linux/include/linux/shrinker.h

/* 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 …

/*
 * Bitmap and deferred work of shrinker::id corresponding to memcg-aware
 * shrinkers, which have elements charged to the memcg.
 */
struct shrinker_info_unit { … };

struct shrinker_info { … };

/*
 * 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 { … };

#define SHRINK_STOP …
#define SHRINK_EMPTY …
/*
 * 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 { … };
#define DEFAULT_SEEKS …

/* Internal flags */
#define SHRINKER_REGISTERED …
#define SHRINKER_ALLOCATED …

/* Flags for users to use */
#define SHRINKER_NUMA_AWARE …
#define SHRINKER_MEMCG_AWARE …
/*
 * 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 …

__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)
{ … }

static inline void shrinker_put(struct shrinker *shrinker)
{ … }

#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 */