linux-kernel - Re: [PATCH 1/2] mm,oom: Move last second allocation to inside the OOM killer.

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Date:   Thu, 2 Nov 2017 20:15:55 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     mhocko@...nel.org, aarcange@...hat.com
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] mm,oom: Move last second allocation to inside the OOM killer.

Michal Hocko wrote:
> I would really suggest you to stick with the changelog I have suggested.
> 
Well, I think that this patch needs to clarify why using ALLOC_WMARK_HIGH.

> On Wed 01-11-17 20:54:27, Tetsuo Handa wrote:
> [...]
> > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> > index 26add8a..118ecdb 100644
> > --- a/mm/oom_kill.c
> > +++ b/mm/oom_kill.c
> > @@ -870,6 +870,19 @@ static void oom_kill_process(struct oom_control *oc, const char *message)
> >  	}
> >  	task_unlock(p);
> >  
> > +	/*
> > +	 * Try really last second allocation attempt after we selected an OOM
> > +	 * victim, for somebody might have managed to free memory while we were
> > +	 * selecting an OOM victim which can take quite some time.
> > +	 */
> > +	if (oc->ac) {
> > +		oc->page = alloc_pages_before_oomkill(oc);
> 
> I would stick the oc->ac check inside alloc_pages_before_oomkill.

OK.

> 
> > +		if (oc->page) {
> > +			put_task_struct(p);
> > +			return;
> > +		}
> > +	}
> > +
> >  	if (__ratelimit(&oom_rs))
> >  		dump_header(oc, p);
> >  
> > @@ -1081,6 +1094,16 @@ bool out_of_memory(struct oom_control *oc)
> >  	select_bad_process(oc);
> >  	/* Found nothing?!?! Either we hang forever, or we panic. */
> >  	if (!oc->chosen && !is_sysrq_oom(oc) && !is_memcg_oom(oc)) {
> > +		/*
> > +		 * Try really last second allocation attempt, for somebody
> > +		 * might have managed to free memory while we were trying to
> > +		 * find an OOM victim.
> > +		 */
> > +		if (oc->ac) {
> > +			oc->page = alloc_pages_before_oomkill(oc);
> > +			if (oc->page)
> > +				return true;
> > +		}
> >  		dump_header(oc, NULL);
> >  		panic("Out of memory and no killable processes...\n");
> >  	}
> 
> Also, is there any strong reason to not do the last allocation after
> select_bad_process rather than having two call sites? I would understand
> that if you wanted to catch for_each_thread inside oom_kill_process but
> you are not doing that.

Unfortunately, we will after all have two call sites because we have
sysctl_oom_kill_allocating_task path.

V2 patch follows. Andrea, will you check that your intent of using high
watermark for last second allocation attempt in the change log is correct?