linux-kernel - Re: [RFC][PATCH 3/5] memcg: Disable preemption in memcg_check

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Date:	Tue, 20 Sep 2011 16:20:31 +0200
From:	Johannes Weiner <hannes@...xchg.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Christoph Lameter <cl@...ux.com>,
	Greg Thelen <gthelen@...gle.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Subject: Re: [RFC][PATCH 3/5] memcg: Disable preemption in
 memcg_check_events()

On Mon, Sep 19, 2011 at 05:20:43PM -0400, Steven Rostedt wrote:
> From: Steven Rostedt <srostedt@...hat.com>
> 
> The code in memcg_check_events() calls this_cpu_read() on
> different variables without disabling preemption, and can cause
> the calculations to be done from two different CPU variables.
> 
> Disable preemption throughout the check to keep apples and oranges
> from becoming a mixed drink.

Makes sense, thanks!

Since the atomic versions are no longer required with preemption
disabled explicitely, could you also make the this_cpu ops in
__memcg_event_check and __mem_cgroup_target_update non-atomic in the
same go?
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