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 */
18struct 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
42struct 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
54static 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
61void btrfs_lru_cache_init(struct btrfs_lru_cache *cache, unsigned int max_size);
62struct btrfs_lru_cache_entry *btrfs_lru_cache_lookup(struct btrfs_lru_cache *cache,
63 u64 key, u64 gen);
64int btrfs_lru_cache_store(struct btrfs_lru_cache *cache,
65 struct btrfs_lru_cache_entry *new_entry,
66 gfp_t gfp);
67void btrfs_lru_cache_remove(struct btrfs_lru_cache *cache,
68 struct btrfs_lru_cache_entry *entry);
69void btrfs_lru_cache_clear(struct btrfs_lru_cache *cache);
70
71#endif
72

source code of linux/fs/btrfs/lru_cache.h