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.
8 * Copyright (C) 2009-2012 Oracle Corp. All rights reserved.
9 * Author: Dan Magenheimer
11 * This work is licensed under the terms of the GNU GPL, version 2.
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>
24 * frontswap_ops is set by frontswap_register_ops to contain the pointers
25 * to the frontswap "backend" implementation functions.
27 static struct frontswap_ops *frontswap_ops __read_mostly;
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.
37 static bool frontswap_writethrough_enabled __read_mostly;
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.
44 static bool frontswap_tmem_exclusive_gets_enabled __read_mostly;
46 #ifdef CONFIG_DEBUG_FS
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.
52 static u64 frontswap_loads;
53 static u64 frontswap_succ_stores;
54 static u64 frontswap_failed_stores;
55 static u64 frontswap_invalidates;
57 static inline void inc_frontswap_loads(void) {
60 static inline void inc_frontswap_succ_stores(void) {
61 frontswap_succ_stores++;
63 static inline void inc_frontswap_failed_stores(void) {
64 frontswap_failed_stores++;
66 static inline void inc_frontswap_invalidates(void) {
67 frontswap_invalidates++;
70 static inline void inc_frontswap_loads(void) { }
71 static inline void inc_frontswap_succ_stores(void) { }
72 static inline void inc_frontswap_failed_stores(void) { }
73 static inline void inc_frontswap_invalidates(void) { }
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
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.
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.
98 * While no backend is registered all calls to frontswap_[store|load|
99 * invalidate_area|invalidate_page] are ignored or fail.
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.
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.
112 static DECLARE_BITMAP(need_init, MAX_SWAPFILES);
115 * Register operations for frontswap, returning previous thus allowing
116 * detection of multiple backends and possible nesting.
118 struct frontswap_ops *frontswap_register_ops(struct frontswap_ops *ops)
120 struct frontswap_ops *old = frontswap_ops;
123 for (i = 0; i < MAX_SWAPFILES; i++) {
124 if (test_and_clear_bit(i, need_init))
128 * We MUST have frontswap_ops set _after_ the frontswap_init's
129 * have been called. Otherwise __frontswap_store might fail. Hence
130 * the barrier to make sure compiler does not re-order us.
136 EXPORT_SYMBOL(frontswap_register_ops);
139 * Enable/disable frontswap writethrough (see above).
141 void frontswap_writethrough(bool enable)
143 frontswap_writethrough_enabled = enable;
145 EXPORT_SYMBOL(frontswap_writethrough);
148 * Enable/disable frontswap exclusive gets (see above).
150 void frontswap_tmem_exclusive_gets(bool enable)
152 frontswap_tmem_exclusive_gets_enabled = enable;
154 EXPORT_SYMBOL(frontswap_tmem_exclusive_gets);
157 * Called when a swap device is swapon'd.
159 void __frontswap_init(unsigned type)
161 struct swap_info_struct *sis = swap_info[type];
165 if (sis->frontswap_map == NULL)
167 frontswap_ops->init(type);
169 BUG_ON(type > MAX_SWAPFILES);
170 set_bit(type, need_init);
174 EXPORT_SYMBOL(__frontswap_init);
176 bool __frontswap_test(struct swap_info_struct *sis,
181 if (frontswap_ops && sis->frontswap_map)
182 ret = test_bit(offset, sis->frontswap_map);
185 EXPORT_SYMBOL(__frontswap_test);
187 static inline void __frontswap_clear(struct swap_info_struct *sis,
190 clear_bit(offset, sis->frontswap_map);
191 atomic_dec(&sis->frontswap_pages);
195 * "Store" data from a page to frontswap and associate it with the page's
196 * swaptype and offset. Page must be locked and in the swap cache.
197 * If frontswap already contains a page with matching swaptype and
198 * offset, the frontswap implementation may either overwrite the data and
199 * return success or invalidate the page from frontswap and return failure.
201 int __frontswap_store(struct page *page)
203 int ret = -1, dup = 0;
204 swp_entry_t entry = { .val = page_private(page), };
205 int type = swp_type(entry);
206 struct swap_info_struct *sis = swap_info[type];
207 pgoff_t offset = swp_offset(entry);
210 * Return if no backend registed.
211 * Don't need to inc frontswap_failed_stores here.
216 BUG_ON(!PageLocked(page));
218 if (__frontswap_test(sis, offset))
220 ret = frontswap_ops->store(type, offset, page);
222 set_bit(offset, sis->frontswap_map);
223 inc_frontswap_succ_stores();
225 atomic_inc(&sis->frontswap_pages);
228 failed dup always results in automatic invalidate of
229 the (older) page from frontswap
231 inc_frontswap_failed_stores();
233 __frontswap_clear(sis, offset);
235 if (frontswap_writethrough_enabled)
236 /* report failure so swap also writes to swap device */
240 EXPORT_SYMBOL(__frontswap_store);
243 * "Get" data from frontswap associated with swaptype and offset that were
244 * specified when the data was put to frontswap and use it to fill the
245 * specified page with data. Page must be locked and in the swap cache.
247 int __frontswap_load(struct page *page)
250 swp_entry_t entry = { .val = page_private(page), };
251 int type = swp_type(entry);
252 struct swap_info_struct *sis = swap_info[type];
253 pgoff_t offset = swp_offset(entry);
255 BUG_ON(!PageLocked(page));
258 * __frontswap_test() will check whether there is backend registered
260 if (__frontswap_test(sis, offset))
261 ret = frontswap_ops->load(type, offset, page);
263 inc_frontswap_loads();
264 if (frontswap_tmem_exclusive_gets_enabled) {
266 __frontswap_clear(sis, offset);
271 EXPORT_SYMBOL(__frontswap_load);
274 * Invalidate any data from frontswap associated with the specified swaptype
275 * and offset so that a subsequent "get" will fail.
277 void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
279 struct swap_info_struct *sis = swap_info[type];
283 * __frontswap_test() will check whether there is backend registered
285 if (__frontswap_test(sis, offset)) {
286 frontswap_ops->invalidate_page(type, offset);
287 __frontswap_clear(sis, offset);
288 inc_frontswap_invalidates();
291 EXPORT_SYMBOL(__frontswap_invalidate_page);
294 * Invalidate all data from frontswap associated with all offsets for the
295 * specified swaptype.
297 void __frontswap_invalidate_area(unsigned type)
299 struct swap_info_struct *sis = swap_info[type];
303 if (sis->frontswap_map == NULL)
305 frontswap_ops->invalidate_area(type);
306 atomic_set(&sis->frontswap_pages, 0);
307 memset(sis->frontswap_map, 0, sis->max / sizeof(long));
309 clear_bit(type, need_init);
311 EXPORT_SYMBOL(__frontswap_invalidate_area);
313 static unsigned long __frontswap_curr_pages(void)
316 unsigned long totalpages = 0;
317 struct swap_info_struct *si = NULL;
319 assert_spin_locked(&swap_lock);
320 for (type = swap_list.head; type >= 0; type = si->next) {
321 si = swap_info[type];
322 totalpages += atomic_read(&si->frontswap_pages);
327 static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused,
331 struct swap_info_struct *si = NULL;
332 int si_frontswap_pages;
333 unsigned long total_pages_to_unuse = total;
334 unsigned long pages = 0, pages_to_unuse = 0;
337 assert_spin_locked(&swap_lock);
338 for (type = swap_list.head; type >= 0; type = si->next) {
339 si = swap_info[type];
340 si_frontswap_pages = atomic_read(&si->frontswap_pages);
341 if (total_pages_to_unuse < si_frontswap_pages) {
342 pages = pages_to_unuse = total_pages_to_unuse;
344 pages = si_frontswap_pages;
345 pages_to_unuse = 0; /* unuse all */
347 /* ensure there is enough RAM to fetch pages from frontswap */
348 if (security_vm_enough_memory_mm(current->mm, pages)) {
352 vm_unacct_memory(pages);
353 *unused = pages_to_unuse;
363 * Used to check if it's necessory and feasible to unuse pages.
364 * Return 1 when nothing to do, 0 when need to shink pages,
365 * error code when there is an error.
367 static int __frontswap_shrink(unsigned long target_pages,
368 unsigned long *pages_to_unuse,
371 unsigned long total_pages = 0, total_pages_to_unuse;
373 assert_spin_locked(&swap_lock);
375 total_pages = __frontswap_curr_pages();
376 if (total_pages <= target_pages) {
381 total_pages_to_unuse = total_pages - target_pages;
382 return __frontswap_unuse_pages(total_pages_to_unuse, pages_to_unuse, type);
386 * Frontswap, like a true swap device, may unnecessarily retain pages
387 * under certain circumstances; "shrink" frontswap is essentially a
388 * "partial swapoff" and works by calling try_to_unuse to attempt to
389 * unuse enough frontswap pages to attempt to -- subject to memory
390 * constraints -- reduce the number of pages in frontswap to the
391 * number given in the parameter target_pages.
393 void frontswap_shrink(unsigned long target_pages)
395 unsigned long pages_to_unuse = 0;
396 int uninitialized_var(type), ret;
399 * we don't want to hold swap_lock while doing a very
400 * lengthy try_to_unuse, but swap_list may change
401 * so restart scan from swap_list.head each time
403 spin_lock(&swap_lock);
404 ret = __frontswap_shrink(target_pages, &pages_to_unuse, &type);
405 spin_unlock(&swap_lock);
407 try_to_unuse(type, true, pages_to_unuse);
410 EXPORT_SYMBOL(frontswap_shrink);
413 * Count and return the number of frontswap pages across all
414 * swap devices. This is exported so that backend drivers can
415 * determine current usage without reading debugfs.
417 unsigned long frontswap_curr_pages(void)
419 unsigned long totalpages = 0;
421 spin_lock(&swap_lock);
422 totalpages = __frontswap_curr_pages();
423 spin_unlock(&swap_lock);
427 EXPORT_SYMBOL(frontswap_curr_pages);
429 static int __init init_frontswap(void)
431 #ifdef CONFIG_DEBUG_FS
432 struct dentry *root = debugfs_create_dir("frontswap", NULL);
435 debugfs_create_u64("loads", S_IRUGO, root, &frontswap_loads);
436 debugfs_create_u64("succ_stores", S_IRUGO, root, &frontswap_succ_stores);
437 debugfs_create_u64("failed_stores", S_IRUGO, root,
438 &frontswap_failed_stores);
439 debugfs_create_u64("invalidates", S_IRUGO,
440 root, &frontswap_invalidates);
445 module_init(init_frontswap);