summaryrefslogtreecommitdiffstats
path: root/mm/frontswap.c
blob: 5faf840f872614d6d33e2391bd0795a5a6333685 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
/*
 * Frontswap frontend
 *
 * This code provides the generic "frontend" layer to call a matching
 * "backend" driver implementation of frontswap.  See
 * Documentation/vm/frontswap.txt for more information.
 *
 * Copyright (C) 2009-2012 Oracle Corp.  All rights reserved.
 * Author: Dan Magenheimer
 *
 * This work is licensed under the terms of the GNU GPL, version 2.
 */

#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/proc_fs.h>
#include <linux/security.h>
#include <linux/capability.h>
#include <linux/module.h>
#include <linux/uaccess.h>
#include <linux/debugfs.h>
#include <linux/frontswap.h>
#include <linux/swapfile.h>

/*
 * frontswap_ops is set by frontswap_register_ops to contain the pointers
 * to the frontswap "backend" implementation functions.
 */
static struct frontswap_ops frontswap_ops __read_mostly;

/*
 * This global enablement flag reduces overhead on systems where frontswap_ops
 * has not been registered, so is preferred to the slower alternative: a
 * function call that checks a non-global.
 */
bool frontswap_enabled __read_mostly;
EXPORT_SYMBOL(frontswap_enabled);

/*
 * If enabled, frontswap_store will return failure even on success.  As
 * a result, the swap subsystem will always write the page to swap, in
 * effect converting frontswap into a writethrough cache.  In this mode,
 * there is no direct reduction in swap writes, but a frontswap backend
 * can unilaterally "reclaim" any pages in use with no data loss, thus
 * providing increases control over maximum memory usage due to frontswap.
 */
static bool frontswap_writethrough_enabled __read_mostly;

#ifdef CONFIG_DEBUG_FS
/*
 * Counters available via /sys/kernel/debug/frontswap (if debugfs is
 * properly configured).  These are for information only so are not protected
 * against increment races.
 */
static u64 frontswap_loads;
static u64 frontswap_succ_stores;
static u64 frontswap_failed_stores;
static u64 frontswap_invalidates;

static inline void inc_frontswap_loads(void) {
	frontswap_loads++;
}
static inline void inc_frontswap_succ_stores(void) {
	frontswap_succ_stores++;
}
static inline void inc_frontswap_failed_stores(void) {
	frontswap_failed_stores++;
}
static inline void inc_frontswap_invalidates(void) {
	frontswap_invalidates++;
}
#else
static inline void inc_frontswap_loads(void) { }
static inline void inc_frontswap_succ_stores(void) { }
static inline void inc_frontswap_failed_stores(void) { }
static inline void inc_frontswap_invalidates(void) { }
#endif
/*
 * Register operations for frontswap, returning previous thus allowing
 * detection of multiple backends and possible nesting.
 */
struct frontswap_ops frontswap_register_ops(struct frontswap_ops *ops)
{
	struct frontswap_ops old = frontswap_ops;

	frontswap_ops = *ops;
	frontswap_enabled = true;
	return old;
}
EXPORT_SYMBOL(frontswap_register_ops);

/*
 * Enable/disable frontswap writethrough (see above).
 */
void frontswap_writethrough(bool enable)
{
	frontswap_writethrough_enabled = enable;
}
EXPORT_SYMBOL(frontswap_writethrough);

/*
 * Called when a swap device is swapon'd.
 */
void __frontswap_init(unsigned type)
{
	struct swap_info_struct *sis = swap_info[type];

	BUG_ON(sis == NULL);
	if (sis->frontswap_map == NULL)
		return;
	if (frontswap_enabled)
		frontswap_ops.init(type);
}
EXPORT_SYMBOL(__frontswap_init);

/*
 * "Store" data from a page to frontswap and associate it with the page's
 * swaptype and offset.  Page must be locked and in the swap cache.
 * If frontswap already contains a page with matching swaptype and
 * offset, the frontswap implmentation may either overwrite the data and
 * return success or invalidate the page from frontswap and return failure.
 */
int __frontswap_store(struct page *page)
{
	int ret = -1, dup = 0;
	swp_entry_t entry = { .val = page_private(page), };
	int type = swp_type(entry);
	struct swap_info_struct *sis = swap_info[type];
	pgoff_t offset = swp_offset(entry);

	BUG_ON(!PageLocked(page));
	BUG_ON(sis == NULL);
	if (frontswap_test(sis, offset))
		dup = 1;
	ret = frontswap_ops.store(type, offset, page);
	if (ret == 0) {
		frontswap_set(sis, offset);
		inc_frontswap_succ_stores();
		if (!dup)
			atomic_inc(&sis->frontswap_pages);
	} else if (dup) {
		/*
		  failed dup always results in automatic invalidate of
		  the (older) page from frontswap
		 */
		frontswap_clear(sis, offset);
		atomic_dec(&sis->frontswap_pages);
		inc_frontswap_failed_stores();
	} else {
		inc_frontswap_failed_stores();
	}
	if (frontswap_writethrough_enabled)
		/* report failure so swap also writes to swap device */
		ret = -1;
	return ret;
}
EXPORT_SYMBOL(__frontswap_store);

/*
 * "Get" data from frontswap associated with swaptype and offset that were
 * specified when the data was put to frontswap and use it to fill the
 * specified page with data. Page must be locked and in the swap cache.
 */
int __frontswap_load(struct page *page)
{
	int ret = -1;
	swp_entry_t entry = { .val = page_private(page), };
	int type = swp_type(entry);
	struct swap_info_struct *sis = swap_info[type];
	pgoff_t offset = swp_offset(entry);

	BUG_ON(!PageLocked(page));
	BUG_ON(sis == NULL);
	if (frontswap_test(sis, offset))
		ret = frontswap_ops.load(type, offset, page);
	if (ret == 0)
		inc_frontswap_loads();
	return ret;
}
EXPORT_SYMBOL(__frontswap_load);

/*
 * Invalidate any data from frontswap associated with the specified swaptype
 * and offset so that a subsequent "get" will fail.
 */
void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
{
	struct swap_info_struct *sis = swap_info[type];

	BUG_ON(sis == NULL);
	if (frontswap_test(sis, offset)) {
		frontswap_ops.invalidate_page(type, offset);
		atomic_dec(&sis->frontswap_pages);
		frontswap_clear(sis, offset);
		inc_frontswap_invalidates();
	}
}
EXPORT_SYMBOL(__frontswap_invalidate_page);

/*
 * Invalidate all data from frontswap associated with all offsets for the
 * specified swaptype.
 */
void __frontswap_invalidate_area(unsigned type)
{
	struct swap_info_struct *sis = swap_info[type];

	BUG_ON(sis == NULL);
	if (sis->frontswap_map == NULL)
		return;
	frontswap_ops.invalidate_area(type);
	atomic_set(&sis->frontswap_pages, 0);
	memset(sis->frontswap_map, 0, sis->max / sizeof(long));
}
EXPORT_SYMBOL(__frontswap_invalidate_area);

static unsigned long __frontswap_curr_pages(void)
{
	int type;
	unsigned long totalpages = 0;
	struct swap_info_struct *si = NULL;

	assert_spin_locked(&swap_lock);
	for (type = swap_list.head; type >= 0; type = si->next) {
		si = swap_info[type];
		totalpages += atomic_read(&si->frontswap_pages);
	}
	return totalpages;
}

/*
 * Frontswap, like a true swap device, may unnecessarily retain pages
 * under certain circumstances; "shrink" frontswap is essentially a
 * "partial swapoff" and works by calling try_to_unuse to attempt to
 * unuse enough frontswap pages to attempt to -- subject to memory
 * constraints -- reduce the number of pages in frontswap to the
 * number given in the parameter target_pages.
 */
void frontswap_shrink(unsigned long target_pages)
{
	struct swap_info_struct *si = NULL;
	int si_frontswap_pages;
	unsigned long total_pages = 0, total_pages_to_unuse;
	unsigned long pages = 0, pages_to_unuse = 0;
	int type;
	bool locked = false;

	/*
	 * we don't want to hold swap_lock while doing a very
	 * lengthy try_to_unuse, but swap_list may change
	 * so restart scan from swap_list.head each time
	 */
	spin_lock(&swap_lock);
	locked = true;
	total_pages = __frontswap_curr_pages();
	if (total_pages <= target_pages)
		goto out;
	total_pages_to_unuse = total_pages - target_pages;
	for (type = swap_list.head; type >= 0; type = si->next) {
		si = swap_info[type];
		si_frontswap_pages = atomic_read(&si->frontswap_pages);
		if (total_pages_to_unuse < si_frontswap_pages) {
			pages = pages_to_unuse = total_pages_to_unuse;
		} else {
			pages = si_frontswap_pages;
			pages_to_unuse = 0; /* unuse all */
		}
		/* ensure there is enough RAM to fetch pages from frontswap */
		if (security_vm_enough_memory_mm(current->mm, pages))
			continue;
		vm_unacct_memory(pages);
		break;
	}
	if (type < 0)
		goto out;
	locked = false;
	spin_unlock(&swap_lock);
	try_to_unuse(type, true, pages_to_unuse);
out:
	if (locked)
		spin_unlock(&swap_lock);
	return;
}
EXPORT_SYMBOL(frontswap_shrink);

/*
 * Count and return the number of frontswap pages across all
 * swap devices.  This is exported so that backend drivers can
 * determine current usage without reading debugfs.
 */
unsigned long frontswap_curr_pages(void)
{
	unsigned long totalpages = 0;

	spin_lock(&swap_lock);
	totalpages = __frontswap_curr_pages();
	spin_unlock(&swap_lock);

	return totalpages;
}
EXPORT_SYMBOL(frontswap_curr_pages);

static int __init init_frontswap(void)
{
#ifdef CONFIG_DEBUG_FS
	struct dentry *root = debugfs_create_dir("frontswap", NULL);
	if (root == NULL)
		return -ENXIO;
	debugfs_create_u64("loads", S_IRUGO, root, &frontswap_loads);
	debugfs_create_u64("succ_stores", S_IRUGO, root, &frontswap_succ_stores);
	debugfs_create_u64("failed_stores", S_IRUGO, root,
				&frontswap_failed_stores);
	debugfs_create_u64("invalidates", S_IRUGO,
				root, &frontswap_invalidates);
#endif
	return 0;
}

module_init(init_frontswap);