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

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Message-ID: <zldrraxaeff5gaffaltgzmnsgc7kvnlltubkaury3mhqlfmgwp@jinkxqagerjy>
Date: Wed, 20 Aug 2025 12:31:59 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Tejun Heo <tj@...nel.org>
Cc: Matyas Hurtik <matyas.hurtik@...77.com>, 
	Michal Koutný <mkoutny@...e.com>, Daniel Sedlak <daniel.sedlak@...77.com>, 
	"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>, 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
Subject: Re: [PATCH v4] memcg: expose socket memory pressure in a cgroup

On Wed, Aug 20, 2025 at 09:03:11AM -1000, Tejun Heo wrote:
> Hello,
> 
> On Wed, Aug 20, 2025 at 06:51:07PM +0200, Matyas Hurtik wrote:
> ...
> > And the read side:
> >   total_duration = 0;
> >   for (; !mem_cgroup_is_root(memcg); memcg = parent_mem_cgroup(memcg))
> >     total_duration += atomic_long_read(&memcg->socket_pressure_duration);
> > Would that work?
> 
> This doesn't make sense to me. Why would a child report the numbers from its
> ancestors?

I think Matyas might wanted to do a tree traversal under the given memcg
and by mistake did this upward traversal. However that will miss the
already deleted memcgs under the given memcg.