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        /* current node being shrunk (for NUMA aware shrinkers) */
  16        int nid;
  17
  18        /*
  19         * How many objects scan_objects should scan and try to reclaim.
  20         * This is reset before every call, so it is safe for callees
  21         * to modify.
  22         */
  23        unsigned long nr_to_scan;
  24
  25        /*
  26         * How many objects did scan_objects process?
  27         * This defaults to nr_to_scan before every call, but the callee
  28         * should track its actual progress.
  29         */
  30        unsigned long nr_scanned;
  31
  32        /* current memcg being shrunk (for memcg aware shrinkers) */
  33        struct mem_cgroup *memcg;
  34};
  35
  36#define SHRINK_STOP (~0UL)
  37#define SHRINK_EMPTY (~0UL - 1)
  38/*
  39 * A callback you can register to apply pressure to ageable caches.
  40 *
  41 * @count_objects should return the number of freeable items in the cache. If
  42 * there are no objects to free, it should return SHRINK_EMPTY, while 0 is
  43 * returned in cases of the number of freeable items cannot be determined
  44 * or shrinker should skip this cache for this time (e.g., their number
  45 * is below shrinkable limit). No deadlock checks should be done during the
  46 * count callback - the shrinker relies on aggregating scan counts that couldn't
  47 * be executed due to potential deadlocks to be run at a later call when the
  48 * deadlock condition is no longer pending.
  49 *
  50 * @scan_objects will only be called if @count_objects returned a non-zero
  51 * value for the number of freeable objects. The callout should scan the cache
  52 * and attempt to free items from the cache. It should then return the number
  53 * of objects freed during the scan, or SHRINK_STOP if progress cannot be made
  54 * due to potential deadlocks. If SHRINK_STOP is returned, then no further
  55 * attempts to call the @scan_objects will be made from the current reclaim
  56 * context.
  57 *
  58 * @flags determine the shrinker abilities, like numa awareness
  59 */
  60struct shrinker {
  61        unsigned long (*count_objects)(struct shrinker *,
  62                                       struct shrink_control *sc);
  63        unsigned long (*scan_objects)(struct shrinker *,
  64                                      struct shrink_control *sc);
  65
  66        long batch;     /* reclaim batch size, 0 = default */
  67        int seeks;      /* seeks to recreate an obj */
  68        unsigned flags;
  69
  70        /* These are for internal use */
  71        struct list_head list;
  72#ifdef CONFIG_MEMCG_KMEM
  73        /* ID in shrinker_idr */
  74        int id;
  75#endif
  76        /* objs pending delete, per node */
  77        atomic_long_t *nr_deferred;
  78};
  79#define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
  80
  81/* Flags */
  82#define SHRINKER_NUMA_AWARE     (1 << 0)
  83#define SHRINKER_MEMCG_AWARE    (1 << 1)
  84
  85extern int prealloc_shrinker(struct shrinker *shrinker);
  86extern void register_shrinker_prepared(struct shrinker *shrinker);
  87extern int register_shrinker(struct shrinker *shrinker);
  88extern void unregister_shrinker(struct shrinker *shrinker);
  89extern void free_prealloced_shrinker(struct shrinker *shrinker);
  90#endif
  91