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Dave Chinnerb0d40c92011-07-08 14:14:42 +10001#ifndef _LINUX_SHRINKER_H
2#define _LINUX_SHRINKER_H
3
4/*
5 * This struct is used to pass information from page reclaim to the shrinkers.
6 * We consolidate the values for easier extention later.
Dave Chinner24f7c6b2013-08-28 10:17:56 +10007 *
8 * The 'gfpmask' refers to the allocation we are currently trying to
9 * fulfil.
10 *
11 * Note that 'shrink' will be passed nr_to_scan == 0 when the VM is
12 * querying the cache size, so a fastpath for that case is appropriate.
Dave Chinnerb0d40c92011-07-08 14:14:42 +100013 */
14struct shrink_control {
15 gfp_t gfp_mask;
16
17 /* How many slab objects shrinker() should scan and try to reclaim */
18 unsigned long nr_to_scan;
19};
20
Dave Chinner24f7c6b2013-08-28 10:17:56 +100021#define SHRINK_STOP (~0UL)
Dave Chinnerb0d40c92011-07-08 14:14:42 +100022/*
23 * A callback you can register to apply pressure to ageable caches.
24 *
Dave Chinner24f7c6b2013-08-28 10:17:56 +100025 * @shrink() should look through the least-recently-used 'nr_to_scan' entries
26 * and attempt to free them up. It should return the number of objects which
27 * remain in the cache. If it returns -1, it means it cannot do any scanning at
28 * this time (eg. there is a risk of deadlock).
Dave Chinnerb0d40c92011-07-08 14:14:42 +100029 *
Dave Chinner24f7c6b2013-08-28 10:17:56 +100030 * @count_objects should return the number of freeable items in the cache. If
31 * there are no objects to free or the number of freeable items cannot be
32 * determined, it should return 0. No deadlock checks should be done during the
33 * count callback - the shrinker relies on aggregating scan counts that couldn't
34 * be executed due to potential deadlocks to be run at a later call when the
35 * deadlock condition is no longer pending.
Dave Chinnerb0d40c92011-07-08 14:14:42 +100036 *
Dave Chinner24f7c6b2013-08-28 10:17:56 +100037 * @scan_objects will only be called if @count_objects returned a non-zero
38 * value for the number of freeable objects. The callout should scan the cache
39 * and attempt to free items from the cache. It should then return the number
40 * of objects freed during the scan, or SHRINK_STOP if progress cannot be made
41 * due to potential deadlocks. If SHRINK_STOP is returned, then no further
42 * attempts to call the @scan_objects will be made from the current reclaim
43 * context.
Dave Chinnerb0d40c92011-07-08 14:14:42 +100044 */
45struct shrinker {
46 int (*shrink)(struct shrinker *, struct shrink_control *sc);
Dave Chinner24f7c6b2013-08-28 10:17:56 +100047 unsigned long (*count_objects)(struct shrinker *,
48 struct shrink_control *sc);
49 unsigned long (*scan_objects)(struct shrinker *,
50 struct shrink_control *sc);
51
Dave Chinnerb0d40c92011-07-08 14:14:42 +100052 int seeks; /* seeks to recreate an obj */
53 long batch; /* reclaim batch size, 0 = default */
54
55 /* These are for internal use */
56 struct list_head list;
Konstantin Khlebnikov83aeead2011-12-08 14:33:54 -080057 atomic_long_t nr_in_batch; /* objs pending delete */
Dave Chinnerb0d40c92011-07-08 14:14:42 +100058};
59#define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
60extern void register_shrinker(struct shrinker *);
61extern void unregister_shrinker(struct shrinker *);
62#endif