linux-kernel - [PATCH 1/2] mm/page_alloc: add same penalty is enough to get round-robin order

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Date:   Sun, 23 Jan 2022 01:35:36 +0000
From:   Wei Yang <richard.weiyang@...il.com>
To:     akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Wei Yang <richard.weiyang@...il.com>
Subject: [PATCH 1/2] mm/page_alloc: add same penalty is enough to get round-robin order

To make node order in round-robin in the same distance group, we add a
penalty to the first node we got in each round.

To get a round-robin order in the same distance group, we don't need to
decrease the penalty since:

  * find_next_best_node() always iterates node in the same order
  * distance matters more then penalty in find_next_best_node()
  * in nodes with the same distance, the first one would be picked up

So it is fine to increase same penalty when we get the first node in the
same distance group.

Signed-off-by: Wei Yang <richard.weiyang@...il.com>
---
 mm/page_alloc.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c5952749ad40..f27afd517652 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6245,13 +6245,12 @@ static void build_thisnode_zonelists(pg_data_t *pgdat)
 static void build_zonelists(pg_data_t *pgdat)
 {
 	static int node_order[MAX_NUMNODES];
-	int node, load, nr_nodes = 0;
+	int node, nr_nodes = 0;
 	nodemask_t used_mask = NODE_MASK_NONE;
 	int local_node, prev_node;
 
 	/* NUMA-aware ordering of nodes */
 	local_node = pgdat->node_id;
-	load = nr_online_nodes;
 	prev_node = local_node;
 
 	memset(node_order, 0, sizeof(node_order));
@@ -6263,11 +6262,10 @@ static void build_zonelists(pg_data_t *pgdat)
 		 */
 		if (node_distance(local_node, node) !=
 		    node_distance(local_node, prev_node))
-			node_load[node] += load;
+			node_load[node] += nr_online_nodes;
 
 		node_order[nr_nodes++] = node;
 		prev_node = node;
-		load--;
 	}
 
 	build_zonelists_in_node_order(pgdat, node_order, nr_nodes);
-- 
2.33.1