mm: vmscan: reclaim highmem zone if buffer_heads is over limit

We have been reclaimed highmem zone if buffer_heads is over limit but
6b4f779 ("mm: vmscan: invoke slab shrinkers from shrink_zone()")
changed the behavior so it doesn't reclaim highmem zone although
buffer_heads is over the limit.  This patch restores the logic.

Fixes: 6b4f779 ("mm: vmscan: invoke slab shrinkers from shrink_zone()")
Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/vmscan.c

@@ -2553,7 +2553,7 @@ static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
 		sc->gfp_mask |= __GFP_HIGHMEM;
 
 	for_each_zone_zonelist_nodemask(zone, z, zonelist,
-					requested_highidx, sc->nodemask) {
+					gfp_zone(sc->gfp_mask), sc->nodemask) {
 		enum zone_type classzone_idx;
 
 		if (!populated_zone(zone))