Btrfs: try harder to avoid btree node splits (5a4267ca) · Commits · 戴 / test

When attempting to move items from our target leaf to its neighbor leaves (right and left), we only need to free data_size - free_space bytes from our leaf in order to add the new item (which has size of data_size bytes). Therefore attempt to move items to the right and left leaves if they have at least data_size - free_space bytes free, instead of data_size bytes free. After 5 runs of the following test, I got a smaller number of btree node splits overall: sysbench --test=fileio --file-num=512 --file-total-size=5G \ --file-test-mode=seqwr --num-threads=512 \ --file-block-size=8192 --max-requests=100000 --file-io-mode=sync Before this change: * 6171 splits (average of 5 test runs) * 61.508Mb/sec of throughput (average of 5 test runs) After this change: * 6036 splits (average of 5 test runs) * 63.533Mb/sec of throughput (average of 5 test runs) An ideal test would not just have multiple threads/processes writing to a file (insertion of file extent items) but also do other operations that result in insertion of items with varied sizes, like file/directory creations, creation of links, symlinks, xattrs, etc. Signed-off-by:

Filipe David Borba Manana <fdmanana@gmail.com> Signed-off-by:

Josef Bacik <jbacik@fb.com> Signed-off-by:

Chris Mason <clm@fb.com>

fs/btrfs/ctree.c

+14 −6

Original line number	Diff line number	Diff line
		@@ -3929,14 +3929,17 @@ static noinline int push_for_double_split(struct btrfs_trans_handle *trans,
		int progress = 0;
		int slot;
		u32 nritems;
		int space_needed = data_size;

		slot = path->slots[0];
		if (slot < btrfs_header_nritems(path->nodes[0]))
		space_needed -= btrfs_leaf_free_space(root, path->nodes[0]);

		/*
		* try to push all the items after our slot into the
		* right leaf
		*/
		ret = push_leaf_right(trans, root, path, 1, data_size, 0, slot);
		ret = push_leaf_right(trans, root, path, 1, space_needed, 0, slot);
		if (ret < 0)
		return ret;

		@@ -3956,7 +3959,7 @@ static noinline int push_for_double_split(struct btrfs_trans_handle *trans,

		/* try to push all the items before our slot into the next leaf */
		slot = path->slots[0];
		ret = push_leaf_left(trans, root, path, 1, data_size, 0, slot);
		ret = push_leaf_left(trans, root, path, 1, space_needed, 0, slot);
		if (ret < 0)
		return ret;

		@@ -4000,13 +4003,18 @@ static noinline int split_leaf(struct btrfs_trans_handle *trans,

		/* first try to make some room by pushing left and right */
		if (data_size && path->nodes[1]) {
		wret = push_leaf_right(trans, root, path, data_size,
		data_size, 0, 0);
		int space_needed = data_size;

		if (slot < btrfs_header_nritems(l))
		space_needed -= btrfs_leaf_free_space(root, l);

		wret = push_leaf_right(trans, root, path, space_needed,
		space_needed, 0, 0);
		if (wret < 0)
		return wret;
		if (wret) {
		wret = push_leaf_left(trans, root, path, data_size,
		data_size, 0, (u32)-1);
		wret = push_leaf_left(trans, root, path, space_needed,
		space_needed, 0, (u32)-1);
		if (wret < 0)
		return wret;
		}

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