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    SubjectRe: [RFC] Tight check of pfn_valid on sparsemem
    On Tue, Jul 13, 2010 at 10:37:00AM +0100, Mel Gorman wrote:
    > I prefer Kamezawa's suggestion of mapping on a ZERO_PAGE-like page full
    > of PageReserved struct pages because it would have better performance
    > and be more in line with maintaining the assumptions of the memory
    > model. If we go in this direction, I would strongly prefer it was an
    > ARM-only thing.

    As I've said, this is not possible without doing some serious page

    Plus the pages that where there become unusable as they don't correspond
    with a PFN or obey phys_to_virt(). So there's absolutely no point to

    Now, why do we free the holes in the mem_map - because these holes can
    be extremely large. Every 512K of hole equates to one page of mem_map
    array. Balance that against memory placed at 0xc0000000 physical on
    some platforms, and with PHYSMEM_BITS at 32 and SECTION_SIZE_BITS at
    19 - well, you do the maths. The result is certainly not pretty.

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