Re: [PATCH v5 2/3] mm/page_owner: add NUMA node filter with nodelist support

[SeongJae Park <sj@kernel.org>]

On Thu,  7 May 2026 14:46:42 +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). This is useful for NUMA-aware memory
> allocation analysis and debugging.
> 
> The filter supports flexible nodelist input formats:
> - Single node: echo "0" > nid
> - Multiple nodes: echo "0,2,3" > nid
> - Node range: echo "0-3" > nid
> - Mixed format: echo "0,2-4,7" > nid
> - Clear filter: echo > nid (empty string)
> 
> The implementation uses nodemask_t for efficient multi-node filtering
> and nodelist_parse() for flexible input parsing. Empty input clears
> the filter.
> 
> Note: Access to nid_mask uses plain load/store without locking because
> nodemask_t is too large (128 bytes) for READ_ONCE/WRITE_ONCE. This is
> safe for debug use: low-frequency changes and torn reads would only
> cause temporary inconsistency in debug output.
> 
> Signed-off-by: Zhen Ni <zhen.ni@easystack.cn>
> ---
> 
> Changes in v5:
> - Optimize nodes_empty() check in page iteration loop
> - Add __data_racy qualifier to nid_mask field

Adding links to previous revisions [1] would be helpful.

> ---
>  mm/page_owner.c | 86 +++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 86 insertions(+)
> 
> diff --git a/mm/page_owner.c b/mm/page_owner.c
[...]
> @@ -700,6 +707,9 @@ 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;
> +	bool filter_by_nid = !nodes_empty(mask);
> +

Shouldn't we separate variable declarations and statements inside a same block?

[...]
> +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;
> +
> +	/*
> +	 * 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

What is the 100 bytes overhead?

> +	 */
> +	if (count > (100 + 6 * MAX_NUMNODES))
> +		return -EINVAL;
> +
> +	kbuf = kmalloc(count + 1, GFP_KERNEL);
> +	if (!kbuf)
> +		return -ENOMEM;

Would it make sense to use kmalloc_objs()?

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


Thanks,
SJ

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