[PATCH][BUGFIX] memcg fix zone congestion

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

ZONE_CONGESTED should be a state of global memory reclaim.
If not, a busy memcg sets this and give unnecessary throttoling in
wait_iff_congested() against memory recalim in other contexts. This makes
system performance bad.

I'll think about "memcg is congested!" flag is required or not, later.
But this fix is required 1st.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
 mm/vmscan.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Index: mmotm-May11/mm/vmscan.c
===================================================================
--- mmotm-May11.orig/mm/vmscan.c
+++ mmotm-May11/mm/vmscan.c
@@ -941,7 +941,8 @@ keep_lumpy:
 	 * back off and wait for congestion to clear because further reclaim
 	 * will encounter the same problem
 	 */
-	if (nr_dirty == nr_congested && nr_dirty != 0)
+	if (scanning_global_lru(sc) &&
+	    nr_dirty == nr_congested && nr_dirty != 0)
 		zone_set_flag(zone, ZONE_CONGESTED);
 
 	free_page_list(&free_pages);

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