From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Sun, 11 Nov 2001 17:34:03 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Sun, 11 Nov 2001 17:33:53 -0500 Received: from pc3-redb4-0-cust118.bre.cable.ntl.com ([213.106.223.118]:3570 "HELO opel.itsolve.co.uk") by vger.kernel.org with SMTP id ; Sun, 11 Nov 2001 17:33:34 -0500 Date: Sun, 11 Nov 2001 22:33:31 +0000 From: Mark Zealey To: linux-kernel@vger.kernel.org Subject: Re: Best kernel config for exactly 1GB ram Message-ID: <20011111223330.B24030@itsolve.co.uk> In-Reply-To: <3BEEE61A.6050002@uhura.rueb.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5i In-Reply-To: <3BEEE61A.6050002@uhura.rueb.com>; from steve@uhura.rueb.com on Sun, Nov 11, 2001 at 02:56:58PM -0600 X-Operating-System: Linux sunbeam 2.2.19 X-Homepage: http://zealos.org/ Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Nov 11, 2001 at 02:56:58PM -0600, Steve Bergman wrote: > Hi, > > > I have just upgraded my athlon 1200 system to 1GB ram. I am unclear as > to how I should configure the kernel for this box. The config.help says > to say no to "high memory support" if the kernel will not run on a > machne with more than 1GB. When I do this I notice that my available > memory as reported by top is ~ 120MB less than if I say I want 4GB > support. I recall that linux reserves some of the address space for > itself (I thought it was just 64MB). > > What are the trade offs involved here? Am I better off sacrificing a > bit of the physical memory for reasons of efficiency elsewhere? When I > request support for up to 4GB, what exactly changes with respect to the > visible virtual address space that apps see, etc? > > This is a desktop machine, so it's not running Oracle or anything like > that. I seem to recall Linus mentioning that big databases tend to like > the large (3GB) virtual address space. Personally, I'd just leave it at the default no high-mem option. The kernel will then be able to 'see' about 960MB of the memory, so you loose about 64MB of it, but it's not worth the kernel using bounce-buffers etc just so you can get 64MB more memory. IIRC there was a 2GB patch that just redefined PAGE_OFFSET or something similar, this means that you could see all the memory, but the max virtual memory a process could see would be 2 gig (as opposed to 3 gig with the default). -- Mark Zealey mark@zealos.org mark@itsolve.co.uk UL++++>$ G!>(GCM/GCS/GS/GM) dpu? s:-@ a16! C++++>$ P++++>+++++$ L+++>+++++$ !E---? W+++>$ N- !o? !w--- O? !M? !V? !PS !PE--@ PGP+? r++ !t---?@ !X---? !R- b+ !tv b+ DI+ D+? G+++ e>+++++ !h++* r!-- y-- (www.geekcode.com)