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Date: Fri, 20 Apr 2007 10:15:00 -0700 (PDT)
From: Christoph Lameter <clameter@sgi.com>
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To: William Lee Irwin III <wli@holomorphy.com>
cc: Mel Gorman <mel@skynet.ie>, linux-kernel@vger.kernel.org,
       Peter Zijlstra <a.p.zijlstra@chello.nl>,
       Nick Piggin <nickpiggin@yahoo.com.au>, Andi Kleen <ak@suse.de>,
       Paul Jackson <pj@sgi.com>, Dave Chinner <dgc@sgi.com>
Subject: Re: [RFC 7/8] Enhance ramfs to support higher order pages
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On Fri, 20 Apr 2007, William Lee Irwin III wrote:
> 
> On Fri, Apr 20, 2007 at 09:30:30AM -0700, Christoph Lameter wrote:
> > We can map arbitrary 4k chunks of larger pages.
> 
> The core VM can do that but the hugetlb architectural code can't fall
> back to smaller page sizes. It also should not be put into a situation
> where it needs to do so given the semantics it must honor.

Wel we could potentially add a handle_pmd_fault to the vm...?
 
> Also, the final assertion is inaccurate. Fault handlers must instantiate
> pages of order mapping->order when faulting in a page of a file with
> a given pagecache size. The semantics of faulting and mmap()'ing are

Why? I agree that the page state of the higher order page must be updated 
consistently but one can use a pte to map a 4k chunk of a higher 
order page.