From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753295AbYDIIzG (ORCPT ); Wed, 9 Apr 2008 04:55:06 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754567AbYDIIyz (ORCPT ); Wed, 9 Apr 2008 04:54:55 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:60952 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752042AbYDIIyy (ORCPT ); Wed, 9 Apr 2008 04:54:54 -0400 Date: Wed, 9 Apr 2008 10:54:40 +0200 From: Ingo Molnar To: Matti Aarnio Cc: Zhao Forrest , Andi Kleen , discuss@x86-64.org, linux-kernel@vger.kernel.org, yhlu.kernel@gmail.com, ak@suse.de Subject: Re: Does Linux have plan to support memory hole remapping? Message-ID: <20080409085440.GB32466@elte.hu> References: <87iqyro3rc.fsf@basil.nowhere.org> <20080409083700.GU3700@mea-ext.zmailer.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080409083700.GU3700@mea-ext.zmailer.org> User-Agent: Mutt/1.5.17 (2007-11-01) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Matti Aarnio wrote: > On Wed, Apr 09, 2008 at 10:01:59AM +0200, Andi Kleen wrote: > > "Zhao Forrest" writes: > > > > > > As we can see from above information that the physical memory in system > > > is 32768MB(32GB). However OS is only using about > > > (32768-512)MB(MemTotal: 33010240 kB). Does this mean that this > > > linux kernel can't use the physical memory remapped > > > from (4G-512M, 4G) to (32G, 32G+512M)? > > > > The linux kernel can only use the memory passed to it by the BIOS. > > Sometimes they need special BIOS setup options to enable remapping. If > > there are no such options and you can't upgrade it you're out of luck > > > > I would suggest you contact your system vendor. > > I second that. On my home machine I have early ASUS AMD x64 board > from a few years ago. For it I did buy CPU with this memory mapping > hardware inside, but the BIOS did not support it correctly until a > year or two latter, thus I was not able to use all of 4 GB of memory I > had installed there. There was support in BIOS from start, but it did > things wrong. having said that - but we'll still consider sane looking patches that allow the remapping of otherwise inactive RAM. [ We might not even have to touch the system chipset beyond what Linux already knows about it: in theory someone might want to try a hack to GART remap such RAM areas and use a sparse mem map entry to map it to Linux - if the identity of that RAM is crystal-clear and there's enough GART space available. But even then it's probably still at best a dangerous and fragile hack. ] Ingo