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

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Message-ID: <466A6042.7030500@de.ibm.com>
Date:	Sat, 09 Jun 2007 10:09:38 +0200
From:	Carsten Otte <cotte@...ibm.com>
To:	Justin Treon <justin_treon_lkml@...oo.com>
CC:	carsteno@...ibm.com, "\"JXrn\" Engel" <joern@...ybastard.org>,
	Christoph Hellwig <hch@...radead.org>,
	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
Subject: Re: [PATCH 2.6.21] cramfs: add cramfs Linear XIP

Justin Treon wrote:
> --- Carsten Otte <cotte@...ibm.com> wrote:
>> The nice thing about this approach is: we use page->count and rmap, 
>> both already exist and are perfectly suited for our purpose.
>> The downside: We need mem_map[] struct page entries behind all memory 
>> segments. Nowerdays we can easily create those via vmem_map/sparsemem.
> Can you give an example of the proper way to use sparsemem in this case?  
We use vmem_map on 390:
- __segment_load[arch/s390/mm/extmem.c] calls add_shared_memory() to 
create struct page entries behind a segment
- segment_unload (same file) calls remove_shared_memory() to remove 
parts of the mem_map array again
- arch/s390/mm/vmem.c implements both callbacks

As far as I know, this can also be archived with sparsemem. 
Unfortunately I don't have an example for sparsemem at hand, I would 
try to use sparse_add_one_section()[mm/sparse.c].


sorry,
Carsten
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