shrinker.h

  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#include <linux/refcount.h>
  8#include <linux/completion.h>
  9
 10#define SHRINKER_UNIT_BITS	BITS_PER_LONG
 11
 12/*
 13 * Bitmap and deferred work of shrinker::id corresponding to memcg-aware
 14 * shrinkers, which have elements charged to the memcg.
 15 */
 16struct shrinker_info_unit {
 17	atomic_long_t nr_deferred[SHRINKER_UNIT_BITS];
 18	DECLARE_BITMAP(map, SHRINKER_UNIT_BITS);
 19};
 20
 21struct shrinker_info {
 22	struct rcu_head rcu;
 23	int map_nr_max;
 24	struct shrinker_info_unit *unit[];
 25};
 26
 27/*
 28 * This struct is used to pass information from page reclaim to the shrinkers.
 29 * We consolidate the values for easier extension later.
 30 *
 31 * The 'gfpmask' refers to the allocation we are currently trying to
 32 * fulfil.
 33 */
 34struct shrink_control {
 35	gfp_t gfp_mask;
 36
 37	/* current node being shrunk (for NUMA aware shrinkers) */
 38	int nid;
 39
 40	/*
 41	 * How many objects scan_objects should scan and try to reclaim.
 42	 * This is reset before every call, so it is safe for callees
 43	 * to modify.
 44	 */
 45	unsigned long nr_to_scan;
 46
 47	/*
 48	 * How many objects did scan_objects process?
 49	 * This defaults to nr_to_scan before every call, but the callee
 50	 * should track its actual progress.
 51	 */
 52	unsigned long nr_scanned;
 53
 54	/* current memcg being shrunk (for memcg aware shrinkers) */
 55	struct mem_cgroup *memcg;
 56};
 57
 58#define SHRINK_STOP (~0UL)
 59#define SHRINK_EMPTY (~0UL - 1)
 60/*
 61 * A callback you can register to apply pressure to ageable caches.
 62 *
 63 * @count_objects should return the number of freeable items in the cache. If
 64 * there are no objects to free, it should return SHRINK_EMPTY, while 0 is
 65 * returned in cases of the number of freeable items cannot be determined
 66 * or shrinker should skip this cache for this time (e.g., their number
 67 * is below shrinkable limit). No deadlock checks should be done during the
 68 * count callback - the shrinker relies on aggregating scan counts that couldn't
 69 * be executed due to potential deadlocks to be run at a later call when the
 70 * deadlock condition is no longer pending.
 71 *
 72 * @scan_objects will only be called if @count_objects returned a non-zero
 73 * value for the number of freeable objects. The callout should scan the cache
 74 * and attempt to free items from the cache. It should then return the number
 75 * of objects freed during the scan, or SHRINK_STOP if progress cannot be made
 76 * due to potential deadlocks. If SHRINK_STOP is returned, then no further
 77 * attempts to call the @scan_objects will be made from the current reclaim
 78 * context.
 79 *
 80 * @flags determine the shrinker abilities, like numa awareness
 81 */
 82struct shrinker {
 83	unsigned long (*count_objects)(struct shrinker *,
 84				       struct shrink_control *sc);
 85	unsigned long (*scan_objects)(struct shrinker *,
 86				      struct shrink_control *sc);
 87
 88	long batch;	/* reclaim batch size, 0 = default */
 89	int seeks;	/* seeks to recreate an obj */
 90	unsigned flags;
 91
 92	/*
 93	 * The reference count of this shrinker. Registered shrinker have an
 94	 * initial refcount of 1, then the lookup operations are now allowed
 95	 * to use it via shrinker_try_get(). Later in the unregistration step,
 96	 * the initial refcount will be discarded, and will free the shrinker
 97	 * asynchronously via RCU after its refcount reaches 0.
 98	 */
 99	refcount_t refcount;
100	struct completion done;	/* use to wait for refcount to reach 0 */
101	struct rcu_head rcu;
102
103	void *private_data;
104
105	/* These are for internal use */
106	struct list_head list;
107#ifdef CONFIG_MEMCG
108	/* ID in shrinker_idr */
109	int id;
110#endif
111#ifdef CONFIG_SHRINKER_DEBUG
112	int debugfs_id;
113	const char *name;
114	struct dentry *debugfs_entry;
115#endif
116	/* objs pending delete, per node */
117	atomic_long_t *nr_deferred;
118};
119#define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
120
121/* Internal flags */
122#define SHRINKER_REGISTERED	BIT(0)
123#define SHRINKER_ALLOCATED	BIT(1)
124
125/* Flags for users to use */
126#define SHRINKER_NUMA_AWARE	BIT(2)
127#define SHRINKER_MEMCG_AWARE	BIT(3)
128/*
129 * It just makes sense when the shrinker is also MEMCG_AWARE for now,
130 * non-MEMCG_AWARE shrinker should not have this flag set.
131 */
132#define SHRINKER_NONSLAB	BIT(4)
133
134__printf(2, 3)
135struct shrinker *shrinker_alloc(unsigned int flags, const char *fmt, ...);
136void shrinker_register(struct shrinker *shrinker);
137void shrinker_free(struct shrinker *shrinker);
138
139static inline bool shrinker_try_get(struct shrinker *shrinker)
140{
141	return refcount_inc_not_zero(&shrinker->refcount);
142}
143
144static inline void shrinker_put(struct shrinker *shrinker)
145{
146	if (refcount_dec_and_test(&shrinker->refcount))
147		complete(&shrinker->done);
148}
149
150#ifdef CONFIG_SHRINKER_DEBUG
151extern int __printf(2, 3) shrinker_debugfs_rename(struct shrinker *shrinker,
152						  const char *fmt, ...);
153#else /* CONFIG_SHRINKER_DEBUG */
154static inline __printf(2, 3)
155int shrinker_debugfs_rename(struct shrinker *shrinker, const char *fmt, ...)
156{
157	return 0;
158}
159#endif /* CONFIG_SHRINKER_DEBUG */
160#endif /* _LINUX_SHRINKER_H */