Re: [PATCH 00/11] cgroup: separate rstat trees

Shakeel Butt
2025-02-24T21:13:41Z

On Thu, Feb 20, 2025 at 08:04:02PM +0000, Yosry Ahmed wrote:
> On Thu, Feb 20, 2025 at 10:14:45AM -0800, JP Kobryn wrote:
> > On 2/20/25 9:59 AM, Yosry Ahmed wrote:
> > > On Thu, Feb 20, 2025 at 09:53:33AM -0800, Shakeel Butt wrote:
> > > > On Thu, Feb 20, 2025 at 05:26:04PM +0000, Yosry Ahmed wrote:
> > > > >
> > > > > Another question is, does it make sense to keep BPF flushing in the
> > > > > "self" css with base stats flushing for now? IIUC BPF flushing is not
> > > > > very popular now anyway, and doing so will remove the need to support
> > > > > flushing and updating things that are not css's. Just food for thought.
> > > > >
> > > >
> > > > Oh if this simplifies the code, I would say go for it.
> > >
> > > I think we wouldn't need cgroup_rstat_ops and some of the refactoring
> > > may not be needed. It will also reduce the memory overhead, and keep it
> > > constant regardless of using BPF which is nice.
> >
> > Yes, this is true. cgroup_rstat_ops was only added to allow cgroup_bpf
> > to make use of rstat. If the bpf flushing remains tied to
> > cgroup_subsys_state::self, then the ops interface and supporting code
> > can be removed. Probably stating the obvious but the trade-off would be
> > that if bpf cgroups are in use, they would account for some extra
> > overhead while flushing the base stats. Is Google making use of bpf-
> > based cgroups?
>
> Ironically I don't know, but I don't expect the BPF flushing to be
> expensive enough to affect this. If someone has the use case that loads
> enough BPF programs to cause a noticeable impact, we can address it
> then.
>
> This series will still be an improvement anyway.

If no one is using the bpf+rstat infra then maybe we should rip it out.
Do you have any concerns?