linux-kernel - Re: [PATCH v5 7/8] mm: Only IPI CPUs to drain local pages if they exist

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Message-ID: <20120105142017.GA27881@csn.ul.ie>
Date:	Thu, 5 Jan 2012 14:20:17 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
Cc:	Gilad Ben-Yossef <gilad@...yossef.com>,
	linux-kernel@...r.kernel.org, Chris Metcalf <cmetcalf@...era.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Russell King <linux@....linux.org.uk>, linux-mm@...ck.org,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>,
	Sasha Levin <levinsasha928@...il.com>,
	Rik van Riel <riel@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, Avi Kivity <avi@...hat.com>
Subject: Re: [PATCH v5 7/8] mm: Only IPI CPUs to drain local pages if they
 exist

On Tue, Jan 03, 2012 at 12:45:45PM -0500, KOSAKI Motohiro wrote:
> >   void drain_all_pages(void)
> >   {
> > -	on_each_cpu(drain_local_pages, NULL, 1);
> > +	int cpu;
> > +	struct per_cpu_pageset *pcp;
> > +	struct zone *zone;
> > +
> 
> get_online_cpu() ?
> 

Just a separate note;

I'm looking at some mysterious CPU hotplug problems that only happen
under heavy load. My strongest suspicion at the moment that the problem
is related to on_each_cpu() being used without get_online_cpu() but you
cannot simply call get_online_cpu() in this path without causing
deadlock.

If/when I get a patch that can complete a CPU hotplug stress test
successfully, I'll post it. It'll collide with this series but it should
be manageable.

-- 
Mel Gorman
SUSE Labs
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