linux-kernel - Re: [PATCH 14/17] xfs: Use new syncing helper

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Date:	Wed, 19 Aug 2009 12:33:15 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Jan Kara <jack@...e.cz>
Cc:	LKML <linux-kernel@...r.kernel.org>, hch@...radead.org,
	Felix Blyakher <felixb@....com>, xfs@....sgi.com
Subject: Re: [PATCH 14/17] xfs: Use new syncing helper

On Wed, Aug 19, 2009 at 06:04:41PM +0200, Jan Kara wrote:
> diff --git a/fs/xfs/linux-2.6/xfs_lrw.c b/fs/xfs/linux-2.6/xfs_lrw.c
> index 7078974..aeb5a39 100644
> --- a/fs/xfs/linux-2.6/xfs_lrw.c
> +++ b/fs/xfs/linux-2.6/xfs_lrw.c
> @@ -817,7 +817,7 @@ write_retry:
>  		xfs_iunlock(xip, iolock);
>  		if (need_i_mutex)
>  			mutex_unlock(&inode->i_mutex);
> -		error2 = sync_page_range(inode, mapping, pos, ret);
> +		error2 = generic_write_sync(file, pos, ret);

I don't think this is very optimal for XFS.  This first starts an
asynchronous writeout of the range in generic_write_sync,
then calls into ->fsync which waits for all I/O on the file to finish,
then forces the log inside xfs_fsync,  then waits for the range again in
generic_write_sync, and after this code calls into
xfs_write_sync_logforce which forces to log _again_.

We should be fine just doing your new filemap_fdatawrite_range helper
here and let xfs_write_sync_logforce do the work.  Long term we should
just get rid of this stupid submit writes before syncing the iode, then
wait crap which is a pain for all modern filesystems.
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