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Dan Magenheimer29f233c2012-04-09 17:09:27 -06001/*
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/*
Konrad Rzeszutek Wilk165c8ae2012-05-15 11:32:15 -040042 * If enabled, frontswap_store will return failure even on success. As
Dan Magenheimer29f233c2012-04-09 17:09:27 -060043 * 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 */
Konrad Rzeszutek Wilk165c8ae2012-05-15 11:32:15 -040057static u64 frontswap_loads;
58static u64 frontswap_succ_stores;
59static u64 frontswap_failed_stores;
Dan Magenheimer29f233c2012-04-09 17:09:27 -060060static u64 frontswap_invalidates;
61
Konrad Rzeszutek Wilk165c8ae2012-05-15 11:32:15 -040062static inline void inc_frontswap_loads(void) {
63 frontswap_loads++;
Dan Magenheimer29f233c2012-04-09 17:09:27 -060064}
Konrad Rzeszutek Wilk165c8ae2012-05-15 11:32:15 -040065static inline void inc_frontswap_succ_stores(void) {
66 frontswap_succ_stores++;
Dan Magenheimer29f233c2012-04-09 17:09:27 -060067}
Konrad Rzeszutek Wilk165c8ae2012-05-15 11:32:15 -040068static inline void inc_frontswap_failed_stores(void) {
69 frontswap_failed_stores++;
Dan Magenheimer29f233c2012-04-09 17:09:27 -060070}
71static inline void inc_frontswap_invalidates(void) {
72 frontswap_invalidates++;
73}
74#else
Konrad Rzeszutek Wilk165c8ae2012-05-15 11:32:15 -040075static inline void inc_frontswap_loads(void) { }
76static inline void inc_frontswap_succ_stores(void) { }
77static inline void inc_frontswap_failed_stores(void) { }
Dan Magenheimer29f233c2012-04-09 17:09:27 -060078static 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)
Sasha Levinef383592012-06-10 12:50:59 +0200114 frontswap_ops.init(type);
Dan Magenheimer29f233c2012-04-09 17:09:27 -0600115}
116EXPORT_SYMBOL(__frontswap_init);
117
118/*
Konrad Rzeszutek Wilk165c8ae2012-05-15 11:32:15 -0400119 * "Store" data from a page to frontswap and associate it with the page's
Dan Magenheimer29f233c2012-04-09 17:09:27 -0600120 * 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 */
Konrad Rzeszutek Wilk165c8ae2012-05-15 11:32:15 -0400125int __frontswap_store(struct page *page)
Dan Magenheimer29f233c2012-04-09 17:09:27 -0600126{
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;
Sasha Levinef383592012-06-10 12:50:59 +0200137 ret = frontswap_ops.store(type, offset, page);
Dan Magenheimer29f233c2012-04-09 17:09:27 -0600138 if (ret == 0) {
139 frontswap_set(sis, offset);
Konrad Rzeszutek Wilk165c8ae2012-05-15 11:32:15 -0400140 inc_frontswap_succ_stores();
Dan Magenheimer29f233c2012-04-09 17:09:27 -0600141 if (!dup)
142 atomic_inc(&sis->frontswap_pages);
Sasha Levind9674dd2012-06-10 12:51:04 +0200143 } else {
Dan Magenheimer29f233c2012-04-09 17:09:27 -0600144 /*
145 failed dup always results in automatic invalidate of
146 the (older) page from frontswap
147 */
Konrad Rzeszutek Wilk165c8ae2012-05-15 11:32:15 -0400148 inc_frontswap_failed_stores();
Sasha Levind9674dd2012-06-10 12:51:04 +0200149 if (dup) {
150 frontswap_clear(sis, offset);
151 atomic_dec(&sis->frontswap_pages);
152 }
Sasha Levin4bb3e312012-06-10 12:51:00 +0200153 }
Dan Magenheimer29f233c2012-04-09 17:09:27 -0600154 if (frontswap_writethrough_enabled)
155 /* report failure so swap also writes to swap device */
156 ret = -1;
157 return ret;
158}
Konrad Rzeszutek Wilk165c8ae2012-05-15 11:32:15 -0400159EXPORT_SYMBOL(__frontswap_store);
Dan Magenheimer29f233c2012-04-09 17:09:27 -0600160
161/*
162 * "Get" data from frontswap associated with swaptype and offset that were
163 * specified when the data was put to frontswap and use it to fill the
164 * specified page with data. Page must be locked and in the swap cache.
165 */
Konrad Rzeszutek Wilk165c8ae2012-05-15 11:32:15 -0400166int __frontswap_load(struct page *page)
Dan Magenheimer29f233c2012-04-09 17:09:27 -0600167{
168 int ret = -1;
169 swp_entry_t entry = { .val = page_private(page), };
170 int type = swp_type(entry);
171 struct swap_info_struct *sis = swap_info[type];
172 pgoff_t offset = swp_offset(entry);
173
174 BUG_ON(!PageLocked(page));
175 BUG_ON(sis == NULL);
176 if (frontswap_test(sis, offset))
Sasha Levinef383592012-06-10 12:50:59 +0200177 ret = frontswap_ops.load(type, offset, page);
Dan Magenheimer29f233c2012-04-09 17:09:27 -0600178 if (ret == 0)
Konrad Rzeszutek Wilk165c8ae2012-05-15 11:32:15 -0400179 inc_frontswap_loads();
Dan Magenheimer29f233c2012-04-09 17:09:27 -0600180 return ret;
181}
Konrad Rzeszutek Wilk165c8ae2012-05-15 11:32:15 -0400182EXPORT_SYMBOL(__frontswap_load);
Dan Magenheimer29f233c2012-04-09 17:09:27 -0600183
184/*
185 * Invalidate any data from frontswap associated with the specified swaptype
186 * and offset so that a subsequent "get" will fail.
187 */
188void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
189{
190 struct swap_info_struct *sis = swap_info[type];
191
192 BUG_ON(sis == NULL);
193 if (frontswap_test(sis, offset)) {
Sasha Levinef383592012-06-10 12:50:59 +0200194 frontswap_ops.invalidate_page(type, offset);
Dan Magenheimer29f233c2012-04-09 17:09:27 -0600195 atomic_dec(&sis->frontswap_pages);
196 frontswap_clear(sis, offset);
197 inc_frontswap_invalidates();
198 }
199}
200EXPORT_SYMBOL(__frontswap_invalidate_page);
201
202/*
203 * Invalidate all data from frontswap associated with all offsets for the
204 * specified swaptype.
205 */
206void __frontswap_invalidate_area(unsigned type)
207{
208 struct swap_info_struct *sis = swap_info[type];
209
210 BUG_ON(sis == NULL);
211 if (sis->frontswap_map == NULL)
212 return;
Sasha Levinef383592012-06-10 12:50:59 +0200213 frontswap_ops.invalidate_area(type);
Dan Magenheimer29f233c2012-04-09 17:09:27 -0600214 atomic_set(&sis->frontswap_pages, 0);
215 memset(sis->frontswap_map, 0, sis->max / sizeof(long));
216}
217EXPORT_SYMBOL(__frontswap_invalidate_area);
218
Sasha Levin96253442012-06-10 12:51:01 +0200219static unsigned long __frontswap_curr_pages(void)
220{
221 int type;
222 unsigned long totalpages = 0;
223 struct swap_info_struct *si = NULL;
224
225 assert_spin_locked(&swap_lock);
226 for (type = swap_list.head; type >= 0; type = si->next) {
227 si = swap_info[type];
228 totalpages += atomic_read(&si->frontswap_pages);
229 }
230 return totalpages;
231}
232
Sasha Levinf1166952012-06-10 12:51:02 +0200233static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused,
234 int *swapid)
235{
236 int ret = -EINVAL;
237 struct swap_info_struct *si = NULL;
238 int si_frontswap_pages;
239 unsigned long total_pages_to_unuse = total;
240 unsigned long pages = 0, pages_to_unuse = 0;
241 int type;
242
243 assert_spin_locked(&swap_lock);
244 for (type = swap_list.head; type >= 0; type = si->next) {
245 si = swap_info[type];
246 si_frontswap_pages = atomic_read(&si->frontswap_pages);
247 if (total_pages_to_unuse < si_frontswap_pages) {
248 pages = pages_to_unuse = total_pages_to_unuse;
249 } else {
250 pages = si_frontswap_pages;
251 pages_to_unuse = 0; /* unuse all */
252 }
253 /* ensure there is enough RAM to fetch pages from frontswap */
254 if (security_vm_enough_memory_mm(current->mm, pages)) {
255 ret = -ENOMEM;
256 continue;
257 }
258 vm_unacct_memory(pages);
259 *unused = pages_to_unuse;
260 *swapid = type;
261 ret = 0;
262 break;
263 }
264
265 return ret;
266}
267
Sasha Levin69217b42012-06-10 12:51:03 +0200268static int __frontswap_shrink(unsigned long target_pages,
269 unsigned long *pages_to_unuse,
270 int *type)
271{
272 unsigned long total_pages = 0, total_pages_to_unuse;
273
274 assert_spin_locked(&swap_lock);
275
276 total_pages = __frontswap_curr_pages();
277 if (total_pages <= target_pages) {
278 /* Nothing to do */
279 *pages_to_unuse = 0;
280 return 0;
281 }
282 total_pages_to_unuse = total_pages - target_pages;
283 return __frontswap_unuse_pages(total_pages_to_unuse, pages_to_unuse, type);
284}
285
Dan Magenheimer29f233c2012-04-09 17:09:27 -0600286/*
287 * Frontswap, like a true swap device, may unnecessarily retain pages
288 * under certain circumstances; "shrink" frontswap is essentially a
289 * "partial swapoff" and works by calling try_to_unuse to attempt to
290 * unuse enough frontswap pages to attempt to -- subject to memory
291 * constraints -- reduce the number of pages in frontswap to the
292 * number given in the parameter target_pages.
293 */
294void frontswap_shrink(unsigned long target_pages)
295{
Sasha Levinf1166952012-06-10 12:51:02 +0200296 unsigned long pages_to_unuse = 0;
297 int type, ret;
Dan Magenheimer29f233c2012-04-09 17:09:27 -0600298
299 /*
300 * we don't want to hold swap_lock while doing a very
301 * lengthy try_to_unuse, but swap_list may change
302 * so restart scan from swap_list.head each time
303 */
304 spin_lock(&swap_lock);
Sasha Levin69217b42012-06-10 12:51:03 +0200305 ret = __frontswap_shrink(target_pages, &pages_to_unuse, &type);
Dan Magenheimer29f233c2012-04-09 17:09:27 -0600306 spin_unlock(&swap_lock);
Sasha Levin69217b42012-06-10 12:51:03 +0200307 if (ret == 0 && pages_to_unuse)
308 try_to_unuse(type, true, pages_to_unuse);
Dan Magenheimer29f233c2012-04-09 17:09:27 -0600309 return;
310}
311EXPORT_SYMBOL(frontswap_shrink);
312
313/*
314 * Count and return the number of frontswap pages across all
315 * swap devices. This is exported so that backend drivers can
316 * determine current usage without reading debugfs.
317 */
318unsigned long frontswap_curr_pages(void)
319{
Dan Magenheimer29f233c2012-04-09 17:09:27 -0600320 unsigned long totalpages = 0;
Dan Magenheimer29f233c2012-04-09 17:09:27 -0600321
322 spin_lock(&swap_lock);
Sasha Levin96253442012-06-10 12:51:01 +0200323 totalpages = __frontswap_curr_pages();
Dan Magenheimer29f233c2012-04-09 17:09:27 -0600324 spin_unlock(&swap_lock);
Sasha Levin96253442012-06-10 12:51:01 +0200325
Dan Magenheimer29f233c2012-04-09 17:09:27 -0600326 return totalpages;
327}
328EXPORT_SYMBOL(frontswap_curr_pages);
329
330static int __init init_frontswap(void)
331{
332#ifdef CONFIG_DEBUG_FS
333 struct dentry *root = debugfs_create_dir("frontswap", NULL);
334 if (root == NULL)
335 return -ENXIO;
Konrad Rzeszutek Wilk165c8ae2012-05-15 11:32:15 -0400336 debugfs_create_u64("loads", S_IRUGO, root, &frontswap_loads);
337 debugfs_create_u64("succ_stores", S_IRUGO, root, &frontswap_succ_stores);
338 debugfs_create_u64("failed_stores", S_IRUGO, root,
339 &frontswap_failed_stores);
Dan Magenheimer29f233c2012-04-09 17:09:27 -0600340 debugfs_create_u64("invalidates", S_IRUGO,
341 root, &frontswap_invalidates);
342#endif
343 return 0;
344}
345
346module_init(init_frontswap);