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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Frontswap frontend
4 *
5 * This code provides the generic "frontend" layer to call a matching
6 * "backend" driver implementation of frontswap. See
7 * Documentation/vm/frontswap.rst for more information.
8 *
9 * Copyright (C) 2009-2012 Oracle Corp. All rights reserved.
10 * Author: Dan Magenheimer
11 */
12
13#include <linux/mman.h>
14#include <linux/swap.h>
15#include <linux/swapops.h>
16#include <linux/security.h>
17#include <linux/module.h>
18#include <linux/debugfs.h>
19#include <linux/frontswap.h>
20#include <linux/swapfile.h>
21
22DEFINE_STATIC_KEY_FALSE(frontswap_enabled_key);
23
24/*
25 * frontswap_ops are added by frontswap_register_ops, and provide the
26 * frontswap "backend" implementation functions. Multiple implementations
27 * may be registered, but implementations can never deregister. This
28 * is a simple singly-linked list of all registered implementations.
29 */
30static struct frontswap_ops *frontswap_ops __read_mostly;
31
32#define for_each_frontswap_ops(ops) \
33 for ((ops) = frontswap_ops; (ops); (ops) = (ops)->next)
34
35/*
36 * If enabled, frontswap_store will return failure even on success. As
37 * a result, the swap subsystem will always write the page to swap, in
38 * effect converting frontswap into a writethrough cache. In this mode,
39 * there is no direct reduction in swap writes, but a frontswap backend
40 * can unilaterally "reclaim" any pages in use with no data loss, thus
41 * providing increases control over maximum memory usage due to frontswap.
42 */
43static bool frontswap_writethrough_enabled __read_mostly;
44
45/*
46 * If enabled, the underlying tmem implementation is capable of doing
47 * exclusive gets, so frontswap_load, on a successful tmem_get must
48 * mark the page as no longer in frontswap AND mark it dirty.
49 */
50static bool frontswap_tmem_exclusive_gets_enabled __read_mostly;
51
52#ifdef CONFIG_DEBUG_FS
53/*
54 * Counters available via /sys/kernel/debug/frontswap (if debugfs is
55 * properly configured). These are for information only so are not protected
56 * against increment races.
57 */
58static u64 frontswap_loads;
59static u64 frontswap_succ_stores;
60static u64 frontswap_failed_stores;
61static u64 frontswap_invalidates;
62
63static inline void inc_frontswap_loads(void)
64{
65 data_race(frontswap_loads++);
66}
67static inline void inc_frontswap_succ_stores(void)
68{
69 data_race(frontswap_succ_stores++);
70}
71static inline void inc_frontswap_failed_stores(void)
72{
73 data_race(frontswap_failed_stores++);
74}
75static inline void inc_frontswap_invalidates(void)
76{
77 data_race(frontswap_invalidates++);
78}
79#else
80static inline void inc_frontswap_loads(void) { }
81static inline void inc_frontswap_succ_stores(void) { }
82static inline void inc_frontswap_failed_stores(void) { }
83static inline void inc_frontswap_invalidates(void) { }
84#endif
85
86/*
87 * Due to the asynchronous nature of the backends loading potentially
88 * _after_ the swap system has been activated, we have chokepoints
89 * on all frontswap functions to not call the backend until the backend
90 * has registered.
91 *
92 * This would not guards us against the user deciding to call swapoff right as
93 * we are calling the backend to initialize (so swapon is in action).
94 * Fortunately for us, the swapon_mutex has been taken by the callee so we are
95 * OK. The other scenario where calls to frontswap_store (called via
96 * swap_writepage) is racing with frontswap_invalidate_area (called via
97 * swapoff) is again guarded by the swap subsystem.
98 *
99 * While no backend is registered all calls to frontswap_[store|load|
100 * invalidate_area|invalidate_page] are ignored or fail.
101 *
102 * The time between the backend being registered and the swap file system
103 * calling the backend (via the frontswap_* functions) is indeterminate as
104 * frontswap_ops is not atomic_t (or a value guarded by a spinlock).
105 * That is OK as we are comfortable missing some of these calls to the newly
106 * registered backend.
107 *
108 * Obviously the opposite (unloading the backend) must be done after all
109 * the frontswap_[store|load|invalidate_area|invalidate_page] start
110 * ignoring or failing the requests. However, there is currently no way
111 * to unload a backend once it is registered.
112 */
113
114/*
115 * Register operations for frontswap
116 */
117void frontswap_register_ops(struct frontswap_ops *ops)
118{
119 DECLARE_BITMAP(a, MAX_SWAPFILES);
120 DECLARE_BITMAP(b, MAX_SWAPFILES);
121 struct swap_info_struct *si;
122 unsigned int i;
123
124 bitmap_zero(a, MAX_SWAPFILES);
125 bitmap_zero(b, MAX_SWAPFILES);
126
127 spin_lock(&swap_lock);
128 plist_for_each_entry(si, &swap_active_head, list) {
129 if (!WARN_ON(!si->frontswap_map))
130 set_bit(si->type, a);
131 }
132 spin_unlock(&swap_lock);
133
134 /* the new ops needs to know the currently active swap devices */
135 for_each_set_bit(i, a, MAX_SWAPFILES)
136 ops->init(i);
137
138 /*
139 * Setting frontswap_ops must happen after the ops->init() calls
140 * above; cmpxchg implies smp_mb() which will ensure the init is
141 * complete at this point.
142 */
143 do {
144 ops->next = frontswap_ops;
145 } while (cmpxchg(&frontswap_ops, ops->next, ops) != ops->next);
146
147 static_branch_inc(&frontswap_enabled_key);
148
149 spin_lock(&swap_lock);
150 plist_for_each_entry(si, &swap_active_head, list) {
151 if (si->frontswap_map)
152 set_bit(si->type, b);
153 }
154 spin_unlock(&swap_lock);
155
156 /*
157 * On the very unlikely chance that a swap device was added or
158 * removed between setting the "a" list bits and the ops init
159 * calls, we re-check and do init or invalidate for any changed
160 * bits.
161 */
162 if (unlikely(!bitmap_equal(a, b, MAX_SWAPFILES))) {
163 for (i = 0; i < MAX_SWAPFILES; i++) {
164 if (!test_bit(i, a) && test_bit(i, b))
165 ops->init(i);
166 else if (test_bit(i, a) && !test_bit(i, b))
167 ops->invalidate_area(i);
168 }
169 }
170}
171EXPORT_SYMBOL(frontswap_register_ops);
172
173/*
174 * Enable/disable frontswap writethrough (see above).
175 */
176void frontswap_writethrough(bool enable)
177{
178 frontswap_writethrough_enabled = enable;
179}
180EXPORT_SYMBOL(frontswap_writethrough);
181
182/*
183 * Enable/disable frontswap exclusive gets (see above).
184 */
185void frontswap_tmem_exclusive_gets(bool enable)
186{
187 frontswap_tmem_exclusive_gets_enabled = enable;
188}
189EXPORT_SYMBOL(frontswap_tmem_exclusive_gets);
190
191/*
192 * Called when a swap device is swapon'd.
193 */
194void __frontswap_init(unsigned type, unsigned long *map)
195{
196 struct swap_info_struct *sis = swap_info[type];
197 struct frontswap_ops *ops;
198
199 VM_BUG_ON(sis == NULL);
200
201 /*
202 * p->frontswap is a bitmap that we MUST have to figure out which page
203 * has gone in frontswap. Without it there is no point of continuing.
204 */
205 if (WARN_ON(!map))
206 return;
207 /*
208 * Irregardless of whether the frontswap backend has been loaded
209 * before this function or it will be later, we _MUST_ have the
210 * p->frontswap set to something valid to work properly.
211 */
212 frontswap_map_set(sis, map);
213
214 for_each_frontswap_ops(ops)
215 ops->init(type);
216}
217EXPORT_SYMBOL(__frontswap_init);
218
219bool __frontswap_test(struct swap_info_struct *sis,
220 pgoff_t offset)
221{
222 if (sis->frontswap_map)
223 return test_bit(offset, sis->frontswap_map);
224 return false;
225}
226EXPORT_SYMBOL(__frontswap_test);
227
228static inline void __frontswap_set(struct swap_info_struct *sis,
229 pgoff_t offset)
230{
231 set_bit(offset, sis->frontswap_map);
232 atomic_inc(&sis->frontswap_pages);
233}
234
235static inline void __frontswap_clear(struct swap_info_struct *sis,
236 pgoff_t offset)
237{
238 clear_bit(offset, sis->frontswap_map);
239 atomic_dec(&sis->frontswap_pages);
240}
241
242/*
243 * "Store" data from a page to frontswap and associate it with the page's
244 * swaptype and offset. Page must be locked and in the swap cache.
245 * If frontswap already contains a page with matching swaptype and
246 * offset, the frontswap implementation may either overwrite the data and
247 * return success or invalidate the page from frontswap and return failure.
248 */
249int __frontswap_store(struct page *page)
250{
251 int ret = -1;
252 swp_entry_t entry = { .val = page_private(page), };
253 int type = swp_type(entry);
254 struct swap_info_struct *sis = swap_info[type];
255 pgoff_t offset = swp_offset(entry);
256 struct frontswap_ops *ops;
257
258 VM_BUG_ON(!frontswap_ops);
259 VM_BUG_ON(!PageLocked(page));
260 VM_BUG_ON(sis == NULL);
261
262 /*
263 * If a dup, we must remove the old page first; we can't leave the
264 * old page no matter if the store of the new page succeeds or fails,
265 * and we can't rely on the new page replacing the old page as we may
266 * not store to the same implementation that contains the old page.
267 */
268 if (__frontswap_test(sis, offset)) {
269 __frontswap_clear(sis, offset);
270 for_each_frontswap_ops(ops)
271 ops->invalidate_page(type, offset);
272 }
273
274 /* Try to store in each implementation, until one succeeds. */
275 for_each_frontswap_ops(ops) {
276 ret = ops->store(type, offset, page);
277 if (!ret) /* successful store */
278 break;
279 }
280 if (ret == 0) {
281 __frontswap_set(sis, offset);
282 inc_frontswap_succ_stores();
283 } else {
284 inc_frontswap_failed_stores();
285 }
286 if (frontswap_writethrough_enabled)
287 /* report failure so swap also writes to swap device */
288 ret = -1;
289 return ret;
290}
291EXPORT_SYMBOL(__frontswap_store);
292
293/*
294 * "Get" data from frontswap associated with swaptype and offset that were
295 * specified when the data was put to frontswap and use it to fill the
296 * specified page with data. Page must be locked and in the swap cache.
297 */
298int __frontswap_load(struct page *page)
299{
300 int ret = -1;
301 swp_entry_t entry = { .val = page_private(page), };
302 int type = swp_type(entry);
303 struct swap_info_struct *sis = swap_info[type];
304 pgoff_t offset = swp_offset(entry);
305 struct frontswap_ops *ops;
306
307 VM_BUG_ON(!frontswap_ops);
308 VM_BUG_ON(!PageLocked(page));
309 VM_BUG_ON(sis == NULL);
310
311 if (!__frontswap_test(sis, offset))
312 return -1;
313
314 /* Try loading from each implementation, until one succeeds. */
315 for_each_frontswap_ops(ops) {
316 ret = ops->load(type, offset, page);
317 if (!ret) /* successful load */
318 break;
319 }
320 if (ret == 0) {
321 inc_frontswap_loads();
322 if (frontswap_tmem_exclusive_gets_enabled) {
323 SetPageDirty(page);
324 __frontswap_clear(sis, offset);
325 }
326 }
327 return ret;
328}
329EXPORT_SYMBOL(__frontswap_load);
330
331/*
332 * Invalidate any data from frontswap associated with the specified swaptype
333 * and offset so that a subsequent "get" will fail.
334 */
335void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
336{
337 struct swap_info_struct *sis = swap_info[type];
338 struct frontswap_ops *ops;
339
340 VM_BUG_ON(!frontswap_ops);
341 VM_BUG_ON(sis == NULL);
342
343 if (!__frontswap_test(sis, offset))
344 return;
345
346 for_each_frontswap_ops(ops)
347 ops->invalidate_page(type, offset);
348 __frontswap_clear(sis, offset);
349 inc_frontswap_invalidates();
350}
351EXPORT_SYMBOL(__frontswap_invalidate_page);
352
353/*
354 * Invalidate all data from frontswap associated with all offsets for the
355 * specified swaptype.
356 */
357void __frontswap_invalidate_area(unsigned type)
358{
359 struct swap_info_struct *sis = swap_info[type];
360 struct frontswap_ops *ops;
361
362 VM_BUG_ON(!frontswap_ops);
363 VM_BUG_ON(sis == NULL);
364
365 if (sis->frontswap_map == NULL)
366 return;
367
368 for_each_frontswap_ops(ops)
369 ops->invalidate_area(type);
370 atomic_set(&sis->frontswap_pages, 0);
371 bitmap_zero(sis->frontswap_map, sis->max);
372}
373EXPORT_SYMBOL(__frontswap_invalidate_area);
374
375static unsigned long __frontswap_curr_pages(void)
376{
377 unsigned long totalpages = 0;
378 struct swap_info_struct *si = NULL;
379
380 assert_spin_locked(&swap_lock);
381 plist_for_each_entry(si, &swap_active_head, list)
382 totalpages += atomic_read(&si->frontswap_pages);
383 return totalpages;
384}
385
386static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused,
387 int *swapid)
388{
389 int ret = -EINVAL;
390 struct swap_info_struct *si = NULL;
391 int si_frontswap_pages;
392 unsigned long total_pages_to_unuse = total;
393 unsigned long pages = 0, pages_to_unuse = 0;
394
395 assert_spin_locked(&swap_lock);
396 plist_for_each_entry(si, &swap_active_head, list) {
397 si_frontswap_pages = atomic_read(&si->frontswap_pages);
398 if (total_pages_to_unuse < si_frontswap_pages) {
399 pages = pages_to_unuse = total_pages_to_unuse;
400 } else {
401 pages = si_frontswap_pages;
402 pages_to_unuse = 0; /* unuse all */
403 }
404 /* ensure there is enough RAM to fetch pages from frontswap */
405 if (security_vm_enough_memory_mm(current->mm, pages)) {
406 ret = -ENOMEM;
407 continue;
408 }
409 vm_unacct_memory(pages);
410 *unused = pages_to_unuse;
411 *swapid = si->type;
412 ret = 0;
413 break;
414 }
415
416 return ret;
417}
418
419/*
420 * Used to check if it's necessary and feasible to unuse pages.
421 * Return 1 when nothing to do, 0 when need to shrink pages,
422 * error code when there is an error.
423 */
424static int __frontswap_shrink(unsigned long target_pages,
425 unsigned long *pages_to_unuse,
426 int *type)
427{
428 unsigned long total_pages = 0, total_pages_to_unuse;
429
430 assert_spin_locked(&swap_lock);
431
432 total_pages = __frontswap_curr_pages();
433 if (total_pages <= target_pages) {
434 /* Nothing to do */
435 *pages_to_unuse = 0;
436 return 1;
437 }
438 total_pages_to_unuse = total_pages - target_pages;
439 return __frontswap_unuse_pages(total_pages_to_unuse, pages_to_unuse, type);
440}
441
442/*
443 * Frontswap, like a true swap device, may unnecessarily retain pages
444 * under certain circumstances; "shrink" frontswap is essentially a
445 * "partial swapoff" and works by calling try_to_unuse to attempt to
446 * unuse enough frontswap pages to attempt to -- subject to memory
447 * constraints -- reduce the number of pages in frontswap to the
448 * number given in the parameter target_pages.
449 */
450void frontswap_shrink(unsigned long target_pages)
451{
452 unsigned long pages_to_unuse = 0;
453 int type, ret;
454
455 /*
456 * we don't want to hold swap_lock while doing a very
457 * lengthy try_to_unuse, but swap_list may change
458 * so restart scan from swap_active_head each time
459 */
460 spin_lock(&swap_lock);
461 ret = __frontswap_shrink(target_pages, &pages_to_unuse, &type);
462 spin_unlock(&swap_lock);
463 if (ret == 0)
464 try_to_unuse(type, true, pages_to_unuse);
465 return;
466}
467EXPORT_SYMBOL(frontswap_shrink);
468
469/*
470 * Count and return the number of frontswap pages across all
471 * swap devices. This is exported so that backend drivers can
472 * determine current usage without reading debugfs.
473 */
474unsigned long frontswap_curr_pages(void)
475{
476 unsigned long totalpages = 0;
477
478 spin_lock(&swap_lock);
479 totalpages = __frontswap_curr_pages();
480 spin_unlock(&swap_lock);
481
482 return totalpages;
483}
484EXPORT_SYMBOL(frontswap_curr_pages);
485
486static int __init init_frontswap(void)
487{
488#ifdef CONFIG_DEBUG_FS
489 struct dentry *root = debugfs_create_dir("frontswap", NULL);
490 if (root == NULL)
491 return -ENXIO;
492 debugfs_create_u64("loads", 0444, root, &frontswap_loads);
493 debugfs_create_u64("succ_stores", 0444, root, &frontswap_succ_stores);
494 debugfs_create_u64("failed_stores", 0444, root,
495 &frontswap_failed_stores);
496 debugfs_create_u64("invalidates", 0444, root, &frontswap_invalidates);
497#endif
498 return 0;
499}
500
501module_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);