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

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Date:   Tue, 17 Jul 2018 13:37:26 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     David Ahern <dsahern@...il.com>
Cc:     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 Tue, Jul 17, 2018 at 12:02 PM David Ahern <dsahern@...il.com> wrote:
> As for the per-namespace tables, it is 4 years later and over that time
> Linux supports a number of features: EVPN which is very mac heavy, VRR
> which doubles mac entries (one against the VRR device and one against
> the lower device) and NOS level features such as mlxsw which has to
> ensure mac entries for nexthop gateaways stay active. In addition there
> are other features on the horizon - like the ability to use namespaces
> to create virtual switches (what Cisco calls a VDC) where you absolutely
> want isolation and not allowing entries from virtual switch to evict
> entries from another. And of course the continued proliferation of
> containerized workloads where isolation is desired.

As long as no change in neigh table code base itself, these can't
address the concern people raised before.


>
> I understand the concern about global resource and limits: as it stands
> you have to increase the limits in init_net to the max expected and hope
> for the best. With per namespace limits you can lower the limits of each
> namespace better control the total impact on the total memory used.

The problem is that the number of containers in a host is usually
not predictable.

Of course, you can say containers limit kernel memory too, but
memcg is not part of netns. I once told David Miller cpuset is the
isolation for isolating per-CPU softnet_data, he didn't like it. Based
on that I don't think you can convince him with memcg as a solution
here.