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  */
  11 struct 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  */
  49 struct 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
  70 extern int register_shrinker(struct shrinker *);
  71 extern void unregister_shrinker(struct shrinker *);
  72 #endif