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Date: Thu, 2 Aug 2007 12:30:14 -0700 (PDT)
From: Christoph Lameter <clameter@sgi.com>
Subject: Re: [PATCH 4/4] vmemmap ppc64: convert VMM_* macros to a real function
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To: Dave Hansen <haveblue@us.ibm.com>
Cc: Andy Whitcroft <apw@shadowen.org>, Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org, linux-arch@vger.kernel.org, Christoph Hellwig <hch@infradead.org>, Nick Piggin <npiggin@suse.de>, Mel Gorman <mel@csn.ul.ie>
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On Thu, 2 Aug 2007, Dave Hansen wrote:

> On Thu, 2007-08-02 at 10:25 +0100, Andy Whitcroft wrote:
> > 
> > +unsigned long __meminit vmemmap_section_start(struct page *page)
> > +{
> > +       unsigned long offset = ((unsigned long)page) -
> > +                                               ((unsigned long)(vmemmap)); 
> 
> Isn't this basically page_to_pfn()?  Can we use it here?

Nope. He cast page to long.

Its equivalent to 

	page_to_pfn(page) * sizeof(struct page)