From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S267179AbUBMWLh (ORCPT ); Fri, 13 Feb 2004 17:11:37 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S267243AbUBMWLh (ORCPT ); Fri, 13 Feb 2004 17:11:37 -0500 Received: from lists.us.dell.com ([143.166.224.162]:1244 "EHLO lists.us.dell.com") by vger.kernel.org with ESMTP id S267179AbUBMWLc (ORCPT ); Fri, 13 Feb 2004 17:11:32 -0500 Date: Fri, 13 Feb 2004 16:09:09 -0600 From: Matt Domsch To: "Martin J. Bligh" Cc: Sean Neakums , Nagy Tibor , xela@slit.de, mochel@osdl.org, bmoyle@mvista.com, orc@pell.chi.il.us, linux-kernel@vger.kernel.org Subject: Re: HIGHMEM Message-ID: <20040213160909.A6102@lists.us.dell.com> References: <402CC114.8080100@dell633.otpefo.com> <6uvfmbktrj.fsf@zork.zork.net> <64200000.1076688313@[10.10.2.4]> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5.1i In-Reply-To: <64200000.1076688313@[10.10.2.4]>; from mbligh@aracnet.com on Fri, Feb 13, 2004 at 08:05:14AM -0800 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 13, 2004 at 08:05:14AM -0800, Martin J. Bligh wrote: > >> We have two Dell Poweredge servers, an older one (PowerEdge 6300) and a > >> newer one (PowerEdge 6400). Both servers have 4GB RAM, but the Linux > >> kernel uses about 500MB less memory in the newer machine. > > > > I may be talking through my hat, but I think that in this case you > > need to select the option for support of 64G highmem. If I recall, > > "4G highmem" refers not to the total amount to the memory, but to the > > highest physical address that can be accessed. > > That's exactly correct. Whether the gain of 500MB of RAM is worth the > overhead of PAE is another question ... but that's how to do it ;-) If the chipset and BIOS can't remap the physical RAM out of the address space needed by the PCI devices and into PAE space, then PAE doesn't buy you anything. You need chipset support for RAM remapping, which doesn't exist on the servers mentioned. Thanks, Matt -- Matt Domsch Sr. Software Engineer, Lead Engineer Dell Linux Solutions linux.dell.com & www.dell.com/linux Linux on Dell mailing lists @ http://lists.us.dell.com