[PATCH 3/8] mm/numa: Introduce nearest_node_nodemask()

[Andrea Righi]

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.

Suggested-by: Yury Norov [NVIDIA] <yury.norov@xxxxxxxxx>
Signed-off-by: Andrea Righi <arighi@xxxxxxxxxx>
---
 include/linux/numa.h |  7 +++++++
 mm/mempolicy.c       | 31 +++++++++++++++++++++++++++++++
 2 files changed, 38 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..488cad280efb3 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -196,6 +196,37 @@ 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: a valid node ID to start the search from.
+ * @mask: a pointer to a nodemask representing the allowed nodes.
+ *
+ * This function iterates over all nodes in @mask and calculates the
+ * distance from the starting @node, then it returns the node ID that is
+ * the closest to @node, or MAX_NUMNODES if no node is found.
+ *
+ * Note that @node must be a valid node ID usable with node_distance(),
+ * providing an invalid node ID (e.g., NUMA_NO_NODE) may result in crashes
+ * or unexpected behavior.
+ */
+int nearest_node_nodemask(int node, nodemask_t *mask)
+{
+	int dist, n, min_dist = INT_MAX, min_node = 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