Re: [PATCH] oom_kill: oom_score_adj broken for processes with small memory usage

From: Andrew Morton
Date: Thu Sep 02 2021 - 15:55:05 EST


On Fri, 16 Jul 2021 07:25:47 -0500 Corey Minyard <cminyard@xxxxxxxxxx> wrote:

> On Fri, Jul 16, 2021 at 07:19:24AM +0200, Michal Hocko wrote:
> > On Thu 01-07-21 07:54:30, minyard@xxxxxxx wrote:
> > > From: Corey Minyard <cminyard@xxxxxxxxxx>
> > >
> > > If you have a process with less than 1000 totalpages, the calculation:
> > >
> > > adj = (long)p->signal->oom_score_adj;
> > > ...
> > > adj *= totalpages / 1000;
> > >
> > > will always result in adj being zero no matter what oom_score_adj is,
> > > which could result in the wrong process being picked for killing.
> > >
> > > Fix by adding 1000 to totalpages before dividing.
> >
> > Yes, this is a known limitation of the oom_score_adj and its scale.
> > Is this a practical problem to be solved though? I mean 0-1000 pages is
> > not really that much different from imprecision at a larger scale where
> > tasks are effectively considered equal.
>
> Known limitation? Is this documented? I couldn't find anything that
> said "oom_score_adj doesn't work at all with programs with <1000 pages
> besides setting the value to -1000".
>
> >
> > I have to say I do not really like the proposed workaround. It doesn't
> > really solve the problem yet it adds another special case.
>
> The problem is that if you have a small program, there is no way to
> set it's priority besides completely disablling the OOM killer for
> it.
>
> I don't understand the special case comment. How is this adding a
> special case? This patch removes a special case. Small programs
> working different than big programs is a special case. Making them all
> work the same is removing an element of surprise from someone expecting
> things to work as documented.
>

Can we please get this resolved one way or the other?