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    SubjectRe: 2.5.73-mm2
    --Christoph Hellwig <hch@infradead.org> wrote (on Saturday, June 28, 2003 17:08:37 +0100):

    > On Sat, Jun 28, 2003 at 08:54:36AM -0700, William Lee Irwin III wrote:
    >> +config HIGHPMD
    >> + bool "Allocate 2nd-level pagetables from highmem"
    >> + depends on HIGHMEM64G
    >> + help
    >> + The VM uses one pmd entry for each pagetable page of physical
    >> + memory allocated. For systems with extreme amounts of highmem,
    >> + this cannot be tolerated. Setting this option will put
    >> + userspace 2nd-level pagetables in highmem.
    >
    > Does this make sense for !HIGHPTE? In fact does it make sense to
    > carry along HIGHPTE as an option still? ..

    Last time I measured it, it had about a 10% overhead in kernel time.
    Seems like a good thing to keep as an option to me. Bill said he
    had some other code to alleviate the overhead, but I don't think
    it's merged ... I'd rather see UKVA (permanently map the pagetables
    on a per-process basis) merged before it becomes "not an option" -
    that gets rid of all the kmapping.

    M.
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