linux-kernel - Re: [PATCH v2 2/9] mm/vmstat: show start

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Message-ID: <8e61d0f4-0c40-6c2d-da60-fa97e2ee7530@redhat.com>
Date:   Thu, 29 Sep 2022 10:15:12 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Doug Berger <opendmb@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Jonathan Corbet <corbet@....net>, Mike Rapoport <rppt@...nel.org>,
        Borislav Petkov <bp@...e.de>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        Muchun Song <songmuchun@...edance.com>,
        KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
        Mel Gorman <mgorman@...e.de>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH v2 2/9] mm/vmstat: show start_pfn when zone spans pages

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@...il.com>
> ---
>   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