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

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Message-Id: <1187106239.3298.2.camel@localhost.localdomain>
Date:	Tue, 14 Aug 2007 12:43:59 -0300
From:	Lucio Correia <ljhc@...ibm.com>
To:	Christoph Lameter <clameter@....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, 2007-08-08 at 13:26 -0700, Christoph Lameter wrote:
> 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.

Hi Christoph,

Shouldn't SLUB falls back to other node also for the case it can't
allocate memory? 

> 
> > 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.


-- 
Lucio Correia
Software Engineer
IBM LTC Brazil

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