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

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Date:   Tue, 6 Aug 2019 20:38:41 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc:     dsahern@...il.com, 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

Tue, Aug 06, 2019 at 08:27:17PM CEST, jakub.kicinski@...ronome.com wrote:
>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..

It's slightly bigger abuse :) But in this thread, we are not discussing
netdevsim, but separate "dev".


>
>> 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 :)

Can we use cgroup for fib and other limitations instead?