From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755309AbYDTWxp (ORCPT ); Sun, 20 Apr 2008 18:53:45 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752822AbYDTWxi (ORCPT ); Sun, 20 Apr 2008 18:53:38 -0400 Received: from relay2.sgi.com ([192.48.171.30]:34659 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752543AbYDTWxh (ORCPT ); Sun, 20 Apr 2008 18:53:37 -0400 Date: Mon, 21 Apr 2008 08:53:11 +1000 From: David Chinner To: Eric Sandeen Cc: Arjan van de Ven , Shawn Bohrer , Ingo Molnar , Andrew Morton , Linux Kernel Mailing List , Thomas Gleixner Subject: Re: x86: 4kstacks default Message-ID: <20080420225311.GI108924158@sgi.com> References: <200804181737.m3IHbabI010051@hera.kernel.org> <20080418142934.38ce6bf4.akpm@linux-foundation.org> <20080419142329.GA5339@elte.hu> <20080419145948.GA4528@lintop> <20080419110034.34b70bd5@laptopd505.fenrus.org> <480AAC20.4050604@sandeen.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <480AAC20.4050604@sandeen.net> 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 Sat, Apr 19, 2008 at 09:36:16PM -0500, Eric Sandeen wrote: > Arjan van de Ven wrote: > > > On the flipside the arguments tend to be > > 1) certain stackings of components still runs the risk of overflowing > > 2) I want to run ndiswrapper > > 3) general, unspecified uneasyness. > > > > For 1), we need to know which they are, and then solve them, because even on x86-64 with 8k stacks > > they can be a problem (just because the stack frames are bigger, although not quite double, there). > > Except, apparently, not, at least in my experience. > > Ask the xfs guys if they see stack overflows on x86_64, or on x86. We see them regularly enough on x86 to know that the first question to any strange crash is "are you using 4k stacks?". In comparison, I have never heard of a single stack overflow on x86_64.... > I've personally never seen common stack problems with xfs on x86_64, but > it's very common on x86. I don't have a great answer for why, but > that's my anecdotal evidence. Why? Because XFS makes extensive use of 64 bit types and so stack usage in the critical paths changes by a relatively small amount between 32 bit and 64 bit machines. IIRC, x86_64 only uses about 30% more stack than x86. So given that the stack doubles on x86_64 and we only increase usage (in XFS) from about 1500 bytes to 2000 bytes of stack usage, we have *lots* more stack space to spare on x86_64 compared to 4k stacks on x86.... Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group