linux-kernel - [RFC] Reproducible OOM with partial workaround

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Message-Id: <201301102158.r0ALwI4i031014@como.maths.usyd.edu.au>
Date:	Fri, 11 Jan 2013 08:58:18 +1100
From:	paul.szabo@...ney.edu.au
To:	linux-mm@...ck.org
Cc:	695182@...s.debian.org, linux-kernel@...r.kernel.org
Subject: [RFC] Reproducible OOM with partial workaround

Dear Linux-MM,

On a machine with i386 kernel and over 32GB RAM, an OOM condition is
reliably obtained simply by writing a few files to some local disk
e.g. with:
  n=0; while [ $n -lt 99 ]; do dd bs=1M count=1024 if=/dev/zero of=x$n; ((n=$n+1)); done
Crash usually occurs after 16 or 32 files written. Seems that the
problem may be avoided by using mem=32G on the kernel boot, and that
it occurs with any amount of RAM over 32GB.

I developed a workaround patch for this particular OOM demo, dropping
filesystem caches when about to exhaust lowmem. However, subsequently
I observed OOM when running many processes (as yet I do not have an
easy-to-reproduce demo of this); so as I suspected, the essence of the
problem is not with FS caches.

Could you please help in finding the cause of this OOM bug?

Please see
http://bugs.debian.org/695182
for details, in particular my workaround patch
http://bugs.debian.org/cgi-bin/bugreport.cgi?msg=101;att=1;bug=695182

(Please reply to me directly, as I am not a subscriber to the linux-mm
mailing list.)

Thanks, Paul

Paul Szabo   psz@...hs.usyd.edu.au   http://www.maths.usyd.edu.au/u/psz/
School of Mathematics and Statistics   University of Sydney    Australia
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