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1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef _LINUX_SHRINKER_H
3#define _LINUX_SHRINKER_H
4
5#include <linux/atomic.h>
6#include <linux/types.h>
7
8/*
9 * This struct is used to pass information from page reclaim to the shrinkers.
10 * We consolidate the values for easier extension later.
11 *
12 * The 'gfpmask' refers to the allocation we are currently trying to
13 * fulfil.
14 */
15struct shrink_control {
16 gfp_t gfp_mask;
17
18 /* current node being shrunk (for NUMA aware shrinkers) */
19 int nid;
20
21 /*
22 * How many objects scan_objects should scan and try to reclaim.
23 * This is reset before every call, so it is safe for callees
24 * to modify.
25 */
26 unsigned long nr_to_scan;
27
28 /*
29 * How many objects did scan_objects process?
30 * This defaults to nr_to_scan before every call, but the callee
31 * should track its actual progress.
32 */
33 unsigned long nr_scanned;
34
35 /* current memcg being shrunk (for memcg aware shrinkers) */
36 struct mem_cgroup *memcg;
37};
38
39#define SHRINK_STOP (~0UL)
40#define SHRINK_EMPTY (~0UL - 1)
41/*
42 * A callback you can register to apply pressure to ageable caches.
43 *
44 * @count_objects should return the number of freeable items in the cache. If
45 * there are no objects to free, it should return SHRINK_EMPTY, while 0 is
46 * returned in cases of the number of freeable items cannot be determined
47 * or shrinker should skip this cache for this time (e.g., their number
48 * is below shrinkable limit). No deadlock checks should be done during the
49 * count callback - the shrinker relies on aggregating scan counts that couldn't
50 * be executed due to potential deadlocks to be run at a later call when the
51 * deadlock condition is no longer pending.
52 *
53 * @scan_objects will only be called if @count_objects returned a non-zero
54 * value for the number of freeable objects. The callout should scan the cache
55 * and attempt to free items from the cache. It should then return the number
56 * of objects freed during the scan, or SHRINK_STOP if progress cannot be made
57 * due to potential deadlocks. If SHRINK_STOP is returned, then no further
58 * attempts to call the @scan_objects will be made from the current reclaim
59 * context.
60 *
61 * @flags determine the shrinker abilities, like numa awareness
62 */
63struct shrinker {
64 unsigned long (*count_objects)(struct shrinker *,
65 struct shrink_control *sc);
66 unsigned long (*scan_objects)(struct shrinker *,
67 struct shrink_control *sc);
68
69 long batch; /* reclaim batch size, 0 = default */
70 int seeks; /* seeks to recreate an obj */
71 unsigned flags;
72
73 /* These are for internal use */
74 struct list_head list;
75#ifdef CONFIG_MEMCG
76 /* ID in shrinker_idr */
77 int id;
78#endif
79#ifdef CONFIG_SHRINKER_DEBUG
80 int debugfs_id;
81 const char *name;
82 struct dentry *debugfs_entry;
83#endif
84 /* objs pending delete, per node */
85 atomic_long_t *nr_deferred;
86};
87#define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
88
89/* Flags */
90#define SHRINKER_REGISTERED (1 << 0)
91#define SHRINKER_NUMA_AWARE (1 << 1)
92#define SHRINKER_MEMCG_AWARE (1 << 2)
93/*
94 * It just makes sense when the shrinker is also MEMCG_AWARE for now,
95 * non-MEMCG_AWARE shrinker should not have this flag set.
96 */
97#define SHRINKER_NONSLAB (1 << 3)
98
99extern int __printf(2, 3) prealloc_shrinker(struct shrinker *shrinker,
100 const char *fmt, ...);
101extern void register_shrinker_prepared(struct shrinker *shrinker);
102extern int __printf(2, 3) register_shrinker(struct shrinker *shrinker,
103 const char *fmt, ...);
104extern void unregister_shrinker(struct shrinker *shrinker);
105extern void free_prealloced_shrinker(struct shrinker *shrinker);
106extern void synchronize_shrinkers(void);
107
108#ifdef CONFIG_SHRINKER_DEBUG
109extern int shrinker_debugfs_add(struct shrinker *shrinker);
110extern struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker,
111 int *debugfs_id);
112extern void shrinker_debugfs_remove(struct dentry *debugfs_entry,
113 int debugfs_id);
114extern int __printf(2, 3) shrinker_debugfs_rename(struct shrinker *shrinker,
115 const char *fmt, ...);
116#else /* CONFIG_SHRINKER_DEBUG */
117static inline int shrinker_debugfs_add(struct shrinker *shrinker)
118{
119 return 0;
120}
121static inline struct dentry *shrinker_debugfs_detach(struct shrinker *shrinker,
122 int *debugfs_id)
123{
124 *debugfs_id = -1;
125 return NULL;
126}
127static inline void shrinker_debugfs_remove(struct dentry *debugfs_entry,
128 int debugfs_id)
129{
130}
131static inline __printf(2, 3)
132int shrinker_debugfs_rename(struct shrinker *shrinker, const char *fmt, ...)
133{
134 return 0;
135}
136#endif /* CONFIG_SHRINKER_DEBUG */
137#endif /* _LINUX_SHRINKER_H */