[PATCH 1/6] mm/numa: Introduce numa_nearest_nodemask()

[Andrea Righi <arighi@xxxxxxxxxx>]

Introduce the new helper numa_nearest_nodemask() to find the closest
node, in a specified nodemask and state, from a given starting node.

Returns MAX_NUMNODES if no node is found.

Cc: Yury Norov <yury.norov@xxxxxxxxx>
Signed-off-by: Andrea Righi <arighi@xxxxxxxxxx>
---
 include/linux/nodemask_types.h |  6 +++++-
 include/linux/numa.h           |  8 +++++++
 mm/mempolicy.c                 | 38 ++++++++++++++++++++++++++++++++++
 3 files changed, 51 insertions(+), 1 deletion(-)

diff --git a/include/linux/nodemask_types.h b/include/linux/nodemask_types.h
index 6b28d97ea6ed0..8d0b7a66c3a49 100644
--- a/include/linux/nodemask_types.h
+++ b/include/linux/nodemask_types.h
@@ -5,6 +5,10 @@
 #include <linux/bitops.h>
 #include <linux/numa.h>
 
-typedef struct { DECLARE_BITMAP(bits, MAX_NUMNODES); } nodemask_t;
+struct nodemask {
+	DECLARE_BITMAP(bits, MAX_NUMNODES);
+};
+
+typedef struct nodemask nodemask_t;
 
 #endif /* __LINUX_NODEMASK_TYPES_H */
diff --git a/include/linux/numa.h b/include/linux/numa.h
index 3567e40329ebc..a549b87d1fca5 100644
--- a/include/linux/numa.h
+++ b/include/linux/numa.h
@@ -27,6 +27,8 @@ static inline bool numa_valid_node(int nid)
 #define __initdata_or_meminfo __initdata
 #endif
 
+struct nodemask;
+
 #ifdef CONFIG_NUMA
 #include <asm/sparsemem.h>
 
@@ -38,6 +40,7 @@ void __init alloc_offline_node_data(int nid);
 
 /* Generic implementation available */
 int numa_nearest_node(int node, unsigned int state);
+int numa_nearest_nodemask(int node, unsigned int state, struct nodemask *mask);
 
 #ifndef memory_add_physaddr_to_nid
 int memory_add_physaddr_to_nid(u64 start);
@@ -55,6 +58,11 @@ static inline int numa_nearest_node(int node, unsigned int state)
 	return NUMA_NO_NODE;
 }
 
+static inline int numa_nearest_nodemask(int node, unsigned int state, struct nodemask *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..1cfee509c7229 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -196,6 +196,44 @@ int numa_nearest_node(int node, unsigned int state)
 }
 EXPORT_SYMBOL_GPL(numa_nearest_node);
 
+/**
+ * numa_nearest_nodemask - Find the node in @mask at the nearest distance
+ *			   from @node.
+ *
+ * @node: the node to start the search from.
+ * @state: the node state to filter nodes by.
+ * @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 numa_nearest_nodemask(int node, unsigned int state, nodemask_t *mask)
+{
+	int dist, n, min_dist = INT_MAX, min_node = MAX_NUMNODES;
+
+	if (node == NUMA_NO_NODE)
+		return MAX_NUMNODES;
+
+	if (node_state(node, state) && node_isset(node, *mask))
+		return node;
+
+	for_each_node_state(n, state) {
+		if (!node_isset(n, *mask))
+			continue;
+		dist = node_distance(node, n);
+		if (dist < min_dist) {
+			min_dist = dist;
+			min_node = n;
+		}
+	}
+
+	return min_node;
+}
+EXPORT_SYMBOL_GPL(numa_nearest_nodemask);
+
 struct mempolicy *get_task_policy(struct task_struct *p)
 {
 	struct mempolicy *pol = p->mempolicy;
-- 
2.48.1