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

[zhen.ni]

在 2026/4/28 22:16, Andrew Morton 写道:
> 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?

After checking similar usage in mm/ (e.g., mm/kmemleak.c),
I'll switch to strncpy_from_user().

The change is straightforward:

    long len;

    len = strncpy_from_user(kbuf, buf, count + 1);
    if (len < 0) {
        ret = -EFAULT;
        goto out_free;
    }
    kbuf[count] = '\0';

I'll make this change in the next version.
> > +	/* 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;
> > +}
Best regards,
Zhen Ni