LXR linux/include/linux/shrinker.h

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