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

[Tejun Heo <tj@kernel.org>]

Hello,

On Tue, Aug 05, 2025 at 08:44:29AM +0200, Daniel Sedlak wrote:
> This patch exposes a new file for each cgroup in sysfs which signals
> the cgroup socket memory pressure. The file is accessible in
> the following path.
> 
>   /sys/fs/cgroup/**/<cgroup name>/memory.net.socket_pressure
> 
> The output value is a cumulative sum of microseconds spent
> under pressure for that particular cgroup.

I'm not sure the pressure name fits the best when the content is the
duration. Note that in the memory.pressure file, the main content is
time-averaged percentages which are the "pressure" numbers. Can this be an
entry in memory.stat which signifies that it's a duration? net_throttle_us
or something like that?

Also, as Shakeel already pointed out, this would need to be accumulated
hierarchically. The tricky thing is determining how the accumulation should
work. Hierarchical summing up is simple and we can use the usual rstat
propagation; however, that would deviate from how pressure durations are
propagated for .pressure metrics, where each cgroup tracks all / some
contention states in its descendants. For simplicity's sake and if the
number ends up in memory.stat, I think simple summing up should be fine as
long as it's so noted in the documentation. Note that this semantical
difference would be another reason to avoid the "pressure" name.

Thanks.

-- 
tejun