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 /*
22 * How many objects did scan_objects process?
23 * This defaults to nr_to_scan before every call, but the callee
24 * should track its actual progress.
25 */
26 unsigned long nr_scanned;
27
28 /* current node being shrunk (for NUMA aware shrinkers) */
29 int nid;
30
31 /* current memcg being shrunk (for memcg aware shrinkers) */
32 struct mem_cgroup *memcg;
33};
34
35#define SHRINK_STOP (~0UL)
36/*
37 * A callback you can register to apply pressure to ageable caches.
38 *
39 * @count_objects should return the number of freeable items in the cache. If
40 * there are no objects to free or the number of freeable items cannot be
41 * determined, it should return 0. No deadlock checks should be done during the
42 * count callback - the shrinker relies on aggregating scan counts that couldn't
43 * be executed due to potential deadlocks to be run at a later call when the
44 * deadlock condition is no longer pending.
45 *
46 * @scan_objects will only be called if @count_objects returned a non-zero
47 * value for the number of freeable objects. The callout should scan the cache
48 * and attempt to free items from the cache. It should then return the number
49 * of objects freed during the scan, or SHRINK_STOP if progress cannot be made
50 * due to potential deadlocks. If SHRINK_STOP is returned, then no further
51 * attempts to call the @scan_objects will be made from the current reclaim
52 * context.
53 *
54 * @flags determine the shrinker abilities, like numa awareness
55 */
56struct shrinker {
57 unsigned long (*count_objects)(struct shrinker *,
58 struct shrink_control *sc);
59 unsigned long (*scan_objects)(struct shrinker *,
60 struct shrink_control *sc);
61
62 int seeks; /* seeks to recreate an obj */
63 long batch; /* reclaim batch size, 0 = default */
64 unsigned long flags;
65
66 /* These are for internal use */
67 struct list_head list;
68 /* objs pending delete, per node */
69 atomic_long_t *nr_deferred;
70};
71#define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
72
73/* Flags */
74#define SHRINKER_NUMA_AWARE (1 << 0)
75#define SHRINKER_MEMCG_AWARE (1 << 1)
76
77extern int register_shrinker(struct shrinker *);
78extern void unregister_shrinker(struct shrinker *);
79#endif