Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753129AbYH0Rgr (ORCPT ); Wed, 27 Aug 2008 13:36:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751247AbYH0Rgi (ORCPT ); Wed, 27 Aug 2008 13:36:38 -0400 Received: from smtp5.pp.htv.fi ([213.243.153.39]:41819 "EHLO smtp5.pp.htv.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750798AbYH0Rgh (ORCPT ); Wed, 27 Aug 2008 13:36:37 -0400 Date: Wed, 27 Aug 2008 20:35:44 +0300 From: Adrian Bunk To: Paul Mundt , Linus Torvalds , Rusty Russell , "Alan D. Brunelle" , "Rafael J. Wysocki" , Linux Kernel Mailing List , Kernel Testers List , Andrew Morton , Arjan van de Ven , Ingo Molnar , linux-embedded@vger.kernel.org Subject: Re: [Bug #11342] Linux 2.6.27-rc3: kernel BUG at mm/vmalloc.c - bisected Message-ID: <20080827173544.GH11734@cs181140183.pp.htv.fi> References: <20080826183051.GB10925@cs181140183.pp.htv.fi> <20080826205916.GB11734@cs181140183.pp.htv.fi> <20080826232411.GC11734@cs181140183.pp.htv.fi> <20080827002316.GE11734@cs181140183.pp.htv.fi> <20080827115829.GF11734@cs181140183.pp.htv.fi> <20080827160052.GA15968@linux-sh.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20080827160052.GA15968@linux-sh.org> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3730 Lines: 90 On Thu, Aug 28, 2008 at 01:00:52AM +0900, Paul Mundt wrote: > On Wed, Aug 27, 2008 at 02:58:30PM +0300, Adrian Bunk wrote: > > On Tue, Aug 26, 2008 at 05:28:37PM -0700, Linus Torvalds wrote: > > > On Wed, 27 Aug 2008, Adrian Bunk wrote: > > > > > > > > When did we get callpaths like like nfs+xfs+md+scsi reliably > > > > working with 4kB stacks on x86-32? > > > > > > XFS may never have been usable, but the rest, sure. > > > > > > And you seem to be making this whole argument an excuse to SUCK, adn an > > > excuse to let gcc crap even more on our stack space. > > > > > > Why? > > > > > > Why aren't you saying that we should be able to do better? Instead, you > > > seem to asking us to do even worse than we do now? > > > > My main point is: > > - getting 4kB stacks working reliably is a hard task > > - having an eye on gcc increasing the stack usage, and fixing it if > > required, is relatively easy > > > > If we should be able to do better at getting (and keeping) 4kB stacks > > working, then coping with possible inlining problems caused by gcc > > should not be a big problem for us. > > > Out of the architectures you've mentioned for 4k stacks, they also tend > to do IRQ stacks, which is something you seem to have overlooked. No, I am aware of that, and on i386 IRQ stacks are only used with 4kB stacks. On i386 it is effectively a step from 6kB to 4kB. > In addition to that, debugging the runaway stack users on 4k tends to be > easier anyways since you end up blowing the stack a lot sooner. On sh > we've had pretty good luck with it, though most of our users are using > fairly deterministic workloads and continually profiling the footprint. > Anything that runs away or uses an insane amount of stack space needs to > be fixed well before that anyways, so catching it sooner is always > preferable. I imagine the same case is true for m68knommu (even sans IRQ > stacks). CONFIG_DEBUG_STACKOVERFLOW should give you the same information, and if wanted with an arbitrary limit. > Things might be more sensitive on x86, but it's certainly not something > that's a huge problem for the various embedded platforms to wire up, > whether they want to go the IRQ stack route or not. How many platforms use 4kB stacks on sh? Only 1 out of 34 defconfigs uses it. Are there any numbers for real life usage. > In any event, lack of support for something on embedded architectures in > the kernel is more often due to apathy/utter indifference on the part of > the architecture maintainer rather than being indicative of any intrinsic > difficulty in supporting the thing in question. Most new "features" on the > lesser maintained architectures tend to end up there either out of peer > pressure or copying-and-pasting accidents rather than any sort of design. > ;-) arm or powerpc aren't exactly lesser maintained architectures. 4kB has shown to be a hard to achieve limit. After more than 4 years in mainline being available on i386 there are still cases where 4kB are not enough. IMHO there seems to currently be a mismatch between it's maintainance cost and the actual number of users. That's in my opinion the main problem with it, no matter in which direction it gets resolved. cu Adrian -- "Is there not promise of rain?" Ling Tan asked suddenly out of the darkness. There had been need of rain for many days. "Only a promise," Lao Er said. Pearl S. Buck - Dragon Seed -- 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/