Re: [PATCH v2 2/9] mm/vmstat: show start_pfn when zone spans pages

[David Hildenbrand]

On 29.09.22 00:32, Doug Berger wrote:
> A zone that overlaps with another zone may span a range of pages
> that are not present. In this case, displaying the start_pfn of
> the zone allows the zone page range to be identified.

I don't understand the intention here.

"/* If unpopulated, no other information is useful */"

Why would the start pfn be of any use here?

What is the user visible impact without that change?

> Signed-off-by: Doug Berger <opendmb@xxxxxxxxx>
> ---
>   mm/vmstat.c | 5 +++++
>   1 file changed, 5 insertions(+)
>
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 90af9a8572f5..e2f19f2b7615 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1717,6 +1717,11 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
>   
>   	/* If unpopulated, no other information is useful */
>   	if (!populated_zone(zone)) {
> +		/* Show start_pfn for empty overlapped zones */
> +		if (zone->spanned_pages)
> +			seq_printf(m,
> +				   "\n  start_pfn:           %lu",
> +				   zone->zone_start_pfn);
>   		seq_putc(m, '\n');
>   		return;
>   	}
--
Thanks,

David / dhildenb