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/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_SHRINKER_H
#define _LINUX_SHRINKER_H
/*
* This struct is used to pass information from page reclaim to the shrinkers.
* We consolidate the values for easier extention later.
*
* The 'gfpmask' refers to the allocation we are currently trying to
* fulfil.
*/
struct shrink_control {
gfp_t gfp_mask;
/*
* 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 node being shrunk (for NUMA aware shrinkers) */
int nid;
/* 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);
int seeks; /* seeks to recreate an obj */
long batch; /* reclaim batch size, 0 = default */
unsigned long flags;
/* These are for internal use */
struct list_head list;
#ifdef CONFIG_MEMCG_KMEM
/* ID in shrinker_idr */
int id;
#endif
/* objs pending delete, per node */
atomic_long_t *nr_deferred;
};
#define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
/* Flags */
#define SHRINKER_NUMA_AWARE (1 << 0)
#define SHRINKER_MEMCG_AWARE (1 << 1)
extern int prealloc_shrinker(struct shrinker *shrinker);
extern void register_shrinker_prepared(struct shrinker *shrinker);
extern int register_shrinker(struct shrinker *shrinker);
extern void unregister_shrinker(struct shrinker *shrinker);
extern void free_prealloced_shrinker(struct shrinker *shrinker);
#endif
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