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 00:02:17 +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

On Thursday 02 August 2007 19:21:18 Mel Gorman wrote:
> The NUMA layer only supports NUMA policies for the highest zone. When
> ZONE_MOVABLE is configured with kernelcore=, the the highest zone becomes
> ZONE_MOVABLE. The result is that policies are only applied to allocations
> like anonymous pages and page cache allocated from ZONE_MOVABLE when the
> zone is used.
> 
> This patch applies policies to the two highest zones when the highest zone
> is ZONE_MOVABLE. As ZONE_MOVABLE consists of pages from the highest "real"
> zone, it's always functionally equivalent.
> 
> The patch has been tested on a variety of machines both NUMA and non-NUMA
> covering x86, x86_64 and ppc64. No abnormal results were seen in kernbench,
> tbench, dbench or hackbench. It passes regression tests from the numactl
> package with and without kernelcore= once numactl tests are patched to
> wait for vmstat counters to update.
 
I must honestly say I really hate the patch. It's a horrible hack and makes fast paths
slower. When I designed mempolicies I especially tried to avoid things
like that, please don't add them through the backdoor now.

-Andi
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