netdev - Re: [PATCH v4] memcg: expose socket memory pressure in a cgroup

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Message-ID: <gqeq3trayjsylgylrl5wdcrrp7r5yorvfxc6puzuplzfvrqwjg@j4rr5vl5dnak>
Date: Wed, 13 Aug 2025 14:03:28 +0200
From: Michal Koutný <mkoutny@...e.com>
To: Tejun Heo <tj@...nel.org>, Daniel Sedlak <daniel.sedlak@...77.com>
Cc: "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>, 
	Kuniyuki Iwashima <kuniyu@...gle.com>, David Ahern <dsahern@...nel.org>, 
	Andrew Morton <akpm@...ux-foundation.org>, Shakeel Butt <shakeel.butt@...ux.dev>, 
	Yosry Ahmed <yosry.ahmed@...ux.dev>, linux-mm@...ck.org, netdev@...r.kernel.org, 
	Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Muchun Song <muchun.song@...ux.dev>, cgroups@...r.kernel.org, 
	Matyas Hurtik <matyas.hurtik@...77.com>
Subject: Re: [PATCH v4] memcg: expose socket memory pressure in a cgroup

On Sat, Aug 09, 2025 at 08:32:22AM -1000, Tejun Heo <tj@...nel.org> wrote:
> Also, as Shakeel already pointed out, this would need to be accumulated
> hierarchically. The tricky thing is determining how the accumulation should
> work. Hierarchical summing up is simple and we can use the usual rstat
> propagation; however, that would deviate from how pressure durations are
> propagated for .pressure metrics, where each cgroup tracks all / some
> contention states in its descendants. For simplicity's sake and if the
> number ends up in memory.stat, I think simple summing up should be fine as
> long as it's so noted in the documentation. Note that this semantical
> difference would be another reason to avoid the "pressure" name.

One more point to clarify -- should the value include throttling from
ancestors or not. (I think both are fine but) this semantic should also
be described in the docs. I.e. current proposal is
	value = sum_children + self
and if you're see that C's value is 0, it doesn't mean its sockets
weren't subject of throttling. It just means you need to check also
values in C ancestors. Does that work?

Thanks,
Michal

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