Btrfs: Raise thresholds for metadata writeback (24ab9cd8) · Commits · 戴 / test

Btrfs metadata writeback is fairly expensive. Once a tree block is written it must be cowed before it can be changed again. The btree writepages code has a threshold based on a count of dirty btree bytes which is updated as IO is sent out. This changes btree_writepages to skip the writeout if there are less than 32MB of dirty bytes from the btrees, improving performance across many workloads. Signed-off-by:

Chris Mason <chris.mason@oracle.com>

fs/btrfs/disk-io.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -556,7 +556,7 @@ static int btree_writepages(struct address_space *mapping,
		if (wbc->sync_mode == WB_SYNC_NONE) {
		u64 num_dirty;
		u64 start = 0;
		unsigned long thresh = 8 * 1024 * 1024;
		unsigned long thresh = 32 * 1024 * 1024;

		if (wbc->for_kupdate)
		return 0;
		@@ -690,7 +690,7 @@ struct extent_buffer btrfs_find_create_tree_block(struct btrfs_root root,
		int btrfs_write_tree_block(struct extent_buffer *buf)
		{
		return btrfs_fdatawrite_range(buf->first_page->mapping, buf->start,
		buf->start + buf->len - 1, WB_SYNC_NONE);
		buf->start + buf->len - 1, WB_SYNC_ALL);
		}

		int btrfs_wait_tree_block_writeback(struct extent_buffer *buf)

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