Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> writes: > 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. Btw, what's the right way to attach struct ops to a cgroup, if there is one? Add a cgroup_id field to the struct and use it in the .reg() callback? Or there is something better? Thanks
