linux-kernel - Re: [patch] memcg: fix unit mismatch in memcg oom limit calculation

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Message-ID: <alpine.DEB.2.00.1011091327420.7730@chino.kir.corp.google.com>
Date:	Tue, 9 Nov 2010 13:31:48 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Greg Thelen <gthelen@...gle.com>
cc:	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Balbir Singh <balbir@...ibm.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [patch] memcg: fix unit mismatch in memcg oom limit
 calculation

On Tue, 9 Nov 2010, Greg Thelen wrote:

> Johannes Weiner <hannes@...xchg.org> writes:
> 
> > Adding the number of swap pages to the byte limit of a memory control
> > group makes no sense.  Convert the pages to bytes before adding them.
> >
> > The only user of this code is the OOM killer, and the way it is used
> > means that the error results in a higher OOM badness value.  Since the
> > cgroup limit is the same for all tasks in the cgroup, the error should
> > have no practical impact at the moment.
> >
> > But let's not wait for future or changing users to trip over it.
> 
> Thanks for the fix.
> 
> > Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> Reviewed-by: Greg Thelen <gthelen@...gle.com>
> 

Nice catch, but it's done in the opposite way: the oom killer doesn't use 
byte limits but page limits.  So this needs to be

	(res_counter_read_u64(&memcg->res, RES_LIMIT) >> PAGE_SHIFT) +
			total_swap_pages;
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