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

Andrea Righi
2025-02-07T21:11:27Z

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@gmail.com>
Signed-off-by: Andrea Righi <arighi@nvidia.com>
---
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