1 /* SPDX-License-Identifier: GPL-2.0 */ 2 #ifndef _LINUX_SHRINKER_H 3 #define _LINUX_SHRINKER_H 4 5 /* 6 * This struct is used to pass information from page reclaim to the shrinkers. 7 * We consolidate the values for easier extention later. 8 * 9 * The 'gfpmask' refers to the allocation we are currently trying to 10 * fulfil. 11 */ 12 struct shrink_control { 13 gfp_t gfp_mask; 14 15 /* 16 * How many objects scan_objects should scan and try to reclaim. 17 * This is reset before every call, so it is safe for callees 18 * to modify. 19 */ 20 unsigned long nr_to_scan; 21 22 /* 23 * How many objects did scan_objects process? 24 * This defaults to nr_to_scan before every call, but the callee 25 * should track its actual progress. 26 */ 27 unsigned long nr_scanned; 28 29 /* current node being shrunk (for NUMA aware shrinkers) */ 30 int nid; 31 32 /* current memcg being shrunk (for memcg aware shrinkers) */ 33 struct mem_cgroup *memcg; 34 }; 35 36 #define SHRINK_STOP (~0UL) 37 /* 38 * A callback you can register to apply pressure to ageable caches. 39 * 40 * @count_objects should return the number of freeable items in the cache. If 41 * there are no objects to free or the number of freeable items cannot be 42 * determined, it should return 0. No deadlock checks should be done during the 43 * count callback - the shrinker relies on aggregating scan counts that couldn't 44 * be executed due to potential deadlocks to be run at a later call when the 45 * deadlock condition is no longer pending. 46 * 47 * @scan_objects will only be called if @count_objects returned a non-zero 48 * value for the number of freeable objects. The callout should scan the cache 49 * and attempt to free items from the cache. It should then return the number 50 * of objects freed during the scan, or SHRINK_STOP if progress cannot be made 51 * due to potential deadlocks. If SHRINK_STOP is returned, then no further 52 * attempts to call the @scan_objects will be made from the current reclaim 53 * context. 54 * 55 * @flags determine the shrinker abilities, like numa awareness 56 */ 57 struct shrinker { 58 unsigned long (*count_objects)(struct shrinker *, 59 struct shrink_control *sc); 60 unsigned long (*scan_objects)(struct shrinker *, 61 struct shrink_control *sc); 62 63 int seeks; /* seeks to recreate an obj */ 64 long batch; /* reclaim batch size, 0 = default */ 65 unsigned long flags; 66 67 /* These are for internal use */ 68 struct list_head list; 69 /* objs pending delete, per node */ 70 atomic_long_t *nr_deferred; 71 }; 72 #define DEFAULT_SEEKS 2 /* A good number if you don't know better. */ 73 74 /* Flags */ 75 #define SHRINKER_NUMA_AWARE (1 << 0) 76 #define SHRINKER_MEMCG_AWARE (1 << 1) 77 78 extern int prealloc_shrinker(struct shrinker *shrinker); 79 extern void register_shrinker_prepared(struct shrinker *shrinker); 80 extern int register_shrinker(struct shrinker *shrinker); 81 extern void unregister_shrinker(struct shrinker *shrinker); 82 extern void free_prealloced_shrinker(struct shrinker *shrinker); 83 #endif 84