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    SubjectRe: [PATCH 1/4] mm: vmscan: Correct check for kswapd sleeping in sleeping_prematurely
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    On Fri, Jun 24, 2011 at 11:44 PM, Mel Gorman <mgorman@suse.de> wrote:
    > During allocator-intensive workloads, kswapd will be woken frequently
    > causing free memory to oscillate between the high and min watermark.
    > This is expected behaviour.
    >
    > A problem occurs if the highest zone is small.  balance_pgdat()
    > only considers unreclaimable zones when priority is DEF_PRIORITY
    > but sleeping_prematurely considers all zones. It's possible for this
    > sequence to occur
    >
    >  1. kswapd wakes up and enters balance_pgdat()
    >  2. At DEF_PRIORITY, marks highest zone unreclaimable
    >  3. At DEF_PRIORITY-1, ignores highest zone setting end_zone
    >  4. At DEF_PRIORITY-1, calls shrink_slab freeing memory from
    >        highest zone, clearing all_unreclaimable. Highest zone
    >        is still unbalanced
    >  5. kswapd returns and calls sleeping_prematurely
    >  6. sleeping_prematurely looks at *all* zones, not just the ones
    >     being considered by balance_pgdat. The highest small zone
    >     has all_unreclaimable cleared but but the zone is not
    >     balanced. all_zones_ok is false so kswapd stays awake
    >
    > This patch corrects the behaviour of sleeping_prematurely to check
    > the zones balance_pgdat() checked.
    >
    > Reported-and-tested-by: Pádraig Brady <P@draigBrady.com>
    > Signed-off-by: Mel Gorman <mgorman@suse.de>
    Reviewed-by: Minchan Kim <minchan.kim@gmail.com>

    --
    Kind regards,
    Minchan Kim
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