linux-kernel - Re: [PATCH] Apply memory policies to top two highest zones when highest zone is ZONE

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Date:	Sat, 4 Aug 2007 10:51:13 +0200
From:	Andi Kleen <ak@...e.de>
To:	Mel Gorman <mel@...net.ie>
Cc:	akpm@...ux-foundation.org, Lee.Schermerhorn@...com,
	clameter@....com, kamezawa.hiroyu@...fujitsu.com,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Apply memory policies to top two highest zones when highest zone is ZONE_MOVABLE


> It only affects hot paths in the NUMA case so non-NUMA users will not care.

For x86-64 most distribution kernels are NUMA these days.

> For NUMA users,  I have posted patches that eliminate multiple zonelists
> altogether which will reduce cache footprint (something like 7K per node on
> x86_64)

How do you get to 7k? We got worst case 3 zones node (normally less);
that's three pointers per GFP level.

> and make things like MPOL_BIND behave in a consistent manner. That 
> would cost on CPU but save on cache which would (hopefully) result in a net
> gain in most cases.

That might be a good tradeoff, but without seeing the patch 
the 7k number sounds very dubious.

> I would like to go with this patch for now just for policies but for
> 2.6.23, we could leave it as "policies only apply to ZONE_MOVABLE when it
> is used" if you really insisted on it. It's less than ideal though for
> sure.

Or disable ZONE_MOVABLE. It seems to be clearly not well thought
out well yet. Perhaps make it dependent on !CONFIG_NUMA.

-Andi
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