linux-kernel - Re: [RFC/PATCH] SLQB: Mark the allocator as broken PowerPC and S390

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Date:	Thu, 17 Sep 2009 14:12:32 +0200
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Pekka Enberg <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	cl@...ux-foundation.org, mingo@...e.hu, npiggin@...e.de,
	sachinp@...ibm.com
Subject: Re: [RFC/PATCH] SLQB: Mark the allocator as broken PowerPC and S390

On Thu, Sep 17, 2009 at 11:57:08AM +0100, Mel Gorman wrote:
> On Thu, Sep 17, 2009 at 01:29:24PM +0300, Pekka Enberg wrote:
> > On Wed, Sep 16, 2009 at 09:37:39AM +0300, Pekka Enberg wrote:
> > > > The SLQB allocator is known to be broken on certain PowerPC and S390
> > > > configurations. Disable the allocator in Kconfig for those architectures
> > > > until the issues are resolved. 
> > > 
> > > Can the issues be summarised?
> > 
> > It's a boot time crash during module load:
> > 
> > http://www.mail-archive.com/linuxppc-dev@lists.ozlabs.org/msg33092.html
> > 
> > AFAICT, it's related to a memoryless node 0. Nick suggested it could be
> > a latent bug in the kernel that's triggered by SLQB.
> 
> The danger is that this isn't a PPC or s390 bug then as such, but a bug where
> there are either memoryless nodes or when node 0 is memoryless.  Hence, there
> is no guarantee that your Kconfig option will catch all instances where this
> bug triggers.  Granted, the configuration is most likely a PPC machine :)

Ok, I just wanted to debug this on s390. But... the bug seems to have
disappeared.
I pulled in

git://git.kernel.org/pub/scm/linux/kernel/git/penberg/slab-2.6.git slqb/core

and tried defconfig (+SLQB) as well as allyesconfig (+SLQB). Both started and
didn't show the crash-before-console-is-active which went away when switching
to a different allocator.
So the s390 restriction seems to be resolved. Don't know why...
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