linux-kernel - Re: [PATCH] move the kernel to 16MB for NUMA-Q

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Message-ID: <466D882D.70001@zytor.com>
Date:	Mon, 11 Jun 2007 10:36:45 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Dave Jones <davej@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Whitcroft <apw@...dowen.org>,
	"H. Peter Anvin" <hpa@...or.com>, Steve Fox <drfickle@...ibm.com>,
	Mel Gorman <mel@....ul.ie>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] move the kernel to 16MB for NUMA-Q

Dave Jones wrote:
> 
> FWIW, waay back when (sometime last year if memory serves)
> Linus suggested changing the default to 0x1000000 for all x86.
> The reasoning was some performance microoptimisation regarding
> 4MB aligned TLBs iirc.
> 
> The details have long since evaded my memory, but as an experiment,
> I made the change to the Fedora kernel.  FC5,FC6 and F7 have been
> this way for a while now, with no obvious problems. Ditto RHEL5.
> We did get some performance numbers at the time of the change,
> but they weren't amazing (basically in the noise).
> Given it never seemed to actually get worse, I never got around
> to reverting it..
> 

Picking the 16 MB base is a bit obnoxious on small-memory machines, 4 MB
would probably be a more reasonable base.  Of course, 16 MB would avoid
  the issue of the handful of machines with memory holes at 15-16 MB.

	-hpa
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