netdev - Re: [PATCH v1 net-next 13/13] net-memcg: Allow decoupling memcg from global protocol memory accounting.

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Message-ID: <CAAVpQUAk4F__D7xdWpt0SEE4WEM_-6V1P7DUw9TGaV=pxZ+tgw@mail.gmail.com>
Date: Tue, 22 Jul 2025 12:03:48 -0700
From: Kuniyuki Iwashima <kuniyu@...gle.com>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Eric Dumazet <edumazet@...gle.com>, "David S. Miller" <davem@...emloft.net>, 
	Jakub Kicinski <kuba@...nel.org>, Neal Cardwell <ncardwell@...gle.com>, Paolo Abeni <pabeni@...hat.com>, 
	Willem de Bruijn <willemb@...gle.com>, Matthieu Baerts <matttbe@...nel.org>, 
	Mat Martineau <martineau@...nel.org>, Johannes Weiner <hannes@...xchg.org>, 
	Michal Hocko <mhocko@...nel.org>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	Andrew Morton <akpm@...ux-foundation.org>, Simon Horman <horms@...nel.org>, 
	Geliang Tang <geliang@...nel.org>, Muchun Song <muchun.song@...ux.dev>, 
	Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org, mptcp@...ts.linux.dev, 
	cgroups@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v1 net-next 13/13] net-memcg: Allow decoupling memcg from
 global protocol memory accounting.

On Tue, Jul 22, 2025 at 11:48 AM Shakeel Butt <shakeel.butt@...ux.dev> wrote:
>
> On Tue, Jul 22, 2025 at 11:18:40AM -0700, Kuniyuki Iwashima wrote:
> > >
> > > I expect this state of jobs with different network accounting config
> > > running concurrently is temporary while the migrationg from one to other
> > > is happening. Please correct me if I am wrong.
> >
> > We need to migrate workload gradually and the system-wide config
> > does not work at all.  AFAIU, there are already years of effort spent
> > on the migration but it's not yet completed at Google.  So, I don't think
> > the need is temporary.
> >
>
> From what I remembered shared borg had completely moved to memcg
> accounting of network memory (with sys container as an exception) years
> ago. Did something change there?

AFAICS, there are some workloads that opted out from memcg and
consumed too much tcp memory due to tcp_mem=UINT_MAX, triggering
OOM and disrupting other workloads.

>
> > >
> > > My main concern with the memcg knob is that it is permanent and it
> > > requires a hierarchical semantics. No need to add a permanent interface
> > > for a temporary need and I don't see a clear hierarchical semantic for
> > > this interface.
> >
> > I don't see merits of having hierarchical semantics for this knob.
> > Regardless of this knob, hierarchical semantics is guaranteed
> > by other knobs.  I think such semantics for this knob just complicates
> > the code with no gain.
> >
>
> Cgroup interfaces are hierarchical and we want to keep it that way.
> Putting non-hierarchical interfaces just makes configuration and setup
> hard to reason about.

Actually, I tried that way in the initial draft version, but even if the
parent's knob is 1 and child one is 0, a harmful scenario didn't come
to my mind.


>
> >
> > >
> > > I am wondering if alternative approches for per-workload settings are
> > > explore starting with BPF.
> > >
>
> Any response on the above? Any alternative approaches explored?

Do you mean flagging each socket by BPF at cgroup hook ?

I think it's overkill and we don't need such finer granularity.

Also it sounds way too hacky to use BPF to correct the weird
behaviour from day0.  We should have more generic way to
control that.  I know this functionality is helpful for some workloads
at Amazon as well.