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    SubjectRe: [patch 2/8] mm: vmscan: disregard swappiness shortly before going OOM
    On Wed, Dec 12, 2012 at 04:43:34PM -0500, Johannes Weiner wrote:
    > When a reclaim scanner is doing its final scan before giving up and
    > there is swap space available, pay no attention to swappiness
    > preference anymore. Just swap.
    >
    > Note that this change won't make too big of a difference for general
    > reclaim: anonymous pages are already force-scanned when there is only
    > very little file cache left, and there very likely isn't when the
    > reclaimer enters this final cycle.
    >
    > Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

    Ok, I see the motivation for your patch but is the block inside still
    wrong for what you want? After your patch the block looks like this

    if (sc->priority || noswap) {
    scan >>= sc->priority;
    if (!scan && force_scan)
    scan = SWAP_CLUSTER_MAX;
    scan = div64_u64(scan * fraction[file], denominator);
    }

    if sc->priority == 0 and swappiness==0 then you enter this block but
    fraction[0] for anonymous pages will also be 0 and because of the ordering
    of statements there, scan will be

    scan = scan * 0 / denominator

    so you are still not reclaiming anonymous pages in the swappiness=0
    case. What did I miss?

    --
    Mel Gorman
    SUSE Labs


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