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

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Message-ID: <20130130125151.GB19069@amd.pavel.ucw.cz>
Date:	Wed, 30 Jan 2013 13:51:51 +0100
From:	Pavel Machek <pavel@....cz>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	paul.szabo@...ney.edu.au, 695182@...s.debian.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC] Reproducible OOM with just a few sleeps

Hi!

> > 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. Noting that (for a machine with 4GB or under) PAE fails where the
> > HIGHMEM4G kernel succeeds and survives.
> 
> You have found a delta, but you're not really making apples-to-apples
> comparisons.  The page tables (a huge consumer of lowmem in your bug
> reports) have much more overhead on a PAE kernel.  A process with a
> single page faulted in with PAE will take at least 4 pagetable pages
> (it's 7 in practice for me with sleeps).  It's 2 pages minimum (and in
> practice with sleeps) on HIGHMEM4G.
> 
> There's probably a bug here.  But, it's incredibly unlikely to be seen
> in practice on anything resembling a modern system.  The 'sleep' issue
> is easily worked around by upgrading to a 64-bit kernel, or using

Are you saying that HIGHMEM configuration with 4GB ram is not expected
to work?
									Pavel
-- 
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