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    SubjectRe: mmap() is slower than read() on SCSI/IDE on 2.0 and 2.1
    Marc Lehmann wrote:
    > On Thu, Dec 17, 1998 at 06:52:50AM +0000, Linus Torvalds wrote:
    > > Umm, the easiest hint is probably to just look at the faulting address.
    > > We have it available, after all.
    > >
    > > I suspect that such a simple heuristic would be fairly accurate, and it
    > > can be coupled with other heuristics to further increase the accuracy.
    > file copy, yes. But grep (and probably lots of others) don't access memory
    > sequentially (as faster search algorithms exist)

    A fast search algorithm, touches memory every n bytes where n is the
    size of the largest constant string that you're searching for.

    That way "n" is typically small, so that you end up hitting the first
    n bytes pretty often.

    If you're acessing

    struct blabla {
    int ...
    float ...
    char [];

    mmapped from a file, you might be looking for a certain float. As long
    as you're doing a linear search, you'll again hit the first few bytes
    of a page pretty often.


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    *-- BitWizard writes Linux device drivers for any device you may have! --*
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