linux-kernel - Re: [PATCH stable-4.14.y] btrfs: always wait on ordered extents at fsync time

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Date:   Wed, 20 Oct 2021 14:32:48 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Anand Jain <anand.jain@...cle.com>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux-btrfs@...r.kernel.org, Josef Bacik <jbacik@...com>,
        Filipe Manana <fdmanana@...e.com>
Subject: Re: [PATCH stable-4.14.y] btrfs: always wait on ordered extents at
 fsync time

On Tue, Oct 19, 2021 at 06:38:20PM +0800, Anand Jain wrote:
> From: Josef Bacik <jbacik@...com>
> 
> Commit b5e6c3e170b77025b5f6174258c7ad71eed2d4de upstream.
> 
> There's a priority inversion that exists currently with btrfs fsync.  In
> some cases we will collect outstanding ordered extents onto a list and
> only wait on them at the very last second.  However this "very last
> second" falls inside of a transaction handle, so if we are in a lower
> priority cgroup we can end up holding the transaction open for longer
> than needed, so if a high priority cgroup is also trying to fsync()
> it'll see latency.
> 
> Signed-off-by: Josef Bacik <jbacik@...com>
> Reviewed-by: Filipe Manana <fdmanana@...e.com>
> Signed-off-by: David Sterba <dsterba@...e.com>
> Signed-off-by: Anand Jain <anand.jain@...cle.com>
> ---
>  fs/btrfs/file.c | 56 ++++---------------------------------------------
>  1 file changed, 4 insertions(+), 52 deletions(-)

Now applied, thanks.

greg k-h