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#include "lru_cache.h"
10
11/*
12 * A cache entry. This is meant to be embedded in a structure of a user of
13 * this module. Similar to how struct list_head and struct rb_node are used.
14 *
15 * Note: it should be embedded as the first element in a struct (offset 0), and
16 * this module assumes it was allocated with kmalloc(), so it calls kfree() when
17 * it needs to free an entry.
18 */
19struct btrfs_lru_cache_entry {
20 struct list_head lru_list;
21 u64 key;
22 /*
23 * Optional generation associated to a key. Use 0 if not needed/used.
24 * Entries with the same key and different generations are stored in a
25 * linked list, so use this only for cases where there's a small number
26 * of different generations.
27 */
28 u64 gen;
29 /*
30 * The maple tree uses unsigned long type for the keys, which is 32 bits
31 * on 32 bits systems, and 64 bits on 64 bits systems. So if we want to
32 * use something like inode numbers as keys, which are always a u64, we
33 * have to deal with this in a special way - we store the key in the
34 * entry itself, as a u64, and the values inserted into the maple tree
35 * are linked lists of entries - so in case we are on a 64 bits system,
36 * that list always has a single entry, while on 32 bits systems it
37 * may have more than one, with each entry having the same value for
38 * their lower 32 bits of the u64 key.
39 */
40 struct list_head list;
41};
42
43struct btrfs_lru_cache {
44 struct list_head lru_list;
45 struct maple_tree entries;
46 /* Number of entries stored in the cache. */
47 unsigned int size;
48 /* Maximum number of entries the cache can have. */
49 unsigned int max_size;
50};
51
52#define btrfs_lru_cache_for_each_entry_safe(cache, entry, tmp) \
53 list_for_each_entry_safe_reverse((entry), (tmp), &(cache)->lru_list, lru_list)
54
55static inline struct btrfs_lru_cache_entry *btrfs_lru_cache_lru_entry(
56 struct btrfs_lru_cache *cache)
57{
58 return list_first_entry_or_null(&cache->lru_list,
59 struct btrfs_lru_cache_entry, lru_list);
60}
61
62void btrfs_lru_cache_init(struct btrfs_lru_cache *cache, unsigned int max_size);
63struct btrfs_lru_cache_entry *btrfs_lru_cache_lookup(struct btrfs_lru_cache *cache,
64 u64 key, u64 gen);
65int btrfs_lru_cache_store(struct btrfs_lru_cache *cache,
66 struct btrfs_lru_cache_entry *new_entry,
67 gfp_t gfp);
68void btrfs_lru_cache_remove(struct btrfs_lru_cache *cache,
69 struct btrfs_lru_cache_entry *entry);
70void btrfs_lru_cache_clear(struct btrfs_lru_cache *cache);
71
72#endif
73

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