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

["Huang, Ying" <ying.huang@intel.com>]

Gregory Price <gourry.memverge@gmail.com> writes:

> 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 <honggyu.kim@sk.com>
> Co-developed-by: Gregory Price <gregory.price@memverge.com>
> Signed-off-by: Gregory Price <gregory.price@memverge.com>
> Co-developed-by: Hyeongtak Ji <hyeongtak.ji@sk.com>
> Signed-off-by: Hyeongtak Ji <hyeongtak.ji@sk.com>
> ---
>  .../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.

I still think that it's a good idea to provide some better default
weight value with HMAT or CDAT if available.  So, better not to make "1"
as part of ABI?

> +
> +		Minimum weight: 1

Can weight be "0"?  Do we need a way to specify that a node don't want
to participate weighted interleave?

> +		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];
> +

It's kind of obscure whether "char" is "signed" or "unsigned".  Given
the max weight is 255 above, it's better to use "u8"?

And, we may need a way to specify whether the weight has been overridden
by the user.  A special value (such as 255) can be used for that.  If
so, the maximum weight should be 254 instead of 255.  As a user space
interface, is it better to use 100 as the maximum value?

>  /**
>   * 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;

kstrtou8(), "unsigned char weight", "char iw_table[]" isn't completely
consistent.  It's better to make them consistent?

> +	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_mempolicy_release(struct kobject *mempolicy_kobj)
> +{
> +	int i;
> +
> +	for (i = 0; i < MAX_NUMNODES; i++)
> +		sysfs_wi_node_release(node_attrs[i], mempolicy_kobj);

IIUC, if this is called in error path (such as, in
add_weighted_interleave_group()), some node_attrs[] element may be
"NULL"?

> +	kobject_put(mempolicy_kobj);
> +}
> +
> +static const struct kobj_type mempolicy_ktype = {
> +	.sysfs_ops = &kobj_sysfs_ops,
> +	.release = sysfs_mempolicy_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, &mempolicy_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 int __init mempolicy_sysfs_init(void)
> +{
> +	int err;
> +	struct kobject *root_kobj;
> +
> +	memset(&iw_table, 1, sizeof(iw_table));
> +
> +	root_kobj = kobject_create_and_add("mempolicy", mm_kobj);
> +	if (!root_kobj) {
> +		pr_err("failed to add mempolicy kobject to the system\n");
> +		return -ENOMEM;
> +	}
> +
> +	err = add_weighted_interleave_group(root_kobj);
> +
> +	if (err)
> +		kobject_put(root_kobj);
> +	return err;
> +
> +}
> +#else
> +static int __init mempolicy_sysfs_init(void)
> +{
> +	/*
> +	 * if sysfs is not enabled MPOL_WEIGHTED_INTERLEAVE defaults to
> +	 * MPOL_INTERLEAVE behavior, but is still defined separately to
> +	 * allow task-local weighted interleave to operate as intended.
> +	 */
> +	memset(&iw_table, 1, sizeof(iw_table));
> +	return 0;
> +}
> +#endif /* CONFIG_SYSFS */
> +late_initcall(mempolicy_sysfs_init);

--
Best Regards,
Huang, Ying