On 06/24/2011 10:44 AM, 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@xxxxxxxxxxxxxx>
Signed-off-by: Mel Gorman<mgorman@xxxxxxx>
Acked-by: Rik van Riel <riel@xxxxxxxxxx>
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