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    SubjectRe: [PATCH 1/4] mm: vmscan: Correct check for kswapd sleeping in sleeping_prematurely
    (2011/06/24 23:44), Mel Gorman 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>
    > ---
    > mm/vmscan.c | 2 +-
    > 1 files changed, 1 insertions(+), 1 deletions(-)
    >
    > diff --git a/mm/vmscan.c b/mm/vmscan.c
    > index 8ff834e..841e3bf 100644
    > --- a/mm/vmscan.c
    > +++ b/mm/vmscan.c
    > @@ -2323,7 +2323,7 @@ static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
    > return true;
    >
    > /* Check the watermark levels */
    > - for (i = 0; i < pgdat->nr_zones; i++) {
    > + for (i = 0; i <= classzone_idx; i++) {
    > struct zone *zone = pgdat->node_zones + i;
    >
    > if (!populated_zone(zone))

    sorry for the delay.
    Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>




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