linux-kernel - Re: oom-killer is crazy? (Was: [PATCH 0/3] uprobes fixes for 3.5)

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Message-ID: <20120608150437.GA31091@redhat.com>
Date:	Fri, 8 Jun 2012 17:04:37 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Dave Jones <davej@...hat.com>, Hugh Dickins <hughd@...gle.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anton Arapov <anton@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linux-kernel@...r.kernel.org
Subject: Re: oom-killer is crazy? (Was: [PATCH 0/3] uprobes fixes for 3.5)

On 06/08, Dave Jones wrote:
>
> On Fri, Jun 08, 2012 at 04:03:28PM +0200, Oleg Nesterov wrote:
>  >
>  > Hmm. oom_badness() does
>  >
>  > 	if (has_capability_noaudit(p, CAP_SYS_ADMIN))
>  > 		points -= 30 * totalpages / 1000;
>  >
>  > very nice, but what if this underflows? points is unsigned long.
>  > points += p->signal->oom_score_adj... looks suspicious too.
>  >
>  > Looks like we should remove "unsigned" from oom_badness() and
>  > its callers? Probably not, it does "return points ? points : 1".
>
> I've been running this from David for a week, but it still isn't right..
>
> 	Dave
>
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index ed0e196..416637f 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -183,7 +183,7 @@ static bool oom_unkillable_task(struct task_struct *p,
>  unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg,
>                           const nodemask_t *nodemask, unsigned long totalpages)
>  {
> -       unsigned long points;
> +       long points;
>
>         if (oom_unkillable_task(p, memcg, nodemask))
>                 return 0;
> @@ -223,7 +223,7 @@ unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg,
>          * Never return 0 for an eligible task regardless of the root bonus and
>          * oom_score_adj (oom_score_adj can't be OOM_SCORE_ADJ_MIN here).
>          */
> -       return points ? points : 1;
> +       return points > 0 ? points : 1;
>  }

I did the same to avoid the problem.

Even if it still isn't right, I think it is much better ;) Currently
oom_badness() is obviously and seriously broken.

Oleg.

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