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) 2009-2010 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/sysctl.h>
17 #include <linux/swap.h>
18 #include <linux/swapops.h>
19 #include <linux/proc_fs.h>
20 #include <linux/security.h>
21 #include <linux/capability.h>
22 #include <linux/module.h>
23 #include <linux/uaccess.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
;
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 int frontswap_enabled
;
39 EXPORT_SYMBOL(frontswap_enabled
);
42 * Useful stats available in /sys/kernel/mm/frontswap. These are for
43 * information only so are not protected against increment/decrement races.
45 static unsigned long frontswap_gets
;
46 static unsigned long frontswap_succ_puts
;
47 static unsigned long frontswap_failed_puts
;
48 static unsigned long frontswap_flushes
;
51 * Register operations for frontswap, returning previous thus allowing
52 * detection of multiple backends and possible nesting
54 struct frontswap_ops
frontswap_register_ops(struct frontswap_ops
*ops
)
56 struct frontswap_ops old
= frontswap_ops
;
59 frontswap_enabled
= 1;
62 EXPORT_SYMBOL(frontswap_register_ops
);
64 /* Called when a swap device is swapon'd */
65 void __frontswap_init(unsigned type
)
67 struct swap_info_struct
*sis
= swap_info
[type
];
70 if (sis
->frontswap_map
== NULL
)
72 if (frontswap_enabled
)
73 (*frontswap_ops
.init
)(type
);
75 EXPORT_SYMBOL(__frontswap_init
);
78 * "Put" data from a page to frontswap and associate it with the page's
79 * swaptype and offset. Page must be locked and in the swap cache.
80 * If frontswap already contains a page with matching swaptype and
81 * offset, the frontswap implmentation may either overwrite the data
82 * and return success or flush the page from frontswap and return failure
84 int __frontswap_put_page(struct page
*page
)
86 int ret
= -1, dup
= 0;
87 swp_entry_t entry
= { .val
= page_private(page
), };
88 int type
= swp_type(entry
);
89 struct swap_info_struct
*sis
= swap_info
[type
];
90 pgoff_t offset
= swp_offset(entry
);
92 BUG_ON(!PageLocked(page
));
94 if (frontswap_test(sis
, offset
))
96 ret
= (*frontswap_ops
.put_page
)(type
, offset
, page
);
98 frontswap_set(sis
, offset
);
99 frontswap_succ_puts
++;
101 atomic_inc(&sis
->frontswap_pages
);
104 failed dup always results in automatic flush of
105 the (older) page from frontswap
107 frontswap_clear(sis
, offset
);
108 atomic_dec(&sis
->frontswap_pages
);
109 frontswap_failed_puts
++;
111 frontswap_failed_puts
++;
114 EXPORT_SYMBOL(__frontswap_put_page
);
117 * "Get" data from frontswap associated with swaptype and offset that were
118 * specified when the data was put to frontswap and use it to fill the
119 * specified page with data. Page must be locked and in the swap cache
121 int __frontswap_get_page(struct page
*page
)
124 swp_entry_t entry
= { .val
= page_private(page
), };
125 int type
= swp_type(entry
);
126 struct swap_info_struct
*sis
= swap_info
[type
];
127 pgoff_t offset
= swp_offset(entry
);
129 BUG_ON(!PageLocked(page
));
131 if (frontswap_test(sis
, offset
))
132 ret
= (*frontswap_ops
.get_page
)(type
, offset
, page
);
137 EXPORT_SYMBOL(__frontswap_get_page
);
140 * Flush any data from frontswap associated with the specified swaptype
141 * and offset so that a subsequent "get" will fail.
143 void __frontswap_flush_page(unsigned type
, pgoff_t offset
)
145 struct swap_info_struct
*sis
= swap_info
[type
];
148 if (frontswap_test(sis
, offset
)) {
149 (*frontswap_ops
.flush_page
)(type
, offset
);
150 atomic_dec(&sis
->frontswap_pages
);
151 frontswap_clear(sis
, offset
);
155 EXPORT_SYMBOL(__frontswap_flush_page
);
158 * Flush all data from frontswap associated with all offsets for the
159 * specified swaptype.
161 void __frontswap_flush_area(unsigned type
)
163 struct swap_info_struct
*sis
= swap_info
[type
];
166 if (sis
->frontswap_map
== NULL
)
168 (*frontswap_ops
.flush_area
)(type
);
169 atomic_set(&sis
->frontswap_pages
, 0);
170 memset(sis
->frontswap_map
, 0, sis
->max
/ sizeof(long));
172 EXPORT_SYMBOL(__frontswap_flush_area
);
175 * Frontswap, like a true swap device, may unnecessarily retain pages
176 * under certain circumstances; "shrink" frontswap is essentially a
177 * "partial swapoff" and works by calling try_to_unuse to attempt to
178 * unuse enough frontswap pages to attempt to -- subject to memory
179 * constraints -- reduce the number of pages in frontswap
181 void frontswap_shrink(unsigned long target_pages
)
186 /* try a few times to maximize chance of try_to_unuse success */
187 for (wrapped
= 0; wrapped
< 3; wrapped
++) {
189 struct swap_info_struct
*si
= NULL
;
190 int si_frontswap_pages
;
191 unsigned long total_pages
= 0, total_pages_to_unuse
;
192 unsigned long pages
= 0, pages_to_unuse
= 0;
196 * we don't want to hold swap_lock while doing a very
197 * lengthy try_to_unuse, but swap_list may change
198 * so restart scan from swap_list.head each time
200 spin_lock(&swap_lock
);
203 for (type
= swap_list
.head
; type
>= 0; type
= si
->next
) {
204 si
= swap_info
[type
];
205 total_pages
+= atomic_read(&si
->frontswap_pages
);
207 if (total_pages
<= target_pages
)
209 total_pages_to_unuse
= total_pages
- target_pages
;
210 for (type
= swap_list
.head
; type
>= 0; type
= si
->next
) {
211 si
= swap_info
[type
];
212 si_frontswap_pages
= atomic_read(&si
->frontswap_pages
);
213 if (total_pages_to_unuse
< si_frontswap_pages
)
214 pages
= pages_to_unuse
= total_pages_to_unuse
;
216 pages
= si_frontswap_pages
;
217 pages_to_unuse
= 0; /* unuse all */
219 if (security_vm_enough_memory_kern(pages
))
221 vm_unacct_memory(pages
);
227 spin_unlock(&swap_lock
);
228 try_to_unuse(type
, true, pages_to_unuse
);
233 spin_unlock(&swap_lock
);
236 EXPORT_SYMBOL(frontswap_shrink
);
239 * Count and return the number of pages frontswap pages across all
240 * swap devices. This is exported so that a kernel module can
241 * determine current usage without reading sysfs.
243 unsigned long frontswap_curr_pages(void)
246 unsigned long totalpages
= 0;
247 struct swap_info_struct
*si
= NULL
;
249 spin_lock(&swap_lock
);
250 for (type
= swap_list
.head
; type
>= 0; type
= si
->next
) {
251 si
= swap_info
[type
];
253 totalpages
+= atomic_read(&si
->frontswap_pages
);
255 spin_unlock(&swap_lock
);
258 EXPORT_SYMBOL(frontswap_curr_pages
);
262 /* see Documentation/ABI/xxx/sysfs-kernel-mm-frontswap */
264 #define FRONTSWAP_ATTR_RO(_name) \
265 static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
266 #define FRONTSWAP_ATTR(_name) \
267 static struct kobj_attribute _name##_attr = \
268 __ATTR(_name, 0644, _name##_show, _name##_store)
270 static ssize_t
curr_pages_show(struct kobject
*kobj
,
271 struct kobj_attribute
*attr
, char *buf
)
273 return sprintf(buf
, "%lu\n", frontswap_curr_pages());
276 static ssize_t
curr_pages_store(struct kobject
*kobj
,
277 struct kobj_attribute
*attr
,
278 const char *buf
, size_t count
)
280 unsigned long target_pages
;
282 if (strict_strtoul(buf
, 10, &target_pages
))
285 frontswap_shrink(target_pages
);
289 FRONTSWAP_ATTR(curr_pages
);
291 static ssize_t
succ_puts_show(struct kobject
*kobj
,
292 struct kobj_attribute
*attr
, char *buf
)
294 return sprintf(buf
, "%lu\n", frontswap_succ_puts
);
296 FRONTSWAP_ATTR_RO(succ_puts
);
298 static ssize_t
failed_puts_show(struct kobject
*kobj
,
299 struct kobj_attribute
*attr
, char *buf
)
301 return sprintf(buf
, "%lu\n", frontswap_failed_puts
);
303 FRONTSWAP_ATTR_RO(failed_puts
);
305 static ssize_t
gets_show(struct kobject
*kobj
,
306 struct kobj_attribute
*attr
, char *buf
)
308 return sprintf(buf
, "%lu\n", frontswap_gets
);
310 FRONTSWAP_ATTR_RO(gets
);
312 static ssize_t
flushes_show(struct kobject
*kobj
,
313 struct kobj_attribute
*attr
, char *buf
)
315 return sprintf(buf
, "%lu\n", frontswap_flushes
);
317 FRONTSWAP_ATTR_RO(flushes
);
319 static struct attribute
*frontswap_attrs
[] = {
320 &curr_pages_attr
.attr
,
321 &succ_puts_attr
.attr
,
322 &failed_puts_attr
.attr
,
328 static struct attribute_group frontswap_attr_group
= {
329 .attrs
= frontswap_attrs
,
333 #endif /* CONFIG_SYSFS */
335 static int __init
init_frontswap(void)
340 err
= sysfs_create_group(mm_kobj
, &frontswap_attr_group
);
341 #endif /* CONFIG_SYSFS */
345 static void __exit
exit_frontswap(void)
347 frontswap_shrink(0UL);
350 module_init(init_frontswap
);
351 module_exit(exit_frontswap
);