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         /*
  22          * How many objects did scan_objects process?
  23          * This defaults to nr_to_scan before every call, but the callee
  24          * should track its actual progress.
  25          */
  26         unsigned long nr_scanned;
  27
  28         /* current node being shrunk (for NUMA aware shrinkers) */
  29         int nid;
  30
  31         /* current memcg being shrunk (for memcg aware shrinkers) */
  32         struct mem_cgroup *memcg;
  33 };
  34
  35 #define SHRINK_STOP (~0UL)
  36 /*
  37  * A callback you can register to apply pressure to ageable caches.
  38  *
  39  * @count_objects should return the number of freeable items in the cache. If
  40  * there are no objects to free or the number of freeable items cannot be
  41  * determined, it should return 0. No deadlock checks should be done during the
  42  * count callback - the shrinker relies on aggregating scan counts that couldn't
  43  * be executed due to potential deadlocks to be run at a later call when the
  44  * deadlock condition is no longer pending.
  45  *
  46  * @scan_objects will only be called if @count_objects returned a non-zero
  47  * value for the number of freeable objects. The callout should scan the cache
  48  * and attempt to free items from the cache. It should then return the number
  49  * of objects freed during the scan, or SHRINK_STOP if progress cannot be made
  50  * due to potential deadlocks. If SHRINK_STOP is returned, then no further
  51  * attempts to call the @scan_objects will be made from the current reclaim
  52  * context.
  53  *
  54  * @flags determine the shrinker abilities, like numa awareness
  55  */
  56 struct shrinker {
  57         unsigned long (*count_objects)(struct shrinker *,
  58                                        struct shrink_control *sc);
  59         unsigned long (*scan_objects)(struct shrinker *,
  60                                       struct shrink_control *sc);
  61
  62         int seeks;      /* seeks to recreate an obj */
  63         long batch;     /* reclaim batch size, 0 = default */
  64         unsigned long flags;
  65
  66         /* These are for internal use */
  67         struct list_head list;
  68         /* objs pending delete, per node */
  69         atomic_long_t *nr_deferred;
  70 };
  71 #define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
  72
  73 /* Flags */
  74 #define SHRINKER_NUMA_AWARE     (1 << 0)
  75 #define SHRINKER_MEMCG_AWARE    (1 << 1)
  76
  77 extern int register_shrinker(struct shrinker *);
  78 extern void unregister_shrinker(struct shrinker *);
  79 #endif