mm: vmscan: move direct reclaim wait_iff_congested into shrink_list

shrink_inactive_list makes decisions on whether to stall based on the
number of dirty pages encountered.  The wait_iff_congested() call in
shrink_page_list does no such thing and it's arbitrary.

This patch moves the decision on whether to set ZONE_CONGESTED and the
wait_iff_congested call into shrink_page_list.  This keeps all the
decisions on whether to stall or not in the one place.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Rik van Riel <riel@redhat.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Cc: Zlatko Calusic <zcalusic@bitsync.net>
Cc: dormando <dormando@rydia.net>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>