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Date:   Fri, 4 Aug 2023 15:34:32 +0200
From:   Michal Hocko <mhocko@suse.com>
To:     Chuyi Zhou <zhouchuyi@bytedance.com>
Cc:     hannes@cmpxchg.org, roman.gushchin@linux.dev, ast@kernel.org,
        daniel@iogearbox.net, andrii@kernel.org, muchun.song@linux.dev,
        bpf@vger.kernel.org, linux-kernel@vger.kernel.org,
        wuyun.abel@bytedance.com, robin.lu@bytedance.com
Subject: Re: [RFC PATCH 1/2] mm, oom: Introduce bpf_select_task
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On Fri 04-08-23 21:15:57, Chuyi Zhou wrote:
[...]
> > +	switch (bpf_oom_evaluate_task(task, oc, &points)) {
> > +		case -EOPNOTSUPP: break; /* No BPF policy */
> > +		case -EBUSY: goto abort; /* abort search process */
> > +		case 0: goto next; /* ignore process */
> > +		default: goto select; /* note the task */
> > +	}
> 
> Why we need to change the *points* value if we do not care about oom_badness
> ? Is it used to record some state? If so, we could record it through bpf
> map.

Strictly speaking we do not need to. That would require BPF to keep the
state internally. Many will do I suppose but we have to keep track of
the victim so that the oom killer knows what to kill so I thought that
it doesn't hurt to keep track of an abstract concept of points as well.
If you think this is not needed then oc->points could be always 0 for
bpf selected victims. The value is not used anyway in the proposed
scheme.

Btw. we will need another hook or metadata for the reporting side of
things. Generally dump_header() to know what has been the selection
policy.

-- 
Michal Hocko
SUSE Labs