linux-kernel - Re: [PATCH 1/2] mm, oom: introduce oom reaper

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Message-ID: <20151218115454.GE28443@dhcp22.suse.cz>
Date:	Fri, 18 Dec 2015 12:54:55 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	David Rientjes <rientjes@...gle.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	Andrea Argangeli <andrea@...nel.org>,
	Rik van Riel <riel@...hat.com>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] mm, oom: introduce oom reaper

On Thu 17-12-15 12:00:04, Andrew Morton wrote:
> On Thu, 17 Dec 2015 11:55:11 -0800 Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> 
> > On Thu, Dec 17, 2015 at 5:02 AM, Michal Hocko <mhocko@...nel.org> wrote:
> > > Ups. You are right. I will go with msleep_interruptible(100).
> > 
> > I don't think that's right.
> > 
> > If a signal happens, that loop is now (again) just busy-looping.
> 
> It's called only by a kernel thread so no signal_pending().

Yes that was the thinking.

> This relationship is a bit unobvious and fragile, but we do it in
> quite a few places.

I guess Linus is right and __set_task_state(current, TASK_IDLE) would be
better and easier to read.
---
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 4b0a5d8b92e1..eed99506b891 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -472,8 +472,10 @@ static void oom_reap_vmas(struct mm_struct *mm)
 	int attempts = 0;
 
 	/* Retry the down_read_trylock(mmap_sem) a few times */
-	while (attempts++ < 10 && !__oom_reap_vmas(mm))
-		msleep_interruptible(100);
+	while (attempts++ < 10 && !__oom_reap_vmas(mm)) {
+		__set_task_state(current, TASK_IDLE);
+		schedule_timeout(HZ/10);
+	}
 
 	/* Drop a reference taken by wake_oom_reaper */
 	mmdrop(mm);
-- 
Michal Hocko
SUSE Labs
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