Re: [PATCH 2.6.21] cramfs: add cramfs Linear XIP

[Carsten Otte <cotte@de.ibm.com>]

Justin Treon wrote:
> --- Carsten Otte <cotte@de.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