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 * This global enablement flag reduces overhead on systems where frontswap_ops
31 * has not been registered, so is preferred to the slower alternative: a
32 * function call that checks a non-global.
34 bool frontswap_enabled __read_mostly;
35 EXPORT_SYMBOL(frontswap_enabled);
38 * If enabled, frontswap_store will return failure even on success. As
39 * a result, the swap subsystem will always write the page to swap, in
40 * effect converting frontswap into a writethrough cache. In this mode,
41 * there is no direct reduction in swap writes, but a frontswap backend
42 * can unilaterally "reclaim" any pages in use with no data loss, thus
43 * providing increases control over maximum memory usage due to frontswap.
45 static bool frontswap_writethrough_enabled __read_mostly;
48 * If enabled, the underlying tmem implementation is capable of doing
49 * exclusive gets, so frontswap_load, on a successful tmem_get must
50 * mark the page as no longer in frontswap AND mark it dirty.
52 static bool frontswap_tmem_exclusive_gets_enabled __read_mostly;
54 #ifdef CONFIG_DEBUG_FS
56 * Counters available via /sys/kernel/debug/frontswap (if debugfs is
57 * properly configured). These are for information only so are not protected
58 * against increment races.
60 static u64 frontswap_loads;
61 static u64 frontswap_succ_stores;
62 static u64 frontswap_failed_stores;
63 static u64 frontswap_invalidates;
65 static inline void inc_frontswap_loads(void) {
68 static inline void inc_frontswap_succ_stores(void) {
69 frontswap_succ_stores++;
71 static inline void inc_frontswap_failed_stores(void) {
72 frontswap_failed_stores++;
74 static inline void inc_frontswap_invalidates(void) {
75 frontswap_invalidates++;
78 static inline void inc_frontswap_loads(void) { }
79 static inline void inc_frontswap_succ_stores(void) { }
80 static inline void inc_frontswap_failed_stores(void) { }
81 static inline void inc_frontswap_invalidates(void) { }
85 * Due to the asynchronous nature of the backends loading potentially
86 * _after_ the swap system has been activated, we have chokepoints
87 * on all frontswap functions to not call the backend until the backend
90 * Specifically when no backend is registered (nobody called
91 * frontswap_register_ops) all calls to frontswap_init (which is done via
92 * swapon -> enable_swap_info -> frontswap_init) are registered and remembered
93 * (via the setting of need_init bitmap) but fail to create tmem_pools. When a
94 * backend registers with frontswap at some later point the previous
95 * calls to frontswap_init are executed (by iterating over the need_init
96 * bitmap) to create tmem_pools and set the respective poolids. All of that is
97 * guarded by us using atomic bit operations on the 'need_init' bitmap.
99 * This would not guards us against the user deciding to call swapoff right as
100 * we are calling the backend to initialize (so swapon is in action).
101 * Fortunatly for us, the swapon_mutex has been taked by the callee so we are
102 * OK. The other scenario where calls to frontswap_store (called via
103 * swap_writepage) is racing with frontswap_invalidate_area (called via
104 * swapoff) is again guarded by the swap subsystem.
106 * While no backend is registered all calls to frontswap_[store|load|
107 * invalidate_area|invalidate_page] are ignored or fail.
109 * The time between the backend being registered and the swap file system
110 * calling the backend (via the frontswap_* functions) is indeterminate as
111 * backend_registered is not atomic_t (or a value guarded by a spinlock).
112 * That is OK as we are comfortable missing some of these calls to the newly
113 * registered backend.
115 * Obviously the opposite (unloading the backend) must be done after all
116 * the frontswap_[store|load|invalidate_area|invalidate_page] start
117 * ignorning or failing the requests - at which point backend_registered
118 * would have to be made in some fashion atomic.
120 static DECLARE_BITMAP(need_init, MAX_SWAPFILES);
121 static bool backend_registered __read_mostly;
124 * Register operations for frontswap, returning previous thus allowing
125 * detection of multiple backends and possible nesting.
127 struct frontswap_ops frontswap_register_ops(struct frontswap_ops *ops)
129 struct frontswap_ops old = frontswap_ops;
132 frontswap_ops = *ops;
133 frontswap_enabled = true;
135 for (i = 0; i < MAX_SWAPFILES; i++) {
136 if (test_and_clear_bit(i, need_init))
137 (*frontswap_ops.init)(i);
140 * We MUST have backend_registered set _after_ the frontswap_init's
141 * have been called. Otherwise __frontswap_store might fail. Hence
142 * the barrier to make sure compiler does not re-order us.
145 backend_registered = true;
148 EXPORT_SYMBOL(frontswap_register_ops);
151 * Enable/disable frontswap writethrough (see above).
153 void frontswap_writethrough(bool enable)
155 frontswap_writethrough_enabled = enable;
157 EXPORT_SYMBOL(frontswap_writethrough);
160 * Enable/disable frontswap exclusive gets (see above).
162 void frontswap_tmem_exclusive_gets(bool enable)
164 frontswap_tmem_exclusive_gets_enabled = enable;
166 EXPORT_SYMBOL(frontswap_tmem_exclusive_gets);
169 * Called when a swap device is swapon'd.
171 void __frontswap_init(unsigned type)
173 struct swap_info_struct *sis = swap_info[type];
175 if (backend_registered) {
177 if (sis->frontswap_map == NULL)
179 (*frontswap_ops.init)(type);
181 BUG_ON(type > MAX_SWAPFILES);
182 set_bit(type, need_init);
186 EXPORT_SYMBOL(__frontswap_init);
188 static inline void __frontswap_clear(struct swap_info_struct *sis, pgoff_t offset)
190 frontswap_clear(sis, offset);
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);
209 if (!backend_registered) {
210 inc_frontswap_failed_stores();
214 BUG_ON(!PageLocked(page));
216 if (frontswap_test(sis, offset))
218 ret = frontswap_ops.store(type, offset, page);
220 frontswap_set(sis, offset);
221 inc_frontswap_succ_stores();
223 atomic_inc(&sis->frontswap_pages);
226 failed dup always results in automatic invalidate of
227 the (older) page from frontswap
229 inc_frontswap_failed_stores();
231 __frontswap_clear(sis, offset);
233 if (frontswap_writethrough_enabled)
234 /* report failure so swap also writes to swap device */
238 EXPORT_SYMBOL(__frontswap_store);
241 * "Get" data from frontswap associated with swaptype and offset that were
242 * specified when the data was put to frontswap and use it to fill the
243 * specified page with data. Page must be locked and in the swap cache.
245 int __frontswap_load(struct page *page)
248 swp_entry_t entry = { .val = page_private(page), };
249 int type = swp_type(entry);
250 struct swap_info_struct *sis = swap_info[type];
251 pgoff_t offset = swp_offset(entry);
253 if (!backend_registered)
256 BUG_ON(!PageLocked(page));
258 if (frontswap_test(sis, offset))
259 ret = frontswap_ops.load(type, offset, page);
261 inc_frontswap_loads();
262 if (frontswap_tmem_exclusive_gets_enabled) {
264 frontswap_clear(sis, offset);
269 EXPORT_SYMBOL(__frontswap_load);
272 * Invalidate any data from frontswap associated with the specified swaptype
273 * and offset so that a subsequent "get" will fail.
275 void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
277 struct swap_info_struct *sis = swap_info[type];
279 if (!backend_registered)
283 if (frontswap_test(sis, offset)) {
284 frontswap_ops.invalidate_page(type, offset);
285 __frontswap_clear(sis, offset);
286 inc_frontswap_invalidates();
289 EXPORT_SYMBOL(__frontswap_invalidate_page);
292 * Invalidate all data from frontswap associated with all offsets for the
293 * specified swaptype.
295 void __frontswap_invalidate_area(unsigned type)
297 struct swap_info_struct *sis = swap_info[type];
299 if (backend_registered) {
301 if (sis->frontswap_map == NULL)
303 (*frontswap_ops.invalidate_area)(type);
304 atomic_set(&sis->frontswap_pages, 0);
305 memset(sis->frontswap_map, 0, sis->max / sizeof(long));
307 clear_bit(type, need_init);
309 EXPORT_SYMBOL(__frontswap_invalidate_area);
311 static unsigned long __frontswap_curr_pages(void)
314 unsigned long totalpages = 0;
315 struct swap_info_struct *si = NULL;
317 assert_spin_locked(&swap_lock);
318 for (type = swap_list.head; type >= 0; type = si->next) {
319 si = swap_info[type];
320 totalpages += atomic_read(&si->frontswap_pages);
325 static int __frontswap_unuse_pages(unsigned long total, unsigned long *unused,
329 struct swap_info_struct *si = NULL;
330 int si_frontswap_pages;
331 unsigned long total_pages_to_unuse = total;
332 unsigned long pages = 0, pages_to_unuse = 0;
335 assert_spin_locked(&swap_lock);
336 for (type = swap_list.head; type >= 0; type = si->next) {
337 si = swap_info[type];
338 si_frontswap_pages = atomic_read(&si->frontswap_pages);
339 if (total_pages_to_unuse < si_frontswap_pages) {
340 pages = pages_to_unuse = total_pages_to_unuse;
342 pages = si_frontswap_pages;
343 pages_to_unuse = 0; /* unuse all */
345 /* ensure there is enough RAM to fetch pages from frontswap */
346 if (security_vm_enough_memory_mm(current->mm, pages)) {
350 vm_unacct_memory(pages);
351 *unused = pages_to_unuse;
361 * Used to check if it's necessory and feasible to unuse pages.
362 * Return 1 when nothing to do, 0 when need to shink pages,
363 * error code when there is an error.
365 static int __frontswap_shrink(unsigned long target_pages,
366 unsigned long *pages_to_unuse,
369 unsigned long total_pages = 0, total_pages_to_unuse;
371 assert_spin_locked(&swap_lock);
373 total_pages = __frontswap_curr_pages();
374 if (total_pages <= target_pages) {
379 total_pages_to_unuse = total_pages - target_pages;
380 return __frontswap_unuse_pages(total_pages_to_unuse, pages_to_unuse, type);
384 * Frontswap, like a true swap device, may unnecessarily retain pages
385 * under certain circumstances; "shrink" frontswap is essentially a
386 * "partial swapoff" and works by calling try_to_unuse to attempt to
387 * unuse enough frontswap pages to attempt to -- subject to memory
388 * constraints -- reduce the number of pages in frontswap to the
389 * number given in the parameter target_pages.
391 void frontswap_shrink(unsigned long target_pages)
393 unsigned long pages_to_unuse = 0;
394 int uninitialized_var(type), ret;
397 * we don't want to hold swap_lock while doing a very
398 * lengthy try_to_unuse, but swap_list may change
399 * so restart scan from swap_list.head each time
401 spin_lock(&swap_lock);
402 ret = __frontswap_shrink(target_pages, &pages_to_unuse, &type);
403 spin_unlock(&swap_lock);
405 try_to_unuse(type, true, pages_to_unuse);
408 EXPORT_SYMBOL(frontswap_shrink);
411 * Count and return the number of frontswap pages across all
412 * swap devices. This is exported so that backend drivers can
413 * determine current usage without reading debugfs.
415 unsigned long frontswap_curr_pages(void)
417 unsigned long totalpages = 0;
419 spin_lock(&swap_lock);
420 totalpages = __frontswap_curr_pages();
421 spin_unlock(&swap_lock);
425 EXPORT_SYMBOL(frontswap_curr_pages);
427 static int __init init_frontswap(void)
429 #ifdef CONFIG_DEBUG_FS
430 struct dentry *root = debugfs_create_dir("frontswap", NULL);
433 debugfs_create_u64("loads", S_IRUGO, root, &frontswap_loads);
434 debugfs_create_u64("succ_stores", S_IRUGO, root, &frontswap_succ_stores);
435 debugfs_create_u64("failed_stores", S_IRUGO, root,
436 &frontswap_failed_stores);
437 debugfs_create_u64("invalidates", S_IRUGO,
438 root, &frontswap_invalidates);
440 frontswap_enabled = 1;
444 module_init(init_frontswap);