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

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Date:	Fri, 20 Apr 2007 10:57:25 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	William Lee Irwin III <wli@...omorphy.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:

> 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.

Yes sadly true. The alternative is to add a page table abstraction layer 
first.

> 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.

Ah. Okay. I have some dysfunctional patches here that implement mmap 
support. Would you be willing to take care of that aspect of things? Then 
I can focus on the other VM pieces. I am going to post them following this 
message. These are an absolute mess. They do not compile etc etc.



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