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    SubjectRe: mapping user space buffer to kernel address space
    Hello,

    > Note that it is usually MUCH better to do this the other way around:
    > having a kernel-side buffer, and mapping that into user space. I don't
    > understand why so many people always want to do it the wrong way around..

    Well, I totally agree. Unfortunately, my fellow driver developers
    seem to think "because it's in UNIX" means "it must be a good idea".
    Pinning pages in memory leaves big holes in processes that can't
    be swapped out on systems that really need the VM to be able
    to work its magic under load.

    Fortunately, VIA and similar schemes try to address the problem
    in the application, OS, _and_ hardware simultaneously.. In the
    future we will probably tell our customers (Fibre Channel) that if
    they really want good performance, they need to use VI instead of
    IP, and to avoid such hacks as pinning user pages for proprietary
    protocols.. My experience has been that systems that do a lot
    of page pinning in UNIX for I/O don't gain much in performance
    anyway, but it _really_ puts a lot of stress on the system compared
    to doing it the right way.

    --
    Eric Lowe
    Software Engineer, Systran Corporation
    elowe@systran.com


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