linux-kernel - Re: [PATCH 2.6.21] cramfs: add cramfs Linear XIP

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Message-ID: <46725A4D.1040404@de.ibm.com>
Date:	Fri, 15 Jun 2007 11:22:21 +0200
From:	Carsten Otte <cotte@...ibm.com>
To:	Jared Hulbert <jaredeh@...il.com>
CC:	carsteno@...ibm.com, Nick Piggin <nickpiggin@...oo.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	richard.griffiths@...driver.com,
	Richard Griffiths <res07ml0@...izon.net>,
	linux-kernel@...r.kernel.org,
	Jörn Engel <joern@...ybastard.org>,
	Heiko Carstens <h.carstens@...ibm.com>
Subject: Re: [PATCH 2.6.21] cramfs: add cramfs Linear XIP

Jared Hulbert wrote:
>> An alternative approach, which does not need to have struct page at
>> hand, would be to use the nopfn vm operations struct. That one would
>> have to rely on get_xip_pfn.
> Of course!  Okay now I'm begining to understand.
Sorry, but I think I was educated yesterday that ->fault() (only in 
-mm) is where we'd be heading. Nopfn is deprecated. But conceptually, 
this does'nt change things.

>> The current path would then be deprecated.
> Why?  Wouldn't both paths be valid options?
The new path via fault works in both cases with and without struct 
page behind. No need to keep the old one as far as I see.

>> If you're interrested in using the later for xip without
>> struct page, I would volounteer to go ahead and implement this?
> I'm very interested in this.
Good. Let me see if I can come up with a patch on this.

> I'm not opposed to using struct page, but I'm confused as to how to
> start that.  As I understand it, which is not well, defined a
> CONFIG_DISCONTIGMEM region to cover the Flash memory would add that to
> my pool of RAM.  That would be 'bad', right?  I don't see how to
> create the page structs and set this memory aside as different.
I fear I am not the right person to answer that question. In the good 
old days before discontigmem/sparse mem/vmem map where invented we 
used to have a hack for that in arch/. Heiko then decided my hack is a 
mess and came up with a good solution to the problem.

so long,
Carsten
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