On 2/3/2021 7:17 PM, fdman...@kernel.org wrote:
From: Filipe Manana <fdman...@suse.com>
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.
Signed-off-by: Filipe Manana <fdman...@suse.com>
Reviewed-by: Anand Jain <anand.j...@oracle.com>
Thanks.
---
fs/btrfs/inode.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 589030cefd90..b10fc42f9e9a 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1657,9 +1657,6 @@ 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);
@@ -1706,6 +1703,7 @@ 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;
