提交 20903032 编写于 作者: F Filipe Manana 提交者: David Sterba

btrfs: avoid checking for RO block group twice during nocow writeback

During the nocow writeback path, we currently iterate the rbtree of block
groups twice: once for checking if the target block group is RO with the
call to btrfs_extent_readonly()), and once again for getting a nocow
reference on the block group with a call to btrfs_inc_nocow_writers().

Since btrfs_inc_nocow_writers() already returns false when the target
block group is RO, remove the call to btrfs_extent_readonly(). Not only
we avoid searching the blocks group rbtree twice, it also helps reduce
contention on the lock that protects it (specially since it is a spin
lock and not a read-write lock). That may make a noticeable difference
on very large filesystems, with thousands of allocated block groups.
Reviewed-by: NAnand Jain <anand.jain@oracle.com>
Reviewed-by: NJosef Bacik <josef@toxicpanda.com>
Signed-off-by: NFilipe Manana <fdmanana@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>
上级 3c179165
......@@ -1674,9 +1674,6 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
*/
btrfs_release_path(path);
/* If extent is RO, we must COW it */
if (btrfs_extent_readonly(fs_info, disk_bytenr))
goto out_check;
ret = btrfs_cross_ref_exist(root, ino,
found_key.offset -
extent_offset, disk_bytenr, false);
......@@ -1723,6 +1720,7 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
WARN_ON_ONCE(freespace_inode);
goto out_check;
}
/* If the extent's block group is RO, we must COW */
if (!btrfs_inc_nocow_writers(fs_info, disk_bytenr))
goto out_check;
nocow = true;
......
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