Re: [PATCH v2 02/23] bpf: initial support for attaching struct ops to cgroups

Tejun Heo
2025-10-29T21:45:47Z

Hello,

On Wed, Oct 29, 2025 at 02:37:38PM -0700, Song Liu wrote:
> On Wed, Oct 29, 2025 at 2:27 PM Tejun Heo <tj@kernel.org> wrote:
> > Doesn't that assume that the programs are more or less stateless? Wouldn't
> > oom handlers want to track historical information, running averages, which
> > process expanded the most and so on?
>
> Yes, this does mean the program needs to store data in some BPF maps.
> Do we have concern with the performance of BPF maps?

It's just a lot more awkward to do and I have a difficult time thinking up
reasons why one would need to do that. If you attach a single struct_ops
instance to one cgroup, you can use global variables, maps, arena to track
what's happening with the cgroup. If you share the same struct_ops across
multiple cgroups, each operation has to scope per-cgroup states. I can see
how that probably makes sense for sockets but cgroups aren't sockets. There
are a lot fewer cgroups and they are organized in a tree.

Thanks.

--
tejun