1 // SPDX-License-Identifier: GPL-2.0-only
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.
9 * Copyright (C) 2009-2012 Oracle Corp. All rights reserved.
10 * Author: Dan Magenheimer
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>
22 DEFINE_STATIC_KEY_FALSE(frontswap_enabled_key
);
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.
30 static const struct frontswap_ops
*frontswap_ops __read_mostly
;
32 #ifdef CONFIG_DEBUG_FS
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.
38 static u64 frontswap_loads
;
39 static u64 frontswap_succ_stores
;
40 static u64 frontswap_failed_stores
;
41 static u64 frontswap_invalidates
;
43 static inline void inc_frontswap_loads(void)
45 data_race(frontswap_loads
++);
47 static inline void inc_frontswap_succ_stores(void)
49 data_race(frontswap_succ_stores
++);
51 static inline void inc_frontswap_failed_stores(void)
53 data_race(frontswap_failed_stores
++);
55 static inline void inc_frontswap_invalidates(void)
57 data_race(frontswap_invalidates
++);
60 static inline void inc_frontswap_loads(void) { }
61 static inline void inc_frontswap_succ_stores(void) { }
62 static inline void inc_frontswap_failed_stores(void) { }
63 static inline void inc_frontswap_invalidates(void) { }
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
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.
79 * While no backend is registered all calls to frontswap_[store|load|
80 * invalidate_area|invalidate_page] are ignored or fail.
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
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.
95 * Register operations for frontswap
97 int frontswap_register_ops(const struct frontswap_ops
*ops
)
103 static_branch_inc(&frontswap_enabled_key
);
108 * Called when a swap device is swapon'd.
110 void frontswap_init(unsigned type
, unsigned long *map
)
112 struct swap_info_struct
*sis
= swap_info
[type
];
114 VM_BUG_ON(sis
== NULL
);
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.
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.
127 frontswap_map_set(sis
, map
);
129 if (!frontswap_enabled())
131 frontswap_ops
->init(type
);
134 static bool __frontswap_test(struct swap_info_struct
*sis
,
137 if (sis
->frontswap_map
)
138 return test_bit(offset
, sis
->frontswap_map
);
142 static inline void __frontswap_set(struct swap_info_struct
*sis
,
145 set_bit(offset
, sis
->frontswap_map
);
146 atomic_inc(&sis
->frontswap_pages
);
149 static inline void __frontswap_clear(struct swap_info_struct
*sis
,
152 clear_bit(offset
, sis
->frontswap_map
);
153 atomic_dec(&sis
->frontswap_pages
);
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.
163 int __frontswap_store(struct page
*page
)
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
);
171 VM_BUG_ON(!frontswap_ops
);
172 VM_BUG_ON(!PageLocked(page
));
173 VM_BUG_ON(sis
== NULL
);
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.
181 if (__frontswap_test(sis
, offset
)) {
182 __frontswap_clear(sis
, offset
);
183 frontswap_ops
->invalidate_page(type
, offset
);
186 ret
= frontswap_ops
->store(type
, offset
, page
);
188 __frontswap_set(sis
, offset
);
189 inc_frontswap_succ_stores();
191 inc_frontswap_failed_stores();
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.
202 int __frontswap_load(struct page
*page
)
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
);
210 VM_BUG_ON(!frontswap_ops
);
211 VM_BUG_ON(!PageLocked(page
));
212 VM_BUG_ON(sis
== NULL
);
214 if (!__frontswap_test(sis
, offset
))
217 /* Try loading from each implementation, until one succeeds. */
218 ret
= frontswap_ops
->load(type
, offset
, page
);
220 inc_frontswap_loads();
225 * Invalidate any data from frontswap associated with the specified swaptype
226 * and offset so that a subsequent "get" will fail.
228 void __frontswap_invalidate_page(unsigned type
, pgoff_t offset
)
230 struct swap_info_struct
*sis
= swap_info
[type
];
232 VM_BUG_ON(!frontswap_ops
);
233 VM_BUG_ON(sis
== NULL
);
235 if (!__frontswap_test(sis
, offset
))
238 frontswap_ops
->invalidate_page(type
, offset
);
239 __frontswap_clear(sis
, offset
);
240 inc_frontswap_invalidates();
244 * Invalidate all data from frontswap associated with all offsets for the
245 * specified swaptype.
247 void __frontswap_invalidate_area(unsigned type
)
249 struct swap_info_struct
*sis
= swap_info
[type
];
251 VM_BUG_ON(!frontswap_ops
);
252 VM_BUG_ON(sis
== NULL
);
254 if (sis
->frontswap_map
== NULL
)
257 frontswap_ops
->invalidate_area(type
);
258 atomic_set(&sis
->frontswap_pages
, 0);
259 bitmap_zero(sis
->frontswap_map
, sis
->max
);
262 static int __init
init_frontswap(void)
264 #ifdef CONFIG_DEBUG_FS
265 struct dentry
*root
= debugfs_create_dir("frontswap", NULL
);
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
);
277 module_init(init_frontswap
);