Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965003AbWH2OoQ (ORCPT ); Tue, 29 Aug 2006 10:44:16 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965005AbWH2OoQ (ORCPT ); Tue, 29 Aug 2006 10:44:16 -0400 Received: from mailer.gwdg.de ([134.76.10.26]:60065 "EHLO mailer.gwdg.de") by vger.kernel.org with ESMTP id S965003AbWH2OoP (ORCPT ); Tue, 29 Aug 2006 10:44:15 -0400 Date: Tue, 29 Aug 2006 16:36:40 +0200 (MEST) From: Jan Engelhardt To: Dong Feng cc: Andi Kleen , Nick Piggin , Arjan van de Ven , Paul Mackerras , Christoph Lameter , David Howells , linux-kernel@vger.kernel.org Subject: Re: The 3G (or nG) Kernel Memory Space Offset In-Reply-To: Message-ID: References: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Spam-Report: Content analysis: 0.0 points, 6.0 required _SUMMARY_ Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1013 Lines: 28 > > The Linux kernel permenantly map 3-4G linear memory space to 0-4G > physical memory space. "3-4G linear memory space" is usually the "kernel space", i.e. 0xc0000000 upwards. mostly the kernel is loaded here (on x86). "0-4G physical memory space" denotes RAM. Since kernelspace is resident, it only seems logical to map it to 0G (that is, the start of RAM), because the end of RAM can be flexible. IOW, you cannot map kernelspace to the physical location 0xc0000000 because there might not be that much RAM. (Also note the PCI memory hole which is near the end of the 4G range.) > My question is that what is the rationality > behind this counterintuitive mapping. Is this just some personal > choice for the earlier kernel developers? Jan Engelhardt -- - 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/