From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753685AbYDWXhX (ORCPT ); Wed, 23 Apr 2008 19:37:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753292AbYDWXhJ (ORCPT ); Wed, 23 Apr 2008 19:37:09 -0400 Received: from relay1.sgi.com ([192.48.171.29]:35260 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752393AbYDWXhI (ORCPT ); Wed, 23 Apr 2008 19:37:08 -0400 Date: Thu, 24 Apr 2008 09:36:52 +1000 From: David Chinner To: Benjamin Herrenschmidt Cc: Ingo Molnar , Andrew Morton , Linux Kernel Mailing List , Arjan van de Ven , Thomas Gleixner Subject: Re: x86: 4kstacks default Message-ID: <20080423233652.GT103491721@sgi.com> References: <200804181737.m3IHbabI010051@hera.kernel.org> <20080418142934.38ce6bf4.akpm@linux-foundation.org> <20080419142329.GA5339@elte.hu> <1208928421.9060.22.camel@pasglop> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1208928421.9060.22.camel@pasglop> User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 23, 2008 at 03:27:01PM +1000, Benjamin Herrenschmidt wrote: > On Sat, 2008-04-19 at 16:23 +0200, Ingo Molnar wrote: > > * Andrew Morton wrote: > > > > > > config 4KSTACKS > > > > bool "Use 4Kb for kernel stacks instead of 8Kb" > > > > - depends on DEBUG_KERNEL > > > > depends on X86_32 > > > > + default y > > > > > > This patch will cause kernels to crash. > > > > what mainline kernels crash and how will they crash? Fedora and other > > distros have had 4K stacks enabled for years: > > > > $ grep 4K /boot/config-2.6.24-9.fc9 > > CONFIG_4KSTACKS=y > > > > and we've conducted tens of thousands of bootup tests with all sorts of > > drivers and kernel options enabled and have yet to see a single crash > > due to 4K stacks. So basically the kernel default just follows the > > common distro default now. (distros and users can still disable it) > > Do we routinely test nasty scenarii such as a GFP_KERNEL allocation deep > in a call stack trying to swap something out to NFS ? I doubt it, because this is the place that a local XFS filesystem typically blows a 4k stack (direct memory reclaim triggering ->writepage). Boot testing does nothing to exercise the potential paths for stack overflows.... Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group