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

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Date:   Fri, 08 Sep 2017 22:16:48 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     yanhaishuang@...s.chinamobile.com
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

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.