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

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Date: Fri, 9 Jun 2023 22:53:50 +0500
From: Shakeel Butt <shakeelb@...gle.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: Abel Wu <wuyun.abel@...edance.com>, Tejun Heo <tj@...nel.org>, 
	Christian Warloe <cwarloe@...gle.com>, Wei Wang <weiwan@...gle.com>, 
	"David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Muchun Song <muchun.song@...ux.dev>, 
	Andrew Morton <akpm@...ux-foundation.org>, David Ahern <dsahern@...nel.org>, 
	Yosry Ahmed <yosryahmed@...gle.com>, "Matthew Wilcox (Oracle)" <willy@...radead.org>, Yu Zhao <yuzhao@...gle.com>, 
	Vasily Averin <vasily.averin@...ux.dev>, Kuniyuki Iwashima <kuniyu@...zon.com>, 
	Martin KaFai Lau <martin.lau@...nel.org>, Xin Long <lucien.xin@...il.com>, 
	Jason Xing <kernelxing@...cent.com>, Michal Hocko <mhocko@...e.com>, 
	Alexei Starovoitov <ast@...nel.org>, open list <linux-kernel@...r.kernel.org>, 
	"open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>, 
	"open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)" <cgroups@...r.kernel.org>, 
	"open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)" <linux-mm@...ck.org>
Subject: Re: [RFC PATCH net-next] sock: Propose socket.urgent for sockmem isolation

On Fri, Jun 9, 2023 at 2:07 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Fri, Jun 9, 2023 at 10:28 AM Abel Wu <wuyun.abel@...edance.com> 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)

I agree with Eric and this is exactly how we at Google overcome the
isolation issue. We have set tcp_mem to unlimited and enabled memcg
accounting of network memory (by surgically incorporating v2 semantics
of network memory accounting in our v1 environment).

I do have one question though:

> This proposal doesn't remove protocal's threshold as we found it
> useful in restraining memory defragment.

Can you explain how you find the global tcp limit useful? What does
memory defragment mean?