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    SubjectRe: [patch 3/3] mm: fault handler to replace nopage and populate
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    On Mon, 2006-10-09 at 13:45 +0200, Nick Piggin wrote:
    > On Mon, Oct 09, 2006 at 09:32:59PM +1000, Benjamin Herrenschmidt wrote:
    > > >
    > > > You'll want to clear VM_PFNMAP after unmapping all pages from it, before
    > > > switching to struct page backing.
    > >
    > > Which means having a list of all vma's ... I suppose I can look at the
    > > truncate code to do that race free but I was hoping I could avoid it
    > > (that's the whole point of using unmap_mapping_range() in fact).
    >
    > Yeah I don't think there is any other way to do it.

    What is the problem if I always keep VM_PFNMAP set ?

    > > > > It also needs update_mmu_cache() I suppose.
    > > >
    > > > Hmm, but it might not be called from a pagefault. Can we get away
    > > > with not calling it? Or is it required by some architectures?
    > >
    > > I think some architectures might be upset if it's not called...
    >
    > But would any get upset if it is called from !pagefault path?

    Probably not... the PTE has been filled so it should be safe, but then,
    I don't know the details of what non-ppc archs do with that callback.

    Ben.


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