linux-kernel - [PATCH 2/7] mm/numa: Introduce nearest_node

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Message-ID: <20250212165006.490130-3-arighi@nvidia.com>
Date: Wed, 12 Feb 2025 17:48:09 +0100
From: Andrea Righi <arighi@...dia.com>
To: Tejun Heo <tj@...nel.org>,
	David Vernet <void@...ifault.com>,
	Changwoo Min <changwoo@...lia.com>
Cc: Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	Ian May <ianm@...dia.com>,
	bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Yury Norov <yury.norov@...il.com>
Subject: [PATCH 2/7] mm/numa: Introduce nearest_node_nodemask()

Introduce the new helper nearest_node_nodemask() to find the closest
node in a specified nodemask from a given starting node.

Returns MAX_NUMNODES if no node is found.

Cc: Yury Norov <yury.norov@...il.com>
Signed-off-by: Andrea Righi <arighi@...dia.com>
---
 include/linux/numa.h |  7 +++++++
 mm/mempolicy.c       | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/include/linux/numa.h b/include/linux/numa.h
index 31d8bf8a951a7..e6baaf6051bcf 100644
--- a/include/linux/numa.h
+++ b/include/linux/numa.h
@@ -31,6 +31,8 @@ void __init alloc_offline_node_data(int nid);
 /* Generic implementation available */
 int numa_nearest_node(int node, unsigned int state);
 
+int nearest_node_nodemask(int node, nodemask_t *mask);
+
 #ifndef memory_add_physaddr_to_nid
 int memory_add_physaddr_to_nid(u64 start);
 #endif
@@ -47,6 +49,11 @@ static inline int numa_nearest_node(int node, unsigned int state)
 	return NUMA_NO_NODE;
 }
 
+static inline int nearest_node_nodemask(int node, nodemask_t *mask)
+{
+	return NUMA_NO_NODE;
+}
+
 static inline int memory_add_physaddr_to_nid(u64 start)
 {
 	return 0;
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 162407fbf2bc7..1e2acf187ea3a 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -196,6 +196,38 @@ int numa_nearest_node(int node, unsigned int state)
 }
 EXPORT_SYMBOL_GPL(numa_nearest_node);
 
+/**
+ * nearest_node_nodemask - Find the node in @mask at the nearest distance
+ *			   from @node.
+ *
+ * @node: the node to start the search from.
+ * @mask: a pointer to a nodemask representing the allowed nodes.
+ *
+ * This function iterates over all nodes in the given state and calculates
+ * the distance to the starting node.
+ *
+ * Returns the node ID in @mask that is the closest in terms of distance
+ * from @node, or MAX_NUMNODES if no node is found.
+ */
+int nearest_node_nodemask(int node, nodemask_t *mask)
+{
+	int dist, n, min_dist = INT_MAX, min_node = MAX_NUMNODES;
+
+	if (node == NUMA_NO_NODE)
+		return MAX_NUMNODES;
+
+	for_each_node_mask(n, *mask) {
+		dist = node_distance(node, n);
+		if (dist < min_dist) {
+			min_dist = dist;
+			min_node = n;
+		}
+	}
+
+	return min_node;
+}
+EXPORT_SYMBOL_GPL(nearest_node_nodemask);
+
 struct mempolicy *get_task_policy(struct task_struct *p)
 {
 	struct mempolicy *pol = p->mempolicy;
-- 
2.48.1