Messages in this thread | | | Date | Sat, 07 Oct 2006 11:14:55 -0400 | From | Jeff Garzik <> | Subject | Re: [patch 3/3] mm: fault handler to replace nopage and populate |
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Nick Piggin wrote: > Nonlinear mappings are (AFAIKS) simply a virtual memory concept that > encodes the virtual address -> file offset differently from linear > mappings. > > I can't see why the filesystem/pagecache code should need to know anything > about it, except for the fact that the ->nopage handler didn't quite pass > down enough information (ie. pgoff). But it is more logical to pass pgoff > rather than have the ->nopage function calculate it itself anyway. And > having the nopage handler install the pte itself is sort of nasty. > > This patch introduces a new fault handler that replaces ->nopage and ->populate > and (hopefully) ->page_mkwrite. Most of the old mechanism is still in place > so there is a lot of duplication and nice cleanups that can be removed if > everyone switches over. > > The rationale for doing this in the first place is that nonlinear mappings > are subject to the pagefault vs invalidate/truncate race too, and it seemed > stupid to duplicate the synchronisation logic rather than just consolidate > the two. > > Comments?
That's pretty nice.
Back when I was writing [the now slated for death] sound/oss/via82xxx_audio.c driver, Linus suggested that I implement ->nopage() for accessing the mmap'able DMA'd audio buffers, rather than using remap_pfn_range(). It worked out very nicely, because it allowed the sound driver to retrieve $N pages for the mmap'able buffer (passed as an s/g list to the hardware) rather than requiring a single humongous buffer returned by pci_alloc_consistent().
And although probably not your primary motivation, your change does IMO improve this area of the kernel.
Jeff
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