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

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Date:	Fri, 15 Jun 2007 13:49:13 +0200
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	carsteno@...ibm.com
Cc:	Jared Hulbert <jaredeh@...il.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

On Fri, Jun 15, 2007 at 11:22:21AM +0200, Carsten Otte wrote:
> Jared Hulbert wrote:
> >>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.

That would be good.

> >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.

I didn't say your old code was a hack. It just didn't work together with
the vmem map approach, so it had to be converted. Otherwise there wouldn't
be a 1:1 kernel mapping or struct pages for your memory region.
If you can write code that doesn't need any struct pages that would make
life a bit easier, since we wouldn't need any pseudo memory hotplug code
that just adds struct pages.
We would still need to add the kernel mapping though.
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