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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);
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);
Konrad Rzeszutek Wilk165c8ae2012-05-15 11:32:15 -0400150 inc_frontswap_failed_stores();
Sasha Levin4bb3e312012-06-10 12:51:00 +0200151 } else {
Konrad Rzeszutek Wilk165c8ae2012-05-15 11:32:15 -0400152 inc_frontswap_failed_stores();
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
219/*
220 * Frontswap, like a true swap device, may unnecessarily retain pages
221 * under certain circumstances; "shrink" frontswap is essentially a
222 * "partial swapoff" and works by calling try_to_unuse to attempt to
223 * unuse enough frontswap pages to attempt to -- subject to memory
224 * constraints -- reduce the number of pages in frontswap to the
225 * number given in the parameter target_pages.
226 */
227void frontswap_shrink(unsigned long target_pages)
228{
229 struct swap_info_struct *si = NULL;
230 int si_frontswap_pages;
231 unsigned long total_pages = 0, total_pages_to_unuse;
232 unsigned long pages = 0, pages_to_unuse = 0;
233 int type;
234 bool locked = false;
235
236 /*
237 * we don't want to hold swap_lock while doing a very
238 * lengthy try_to_unuse, but swap_list may change
239 * so restart scan from swap_list.head each time
240 */
241 spin_lock(&swap_lock);
242 locked = true;
243 total_pages = 0;
244 for (type = swap_list.head; type >= 0; type = si->next) {
245 si = swap_info[type];
246 total_pages += atomic_read(&si->frontswap_pages);
247 }
248 if (total_pages <= target_pages)
249 goto out;
250 total_pages_to_unuse = total_pages - target_pages;
251 for (type = swap_list.head; type >= 0; type = si->next) {
252 si = swap_info[type];
253 si_frontswap_pages = atomic_read(&si->frontswap_pages);
Sasha Levin4bb3e312012-06-10 12:51:00 +0200254 if (total_pages_to_unuse < si_frontswap_pages) {
Dan Magenheimer29f233c2012-04-09 17:09:27 -0600255 pages = pages_to_unuse = total_pages_to_unuse;
Sasha Levin4bb3e312012-06-10 12:51:00 +0200256 } else {
Dan Magenheimer29f233c2012-04-09 17:09:27 -0600257 pages = si_frontswap_pages;
258 pages_to_unuse = 0; /* unuse all */
259 }
260 /* ensure there is enough RAM to fetch pages from frontswap */
261 if (security_vm_enough_memory_mm(current->mm, pages))
262 continue;
263 vm_unacct_memory(pages);
264 break;
265 }
266 if (type < 0)
267 goto out;
268 locked = false;
269 spin_unlock(&swap_lock);
270 try_to_unuse(type, true, pages_to_unuse);
271out:
272 if (locked)
273 spin_unlock(&swap_lock);
274 return;
275}
276EXPORT_SYMBOL(frontswap_shrink);
277
278/*
279 * Count and return the number of frontswap pages across all
280 * swap devices. This is exported so that backend drivers can
281 * determine current usage without reading debugfs.
282 */
283unsigned long frontswap_curr_pages(void)
284{
285 int type;
286 unsigned long totalpages = 0;
287 struct swap_info_struct *si = NULL;
288
289 spin_lock(&swap_lock);
290 for (type = swap_list.head; type >= 0; type = si->next) {
291 si = swap_info[type];
292 totalpages += atomic_read(&si->frontswap_pages);
293 }
294 spin_unlock(&swap_lock);
295 return totalpages;
296}
297EXPORT_SYMBOL(frontswap_curr_pages);
298
299static int __init init_frontswap(void)
300{
301#ifdef CONFIG_DEBUG_FS
302 struct dentry *root = debugfs_create_dir("frontswap", NULL);
303 if (root == NULL)
304 return -ENXIO;
Konrad Rzeszutek Wilk165c8ae2012-05-15 11:32:15 -0400305 debugfs_create_u64("loads", S_IRUGO, root, &frontswap_loads);
306 debugfs_create_u64("succ_stores", S_IRUGO, root, &frontswap_succ_stores);
307 debugfs_create_u64("failed_stores", S_IRUGO, root,
308 &frontswap_failed_stores);
Dan Magenheimer29f233c2012-04-09 17:09:27 -0600309 debugfs_create_u64("invalidates", S_IRUGO,
310 root, &frontswap_invalidates);
311#endif
312 return 0;
313}
314
315module_init(init_frontswap);