vmscan: synchronous lumpy reclaim should not call congestion_wait()

congestion_wait() means "wait until queue congestion is cleared".
However, synchronous lumpy reclaim does not need this congestion_wait() as
shrink_page_list(PAGEOUT_IO_SYNC) uses wait_on_page_writeback() and it
provides the necessary waiting.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Reviewed-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Wu Fengguang <fengguang.wu@intel.com>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/vmscan.c

@@ -1340,8 +1340,6 @@ shrink_inactive_list(unsigned long nr_to_scan, struct zone *zone,
 
 	/* Check if we should syncronously wait for writeback */
 	if (should_reclaim_stall(nr_taken, nr_reclaimed, priority, sc)) {
-		congestion_wait(BLK_RW_ASYNC, HZ/10);
-
 		/*
 		 * The attempt at page out may have made some
 		 * of the pages active, mark them inactive again.