linux-kernel - Re: [PATCH] res_counter: fix off-by-one bug in setting limit

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Message-ID: <48BB811D.6070106@cn.fujitsu.com>
Date:	Mon, 01 Sep 2008 13:43:57 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Pavel Emelianov <xemul@...nvz.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] res_counter: fix off-by-one bug in setting limit

KAMEZAWA Hiroyuki wrote:
> On Mon, 01 Sep 2008 13:08:55 +0800
> Li Zefan <lizf@...fujitsu.com> wrote:
> 
>> I found we can no longer set limit to 0 with 2.6.27-rcX:
>>  # mount -t cgroup -omemory xxx /mnt
>>  # mkdir /mnt/0
>>  # echo 0 > /mnt/0/memory.limit_in_bytes
>>  bash: echo: write error: Device or resource busy
>>
>> It turned out 'limit' can't be set to 'usage', which is wrong IMO.
>>
>> Signed-off-by: Li Zefan <lizf@...fujitsu.com>
> 
> But setting limit to 0(usage) in memcg is buggy operation unless you want to see OOM..
> Hmm..
> 

I used to set 0 limit to test OOM in memcg. I don't think 0 limit is buggy, there's no
much difference with 0 limit and a very low limit.

And the real issue is, now we can set limit to > usage, but not >= usage. It's odd that
usage can reach to limit but limit can't be shrinked to usage.

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