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