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    SubjectRe: why swap at all?
    Hello!

    > But swap behaviour kills performance even when memory is more than adequate.
    > Consider building a DVD image in a 4GB system. The i/o forces all of the
    > unused programs out, in spite of the fact that an extra 100MB doesn't make a
    > measurable difference in performance. But when I click Mozilla paging most of
    > it in from disk make a big difference in performance to the user.

    I think that kernel cannot know that you need some data once or more.
    This is fadvise for.
    With my wrapper (http://kernel.umbrella.ro) for fadvise you can do this:
    NOCA_SIZE=128 NOCA_READ=1 NOCA_WRITE=1 NOCA_RA=1 \
    noca mkisofs -R -o /tmp/1.iso /tmp/data

    This means:
    NOCA_SIZE: Call fadvise only after 128KiB was read/wrote.
    NOCA_RA: call fadvise with POSIX_FADV_SEQUENTIAL
    NOCA_READ: use fadvise(POSIX_FADV_DONTNEED) for reads (because you don't
    need anymore the source files)
    NOCA_WRITE: use fadvise(POSIX_FADV_DONTNEED) for writes (because it's
    useless to cache the end of the ISO)

    Do this program resolve your problem?

    > The problems with small memory are different in kind, when not even the
    > programs will fit in memory at the same time, or will leave next to nothing
    > for i/o, swap is required for performance. But on a large memory system I
    > believe the gain to pain ratio is way too low with the current VM. The
    > solution at the moment is to turn off swap, which as you note has other
    > problems (can't move between zones without swap?) which in theory could
    > really hang a system.
    >
    > --
    > -bill davidsen (davidsen@tmr.com)
    > "The secret to procrastination is to put things off until the
    > last possible moment - but no longer" -me
    > -
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    > Please read the FAQ at http://www.tux.org/lkml/
    >

    ---
    Catalin(ux aka Dino) BOIE
    catab at deuroconsult.ro
    http://kernel.umbrella.ro/
    -
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