Re: [PATCH v5 01/11] mm/mempolicy: implement the sysfs-based weighted_interleave interface

From: Rakie Kim <rakie.kim@sk.com>

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 sysfs is disabled in the config, the global interleave weights
will default to "1" for all nodes.

Signed-off-by: Rakie Kim <rakie.kim@sk.com>
Signed-off-by: Honggyu Kim <redacted>
Co-developed-by: Gregory Price <redacted>
Signed-off-by: Gregory Price <redacted>
Co-developed-by: Hyeongtak Ji <redacted>
Signed-off-by: Hyeongtak Ji <redacted>
---
 .../ABI/testing/sysfs-kernel-mm-mempolicy     |   4 +
 ...fs-kernel-mm-mempolicy-weighted-interleave |  22 +++
 mm/mempolicy.c                                | 156 ++++++++++++++++++
 3 files changed, 182 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@kvack.org>
+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..aa27fdf08c19
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-kernel-mm-mempolicy-weighted-interleave

@@ -0,0 +1,22 @@
+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:	Weight configuration interface for nodeN
+
+		The interleave weight for a memory node (N). These weights are
+		utilized by processes which have set their 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.
+
+		Writing an empty string resets the weight value to 1.

+		Maximum weight: 255

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 10a590ee1c89..0e77633b07a5 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c

@@ -131,6 +131,8 @@ static struct mempolicy default_policy = {
 
 static struct mempolicy preferred_node_policy[MAX_NUMNODES];
 
+static char iw_table[MAX_NUMNODES];
+

 /**
  * numa_nearest_node - Find nearest node by state
  * @node: Node id to start the search

@@ -3067,3 +3069,157 @@ 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;
+
+	node_attr = container_of(attr, struct iw_node_attr, kobj_attr);
+	return sysfs_emit(buf, "%d\n", iw_table[node_attr->nid]);
+}
+
+static ssize_t node_store(struct kobject *kobj, struct kobj_attribute *attr,
+			  const char *buf, size_t count)
+{
+	struct iw_node_attr *node_attr;
+	unsigned char weight = 0;
+
+	node_attr = container_of(attr, struct iw_node_attr, kobj_attr);
+	/* If no input, set default weight to 1 */
+	if (count == 0 || sysfs_streq(buf, ""))
+		weight = 1;
+	else if (kstrtou8(buf, 0, &weight) || !weight)
+		return -EINVAL;
+
+	iw_table[node_attr->nid] = weight;