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    SubjectRe: Bug: Discontigmem virt_to_page() [Alpha,ARM,Mips64?]
    >> Again note that nonlinear can do nothing to help you there, the
    >> limitation you deal with is pci32 and the GFP API, not at all about
    >> discontigmem or nonlinear.
    > While I don't have a particular plan to address what changes to the
    > GFP API might be required to make these scenarios work, a quick thought
    > is to pass in indices into a table of zones corresponding to regions of
    > memory addressible by some devices and not others. It'd give rise to a
    > partition like what is already present with foreknowledge of ISA DMA
    > and 32-bit PCI, but there would be strange corner cases, for instance,
    > devices claiming to be 32-bit PCI that don't wire all the address lines.
    > I'm not entirely sure how smoothly these cases are now handled anyway.

    In my mind, one possibility for a powerful API would be to specify a
    mask of acceptable physical addresses, and a "state" for what kind of
    mapping you wanted - global kernel permanently mapped address, unmapped
    address, per-task kernel mapped address, per-address space kernel
    mapped address, etc.

    Without thinking about it too much (aka I'm sticking my neck out and
    am going to get shot down ;-)) it would seem possible to do the phys
    mask idea inside the current buddy system without too much problem
    if the mask was aligned on 2^MAX_ORDER * sizeof(struct page) boundarys?
    I need to think about that one some more, but I thought I'd throw it
    out to see what people think ...


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