linux-kernel - Re: [RFC PATCH v2 1/5] mm, oom: Introduce bpf_oom_evaluate

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Message-ID: <93627e45-dc67-fd31-ef43-a93f580b0d6e@bytedance.com>
Date:   Thu, 17 Aug 2023 10:51:19 +0800
From:   Chuyi Zhou <zhouchuyi@...edance.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, muchun.song@...ux.dev,
        bpf <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        wuyun.abel@...edance.com, robin.lu@...edance.com,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [RFC PATCH v2 1/5] mm, oom: Introduce bpf_oom_evaluate_task

Hello,

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