linux-kernel - Re: [PATCH] 2.6.23-rc1-mm1 - fix missing numa_zonelist

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Message-ID: <20070802161829.GB22493@skynet.ie>
Date:	Thu, 2 Aug 2007 17:18:29 +0100
From:	mel@...net.ie (Mel Gorman)
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Christoph Lameter <clameter@....com>
Subject: Re: [PATCH] 2.6.23-rc1-mm1 - fix missing numa_zonelist_order sysctl

On (02/08/07 17:14), Mel Gorman didst pronounce:
> On (02/08/07 09:44), KAMEZAWA Hiroyuki didst pronounce:
> > On Wed, 01 Aug 2007 15:02:51 -0400
> > Lee Schermerhorn <Lee.Schermerhorn@...com> wrote:
> > > [But, maybe reordering the zonelists is not such a good idea
> > > when ZONE_MOVABLE is populated?]
> > > 
> > 
> > It's case-by-case I think. In zone order with ZONE_MOVABLE case,
> > user's page cache will not use ZONE_NORMAL until ZONE_MOVABLE in all node
> > is exhausted. This is an expected behavior, I think.
> > 
> 
> This is expected behaviour. I see no reason for lower zones to be used
> for allocations that use memory from a higher zone with free memory.
> 

Bah. I should have thought of this better.

If you are using ZONE_MOVABLE and the zonelist is in zone order, one would
use memory from remote nodes when suitable local memory was available. I don't
have a quick answer on how this should be handled. The answer may be
something like;

o When ordering zonelists by nodes, order them so that the movable zone
  is paired with the next highest zones in a zonelist before moving to the
  next node

> > I think the real problem is the scheme for "How to set zone movable size to
> > appropriate value for the system". This needs more study and documentation.
> > (but maybe depends on system configuration to some extent.)
> > 
> 
> It depends on the system configuration and the workload requirements.
> Right now, there isn't exact information available on what size the zone
> should be. It'll need to be studied over a period of time.
> 
> -- 
> Mel Gorman
> Part-time Phd Student                          Linux Technology Center
> University of Limerick                         IBM Dublin Software Lab
> 
> --
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-- 
-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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