Messages in this thread | | | Date | Fri, 08 Jun 2007 21:04:17 +0200 | From | Carsten Otte <> | Subject | Re: [PATCH 2.6.21] cramfs: add cramfs Linear XIP |
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Jörn Engel wrote: > Nitbit: Sooner or later the point/unpoint should get replaced by > something with page granularity. Something also needs to keep lists of > mapped pages and invalidate them whenever the device is written to. > That could be done in the filesystem or device driver. I believe the > device driver would be a better solution. I think it needs to work like this: - temporary references (for read/write syscalls and friends) get retrieved via get_xip_page and returned again via to-be-invented put_page/page_cache_release - permanent references (for mapping to userland) get retrieved via get_xip_page and don't get returned until unmap - the device driver can access page->count via a helper function provided by mm. This way, it can identify which pages are in use. - In order to get references back, the device driver can call a callback provided by the file system. A default implementation will go to filemap_xip.c. This callback would use rmap to find all mappings, and unmap the page via xip_file_unmap()[mm/filemap_xip.c].
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.
Opinions?
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