mm: clean up zone flags

Page reclaim tests zone_is_reclaim_dirty(), but the site that actually
sets this state does zone_set_flag(zone, ZONE_TAIL_LRU_DIRTY), sending the
reader through layers indirection just to track down a simple bit.

Remove all zone flag wrappers and just use bitops against zone->flags
directly.  It's just as readable and the lines are barely any longer.

Also rename ZONE_TAIL_LRU_DIRTY to ZONE_DIRTY to match ZONE_WRITEBACK, and
remove the zone_flags_t typedef.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/oom_kill.c

@@ -565,7 +565,7 @@ bool oom_zonelist_trylock(struct zonelist *zonelist, gfp_t gfp_mask)
 
 	spin_lock(&zone_scan_lock);
 	for_each_zone_zonelist(zone, z, zonelist, gfp_zone(gfp_mask))
-		if (zone_is_oom_locked(zone)) {
+		if (test_bit(ZONE_OOM_LOCKED, &zone->flags)) {
 			ret = false;
 			goto out;
 		}
@@ -575,7 +575,7 @@ bool oom_zonelist_trylock(struct zonelist *zonelist, gfp_t gfp_mask)
 	 * call to oom_zonelist_trylock() doesn't succeed when it shouldn't.
 	 */
 	for_each_zone_zonelist(zone, z, zonelist, gfp_zone(gfp_mask))
-		zone_set_flag(zone, ZONE_OOM_LOCKED);
+		set_bit(ZONE_OOM_LOCKED, &zone->flags);
 
 out:
 	spin_unlock(&zone_scan_lock);
@@ -594,7 +594,7 @@ void oom_zonelist_unlock(struct zonelist *zonelist, gfp_t gfp_mask)
 
 	spin_lock(&zone_scan_lock);
 	for_each_zone_zonelist(zone, z, zonelist, gfp_zone(gfp_mask))
-		zone_clear_flag(zone, ZONE_OOM_LOCKED);
+		clear_bit(ZONE_OOM_LOCKED, &zone->flags);
 	spin_unlock(&zone_scan_lock);
 }