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  */
  12 struct 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  */
  57 struct 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
  78 extern int register_shrinker(struct shrinker *);
  79 extern void unregister_shrinker(struct shrinker *);
  80 #endif