linux-kernel - Re: [PATCH] memcg: remove unneeded preempt

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Message-ID: <1314299115.26922.2.camel@twins>
Date:	Thu, 25 Aug 2011 21:05:15 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	James Bottomley <James.bottomley@...senPartnership.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Thelen <gthelen@...gle.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Balbir Singh <bsingharora@...il.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH] memcg: remove unneeded preempt_disable

On Thu, 2011-08-25 at 13:46 -0500, Christoph Lameter wrote:
> 
> RISC cpus have instruction to construct complex atomic actions by the cpu
> as I have shown before for ARM. 

Also, I thought this_cpu thing's were at best locally atomic. If you
make them full blown atomic ops then even __this_cpu ops will have to be
full atomic ops, otherwise:


CPU0			CPU(1)

this_cpu_inc(&foo);	preempt_disable();
			__this_cpu_inc(&foo);
			preempt_enable();

might step on each other's toes.
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