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SubjectRe: [RFC PATCH v2 1/5] mm, oom: Introduce bpf_oom_evaluate_task
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Hello,

在 2023/8/17 10:07, Alexei Starovoitov 写道:
> On Thu, Aug 10, 2023 at 1:13 AM Chuyi Zhou <zhouchuyi@bytedance.com> 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?

Thanks.

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