1 #ifndef _LINUX_SHRINKER_H
2 #define _LINUX_SHRINKER_H
5 * This struct is used to pass information from page reclaim to the shrinkers.
6 * We consolidate the values for easier extention later.
8 * The 'gfpmask' refers to the allocation we are currently trying to
11 * Note that 'shrink' will be passed nr_to_scan == 0 when the VM is
12 * querying the cache size, so a fastpath for that case is appropriate.
14 struct shrink_control {
17 /* How many slab objects shrinker() should scan and try to reclaim */
18 unsigned long nr_to_scan;
20 /* shrink from these nodes */
21 nodemask_t nodes_to_scan;
24 #define SHRINK_STOP (~0UL)
26 * A callback you can register to apply pressure to ageable caches.
28 * @shrink() should look through the least-recently-used 'nr_to_scan' entries
29 * and attempt to free them up. It should return the number of objects which
30 * remain in the cache. If it returns -1, it means it cannot do any scanning at
31 * this time (eg. there is a risk of deadlock).
33 * @count_objects should return the number of freeable items in the cache. If
34 * there are no objects to free or the number of freeable items cannot be
35 * determined, it should return 0. No deadlock checks should be done during the
36 * count callback - the shrinker relies on aggregating scan counts that couldn't
37 * be executed due to potential deadlocks to be run at a later call when the
38 * deadlock condition is no longer pending.
40 * @scan_objects will only be called if @count_objects returned a non-zero
41 * value for the number of freeable objects. The callout should scan the cache
42 * and attempt to free items from the cache. It should then return the number
43 * of objects freed during the scan, or SHRINK_STOP if progress cannot be made
44 * due to potential deadlocks. If SHRINK_STOP is returned, then no further
45 * attempts to call the @scan_objects will be made from the current reclaim
49 int (*shrink)(struct shrinker *, struct shrink_control *sc);
50 unsigned long (*count_objects)(struct shrinker *,
51 struct shrink_control *sc);
52 unsigned long (*scan_objects)(struct shrinker *,
53 struct shrink_control *sc);
55 int seeks; /* seeks to recreate an obj */
56 long batch; /* reclaim batch size, 0 = default */
58 /* These are for internal use */
59 struct list_head list;
60 atomic_long_t nr_in_batch; /* objs pending delete */
62 #define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
63 extern void register_shrinker(struct shrinker *);
64 extern void unregister_shrinker(struct shrinker *);