linux-kernel - Re: x86: 4kstacks default

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Date:	Wed, 23 Apr 2008 15:27:01 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: x86: 4kstacks default


On Sat, 2008-04-19 at 16:23 +0200, Ingo Molnar wrote:
> * Andrew Morton <akpm@...ux-foundation.org> 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 ?

Ben.


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