netdev - Re: [PATCH RFC/RFT net-next 00/17] net: Convert neighbor tables to per-namespace

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Date:   Wed, 25 Jul 2018 12:13:30 -0600
From:   David Ahern <dsahern@...il.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        David Miller <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        nikita.leshchenko@...cle.com,
        Roopa Prabhu <roopa@...ulusnetworks.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Ido Schimmel <idosch@...lanox.com>,
        Jiri Pirko <jiri@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Alexander Aring <alex.aring@...il.com>,
        linux-wpan@...r.kernel.org,
        NetFilter <netfilter-devel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC/RFT net-next 00/17] net: Convert neighbor tables to
 per-namespace

On 7/25/18 11:38 AM, Eric W. Biederman wrote:
> 
> Absolutely NOT.  Global thresholds are exactly correct given the fact
> you are running on a single kernel.
> 
> Memory is not free (Even though we are swimming in enough of it memory
> rarely matters).  One of the few remaining challenges is for containers
> is finding was to limit resources in such a way that one application
> does not mess things up for another container during ordinary usage.
> 
> It looks like the neighbour tables absolutely are that kind of problem,
> because the artificial limits are too strict.   Completely giving up on
> limits does not seem right approach either.  We need to fix the limits
> we have (perhaps making them go away entirely), not just apply a
> band-aid.  Let's get to the bottom of this and make the system better.

Eric: yes, they all share the global resource of memory and there should
be limits on how many entries a remote entity can create.

Network namespaces can provide a separation such that one namespace does
not disrupt networking in another. It is absolutely appropriate to do
so. Your rigid stance is inconsistent given the basic meaning of a
network namespace and the parallels to this same problem -- bridges,
vxlans, and ip fragments. Only neighbor tables are not per-device or per
namespace; your insistence on global limits is missing the mark and wrong.