linux-kernel - Re: [PATCH 5/6] writeback: try more writeback as long as something was written

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Message-ID: <20110421075258.GB12436@dastard>
Date:	Thu, 21 Apr 2011 17:52:58 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@...ux.vnet.ibm.com>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	Itaru Kitayama <kitayama@...bb4u.ne.jp>,
	Minchan Kim <minchan.kim@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: [PATCH 5/6] writeback: try more writeback as long as something
 was written

On Thu, Apr 21, 2011 at 03:14:26AM -0400, Christoph Hellwig wrote:
> On Thu, Apr 21, 2011 at 05:09:47PM +1000, Dave Chinner wrote:
> > Likely just timing. When IO completes and updates the inode IO size,
> > XFS calls mark_inode_dirty() again to ensure that the metadata that
> > was changed gets written out at a later point in time.
> > Hence every single file that is created by the test will be marked
> > dirty again after the first write has returned and disappeared.
> > 
> > Why you see different numbers? it's timing dependent based on Io
> > completion rates - if you have a fast disk the IO completion can
> > occur before write_inode() is called and so the inode can be written
> > and the dirty page state removed in the one writeback_single_inode()
> > call...
> > 
> > That's my initial guess without looking at it in any real detail,
> > anyway.
> 
> We shouldn't have I_DIRTY_PAGES set for that case, as we only redirty
> metadata.  But we're actually doing a xfs_mark_inode_dirty, which
> dirties all of I_DIRTY, which includes I_DIRTY_PAGES.  I guess it
> should change to
> 
> 	__mark_inode_dirty(inode, I_DIRTY_SYNC | I_DIRTY_DATASYNC);

Probably should. Using xfs_mark_inode_dirty_sync() might be the best
thing to do.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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