On Fri, Dec 03, 2010 at 01:00:49AM +0900, Minchan Kim wrote: > If we wake up prematurely, it means we should keep going on > reclaiming not new order page but at old order page. > Sometime new order can be smaller than old order by below > race so it could make failure of old order page reclaiming. > > T0: Task 1 wakes up kswapd with order-3 > T1: So, kswapd starts to reclaim pages using balance_pgdat > T2: Task 2 wakes up kswapd with order-2 because pages reclaimed > by T1 are consumed quickly. > T3: kswapd exits balance_pgdat and will do following: > T4-1: In beginning of kswapd's loop, pgdat->kswapd_max_order will > be reset with zero. > T4-2: 'order' will be set to pgdat->kswapd_max_order(0), since it > enters the false branch of 'if (order (3) < new_order (2))' > T4-3: If previous balance_pgdat can't meet requirement of order-2 > free pages by high watermark, it will start reclaiming again. > So balance_pgdat will use order-0 to do reclaim while it > really should use order-2 at the moment. > T4-4: At last, Task 1 can't get the any page if it wanted with > GFP_ATOMIC. > > Reported-by: Shaohua Li <shaohua.li@xxxxxxxxx> > Signed-off-by: Minchan Kim <minchan.kim@xxxxxxxxx> > Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> > Reviewed-by: Shaohua Li <shaohua.li@xxxxxxxxx> > Cc: Mel Gorman <mel@xxxxxxxxx> Acked-by: Mel Gorman <mel@xxxxxxxxx> -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>