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

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Message-ID: <telhuoj5bj5eskhicysxkblc4vr6qlcq3vx7pgi6p34g4zfwxw@6vm2r2hg3my4>
Date: Tue, 22 Jul 2025 10:50:12 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Michal Koutný <mkoutny@...e.com>
Cc: 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, Matyas Hurtik <matyas.hurtik@...77.com>
Subject: Re: [PATCH v3] memcg: expose socket memory pressure in a cgroup

On Tue, Jul 22, 2025 at 10:57:31AM +0200, Michal Koutný wrote:
> 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.


Yes vmpressure is legacy and we should not expose raw underlying number
to the userspace. How about just 0 or 1 and use
mem_cgroup_under_socket_pressure() underlying? In future if we change
the underlying implementation, the output of this interface should be
consistent.