linux-kernel - Re: [PATCH 2/2] mlock use lru_add_drain_all

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Date:	Tue, 6 Oct 2009 12:27:27 -0400 (EDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
cc:	LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH 2/2] mlock use lru_add_drain_all_async()

On Tue, 6 Oct 2009, KOSAKI Motohiro wrote:

>   Suppose you have 2 cpus, cpu1 is busy doing a SCHED_FIFO-99 while(1),
>   cpu0 does mlock()->lru_add_drain_all(), which does
>   schedule_on_each_cpu(), which then waits for all cpus to complete the
>   work. Except that cpu1, which is busy with the RT task, will never run
>   keventd until the RT load goes away.
>
>   This is not so much an actual deadlock as a serious starvation case.
>
> Actually, mlock() doesn't need to wait to finish lru_add_drain_all().
> Thus, this patch replace it with lru_add_drain_all_async().

Ok so this will queue up lots of events for the cpu doing a RT task. If
the RT task is continuous then they will be queued there forever?
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