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         /* 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  */
  48 struct 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
  68 extern int register_shrinker(struct shrinker *);
  69 extern void unregister_shrinker(struct shrinker *);
  70 #endif