linux-kernel - Re: [PATCH] Fix boot problem in situations where the boot CPU is running on a memoryless node

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Message-ID: <20080123213637.GE3848@us.ibm.com>
Date:	Wed, 23 Jan 2008 13:36:37 -0800
From:	Nishanth Aravamudan <nacc@...ibm.com>
To:	Christoph Lameter <clameter@....com>
Cc:	Pekka Enberg <penberg@...helsinki.fi>, Mel Gorman <mel@....ul.ie>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...abs.org,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	lee.schermerhorn@...com, Linux MM <linux-mm@...ck.org>,
	Olaf Hering <olaf@...fle.de>
Subject: Re: [PATCH] Fix boot problem in situations where the boot CPU is
	running on a memoryless node

On 23.01.2008 [13:14:26 -0800], Christoph Lameter wrote:
> On Wed, 23 Jan 2008, Pekka Enberg wrote:
> 
> > I think Mel said that their configuration did work with 2.6.23
> > although I also wonder how that's possible. AFAIK there has been some
> > changes in the page allocator that might explain this. That is, if
> > kmem_getpages() returned pages for memoryless node before, bootstrap
> > would have worked.
> 
> Regular kmem_getpages is called with GFP_THISNODE set. There was some
> breakage in 2.6.22 and before with GFP_THISNODE returning pages from
> the wrong node if a node had no memory. So it may have worked
> accidentally and in an unsafe manner because the pages would have been
> associated with the wrong node which could trigger bug ons and locking
> troubles.

Right, so it might have functioned before, but the correctness was
wobbly at best... Certainly the memoryless patch series has tightened
that up, but we missed these SLAB issues.

I see that your patch fixed Olaf's machine, Pekka. Nice work on
everyone's part tracking this stuff down.

Thanks,
Nish
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