mm: forbid lumpy-reclaim in shrink_active_list()

Reset the reclaim mode in shrink_active_list() to RECLAIM_MODE_SINGLE |
RECLAIM_MODE_ASYNC.  (sync/async sign is used only in shrink_page_list
and does not affect shrink_active_list)

Currenly shrink_active_list() sometimes works in lumpy-reclaim mode, if
RECLAIM_MODE_LUMPYRECLAIM is left over from an earlier
shrink_inactive_list().  Meanwhile, in age_active_anon()
sc->reclaim_mode is totally zero.  So the current behavior is too
complex and confusing, and this looks like bug.

In general, shrink_active_list() populates the inactive list for the
next shrink_inactive_list().  Lumpy shring_inactive_list() isolates
pages around the chosen one from both the active and inactive lists.
So, there is no reason for lumpy isolation in shrink_active_list().

See also: https://lkml.org/lkml/2012/3/15/583

Signed-off-by: Konstantin Khlebnikov <[email protected]>
Proposed-by: Hugh Dickins <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: KAMEZAWA Hiroyuki <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/vmscan.c

@@ -1690,6 +1690,8 @@ static void shrink_active_list(unsigned long nr_to_scan,
 
 	lru_add_drain();
 
+	reset_reclaim_mode(sc);
+
 	if (!sc->may_unmap)
 		isolate_mode |= ISOLATE_UNMAPPED;
 	if (!sc->may_writepage)