Home Home > GIT Browse
summaryrefslogtreecommitdiff
blob: 8d82809eb0859a49faea0ade42251daab1419982 (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
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
/*
 * 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/mman.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/security.h>
#include <linux/module.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;

/*
 * 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;

/*
 * If enabled, the underlying tmem implementation is capable of doing
 * exclusive gets, so frontswap_load, on a successful tmem_get must
 * mark the page as no longer in frontswap AND mark it dirty.
 */
static bool frontswap_tmem_exclusive_gets_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

/*
 * Due to the asynchronous nature of the backends loading potentially
 * _after_ the swap system has been activated, we have chokepoints
 * on all frontswap functions to not call the backend until the backend
 * has registered.
 *
 * Specifically when no backend is registered (nobody called
 * frontswap_register_ops) all calls to frontswap_init (which is done via
 * swapon -> enable_swap_info -> frontswap_init) are registered and remembered
 * (via the setting of need_init bitmap) but fail to create tmem_pools. When a
 * backend registers with frontswap at some later point the previous
 * calls to frontswap_init are executed (by iterating over the need_init
 * bitmap) to create tmem_pools and set the respective poolids. All of that is
 * guarded by us using atomic bit operations on the 'need_init' bitmap.
 *
 * This would not guards us against the user deciding to call swapoff right as
 * we are calling the backend to initialize (so swapon is in action).
 * Fortunatly for us, the swapon_mutex has been taked by the callee so we are
 * OK. The other scenario where calls to frontswap_store (called via
 * swap_writepage) is racing with frontswap_invalidate_area (called via
 * swapoff) is again guarded by the swap subsystem.
 *
 * While no backend is registered all calls to frontswap_[store|load|
 * invalidate_area|invalidate_page] are ignored or fail.
 *
 * The time between the backend being registered and the swap file system
 * calling the backend (via the frontswap_* functions) is indeterminate as
 * frontswap_ops is not atomic_t (or a value guarded by a spinlock).
 * That is OK as we are comfortable missing some of these calls to the newly
 * registered backend.
 *
 * Obviously the opposite (unloading the backend) must be done after all
 * the frontswap_[store|load|invalidate_area|invalidate_page] start
 * ignorning or failing the requests - at which point frontswap_ops
 * would have to be made in some fashion atomic.
 */
static DECLARE_BITMAP(need_init, MAX_SWAPFILES);

/*
 * 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;
	int i;

	for (i = 0; i < MAX_SWAPFILES; i++) {
		if (test_and_clear_bit(i, need_init)) {
			struct swap_info_struct *sis = swap_info[i];
			/* __frontswap_init _should_ have set it! */
			if (!sis->frontswap_map)
				return ERR_PTR(-EINVAL);
			ops->init(i);
		}
	}
	/*
	 * We MUST have frontswap_ops set _after_ the frontswap_init's
	 * have been called. Otherwise __frontswap_store might fail. Hence
	 * the barrier to make sure compiler does not re-order us.
	 */
	barrier();
	frontswap_ops = ops;
	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);

/*
 * Enable/disable frontswap exclusive gets (see above).
 */
void frontswap_tmem_exclusive_gets(bool enable)
{
	frontswap_tmem_exclusive_gets_enabled = enable;
}
EXPORT_SYMBOL(frontswap_tmem_exclusive_gets);

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

	BUG_ON(sis == NULL);

	/*
	 * p->frontswap is a bitmap that we MUST have to figure out which page
	 * has gone in frontswap. Without it there is no point of continuing.
	 */
	if (WARN_ON(!map))
		return;
	/*
	 * Irregardless of whether the frontswap backend has been loaded
	 * before this function or it will be later, we _MUST_ have the
	 * p->frontswap set to something valid to work properly.
	 */
	frontswap_map_set(sis, map);
	if (frontswap_ops)
		frontswap_ops->init(type);
	else {
		BUG_ON(type >= MAX_SWAPFILES);
		set_bit(type, need_init);
	}
}
EXPORT_SYMBOL(__frontswap_init);

bool __frontswap_test(struct swap_info_struct *sis,
				pgoff_t offset)
{
	bool ret = false;

	if (frontswap_ops && sis->frontswap_map)
		ret = test_bit(offset, sis->frontswap_map);
	return ret;
}
EXPORT_SYMBOL(__frontswap_test);

static inline void __frontswap_clear(struct swap_info_struct *sis,
				pgoff_t offset)
{
	clear_bit(offset, sis->frontswap_map);
	atomic_dec(&sis->frontswap_pages);
}

/*
 * "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 implementation 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);

	/*
	 * Return if no backend registed.
	 * Don't need to inc frontswap_failed_stores here.
	 */
	if (!frontswap_ops)
		return ret;

	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) {
		set_bit(offset, sis->frontswap_map);
		inc_frontswap_succ_stores();
		if (!dup)
			atomic_inc(&sis->frontswap_pages);
	} else {
		/*
		  failed dup always results in automatic invalidate of
		  the (older) page from frontswap
		 */
		inc_frontswap_failed_stores();
		if (dup) {
			__frontswap_clear(sis, offset);
			frontswap_ops->invalidate_page(type, offset);
		}
	}
	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);
	/*
	 * __frontswap_test() will check whether there is backend registered
	 */
	if (__frontswap_test(sis, offset))
		ret = frontswap_ops->load(type, offset, page);
	if (ret == 0) {
		inc_frontswap_loads();
		if (frontswap_tmem_exclusive_gets_enabled) {
			SetPageDirty(page);
			__frontswap_clear(sis, offset);
		}
	}
	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);
	/*
	 * __frontswap_test() will check whether there is backend registered
	 */
	if (__frontswap_test(sis, offset)) {
		frontswap_ops->invalidate_page(type, offset);
		__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];

	if (frontswap_ops) {
		BUG_ON(sis == NULL);
		if (sis->frontswap_map == NULL)
			return;
		frontswap_ops->invalidate_area(type);
		atomic_set(&sis->frontswap_pages, 0);
		bitmap_zero(sis->frontswap_map, sis->max);
	}
	clear_bit(type, need_init);
}
EXPORT_SYMBOL(__frontswap_invalidate_area);

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

	assert_spin_locked(&swap_lock);
	plist_for_each_entry(si, &swap_active_head, list)
		totalpages += atomic_read(&si->frontswap_pages);
	return totalpages;
}

static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused,
					int *swapid)
{
	int ret = -EINVAL;
	struct swap_info_struct *si = NULL;
	int si_frontswap_pages;
	unsigned long total_pages_to_unuse = total;
	unsigned long pages = 0, pages_to_unuse = 0;

	assert_spin_locked(&swap_lock);
	plist_for_each_entry(si, &swap_active_head, list) {
		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)) {
			ret = -ENOMEM;
			continue;
		}
		vm_unacct_memory(pages);
		*unused = pages_to_unuse;
		*swapid = si->type;
		ret = 0;
		break;
	}

	return ret;
}

/*
 * Used to check if it's necessory and feasible to unuse pages.
 * Return 1 when nothing to do, 0 when need to shink pages,
 * error code when there is an error.
 */
static int __frontswap_shrink(unsigned long target_pages,
				unsigned long *pages_to_unuse,
				int *type)
{
	unsigned long total_pages = 0, total_pages_to_unuse;

	assert_spin_locked(&swap_lock);

	total_pages = __frontswap_curr_pages();
	if (total_pages <= target_pages) {
		/* Nothing to do */
		*pages_to_unuse = 0;
		return 1;
	}
	total_pages_to_unuse = total_pages - target_pages;
	return __frontswap_unuse_pages(total_pages_to_unuse, pages_to_unuse, type);
}

/*
 * 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)
{
	unsigned long pages_to_unuse = 0;
	int uninitialized_var(type), ret;

	/*
	 * 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_active_head each time
	 */
	spin_lock(&swap_lock);
	ret = __frontswap_shrink(target_pages, &pages_to_unuse, &type);
	spin_unlock(&swap_lock);
	if (ret == 0)
		try_to_unuse(type, true, pages_to_unuse);
	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);