linux-kernel - Re: [PATCH resend^2] mm: increase RECLAIM

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Message-ID: <1302655746.8321.4001.camel@nimitz>
Date:	Tue, 12 Apr 2011 17:49:06 -0700
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Chris McDermott <lcm@...ux.vnet.ibm.com>
Subject: Re: [PATCH resend^2] mm: increase RECLAIM_DISTANCE to 30

On Tue, 2011-04-12 at 17:22 -0700, David Rientjes wrote:
> On Mon, 11 Apr 2011, Dave Hansen wrote:
> I know specifically of pieces of x86 hardware that set the information
> > in the BIOS to '21' *specifically* so they'll get the zone_reclaim_mode
> > behavior which that implies.
> 
> That doesn't seem like an argument against this patch, it's an improper 
> configuration unless the remote memory access has a latency of 2.1x that 
> of a local access between those two nodes.  If that's the case, then it's 
> accurately following the ACPI spec and the VM has made its policy decision 
> to enable zone_reclaim_mode as a result.

Heh, if the kernel broke on every system that didn't follow _some_ spec,
it wouldn't boot in very many places.

When you have a hammer, everything looks like a nail.  When you're a
BIOS developer, you start thwacking at the kernel with munged ACPI
tables instead of boot options.  Folks do this in the real world, and I
think if we can't put their names and addresses next to the code that
works around this, we might as well put the DMI strings of their
hardware. :) 

-- Dave

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