per-zone and reclaim enhancements for memory controller: add scan_global_lru macro

This is used to detect which scan_control scans global lru or mem_cgroup lru.
And compiled to be static value (1) when memory controller is not configured.
This may make the meaning obvious.
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Herbert Poetzl <herbert@13thfloor.at>
Cc: Kirill Korotaev <dev@sw.ru>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Paul Menage <menage@google.com>
Cc: Pavel Emelianov <xemul@openvz.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/vmscan.c

@@ -126,6 +126,12 @@ long vm_total_pages;	/* The total number of pages which the VM controls */
 static LIST_HEAD(shrinker_list);
 static DECLARE_RWSEM(shrinker_rwsem);
 
+#ifdef CONFIG_CGROUP_MEM_CONT
+#define scan_global_lru(sc)	(!(sc)->mem_cgroup)
+#else
+#define scan_global_lru(sc)	(1)
+#endif
+
 /*
  * Add a shrinker callback to be called from the vm
  */
@@ -1280,12 +1286,13 @@ static unsigned long do_try_to_free_pages(struct zone **zones, gfp_t gfp_mask,
 		 * Don't shrink slabs when reclaiming memory from
 		 * over limit cgroups
 		 */
-		if (sc->mem_cgroup == NULL)
+		if (scan_global_lru(sc)) {
 			shrink_slab(sc->nr_scanned, gfp_mask, lru_pages);
 			if (reclaim_state) {
 				nr_reclaimed += reclaim_state->reclaimed_slab;
 				reclaim_state->reclaimed_slab = 0;
 			}
+		}
 		total_scanned += sc->nr_scanned;
 		if (nr_reclaimed >= sc->swap_cluster_max) {
 			ret = 1;
@@ -1311,7 +1318,7 @@ static unsigned long do_try_to_free_pages(struct zone **zones, gfp_t gfp_mask,
 			congestion_wait(WRITE, HZ/10);
 	}
 	/* top priority shrink_caches still had more to do? don't OOM, then */
-	if (!sc->all_unreclaimable && sc->mem_cgroup == NULL)
+	if (!sc->all_unreclaimable && scan_global_lru(sc))
 		ret = 1;
 out:
 	/*