On Fri, Aug 02, 2013 at 11:37:24AM -0400, Johannes Weiner wrote: > When the page allocator fails to get a page from all zones in its > given zonelist, it wakes up the per-node kswapds for all zones that > are at their low watermark. > > However, with a system under load the free pages in a zone can > fluctuate enough that the allocation fails but the kswapd wakeup is > also skipped while the zone is still really close to the low > watermark. > > When one node misses a wakeup like this, it won't be aged before all > the other node's zones are down to their low watermarks again. And > skipping a full aging cycle is an obvious fairness problem. > > Kswapd runs until the high watermarks are restored, so it should also > be woken when the high watermarks are not met. This ages nodes more > equally and creates a safety margin for the page counter fluctuation. > > By using zone_balanced(), it will now check, in addition to the > watermark, if compaction requires more order-0 pages to create a > higher order page. > > Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> > Reviewed-by: Rik van Riel <riel@xxxxxxxxxx> Acked-by: Mel Gorman <mgorman@xxxxxxx> -- Mel Gorman SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>