[PATCH v3 1/4] mm/mempolicy: implement the sysfs-based weighted_interleave interface

[Gregory Price]

From: Rakie Kim <rakie.kim@xxxxxx>

This patch provides a way to set interleave weight information under
sysfs at /sys/kernel/mm/mempolicy/weighted_interleave/nodeN

The sysfs structure is designed as follows.

  $ tree /sys/kernel/mm/mempolicy/
  /sys/kernel/mm/mempolicy/ [1]
  └── weighted_interleave [2]
      ├── node0 [3]
      └── node1

Each file above can be explained as follows.

[1] mm/mempolicy: configuration interface for mempolicy subsystem

[2] weighted_interleave/: config interface for weighted interleave policy

[3] weighted_interleave/nodeN: weight for nodeN

If a node value is set to `0`, the system-default value will be used.
As of this patch, the system-default for all nodes is always 1.

Suggested-by: Huang Ying <ying.huang@xxxxxxxxx>
Signed-off-by: Rakie Kim <rakie.kim@xxxxxx>
Signed-off-by: Honggyu Kim <honggyu.kim@xxxxxx>
Co-developed-by: Gregory Price <gregory.price@xxxxxxxxxxxx>
Signed-off-by: Gregory Price <gregory.price@xxxxxxxxxxxx>
Co-developed-by: Hyeongtak Ji <hyeongtak.ji@xxxxxx>
Signed-off-by: Hyeongtak Ji <hyeongtak.ji@xxxxxx>
---
 .../ABI/testing/sysfs-kernel-mm-mempolicy     |   4 +
 ...fs-kernel-mm-mempolicy-weighted-interleave |  25 ++
 mm/mempolicy.c                                | 224 ++++++++++++++++++
 3 files changed, 253 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-kernel-mm-mempolicy
 create mode 100644 Documentation/ABI/testing/sysfs-kernel-mm-mempolicy-weighted-interleave

diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-mempolicy b/Documentation/ABI/testing/sysfs-kernel-mm-mempolicy
new file mode 100644
index 000000000000..2dcf24f4384a
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-kernel-mm-mempolicy
@@ -0,0 +1,4 @@
+What:		/sys/kernel/mm/mempolicy/
+Date:		December 2023
+Contact:	Linux memory management mailing list <linux-mm@xxxxxxxxx>
+Description:	Interface for Mempolicy
diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-mempolicy-weighted-interleave b/Documentation/ABI/testing/sysfs-kernel-mm-mempolicy-weighted-interleave
new file mode 100644
index 000000000000..0062b02703ff
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-kernel-mm-mempolicy-weighted-interleave
@@ -0,0 +1,25 @@
+What:		/sys/kernel/mm/mempolicy/weighted_interleave/
+Date:		January 2024
+Contact:	Linux memory management mailing list <linux-mm@xxxxxxxxx>
+Description:	Configuration Interface for the Weighted Interleave policy
+
+What:		/sys/kernel/mm/mempolicy/weighted_interleave/nodeN
+Date:		January 2024
+Contact:	Linux memory management mailing list <linux-mm@xxxxxxxxx>
+Description:	Weight configuration interface for nodeN
+
+		The interleave weight for a memory node (N). These weights are
+		utilized by taskss which have set their mempolicy to
+		MPOL_WEIGHTED_INTERLEAVE.
+
+		These weights only affect new allocations, and changes at runtime
+		will not cause migrations on already allocated pages.
+
+		The minimum weight for a node is always 1.
+
+		Minimum weight: 1
+		Maximum weight: 255
+
+		Writing an empty string or `0` will reset the weight to the
+		system default. The system default may be set by the kernel
+		or drivers at boot or during hotplug events.
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 10a590ee1c89..f1627d45b0c8 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -131,6 +131,17 @@ static struct mempolicy default_policy = {
 
 static struct mempolicy preferred_node_policy[MAX_NUMNODES];
 
+/*
+ * iw_table is the sysfs-set interleave weight table, a value of 0 denotes
+ * system-default value should be used. A NULL iw_table also denotes that
+ * system-default values should be used. Until the system-default table
+ * is implemented, the system-default is always 1.
+ *
+ * iw_table is RCU protected
+ */
+static u8 __rcu *iw_table;
+static DEFINE_MUTEX(iw_table_lock);
+
 /**
  * numa_nearest_node - Find nearest node by state
  * @node: Node id to start the search
@@ -3067,3 +3078,216 @@ void mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
 		p += scnprintf(p, buffer + maxlen - p, ":%*pbl",
 			       nodemask_pr_args(&nodes));
 }
+
+#ifdef CONFIG_SYSFS
+struct iw_node_attr {
+	struct kobj_attribute kobj_attr;
+	int nid;
+};
+
+static ssize_t node_show(struct kobject *kobj, struct kobj_attribute *attr,
+			 char *buf)
+{
+	struct iw_node_attr *node_attr;
+	u8 weight;
+	u8 __rcu *table;
+
+	node_attr = container_of(attr, struct iw_node_attr, kobj_attr);
+
+	rcu_read_lock();
+	table = rcu_dereference(iw_table);
+	weight = table ? table[node_attr->nid] : 1;
+	rcu_read_unlock();
+
+	return sysfs_emit(buf, "%d\n", weight);
+}
+
+static ssize_t node_store(struct kobject *kobj, struct kobj_attribute *attr,
+			  const char *buf, size_t count)
+{
+	struct iw_node_attr *node_attr;
+	u8 __rcu *new;
+	u8 __rcu *old;
+	u8 weight = 0;
+
+	node_attr = container_of(attr, struct iw_node_attr, kobj_attr);
+	if (count == 0 || sysfs_streq(buf, ""))
+		weight = 0;
+	else if (kstrtou8(buf, 0, &weight))
+		return -EINVAL;
+
+	/*
+	 * The default weight is 1, for now. When the kernel-internal
+	 * default weight array is implemented, 0 will be a directive to
+	 * the allocators to use the system-default weight instead.
+	 */
+	if (!weight)
+		weight = 1;
+
+	new = kmalloc(nr_node_ids, GFP_KERNEL);
+	if (!new)
+		return -ENOMEM;
+
+	mutex_lock(&iw_table_lock);
+	old = rcu_dereference_protected(iw_table,
+					lockdep_is_held(&iw_table_lock));
+	if (old)
+		memcpy(new, old, nr_node_ids);
+	else
+		memset(new, 1, nr_node_ids);
+	new[node_attr->nid] = weight;
+	rcu_assign_pointer(iw_table, new);
+	mutex_unlock(&iw_table_lock);
+	synchronize_rcu();
+	kfree(old);
+	return count;
+}
+
+static struct iw_node_attr **node_attrs;
+
+static void sysfs_wi_node_release(struct iw_node_attr *node_attr,
+				  struct kobject *parent)
+{
+	if (!node_attr)
+		return;
+	sysfs_remove_file(parent, &node_attr->kobj_attr.attr);
+	kfree(node_attr->kobj_attr.attr.name);
+	kfree(node_attr);
+}
+
+static void sysfs_wi_release(struct kobject *wi_kobj)
+{
+	int i;
+
+	for (i = 0; i < nr_node_ids; i++)
+		sysfs_wi_node_release(node_attrs[i], wi_kobj);
+	kobject_put(wi_kobj);
+}
+
+static const struct kobj_type wi_ktype = {
+	.sysfs_ops = &kobj_sysfs_ops,
+	.release = sysfs_wi_release,
+};
+
+static int add_weight_node(int nid, struct kobject *wi_kobj)
+{
+	struct iw_node_attr *node_attr;
+	char *name;
+
+	node_attr = kzalloc(sizeof(*node_attr), GFP_KERNEL);
+	if (!node_attr)
+		return -ENOMEM;
+
+	name = kasprintf(GFP_KERNEL, "node%d", nid);
+	if (!name) {
+		kfree(node_attr);
+		return -ENOMEM;
+	}
+
+	sysfs_attr_init(&node_attr->kobj_attr.attr);
+	node_attr->kobj_attr.attr.name = name;
+	node_attr->kobj_attr.attr.mode = 0644;
+	node_attr->kobj_attr.show = node_show;
+	node_attr->kobj_attr.store = node_store;
+	node_attr->nid = nid;
+
+	if (sysfs_create_file(wi_kobj, &node_attr->kobj_attr.attr)) {
+		kfree(node_attr->kobj_attr.attr.name);
+		kfree(node_attr);
+		pr_err("failed to add attribute to weighted_interleave\n");
+		return -ENOMEM;
+	}
+
+	node_attrs[nid] = node_attr;
+	return 0;
+}
+
+static int add_weighted_interleave_group(struct kobject *root_kobj)
+{
+	struct kobject *wi_kobj;
+	int nid, err;
+
+	wi_kobj = kzalloc(sizeof(struct kobject), GFP_KERNEL);
+	if (!wi_kobj)
+		return -ENOMEM;
+
+	err = kobject_init_and_add(wi_kobj, &wi_ktype, root_kobj,
+				   "weighted_interleave");
+	if (err) {
+		kfree(wi_kobj);
+		return err;
+	}
+
+	for_each_node_state(nid, N_POSSIBLE) {
+		err = add_weight_node(nid, wi_kobj);
+		if (err) {
+			pr_err("failed to add sysfs [node%d]\n", nid);
+			break;
+		}
+	}
+	if (err)
+		kobject_put(wi_kobj);
+	return 0;
+}
+
+static void mempolicy_kobj_release(struct kobject *kobj)
+{
+	u8 __rcu *old;
+
+	mutex_lock(&iw_table_lock);
+	old = rcu_dereference_protected(iw_table,
+					lockdep_is_held(&iw_table_lock));
+	rcu_assign_pointer(iw_table, NULL);
+	mutex_unlock(&iw_table_lock);
+	synchronize_rcu();
+	kfree(old);
+	kfree(node_attrs);
+	kfree(kobj);
+}
+
+static const struct kobj_type mempolicy_ktype = {
+	.release = mempolicy_kobj_release
+};
+
+static int __init mempolicy_sysfs_init(void)
+{
+	int err;
+	static struct kobject *mempolicy_kobj;
+
+	mempolicy_kobj = kzalloc(sizeof(*mempolicy_kobj), GFP_KERNEL);
+	if (!mempolicy_kobj) {
+		err = -ENOMEM;
+		goto err_out;
+	}
+
+	node_attrs = kcalloc(nr_node_ids, sizeof(struct iw_node_attr *),
+			     GFP_KERNEL);
+	if (!node_attrs) {
+		err = -ENOMEM;
+		goto mempol_out;
+	}
+
+	err = kobject_init_and_add(mempolicy_kobj, &mempolicy_ktype, mm_kobj,
+				   "mempolicy");
+	if (err)
+		goto node_out;
+
+	err = add_weighted_interleave_group(mempolicy_kobj);
+	if (err) {
+		pr_err("mempolicy sysfs structure failed to initialize\n");
+		kobject_put(mempolicy_kobj);
+		return err;
+	}
+
+	return err;
+node_out:
+	kfree(node_attrs);
+mempol_out:
+	kfree(mempolicy_kobj);
+err_out:
+	pr_err("failed to add mempolicy kobject to the system\n");
+	return err;
+}
+
+late_initcall(mempolicy_sysfs_init);
+#endif /* CONFIG_SYSFS */
-- 
2.39.1