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

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Date:   Tue, 24 Jul 2018 15:09:25 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     David Ahern <dsahern@...il.com>
Cc:     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>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH RFC/RFT net-next 00/17] net: Convert neighbor tables to per-namespace

On Tue, Jul 24, 2018 at 8:14 AM David Ahern <dsahern@...il.com> wrote:
>
> On 7/19/18 11:12 AM, Cong Wang wrote:
> > On Thu, Jul 19, 2018 at 9:16 AM David Ahern <dsahern@...il.com> wrote:
> >>
> >> Chatting with Nikolay about this and he brought up a good corollary - ip
> >> fragmentation. It really is a similar problem in that memory is consumed
> >> as a result of packets received from an external entity. The ipfrag
> >> sysctls are per namespace with a limit that non-init_net namespaces can
> >> not set high_thresh > the current value of init_net. Potential memory
> >> consumed by fragments scales with the number of namespaces which is the
> >> primary concern with making neighbor tables per namespace.
> >
> > Nothing new, already discussed:
> > https://marc.info/?l=linux-netdev&m=140391416215988&w=2
> >
> > :)
> >
>
> Neighbor tables, bridge fdbs, vxlan fdbs and ip fragments all consume
> local memory resources due to received packets. bridge and vxlan fdb's
> are fairly straightforward analogs to neighbor entries; they are per
> device with no limits on the number of entries. Fragments have memory
> limits per namespace. So neighbor tables are the only ones with this
> strict limitation and concern on memory consumption.
>
> I get the impression there is no longer a strong resistance against
> moving the tables to per namespace, but deciding what is the right
> approach to handle backwards compatibility. Correct? Changing the
> accounting is inevitably going to be noticeable to some use case(s), but
> with sysctl settings it is a simple runtime update once the user knows
> to make the change.

This question definitely should go to Eric Biederman who was against
my proposal.

Let's add Eric into CC.