linux-kernel - Re: Bug#695182: [RFC] Reproducible OOM with just a few sleeps

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Message-ID: <1358210073.15692.60.camel@deadeye.wl.decadent.org.uk>
Date:	Tue, 15 Jan 2013 00:34:33 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	paul.szabo@...ney.edu.au, 695182@...s.debian.org
Cc:	dave@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: Bug#695182: [RFC] Reproducible OOM with just a few sleeps

On Tue, 2013-01-15 at 07:36 +1100, paul.szabo@...ney.edu.au wrote:
> Dear Dave,
> 
> >> Seems that any i386 PAE machine will go OOM just by running a few
> >> processes. To reproduce:
> >>   sh -c 'n=0; while [ $n -lt 19999 ]; do sleep 600 & ((n=n+1)); done'
> >> ...
> > I think what you're seeing here is that, as the amount of total memory
> > increases, the amount of lowmem available _decreases_ due to inflation
> > of mem_map[] (and a few other more minor things).  The number of sleeps
> > you can do is bound by the number of processes, as you noticed from
> > ulimit.  Creating processes that don't use much memory eats a relatively
> > large amount of low memory.
> > This is a sad (and counterintuitive) fact: more RAM actually *CREATES*
> > RAM bottlenecks on 32-bit systems.
> 
> I understand that more RAM leaves less lowmem. What is unacceptable is
> that PAE crashes or freezes with OOM: it should gracefully handle the
> issue.
[...]

Sorry, let me know where to send your refund.

Ben.

-- 
Ben Hutchings
Quantity is no substitute for quality, but it's the only one we've got.

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