Message-ID: <466D882D.70001@zytor.com>
Date: Mon, 11 Jun 2007 10:36:45 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
User-Agent: Thunderbird 2.0.0.0 (X11/20070419)
MIME-Version: 1.0
To: Dave Jones <davej@redhat.com>, Andrew Morton <akpm@linux-foundation.org>,
       Andy Whitcroft <apw@shadowen.org>, "H. Peter Anvin" <hpa@zytor.com>,
       Steve Fox <drfickle@us.ibm.com>, Mel Gorman <mel@csn.ul.ie>,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH] move the kernel to 16MB for NUMA-Q
References: <466D550C.4030600@shadowen.org> <63a08cc7547f14065becdf9a94d0d529@pinky> <20070611091558.f468f205.akpm@linux-foundation.org> <20070611172006.GI9174@redhat.com>
In-Reply-To: <20070611172006.GI9174@redhat.com>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1119
Lines: 26

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
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/