[PATCH v2 2/2] mm/page_alloc: refactor build_node_zonelist() out of build_zonelists()

[Gregory Price]

Extract per-node fallback-list construction into build_node_zonelist().
Build each selected node directly into the destination zonelist so no
intermediate node_order array or node count is needed. Print the fallback
order as each node is added.

This lets us build new zonelists from candidate nodemasks instead of just
the default N_MEMORY node state list.

No functional change: build_zonelists() builds and prints the same FALLBACK
list over N_MEMORY with node_load updates as before.

Signed-off-by: Gregory Price <gourry@xxxxxxxxxx>
---
 mm/page_alloc.c | 63 ++++++++++++++++++-------------------------------
 1 file changed, 23 insertions(+), 40 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 7efce139d562..d1888d5630e0 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5857,31 +5857,6 @@ int find_next_best_node_in(int node, nodemask_t *used_node_mask,
 }
 
 
-/*
- * Build zonelists ordered by node and zones within node.
- * This results in maximum locality--normal zone overflows into local
- * DMA zone, if any--but risks exhausting DMA zone.
- */
-static void build_zonelists_in_node_order(pg_data_t *pgdat, int *node_order,
-		unsigned nr_nodes)
-{
-	struct zoneref *zonerefs;
-	int i;
-
-	zonerefs = pgdat->node_zonelists[ZONELIST_FALLBACK]._zonerefs;
-
-	for (i = 0; i < nr_nodes; i++) {
-		int nr_zones;
-
-		pg_data_t *node = NODE_DATA(node_order[i]);
-
-		nr_zones = build_zonerefs_node(node, zonerefs);
-		zonerefs += nr_zones;
-	}
-	zonerefs->zone = NULL;
-	zonerefs->zone_idx = 0;
-}
-
 /*
  * Build __GFP_THISNODE zonelists
  */
@@ -5897,20 +5872,24 @@ static void build_thisnode_zonelists(pg_data_t *pgdat)
 	zonerefs->zone_idx = 0;
 }
 
-static void build_zonelists(pg_data_t *pgdat)
+/*
+ * Build one zonelist ordered by node and zones within node. This results in
+ * maximum locality--normal zone overflows into local DMA zone, if any--but
+ * risks exhausting DMA zone.
+ */
+static void build_node_zonelist(pg_data_t *pgdat, const nodemask_t *candidates,
+				int zlidx)
 {
-	static int node_order[MAX_NUMNODES];
-	int node, nr_nodes = 0;
+	struct zoneref *zonerefs = pgdat->node_zonelists[zlidx]._zonerefs;
 	nodemask_t used_mask = NODE_MASK_NONE;
-	int local_node, prev_node;
+	int local_node = pgdat->node_id;
+	int prev_node = local_node;
+	int node;
 
-	/* NUMA-aware ordering of nodes */
-	local_node = pgdat->node_id;
-	prev_node = local_node;
+	pr_info("Fallback order for Node %d: ", local_node);
 
-	memset(node_order, 0, sizeof(node_order));
 	while ((node = find_next_best_node_in(local_node, &used_mask,
-					      &node_states[N_MEMORY])) >= 0) {
+					      candidates)) >= 0) {
 		/*
 		 * We don't want to pressure a particular node.
 		 * So adding penalty to the first node in same
@@ -5920,18 +5899,22 @@ static void build_zonelists(pg_data_t *pgdat)
 		    node_distance(local_node, prev_node))
 			node_load[node] += 1;
 
-		node_order[nr_nodes++] = node;
+		zonerefs += build_zonerefs_node(NODE_DATA(node), zonerefs);
+		pr_cont("%d ", node);
 		prev_node = node;
 	}
 
-	build_zonelists_in_node_order(pgdat, node_order, nr_nodes);
-	build_thisnode_zonelists(pgdat);
-	pr_info("Fallback order for Node %d: ", local_node);
-	for (node = 0; node < nr_nodes; node++)
-		pr_cont("%d ", node_order[node]);
+	zonerefs->zone = NULL;
+	zonerefs->zone_idx = 0;
 	pr_cont("\n");
 }
 
+static void build_zonelists(pg_data_t *pgdat)
+{
+	build_node_zonelist(pgdat, &node_states[N_MEMORY], ZONELIST_FALLBACK);
+	build_thisnode_zonelists(pgdat);
+}
+
 #ifdef CONFIG_HAVE_MEMORYLESS_NODES
 /*
  * Return node id of node used for "local" allocations.
-- 
2.55.0