linux-kernel - Re: [RFC 7/8] Enhance ramfs to support higher order pages

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Message-ID: <20070420171928.GA2986@holomorphy.com>
Date:	Fri, 20 Apr 2007 10:19:28 -0700
From:	William Lee Irwin III <wli@...omorphy.com>
To:	Christoph Lameter <clameter@....com>
Cc:	Mel Gorman <mel@...net.ie>, linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Nick Piggin <nickpiggin@...oo.com.au>, Andi Kleen <ak@...e.de>,
	Paul Jackson <pj@....com>, Dave Chinner <dgc@....com>
Subject: Re: [RFC 7/8] Enhance ramfs to support higher order pages

On Fri, 20 Apr 2007, William Lee Irwin III wrote:
>> 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.

On Fri, Apr 20, 2007 at 10:15:00AM -0700, Christoph Lameter wrote:
> Wel we could potentially add a handle_pmd_fault to the vm...?

Unconscionably foul. I guess x86-uber-alles pagetables in the core vm
is the Linux way, though.


On Fri, 20 Apr 2007, William Lee Irwin III wrote:
>> 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

On Fri, Apr 20, 2007 at 10:15:00AM -0700, Christoph Lameter wrote:
> 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.

Probably just terminological disagreement here. I was referring to
allocating the higher-order page from the fault path here, not mapping
it or a piece of it with a user pte.


-- wli
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