include/linux/shrinker.h

   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 extension 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