linux-kernel - Re: [PATCH 3/8] ext4: Warn if direct reclaim tries to writeback pages

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Message-ID: <20110803134420.GH19099@suse.de>
Date:	Wed, 3 Aug 2011 14:44:20 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Johannes Weiner <jweiner@...hat.com>
Cc:	Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
	XFS <xfs@....sgi.com>, Dave Chinner <david@...morbit.com>,
	Christoph Hellwig <hch@...radead.org>,
	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Rik van Riel <riel@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>
Subject: Re: [PATCH 3/8] ext4: Warn if direct reclaim tries to writeback pages

On Wed, Aug 03, 2011 at 01:06:29PM +0200, Johannes Weiner wrote:
> On Wed, Aug 03, 2011 at 12:58:19PM +0200, Johannes Weiner wrote:
> > On Thu, Jul 21, 2011 at 05:28:45PM +0100, Mel Gorman wrote:
> > > Direct reclaim should never writeback pages. Warn if an attempt
> > > is made.
> > > 
> > > Signed-off-by: Mel Gorman <mgorman@...e.de>
> > 
> > Acked-by: Johannes Weiner <jweiner@...hat.com>
> 
> Oops, too fast.
> 
> Shouldn't the WARN_ON() be at the top of the function, rather than
> just warn when the write is deferred due to delalloc?

I thought it made more sense to put the warning at the point where ext4
would normally ignore ->writepage.

That said, in my current revision of the series, I've dropped these
patches altogether as page migration should be able to trigger the same
warnings but be called from paths that are of less concern for stack
overflows (or at the very least be looked at as a separate series).

-- 
Mel Gorman
SUSE Labs
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