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Date: Tue, 6 Jul 2010 22:27:58 +0200
From: Johannes Weiner <hannes@cmpxchg.org>
To: Mel Gorman <mel@csn.ul.ie>
Cc: Minchan Kim <minchan.kim@gmail.com>,
       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
       Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
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       KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
       Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: [PATCH 12/14] vmscan: Do not writeback pages in direct reclaim
Message-ID: <20100706202758.GC18210@cmpxchg.org>
References: <20100702125155.69c02f85.akpm@linux-foundation.org>
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On Tue, Jul 06, 2010 at 04:25:39PM +0100, Mel Gorman wrote:
> On Tue, Jul 06, 2010 at 08:24:57PM +0900, Minchan Kim wrote:
> > but it is still problem in case of swap file.
> > That's because swapout on swapfile cause file system writepage which
> > makes kernel stack overflow.
> 
> I don't *think* this is a problem unless I missed where writing out to
> swap enters teh filesystem code. I'll double check.

It bypasses the fs.  On swapon, the blocks are resolved
(mm/swapfile.c::setup_swap_extents) and then the writeout path uses
bios directly (mm/page_io.c::swap_writepage).

(GFP_NOFS still includes __GFP_IO, so allows swapping)

	Hannes