linux-kernel - Re: SLUB doesn't work with kdump kernel on Cell

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Date:	Wed, 8 Aug 2007 13:26:04 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Lucio Correia <ljhc@...ibm.com>
cc:	linux-kernel@...r.kernel.org, Arnd Bergmann <arndb@...db.de>
Subject: Re: SLUB doesn't work with kdump kernel on Cell

On Wed, 8 Aug 2007, Lucio Correia wrote:

> Hi Christoph,
> 
> I found a problem with SLUB when trying to boot a kdump kernel on a Cell
> QS20 Blade running Fedora 7, kernel 2.6.22.5. If I use SLAB for the
> kdump kernel, everything works ok. The fact is that SLUB doesn't find a
> page frame for allocation in the current node, due to the flag
> GFP_THISNODE on a call to new_slab, and stops at a BUG_ON on line 1802
> of slub.c. 

This is due to the node 1 having only one page. Could you just switch node 
1 off?

SLAB boots because it falls back to node 0 for the control structures. So 
it creates useless control structures for node 1. These are then never 
used since any allocation  attempt to node 1 falls back to node 0.

> I understand that this flag should not be removed, and that there is a
> better solution, but it demonstrates the problem. Could you give me some
> direction on the better way to solve this problem?

Do not create a node that just has one page in it?

Or make it truly empty? An empty node will cause GFP_THISNODE to fall back 
and you then have the same useless control structure allocation as on 
SLAB.

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