linux-kernel - Re: [PATCH] ipv4: Namespaceify tcp_max

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Date:   Sat, 9 Sep 2017 18:21:59 +0800
From:   严海双 <yanhaishuang@...s.chinamobile.com>
To:     David Miller <davem@...emloft.net>
Cc:     xiyou.wangcong@...il.com, kuznet@....inr.ac.ru,
        yoshfuji@...ux-ipv6.org, edumazet@...gle.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ipv4: Namespaceify tcp_max_orphans knob



> On 2017年9月9日, at 下午1:16, David Miller <davem@...emloft.net> wrote:
> 
> From: 严海双 <yanhaishuang@...s.chinamobile.com>
> Date: Sat, 9 Sep 2017 13:09:57 +0800
> 
>> 
>> 
>>> On 2017年9月9日, at 下午12:35, Cong Wang <xiyou.wangcong@...il.com> wrote:
>>> 
>>> On Fri, Sep 8, 2017 at 6:25 PM, 严海双 <yanhaishuang@...s.chinamobile.com> wrote:
>>>> 
>>>> 
>>>>> On 2017年9月9日, at 上午6:13, Cong Wang <xiyou.wangcong@...il.com> wrote:
>>>>> 
>>>>> On Wed, Sep 6, 2017 at 8:10 PM, Haishuang Yan
>>>>> <yanhaishuang@...s.chinamobile.com> wrote:
>>>>>> Different namespace application might require different maximal number
>>>>>> of TCP sockets independently of the host.
>>>>> 
>>>>> So after your patch we could have N * net->ipv4.sysctl_tcp_max_orphans
>>>>> in a whole system, right? This just makes OOM easier to trigger.
>>>>> 
>>>> 
>>>> From my understanding, before the patch, we had N * net->ipv4.sysctl_tcp_max_orphans,
>>>> and after the patch, we could have ns1.sysctl_tcp_max_orphans + ns2.sysctl_tcp_max_orphans
>>>> + ns3.sysctl_tcp_max_orphans, is that right? Thanks for your reviewing.
>>> 
>>> Nope, by N I mean the number of containers. Before your patch, the limit
>>> is global, after your patch it is per container.
>>> 
>> 
>> Yeah, for example, if there is N containers, before the patch, I mean the limit is:
>> 
>> 	N * net->ipv4.sysctl_tcp_max_orphans
>> 
>> After the patch, the limit is:
>> 
>> 	ns1. net->ipv4.sysctl_tcp_max_orphans + ns2. net->ipv4.sysctl_tcp_max_orphans + …
> 
> Not true.
> 
> Please remove "N" from your equation of the current situation.
> 
> "sysctl_tcp_max_orphans" applies to entire system, it is a global limit,
> comparing one limit against all orphans in the system, there is no N.

Yes, it’s right. I browse the source code and found that it’s a global limit, 
sorry for my mistake.

Thanks David and Cong.