1/* SPDX-License-Identifier: GPL-2.0 */
 2
 3#ifndef BTRFS_LRU_CACHE_H
 4#define BTRFS_LRU_CACHE_H
 5
 6#include <linux/maple_tree.h>
 7#include <linux/list.h>
 8
 9/*
10 * A cache entry. This is meant to be embedded in a structure of a user of
11 * this module. Similar to how struct list_head and struct rb_node are used.
12 *
13 * Note: it should be embedded as the first element in a struct (offset 0), and
14 * this module assumes it was allocated with kmalloc(), so it calls kfree() when
15 * it needs to free an entry.
16 */
17struct btrfs_lru_cache_entry {
18	struct list_head lru_list;
19	u64 key;
20	/*
21	 * Optional generation associated to a key. Use 0 if not needed/used.
22	 * Entries with the same key and different generations are stored in a
23	 * linked list, so use this only for cases where there's a small number
24	 * of different generations.
25	 */
26	u64 gen;
27	/*
28	 * The maple tree uses unsigned long type for the keys, which is 32 bits
29	 * on 32 bits systems, and 64 bits on 64 bits systems. So if we want to
30	 * use something like inode numbers as keys, which are always a u64, we
31	 * have to deal with this in a special way - we store the key in the
32	 * entry itself, as a u64, and the values inserted into the maple tree
33	 * are linked lists of entries - so in case we are on a 64 bits system,
34	 * that list always has a single entry, while on 32 bits systems it
35	 * may have more than one, with each entry having the same value for
36	 * their lower 32 bits of the u64 key.
37	 */
38	struct list_head list;
39};
40
41struct btrfs_lru_cache {
42	struct list_head lru_list;
43	struct maple_tree entries;
44	/* Number of entries stored in the cache. */
45	unsigned int size;
46	/* Maximum number of entries the cache can have. */
47	unsigned int max_size;
48};
49
50#define btrfs_lru_cache_for_each_entry_safe(cache, entry, tmp)		\
51	list_for_each_entry_safe_reverse((entry), (tmp), &(cache)->lru_list, lru_list)
52
53static inline unsigned int btrfs_lru_cache_size(const struct btrfs_lru_cache *cache)
54{
55	return cache->size;
56}
57
58static inline struct btrfs_lru_cache_entry *btrfs_lru_cache_lru_entry(
59					      struct btrfs_lru_cache *cache)
60{
61	return list_first_entry_or_null(&cache->lru_list,
62					struct btrfs_lru_cache_entry, lru_list);
63}
64
65void btrfs_lru_cache_init(struct btrfs_lru_cache *cache, unsigned int max_size);
66struct btrfs_lru_cache_entry *btrfs_lru_cache_lookup(struct btrfs_lru_cache *cache,
67						     u64 key, u64 gen);
68int btrfs_lru_cache_store(struct btrfs_lru_cache *cache,
69			  struct btrfs_lru_cache_entry *new_entry,
70			  gfp_t gfp);
71void btrfs_lru_cache_remove(struct btrfs_lru_cache *cache,
72			    struct btrfs_lru_cache_entry *entry);
73void btrfs_lru_cache_clear(struct btrfs_lru_cache *cache);
74
75#endif