From: Rakie Kim <[email protected]>
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 <[email protected]>
Signed-off-by: Rakie Kim <[email protected]>
Signed-off-by: Honggyu Kim <[email protected]>
Co-developed-by: Gregory Price <[email protected]>
Signed-off-by: Gregory Price <[email protected]>
Co-developed-by: Hyeongtak Ji <[email protected]>
Signed-off-by: Hyeongtak Ji <[email protected]>
---
.../ABI/testing/sysfs-kernel-mm-mempolicy | 4 +
...fs-kernel-mm-mempolicy-weighted-interleave | 26 ++
mm/mempolicy.c | 231 ++++++++++++++++++
3 files changed, 261 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 <[email protected]>
+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..e6a38139bf0f
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-kernel-mm-mempolicy-weighted-interleave
@@ -0,0 +1,26 @@
+What: /sys/kernel/mm/mempolicy/weighted_interleave/
+Date: December 2023
+Contact: Linux memory management mailing list <[email protected]>
+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 <[email protected]>
+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.
+
+ 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..ae925216798f 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -131,6 +131,16 @@ 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. Until system-defaults are 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 +3077,224 @@ 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, this should be updated to
+ * collect the system-default weight of the node if the user passes 0.
+ */
+ if (!weight)
+ weight = 1;
+
+ /* We only need to allocate up to the number of possible nodes */
+ 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[MAX_NUMNODES];
+
+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 < MAX_NUMNODES; 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;
+ }
+
+ memset(node_attrs, 0, sizeof(node_attrs));
+ 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();
+ /* Never free the default table, it's always in use */
+ kfree(old);
+ kfree(kobj);
+}
+
+static const struct kobj_type mempolicy_ktype = {
+ .release = mempolicy_kobj_release
+};
+
+static struct kobject *mempolicy_kobj;
+static int __init mempolicy_sysfs_init(void)
+{
+ int err;
+ struct kobject *mempolicy_kobj;
+
+ /* A NULL iw_table is interpreted by interleave logic as "all 1s" */
+ iw_table = NULL;
+ mempolicy_kobj = kzalloc(sizeof(*mempolicy_kobj), GFP_KERNEL);
+ if (!mempolicy_kobj) {
+ pr_err("failed to add mempolicy kobject to the system\n");
+ return -ENOMEM;
+ }
+ err = kobject_init_and_add(mempolicy_kobj, &mempolicy_ktype, mm_kobj,
+ "mempolicy");
+ if (err) {
+ kfree(mempolicy_kobj);
+ return err;
+ }
+
+ err = add_weighted_interleave_group(mempolicy_kobj);
+
+ if (err) {
+ kobject_put(mempolicy_kobj);
+ return err;
+ }
+
+ return err;
+}
+
+static void __exit mempolicy_exit(void)
+{
+ if (mempolicy_kobj)
+ kobject_put(mempolicy_kobj);
+}
+
+#else
+static int __init mempolicy_sysfs_init(void)
+{
+ /* A NULL iw_table is interpreted by interleave logic as "all 1s" */
+ iw_table = NULL;
+ return 0;
+}
+
+static void __exit mempolicy_exit(void) { }
+#endif /* CONFIG_SYSFS */
+late_initcall(mempolicy_sysfs_init);
+module_exit(mempolicy_exit);
--
2.39.1
Gregory Price <[email protected]> writes:
> From: Rakie Kim <[email protected]>
>
> 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 <[email protected]>
> Signed-off-by: Rakie Kim <[email protected]>
> Signed-off-by: Honggyu Kim <[email protected]>
> Co-developed-by: Gregory Price <[email protected]>
> Signed-off-by: Gregory Price <[email protected]>
> Co-developed-by: Hyeongtak Ji <[email protected]>
> Signed-off-by: Hyeongtak Ji <[email protected]>
> ---
> .../ABI/testing/sysfs-kernel-mm-mempolicy | 4 +
> ...fs-kernel-mm-mempolicy-weighted-interleave | 26 ++
> mm/mempolicy.c | 231 ++++++++++++++++++
> 3 files changed, 261 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 <[email protected]>
> +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..e6a38139bf0f
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-kernel-mm-mempolicy-weighted-interleave
> @@ -0,0 +1,26 @@
> +What: /sys/kernel/mm/mempolicy/weighted_interleave/
> +Date: December 2023
May be not a big deal. The date should be "January 2024"?
> +Contact: Linux memory management mailing list <[email protected]>
> +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 <[email protected]>
> +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
s/processes/tasks or memory areas/
> + MPOL_WEIGHTED_INTERLEAVE and have opted into global weights by
> + omitting a task-local weight array.
Now, we haven't introduced task-local weight array. So, leave this
until we introduce that?
> +
> + 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..ae925216798f 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -131,6 +131,16 @@ 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. Until system-defaults are 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 +3077,224 @@ 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, this should be updated to
> + * collect the system-default weight of the node if the user passes 0.
> + */
> + if (!weight)
> + weight = 1;
From functionality point of view, it's OK to set "weight = 1" here now.
But when we add system default weight table in the future, we need to
use "weight = 0". Otherwise, we cannot distinguish whether the default
value have been customized via sysfs. So, I suggest to use that rule.
> +
> + /* We only need to allocate up to the number of possible nodes */
This comment appears not necessary.
> + 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);
With similar reason as above ("From functionality..."), I suggest to set
"0" here.
> + 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[MAX_NUMNODES];
node_attrs[] can be allocated dynamically too. Just a suggestion.
> +
> +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 < MAX_NUMNODES; i++)
Nitpick, nr_node_ids should be OK here.
> + 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;
> + }
> +
> + memset(node_attrs, 0, sizeof(node_attrs));
> + 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();
> + /* Never free the default table, it's always in use */
Obsolete comment?
> + kfree(old);
It appears unnecessary to free iw_table in error path. But this isn't a
big deal because error path will almost never be executed in practice.
> + kfree(kobj);
> +}
> +
> +static const struct kobj_type mempolicy_ktype = {
> + .release = mempolicy_kobj_release
> +};
> +
> +static struct kobject *mempolicy_kobj;
> +static int __init mempolicy_sysfs_init(void)
> +{
> + int err;
> + struct kobject *mempolicy_kobj;
This overrides the global "mempolicy_kobj" defined before function. But
I don't think we need the global definition.
> +
> + /* A NULL iw_table is interpreted by interleave logic as "all 1s" */
As I suggested above, it will be "all 0s", that is, use default weight.
> + iw_table = NULL;
The default value is NULL already, it appears unnecessary to do this.
> + mempolicy_kobj = kzalloc(sizeof(*mempolicy_kobj), GFP_KERNEL);
> + if (!mempolicy_kobj) {
> + pr_err("failed to add mempolicy kobject to the system\n");
> + return -ENOMEM;
> + }
> + err = kobject_init_and_add(mempolicy_kobj, &mempolicy_ktype, mm_kobj,
> + "mempolicy");
> + if (err) {
> + kfree(mempolicy_kobj);
> + return err;
> + }
> +
> + err = add_weighted_interleave_group(mempolicy_kobj);
> +
> + if (err) {
> + kobject_put(mempolicy_kobj);
> + return err;
> + }
> +
> + return err;
> +}
> +
> +static void __exit mempolicy_exit(void)
> +{
> + if (mempolicy_kobj)
> + kobject_put(mempolicy_kobj);
> +}
> +
> +#else
> +static int __init mempolicy_sysfs_init(void)
> +{
> + /* A NULL iw_table is interpreted by interleave logic as "all 1s" */
> + iw_table = NULL;
> + return 0;
> +}
> +
> +static void __exit mempolicy_exit(void) { }
> +#endif /* CONFIG_SYSFS */
> +late_initcall(mempolicy_sysfs_init);
> +module_exit(mempolicy_exit);
mempolicy.c will not be compiled as module, so we don't need
module_exit().
--
Best Regards,
Huang, Ying
On Mon, Jan 22, 2024 at 04:03:53PM +0800, Huang, Ying wrote:
> Gregory Price <[email protected]> writes:
>
> > + /*
> > + * The default weight is 1 (for now), when the kernel-internal
> > + * default weight array is implemented, this should be updated to
> > + * collect the system-default weight of the node if the user passes 0.
> > + */
> > + if (!weight)
> > + weight = 1;
>
> From functionality point of view, it's OK to set "weight = 1" here now.
> But when we add system default weight table in the future, we need to
> use "weight = 0". Otherwise, we cannot distinguish whether the default
> value have been customized via sysfs. So, I suggest to use that rule.
>
[... snip ...]
> > + else
> > + memset(new, 1, nr_node_ids);
>
> With similar reason as above ("From functionality..."), I suggest to set
> "0" here.
>
blah - the comment is misleading at best. The future patch should pass
0 through to the sysfs table and the allocators updated to collect the
system-default weight of the node.
re: doing it this way right now -
I chose to do it this way for now because it ultimately simplifies the
logic in the allocators - all of which will need to be updated with the
future patch set regardless of our implementation choice now.
e.g.
rcu_read_lock();
table = rcu_dereference(iw_table);
if (!policy->wil.cur_weight)
policy->wil.cur_weight = table ? table[next] : 1;
^^^ only need single conditional now
rcu_read_unlock();
This logic will need to be updated to use default table values, so I
chose the simpler implementation and left the change to be explicit
at the time the default table is implemented.
If you prefer it the other way now, I can change it, but this seemed
cleaner and simpler for the time being.
> > + 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[MAX_NUMNODES];
>
> node_attrs[] can be allocated dynamically too. Just a suggestion.
>
ack to this and other references to nr_node_ids, will change.
> > + kfree(old);
>
> It appears unnecessary to free iw_table in error path. But this isn't a
> big deal because error path will almost never be executed in practice.
>
checkpatch.pl yells at you if you do null checks before kfree :]
> > + int err;
> > + struct kobject *mempolicy_kobj;
>
> This overrides the global "mempolicy_kobj" defined before function. But
> I don't think we need the global definition.
>
Assuming the exit path isn't needed then yeah the global isn't needed.
> > +static int __init mempolicy_sysfs_init(void)
> > +{
> > + /* A NULL iw_table is interpreted by interleave logic as "all 1s" */
> > + iw_table = NULL;
> > + return 0;
> > +}
> > +
> > +static void __exit mempolicy_exit(void) { }
> > +#endif /* CONFIG_SYSFS */
> > +late_initcall(mempolicy_sysfs_init);
> > +module_exit(mempolicy_exit);
>
> mempolicy.c will not be compiled as module, so we don't need
> module_exit().
>
ack