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    SubjectRe: Why active list and inactive list?
    Nick Piggin wrote:

    > The other nice thing about it was that it didn't have a hard
    > cutoff that the current reclaim_mapped toggle does -- you could
    > opt to scan the mapped list at a lower ratio than the unmapped
    > one. Of course, it also has some downsides too, and would
    > require retuning...

    Here's a simple idea for tuning.

    For each list we keep track of:
    1) the size of the list
    2) the rate at which we scan the list
    3) the fraction of (non new) pages that get

    That way we can determine which list has the largest
    fraction of "idle" pages sitting around and consequently
    which list should be scanned more aggressively.

    For each list we can calculate how frequently the pages
    in the list are being used:

    pressure = referenced percentage * scan rate / list size

    The VM can equalize the pressure by scanning the list with
    lower usage less than the other list. This way the VM can
    give the right amount of memory to each type.

    Of course, each list needs to be divided into inactive and
    active like the current VM, in order to make sure that the
    pages which are used once cannot push the real working set
    of that list out of memory.

    There is a more subtle problem when the list's working set
    is larger than the amount of memory the list has. In that
    situation the VM will be faulting pages back in just after
    they got evicted. Something like my /proc/refaults code
    can detect that and adjust the size of the undersized list

    Of course, once we properly distinguish between the more
    frequently and less frequently accessed pages within each
    of the page sets (mapped/anonymous vs. unmapped) and have
    the pressure between the lists equalized, why do we need
    to keep them separate again?

    Politics is the struggle between those who want to make their country
    the best in the world, and those who believe it already is. Each group
    calls the other unpatriotic.
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      Last update: 2007-01-23 06:03    [W:0.024 / U:46.264 seconds]
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