[PATCH v9 0/3] Enhance sysfs handling for memory hotplug in weighted interleave

[PATCH v9 0/3] Enhance sysfs handling for memory hotplug in weighted interleave

[Rakie Kim]

The following patch series enhances the weighted interleave policy in the
memory management subsystem by improving sysfs handling, fixing memory leaks,
and introducing dynamic sysfs updates for memory hotplug support.

Changes from v8:
https://lore.kernel.org/all/20250416113123.629-1-rakie.kim@sk.com/
- Updated lock usage during sysfs entry creation
- Fixed sysfs removal warning triggered during exception handling paths

Changes from v7:
https://lore.kernel.org/all/20250408073243.488-1-rakie.kim@sk.com/
- Refactored error handling paths to remove unnecessary `goto` usage
- Renamed unclear variables and functions for better readability

Changes from v6:
https://lore.kernel.org/all/20250404074623.1179-1-rakie.kim@sk.com/
- Removed redundant error handling in MEM_OFFLINE case

Changes from v5:
https://lore.kernel.org/all/20250402014906.1086-1-rakie.kim@sk.com/
- Added lock protection to sensitive sections

Changes from v4:
https://lore.kernel.org/all/20250401090901.1050-1-rakie.kim@sk.com/
- Added missing `kobject_del()` when removing a kobject
- Extended locking coverage to protect shared state

Changes from v3:
https://lore.kernel.org/all/20250320041749.881-1-rakie.kim@sk.com/
- Added error handling for allocation and cleanup paths
- Replaced static node attribute list with flexible array
- Reorganized four patches into three based on their functional scope

Changes from v2:
https://lore.kernel.org/all/20250312075628.648-1-rakie.kim@sk.com/
- Clarified commit messages
- Refactored to avoid passing the global structure as a parameter

Changes from v1:
https://lore.kernel.org/all/20250307063534.540-1-rakie.kim@sk.com/
- Fixed memory leaks related to `kobject` lifecycle
- Refactored sysfs layout for hotplug readiness
- Introduced initial memory hotplug support for weighted interleave

### Introduction
The weighted interleave policy distributes memory allocations across multiple
NUMA nodes based on their performance weight, thereby optimizing memory
bandwidth utilization. The weight values are configured through sysfs.

Previously, sysfs entries for weighted interleave were managed statically
at initialization. This led to several issues:
- Memory Leaks: Improper `kobject` teardown caused memory leaks
  when initialization failed or when nodes were removed.
- Lack of Dynamic Updates: Sysfs attributes were created only during
  initialization, preventing nodes added at runtime from being recognized.
- Handling of Unusable Nodes: Sysfs entries were generated for all
  possible nodes (`N_POSSIBLE`), including memoryless or unavailable nodes,
  leading to sysfs entries for unusable nodes and potential
  misconfigurations.

### Patch Overview
1. [PATCH 1/3] mm/mempolicy: Fix memory leaks in weighted interleave sysfs
   - Ensures proper cleanup of `kobject` allocations.
   - Adds `kobject_del()` before `kobject_put()` to clean up sysfs state correctly.
   - Prevents memory/resource leaks and improves teardown behavior.
   - Ensures that `sysfs_remove_file()` is not called from the release path
     after `kobject_del()` has cleared sysfs state, to avoid potential
     inconsistencies and warnings in the kernfs subsystem.

2. [PATCH 2/3] mm/mempolicy: Prepare weighted interleave sysfs for memory hotplug
   - Refactors static sysfs layout into a new `sysfs_wi_group` structure.
   - Makes per-node sysfs attributes accessible to external modules.
   - Lays groundwork for future hotplug support by enabling runtime modification.

3. [PATCH 3/3] mm/mempolicy: Support memory hotplug in weighted interleave
   - Dynamically adds/removes sysfs entries when nodes are online/offline.
   - Limits sysfs creation to nodes with memory, avoiding unusable node entries.
   - Hooks into memory hotplug notifier for runtime updates.

These patches have been tested under CXL-based memory configurations,
including hotplug scenarios, to ensure proper behavior and stability.

 mm/mempolicy.c | 240 ++++++++++++++++++++++++++++++-------------------
 1 file changed, 148 insertions(+), 92 deletions(-)


base-commit: 8ffd015db85fea3e15a77027fda6c02ced4d2444
-- 
2.34.1

[PATCH v9 1/3] mm/mempolicy: Fix memory leaks in weighted interleave sysfs

[Rakie Kim]

Memory leaks occurred when removing sysfs attributes for weighted
interleave. Improper kobject deallocation led to unreleased memory
when initialization failed or when nodes were removed.

This patch resolves the issue by replacing unnecessary `kfree()`
calls with proper `kobject_del()` and `kobject_put()` sequences,
ensuring correct teardown and preventing memory leaks.

By explicitly calling `kobject_del()` before `kobject_put()`, the
release function is now invoked safely, and internal sysfs state is
correctly cleaned up. This guarantees that the memory associated with
the kobject is fully released and avoids resource leaks, thereby
improving system stability.

Additionally, sysfs_remove_file() is no longer called from the release
function to avoid accessing invalid sysfs state after kobject_del().
All attribute removals are now done before kobject_del(), preventing
WARN_ON() in kernfs and ensuring safe and consistent cleanup of sysfs
entries.

Fixes: dce41f5ae253 ("mm/mempolicy: implement the sysfs-based weighted_interleave interface")
Signed-off-by: Rakie Kim <rakie.kim@sk.com>
Reviewed-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Joshua Hahn <joshua.hahnjy@gmail.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
---
 mm/mempolicy.c | 121 ++++++++++++++++++++++++-------------------------
 1 file changed, 59 insertions(+), 62 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index b28a1e6ae096..293b4b347975 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -3463,8 +3463,8 @@ static ssize_t node_store(struct kobject *kobj, struct kobj_attribute *attr,
 
 static struct iw_node_attr **node_attrs;
 
-static void sysfs_wi_node_release(struct iw_node_attr *node_attr,
-				  struct kobject *parent)
+static void sysfs_wi_node_delete(struct iw_node_attr *node_attr,
+				 struct kobject *parent)
 {
 	if (!node_attr)
 		return;
@@ -3473,18 +3473,42 @@ static void sysfs_wi_node_release(struct iw_node_attr *node_attr,
 	kfree(node_attr);
 }
 
-static void sysfs_wi_release(struct kobject *wi_kobj)
+static void sysfs_wi_node_delete_all(struct kobject *wi_kobj)
 {
-	int i;
+	int nid;
 
-	for (i = 0; i < nr_node_ids; i++)
-		sysfs_wi_node_release(node_attrs[i], wi_kobj);
-	kobject_put(wi_kobj);
+	for (nid = 0; nid < nr_node_ids; nid++)
+		sysfs_wi_node_delete(node_attrs[nid], wi_kobj);
+}
+
+static void iw_table_free(void)
+{
+	u8 *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);
+}
+
+static void wi_cleanup(struct kobject *wi_kobj) {
+	sysfs_wi_node_delete_all(wi_kobj);
+	iw_table_free();
+	kfree(node_attrs);
+}
+
+static void wi_kobj_release(struct kobject *wi_kobj)
+{
+	kfree(wi_kobj);
 }
 
 static const struct kobj_type wi_ktype = {
 	.sysfs_ops = &kobj_sysfs_ops,
-	.release = sysfs_wi_release,
+	.release = wi_kobj_release,
 };
 
 static int add_weight_node(int nid, struct kobject *wi_kobj)
@@ -3525,85 +3549,58 @@ static int add_weighted_interleave_group(struct kobject *root_kobj)
 	struct kobject *wi_kobj;
 	int nid, err;
 
+	node_attrs = kcalloc(nr_node_ids, sizeof(struct iw_node_attr *),
+			     GFP_KERNEL);
+	if (!node_attrs)
+		return -ENOMEM;
+
 	wi_kobj = kzalloc(sizeof(struct kobject), GFP_KERNEL);
-	if (!wi_kobj)
+	if (!wi_kobj) {
+		kfree(node_attrs);
 		return -ENOMEM;
+	}
 
 	err = kobject_init_and_add(wi_kobj, &wi_ktype, root_kobj,
 				   "weighted_interleave");
-	if (err) {
-		kfree(wi_kobj);
-		return err;
-	}
+	if (err)
+		goto err_put_kobj;
 
 	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;
+			goto err_cleanup_kobj;
 		}
 	}
-	if (err)
-		kobject_put(wi_kobj);
-	return 0;
-}
 
-static void mempolicy_kobj_release(struct kobject *kobj)
-{
-	u8 *old;
+	return 0;
 
-	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);
+err_cleanup_kobj:
+	wi_cleanup(wi_kobj);
+	kobject_del(wi_kobj);
+err_put_kobj:
+	kobject_put(wi_kobj);
+	return err;
 }
 
-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;
-	}
+	mempolicy_kobj = kobject_create_and_add("mempolicy", mm_kobj);
+	if (!mempolicy_kobj)
+		return -ENOMEM;
 
-	err = kobject_init_and_add(mempolicy_kobj, &mempolicy_ktype, mm_kobj,
-				   "mempolicy");
+	err = add_weighted_interleave_group(mempolicy_kobj);
 	if (err)
-		goto node_out;
+		goto err_kobj;
 
-	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 0;
 
-	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");
+err_kobj:
+	kobject_del(mempolicy_kobj);
+	kobject_put(mempolicy_kobj);
 	return err;
 }
 
-- 
2.34.1

[PATCH v9 2/3] mm/mempolicy: Prepare weighted interleave sysfs for memory hotplug

[Rakie Kim]

Previously, the weighted interleave sysfs structure was statically
managed during initialization. This prevented new nodes from being
recognized when memory hotplug events occurred, limiting the ability
to update or extend sysfs entries dynamically at runtime.

To address this, this patch refactors the sysfs infrastructure and
encapsulates it within a new structure, `sysfs_wi_group`, which holds
both the kobject and an array of node attribute pointers.

By allocating this group structure globally, the per-node sysfs
attributes can be managed beyond initialization time, enabling
external modules to insert or remove node entries in response to
events such as memory hotplug or node online/offline transitions.

Instead of allocating all per-node sysfs attributes at once, the
initialization path now uses the existing sysfs_wi_node_add() and
sysfs_wi_node_delete() helpers. This refactoring makes it possible
to modularly manage per-node sysfs entries and ensures the
infrastructure is ready for runtime extension.

Signed-off-by: Rakie Kim <rakie.kim@sk.com>
Reviewed-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Joshua Hahn <joshua.hahnjy@gmail.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
---
 mm/mempolicy.c | 64 ++++++++++++++++++++++++--------------------------
 1 file changed, 31 insertions(+), 33 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 293b4b347975..97b52d65b3ba 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -3419,6 +3419,13 @@ struct iw_node_attr {
 	int nid;
 };
 
+struct sysfs_wi_group {
+	struct kobject wi_kobj;
+	struct iw_node_attr *nattrs[];
+};
+
+static struct sysfs_wi_group *wi_group;
+
 static ssize_t node_show(struct kobject *kobj, struct kobj_attribute *attr,
 			 char *buf)
 {
@@ -3461,24 +3468,23 @@ static ssize_t node_store(struct kobject *kobj, struct kobj_attribute *attr,
 	return count;
 }
 
-static struct iw_node_attr **node_attrs;
-
-static void sysfs_wi_node_delete(struct iw_node_attr *node_attr,
-				 struct kobject *parent)
+static void sysfs_wi_node_delete(int nid)
 {
-	if (!node_attr)
+	if (!wi_group->nattrs[nid])
 		return;
-	sysfs_remove_file(parent, &node_attr->kobj_attr.attr);
-	kfree(node_attr->kobj_attr.attr.name);
-	kfree(node_attr);
+
+	sysfs_remove_file(&wi_group->wi_kobj,
+			  &wi_group->nattrs[nid]->kobj_attr.attr);
+	kfree(wi_group->nattrs[nid]->kobj_attr.attr.name);
+	kfree(wi_group->nattrs[nid]);
 }
 
-static void sysfs_wi_node_delete_all(struct kobject *wi_kobj)
+static void sysfs_wi_node_delete_all(void)
 {
 	int nid;
 
 	for (nid = 0; nid < nr_node_ids; nid++)
-		sysfs_wi_node_delete(node_attrs[nid], wi_kobj);
+		sysfs_wi_node_delete(nid);
 }
 
 static void iw_table_free(void)
@@ -3495,15 +3501,14 @@ static void iw_table_free(void)
 	kfree(old);
 }
 
-static void wi_cleanup(struct kobject *wi_kobj) {
-	sysfs_wi_node_delete_all(wi_kobj);
+static void wi_cleanup(void) {
+	sysfs_wi_node_delete_all();
 	iw_table_free();
-	kfree(node_attrs);
 }
 
 static void wi_kobj_release(struct kobject *wi_kobj)
 {
-	kfree(wi_kobj);
+	kfree(wi_group);
 }
 
 static const struct kobj_type wi_ktype = {
@@ -3511,7 +3516,7 @@ static const struct kobj_type wi_ktype = {
 	.release = wi_kobj_release,
 };
 
-static int add_weight_node(int nid, struct kobject *wi_kobj)
+static int sysfs_wi_node_add(int nid)
 {
 	struct iw_node_attr *node_attr;
 	char *name;
@@ -3533,40 +3538,33 @@ static int add_weight_node(int nid, struct kobject *wi_kobj)
 	node_attr->kobj_attr.store = node_store;
 	node_attr->nid = nid;
 
-	if (sysfs_create_file(wi_kobj, &node_attr->kobj_attr.attr)) {
+	if (sysfs_create_file(&wi_group->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;
+	wi_group->nattrs[nid] = node_attr;
 	return 0;
 }
 
-static int add_weighted_interleave_group(struct kobject *root_kobj)
+static int __init add_weighted_interleave_group(struct kobject *mempolicy_kobj)
 {
-	struct kobject *wi_kobj;
 	int nid, err;
 
-	node_attrs = kcalloc(nr_node_ids, sizeof(struct iw_node_attr *),
-			     GFP_KERNEL);
-	if (!node_attrs)
-		return -ENOMEM;
-
-	wi_kobj = kzalloc(sizeof(struct kobject), GFP_KERNEL);
-	if (!wi_kobj) {
-		kfree(node_attrs);
+	wi_group = kzalloc(struct_size(wi_group, nattrs, nr_node_ids),
+			   GFP_KERNEL);
+	if (!wi_group)
 		return -ENOMEM;
-	}
 
-	err = kobject_init_and_add(wi_kobj, &wi_ktype, root_kobj,
+	err = kobject_init_and_add(&wi_group->wi_kobj, &wi_ktype, mempolicy_kobj,
 				   "weighted_interleave");
 	if (err)
 		goto err_put_kobj;
 
 	for_each_node_state(nid, N_POSSIBLE) {
-		err = add_weight_node(nid, wi_kobj);
+		err = sysfs_wi_node_add(nid);
 		if (err) {
 			pr_err("failed to add sysfs [node%d]\n", nid);
 			goto err_cleanup_kobj;
@@ -3576,10 +3574,10 @@ static int add_weighted_interleave_group(struct kobject *root_kobj)
 	return 0;
 
 err_cleanup_kobj:
-	wi_cleanup(wi_kobj);
-	kobject_del(wi_kobj);
+	wi_cleanup();
+	kobject_del(&wi_group->wi_kobj);
 err_put_kobj:
-	kobject_put(wi_kobj);
+	kobject_put(&wi_group->wi_kobj);
 	return err;
 }
 
-- 
2.34.1

[PATCH v9 3/3] mm/mempolicy: Support memory hotplug in weighted interleave

[Rakie Kim]

The weighted interleave policy distributes page allocations across multiple
NUMA nodes based on their performance weight, thereby improving memory
bandwidth utilization. The weight values for each node are configured
through sysfs.

Previously, sysfs entries for configuring weighted interleave were created
for all possible nodes (N_POSSIBLE) at initialization, including nodes that
might not have memory. However, not all nodes in N_POSSIBLE are usable at
runtime, as some may remain memoryless or offline.
This led to sysfs entries being created for unusable nodes, causing
potential misconfiguration issues.

To address this issue, this patch modifies the sysfs creation logic to:
1) Limit sysfs entries to nodes that are online and have memory, avoiding
   the creation of sysfs entries for nodes that cannot be used.
2) Support memory hotplug by dynamically adding and removing sysfs entries
   based on whether a node transitions into or out of the N_MEMORY state.

Additionally, the patch ensures that sysfs attributes are properly managed
when nodes go offline, preventing stale or redundant entries from persisting
in the system.

By making these changes, the weighted interleave policy now manages its
sysfs entries more efficiently, ensuring that only relevant nodes are
considered for interleaving, and dynamically adapting to memory hotplug
events.

Co-developed-by: Honggyu Kim <honggyu.kim@sk.com>
Signed-off-by: Honggyu Kim <honggyu.kim@sk.com>
Co-developed-by: Yunjeong Mun <yunjeong.mun@sk.com>
Signed-off-by: Yunjeong Mun <yunjeong.mun@sk.com>
Signed-off-by: Rakie Kim <rakie.kim@sk.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Joshua Hahn <joshua.hahnjy@gmail.com>
Reviewed-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: David Hildenbrand <david@redhat.com>
---
 mm/mempolicy.c | 107 ++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 84 insertions(+), 23 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 97b52d65b3ba..74b4e2a6c786 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -113,6 +113,7 @@
 #include <asm/tlbflush.h>
 #include <asm/tlb.h>
 #include <linux/uaccess.h>
+#include <linux/memory.h>
 
 #include "internal.h"
 
@@ -3421,6 +3422,7 @@ struct iw_node_attr {
 
 struct sysfs_wi_group {
 	struct kobject wi_kobj;
+	struct mutex kobj_lock;
 	struct iw_node_attr *nattrs[];
 };
 
@@ -3470,13 +3472,24 @@ static ssize_t node_store(struct kobject *kobj, struct kobj_attribute *attr,
 
 static void sysfs_wi_node_delete(int nid)
 {
-	if (!wi_group->nattrs[nid])
+	struct iw_node_attr *attr;
+
+	if (nid < 0 || nid >= nr_node_ids)
+		return;
+
+	mutex_lock(&wi_group->kobj_lock);
+	attr = wi_group->nattrs[nid];
+	if (!attr) {
+		mutex_unlock(&wi_group->kobj_lock);
 		return;
+	}
+
+	wi_group->nattrs[nid] = NULL;
+	mutex_unlock(&wi_group->kobj_lock);
 
-	sysfs_remove_file(&wi_group->wi_kobj,
-			  &wi_group->nattrs[nid]->kobj_attr.attr);
-	kfree(wi_group->nattrs[nid]->kobj_attr.attr.name);
-	kfree(wi_group->nattrs[nid]);
+	sysfs_remove_file(&wi_group->wi_kobj, &attr->kobj_attr.attr);
+	kfree(attr->kobj_attr.attr.name);
+	kfree(attr);
 }
 
 static void sysfs_wi_node_delete_all(void)
@@ -3518,35 +3531,77 @@ static const struct kobj_type wi_ktype = {
 
 static int sysfs_wi_node_add(int nid)
 {
-	struct iw_node_attr *node_attr;
+	int ret = 0;
 	char *name;
+	struct iw_node_attr *new_attr;
 
-	node_attr = kzalloc(sizeof(*node_attr), GFP_KERNEL);
-	if (!node_attr)
+	if (nid < 0 || nid >= nr_node_ids) {
+		pr_err("invalid node id: %d\n", nid);
+		return -EINVAL;
+	}
+
+	new_attr = kzalloc(sizeof(*new_attr), GFP_KERNEL);
+	if (!new_attr)
 		return -ENOMEM;
 
 	name = kasprintf(GFP_KERNEL, "node%d", nid);
 	if (!name) {
-		kfree(node_attr);
+		kfree(new_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;
+	sysfs_attr_init(&new_attr->kobj_attr.attr);
+	new_attr->kobj_attr.attr.name = name;
+	new_attr->kobj_attr.attr.mode = 0644;
+	new_attr->kobj_attr.show = node_show;
+	new_attr->kobj_attr.store = node_store;
+	new_attr->nid = nid;
 
-	if (sysfs_create_file(&wi_group->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;
+	mutex_lock(&wi_group->kobj_lock);
+	if (wi_group->nattrs[nid]) {
+		mutex_unlock(&wi_group->kobj_lock);
+		pr_info("node%d already exists\n", nid);
+		goto out;
 	}
 
-	wi_group->nattrs[nid] = node_attr;
+	ret = sysfs_create_file(&wi_group->wi_kobj, &new_attr->kobj_attr.attr);
+	if (ret) {
+		mutex_unlock(&wi_group->kobj_lock);
+		goto out;
+	}
+	wi_group->nattrs[nid] = new_attr;
+	mutex_unlock(&wi_group->kobj_lock);
 	return 0;
+
+out:
+	kfree(new_attr->kobj_attr.attr.name);
+	kfree(new_attr);
+	return ret;
+}
+
+static int wi_node_notifier(struct notifier_block *nb,
+			       unsigned long action, void *data)
+{
+	int err;
+	struct memory_notify *arg = data;
+	int nid = arg->status_change_nid;
+
+	if (nid < 0)
+		return NOTIFY_OK;
+
+	switch (action) {
+	case MEM_ONLINE:
+		err = sysfs_wi_node_add(nid);
+		if (err)
+			pr_err("failed to add sysfs for node%d during hotplug: %d\n",
+			       nid, err);
+		break;
+	case MEM_OFFLINE:
+		sysfs_wi_node_delete(nid);
+		break;
+	}
+
+	return NOTIFY_OK;
 }
 
 static int __init add_weighted_interleave_group(struct kobject *mempolicy_kobj)
@@ -3557,20 +3612,26 @@ static int __init add_weighted_interleave_group(struct kobject *mempolicy_kobj)
 			   GFP_KERNEL);
 	if (!wi_group)
 		return -ENOMEM;
+	mutex_init(&wi_group->kobj_lock);
 
 	err = kobject_init_and_add(&wi_group->wi_kobj, &wi_ktype, mempolicy_kobj,
 				   "weighted_interleave");
 	if (err)
 		goto err_put_kobj;
 
-	for_each_node_state(nid, N_POSSIBLE) {
+	for_each_online_node(nid) {
+		if (!node_state(nid, N_MEMORY))
+			continue;
+
 		err = sysfs_wi_node_add(nid);
 		if (err) {
-			pr_err("failed to add sysfs [node%d]\n", nid);
+			pr_err("failed to add sysfs for node%d during init: %d\n",
+			       nid, err);
 			goto err_cleanup_kobj;
 		}
 	}
 
+	hotplug_memory_notifier(wi_node_notifier, DEFAULT_CALLBACK_PRI);
 	return 0;
 
 err_cleanup_kobj:
-- 
2.34.1

Re: [PATCH v9 0/3] Enhance sysfs handling for memory hotplug in weighted interleave

[Rakie Kim]

On Thu, 17 Apr 2025 16:28:34 +0900 Rakie Kim <rakie.kim@sk.com> wrote:
> These patches have been tested under CXL-based memory configurations,
> including hotplug scenarios, to ensure proper behavior and stability.
> 
>  mm/mempolicy.c | 240 ++++++++++++++++++++++++++++++-------------------
>  1 file changed, 148 insertions(+), 92 deletions(-)
> 
> base-commit: 8ffd015db85fea3e15a77027fda6c02ced4d2444
> -- 

To Andrew

I sincerely apologize for causing repeated inconvenience. The series of
patches version v8 that was merged into -mm, mm-new today needs
additional corrections.
Link: https://lore.kernel.org/all/6800742de6315_130fd2949c@dwillia2-mobl3.amr.corp.intel.com.notmuch/
Therefore, I have updated a new version v9, in which the problems have
been addressed.

I would greatly appreciate it if you could drop the existing v8 and
replace it with the new version v9. Below is the information regarding
the v8 patch series that needs to be dropped.
Once again, I truly apologize for the inconvenience.

<1>
The patch titled:
     Subject: mm/mempolicy: fix memory leaks in weighted interleave sysfs
Filename:
     mm-mempolicy-fix-memory-leaks-in-weighted-interleave-sysfs.patch

<2>
The patch titled:
     Subject: mm/mempolicy: prepare weighted interleave sysfs for memory hotplug
Filename:
     mm-mempolicy-prepare-weighted-interleave-sysfs-for-memory-hotplug.patch

<3>
The patch titled:
     Subject: mm/mempolicy: support memory hotplug in weighted interleave
Filename:
     mm-mempolicy-support-memory-hotplug-in-weighted-interleave.patch

Rakie

Re: [PATCH v9 0/3] Enhance sysfs handling for memory hotplug in weighted interleave

[Andrew Morton]

On Thu, 17 Apr 2025 17:10:08 +0900 Rakie Kim <rakie.kim@sk.com> wrote:

> I sincerely apologize for causing repeated inconvenience. The series of
> patches version v8 that was merged into -mm, mm-new today needs
> additional corrections.
> Link: https://lore.kernel.org/all/6800742de6315_130fd2949c@dwillia2-mobl3.amr.corp.intel.com.notmuch/
> Therefore, I have updated a new version v9, in which the problems have
> been addressed.

No probs, this is why mm.git workflow (mm-new -> mm-unstable ->
mm-stable -> mainline) operates as it does - to easily permit revisions
and replacements as patches move towards their final state.

Please note that I added a cc:stable to your [1/N] patch - sysfs leaks
should be fixed in earlier kernels.  I considered this to be low
priority - if it's higher priority than this patch should best have
been separated from the series, so it can take a different merge path
from the other patches.  

Re: [PATCH v9 0/3] Enhance sysfs handling for memory hotplug in weighted interleave

[Dan Williams]

Andrew Morton wrote:
> On Thu, 17 Apr 2025 17:10:08 +0900 Rakie Kim <rakie.kim@sk.com> wrote:
> 
> > I sincerely apologize for causing repeated inconvenience. The series of
> > patches version v8 that was merged into -mm, mm-new today needs
> > additional corrections.
> > Link: https://lore.kernel.org/all/6800742de6315_130fd2949c@dwillia2-mobl3.amr.corp.intel.com.notmuch/
> > Therefore, I have updated a new version v9, in which the problems have
> > been addressed.
> 
> No probs, this is why mm.git workflow (mm-new -> mm-unstable ->
> mm-stable -> mainline) operates as it does - to easily permit revisions
> and replacements as patches move towards their final state.
> 
> Please note that I added a cc:stable to your [1/N] patch - sysfs leaks
> should be fixed in earlier kernels.  I considered this to be low
> priority - if it's higher priority than this patch should best have
> been separated from the series, so it can take a different merge path
> from the other patches.  

The risk of leak is low because it only appears to trigger if setup
fails. Setup only fails due to -ENOMEM which is unlikely to happen from
a late_initcall() when memory pressure is low.

Re: [PATCH v9 0/3] Enhance sysfs handling for memory hotplug in weighted interleave

[Dan Williams]

Andrew Morton wrote:
> On Thu, 17 Apr 2025 17:10:08 +0900 Rakie Kim <rakie.kim@sk.com> wrote:
> 
> > I sincerely apologize for causing repeated inconvenience. The series of
> > patches version v8 that was merged into -mm, mm-new today needs
> > additional corrections.
> > Link: https://lore.kernel.org/all/6800742de6315_130fd2949c@dwillia2-mobl3.amr.corp.intel.com.notmuch/
> > Therefore, I have updated a new version v9, in which the problems have
> > been addressed.
> 
> No probs, this is why mm.git workflow (mm-new -> mm-unstable ->
> mm-stable -> mainline) operates as it does - to easily permit revisions
> and replacements as patches move towards their final state.

Perhaps something like the update below to the mm-commits@ notification
template, because I think folks misread early acceptance into mm-new as
"Hooray, I'm done!" instead of "Ok, now more review might be inbound
because Andrew has put this patch on his radar, but I am not done until
this hits mm-stable".

---
--- template.orig	2025-04-17 15:48:49.913337459 -0700
+++ template	2025-04-17 15:51:57.294617179 -0700
@@ -1,10 +1,16 @@
 The patch titled
      Subject: $subject
 has been added to the -mm mm-new branch.  Its filename is
      $patch_name
 
 This patch will shortly appear at
      https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/$patch_name
 
 This patch will later appear in the mm-new branch at
     git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
+
+Note, mm-new is a provisional staging ground for work-in-progress
+patches, and acceptance into mm-new is a notification for others take
+notice and finish up reviews. Please do not hesitate to respond to
+review feedback and post updated versions to replace or incrementally
+fixup patches in mm-new.
---

...otherwise, documentation like that would be good fodder for a mm
"maintainer profile" [1].

[1]: https://docs.kernel.org/process/maintainer-handbooks.html

Re: [PATCH v9 0/3] Enhance sysfs handling for memory hotplug in weighted interleave

[Andrew Morton]

On Thu, 17 Apr 2025 15:41:30 -0700 Dan Williams <dan.j.williams@intel.com> wrote:

> Andrew Morton wrote:
> > On Thu, 17 Apr 2025 17:10:08 +0900 Rakie Kim <rakie.kim@sk.com> wrote:
> > 
> > > I sincerely apologize for causing repeated inconvenience. The series of
> > > patches version v8 that was merged into -mm, mm-new today needs
> > > additional corrections.
> > > Link: https://lore.kernel.org/all/6800742de6315_130fd2949c@dwillia2-mobl3.amr.corp.intel.com.notmuch/
> > > Therefore, I have updated a new version v9, in which the problems have
> > > been addressed.
> > 
> > No probs, this is why mm.git workflow (mm-new -> mm-unstable ->
> > mm-stable -> mainline) operates as it does - to easily permit revisions
> > and replacements as patches move towards their final state.
> > 
> > Please note that I added a cc:stable to your [1/N] patch - sysfs leaks
> > should be fixed in earlier kernels.  I considered this to be low
> > priority - if it's higher priority than this patch should best have
> > been separated from the series, so it can take a different merge path
> > from the other patches.  
> 
> The risk of leak is low because it only appears to trigger if setup
> fails. Setup only fails due to -ENOMEM which is unlikely to happen from
> a late_initcall() when memory pressure is low.

Oh, OK, thanks.  I added the above paragraph to the changelog and
removed the cc:stable.

Generally, we assume that -ENOMEM doesn't happen in __init code.  If it
does, the kernel is totally messed up anyway)