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 /* current node being shrunk (for NUMA aware shrinkers) */ 16 int nid; 17 18 /* 19 * How many objects scan_objects should scan and try to reclaim. 20 * This is reset before every call, so it is safe for callees 21 * to modify. 22 */ 23 unsigned long nr_to_scan; 24 25 /* 26 * How many objects did scan_objects process? 27 * This defaults to nr_to_scan before every call, but the callee 28 * should track its actual progress. 29 */ 30 unsigned long nr_scanned; 31 32 /* current memcg being shrunk (for memcg aware shrinkers) */ 33 struct mem_cgroup *memcg; 34 }; 35 36 #define SHRINK_STOP (~0UL) 37 #define SHRINK_EMPTY (~0UL - 1) 38 /* 39 * A callback you can register to apply pressure to ageable caches. 40 * 41 * @count_objects should return the number of freeable items in the cache. If 42 * there are no objects to free, it should return SHRINK_EMPTY, while 0 is 43 * returned in cases of the number of freeable items cannot be determined 44 * or shrinker should skip this cache for this time (e.g., their number 45 * is below shrinkable limit). No deadlock checks should be done during the 46 * count callback - the shrinker relies on aggregating scan counts that couldn't 47 * be executed due to potential deadlocks to be run at a later call when the 48 * deadlock condition is no longer pending. 49 * 50 * @scan_objects will only be called if @count_objects returned a non-zero 51 * value for the number of freeable objects. The callout should scan the cache 52 * and attempt to free items from the cache. It should then return the number 53 * of objects freed during the scan, or SHRINK_STOP if progress cannot be made 54 * due to potential deadlocks. If SHRINK_STOP is returned, then no further 55 * attempts to call the @scan_objects will be made from the current reclaim 56 * context. 57 * 58 * @flags determine the shrinker abilities, like numa awareness 59 */ 60 struct shrinker { 61 unsigned long (*count_objects)(struct shrinker *, 62 struct shrink_control *sc); 63 unsigned long (*scan_objects)(struct shrinker *, 64 struct shrink_control *sc); 65 66 long batch; /* reclaim batch size, 0 = default */ 67 int seeks; /* seeks to recreate an obj */ 68 unsigned flags; 69 70 /* These are for internal use */ 71 struct list_head list; 72 #ifdef CONFIG_MEMCG 73 /* ID in shrinker_idr */ 74 int id; 75 #endif 76 /* objs pending delete, per node */ 77 atomic_long_t *nr_deferred; 78 }; 79 #define DEFAULT_SEEKS 2 /* A good number if you don't know better. */ 80 81 /* Flags */ 82 #define SHRINKER_REGISTERED (1 << 0) 83 #define SHRINKER_NUMA_AWARE (1 << 1) 84 #define SHRINKER_MEMCG_AWARE (1 << 2) 85 /* 86 * It just makes sense when the shrinker is also MEMCG_AWARE for now, 87 * non-MEMCG_AWARE shrinker should not have this flag set. 88 */ 89 #define SHRINKER_NONSLAB (1 << 3) 90 91 extern int prealloc_shrinker(struct shrinker *shrinker); 92 extern void register_shrinker_prepared(struct shrinker *shrinker); 93 extern int register_shrinker(struct shrinker *shrinker); 94 extern void unregister_shrinker(struct shrinker *shrinker); 95 extern void free_prealloced_shrinker(struct shrinker *shrinker); 96 #endif 97