Re: [PATCH v3 3/4] mm/page_owner: add NUMA node filter with nodelist support

[SeongJae Park <sj@kernel.org>]

On Tue, 28 Apr 2026 15:11:11 +0800 Zhen Ni <zhen.ni@easystack.cn> wrote:

> Add NUMA node filtering functionality to page_owner to allow
> filtering pages by specific NUMA node(s) using nodelist format.
> 
> The filter allows users to focus on pages from specific NUMA nodes,
> which is useful for NUMA-aware memory allocation analysis and debugging.
> 
> Supported input formats:
> - Single node: echo "2" > nid
> - Multiple nodes: echo "0,2,3" > nid
> - Node range: echo "0-3" > nid
> - Mixed format: echo "0,2-4,7" > nid
> - Disable filter: echo "-1" > nid
> 
> Link: https://lore.kernel.org/linux-mm/20260417154638.22370-4-zhen.ni@easystack.cn/
> Link: https://lore.kernel.org/linux-mm/20260419155540.376847-4-zhen.ni@easystack.cn/

Seems the above two links are for v1 and v2 of this patch.  I think putting
those with the context at commentary area [1] could be useful.

> Suggested-by: Zi Yan <ziy@nvidia.com>
> Signed-off-by: Zhen Ni <zhen.ni@easystack.cn>
> ---
[...]
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index 6d87b6948cfa..e674a374669a 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -685,6 +685,7 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos)
>  	struct page_ext *page_ext;
>  	struct page_owner *page_owner;
>  	depot_stack_handle_t handle;
> +	nodemask_t mask;
>  
>  	if (!static_branch_unlikely(&page_owner_inited))
>  		return -EINVAL;
> @@ -698,6 +699,8 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos)
>  	while (!pfn_valid(pfn) && (pfn & (MAX_ORDER_NR_PAGES - 1)) != 0)
>  		pfn++;
>  
> +	mask = owner_filter.nid_mask;
> +

READ_ONCE() was used for owner_filter.print_mode.  Should nid_mask also read
using READ_ONCE()?

>  	/* Find an allocated page */
>  	for (; pfn < max_pfn; pfn++) {
>  		/*
> @@ -730,6 +733,14 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos)
>  		if (unlikely(!page_ext))
>  			continue;
>  
> +		/* NUMA node filter using bitmask */
> +		if (!nodes_empty(mask)) {
> +			int nid = page_to_nid(page);
> +
> +			if (!node_isset(nid, mask))
> +				goto ext_put_continue;
> +		}
> +
>  		/*
>  		 * Some pages could be missed by concurrent allocation or free,
>  		 * because we don't hold the zone lock.
> @@ -1009,6 +1020,75 @@ DEFINE_SIMPLE_ATTRIBUTE(page_owner_print_mode_fops,
>  			&page_owner_print_mode_get,
>  			&page_owner_print_mode_set, "%lld");
>  
> +static ssize_t nid_filter_write(struct file *file,
> +				 const char __user *buf,
> +				 size_t count, loff_t *ppos)
> +{
> +	char *kbuf;
> +	nodemask_t mask;
> +	int ret;
> +	int val;
> +
> +	/*
> +	 * Limit input size to handle worst-case nodelist (all nodes).
> +	 * Worst case per node: ",NNNNN" (comma + 5-digit node number) = 6 bytes.
> +	 * Formula: 100 bytes overhead + 6 * MAX_NUMNODES
> +	 */
> +	if (count > (100 + 6 * MAX_NUMNODES))
> +		return -EINVAL;
> +
> +	kbuf = kmalloc(count + 1, GFP_KERNEL);
> +	if (!kbuf)
> +		return -ENOMEM;
> +
> +	if (copy_from_user(kbuf, buf, count)) {
> +		ret = -EFAULT;
> +		goto out_free;
> +	}
> +	kbuf[count] = '\0';
> +
> +	/* Support: "-1" to clear, or nodelist format like "0", "0,2", "0-3" */
> +	if (kstrtoint(kbuf, 10, &val) == 0 && val == -1)
> +		nodes_clear(mask);
> +	else if (nodelist_parse(kbuf, mask)) {
> +		ret = -EINVAL;
> +		goto out_free;
> +	}

Doesn't empty string input to nodelist_parse() clears the mask?  Can't it be
reused?

> +
> +	owner_filter.nid_mask = mask;
> +	ret = count;
> +
> +out_free:
> +	kfree(kbuf);
> +	return ret;
> +}
> +
> +static int nid_filter_show(struct seq_file *m, void *v)
> +{
> +	nodemask_t mask = owner_filter.nid_mask;
> +
> +	if (nodes_empty(mask))
> +		seq_puts(m, "-1\n");
> +	else
> +		seq_printf(m, "%*pbl\n", nodemask_pr_args(&mask));
> +
> +	return 0;
> +}
> +
> +static int nid_filter_open(struct inode *inode, struct file *file)
> +{
> +	return single_open(file, nid_filter_show, NULL);
> +}
> +
> +static const struct file_operations nid_filter_fops = {
> +	.owner		= THIS_MODULE,
> +	.open		= nid_filter_open,
> +	.read		= seq_read,
> +	.llseek		= seq_lseek,
> +	.write		= nid_filter_write,
> +	.release	= single_release,
> +};
> +
>  
>  static int __init pageowner_init(void)
>  {
> @@ -1024,6 +1104,8 @@ static int __init pageowner_init(void)
>  	filter_dir = debugfs_create_dir("page_owner_filter", NULL);
>  	debugfs_create_file("print_mode", 0600, filter_dir, NULL,
>  			    &page_owner_print_mode_fops);
> +	debugfs_create_file("nid", 0600, filter_dir, NULL,
> +			    &nid_filter_fops);

Why don't you use 'page_owner_' prefix like other fops, for consistency?

>  
>  	dir = debugfs_create_dir("page_owner_stacks", NULL);
>  	debugfs_create_file("show_stacks", 0400, dir,
> -- 
> 2.20.1

[1] https://docs.kernel.org/process/submitting-patches.html#commentary


Thanks,
SJ