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

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Message-ID: <fa039702-3d60-4dc0-803a-b094b41fd2b9@cdn77.com>
Date: Wed, 20 Aug 2025 22:37:49 +0200
From: Matyas Hurtik <matyas.hurtik@...77.com>
To: Tejun Heo <tj@...nel.org>
Cc: 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>,
 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
Subject: Re: [PATCH v4] memcg: expose socket memory pressure in a cgroup

Hello,

On 8/20/25 9:03 PM, Tejun Heo wrote:
> 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?

Result of mem_cgroup_under_socket_pressure() depends on
whether self or any ancestors have had socket_pressure set.

So any duration of an ancestor being throttled would also
mean the child was being throttled.

By summing our and our ancestors socket_pressure_duration
we should get our total time being throttled
(possibly more because of overlaps).

Thanks,
Matyas