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    SubjectRe: speeding up swapoff
    On Wed, 29 Aug 2007 09:29:32 -0400
    Daniel Drake <ddrake@brontes3d.com> wrote:


    Hi,

    > I've spent some time trying to understand why swapoff is such a slow
    > operation.
    >
    > My experiments show that when there is not much free physical memory,
    > swapoff moves pages out of swap at a rate of approximately 5mb/sec.

    sounds like about disk speed (at random-seek IO pattern)


    > I'm happy to spend a few more hours looking into implementing this but
    > would greatly appreciate any advice from those in-the-know on if my
    > ideas are broken to start with...

    before you go there... is this a "real life" problem? Or just a
    mostly-artificial corner case? (the answer to that obviously is
    relevant for the 'should we really care' question)

    Another question, if this is during system shutdown, maybe that's a
    valid case for flushing most of the pagecache first (from userspace)
    since most of what's there won't be used again anyway. If that's enough
    to make this go faster...

    A third question, have you investigated what happens if a process gets
    killed that has pages in swap; as long as we don't page those in but
    just forget about them, that would solve the shutdown problem nicely
    (since we kill stuff first anyway there)

    -
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