Re: [PATCH v4 1/3] mm: add thp_utilization metrics to debugfs

["Huang, Ying" <ying.huang@intel.com>]

<alexlzhu@fb.com> writes:

[snip]

> +static void thp_util_scan(unsigned long pfn_end)
> +{
> +	struct page *page = NULL;
> +	int bucket, current_pfn, num_utilized_pages;
> +	int i;
> +	/*
> +	 * Scan through each memory zone in chunks of THP_UTIL_SCAN_SIZE
> +	 * PFNs every second looking for anonymous THPs.
> +	 */
> +	for (i = 0; i < THP_UTIL_SCAN_SIZE; i++) {
> +		current_pfn = thp_scan.pfn;
> +		thp_scan.pfn += HPAGE_PMD_NR;
> +		if (current_pfn >= pfn_end)
> +			return;
> +
> +		page = pfn_to_online_page(current_pfn);
> +		if (!page)
> +			continue;

If my understanding were correct, the page may be offlined during
pfn_to_online_page() and the following code.  So we need to call
get/put_online_mems().

If my understanding were incorrect, can anyone teach me on this?

> +
> +		num_utilized_pages = thp_number_utilized_pages(page_folio(page));
> +		bucket = thp_utilization_bucket(num_utilized_pages);
> +		if (bucket < 0)
> +			continue;
> +
> +		thp_scan.buckets[bucket].nr_thps++;
> +		thp_scan.buckets[bucket].nr_zero_pages += (HPAGE_PMD_NR - num_utilized_pages);
> +	}
> +}
> +

Best Regards,
Huang, Ying