Date: Wed, 4 May 2011 08:59:28 -0500 (CDT)
From: Christoph Lameter <cl@linux.com>
To: David Rientjes <rientjes@google.com>
cc: Geert Uytterhoeven <geert@linux-m68k.org>,
        James Bottomley <James.Bottomley@suse.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Pekka Enberg <penberg@cs.helsinki.fi>, linux-m68k@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [git pull] m68k SLUB fix for 2.6.39
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On Tue, 3 May 2011, David Rientjes wrote:

> So we're in the unfortunate position where slub works fine for some
> architectures with DISCONTIGMEM and not with others.  It seems like the
> problems originating on James' hppa aren't related to slab allocation at
> all, though, so I'm wondering if we should rethink disallowing SLUB as it
> sits in Linus' tree right now for everything that uses DISCONTINGMEM
> without NUMA and not force them to enable CONFIG_BROKEN?
>
> Perhaps change the kconfig entry to only block slub for parisc instead?

As i have explained multiple times before: This is a generic issue with a
kernel configuration that has DISCONTIGMEM on and NUMA configured off.
Core code in various subsystems makes various assumptions in the !NUMA
case. F.e. page_to_nid(page) == 0. Slub is one of them.

DISCONTIGMEM works fine on !NUMA if it just has a single node which is 0.
But in James' hppa we have multiple nodes and thus a fundamental problem
with node 1 existing in a non NUMA environment. We then have a strange
mixture of NUMA nodes existing in DISCONTIGMEM code and the core code
assuming there are none. This can lead to numerous weird problems.

IMHO A config broken for DISCONTIG and !NUMA for arches that can actually
use multiple DISCONTIG nodes would be the proper thing.

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