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    SubjectRe: Improvement on memory subsystem
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    On Wed, 19 Jul 2006 10:18:44 BST, Ian Stirling said:

    > To paraphrase shakespear - all the world is not a P4 - and all the swap
    > devices are not hard disks.

    Been there, done that. I used to admin a net of Sun 3/50s where /dev/swap
    was a symlink to a file on an NFS server, because the "shoebox" local hard
    drives for those were so slow that throwing it across the ethernet to a
    3/280 with Fujitsu Super-Eagles was faster...

    > For example - I've got a 486/33 laptop with 12M RAM that I sometimes use
    > , with swapping to a 128M PCMCIA RAM card that I got from somewhere.

    If we go to the effort of writing code that tries to be smart about grouping
    swap reads/writes by cost, it's easy enough to flag any sort of ram-disk device
    as a 'zero seek time' device. Remember that I suggested making it dependent
    on "how long until the next pass of the elevator" - for a ramdisk that basically
    is zero, so the algorithm easily degenerates into "just queue the requests in
    expected order you'll need the results".

    > 20K instructions wasted on a device with no seek time is just annoying.

    On the other hand, how long does it take to move a 4K page across the
    PCMCIA interface? If you're seeing deep queues on it, you may *still*
    want to optimize the order of requests...

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