fs/btrfs/lru_cache.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2
   3 #ifndef BTRFS_LRU_CACHE_H
   4 #define BTRFS_LRU_CACHE_H
   5
   6 #include <linux/types.h>
   7 #include <linux/maple_tree.h>
   8 #include <linux/list.h>
   9
  10 /*
  11  * A cache entry. This is meant to be embedded in a structure of a user of
  12  * this module. Similar to how struct list_head and struct rb_node are used.
  13  *
  14  * Note: it should be embedded as the first element in a struct (offset 0), and
  15  * this module assumes it was allocated with kmalloc(), so it calls kfree() when
  16  * it needs to free an entry.
  17  */
  18 struct btrfs_lru_cache_entry {
  19         struct list_head lru_list;
  20         u64 key;
  21         /*
  22          * Optional generation associated to a key. Use 0 if not needed/used.
  23          * Entries with the same key and different generations are stored in a
  24          * linked list, so use this only for cases where there's a small number
  25          * of different generations.
  26          */
  27         u64 gen;
  28         /*
  29          * The maple tree uses unsigned long type for the keys, which is 32 bits
  30          * on 32 bits systems, and 64 bits on 64 bits systems. So if we want to
  31          * use something like inode numbers as keys, which are always a u64, we
  32          * have to deal with this in a special way - we store the key in the
  33          * entry itself, as a u64, and the values inserted into the maple tree
  34          * are linked lists of entries - so in case we are on a 64 bits system,
  35          * that list always has a single entry, while on 32 bits systems it
  36          * may have more than one, with each entry having the same value for
  37          * their lower 32 bits of the u64 key.
  38          */
  39         struct list_head list;
  40 };
  41
  42 struct btrfs_lru_cache {
  43         struct list_head lru_list;
  44         struct maple_tree entries;
  45         /* Number of entries stored in the cache. */
  46         unsigned int size;
  47         /* Maximum number of entries the cache can have. */
  48         unsigned int max_size;
  49 };
  50
  51 #define btrfs_lru_cache_for_each_entry_safe(cache, entry, tmp)          \
  52         list_for_each_entry_safe_reverse((entry), (tmp), &(cache)->lru_list, lru_list)
  53
  54 static inline struct btrfs_lru_cache_entry *btrfs_lru_cache_lru_entry(
  55                                               struct btrfs_lru_cache *cache)
  56 {
  57         return list_first_entry_or_null(&cache->lru_list,
  58                                         struct btrfs_lru_cache_entry, lru_list);
  59 }
  60
  61 void btrfs_lru_cache_init(struct btrfs_lru_cache *cache, unsigned int max_size);
  62 struct btrfs_lru_cache_entry *btrfs_lru_cache_lookup(struct btrfs_lru_cache *cache,
  63                                                      u64 key, u64 gen);
  64 int btrfs_lru_cache_store(struct btrfs_lru_cache *cache,
  65                           struct btrfs_lru_cache_entry *new_entry,
  66                           gfp_t gfp);
  67 void btrfs_lru_cache_remove(struct btrfs_lru_cache *cache,
  68                             struct btrfs_lru_cache_entry *entry);
  69 void btrfs_lru_cache_clear(struct btrfs_lru_cache *cache);
  70
  71 #endif