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

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Message-ID: <xr93iq068dyd.fsf@ninji.mtv.corp.google.com>
Date:	Tue, 09 Nov 2010 12:00:26 -0800
From:	Greg Thelen <gthelen@...gle.com>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	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

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>

> ---
>  mm/memcontrol.c |    5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1552,8 +1552,9 @@ u64 mem_cgroup_get_limit(struct mem_cgro
>  	u64 limit;
>  	u64 memsw;
>  
> -	limit = res_counter_read_u64(&memcg->res, RES_LIMIT) +
> -			total_swap_pages;
> +	limit = res_counter_read_u64(&memcg->res, RES_LIMIT);
> +	limit += total_swap_pages << PAGE_SHIFT;
> +
>  	memsw = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
>  	/*
>  	 * If memsw is finite and limits the amount of swap space available
--
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