1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef _LINUX_SHRINKER_H
3#define _LINUX_SHRINKER_H
4
5/*
6 * This struct is used to pass information from page reclaim to the shrinkers.
7 * We consolidate the values for easier extention later.
8 *
9 * The 'gfpmask' refers to the allocation we are currently trying to
10 * fulfil.
11 */
12struct shrink_control {
13 gfp_t gfp_mask;
14
15 /* current node being shrunk (for NUMA aware shrinkers) */
16 int nid;
17
18 /*
19 * How many objects scan_objects should scan and try to reclaim.
20 * This is reset before every call, so it is safe for callees
21 * to modify.
22 */
23 unsigned long nr_to_scan;
24
25 /*
26 * How many objects did scan_objects process?
27 * This defaults to nr_to_scan before every call, but the callee
28 * should track its actual progress.
29 */
30 unsigned long nr_scanned;
31
32 /* current memcg being shrunk (for memcg aware shrinkers) */
33 struct mem_cgroup *memcg;
34};
35
36#define SHRINK_STOP (~0UL)
37#define SHRINK_EMPTY (~0UL - 1)
38/*
39 * A callback you can register to apply pressure to ageable caches.
40 *
41 * @count_objects should return the number of freeable items in the cache. If
42 * there are no objects to free, it should return SHRINK_EMPTY, while 0 is
43 * returned in cases of the number of freeable items cannot be determined
44 * or shrinker should skip this cache for this time (e.g., their number
45 * is below shrinkable limit). No deadlock checks should be done during the
46 * count callback - the shrinker relies on aggregating scan counts that couldn't
47 * be executed due to potential deadlocks to be run at a later call when the
48 * deadlock condition is no longer pending.
49 *
50 * @scan_objects will only be called if @count_objects returned a non-zero
51 * value for the number of freeable objects. The callout should scan the cache
52 * and attempt to free items from the cache. It should then return the number
53 * of objects freed during the scan, or SHRINK_STOP if progress cannot be made
54 * due to potential deadlocks. If SHRINK_STOP is returned, then no further
55 * attempts to call the @scan_objects will be made from the current reclaim
56 * context.
57 *
58 * @flags determine the shrinker abilities, like numa awareness
59 */
60struct shrinker {
61 unsigned long (*count_objects)(struct shrinker *,
62 struct shrink_control *sc);
63 unsigned long (*scan_objects)(struct shrinker *,
64 struct shrink_control *sc);
65
66 long batch; /* reclaim batch size, 0 = default */
67 int seeks; /* seeks to recreate an obj */
68 unsigned flags;
69
70 /* These are for internal use */
71 struct list_head list;
72#ifdef CONFIG_MEMCG_KMEM
73 /* ID in shrinker_idr */
74 int id;
75#endif
76 /* objs pending delete, per node */
77 atomic_long_t *nr_deferred;
78};
79#define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
80
81/* Flags */
82#define SHRINKER_NUMA_AWARE (1 << 0)
83#define SHRINKER_MEMCG_AWARE (1 << 1)
84
85extern int prealloc_shrinker(struct shrinker *shrinker);
86extern void register_shrinker_prepared(struct shrinker *shrinker);
87extern int register_shrinker(struct shrinker *shrinker);
88extern void unregister_shrinker(struct shrinker *shrinker);
89extern void free_prealloced_shrinker(struct shrinker *shrinker);
90#endif
91