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