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    SubjectRe: [RFC][PATCH 0/4] VM split active lists


    Nick Piggin wrote:

    >
    > OK, the theory is that mapped pagecache pages are worth more than
    > unmapped pages. This is a good theory because mapped pages will
    > usually have far more random access patterns, so pagein *and* pageout
    > will be much less efficient. Also, applications are probably coded to
    > be more suited to blocking in read() than a random code / anon memory
    > page. So a factor of >= 16 wouldn't be out of the question.
    >

    Just a followup - there is a small but significant bug in patch
    #4/4. In shrink_zone, mapped_ratio should be divided by
    nr_active_unmapped. I have this fixed, hugepage compile problems
    fixed, and a mapped_page_cost tunable in place of swappiness. So
    anyone interested in testing should please ask me for my latest
    patch.

    I'm getting some preliminary numbers now. They're pretty good,
    looks like they should be similar to dont-rotate-active-list
    which isn't too surprising.

    Interestingly, mapped_page_cost of 8 is close to optimal for
    swapping-kbuild throughput. Values of 4 and 16 are both worse.
    mapped_page_cost is in units of unmapped page cost. Maybe it is
    just me, but I find this scheme is more meaningful and provides
    more control than swappiness.

    -
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