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        /* shrink from these nodes */
  22        nodemask_t nodes_to_scan;
  23        /* current node being shrunk (for NUMA aware shrinkers) */
  24        int nid;
  25};
  26
  27#define SHRINK_STOP (~0UL)
  28/*
  29 * A callback you can register to apply pressure to ageable caches.
  30 *
  31 * @count_objects should return the number of freeable items in the cache. If
  32 * there are no objects to free or the number of freeable items cannot be
  33 * determined, it should return 0. No deadlock checks should be done during the
  34 * count callback - the shrinker relies on aggregating scan counts that couldn't
  35 * be executed due to potential deadlocks to be run at a later call when the
  36 * deadlock condition is no longer pending.
  37 *
  38 * @scan_objects will only be called if @count_objects returned a non-zero
  39 * value for the number of freeable objects. The callout should scan the cache
  40 * and attempt to free items from the cache. It should then return the number
  41 * of objects freed during the scan, or SHRINK_STOP if progress cannot be made
  42 * due to potential deadlocks. If SHRINK_STOP is returned, then no further
  43 * attempts to call the @scan_objects will be made from the current reclaim
  44 * context.
  45 *
  46 * @flags determine the shrinker abilities, like numa awareness
  47 */
  48struct shrinker {
  49        unsigned long (*count_objects)(struct shrinker *,
  50                                       struct shrink_control *sc);
  51        unsigned long (*scan_objects)(struct shrinker *,
  52                                      struct shrink_control *sc);
  53
  54        int seeks;      /* seeks to recreate an obj */
  55        long batch;     /* reclaim batch size, 0 = default */
  56        unsigned long flags;
  57
  58        /* These are for internal use */
  59        struct list_head list;
  60        /* objs pending delete, per node */
  61        atomic_long_t *nr_deferred;
  62};
  63#define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
  64
  65/* Flags */
  66#define SHRINKER_NUMA_AWARE (1 << 0)
  67
  68extern int register_shrinker(struct shrinker *);
  69extern void unregister_shrinker(struct shrinker *);
  70#endif
  71