From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030506AbXDWRCA (ORCPT ); Mon, 23 Apr 2007 13:02:00 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030357AbXDWRCA (ORCPT ); Mon, 23 Apr 2007 13:02:00 -0400 Received: from gw.goop.org ([64.81.55.164]:36709 "EHLO mail.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030506AbXDWRCA (ORCPT ); Mon, 23 Apr 2007 13:02:00 -0400 Message-ID: <462CE69E.8040207@goop.org> Date: Mon, 23 Apr 2007 10:02:22 -0700 From: Jeremy Fitzhardinge User-Agent: Thunderbird 1.5.0.10 (X11/20070302) MIME-Version: 1.0 To: "H. Peter Anvin" CC: "Eric W. Biederman" , Chuck Ebbert , Andi Kleen , Andrew Morton , virtualization@lists.osdl.org, lkml , Zachary Amsden , Chris Wright , Linus Torvalds Subject: Re: [PATCH 10/28] i386: map enough initial memory to create lowmem mappings References: <20070414204154.871250608@goop.org> <200704192250.52633.ak@suse.de> <4627D756.5020405@zytor.com> <200704192304.01053.ak@suse.de> <4627DB0C.2010804@zytor.com> <4627DDAD.4070805@redhat.com> <4627E099.209@goop.org> <462CE027.4030302@goop.org> <462CE1E0.9060007@zytor.com> In-Reply-To: <462CE1E0.9060007@zytor.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org H. Peter Anvin wrote: > Since we allocate the maximum possible memory statically, I fail to > see how holes could make the situation any worse, or better. No, we map enough space to map 4G (~4 pages), but we don't actually map 4G. If a hole happened to start within that 4 page mapping, then the memory still wouldn't be available for allocation. I think this is a bit of a spurious argument though, since if it were really a problem we'd have to worry about holes hitting the kernel image too. As far as I can see, that's not considered to be a problem. I think the real point is that there's currently a subtle dependency between head.S and bootmem allocation which happens between start_kernel and pagetable_init. Your patch preventing over-mapping should make them easier to smoke out as it currently stands, but eliminating the problem by making alloc_bootmem create the mappings for itself does have appeal. There would still be the dependency on head.S to map the kernel itself and the bootmem allocator bitmap. J