2011/9/29 Minchan Kim <minchan.kim@xxxxxxxxx>: > When racing between putback_lru_page and shmem_lock with lock=0 happens, > progrom execution order is as follows, but clear_bit in processor #1 > could be reordered right before spin_unlock of processor #1. > Then, the page would be stranded on the unevictable list. > > spin_lock > SetPageLRU > spin_unlock > clear_bit(AS_UNEVICTABLE) > spin_lock > if PageLRU() > if !test_bit(AS_UNEVICTABLE) > move evictable list > smp_mb > if !test_bit(AS_UNEVICTABLE) > move evictable list > spin_unlock > > But, pagevec_lookup in scan_mapping_unevictable_pages has rcu_read_[un]lock so > it could protect reordering before reaching test_bit(AS_UNEVICTABLE) on processor #1 > so this problem never happens. But it's a unexpected side effect and we should > solve this problem properly. > > This patch adds a barrier after mapping_clear_unevictable. > > side-note: I didn't meet this problem but just found during review. > > Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> > Cc: Mel Gorman <mel@xxxxxxxxx> > Cc: Rik van Riel <riel@xxxxxxxxxx> > Cc: Lee Schermerhorn <lee.schermerhorn@xxxxxx> > Acked-by: Johannes Weiner <jweiner@xxxxxxxxxx> > Signed-off-by: Minchan Kim <minchan.kim@xxxxxxxxx> Acked-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href