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1/*
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/mman.h>
15#include <linux/swap.h>
16#include <linux/swapops.h>
17#include <linux/security.h>
18#include <linux/module.h>
19#include <linux/debugfs.h>
20#include <linux/frontswap.h>
21#include <linux/swapfile.h>
22
23DEFINE_STATIC_KEY_FALSE(frontswap_enabled_key);
24
25/*
26 * frontswap_ops are added by frontswap_register_ops, and provide the
27 * frontswap "backend" implementation functions. Multiple implementations
28 * may be registered, but implementations can never deregister. This
29 * is a simple singly-linked list of all registered implementations.
30 */
31static struct frontswap_ops *frontswap_ops __read_mostly;
32
33#define for_each_frontswap_ops(ops) \
34 for ((ops) = frontswap_ops; (ops); (ops) = (ops)->next)
35
36/*
37 * If enabled, frontswap_store will return failure even on success. As
38 * a result, the swap subsystem will always write the page to swap, in
39 * effect converting frontswap into a writethrough cache. In this mode,
40 * there is no direct reduction in swap writes, but a frontswap backend
41 * can unilaterally "reclaim" any pages in use with no data loss, thus
42 * providing increases control over maximum memory usage due to frontswap.
43 */
44static bool frontswap_writethrough_enabled __read_mostly;
45
46/*
47 * If enabled, the underlying tmem implementation is capable of doing
48 * exclusive gets, so frontswap_load, on a successful tmem_get must
49 * mark the page as no longer in frontswap AND mark it dirty.
50 */
51static bool frontswap_tmem_exclusive_gets_enabled __read_mostly;
52
53#ifdef CONFIG_DEBUG_FS
54/*
55 * Counters available via /sys/kernel/debug/frontswap (if debugfs is
56 * properly configured). These are for information only so are not protected
57 * against increment races.
58 */
59static u64 frontswap_loads;
60static u64 frontswap_succ_stores;
61static u64 frontswap_failed_stores;
62static u64 frontswap_invalidates;
63
64static inline void inc_frontswap_loads(void) {
65 frontswap_loads++;
66}
67static inline void inc_frontswap_succ_stores(void) {
68 frontswap_succ_stores++;
69}
70static inline void inc_frontswap_failed_stores(void) {
71 frontswap_failed_stores++;
72}
73static inline void inc_frontswap_invalidates(void) {
74 frontswap_invalidates++;
75}
76#else
77static inline void inc_frontswap_loads(void) { }
78static inline void inc_frontswap_succ_stores(void) { }
79static inline void inc_frontswap_failed_stores(void) { }
80static inline void inc_frontswap_invalidates(void) { }
81#endif
82
83/*
84 * Due to the asynchronous nature of the backends loading potentially
85 * _after_ the swap system has been activated, we have chokepoints
86 * on all frontswap functions to not call the backend until the backend
87 * has registered.
88 *
89 * This would not guards us against the user deciding to call swapoff right as
90 * we are calling the backend to initialize (so swapon is in action).
91 * Fortunatly for us, the swapon_mutex has been taked by the callee so we are
92 * OK. The other scenario where calls to frontswap_store (called via
93 * swap_writepage) is racing with frontswap_invalidate_area (called via
94 * swapoff) is again guarded by the swap subsystem.
95 *
96 * While no backend is registered all calls to frontswap_[store|load|
97 * invalidate_area|invalidate_page] are ignored or fail.
98 *
99 * The time between the backend being registered and the swap file system
100 * calling the backend (via the frontswap_* functions) is indeterminate as
101 * frontswap_ops is not atomic_t (or a value guarded by a spinlock).
102 * That is OK as we are comfortable missing some of these calls to the newly
103 * registered backend.
104 *
105 * Obviously the opposite (unloading the backend) must be done after all
106 * the frontswap_[store|load|invalidate_area|invalidate_page] start
107 * ignoring or failing the requests. However, there is currently no way
108 * to unload a backend once it is registered.
109 */
110
111/*
112 * Register operations for frontswap
113 */
114void frontswap_register_ops(struct frontswap_ops *ops)
115{
116 DECLARE_BITMAP(a, MAX_SWAPFILES);
117 DECLARE_BITMAP(b, MAX_SWAPFILES);
118 struct swap_info_struct *si;
119 unsigned int i;
120
121 bitmap_zero(a, MAX_SWAPFILES);
122 bitmap_zero(b, MAX_SWAPFILES);
123
124 spin_lock(&swap_lock);
125 plist_for_each_entry(si, &swap_active_head, list) {
126 if (!WARN_ON(!si->frontswap_map))
127 set_bit(si->type, a);
128 }
129 spin_unlock(&swap_lock);
130
131 /* the new ops needs to know the currently active swap devices */
132 for_each_set_bit(i, a, MAX_SWAPFILES)
133 ops->init(i);
134
135 /*
136 * Setting frontswap_ops must happen after the ops->init() calls
137 * above; cmpxchg implies smp_mb() which will ensure the init is
138 * complete at this point.
139 */
140 do {
141 ops->next = frontswap_ops;
142 } while (cmpxchg(&frontswap_ops, ops->next, ops) != ops->next);
143
144 static_branch_inc(&frontswap_enabled_key);
145
146 spin_lock(&swap_lock);
147 plist_for_each_entry(si, &swap_active_head, list) {
148 if (si->frontswap_map)
149 set_bit(si->type, b);
150 }
151 spin_unlock(&swap_lock);
152
153 /*
154 * On the very unlikely chance that a swap device was added or
155 * removed between setting the "a" list bits and the ops init
156 * calls, we re-check and do init or invalidate for any changed
157 * bits.
158 */
159 if (unlikely(!bitmap_equal(a, b, MAX_SWAPFILES))) {
160 for (i = 0; i < MAX_SWAPFILES; i++) {
161 if (!test_bit(i, a) && test_bit(i, b))
162 ops->init(i);
163 else if (test_bit(i, a) && !test_bit(i, b))
164 ops->invalidate_area(i);
165 }
166 }
167}
168EXPORT_SYMBOL(frontswap_register_ops);
169
170/*
171 * Enable/disable frontswap writethrough (see above).
172 */
173void frontswap_writethrough(bool enable)
174{
175 frontswap_writethrough_enabled = enable;
176}
177EXPORT_SYMBOL(frontswap_writethrough);
178
179/*
180 * Enable/disable frontswap exclusive gets (see above).
181 */
182void frontswap_tmem_exclusive_gets(bool enable)
183{
184 frontswap_tmem_exclusive_gets_enabled = enable;
185}
186EXPORT_SYMBOL(frontswap_tmem_exclusive_gets);
187
188/*
189 * Called when a swap device is swapon'd.
190 */
191void __frontswap_init(unsigned type, unsigned long *map)
192{
193 struct swap_info_struct *sis = swap_info[type];
194 struct frontswap_ops *ops;
195
196 VM_BUG_ON(sis == NULL);
197
198 /*
199 * p->frontswap is a bitmap that we MUST have to figure out which page
200 * has gone in frontswap. Without it there is no point of continuing.
201 */
202 if (WARN_ON(!map))
203 return;
204 /*
205 * Irregardless of whether the frontswap backend has been loaded
206 * before this function or it will be later, we _MUST_ have the
207 * p->frontswap set to something valid to work properly.
208 */
209 frontswap_map_set(sis, map);
210
211 for_each_frontswap_ops(ops)
212 ops->init(type);
213}
214EXPORT_SYMBOL(__frontswap_init);
215
216bool __frontswap_test(struct swap_info_struct *sis,
217 pgoff_t offset)
218{
219 if (sis->frontswap_map)
220 return test_bit(offset, sis->frontswap_map);
221 return false;
222}
223EXPORT_SYMBOL(__frontswap_test);
224
225static inline void __frontswap_set(struct swap_info_struct *sis,
226 pgoff_t offset)
227{
228 set_bit(offset, sis->frontswap_map);
229 atomic_inc(&sis->frontswap_pages);
230}
231
232static inline void __frontswap_clear(struct swap_info_struct *sis,
233 pgoff_t offset)
234{
235 clear_bit(offset, sis->frontswap_map);
236 atomic_dec(&sis->frontswap_pages);
237}
238
239/*
240 * "Store" data from a page to frontswap and associate it with the page's
241 * swaptype and offset. Page must be locked and in the swap cache.
242 * If frontswap already contains a page with matching swaptype and
243 * offset, the frontswap implementation may either overwrite the data and
244 * return success or invalidate the page from frontswap and return failure.
245 */
246int __frontswap_store(struct page *page)
247{
248 int ret = -1;
249 swp_entry_t entry = { .val = page_private(page), };
250 int type = swp_type(entry);
251 struct swap_info_struct *sis = swap_info[type];
252 pgoff_t offset = swp_offset(entry);
253 struct frontswap_ops *ops;
254
255 VM_BUG_ON(!frontswap_ops);
256 VM_BUG_ON(!PageLocked(page));
257 VM_BUG_ON(sis == NULL);
258
259 /*
260 * If a dup, we must remove the old page first; we can't leave the
261 * old page no matter if the store of the new page succeeds or fails,
262 * and we can't rely on the new page replacing the old page as we may
263 * not store to the same implementation that contains the old page.
264 */
265 if (__frontswap_test(sis, offset)) {
266 __frontswap_clear(sis, offset);
267 for_each_frontswap_ops(ops)
268 ops->invalidate_page(type, offset);
269 }
270
271 /* Try to store in each implementation, until one succeeds. */
272 for_each_frontswap_ops(ops) {
273 ret = ops->store(type, offset, page);
274 if (!ret) /* successful store */
275 break;
276 }
277 if (ret == 0) {
278 __frontswap_set(sis, offset);
279 inc_frontswap_succ_stores();
280 } else {
281 inc_frontswap_failed_stores();
282 }
283 if (frontswap_writethrough_enabled)
284 /* report failure so swap also writes to swap device */
285 ret = -1;
286 return ret;
287}
288EXPORT_SYMBOL(__frontswap_store);
289
290/*
291 * "Get" data from frontswap associated with swaptype and offset that were
292 * specified when the data was put to frontswap and use it to fill the
293 * specified page with data. Page must be locked and in the swap cache.
294 */
295int __frontswap_load(struct page *page)
296{
297 int ret = -1;
298 swp_entry_t entry = { .val = page_private(page), };
299 int type = swp_type(entry);
300 struct swap_info_struct *sis = swap_info[type];
301 pgoff_t offset = swp_offset(entry);
302 struct frontswap_ops *ops;
303
304 VM_BUG_ON(!frontswap_ops);
305 VM_BUG_ON(!PageLocked(page));
306 VM_BUG_ON(sis == NULL);
307
308 if (!__frontswap_test(sis, offset))
309 return -1;
310
311 /* Try loading from each implementation, until one succeeds. */
312 for_each_frontswap_ops(ops) {
313 ret = ops->load(type, offset, page);
314 if (!ret) /* successful load */
315 break;
316 }
317 if (ret == 0) {
318 inc_frontswap_loads();
319 if (frontswap_tmem_exclusive_gets_enabled) {
320 SetPageDirty(page);
321 __frontswap_clear(sis, offset);
322 }
323 }
324 return ret;
325}
326EXPORT_SYMBOL(__frontswap_load);
327
328/*
329 * Invalidate any data from frontswap associated with the specified swaptype
330 * and offset so that a subsequent "get" will fail.
331 */
332void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
333{
334 struct swap_info_struct *sis = swap_info[type];
335 struct frontswap_ops *ops;
336
337 VM_BUG_ON(!frontswap_ops);
338 VM_BUG_ON(sis == NULL);
339
340 if (!__frontswap_test(sis, offset))
341 return;
342
343 for_each_frontswap_ops(ops)
344 ops->invalidate_page(type, offset);
345 __frontswap_clear(sis, offset);
346 inc_frontswap_invalidates();
347}
348EXPORT_SYMBOL(__frontswap_invalidate_page);
349
350/*
351 * Invalidate all data from frontswap associated with all offsets for the
352 * specified swaptype.
353 */
354void __frontswap_invalidate_area(unsigned type)
355{
356 struct swap_info_struct *sis = swap_info[type];
357 struct frontswap_ops *ops;
358
359 VM_BUG_ON(!frontswap_ops);
360 VM_BUG_ON(sis == NULL);
361
362 if (sis->frontswap_map == NULL)
363 return;
364
365 for_each_frontswap_ops(ops)
366 ops->invalidate_area(type);
367 atomic_set(&sis->frontswap_pages, 0);
368 bitmap_zero(sis->frontswap_map, sis->max);
369}
370EXPORT_SYMBOL(__frontswap_invalidate_area);
371
372static unsigned long __frontswap_curr_pages(void)
373{
374 unsigned long totalpages = 0;
375 struct swap_info_struct *si = NULL;
376
377 assert_spin_locked(&swap_lock);
378 plist_for_each_entry(si, &swap_active_head, list)
379 totalpages += atomic_read(&si->frontswap_pages);
380 return totalpages;
381}
382
383static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused,
384 int *swapid)
385{
386 int ret = -EINVAL;
387 struct swap_info_struct *si = NULL;
388 int si_frontswap_pages;
389 unsigned long total_pages_to_unuse = total;
390 unsigned long pages = 0, pages_to_unuse = 0;
391
392 assert_spin_locked(&swap_lock);
393 plist_for_each_entry(si, &swap_active_head, list) {
394 si_frontswap_pages = atomic_read(&si->frontswap_pages);
395 if (total_pages_to_unuse < si_frontswap_pages) {
396 pages = pages_to_unuse = total_pages_to_unuse;
397 } else {
398 pages = si_frontswap_pages;
399 pages_to_unuse = 0; /* unuse all */
400 }
401 /* ensure there is enough RAM to fetch pages from frontswap */
402 if (security_vm_enough_memory_mm(current->mm, pages)) {
403 ret = -ENOMEM;
404 continue;
405 }
406 vm_unacct_memory(pages);
407 *unused = pages_to_unuse;
408 *swapid = si->type;
409 ret = 0;
410 break;
411 }
412
413 return ret;
414}
415
416/*
417 * Used to check if it's necessory and feasible to unuse pages.
418 * Return 1 when nothing to do, 0 when need to shink pages,
419 * error code when there is an error.
420 */
421static int __frontswap_shrink(unsigned long target_pages,
422 unsigned long *pages_to_unuse,
423 int *type)
424{
425 unsigned long total_pages = 0, total_pages_to_unuse;
426
427 assert_spin_locked(&swap_lock);
428
429 total_pages = __frontswap_curr_pages();
430 if (total_pages <= target_pages) {
431 /* Nothing to do */
432 *pages_to_unuse = 0;
433 return 1;
434 }
435 total_pages_to_unuse = total_pages - target_pages;
436 return __frontswap_unuse_pages(total_pages_to_unuse, pages_to_unuse, type);
437}
438
439/*
440 * Frontswap, like a true swap device, may unnecessarily retain pages
441 * under certain circumstances; "shrink" frontswap is essentially a
442 * "partial swapoff" and works by calling try_to_unuse to attempt to
443 * unuse enough frontswap pages to attempt to -- subject to memory
444 * constraints -- reduce the number of pages in frontswap to the
445 * number given in the parameter target_pages.
446 */
447void frontswap_shrink(unsigned long target_pages)
448{
449 unsigned long pages_to_unuse = 0;
450 int uninitialized_var(type), ret;
451
452 /*
453 * we don't want to hold swap_lock while doing a very
454 * lengthy try_to_unuse, but swap_list may change
455 * so restart scan from swap_active_head each time
456 */
457 spin_lock(&swap_lock);
458 ret = __frontswap_shrink(target_pages, &pages_to_unuse, &type);
459 spin_unlock(&swap_lock);
460 if (ret == 0)
461 try_to_unuse(type, true, pages_to_unuse);
462 return;
463}
464EXPORT_SYMBOL(frontswap_shrink);
465
466/*
467 * Count and return the number of frontswap pages across all
468 * swap devices. This is exported so that backend drivers can
469 * determine current usage without reading debugfs.
470 */
471unsigned long frontswap_curr_pages(void)
472{
473 unsigned long totalpages = 0;
474
475 spin_lock(&swap_lock);
476 totalpages = __frontswap_curr_pages();
477 spin_unlock(&swap_lock);
478
479 return totalpages;
480}
481EXPORT_SYMBOL(frontswap_curr_pages);
482
483static int __init init_frontswap(void)
484{
485#ifdef CONFIG_DEBUG_FS
486 struct dentry *root = debugfs_create_dir("frontswap", NULL);
487 if (root == NULL)
488 return -ENXIO;
489 debugfs_create_u64("loads", S_IRUGO, root, &frontswap_loads);
490 debugfs_create_u64("succ_stores", S_IRUGO, root, &frontswap_succ_stores);
491 debugfs_create_u64("failed_stores", S_IRUGO, root,
492 &frontswap_failed_stores);
493 debugfs_create_u64("invalidates", S_IRUGO,
494 root, &frontswap_invalidates);
495#endif
496 return 0;
497}
498
499module_init(init_frontswap);
1/*
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/*
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.
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 */
57static u64 frontswap_loads;
58static u64 frontswap_succ_stores;
59static u64 frontswap_failed_stores;
60static u64 frontswap_invalidates;
61
62static inline void inc_frontswap_loads(void) {
63 frontswap_loads++;
64}
65static inline void inc_frontswap_succ_stores(void) {
66 frontswap_succ_stores++;
67}
68static inline void inc_frontswap_failed_stores(void) {
69 frontswap_failed_stores++;
70}
71static inline void inc_frontswap_invalidates(void) {
72 frontswap_invalidates++;
73}
74#else
75static inline void inc_frontswap_loads(void) { }
76static inline void inc_frontswap_succ_stores(void) { }
77static inline void inc_frontswap_failed_stores(void) { }
78static 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)
114 (*frontswap_ops.init)(type);
115}
116EXPORT_SYMBOL(__frontswap_init);
117
118/*
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.
124 */
125int __frontswap_store(struct page *page)
126{
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;
137 ret = (*frontswap_ops.store)(type, offset, page);
138 if (ret == 0) {
139 frontswap_set(sis, offset);
140 inc_frontswap_succ_stores();
141 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);
150 inc_frontswap_failed_stores();
151 } else
152 inc_frontswap_failed_stores();
153 if (frontswap_writethrough_enabled)
154 /* report failure so swap also writes to swap device */
155 ret = -1;
156 return ret;
157}
158EXPORT_SYMBOL(__frontswap_store);
159
160/*
161 * "Get" data from frontswap associated with swaptype and offset that were
162 * specified when the data was put to frontswap and use it to fill the
163 * specified page with data. Page must be locked and in the swap cache.
164 */
165int __frontswap_load(struct page *page)
166{
167 int ret = -1;
168 swp_entry_t entry = { .val = page_private(page), };
169 int type = swp_type(entry);
170 struct swap_info_struct *sis = swap_info[type];
171 pgoff_t offset = swp_offset(entry);
172
173 BUG_ON(!PageLocked(page));
174 BUG_ON(sis == NULL);
175 if (frontswap_test(sis, offset))
176 ret = (*frontswap_ops.load)(type, offset, page);
177 if (ret == 0)
178 inc_frontswap_loads();
179 return ret;
180}
181EXPORT_SYMBOL(__frontswap_load);
182
183/*
184 * Invalidate any data from frontswap associated with the specified swaptype
185 * and offset so that a subsequent "get" will fail.
186 */
187void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
188{
189 struct swap_info_struct *sis = swap_info[type];
190
191 BUG_ON(sis == NULL);
192 if (frontswap_test(sis, offset)) {
193 (*frontswap_ops.invalidate_page)(type, offset);
194 atomic_dec(&sis->frontswap_pages);
195 frontswap_clear(sis, offset);
196 inc_frontswap_invalidates();
197 }
198}
199EXPORT_SYMBOL(__frontswap_invalidate_page);
200
201/*
202 * Invalidate all data from frontswap associated with all offsets for the
203 * specified swaptype.
204 */
205void __frontswap_invalidate_area(unsigned type)
206{
207 struct swap_info_struct *sis = swap_info[type];
208
209 BUG_ON(sis == NULL);
210 if (sis->frontswap_map == NULL)
211 return;
212 (*frontswap_ops.invalidate_area)(type);
213 atomic_set(&sis->frontswap_pages, 0);
214 memset(sis->frontswap_map, 0, sis->max / sizeof(long));
215}
216EXPORT_SYMBOL(__frontswap_invalidate_area);
217
218/*
219 * Frontswap, like a true swap device, may unnecessarily retain pages
220 * under certain circumstances; "shrink" frontswap is essentially a
221 * "partial swapoff" and works by calling try_to_unuse to attempt to
222 * unuse enough frontswap pages to attempt to -- subject to memory
223 * constraints -- reduce the number of pages in frontswap to the
224 * number given in the parameter target_pages.
225 */
226void frontswap_shrink(unsigned long target_pages)
227{
228 struct swap_info_struct *si = NULL;
229 int si_frontswap_pages;
230 unsigned long total_pages = 0, total_pages_to_unuse;
231 unsigned long pages = 0, pages_to_unuse = 0;
232 int type;
233 bool locked = false;
234
235 /*
236 * we don't want to hold swap_lock while doing a very
237 * lengthy try_to_unuse, but swap_list may change
238 * so restart scan from swap_list.head each time
239 */
240 spin_lock(&swap_lock);
241 locked = true;
242 total_pages = 0;
243 for (type = swap_list.head; type >= 0; type = si->next) {
244 si = swap_info[type];
245 total_pages += atomic_read(&si->frontswap_pages);
246 }
247 if (total_pages <= target_pages)
248 goto out;
249 total_pages_to_unuse = total_pages - target_pages;
250 for (type = swap_list.head; type >= 0; type = si->next) {
251 si = swap_info[type];
252 si_frontswap_pages = atomic_read(&si->frontswap_pages);
253 if (total_pages_to_unuse < si_frontswap_pages)
254 pages = pages_to_unuse = total_pages_to_unuse;
255 else {
256 pages = si_frontswap_pages;
257 pages_to_unuse = 0; /* unuse all */
258 }
259 /* ensure there is enough RAM to fetch pages from frontswap */
260 if (security_vm_enough_memory_mm(current->mm, pages))
261 continue;
262 vm_unacct_memory(pages);
263 break;
264 }
265 if (type < 0)
266 goto out;
267 locked = false;
268 spin_unlock(&swap_lock);
269 try_to_unuse(type, true, pages_to_unuse);
270out:
271 if (locked)
272 spin_unlock(&swap_lock);
273 return;
274}
275EXPORT_SYMBOL(frontswap_shrink);
276
277/*
278 * Count and return the number of frontswap pages across all
279 * swap devices. This is exported so that backend drivers can
280 * determine current usage without reading debugfs.
281 */
282unsigned long frontswap_curr_pages(void)
283{
284 int type;
285 unsigned long totalpages = 0;
286 struct swap_info_struct *si = NULL;
287
288 spin_lock(&swap_lock);
289 for (type = swap_list.head; type >= 0; type = si->next) {
290 si = swap_info[type];
291 totalpages += atomic_read(&si->frontswap_pages);
292 }
293 spin_unlock(&swap_lock);
294 return totalpages;
295}
296EXPORT_SYMBOL(frontswap_curr_pages);
297
298static int __init init_frontswap(void)
299{
300#ifdef CONFIG_DEBUG_FS
301 struct dentry *root = debugfs_create_dir("frontswap", NULL);
302 if (root == NULL)
303 return -ENXIO;
304 debugfs_create_u64("loads", S_IRUGO, root, &frontswap_loads);
305 debugfs_create_u64("succ_stores", S_IRUGO, root, &frontswap_succ_stores);
306 debugfs_create_u64("failed_stores", S_IRUGO, root,
307 &frontswap_failed_stores);
308 debugfs_create_u64("invalidates", S_IRUGO,
309 root, &frontswap_invalidates);
310#endif
311 return 0;
312}
313
314module_init(init_frontswap);