linux-kernel - Re: [PATCH 18/19] btrfs: only dirty the inode in btrfs_update

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Date:   Fri, 15 Dec 2017 08:03:59 -0500
From:   Jeff Layton <jlayton@...nel.org>
To:     linux-fsdevel@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, hch@....de, neilb@...e.de,
        bfields@...ldses.org, amir73il@...il.com, jack@...e.de,
        viro@...iv.linux.org.uk, Josef Bacik <jbacik@...com>,
        Chris Mason <clm@...com>, Omar Sandoval <osandov@...com>,
        David Howells <dhowells@...hat.com>
Subject: Re: [PATCH 18/19] btrfs: only dirty the inode in btrfs_update_time
 if something was changed

On Wed, 2017-12-13 at 09:20 -0500, Jeff Layton wrote:
> From: Jeff Layton <jlayton@...hat.com>
> 
> At this point, we know that "now" and the file times may differ, and we
> suspect that the i_version has been flagged to be bumped. Attempt to
> bump the i_version, and only mark the inode dirty if that actually
> occurred or if one of the times was updated.
> 
> Signed-off-by: Jeff Layton <jlayton@...hat.com>
> ---
>  fs/btrfs/inode.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index ac25389b39de..2e50a977fb06 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -6106,19 +6106,20 @@ static int btrfs_update_time(struct inode *inode, struct timespec *now,
>  			     int flags)
>  {
>  	struct btrfs_root *root = BTRFS_I(inode)->root;
> +	bool dirty = flags & ~S_VERSION;
>  
>  	if (btrfs_root_readonly(root))
>  		return -EROFS;
>  
>  	if (flags & S_VERSION)
> -		inode_inc_iversion(inode);
> +		dirty |= inode_maybe_inc_iversion(inode, dirty);
>  	if (flags & S_CTIME)
>  		inode->i_ctime = *now;
>  	if (flags & S_MTIME)
>  		inode->i_mtime = *now;
>  	if (flags & S_ATIME)
>  		inode->i_atime = *now;
> -	return btrfs_dirty_inode(inode);
> +	return dirty ? btrfs_dirty_inode(inode) : 0;
>  }
>  
>  /*

I had some bogus handling for SB_LAZYTIME in the corresponding patch for
generic_update_time. I've fixed in my tree, but now I'm wondering...

Should btrfs not be dirtying the inode here if SB_LAZYTIME is set and
the only update is to the atime?
-- 
Jeff Layton <jlayton@...nel.org>