Re: [RFC PATCH 01/11] mm/mempolicy: implement the sysfs-based weighted_interleave interface

+What:		/sys/kernel/mm/mempolicy/weighted_interleave/
+Date:		December 2023
+Contact:	Linux memory management mailing list <linux-mm@kvack.org>
+Description:	Configuration Interface for the Weighted Interleave policy
+
+What:		/sys/kernel/mm/mempolicy/weighted_interleave/nodeN/
+Date:		December 2023
+Contact:	Linux memory management mailing list <linux-mm@kvack.org>
+Description:	Configuration interface for accesses initiated from nodeN
+
+		The directory to configure access initiator weights for nodeN.
+
+		Possible numa nodes which have not been marked as a CPU node
+		at boot will not have a nodeN directory made for them at boot.

+
+What:		/sys/kernel/mm/mempolicy/weighted_interleave/nodeN/nodeM
+		/sys/kernel/mm/mempolicy/weighted_interleave/nodeN/nodeM/weight
+Date:		December 2023
+Contact:	Linux memory management mailing list <linux-mm@kvack.org>
+Description:	Configuration interface for target nodes accessed from nodeNN
+
+		The interleave weight for a memory node (M) from initiating
+		node (N). These weights are utilized by processes which have set
+		the mempolicy to MPOL_WEIGHTED_INTERLEAVE and have opted into
+		global weights by omitting a task-local weight array.
+
+		These weights only affect new allocations, and changes at runtime
+		will not cause migrations on already allocated pages.
+
+		If the weight of 0 is desired, the appropriate way to do this is
+		by removing the node from the weighted interleave nodemask.
+
+		Minimum weight: 1
+		Maximum weight: 255

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 10a590ee1c89..ce332b5e7a03 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c

@@ -131,6 +131,11 @@ static struct mempolicy default_policy = {

static struct mempolicy preferred_node_policy[MAX_NUMNODES];

+struct interleave_weight_table {
+	unsigned char weights[MAX_NUMNODES];
+};
+static struct interleave_weight_table *iw_table;
+
/**
 * numa_nearest_node - Find nearest node by state
 * @node: Node id to start the search

@@ -3067,3 +3072,224 @@ void mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)

	p += scnprintf(p, buffer + maxlen - p, ":%*pbl",
		       nodemask_pr_args(&nodes));
}
+
+struct iw_node_info {
+	struct kobject kobj;
+	int src;
+	int dst;
+};
+
+static ssize_t node_weight_show(struct kobject *kobj,
+				struct kobj_attribute *attr, char *buf)
+{
+	struct iw_node_info *node_info = container_of(kobj, struct iw_node_info,
+						      kobj);
+	return sysfs_emit(buf, "%d\n",
+			  iw_table[node_info->src].weights[node_info->dst]);
+}
+
+static ssize_t node_weight_store(struct kobject *kobj,
+				 struct kobj_attribute *attr,
+				 const char *buf, size_t count)
+{
+	unsigned char weight = 0;
+	struct iw_node_info *node_info = NULL;
+
+	node_info = container_of(kobj, struct iw_node_info, kobj);
+
+	if (kstrtou8(buf, 0, &weight) || !weight)
+		return -EINVAL;
+
+	iw_table[node_info->src].weights[node_info->dst] = weight;
+
+	return count;
+}

+static int __init mempolicy_sysfs_init(void)
+{
+	int err, nid;
+	int cpunodes = 0;
+	struct kobject *root_kobj;
+
+	for_each_node_state(nid, N_CPU)
+		cpunodes += 1;
+	iw_table = kmalloc_array(cpunodes, sizeof(*iw_table), GFP_KERNEL);
+	if (!iw_table) {
+		pr_err("failed to create interleave weight table\n");
+		err = -ENOMEM;
+		goto fail_obj;