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

[Shakeel Butt <shakeel.butt@linux.dev>]

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@cdn77.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.