netdev - Re: [PATCH net-next 06/11] netfilter: nf_flow_table: count and limit hw offloaded entries

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Date:   Fri, 20 May 2022 10:56:06 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Pablo Neira Ayuso <pablo@...filter.org>
Cc:     netfilter-devel@...r.kernel.org, davem@...emloft.net,
        netdev@...r.kernel.org, pabeni@...hat.com,
        Felix Fietkau <nbd@....name>
Subject: Re: [PATCH net-next 06/11] netfilter: nf_flow_table: count and
 limit hw offloaded entries

On Fri, 20 May 2022 09:44:57 +0200 Pablo Neira Ayuso wrote:
> > Why a sysctl and not a netlink attr per table or per device?  
> 
> Per-device is not an option, because the flowtable represents a
> compound of devices.
> 
> Moreover, in tc ct act the flowtable is not bound to a device, while
> in netfilter/nf_tables it is.
> 
> tc ct act does not expose flowtables to userspace in any way, they
> internally allocate one flowtable per zone. I assume there os no good
> netlink interface for them.
> 
> For netfilter/nftables, it should be possible to add per-flowtable
> netlink attributes, my plan is to extend the flowtable netlink
> attribute to add a flowtable maximum size.
> 
> This sysctl count and limit hw will just work as a global limit (which
> is optional), my plan is that the upcoming per-flowtable limit will
> just override this global limit.
> 
> I think it is a reasonable tradeoff for the different requirements of
> the flowtable infrastructure users given there are two clients
> currently for this code.

net namespace is a software administrative unit, setting HW offload
limits on it does not compute for me. It's worse than a module param.

Can we go back to the problem statement? It sounds like the device
has limited but unknown capacity and the sysctl is supposed to be set
by the user magically to the right size, preventing HW flow table from
filling up? Did I get it right? If so some form of request flow control
seems like a better idea...