linux-kernel - Re: [RFC PATCH 1/2] mm, oom: Introduce bpf_select

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Message-ID: <ZNCXgsZL7bKsCEBM@dhcp22.suse.cz>
Date:   Mon, 7 Aug 2023 09:04:34 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Chuyi Zhou <zhouchuyi@...edance.com>
Cc:     hannes@...xchg.org, roman.gushchin@...ux.dev, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org, muchun.song@...ux.dev,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        wuyun.abel@...edance.com, robin.lu@...edance.com
Subject: Re: [RFC PATCH 1/2] mm, oom: Introduce bpf_select_task

On Mon 07-08-23 10:21:09, Chuyi Zhou wrote:
> 
> 
> 在 2023/8/4 21:34, Michal Hocko 写道:
> > 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.
> > 
> OK. Maybe a integer like policy_type is enough to distinguish different
> policies and the default method is zero. Or we can let BPF return a string
> like policy_name.
> 
> Which one should I start implementing in next version? Do you have a better
> idea?

String seems to be more descriptive.
-- 
Michal Hocko
SUSE Labs