mm: zone_reclaim: remove ZONE_RECLAIM_LOCKED

Zone reclaim locked breaks zone_reclaim_mode=1. If more than one
thread allocates memory at the same time, it forces a premature
allocation into remote NUMA nodes even when there's plenty of clean
cache to reclaim in the local nodes.
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Acked-by: Rafael Aquini <aquini@redhat.com>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>

include/linux/mmzone.h

@@ -530,7 +530,6 @@ struct zone {
 } ____cacheline_internodealigned_in_smp;
 
 enum zone_flags {
-	ZONE_RECLAIM_LOCKED,		/* prevents concurrent reclaim */
 	ZONE_OOM_LOCKED,		/* zone is in OOM killer zonelist */
 	ZONE_CONGESTED,			/* zone has many dirty pages backed by
 					 * a congested BDI

mm/vmscan.c

@@ -3743,11 +3743,7 @@ int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
 	if (node_state(node_id, N_CPU) && node_id != numa_node_id())
 		return ZONE_RECLAIM_NOSCAN;
 
-	if (test_and_set_bit(ZONE_RECLAIM_LOCKED, &zone->flags))
-		return ZONE_RECLAIM_NOSCAN;
-
 	ret = __zone_reclaim(zone, gfp_mask, order);
-	clear_bit(ZONE_RECLAIM_LOCKED, &zone->flags);
 
 	if (!ret)
 		count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);