linux-kernel - Re: [PATCH 1/3] slqb: Do not use DEFINE_PER

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Date:	Mon, 21 Sep 2009 16:31:42 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Sachin Sant <sachinp@...ibm.com>, Tejun Heo <tj@...nel.org>,
	Nick Piggin <npiggin@...e.de>,
	Christoph Lameter <cl@...ux-foundation.org>,
	heiko.carstens@...ibm.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH 1/3] slqb: Do not use DEFINE_PER_CPU for per-node data

On Mon, Sep 21, 2009 at 4:04 PM, Mel Gorman <mel@....ul.ie> wrote:
>> The "per-cpu" area in this case is actually a per-node area. This implied that
>> it was either racing (but the locking looked sound), a buffer overflow (but
>> I couldn't find one) or the per-cpu areas were being written to by something
>> else unrelated.
>
> This latter guess was close to the mark but not for the reasons I was
> guessing. There isn't magic per-cpu-area-freeing going on. Once I examined
> the implementation of per-cpu data, it was clear that the per-cpu areas for
> the node IDs were never being allocated in the first place on PowerPC. It's
> probable that this never worked but that it took a long time before SLQB
> was run on a memoryless configuration.
>
> This patch would replace patch 1 of the first hatchet job I did. It's possible
> a similar patch is needed for S390. I haven't looked at the implementation
> there and I don't have a means of testing it.

Other architectures could be affected as well which makes me think
"hatchet job number one" is the way forward. Nick?

                        Pekka
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