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This allows an optional generation number to be associated to each entry of the lru cache. Entries with the same key but different generations, are stored in the linked list to which the maple tree points to. This is meant to be used when there's a small number of different generations, so the impact of searching a linked list is negligible. The goal is to get rid of the open coded name cache in the send code (which uses a radix tree and a similar linked list of values/entries) and use instead the lru cache module. For that particular use case we have at most 2 generations that are associated to each key (inode number): one generation for the send root and another generation for the parent root. The actual migration of the send name cache is done in the next patch in the series. This patch is part of a larger patchset and the changelog of the last patch in the series contains a sample performance test and results. The patches that comprise the patchset are the following: btrfs: send: directly return from did_overwrite_ref() and simplify it btrfs: send: avoid unnecessary generation search at did_overwrite_ref() btrfs: send: directly return from will_overwrite_ref() and simplify it btrfs: send: avoid extra b+tree searches when checking reference overrides btrfs: send: remove send_progress argument from can_rmdir() btrfs: send: avoid duplicated orphan dir allocation and initialization btrfs: send: avoid unnecessary orphan dir rbtree search at can_rmdir() btrfs: send: reduce searches on parent root when checking if dir can be removed btrfs: send: iterate waiting dir move rbtree only once when processing refs btrfs: send: initialize all the red black trees earlier btrfs: send: genericize the backref cache to allow it to be reused btrfs: adapt lru cache to allow for 64 bits keys on 32 bits systems btrfs: send: cache information about created directories btrfs: allow a generation number to be associated with lru cache entries btrfs: add an api to delete a specific entry from the lru cache btrfs: send: use the lru cache to implement the name cache btrfs: send: update size of roots array for backref cache entries btrfs: send: cache utimes operations for directories if possible Signed-off-by: Filipe Manana <fdmanana@suse.com> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
64 lines
2.2 KiB
C
64 lines
2.2 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef BTRFS_LRU_CACHE_H
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#define BTRFS_LRU_CACHE_H
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#include <linux/maple_tree.h>
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#include <linux/list.h>
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/*
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* A cache entry. This is meant to be embedded in a structure of a user of
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* this module. Similar to how struct list_head and struct rb_node are used.
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*
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* Note: it should be embedded as the first element in a struct (offset 0), and
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* this module assumes it was allocated with kmalloc(), so it calls kfree() when
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* it needs to free an entry.
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*/
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struct btrfs_lru_cache_entry {
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struct list_head lru_list;
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u64 key;
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/*
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* Optional generation associated to a key. Use 0 if not needed/used.
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* Entries with the same key and different generations are stored in a
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* linked list, so use this only for cases where there's a small number
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* of different generations.
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*/
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u64 gen;
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/*
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* The maple tree uses unsigned long type for the keys, which is 32 bits
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* on 32 bits systems, and 64 bits on 64 bits systems. So if we want to
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* use something like inode numbers as keys, which are always a u64, we
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* have to deal with this in a special way - we store the key in the
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* entry itself, as a u64, and the values inserted into the maple tree
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* are linked lists of entries - so in case we are on a 64 bits system,
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* that list always has a single entry, while on 32 bits systems it
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* may have more than one, with each entry having the same value for
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* their lower 32 bits of the u64 key.
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*/
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struct list_head list;
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};
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struct btrfs_lru_cache {
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struct list_head lru_list;
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struct maple_tree entries;
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/* Number of entries stored in the cache. */
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unsigned int size;
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/* Maximum number of entries the cache can have. */
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unsigned int max_size;
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};
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static inline unsigned int btrfs_lru_cache_size(const struct btrfs_lru_cache *cache)
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{
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return cache->size;
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}
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void btrfs_lru_cache_init(struct btrfs_lru_cache *cache, unsigned int max_size);
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struct btrfs_lru_cache_entry *btrfs_lru_cache_lookup(struct btrfs_lru_cache *cache,
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u64 key, u64 gen);
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int btrfs_lru_cache_store(struct btrfs_lru_cache *cache,
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struct btrfs_lru_cache_entry *new_entry,
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gfp_t gfp);
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void btrfs_lru_cache_clear(struct btrfs_lru_cache *cache);
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#endif
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