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
;
22 /* current node being shrunk (for NUMA aware shrinkers) */
26 #define SHRINK_STOP (~0UL)
28 * A callback you can register to apply pressure to ageable caches.
30 * @shrink() should look through the least-recently-used 'nr_to_scan' entries
31 * and attempt to free them up. It should return the number of objects which
32 * remain in the cache. If it returns -1, it means it cannot do any scanning at
33 * this time (eg. there is a risk of deadlock).
35 * @count_objects should return the number of freeable items in the cache. If
36 * there are no objects to free or the number of freeable items cannot be
37 * determined, it should return 0. No deadlock checks should be done during the
38 * count callback - the shrinker relies on aggregating scan counts that couldn't
39 * be executed due to potential deadlocks to be run at a later call when the
40 * deadlock condition is no longer pending.
42 * @scan_objects will only be called if @count_objects returned a non-zero
43 * value for the number of freeable objects. The callout should scan the cache
44 * and attempt to free items from the cache. It should then return the number
45 * of objects freed during the scan, or SHRINK_STOP if progress cannot be made
46 * due to potential deadlocks. If SHRINK_STOP is returned, then no further
47 * attempts to call the @scan_objects will be made from the current reclaim
50 * @flags determine the shrinker abilities, like numa awareness
53 int (*shrink
)(struct shrinker
*, struct shrink_control
*sc
);
54 unsigned long (*count_objects
)(struct shrinker
*,
55 struct shrink_control
*sc
);
56 unsigned long (*scan_objects
)(struct shrinker
*,
57 struct shrink_control
*sc
);
59 int seeks
; /* seeks to recreate an obj */
60 long batch
; /* reclaim batch size, 0 = default */
63 /* These are for internal use */
64 struct list_head list
;
65 /* objs pending delete, per node */
66 atomic_long_t
*nr_deferred
;
68 #define DEFAULT_SEEKS 2 /* A good number if you don't know better. */
71 #define SHRINKER_NUMA_AWARE (1 << 0)
73 extern int register_shrinker(struct shrinker
*);
74 extern void unregister_shrinker(struct shrinker
*);
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