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    SubjectRe: New Feature Idea: Compress swap file
    On Fri, 20 Feb 1998, Sergio Devojno Bruder wrote:

    > At 18:12 19/02/98 -0800, ;The Doctor What wrote:
    > What about this:
    > - Our objective is performance, by reducing the amount of read/write to
    > the swap;
    > - Compress by pages and write the compressed pages in 4k pages, possibly
    > WASTING space
    > in each page.. (it's ok);
    > - But you can't guarantee that we can compress all cases. Make a map of
    > the pages
    > compressed/not-compressed. A 200MB swap will use 6400 bytes of memory
    > with compressed/
    > not compressed bits;

    What all you folks seem to forget is that _seek_ time
    is, by far, the dominant factor in swapping.

    Let's assume a 2MB/second, 9ms seek, 5400RPM disk.
    With a disk like this, is takes 9 + (60000 (ms/min) / 5400) / 2 =
    14.5 ms to find a certain position on the disk.
    And it takes 2meg/4k = 1/512th = 2ms to transfer the block.

    This means that we won't get a performance increase from
    compressed swapping.

    Clustered swapping however, _is_ going to make a _huge_
    difference. So if you want performance, better focus on
    something that will work.

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