/* 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;

  	/* 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;

  
  	/* These are for internal use */
  	struct list_head list;

  #ifdef CONFIG_MEMCG

  	/* 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)

  /*
   * 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	(1 << 2)

  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