On Mon, Feb 24, 2025 at 01:13:35PM -0800, Shakeel Butt wrote: > 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? We did not end up using the BPF+rstat infra, so I have no objection over removing that. They are kfuncs and supposedly there is no guarantee for them hanging around. However, looking back at the patch series [1], there were 3 main components: (a) cgroup_iter BPF programs support. (b) kfunc hooks for BPF+rstat infra. (c) Selftests. I am not sure if there are other users for cgroup_iter for different purposes than BPF+rstat, and I am not sure if we can remove an iterator program type (in terms of stability). We can drop the kfunc hooks, but they are not really a big deal imo. I am fine either way. If we remove (b) we can also remove the corresponding test, but not the test for cgroup_iter as long as it stays. [1]https://lore.kernel.org/all/20220824233117.1312810-1-haoluo@xxxxxxxxxx/
