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