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 struct shrink_control {
   9         gfp_t gfp_mask;
  10
  11         /* How many slab objects shrinker() should scan and try to reclaim */
  12         unsigned long nr_to_scan;
  13 };
  14
  15 /*
  16  * A callback you can register to apply pressure to ageable caches.
  17  *
  18  * 'sc' is passed shrink_control which includes a count 'nr_to_scan'
  19  * and a 'gfpmask'.  It should look through the least-recently-used
  20  * 'nr_to_scan' entries and attempt to free them up.  It should return
  21  * the number of objects which remain in the cache.  If it returns -1, it means
  22  * it cannot do any scanning at this time (eg. there is a risk of deadlock).
  23  * The callback must not return -1 if nr_to_scan is zero.
  24  *
  25  * The 'gfpmask' refers to the allocation we are currently trying to
  26  * fulfil.
  27  *
  28  * Note that 'shrink' will be passed nr_to_scan == 0 when the VM is
  29  * querying the cache size, so a fastpath for that case is appropriate.
  30  */
  31 struct shrinker {
  32         int (*shrink)(struct shrinker *, struct shrink_control *sc);
  33         int seeks;      /* seeks to recreate an obj */
  34         long batch;     /* reclaim batch size, 0 = default */
  35
  36         /* These are for internal use */
  37         struct list_head list;
  38         atomic_long_t nr_in_batch; /* objs pending delete */
  39 };
  40 #define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
  41 extern void register_shrinker(struct shrinker *);
  42 extern void unregister_shrinker(struct shrinker *);
  43 #endif