On Wed, Apr 17, 2019 at 11:31:06AM +0100, fdmanana@xxxxxxxxxx wrote:
> From: Filipe Manana <fdmanana@xxxxxxxx>
>
> Commit 41bd6067692382 ("Btrfs: fix fsync of files with multiple hard links
> in new directories") introduced a path that makes fsync fallback to a full
> transaction commit in order to avoid losing hard links and new ancestors
> of the fsynced inode. That path is triggered only when the inode has more
> than one hard link and either has a new hard link created in the current
> transaction or the inode was evicted and reloaded in the current
> transaction.
>
> That path ends up getting triggered very often (hundreds of times) during
> the course of pgbench benchmarks, resulting in performance drops of about
> 20%.
>
> This change restores the performance by not triggering the full transaction
> commit in those cases, and instead iterate the fs/subvolume tree in search
> of all possible new ancestors, for all hard links, to log them.
>
> Reported-by: Zhao Yuhu <zyuhu@xxxxxxxx>
> Tested-by: James Wang <jnwang@xxxxxxxx>
> Signed-off-by: Filipe Manana <fdmanana@xxxxxxxx>
Added to misc-next, thanks.
