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    SubjectRe: [PATCH 30/34] mm: vmscan: Do not force kswapd to scan small targets
    On Mon, Jul 23, 2012 at 02:38:43PM +0100, Mel Gorman wrote:
    > commit ad2b8e601099a23dffffb53f91c18d874fe98854 upstream - WARNING: this is a substitute patch.
    >
    > Stable note: Not tracked in Bugzilla. This is a substitute for an
    > upstream commit addressing a completely different issue that
    > accidentally contained an important fix. The workload this patch
    > helps was memcached when IO is started in the background. memcached
    > should stay resident but without this patch it gets swapped more
    > than it should. Sometimes this manifests as a drop in throughput
    > but mostly it was observed through /proc/vmstat.
    >
    > Commit [246e87a9: memcg: fix get_scan_count() for small targets] was
    > meant to fix a problem whereby small scan targets on memcg were ignored
    > causing priority to raise too sharply. It forced scanning to take place
    > if the target was small, memcg or kswapd.
    >
    > >From the time it was introduced it cause excessive reclaim by kswapd
    > with workloads being pushed to swap that previously would have stayed
    > resident. This was accidentally fixed by commit [ad2b8e60: mm: memcg:
    > remove optimization of keeping the root_mem_cgroup LRU lists empty] but
    > that patchset is not suitable for backporting.
    >
    > The original patch came with no information on what workloads it benefits
    > but the cost of it is obvious in that it forces scanning to take place
    > on lists that would otherwise have been ignored such as small anonymous
    > inactive lists. This patch partially reverts 246e87a9 so that small lists
    > are not force scanned which means that IO-intensive workloads with small
    > amounts of anonymous memory will not be swapped.
    >
    > Signed-off-by: Mel Gorman <mgorman@suse.de>
    > ---
    > mm/vmscan.c | 3 ---
    > 1 file changed, 3 deletions(-)

    I don't understand this patch. The original
    ad2b8e601099a23dffffb53f91c18d874fe98854 commit touched the file
    mm/memcontrol.c and seemed to do something quite different from what you
    have done below.

    I'm all for fixing things in a different way than what was done in
    Linus's tree, IF there is a reason to, but the comparison between these
    two patches (yours and upstream) are not making any sense at all.

    confused,

    greg k-h


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