LXR linux/include/linux/shrinker.h

   1/* SPDX-License-Identifier: GPL-2.0 */
   2#ifndef _LINUX_SHRINKER_H
   3#define _LINUX_SHRINKER_H
   4
   5/*
   6 * This struct is used to pass information from page reclaim to the shrinkers.
   7 * We consolidate the values for easier extention later.
   8 *
   9 * The 'gfpmask' refers to the allocation we are currently trying to
  10 * fulfil.
  11 */
  12struct shrink_control {
  13        gfp_t gfp_mask;
  14
  15        /*
  16         * How many objects scan_objects should scan and try to reclaim.
  17         * This is reset before every call, so it is safe for callees
  18         * to modify.
  19         */
  20        unsigned long nr_to_scan;
  21
  22        /*
  23         * How many objects did scan_objects process?
  24         * This defaults to nr_to_scan before every call, but the callee
  25         * should track its actual progress.
  26         */
  27        unsigned long nr_scanned;
  28
  29        /* current node being shrunk (for NUMA aware shrinkers) */
  30        int nid;
  31
  32        /* current memcg being shrunk (for memcg aware shrinkers) */
  33        struct mem_cgroup *memcg;
  34};
  35
  36#define SHRINK_STOP (~0UL)
  37/*
  38 * A callback you can register to apply pressure to ageable caches.
  39 *
  40 * @count_objects should return the number of freeable items in the cache. If
  41 * there are no objects to free or the number of freeable items cannot be
  42 * determined, it should return 0. No deadlock checks should be done during the
  43 * count callback - the shrinker relies on aggregating scan counts that couldn't
  44 * be executed due to potential deadlocks to be run at a later call when the
  45 * deadlock condition is no longer pending.
  46 *
  47 * @scan_objects will only be called if @count_objects returned a non-zero
  48 * value for the number of freeable objects. The callout should scan the cache
  49 * and attempt to free items from the cache. It should then return the number
  50 * of objects freed during the scan, or SHRINK_STOP if progress cannot be made
  51 * due to potential deadlocks. If SHRINK_STOP is returned, then no further
  52 * attempts to call the @scan_objects will be made from the current reclaim
  53 * context.
  54 *
  55 * @flags determine the shrinker abilities, like numa awareness
  56 */
  57struct shrinker {
  58        unsigned long (*count_objects)(struct shrinker *,
  59                                       struct shrink_control *sc);
  60        unsigned long (*scan_objects)(struct shrinker *,
  61                                      struct shrink_control *sc);
  62
  63        int seeks;      /* seeks to recreate an obj */
  64        long batch;     /* reclaim batch size, 0 = default */
  65        unsigned long flags;
  66
  67        /* These are for internal use */
  68        struct list_head list;
  69        /* objs pending delete, per node */
  70        atomic_long_t *nr_deferred;
  71};
  72#define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
  73
  74/* Flags */
  75#define SHRINKER_NUMA_AWARE     (1 << 0)
  76#define SHRINKER_MEMCG_AWARE    (1 << 1)
  77
  78extern int register_shrinker(struct shrinker *);
  79extern void unregister_shrinker(struct shrinker *);
  80#endif
  81