netdev - Re: [RFC] implicit per-namespace devlink instance to set kernel resource limitations

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Date:   Tue, 6 Aug 2019 11:27:17 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Jiri Pirko <jiri@...nulli.us>, dsahern@...il.com
Cc:     netdev@...r.kernel.org, davem@...emloft.net, mlxsw@...lanox.com,
        andrew@...n.ch, f.fainelli@...il.com, vivien.didelot@...il.com,
        mkubecek@...e.cz, stephen@...workplumber.org, daniel@...earbox.net,
        brouer@...hat.com, eric.dumazet@...il.com
Subject: Re: [RFC] implicit per-namespace devlink instance to set kernel
 resource limitations

On Tue, 6 Aug 2019 18:40:36 +0200, Jiri Pirko wrote:
> Hi all.
> 
> I just discussed this with DavidA and I would like to bring this to
> broader audience. David wants to limit kernel resources in network
> namespaces, for example fibs, fib rules, etc.
> 
> He claims that devlink api is rich enough to program this limitations
> as it already does for mlxsw hw resources for example. 

TBH I don't see how you changed anything to do with FIB notifications,
so the fact that the accounting is off now is a bit confusing. I don't
understand how devlink, FIB and namespaces mix :(

> If we have this api for hardware, why don't to reuse it for the
> kernel and it's resources too?

IMHO the netdevsim use of this API is a slight abuse, to prove the
device can fail the FIB changes, nothing more..

> So the proposal is to have some new device, say "kernelnet", that
> would implicitly create per-namespace devlink instance. This devlink
> instance would be used to setup resource limits. Like:
> 
> devlink resource set kernelnet path /IPv4/fib size 96
> devlink -N ns1name resource set kernelnet path /IPv6/fib size 100
> devlink -N ns2name resource set kernelnet path /IPv4/fib-rules size 8
> 
> To me it sounds a bit odd for kernel namespace to act as a device, but
> thinking about it more, it makes sense. Probably better than to define
> a new api. User would use the same tool to work with kernel and hw.
> 
> Also we can implement other devlink functionality, like dpipe.
> User would then have visibility of network pipeline, tables,
> utilization, etc. It is related to the resources too.
> 
> What do you think?

I'm no expert here but seems counter intuitive that device tables would
be aware of namespaces in the first place. Are we not reinventing
cgroup controllers based on a device API? IMHO from a perspective of
someone unfamiliar with routing offload this seems backwards :)