Messages in this thread | | | Date | Thu, 14 Jun 2007 15:57:46 +0200 | From | Carsten Otte <> | Subject | Re: [PATCH 2.6.21] cramfs: add cramfs Linear XIP |
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Jared Hulbert wrote: >> Nick Piggin wrote: >> > The question is, why is that not enough (I haven't looked at these >> > patches enough to work out if there is anything more they provide). >> I think, it just takes trying things out. From reading the code, I >> think this should work well for the filemap_xip code with no struct page. >> Also, we need eliminate nopage() to get rid of the struct page. >> Unfortunately I don't find time to try this out for now, and on 390 we >> can live with struct page for the time being. In contrast to the >> embedded platforms, the mem_mep array gets swapped out to disk by our >> hypervisor. > > Can you help me understand the comment about nopage()? Do you mean > set xip_file_vm_ops.nopage to NULL?
Yes, but not without replacement. Today, the page table entry for xip mappings is created like this: __handle_mm_fault calls handle_pte_fault, which calls do_no_page [all in mm/memory.c]. do_no_page does call the ->nopage operation, and creates a page table entry. The ->nopage operation is set to xip_file_nopage() [mm/filemap_xip.c], which calls the get_xip_page address space operation. For ext2, this is implemented in ext2_get_xip_page (fs/ext2/xip.c). In this process, the struct page entry in mem_map is looked up in ext2_get_xip_page(), returned to xip_file_nopage, then returned to do_no_page. 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. The current path would then be deprecated. If you're interrested in using the later for xip without struct page, I would volounteer to go ahead and implement this?
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