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

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Date:	Thu, 21 Apr 2011 04:00:39 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Dave Chinner <david@...morbit.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	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 05:52:58PM +1000, Dave Chinner wrote:
> > 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.

That's not correct either - we need to set I_DIRTY_DATASYNC so that it
gets caught by fsync and not just fdatasync.

But thinking about it I'm actually not sure we need it at all.  We already
wait for the i_iocount to go to zero both in fsync and ->sync_fs, which will
catch pending I/O completions even without any VFS dirty state.  So just
marking the inode dirty (as I_DIRTY_SYNC | I_DIRTY_DATASYNC) on I/O
completion should be enough these days.

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