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authorFilipe Manana <fdmanana@suse.com>2020-05-18 12:15:00 +0100
committerDavid Sterba <dsterba@suse.com>2020-05-25 11:25:37 +0200
commitcc14600c1516f6c679cab1c503a34841d58050a6 (patch)
tree1c4dd001d0aaf7b0acc033358b79846e0c12c804 /fs/btrfs/file-item.c
parente289f03ea79bbc6574b78ac25682555423a91cbb (diff)
btrfs: make checksum item extension more efficient
When we want to add checksums into the checksums tree, or a log tree, we try whenever possible to extend existing checksum items, as this helps reduce amount of metadata space used, since adding a new item uses extra metadata space for a btrfs_item structure (25 bytes). However we have two inefficiencies in the current approach: 1) After finding a checksum item that covers a range with an end offset that matches the start offset of the checksum range we want to insert, we release the search path populated by btrfs_lookup_csum() and then do another COW search on tree with the goal of getting additional space for at least one checksum. Doing this path release and then searching again is a waste of time because very often the leaf already has enough free space for at least one more checksum; 2) After the COW search that guarantees we get free space in the leaf for at least one more checksum, we end up not doing the extension of the previous checksum item, and fallback to insertion of a new checksum item, if the leaf doesn't have an amount of free space larger then the space required for 2 checksums plus one btrfs_item structure - this is pointless for two reasons: a) We want to extend an existing item, so we don't need to account for a btrfs_item structure (25 bytes); b) We made the COW search with an insertion size for 1 single checksum, so if the leaf ends up with a free space amount smaller then 2 checksums plus the size of a btrfs_item structure, we give up on the extension of the existing item and jump to the 'insert' label, where we end up releasing the path and then doing yet another search to insert a new checksum item for a single checksum. Fix these inefficiencies by doing the following: - For case 1), before releasing the path just check if the leaf already has enough space for at least 1 more checksum, and if it does, jump directly to the item extension code, with releasing our current path, which was already COWed by btrfs_lookup_csum(); - For case 2), fix the logic so that for item extension we require only that the leaf has enough free space for 1 checksum, and not a minimum of 2 checksums plus space for a btrfs_item structure. Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs/btrfs/file-item.c')
-rw-r--r--fs/btrfs/file-item.c27
1 files changed, 17 insertions, 10 deletions
diff --git a/fs/btrfs/file-item.c b/fs/btrfs/file-item.c
index 8cdd06ea0e67..687529c61d13 100644
--- a/fs/btrfs/file-item.c
+++ b/fs/btrfs/file-item.c
@@ -907,9 +907,22 @@ again:
}
/*
- * at this point, we know the tree has an item, but it isn't big
- * enough yet to put our csum in. Grow it
+ * At this point, we know the tree has a checksum item that ends at an
+ * offset matching the start of the checksum range we want to insert.
+ * We try to extend that item as much as possible and then add as many
+ * checksums to it as they fit.
+ *
+ * First check if the leaf has enough free space for at least one
+ * checksum. If it has go directly to the item extension code, otherwise
+ * release the path and do a search for insertion before the extension.
*/
+ if (btrfs_leaf_free_space(leaf) >= csum_size) {
+ btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);
+ csum_offset = (bytenr - found_key.offset) >>
+ fs_info->sb->s_blocksize_bits;
+ goto extend_csum;
+ }
+
btrfs_release_path(path);
ret = btrfs_search_slot(trans, root, &file_key, path,
csum_size, 1);
@@ -933,19 +946,13 @@ again:
goto insert;
}
+extend_csum:
if (csum_offset == btrfs_item_size_nr(leaf, path->slots[0]) /
csum_size) {
int extend_nr;
u64 tmp;
u32 diff;
- u32 free_space;
-
- if (btrfs_leaf_free_space(leaf) <
- sizeof(struct btrfs_item) + csum_size * 2)
- goto insert;
- free_space = btrfs_leaf_free_space(leaf) -
- sizeof(struct btrfs_item) - csum_size;
tmp = sums->len - total_bytes;
tmp >>= fs_info->sb->s_blocksize_bits;
WARN_ON(tmp < 1);
@@ -956,7 +963,7 @@ again:
MAX_CSUM_ITEMS(fs_info, csum_size) * csum_size);
diff = diff - btrfs_item_size_nr(leaf, path->slots[0]);
- diff = min(free_space, diff);
+ diff = min_t(u32, btrfs_leaf_free_space(leaf), diff);
diff /= csum_size;
diff *= csum_size;