linux-kernel - Re: oom-kill && frozen()

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Message-ID: <20131113181543.GA22041@redhat.com>
Date:	Wed, 13 Nov 2013 19:15:43 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Tejun Heo <tj@...nel.org>, David Rientjes <rientjes@...gle.com>,
	David Laight <David.Laight@...LAB.COM>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Ingo Molnar <mingo@...nel.org>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: oom-kill && frozen()

On 11/13, Peter Zijlstra wrote:
>
> On Wed, Nov 13, 2013 at 06:07:24PM +0100, Oleg Nesterov wrote:
> > 	4. Finally, change try_to_wake_up() path to do
> >
> > 		-	p->state = TASK_WAKING;
> > 		+	p->state &= ~state;
> > 		+	if (p->state & ~(TASK_DEAD | TASK_WAKEKILL | TASK_PARKED))
> > 		+		return;
> > 		+	else
> > 		+		p->state = TASK_WAKING;
> >
> > 	   IOW, if the task sleeps in, say, TASK_INTERRUPTIBLE | __TASK_FROZEN
> > 	   then it need both try_to_wake_up(TASK_INTERRUPTIBLE) and
> > 	   try_to_wake_up(__TASK_FROZEN) to wake up.
>
> > Tejun, Peter, do you think this makes any sense? I am just curious, but
> > "selective wakeup" looks potentially useful.
>
> I've never looked at any of this freeze stuff, so I cannot comment too
> much. However we should be very careful not to add too much to relative
> hot paths for the relative rare case of freezing stuff.

Yes, yes, sure.

Plus my description was confusing and incomplete (and I am sure I missed
something more). I forgot to mention that freeze_task() should also add
the FROZEN state if it sees FROZEN qualifier, this needs more changes.

So please forget. May be I'll _try_ to make something working (at least
for discussion), but I am not sure.

Oleg.

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