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

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Message-ID: <20080507233944.GG23990@us.ibm.com>
Date:	Wed, 7 May 2008 16:39:44 -0700
From:	Nishanth Aravamudan <nacc@...ibm.com>
To:	Hugh Dickins <hugh@...itas.com>
Cc:	Hans Rosenfeld <hans.rosenfeld@....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>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] x86: fix PAE pmd_bad bootup warning

On 06.05.2008 [21:36:59 +0100], Hugh Dickins wrote:
> On Tue, 6 May 2008, Hans Rosenfeld wrote:
> > On Tue, May 06, 2008 at 08:49:23PM +0100, Hugh Dickins wrote:
> > > So Hans' original hugepage leak remains unexplained and unfixed.
> > > Hans, did you find that hugepage leak with a standard kernel, or were
> > > you perhaps trying out some hugepage-using patch of your own, without
> > > marking the vma VM_HUGETLB?  Or were you expecting the hugetlbfs file
> > > to truncate itself once all mmappers had gone?  If the standard kernel
> > > leaks hugepages, I'm surprised the hugetlb guys don't know about it.
> > 
> > I used a standard kernel (well, not quite, I had made some changes to
> > the /proc/pid/pagemap code, but nothing that would affect the hugepage
> > stuff) and some simple test program that would just mmap a hugepage.
> > 
> > I expected that any hugepage that a process had mmapped would
> > automatically be returned to the system when the process exits. That was
> > not the case, the process exited and the hugepage was lost (unless I
> > changed the program to explicitly munmap the hugepage before exiting).
> > Removing the hugetlbfs file containing the hugepage also didn't free the
> > page.
> 
> Hmm.  That doesn't fit with my experience: I've not found an explicit
> munmap makes any difference (I wouldn't expect it to), but removing
> the file once all openers gone does free everything up.  I guess I'm
> overlooking something more experienced hugepagers will soon light
> upon.

Nothing strikes me immediately. What you described is what I expected.
As Dave pointed out separately, are you able to unmount hugetlbfs at
this point?

Hans, can you send out a sample application's source? What kernel were
you testing on?

Thanks,
Nish

-- 
Nishanth Aravamudan <nacc@...ibm.com>
IBM Linux Technology Center
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