linux-kernel - Re: [RFC PATCH 0/3] Fix SLQB on memoryless configurations V2

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Message-ID: <20090921180739.GT12726@csn.ul.ie>
Date:	Mon, 21 Sep 2009 19:07:39 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Nick Piggin <npiggin@...e.de>,
	Pekka Enberg <penberg@...helsinki.fi>,
	heiko.carstens@...ibm.com, sachinp@...ibm.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Tejun Heo <tj@...nel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [RFC PATCH 0/3] Fix SLQB on memoryless configurations V2

On Mon, Sep 21, 2009 at 01:54:12PM -0400, Christoph Lameter wrote:
> Lets just keep SLQB back until the basic issues with memoryless nodes are
> resolved.

It's not even super-clear that the memoryless nodes issues are entirely
related to SLQB. Sachin for example says that there was a stall issue
with memoryless nodes that could be triggered without SLQB. Sachin, is
that still accurate?

If so, it's possible that SLQB somehow exasperates the problem in some
unknown fashion.

> There does not seem to be an easy way to deal with this. Some
> thought needs to go into how memoryless node handling relates to per cpu
> lists and locking. List handling issues need to be addressed before SLQB.
> can work reliably. The same issues can surface on x86 platforms with weird
> NUMA memory setups.
> 

Can you spot if there is something fundamentally wrong with patch 2? I.e. what
is wrong with treating the closest node as local instead of only the
closest node?

> Or just allow SLQB for !NUMA configurations and merge it now.
> 

Forcing SLQB !NUMA will not rattle out any existing list issues
unfortunately :(.

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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