mm/zonelist: enumerate zonelists array index

Hardcoding index to zonelists array in gfp_zonelist() is not a good
idea, let's enumerate it to improve readability.

No functional change.

[akpm@linux-foundation.org: coding-style fixes]
[akpm@linux-foundation.org: fix CONFIG_NUMA=n build]
[n-horiguchi@ah.jp.nec.com: fix warning in comparing enumerator]
Signed-off-by: Yaowei Bai <baiyaowei@cmss.chinamobile.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/gfp.h

@@ -384,10 +384,11 @@ static inline enum zone_type gfp_zone(gfp_t flags)
 
 static inline int gfp_zonelist(gfp_t flags)
 {
-	if (IS_ENABLED(CONFIG_NUMA) && unlikely(flags & __GFP_THISNODE))
-		return 1;
-
-	return 0;
+#ifdef CONFIG_NUMA
+	if (unlikely(flags & __GFP_THISNODE))
+		return ZONELIST_NOFALLBACK;
+#endif
+	return ZONELIST_FALLBACK;
 }
 
 /*

include/linux/mmzone.h

@@ -571,19 +571,17 @@ static inline bool zone_is_empty(struct zone *zone)
 /* Maximum number of zones on a zonelist */
 #define MAX_ZONES_PER_ZONELIST (MAX_NUMNODES * MAX_NR_ZONES)
 
+enum {
+	ZONELIST_FALLBACK,	/* zonelist with fallback */
 #ifdef CONFIG_NUMA
-
-/*
- * The NUMA zonelists are doubled because we need zonelists that restrict the
- * allocations to a single node for __GFP_THISNODE.
- *
- * [0]	: Zonelist with fallback
- * [1]	: No fallback (__GFP_THISNODE)
+	/*
+	 * The NUMA zonelists are doubled because we need zonelists that
+	 * restrict the allocations to a single node for __GFP_THISNODE.
 	 */
-#define MAX_ZONELISTS 2
-#else
-#define MAX_ZONELISTS 1
+	ZONELIST_NOFALLBACK,	/* zonelist without fallback (__GFP_THISNODE) */
 #endif
+	MAX_ZONELISTS
+};
 
 /*
  * This struct contains information about a zone in a zonelist. It is stored

mm/page_alloc.c

@@ -4148,8 +4148,7 @@ static void set_zonelist_order(void)
 
 static void build_zonelists(pg_data_t *pgdat)
 {
-	int j, node, load;
-	enum zone_type i;
+	int i, node, load;
 	nodemask_t used_mask;
 	int local_node, prev_node;
 	struct zonelist *zonelist;
@@ -4169,7 +4168,7 @@ static void build_zonelists(pg_data_t *pgdat)
 	nodes_clear(used_mask);
 
 	memset(node_order, 0, sizeof(node_order));
-	j = 0;
+	i = 0;
 
 	while ((node = find_next_best_node(local_node, &used_mask)) >= 0) {
 		/*
@@ -4186,12 +4185,12 @@ static void build_zonelists(pg_data_t *pgdat)
 		if (order == ZONELIST_ORDER_NODE)
 			build_zonelists_in_node_order(pgdat, node);
 		else
-			node_order[j++] = node;	/* remember order */
+			node_order[i++] = node;	/* remember order */
 	}
 
 	if (order == ZONELIST_ORDER_ZONE) {
 		/* calculate node order -- i.e., DMA last! */
-		build_zonelists_in_zone_order(pgdat, j);
+		build_zonelists_in_zone_order(pgdat, i);
 	}
 
 	build_thisnode_zonelists(pgdat);