Re: [PATCH v5 2/2] sched/numa: add statistics of numa balance task

[Chen, Yu C]

On 6/17/2025 5:30 PM, Michal Koutný wrote:
> On Tue, Jun 03, 2025 at 10:46:06PM +0800, "Chen, Yu C" <yu.c.chen@xxxxxxxxx> wrote:
> > My understanding is that the "misplaced" container is not strictly tied
> > to set_mempolicy or cpuset configuration, but is mainly caused by the
> > scheduler's generic load balancer.
>
> You are convincing me with this that, cpu.stat fits the concept better.
> Doesn't that sound like that to you?
>
> > Regarding the threaded subtrees mode, I was previously unfamiliar with
> > it and have been trying to understand it better.
>
> No problem.
>
> > If I understand correctly, if threads within a single process are
> > placed in different cgroups via cpuset, we might need to scan
> > /proc/<PID>/sched to collect NUMA task migration/swap statistics.
>
> The premise of your series was that you didn't want to do that :-)
>
> > I agree with your prior point that NUMA balancing task activity is not
> > directly
> > associated with either the Memory controller or the CPU controller. Although
> > showing this data in cpu.stat might seem more appropriate, we expose it in
> > memory.stat due to the following trade-offs(or as an exception for
> > NUMA balancing):
> >
> > 1.It aligns with existing NUMA-related metrics already present in
> > memory.stat.
>
> That one I'd buy into. OTOH, I'd hope this could be overcome with
> documentation.
>
> > 2.It simplifies code implementation.
>
> I'd say that only applies when accepting memory.stat as the better
> place. I think the appropriately matching API should be picked first and
> implementation is only secondary to that.

Thanks for this guidance.

>  From your reasoning above, I think that the concept is closer to be in
> cpu.stat ¯\_(ツ)_/¯
OK. Since this change has already been addressed in upstream kernel,
I can update the numa_task_migrated/numa_task_swapped fields in
Documentation/admin-guide/cgroup-v2.rst to mention that, these
activities are not memory related but put here because they are
closer to numa balance's page statistics.
Or do you want me to submit a patch to move the items from
memory.stat to cpu.stat?

thanks,
Chenyu



> Michal