linux-kernel - Re: crash in kmem_cache

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Date:	Tue, 22 Jan 2008 23:10:58 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	Christoph Lameter <clameter@....com>
Cc:	Olaf Hering <olaf@...fle.de>,
	Pekka Enberg <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	hanth Aravamudan <nacc@...ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	lee.schermerhorn@...com, Linux MM <linux-mm@...ck.org>,
	akpm@...ux-foundation.org
Subject: Re: crash in kmem_cache_init

On (22/01/08 14:57), Christoph Lameter didst pronounce:
> On Tue, 22 Jan 2008, Mel Gorman wrote:
> 
> > > > Whatever this was a problem fixed in the past or not, it's broken again now
> > > > :( . It's possible that there is a __GFP_THISNODE that can be dropped early
> > > > at boot-time that would also fix this problem in a way that doesn't
> > > > affect runtime (like altering cache_grow in my patch does).
> > > 
> > > The dropping of GFP_THISNODE has the same effect as your patch. 
> > 
> > The dropping of it totally? If so, this patch might fix a boot but it'll
> > potentially be a performance regression on NUMA machines that only have
> > nodes with memory, right?
> 
> No the dropping during early allocations.,
> 

We can live with that if the machine otherwise survives during tests.
They are kicked off at the moment with CONFIG_SLAB_DEBUG set but the point
is moot if the patch doesn't work for Olaf. Am still waiting to hear if
the two patches in combination work for him.

> > o 0
> > o 2
> > Nodes with regular memory
> > o 2
> > Current running CPU 0 is associated with node 0
> > Current node is 0
> > 
> > So node 2 has regular memory but it's trying to use node 0 at a glance.
> > I've attached the patch I used against 2.6.24-rc8. It includes the revert.
> 
> We need the current processor to be attached to a node that has 
> memory. We cannot fall back that early because the structures for the 
> other nodes do not exist yet.
> 

Or bodge it early in the boot process so that a node with memory is
always used.

> > Online nodes
> > o 0
> > o 2
> > Nodes with regular memory
> > o 2
> > Current running CPU 0 is associated with node 0
> > Current node is 0
> >  o kmem_list3_init
> 
> This needs to be node 2.
> 

Rather it should be 2. I'll admit the physical setup of this machine is
.... less than ideal but clearly it's something that can happen even if
it's a bad idea.

> > [c0000000005c3b40] c0000000000dadec .cache_grow+0x7c/0x338
> > [c0000000005c3c00] c0000000000db54c .fallback_alloc+0x1c0/0x224
> 
> Fallback during bootstrap.
> 

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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