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    SubjectRe: [RFC] Tight check of pfn_valid on sparsemem
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    On Wed, 2010-07-14 at 00:43 +0900, Minchan Kim wrote:
    > 3 is not a big deal than 2 about memory usage.
    > If the system use memory space fully(MAX_PHYSMEM_BITS 31), it just consumes
    > 1024(128 * 8) byte. So now I think best solution is 2.
    >
    > Russell. What do you think about it?

    I'm not Russell, but I'll tell you what I think. :)

    Make the sections 16MB. You suggestion to add the start/end pfns
    _doubles_ the size of the structure, and its size overhead. We have
    systems with a pretty tremendous amount of memory with 16MB sections.

    If you _really_ can't make the section size smaller, and the vast
    majority of the sections are fully populated, you could hack something
    in. We could, for instance, have a global list that's mostly readonly
    which tells you which sections need to be have their sizes closely
    inspected. That would work OK if, for instance, you only needed to
    check a couple of memory sections in the system. It'll start to suck if
    you made the lists very long.

    -- Dave



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