struct *sis = swap_info[type]; | |
131 | pgoff_t offset = swp_offset(entry); | |
132 | ||
133 | BUG_ON(!PageLocked(page)); | |
134 | BUG_ON(sis == NULL); | |
135 | if (frontswap_test(sis, offset)) | |
136 | dup = 1; | |
165c8aed | 137 | ret = (*frontswap_ops.store)(type, offset, page); |
29f233cf DM |
138 | if (ret == 0) { |
139 | frontswap_set(sis, offset); | |
165c8aed | 140 | inc_frontswap_succ_stores(); |
29f233cf DM |
141 | if (!dup) |
142 | atomic_inc(&sis->frontswap_pages); | |
143 | } else if (dup) { | |
144 | /* | |
145 | failed dup always results in automatic invalidate of | |
146 | the (older) page from frontswap | |
147 | */ | |
148 | frontswap_clear(sis, offset); | |
149 | atomic_dec(&sis->frontswap_pages); | |
165c8aed | 150 | inc_frontswap_failed_stores(); |
29f233cf | 151 | } else |
165c8aed | 152 | inc_frontswap_failed_stores(); |
29f233cf DM |
153 | if (frontswap_writethrough_enabled) |
154 | /* report failure so swap also writes to swap device */ | |
155 | ret = -1; | |
156 | return ret; | |
157 | } | |
165c8aed | 158 | EXPORT_SYMBOL(__frontswap_store); |
29f233cf DM |
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 | */ | |
165c8aed | 165 | int __frontswap_load(struct page *page) |
29f233cf DM |
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)) | |
165c8aed | 176 | ret = (*frontswap_ops.load)(type, offset, page); |
29f233cf | 177 | if (ret == 0) |
165c8aed | 178 | inc_frontswap_loads(); |
29f233cf DM |
179 | return ret; |
180 | } | |
165c8aed | 181 | EXPORT_SYMBOL(__frontswap_load); |
29f233cf DM |
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 | atomic_dec(&sis->frontswap_pages); | |
195 | frontswap_clear(sis, offset); | |
196 | inc_frontswap_invalidates(); | |
197 | } | |
198 | } | |
199 | EXPORT_SYMBOL(__frontswap_invalidate_page); | |
200 | ||
201 | /* | |
202 | * Invalidate all data from frontswap associated with all offsets for the | |
203 | * specified swaptype. | |
204 | */ | |
205 | void __frontswap_invalidate_area(unsigned type) | |
206 | { | |
207 | struct swap_info_struct *sis = swap_info[type]; | |
208 | ||
209 | BUG_ON(sis == NULL); | |
210 | if (sis->frontswap_map == NULL) | |
211 | return; | |
212 | (*frontswap_ops.invalidate_area)(type); | |
213 | atomic_set(&sis->frontswap_pages, 0); | |
214 | memset(sis->frontswap_map, 0, sis->max / sizeof(long)); | |
215 | } | |
216 | EXPORT_SYMBOL(__frontswap_invalidate_area); | |
217 | ||
218 | /* | |
219 | * Frontswap, like a true swap device, may unnecessarily retain pages | |
220 | * under certain circumstances; "shrink" frontswap is essentially a | |
221 | * "partial swapoff" and works by calling try_to_unuse to attempt to | |
222 | * unuse enough frontswap pages to attempt to -- subject to memory | |
223 | * constraints -- reduce the number of pages in frontswap to the | |
224 | * number given in the parameter target_pages. | |
225 | */ | |
226 | void frontswap_shrink(unsigned long target_pages) | |
227 | { | |
228 | struct swap_info_struct *si = NULL; | |
229 | int si_frontswap_pages; | |
230 | unsigned long total_pages = 0, total_pages_to_unuse; | |
231 | unsigned long pages = 0, pages_to_unuse = 0; | |
232 | int type; | |
233 | bool locked = false; | |
234 | ||
235 | /* | |
236 | * we don't want to hold swap_lock while doing a very | |
237 | * lengthy try_to_unuse, but swap_list may change | |
238 | * so restart scan from swap_list.head each time | |
239 | */ | |
240 | spin_lock(&swap_lock); | |
241 | locked = true; | |
242 | total_pages = 0; | |
243 | for (type = swap_list.head; type >= 0; type = si->next) { | |
244 | si = swap_info[type]; | |
245 | total_pages += atomic_read(&si->frontswap_pages); | |
246 | } | |
247 | if (total_pages <= target_pages) | |
248 | goto out; | |
249 | total_pages_to_unuse = total_pages - target_pages; | |
250 | for (type = swap_list.head; type >= 0; type = si->next) { | |
251 | si = swap_info[type]; | |
252 | si_frontswap_pages = atomic_read(&si->frontswap_pages); | |
253 | if (total_pages_to_unuse < si_frontswap_pages) | |
254 | pages = pages_to_unuse = total_pages_to_unuse; | |
255 | else { | |
256 | pages = si_frontswap_pages; | |
257 | pages_to_unuse = 0; /* unuse all */ | |
258 | } | |
259 | /* ensure there is enough RAM to fetch pages from frontswap */ | |
260 | if (security_vm_enough_memory_mm(current->mm, pages)) | |
261 | continue; | |
262 | vm_unacct_memory(pages); | |
263 | break; | |
264 | } | |
265 | if (type < 0) | |
266 | goto out; | |
267 | locked = false; | |
268 | spin_unlock(&swap_lock); | |
269 | try_to_unuse(type, true, pages_to_unuse); | |
270 | out: | |
271 | if (locked) | |
272 | spin_unlock(&swap_lock); | |
273 | return; | |
274 | } | |
275 | EXPORT_SYMBOL(frontswap_shrink); | |
276 | ||
277 | /* | |
278 | * Count and return the number of frontswap pages across all | |
279 | * swap devices. This is exported so that backend drivers can | |
280 | * determine current usage without reading debugfs. | |
281 | */ | |
282 | unsigned long frontswap_curr_pages(void) | |
283 | { | |
284 | int type; | |
285 | unsigned long totalpages = 0; | |
286 | struct swap_info_struct *si = NULL; | |
287 | ||
288 | spin_lock(&swap_lock); | |
289 | for (type = swap_list.head; type >= 0; type = si->next) { | |
290 | si = swap_info[type]; | |
291 | totalpages += atomic_read(&si->frontswap_pages); | |
292 | } | |
293 | spin_unlock(&swap_lock); | |
294 | return totalpages; | |
295 | } | |
296 | EXPORT_SYMBOL(frontswap_curr_pages); | |
297 | ||
298 | static int __init init_frontswap(void) | |
299 | { | |
300 | #ifdef CONFIG_DEBUG_FS | |
301 | struct dentry *root = debugfs_create_dir("frontswap", NULL); | |
302 | if (root == NULL) | |
303 | return -ENXIO; | |
165c8aed KRW |
304 | debugfs_create_u64("loads", S_IRUGO, root, &frontswap_loads); |
305 | debugfs_create_u64("succ_stores", S_IRUGO, root, &frontswap_succ_stores); | |
306 | debugfs_create_u64("failed_stores", S_IRUGO, root, | |
307 | &frontswap_failed_stores); | |
29f233cf DM |
308 | debugfs_create_u64("invalidates", S_IRUGO, |
309 | root, &frontswap_invalidates); | |
310 | #endif | |
311 | return 0; | |
312 | } | |
313 | ||
314 | module_init(init_frontswap); |