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

From: Cong Wang <xiyou.wangcong@gmail.com>
To: David Ahern <dsahern@gmail.com>
Cc: David Miller <davem@davemloft.net>,
	Linux Kernel Network Developers <netdev@vger.kernel.org>,
	nikita.leshchenko@oracle.com,
	Roopa Prabhu <roopa@cumulusnetworks.com>,
	Stephen Hemminger <stephen@networkplumber.org>,
	Ido Schimmel <idosch@mellanox.com>,
	Jiri Pirko <jiri@mellanox.com>,
	Saeed Mahameed <saeedm@mellanox.com>,
	Alexander Aring <alex.aring@gmail.com>,
	linux-wpan@vger.kernel.org,
	NetFilter <netfilter-devel@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"Eric W. Biederman" <ebiederm@xmission.com>
Subject: Re: [PATCH RFC/RFT net-next 00/17] net: Convert neighbor tables to per-namespace
Date: Tue, 24 Jul 2018 15:09:25 -0700	[thread overview]
Message-ID: <CAM_iQpUc-H2kZCBevePs6g-8qKyJkUhdd1ZDSQgYsCG0ChfC2w@mail.gmail.com> (raw)
In-Reply-To: <5021d874-8e99-6eba-f24b-4257c62d4457@gmail.com>

On Tue, Jul 24, 2018 at 8:14 AM David Ahern <dsahern@gmail.com> wrote:
>
> On 7/19/18 11:12 AM, Cong Wang wrote:
> > On Thu, Jul 19, 2018 at 9:16 AM David Ahern <dsahern@gmail.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.