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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/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 */
31static 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 */
38bool frontswap_enabled __read_mostly;
39EXPORT_SYMBOL(frontswap_enabled);
40
41/*
42 * If enabled, frontswap_store will return failure even on success. As
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 */
49static 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 */
57static u64 frontswap_loads;
58static u64 frontswap_succ_stores;
59static u64 frontswap_failed_stores;
60static u64 frontswap_invalidates;
61
62static inline void inc_frontswap_loads(void) {
63 frontswap_loads++;
64}
65static inline void inc_frontswap_succ_stores(void) {
66 frontswap_succ_stores++;
67}
68static inline void inc_frontswap_failed_stores(void) {
69 frontswap_failed_stores++;
70}
71static inline void inc_frontswap_invalidates(void) {
72 frontswap_invalidates++;
73}
74#else
75static inline void inc_frontswap_loads(void) { }
76static inline void inc_frontswap_succ_stores(void) { }
77static inline void inc_frontswap_failed_stores(void) { }
78static 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 */
84struct 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}
92EXPORT_SYMBOL(frontswap_register_ops);
93
94/*
95 * Enable/disable frontswap writethrough (see above).
96 */
97void frontswap_writethrough(bool enable)
98{
99 frontswap_writethrough_enabled = enable;
100}
101EXPORT_SYMBOL(frontswap_writethrough);
102
103/*
104 * Called when a swap device is swapon'd.
105 */
106void __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}
116EXPORT_SYMBOL(__frontswap_init);
117
118/*
119 * "Store" data from a page to frontswap and associate it with the page's
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 */
125int __frontswap_store(struct page *page)
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;
137 ret = (*frontswap_ops.store)(type, offset, page);
138 if (ret == 0) {
139 frontswap_set(sis, offset);
140 inc_frontswap_succ_stores();
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);
150 inc_frontswap_failed_stores();
151 } else
152 inc_frontswap_failed_stores();
153 if (frontswap_writethrough_enabled)
154 /* report failure so swap also writes to swap device */
155 ret = -1;
156 return ret;
157}
158EXPORT_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 */
165int __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}
181EXPORT_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 */
187void __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}
199EXPORT_SYMBOL(__frontswap_invalidate_page);
200
201/*
202 * Invalidate all data from frontswap associated with all offsets for the
203 * specified swaptype.
204 */
205void __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}
216EXPORT_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 */
226void 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);
270out:
271 if (locked)
272 spin_unlock(&swap_lock);
273 return;
274}
275EXPORT_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 */
282unsigned 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}
296EXPORT_SYMBOL(frontswap_curr_pages);
297
298static 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;
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);
308 debugfs_create_u64("invalidates", S_IRUGO,
309 root, &frontswap_invalidates);
310#endif
311 return 0;
312}
313
314module_init(init_frontswap);