Linux kernel mirror (for testing)
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linux
1#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.
7 *
8 * The 'gfpmask' refers to the allocation we are currently trying to
9 * fulfil.
10 */
11struct shrink_control {
12 gfp_t gfp_mask;
13
14 /*
15 * How many objects scan_objects should scan and try to reclaim.
16 * This is reset before every call, so it is safe for callees
17 * to modify.
18 */
19 unsigned long nr_to_scan;
20
21 /* current node being shrunk (for NUMA aware shrinkers) */
22 int nid;
23};
24
25#define SHRINK_STOP (~0UL)
26/*
27 * A callback you can register to apply pressure to ageable caches.
28 *
29 * @count_objects should return the number of freeable items in the cache. If
30 * there are no objects to free or the number of freeable items cannot be
31 * determined, it should return 0. No deadlock checks should be done during the
32 * count callback - the shrinker relies on aggregating scan counts that couldn't
33 * be executed due to potential deadlocks to be run at a later call when the
34 * deadlock condition is no longer pending.
35 *
36 * @scan_objects will only be called if @count_objects returned a non-zero
37 * value for the number of freeable objects. The callout should scan the cache
38 * and attempt to free items from the cache. It should then return the number
39 * of objects freed during the scan, or SHRINK_STOP if progress cannot be made
40 * due to potential deadlocks. If SHRINK_STOP is returned, then no further
41 * attempts to call the @scan_objects will be made from the current reclaim
42 * context.
43 *
44 * @flags determine the shrinker abilities, like numa awareness
45 */
46struct shrinker {
47 unsigned long (*count_objects)(struct shrinker *,
48 struct shrink_control *sc);
49 unsigned long (*scan_objects)(struct shrinker *,
50 struct shrink_control *sc);
51
52 int seeks; /* seeks to recreate an obj */
53 long batch; /* reclaim batch size, 0 = default */
54 unsigned long flags;
55
56 /* These are for internal use */
57 struct list_head list;
58 /* objs pending delete, per node */
59 atomic_long_t *nr_deferred;
60};
61#define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
62
63/* Flags */
64#define SHRINKER_NUMA_AWARE (1 << 0)
65
66extern int register_shrinker(struct shrinker *);
67extern void unregister_shrinker(struct shrinker *);
68#endif