linux-kernel - Re: [git pull] m68k SLUB fix for 2.6.39

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Message-ID: <alpine.DEB.2.00.1105040851090.5495@router.home>
Date:	Wed, 4 May 2011 08:59:28 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	David Rientjes <rientjes@...gle.com>
cc:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	James Bottomley <James.Bottomley@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	linux-m68k@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [git pull] m68k SLUB fix for 2.6.39

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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