netdev - Re: [PATCH v5] memcg: expose socket memory pressure in a cgroup

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Message-ID: <cfoc35cqn7sa63w6kufwvq7rs6s7xiivfbmr752h4rmur4demz@d7joq6oho6qc>
Date: Wed, 15 Oct 2025 11:39:34 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Kuniyuki Iwashima <kuniyu@...gle.com>
Cc: Daniel Sedlak <daniel.sedlak@...77.com>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	Jonathan Corbet <corbet@....net>, Neal Cardwell <ncardwell@...gle.com>, 
	David Ahern <dsahern@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, 
	Yosry Ahmed <yosry.ahmed@...ux.dev>, linux-mm@...ck.org, netdev@...r.kernel.org, 
	Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>, 
	Muchun Song <muchun.song@...ux.dev>, cgroups@...r.kernel.org, Tejun Heo <tj@...nel.org>, 
	Michal Koutný <mkoutny@...e.com>, Matyas Hurtik <matyas.hurtik@...77.com>
Subject: Re: [PATCH v5] memcg: expose socket memory pressure in a cgroup

On Wed, Oct 15, 2025 at 11:21:17AM -0700, Kuniyuki Iwashima wrote:
> On Tue, Oct 14, 2025 at 1:33 PM Shakeel Butt <shakeel.butt@...ux.dev> wrote:
> >
> > On Mon, Oct 13, 2025 at 04:30:53PM +0200, Daniel Sedlak wrote:
> > [...]
> > > > > > > How about we track the actions taken by the callers of
> > > > > > > mem_cgroup_sk_under_memory_pressure()? Basically if network stack
> > > > > > > reduces the buffer size or whatever the other actions it may take when
> > > > > > > mem_cgroup_sk_under_memory_pressure() returns, tracking those actions
> > > > > > > is what I think is needed here, at least for the debugging use-case.
> > >
> > > I am not against it, but I feel that conveying those tracked actions (or how
> > > to represent them) to the user will be much harder. Are there already
> > > existing APIs to push this information to the user?
> > >
> >
> > I discussed with Wei Wang and she suggested we should start tracking the
> > calls to tcp_adjust_rcv_ssthresh() first. So, something like the
> > following. I would like feedback frm networking folks as well:
> 
> I think we could simply put memcg_memory_event() in
> mem_cgroup_sk_under_memory_pressure() when it returns
> true.
> 
> Other than tcp_adjust_rcv_ssthresh(), if tcp_under_memory_pressure()
> returns true, it indicates something bad will happen, failure to expand
> rcvbuf and sndbuf, need to prune out-of-order queue more aggressively,
> FIN deferred to a retransmitted packet.
> 
> Also, we could cover mptcp and sctp too.
> 

I wanted to start simple and focus on one specific action but I am open
to other actins as well. Do we want a generic network throttled metric
or do we want different metric for different action? At the moment I
think for memcg, a single metric would be sufficient and then we can
have tracepoints for more fine grained debugging.