From: Dave Chen Date: Mon, 4 May 2026 01:43:56 +0000 (+0800) Subject: btrfs: optimize fill_holes() to merge a new hole with both adjacent items X-Git-Url: http://git.ipfire.org/gitweb/?a=commitdiff_plain;h=022568f8d529e93a46c65cd52427cc61c22ac4aa;p=thirdparty%2Flinux.git btrfs: optimize fill_holes() to merge a new hole with both adjacent items fill_holes() currently merges a punched hole with either the previous or the next file extent item, but never both in the same call. When holes are punched in a non-sequential order this leaves consecutive hole items in the inode's subvolume tree that should have been collapsed into a single one. This is a minor metadata optimization that reduces the number of file extent items when holes are punched in non-sequential order. While having extra file extent items is harmless and has no functional impact, reducing metadata overhead can benefit workloads with heavily fragmented hole patterns. For example: fallocate -p -o 4K -l 4K ${FILE} fallocate -p -o 12K -l 4K ${FILE} fallocate -p -o 8K -l 4K ${FILE} After the third punch the [4K, 8K) and [12K, 16K) holes become adjacent to the new [8K, 12K) hole, but fill_holes() merges only one side and leaves two separate hole items ([4K, 12K) and [12K, 16K)) instead of the expected single [4K, 16K) hole item. Fix this by checking both path->slots[0] - 1 and path->slots[0] in one pass: - If only the previous slot is mergeable, extend it forward as before. - If only the next slot is mergeable, extend it backward and update its key offset as before. - If both are mergeable, extend the previous item to cover the new hole plus the next item, and remove the redundant next item with btrfs_del_items(). Because the merge path may now delete an item, switch the initial btrfs_search_slot() call from a plain lookup (ins_len = 0) to a search-for-deletion (ins_len = -1), so the leaf is prepared for a possible item removal. Note: This optimization only applies to filesystems without the NO_HOLES feature enabled. Since NO_HOLES is now the default, this primarily benefits older filesystems or those explicitly created with NO_HOLES disabled. Signed-off-by: Dave Chen Reviewed-by: Filipe Manana Signed-off-by: Filipe Manana Signed-off-by: David Sterba --- diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c index a63d2ac676594..43792d5a792c1 100644 --- a/fs/btrfs/file.c +++ b/fs/btrfs/file.c @@ -2072,6 +2072,10 @@ static int fill_holes(struct btrfs_trans_handle *trans, struct btrfs_file_extent_item *fi; struct extent_map *hole_em; struct btrfs_key key; + int modify_slot = -1; + int del_slot = -1; + bool update_offset = false; + u64 num_bytes = 0; int ret; if (btrfs_fs_incompat(fs_info, NO_HOLES)) @@ -2081,7 +2085,7 @@ static int fill_holes(struct btrfs_trans_handle *trans, key.type = BTRFS_EXTENT_DATA_KEY; key.offset = offset; - ret = btrfs_search_slot(trans, root, &key, path, 0, 1); + ret = btrfs_search_slot(trans, root, &key, path, -1, 1); if (ret <= 0) { /* * We should have dropped this offset, so if we find it then @@ -2094,33 +2098,44 @@ static int fill_holes(struct btrfs_trans_handle *trans, leaf = path->nodes[0]; if (hole_mergeable(inode, leaf, path->slots[0] - 1, offset, end)) { - u64 num_bytes; - - path->slots[0]--; - fi = btrfs_item_ptr(leaf, path->slots[0], + fi = btrfs_item_ptr(leaf, path->slots[0] - 1, struct btrfs_file_extent_item); num_bytes = btrfs_file_extent_num_bytes(leaf, fi) + end - offset; - btrfs_set_file_extent_num_bytes(leaf, fi, num_bytes); - btrfs_set_file_extent_ram_bytes(leaf, fi, num_bytes); - btrfs_set_file_extent_offset(leaf, fi, 0); - btrfs_set_file_extent_generation(leaf, fi, trans->transid); - goto out; + modify_slot = path->slots[0] - 1; } - if (hole_mergeable(inode, leaf, path->slots[0], offset, end)) { - u64 num_bytes; - - key.offset = offset; - btrfs_set_item_key_safe(trans, path, &key); fi = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_file_extent_item); - num_bytes = btrfs_file_extent_num_bytes(leaf, fi) + end - - offset; + if (modify_slot != -1) { + num_bytes += btrfs_file_extent_num_bytes(leaf, fi); + del_slot = path->slots[0]; + } else { + num_bytes = btrfs_file_extent_num_bytes(leaf, fi) + + end - offset; + modify_slot = path->slots[0]; + update_offset = true; + } + } + if (modify_slot >= 0) { + fi = btrfs_item_ptr(leaf, modify_slot, + struct btrfs_file_extent_item); btrfs_set_file_extent_num_bytes(leaf, fi, num_bytes); btrfs_set_file_extent_ram_bytes(leaf, fi, num_bytes); + if (update_offset) { + key.offset = offset; + btrfs_set_item_key_safe(trans, path, &key); + } btrfs_set_file_extent_offset(leaf, fi, 0); btrfs_set_file_extent_generation(leaf, fi, trans->transid); + if (del_slot >= 0) { + ret = btrfs_del_items(trans, root, path, del_slot, 1); + if (ret) { + btrfs_abort_transaction(trans, ret); + btrfs_release_path(path); + return ret; + } + } goto out; } btrfs_release_path(path);