linux-kernel - Re: [PATCH] x86: fix PAE pmd

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Date:	Thu, 8 May 2008 16:34:53 +0200
From:	Hans Rosenfeld <hans.rosenfeld@....com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	Hugh Dickins <hugh@...itas.com>, Ingo Molnar <mingo@...e.hu>,
	Jeff Chua <jeff.chua.linux@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Gabriel C <nix.or.die@...glemail.com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Nishanth Aravamudan <nacc@...ibm.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] x86: fix PAE pmd_bad bootup warning

On Tue, May 06, 2008 at 01:42:59PM -0700, Dave Hansen wrote:
> Could you post the code you're using to do this?  I have to wonder if
> you're leaving a fd open somewhere.  Even if you rm the hugepage file,
> it'll stay allocated if you have a fd open, or if *someone* is still
> mapping it. 

A stripped-down program exposing the leak is attached. It doesn't fork
or do any other fancy stuff, so I don't see a way it could leave any fd
open.

While trying to reproduce this, I noticed that the huge page wouldn't
leak when I just mmapped it and exited without explicitly unmapping, as
I described before. The huge page is leaked only when the
/proc/self/pagemap entry for the huge page is read. The kernel I tested
with was 2.6.26-rc1-00179-g3de2403.

> Can you umount your hugetlbfs?

Yes, but the pages remain lost.

Hans


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