netdev - Re: [PATCH v3] memcg: expose socket memory pressure in a cgroup

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Message-ID: <ni4axiks6hvap3ixl6i23q7grjbki3akeea2xxzhdlkmrj5hpb@qt3vtmiayvpz>
Date: Tue, 22 Jul 2025 10:57:31 +0200
From: Michal Koutný <mkoutny@...e.com>
To: Daniel Sedlak <daniel.sedlak@...77.com>, 
	Shakeel Butt <shakeel.butt@...ux.dev>
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>, 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 v3] memcg: expose socket memory pressure in a cgroup

Hello Daniel.

On Tue, Jul 22, 2025 at 09:11:46AM +0200, Daniel Sedlak <daniel.sedlak@...77.com> wrote:
>   /sys/fs/cgroup/**/<cgroup name>/memory.net.socket_pressure
> 
> The output value is an integer matching the internal semantics of the
> struct mem_cgroup for socket_pressure. It is a periodic re-arm clock,
> representing the end of the said socket memory pressure, and once the
> clock is re-armed it is set to jiffies + HZ.

I don't find it ideal to expose this value in its raw form that is
rather an implementation detail.

IIUC, the information is possibly valid only during one jiffy interval.
How would be the userspace consuming this?

I'd consider exposing this as a cummulative counter in memory.stat for
simplicity (or possibly cummulative time spent in the pressure
condition).

Shakeel, how useful is this vmpressure per-cgroup tracking nowadays? I
thought it's kind of legacy.

Thanks,
Michal

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