On Tue, Aug 26, 2025 at 11:01 AM Martin KaFai Lau <martin.lau@xxxxxxxxx> wrote: > > On 8/25/25 10:00 AM, Roman Gushchin wrote: > > Martin KaFai Lau <martin.lau@xxxxxxxxx> writes: > > > >> On 8/20/25 5:24 PM, Roman Gushchin wrote: > >>>> How is it decided who gets to run before the other? Is it based on > >>>> order of attachment (which can be non-deterministic)? > >>> Yeah, now it's the order of attachment. > >>> > >>>> There was a lot of discussion on something similar for tc progs, and > >>>> we went with specific flags that capture partial ordering constraints > >>>> (instead of priorities that may collide). > >>>> https://lore.kernel.org/all/20230719140858.13224-2-daniel@xxxxxxxxxxxxx > >>>> It would be nice if we can find a way of making this consistent. > >> > >> +1 > >> > >> The cgroup bpf prog has recently added the mprog api support also. If > >> the simple order of attachment is not enough and needs to have > >> specific ordering, we should make the bpf struct_ops support the same > >> mprog api instead of asking each subsystem creating its own. > >> > >> fyi, another need for struct_ops ordering is to upgrade the > >> BPF_PROG_TYPE_SOCK_OPS api to struct_ops for easier extension in the > >> future. Slide 13 in > >> https://drive.google.com/file/d/1wjKZth6T0llLJ_ONPAL_6Q_jbxbAjByp/view > > > > Does it mean it's better now to keep it simple in the context of oom > > patches with the plan to later reuse the generic struct_ops > > infrastructure? > > > > Honestly, I believe that the simple order of attachment should be > > good enough for quite a while, so I'd not over-complicate this, > > unless it's not fixable later. > > I think the simple attachment ordering is fine. Presumably the current link list > in patch 1 can be replaced by the mprog in the future. Other experts can chime > in if I have missed things. I don't think the proposed approach of: list_for_each_entry_srcu(bpf_oom, &bpf_oom_handlers, node, false) { is extensible without breaking things. Sooner or later people will want bpf-oom handlers to be per container, so we have to think upfront how to do it. I would start with one bpf-oom prog per memcg and extend with mprog later. Effectively placing 'struct bpf_oom_ops *' into oc->memcg, and having one global bpf_oom_ops when oc->memcg == NULL. I'm sure other designs are possible, but lets make sure container scope is designed from the beginning. mprog-like multi prog behavior per container can be added later.
