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    SubjectWhy preallocate pmd in x86 32-bit PAE?
    I'm looking at unifying asm-x86/pgalloc*.h, and so I'm trying to make
    things as similar as possible between 32 and 64-bit.

    Once difference is that 64-bit incrementally allocates all levels of the
    pagetable, whereas 32-bit PAE preallocates the 4 pmds when it allocates
    the pgd. What's the rationale for this? What pitfalls would there be
    in making them incrementally allocated?

    Preallocation makes sense from the perspective that they will all be
    allocated almost immediately in a typical process. But it is a somewhat
    arbitrary difference from 64-bit, and since 64-bit can't reasonably
    preallocate any pagetable levels, it seems sensible to change 32-bit to
    match.

    Thanks,
    J
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