linux-kernel - Re: [PATCH 0/3] Removal of lumpy reclaim V2

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Date:	Thu, 12 Apr 2012 10:32:09 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Rik van Riel <riel@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	Hugh Dickins <hughd@...gle.com>, Ying Han <yinghan@...gle.com>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] Removal of lumpy reclaim V2

On Wed, Apr 11, 2012 at 02:06:11PM -0400, Rik van Riel wrote:
> On 04/11/2012 01:52 PM, Mel Gorman wrote:
> >On Wed, Apr 11, 2012 at 01:17:02PM -0400, Rik van Riel wrote:
> 
> >>Next step: get rid of __GFP_NO_KSWAPD for THP, first
> >>in the -mm kernel
> >>
> >
> >Initially the flag was introduced because kswapd reclaimed too
> >aggressively. One would like to believe that it would be less of a problem
> >now but we must avoid a situation where the CPU and reclaim cost of kswapd
> >exceeds the benefit of allocating a THP.
> 
> Since kswapd and the direct reclaim code now use
> the same conditionals for calling compaction,
> the cost ought to be identical.
> 

kswapd has different retry logic for reclaim and can stay awake if there
are continual calls to wakeup_kswapd() setting pgdat->kswapd_max_order
and kswapd makes forward progress. It's not identical enough that I would
express 100% confidence that it will be free of problems.

-- 
Mel Gorman
SUSE Labs
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