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/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_SHRINKER_H
#define _LINUX_SHRINKER_H
#include <linux/atomic.h>
#include <linux/types.h>
#include <linux/refcount.h>
#include <linux/completion.h>
#define SHRINKER_UNIT_BITS BITS_PER_LONG
/*
* Bitmap and deferred work of shrinker::id corresponding to memcg-aware
* shrinkers, which have elements charged to the memcg.
*/
struct shrinker_info_unit {
atomic_long_t nr_deferred[SHRINKER_UNIT_BITS];
DECLARE_BITMAP(map, SHRINKER_UNIT_BITS);
};
struct shrinker_info {
struct rcu_head rcu;
int map_nr_max;
struct shrinker_info_unit *unit[];
};
/*
* This struct is used to pass information from page reclaim to the shrinkers.
* We consolidate the values for easier extension later.
*
* The 'gfpmask' refers to the allocation we are currently trying to
* fulfil.
*/
struct shrink_control {
gfp_t gfp_mask;
/* current node being shrunk (for NUMA aware shrinkers) */
int nid;
/*
* How many objects scan_objects should scan and try to reclaim.
* This is reset before every call, so it is safe for callees
* to modify.
*/
unsigned long nr_to_scan;
/*
* How many objects did scan_objects process?
* This defaults to nr_to_scan before every call, but the callee
* should track its actual progress.
*/
unsigned long nr_scanned;
/* current memcg being shrunk (for memcg aware shrinkers) */
struct mem_cgroup *memcg;
};
#define SHRINK_STOP (~0UL)
#define SHRINK_EMPTY (~0UL - 1)
/*
* A callback you can register to apply pressure to ageable caches.
*
* @count_objects should return the number of freeable items in the cache. If
* there are no objects to free, it should return SHRINK_EMPTY, while 0 is
* returned in cases of the number of freeable items cannot be determined
* or shrinker should skip this cache for this time (e.g., their number
* is below shrinkable limit). No deadlock checks should be done during the
* count callback - the shrinker relies on aggregating scan counts that couldn't
* be executed due to potential deadlocks to be run at a later call when the
* deadlock condition is no longer pending.
*
* @scan_objects will only be called if @count_objects returned a non-zero
* value for the number of freeable objects. The callout should scan the cache
* and attempt to free items from the cache. It should then return the number
* of objects freed during the scan, or SHRINK_STOP if progress cannot be made
* due to potential deadlocks. If SHRINK_STOP is returned, then no further
* attempts to call the @scan_objects will be made from the current reclaim
* context.
*
* @flags determine the shrinker abilities, like numa awareness
*/
struct shrinker {
unsigned long (*count_objects)(struct shrinker *,
struct shrink_control *sc);
unsigned long (*scan_objects)(struct shrinker *,
struct shrink_control *sc);
long batch; /* reclaim batch size, 0 = default */
int seeks; /* seeks to recreate an obj */
unsigned flags;
/*
* The reference count of this shrinker. Registered shrinker have an
* initial refcount of 1, then the lookup operations are now allowed
* to use it via shrinker_try_get(). Later in the unregistration step,
* the initial refcount will be discarded, and will free the shrinker
* asynchronously via RCU after its refcount reaches 0.
*/
refcount_t refcount;
struct completion done; /* use to wait for refcount to reach 0 */
struct rcu_head rcu;
void *private_data;
/* These are for internal use */
struct list_head list;
#ifdef CONFIG_MEMCG
/* ID in shrinker_idr */
int id;
#endif
#ifdef CONFIG_SHRINKER_DEBUG
int debugfs_id;
const char *name;
struct dentry *debugfs_entry;
#endif
/* objs pending delete, per node */
atomic_long_t *nr_deferred;
};
#define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
/* Internal flags */
#define SHRINKER_REGISTERED BIT(0)
#define SHRINKER_ALLOCATED BIT(1)
/* Flags for users to use */
#define SHRINKER_NUMA_AWARE BIT(2)
#define SHRINKER_MEMCG_AWARE BIT(3)
/*
* It just makes sense when the shrinker is also MEMCG_AWARE for now,
* non-MEMCG_AWARE shrinker should not have this flag set.
*/
#define SHRINKER_NONSLAB BIT(4)
__printf(2, 3)
struct shrinker *shrinker_alloc(unsigned int flags, const char *fmt, ...);
void shrinker_register(struct shrinker *shrinker);
void shrinker_free(struct shrinker *shrinker);
static inline bool shrinker_try_get(struct shrinker *shrinker)
{
return refcount_inc_not_zero(&shrinker->refcount);
}
static inline void shrinker_put(struct shrinker *shrinker)
{
if (refcount_dec_and_test(&shrinker->refcount))
complete(&shrinker->done);
}
#ifdef CONFIG_SHRINKER_DEBUG
extern int __printf(2, 3) shrinker_debugfs_rename(struct shrinker *shrinker,
const char *fmt, ...);
#else /* CONFIG_SHRINKER_DEBUG */
static inline __printf(2, 3)
int shrinker_debugfs_rename(struct shrinker *shrinker, const char *fmt, ...)
{
return 0;
}
#endif /* CONFIG_SHRINKER_DEBUG */
#endif /* _LINUX_SHRINKER_H */