netdev - Re: [PATCH net-next] tcp: account for memory pressure signaled by cgroup

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Message-ID: <CANn89iKQQ4TFx9Ch9pyDJro=tchVtySQfJTygCxjRP+zPkZfgg@mail.gmail.com>
Date: Tue, 8 Jul 2025 00:01:21 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: Daniel Sedlak <daniel.sedlak@...77.com>
Cc: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, Jonathan Corbet <corbet@....net>, 
	Neal Cardwell <ncardwell@...gle.com>, Kuniyuki Iwashima <kuniyu@...gle.com>, 
	David Ahern <dsahern@...nel.org>, Jiayuan Chen <jiayuan.chen@...ux.dev>, 
	Christian Hopps <chopps@...n.net>, Sabrina Dubroca <sd@...asysnail.net>, netdev@...r.kernel.org, 
	linux-doc@...r.kernel.org, Matyas Hurtik <matyas.hurtik@...77.com>
Subject: Re: [PATCH net-next] tcp: account for memory pressure signaled by cgroup

On Mon, Jul 7, 2025 at 11:45 PM Daniel Sedlak <daniel.sedlak@...77.com> wrote:
>
> Hi Eric,
> Thank you for your feedback.
>
> On 7/7/25 2:48 PM, Eric Dumazet wrote:
> > On Mon, Jul 7, 2025 at 3:55 AM Daniel Sedlak <daniel.sedlak@...77.com> wrote:
> >>
> >> Currently, we have two memory pressure counters for TCP sockets [1],
> >> which we manipulate only when the memory pressure is signalled through
> >> the proto struct [2].
> >>
> >> However, the memory pressure can also be signaled through the cgroup
> >> memory subsystem, which we do not reflect in the netstat counters.
> >>
> >> This patch adds a new counter to account for memory pressure signaled by
> >> the memory cgroup.
> >
> > OK, but please amend the changelog to describe how to look at the
> > per-cgroup information.
>
> Sure, I will explain it more in v2. I was not sure how much of a
> "storytelling" is appropriate in the commit message.
>
>
> > I am sure that having some details on how to find the faulty cgroup
> > would also help.
>
> Right now, we have a rather fragile bpftrace script for that, but we
> have a WIP patch for memory management, which will expose which cgroup
> is having "difficulties", but that is still ongoing work.
>
> Or do you have any suggestions on how we can incorporate this
> information about "this particular cgroup is under pressure" into the
> net subsystem? Maybe a log line?

Perhaps an additional trace point ?

bpftrace would require to ship a separate program...

Ideally we could trace the cgroup path, or at least the pid.