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

[Andrew Morton]

On Tue, 28 Apr 2026 15:11:11 +0800 Zhen Ni <zhen.ni@xxxxxxxxxxxx> 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
> 
> ...
>
> +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';

strncpy_from_user() was not useful here?

> +	/* 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;
> +	}
> +
> +	owner_filter.nid_mask = mask;
> +	ret = count;
> +
> +out_free:
> +	kfree(kbuf);
> +	return ret;
> +}