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    SubjectRe: [PATCH 8/8] mm: vmscan: Do not writeback filesystem pages from kswapd
    On Fri, Jul 22, 2011 at 02:57:12PM +0200, Peter Zijlstra wrote:
    > On Thu, 2011-07-21 at 17:28 +0100, Mel Gorman wrote:
    > > Assuming that flusher threads will always write back dirty pages promptly
    > > then it is always faster for reclaimers to wait for flushers. This patch
    > > prevents kswapd writing back any filesystem pages.
    > That is a somewhat sort changelog for such a big assumption ;-)

    That is an understatement but the impact of the patch is discussed in
    detail in the leader. On NUMA, this patch has a negative impact so
    I put no effort into the changelog. The patch is part of the series
    because it was specifically asked for.

    > I think it can use a few extra words to explain the need to clean pages
    > from @zone vs writeback picks whatever fits best on disk and how that
    > works out wrt the assumption.

    At the time of writing the changelog, I knew that flushers were
    not finding pages from the correct zones quickly enough in the NUMA
    usecase. The changelog documents the assumptions testing shows them to
    be false.

    > What requirements does this place on writeback and how does it meet
    > them.

    It places a requirement on writeback to prioritise pages from zones
    under memory pressure. It doesn't meet them. I mention in the leader
    that I think patch 8 should be dropped which is why the changelog

    Mel Gorman
    SUSE Labs

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