Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765973AbXFGRlJ (ORCPT ); Thu, 7 Jun 2007 13:41:09 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758480AbXFGRk5 (ORCPT ); Thu, 7 Jun 2007 13:40:57 -0400 Received: from lucidpixels.com ([75.144.35.66]:60428 "EHLO lucidpixels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752702AbXFGRk5 (ORCPT ); Thu, 7 Jun 2007 13:40:57 -0400 Date: Thu, 7 Jun 2007 13:40:55 -0400 (EDT) From: Justin Piszcz X-X-Sender: jpiszcz@p34.internal.lan To: Jesse Barnes cc: Andi Kleen , linux-kernel@vger.kernel.org, "Eric W. Biederman" Subject: Re: [PATCH] trim memory not covered by WB MTRRs In-Reply-To: <200706071035.18356.jesse.barnes@intel.com> Message-ID: References: <200706061229.24486.jesse.barnes@intel.com> <20070607081619.GA15226@one.firstfloor.org> <200706071035.18356.jesse.barnes@intel.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1768 Lines: 45 On Thu, 7 Jun 2007, Jesse Barnes wrote: > On Thursday, June 7, 2007 1:16 am Andi Kleen wrote: >> On Wed, Jun 06, 2007 at 12:29:23PM -0700, Jesse Barnes wrote: >>> On some machines, buggy BIOSes don't properly setup WB MTRRs to >>> cover all available RAM, meaning the last few megs (or even gigs) >>> of memory will be marked uncached. Since Linux tends to allocate >>> from high memory addresses first, this causes the machine to be >>> unusably slow as soon as the kernel starts really using memory >>> (i.e. right around init time). >> >> In theory -- while not recommended -- a BIOS could also >> use a default fallback MTRR for cached and use explicit MTRRs to >> map the non existing ranges uncached. Would it make sense to handle >> this case? > > Probably. I could just check the default memory type and bail out if > it's cacheable. > >> Should also probably have some command line option >> to disable the check in case something bad happens with it. > > Sure. > >> Another thing that might be sense to investigate in relationship >> to this patch is large page mappings with MTRRs. iirc P4 and also K8 >> splits pages internally with MTRR boundaries and might have some >> other bad side effects. Should we use this as hints to use 4K pages >> for the boundary areas? > > Or I could trim to the nearest large page boundary... We'd lose a > little more memory but it would keep things simple. > > Jesse > How much more memory are we going to lose? Is mem= a better option if its going to keep decreasing? - 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/