linux-kernel - Re: [PATCH 2/6] change alloc function in pcpu_alloc

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Message-ID: <4BC6BE78.1030503@kernel.org>
Date:	Thu, 15 Apr 2010 16:21:28 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Minchan Kim <minchan.kim@...il.com>
CC:	Mel Gorman <mel@....ul.ie>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Bob Liu <lliubbo@...il.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [PATCH 2/6] change alloc function in pcpu_alloc_pages

Hello,

On 04/15/2010 10:31 AM, Minchan Kim wrote:
> Hi, Tejun.
>> This being a pretty cold path, I don't really see much benefit in
>> converting it to alloc_pages_node_exact().  It ain't gonna make any
>> difference.  I'd rather stay with the safer / boring one unless
>> there's a pressing reason to convert.
> 
> Actually, It's to weed out not-good API usage as well as some
> performance gain.  But I don't think to need it strongly.
> Okay. Please keep in mind about this and correct it if you confirms
> it in future. :)

Hmm... if most users are converting over to alloc_pages_node_exact(),
I think it would be better to convert percpu too.  I thought it was a
performance optimization (of rather silly kind too).  So, this is to
weed out -1 node id usage?  Wouldn't it be better to update
alloc_pages_node() such that it whines once per each caller if it's
called with -1 node id and after updating most users convert the
warning into WARN_ON_ONCE()?  Having two variants for this seems
rather extreme to me.

Thanks.

-- 
tejun
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