linux-kernel - Re: Kernel falls apart under light memory pressure (i.e. linking vmlinux)

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Date:	Thu, 19 May 2011 11:00:24 -0400
From:	Andrew Lutomirski <luto@....edu>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Minchan Kim <minchan.kim@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Mel Gorman <mgorman@...e.de>,
	Johannes Weiner <hannes@...xchg.org>,
	Rik van Riel <riel@...hat.com>
Subject: Re: Kernel falls apart under light memory pressure (i.e. linking vmlinux)

On Thu, May 19, 2011 at 10:51 AM, Wu Fengguang <fengguang.wu@...el.com> wrote:
>> > I had 6GB swap available, so there shouldn't have
>> > been any OOM.
>>
>> Yes. It's strange but we have seen such case several times, AFAIR.
>
> I noticed that the test script mounted a "ramfs" not "tmpfs", hence
> the 1.4G pages won't be swapped?

That's intentional.

I run LVM over dm-crypt on an SSD, and I thought that might be part of
the problem.  I wanted a script that would see if I could reproduce
the problem without stressing that system too much, so I created a
second backing store on dm-crypt over ramfs so that no real I/O will
happen.  The script is quite effective at bringing down my system, so
I haven't changed it.

(I have 6GB of "real" swap on the LVM, so pinning 1500MB into RAM
ought to cause some thrashing but not take the system down.  And this
script with a larger ramfs does not take down my desktop, which is an
8GB Sandy Bridge box.  But whatever the underlying bug is seems to
mainly affect Sandy Bridge *laptops*, so maybe that's expected.)

--Andy

>
> Thanks,
> Fengguang
>
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