diff options
Diffstat (limited to 'fs/btrfs/backref.h')
| -rw-r--r-- | fs/btrfs/backref.h | 27 |
1 files changed, 27 insertions, 0 deletions
diff --git a/fs/btrfs/backref.h b/fs/btrfs/backref.h index 5f468f0defda..fda78db50be6 100644 --- a/fs/btrfs/backref.h +++ b/fs/btrfs/backref.h @@ -23,6 +23,8 @@ struct btrfs_backref_shared_cache_entry { bool is_shared; }; +#define BTRFS_BACKREF_CTX_PREV_EXTENTS_SIZE 8 + struct btrfs_backref_share_check_ctx { /* Ulists used during backref walking. */ struct ulist refs; @@ -32,6 +34,31 @@ struct btrfs_backref_share_check_ctx { */ struct btrfs_backref_shared_cache_entry path_cache_entries[BTRFS_MAX_LEVEL]; bool use_path_cache; + /* + * Cache the sharedness result for the last few extents we have found, + * but only for extents for which we have multiple file extent items + * that point to them. + * It's very common to have several file extent items that point to the + * same extent (bytenr) but with different offsets and lengths. This + * typically happens for COW writes, partial writes into prealloc + * extents, NOCOW writes after snapshoting a root, hole punching or + * reflinking within the same file (less common perhaps). + * So keep a small cache with the lookup results for the extent pointed + * by the last few file extent items. This cache is checked, with a + * linear scan, whenever btrfs_is_data_extent_shared() is called, so + * it must be small so that it does not negatively affect performance in + * case we don't have multiple file extent items that point to the same + * data extent. + */ + struct { + u64 bytenr; + bool is_shared; + } prev_extents_cache[BTRFS_BACKREF_CTX_PREV_EXTENTS_SIZE]; + /* + * The slot in the prev_extents_cache array that will be used for + * storing the sharedness result of a new data extent. + */ + int prev_extents_cache_slot; }; typedef int (iterate_extent_inodes_t)(u64 inum, u64 offset, u64 root, |