linux-kernel - [PATCH 1/2] mm: page_alloc: skip memoryless nodes entirely

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Date:   Wed, 15 Feb 2023 23:24:11 +0800
From:   Qi Zheng <zhengqi.arch@...edance.com>
To:     akpm@...ux-foundation.org, vbabka@...e.cz, david@...hat.com,
        rppt@...nel.org, mhocko@...e.com
Cc:     willy@...radead.org, mgorman@...hsingularity.net,
        osalvador@...e.de, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Qi Zheng <zhengqi.arch@...edance.com>
Subject: [PATCH 1/2] mm: page_alloc: skip memoryless nodes entirely

In find_next_best_node(), We skipped the memoryless nodes
when building the zonelists of other normal nodes (N_NORMAL),
but did not skip the memoryless node itself when building
the zonelist. This will cause it to be traversed at runtime.

For example, say we have node0 and node1, node0 is memoryless
node, then the fallback order of node0 and node1 as follows:

[    0.153005] Fallback order for Node 0: 0 1
[    0.153564] Fallback order for Node 1: 1

After this patch, we skip memoryless node0 entirely, then
the fallback order of node0 and node1 as follows:

[    0.155236] Fallback order for Node 0: 1
[    0.155806] Fallback order for Node 1: 1

So it becomes completely invisible, which will reduce runtime
overhead.

Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
---
 mm/page_alloc.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 0745aedebb37..f0b17dd71bec 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6377,8 +6377,11 @@ int find_next_best_node(int node, nodemask_t *used_node_mask)
 	int min_val = INT_MAX;
 	int best_node = NUMA_NO_NODE;
 
-	/* Use the local node if we haven't already */
-	if (!node_isset(node, *used_node_mask)) {
+	/*
+	 * Use the local node if we haven't already. But for memoryless local
+	 * node, we should skip it and fallback to other nodes.
+	 */
+	if (!node_isset(node, *used_node_mask) && node_state(node, N_MEMORY)) {
 		node_set(node, *used_node_mask);
 		return node;
 	}
-- 
2.20.1