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    SubjectRe: bad lmbench numbers for mmap
       Date: Sat, 17 Apr 1999 03:11:45 +0200
    From: Jamie Lokier <>

    Speaking of which. In principle, freeing page tables should make
    munmap() *faster*, because then you don't have to clear the page

    I note 2.2.6-pre3 isn't doing that.

    Yes do have to clear them, for two reasons:

    1) So that the hardware MMU doesn't see valid entries after the
    tlb flush. (or in the case of clever software TLB miss strategies
    like that implemeted in the Alpha PAL code or in our sparc64 port,
    making sure the virtual page table mappings go away properly too)

    2) For the sake of the page table caching we do on all ports now.

    For #2, if a page table chunk is cached, it works so efficiently
    because it knows the chunks have been cleared out by the callers at
    some point before being free'd.

    David S. Miller

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