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

From: Lucio Correia
Date: Tue Aug 14 2007 - 11:43:31 EST


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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