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.
8 * Copyright (C) 2009-2012 Oracle Corp. All rights reserved.
9 * Author: Dan Magenheimer
11 * This work is licensed under the terms of the GNU GPL, version 2.
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>
28 * frontswap_ops is set by frontswap_register_ops to contain the pointers
29 * to the frontswap "backend" implementation functions.
31 static struct frontswap_ops frontswap_ops __read_mostly;
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.
38 bool frontswap_enabled __read_mostly;
39 EXPORT_SYMBOL(frontswap_enabled);
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.
49 static bool frontswap_writethrough_enabled __read_mostly;
51 #ifdef CONFIG_DEBUG_FS
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.
57 static u64 frontswap_loads;
58 static u64 frontswap_succ_stores;
59 static u64 frontswap_failed_stores;
60 static u64 frontswap_invalidates;
62 static inline void inc_frontswap_loads(void) {
65 static inline void inc_frontswap_succ_stores(void) {
66 frontswap_succ_stores++;
68 static inline void inc_frontswap_failed_stores(void) {
69 frontswap_failed_stores++;
71 static inline void inc_frontswap_invalidates(void) {
72 frontswap_invalidates++;
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) { }
78 static inline void inc_frontswap_invalidates(void) { }
81 * Register operations for frontswap, returning previous thus allowing
82 * detection of multiple backends and possible nesting.
84 struct frontswap_ops frontswap_register_ops(struct frontswap_ops *ops)
86 struct frontswap_ops old = frontswap_ops;
89 frontswap_enabled = true;
92 EXPORT_SYMBOL(frontswap_register_ops);
95 * Enable/disable frontswap writethrough (see above).
97 void frontswap_writethrough(bool enable)
99 frontswap_writethrough_enabled = enable;
101 EXPORT_SYMBOL(frontswap_writethrough);
104 * Called when a swap device is swapon'd.
106 void __frontswap_init(unsigned type)
108 struct swap_info_struct *sis = swap_info[type];
111 if (sis->frontswap_map == NULL)
113 if (frontswap_enabled)
114 frontswap_ops.init(type);
116 EXPORT_SYMBOL(__frontswap_init);
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.
125 int __frontswap_store(struct page *page)
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);
133 BUG_ON(!PageLocked(page));
135 if (frontswap_test(sis, offset))
137 ret = frontswap_ops.store(type, offset, page);
139 frontswap_set(sis, offset);
140 inc_frontswap_succ_stores();
142 atomic_inc(&sis->frontswap_pages);
145 failed dup always results in automatic invalidate of
146 the (older) page from frontswap
148 frontswap_clear(sis, offset);
149 atomic_dec(&sis->frontswap_pages);
150 inc_frontswap_failed_stores();
152 inc_frontswap_failed_stores();
154 if (frontswap_writethrough_enabled)
155 /* report failure so swap also writes to swap device */
159 EXPORT_SYMBOL(__frontswap_store);
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.
166 int __frontswap_load(struct page *page)
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);
174 BUG_ON(!PageLocked(page));
176 if (frontswap_test(sis, offset))
177 ret = frontswap_ops.load(type, offset, page);
179 inc_frontswap_loads();
182 EXPORT_SYMBOL(__frontswap_load);
185 * Invalidate any data from frontswap associated with the specified swaptype
186 * and offset so that a subsequent "get" will fail.
188 void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
190 struct swap_info_struct *sis = swap_info[type];
193 if (frontswap_test(sis, offset)) {
194 frontswap_ops.invalidate_page(type, offset);
195 atomic_dec(&sis->frontswap_pages);
196 frontswap_clear(sis, offset);
197 inc_frontswap_invalidates();
200 EXPORT_SYMBOL(__frontswap_invalidate_page);
203 * Invalidate all data from frontswap associated with all offsets for the
204 * specified swaptype.
206 void __frontswap_invalidate_area(unsigned type)
208 struct swap_info_struct *sis = swap_info[type];
211 if (sis->frontswap_map == NULL)
213 frontswap_ops.invalidate_area(type);
214 atomic_set(&sis->frontswap_pages, 0);
215 memset(sis->frontswap_map, 0, sis->max / sizeof(long));
217 EXPORT_SYMBOL(__frontswap_invalidate_area);
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.
227 void frontswap_shrink(unsigned long target_pages)
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;
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
241 spin_lock(&swap_lock);
244 for (type = swap_list.head; type >= 0; type = si->next) {
245 si = swap_info[type];
246 total_pages += atomic_read(&si->frontswap_pages);
248 if (total_pages <= target_pages)
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);
254 if (total_pages_to_unuse < si_frontswap_pages) {
255 pages = pages_to_unuse = total_pages_to_unuse;
257 pages = si_frontswap_pages;
258 pages_to_unuse = 0; /* unuse all */
260 /* ensure there is enough RAM to fetch pages from frontswap */
261 if (security_vm_enough_memory_mm(current->mm, pages))
263 vm_unacct_memory(pages);
269 spin_unlock(&swap_lock);
270 try_to_unuse(type, true, pages_to_unuse);
273 spin_unlock(&swap_lock);
276 EXPORT_SYMBOL(frontswap_shrink);
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.
283 unsigned long frontswap_curr_pages(void)
286 unsigned long totalpages = 0;
287 struct swap_info_struct *si = NULL;
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);
294 spin_unlock(&swap_lock);
297 EXPORT_SYMBOL(frontswap_curr_pages);
299 static int __init init_frontswap(void)
301 #ifdef CONFIG_DEBUG_FS
302 struct dentry *root = debugfs_create_dir("frontswap", NULL);
305 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);
309 debugfs_create_u64("invalidates", S_IRUGO,
310 root, &frontswap_invalidates);
315 module_init(init_frontswap);