On Thu, Aug 17, 2023 at 8:30 PM Chuyi Zhou <zhouchuyi@xxxxxxxxxxxxx> wrote:
>
> Hello,
> 在 2023/8/17 11:22, Alexei Starovoitov 写道:
> > On Wed, Aug 16, 2023 at 7:51 PM Chuyi Zhou <zhouchuyi@xxxxxxxxxxxxx> wrote:
> >>
> >> Hello,
> >>
> >> 在 2023/8/17 10:07, Alexei Starovoitov 写道:
> >>> On Thu, Aug 10, 2023 at 1:13 AM Chuyi Zhou <zhouchuyi@xxxxxxxxxxxxx> wrote:
> >>>> static int oom_evaluate_task(struct task_struct *task, void *arg)
> >>>> {
> >>>> struct oom_control *oc = arg;
> >>>> @@ -317,6 +339,26 @@ static int oom_evaluate_task(struct task_struct *task, void *arg)
> >>>> if (!is_memcg_oom(oc) && !oom_cpuset_eligible(task, oc))
> >>>> goto next;
> >>>>
> >>>> + /*
> >>>> + * If task is allocating a lot of memory and has been marked to be
> >>>> + * killed first if it triggers an oom, then select it.
> >>>> + */
> >>>> + if (oom_task_origin(task)) {
> >>>> + points = LONG_MAX;
> >>>> + goto select;
> >>>> + }
> >>>> +
> >>>> + switch (bpf_oom_evaluate_task(task, oc)) {
> >>>> + case BPF_EVAL_ABORT:
> >>>> + goto abort; /* abort search process */
> >>>> + case BPF_EVAL_NEXT:
> >>>> + goto next; /* ignore the task */
> >>>> + case BPF_EVAL_SELECT:
> >>>> + goto select; /* select the task */
> >>>> + default:
> >>>> + break; /* No BPF policy */
> >>>> + }
> >>>> +
> >>>
> >>> I think forcing bpf prog to look at every task is going to be limiting
> >>> long term.
> >>> It's more flexible to invoke bpf prog from out_of_memory()
> >>> and if it doesn't choose a task then fallback to select_bad_process().
> >>> I believe that's what Roman was proposing.
> >>> bpf can choose to iterate memcg or it might have some side knowledge
> >>> that there are processes that can be set as oc->chosen right away,
> >>> so it can skip the iteration.
> >>
> >> IIUC, We may need some new bpf features if we want to iterating
> >> tasks/memcg in BPF, sush as:
> >> bpf_for_each_task
> >> bpf_for_each_memcg
> >> bpf_for_each_task_in_memcg
> >> ...
> >>
> >> It seems we have some work to do first in the BPF side.
> >> Will these iterating features be useful in other BPF scenario except OOM
> >> Policy?
> >
> > Yes.
> > Use open coded iterators though.
> > Like example in
> > https://lore.kernel.org/all/20230810183513.684836-4-davemarchevsky@xxxxxx/
> >
> > bpf_for_each(task_vma, vma, task, 0) { ... }
> > will safely iterate vma-s of the task.
> > Similarly struct css_task_iter can be hidden inside bpf open coded iterator.
> OK. I think the following APIs whould be useful and I am willing to
> start with these in another bpf-next RFC patchset:
>
> 1. bpf_for_each(task). Just like for_each_process(p) in kernel to
> itearing all tasks in the system with rcu_read_lock().
>
> 2. bpf_for_each(css_task, task, css). It works like
> css_task_iter_{start, next, end} and would be used to iterating
> tasks/threads under a css.
>
> 3. bpf_for_each(descendant_css, css, root_css, {PRE, POST}). It works
> like css_next_descendant_{pre, post} to iterating all descendant.
>
> If you have better ideas or any advice, please let me know.
Sounds great. Such 3 new iterators are unrelated to oom discussion and
can be developed/landed in parallel.
They will be useful in other bpf programs.
