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

SeongJae Park
2026-04-29T01:28:11Z

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