Re: [RFC PATCH net-next] sock: Propose socket.urgent for sockmem isolation

[Eric Dumazet]

On Fri, Jun 9, 2023 at 10:28 AM Abel Wu <wuyun.abel@xxxxxxxxxxxxx> wrote:
>
> This is just a PoC patch intended to resume the discussion about
> tcpmem isolation opened by Google in LPC'22 [1].
>
> We are facing the same problem that the global shared threshold can
> cause isolation issues. Low priority jobs can hog TCP memory and
> adversely impact higher priority jobs. What's worse is that these
> low priority jobs usually have smaller cpu weights leading to poor
> ability to consume rx data.
>
> To tackle this problem, an interface for non-root cgroup memory
> controller named 'socket.urgent' is proposed. It determines whether
> the sockets of this cgroup and its descendants can escape from the
> constrains or not under global socket memory pressure.
>
> The 'urgent' semantics will not take effect under memcg pressure in
> order to protect against worse memstalls, thus will be the same as
> before without this patch.
>
> This proposal doesn't remove protocal's threshold as we found it
> useful in restraining memory defragment. As aforementioned the low
> priority jobs can hog lots of memory, which is unreclaimable and
> unmovable, for some time due to small cpu weight.
>
> So in practice we allow high priority jobs with net-memcg accounting
> enabled to escape the global constrains if the net-memcg itselt is
> not under pressure. While for lower priority jobs, the budget will
> be tightened as the memory usage of 'urgent' jobs increases. In this
> way we can finally achieve:
>
>   - Important jobs won't be priority inversed by the background
>     jobs in terms of socket memory pressure/limit.
>
>   - Global constrains are still effective, but only on non-urgent
>     jobs, useful for admins on policy decision on defrag.
>
> Comments/Ideas are welcomed, thanks!
>

This seems to go in a complete opposite direction than memcg promises.

Can we fix memcg, so that :

Each group can use the memory it was provisioned (this includes TCP buffers)

Global tcp_memory can disappear (set tcp_mem to infinity)