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Subject: Re: [PATCH] Revert "mm/vmstat.c: do not show lowmem reserve
 protection information of empty zone"
To:     Baoquan He <bhe@redhat.com>, linux-kernel@vger.kernel.org
Cc:     linux-mm@kvack.org, akpm@linux-foundation.org,
        sonnyrao@chromium.org, yuzhao@google.com, rientjes@google.com
References: <20200811075412.12872-1-bhe@redhat.com>
From:   David Hildenbrand <david@redhat.com>
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Organization: Red Hat GmbH
Message-ID: <22a7882b-cc18-0c6d-1ab5-7e0ea6a53469@redhat.com>
Date:   Tue, 11 Aug 2020 10:34:17 +0200
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On 11.08.20 09:54, Baoquan He wrote:
> This reverts commit 26e7deadaae1755faf1f6d1a68988c4b8348df59.
> 
> Sonny reported that one of their tests started failing on the latest
> kernel on their Chrome OS platform. The root cause is that the above
> commit removed the protection line of empty zone, while the parser used
> in the test relies on the protection line to mark the end of each zone.
> 
> Let's revert it to avoid breaking userspace testing or applications.
> 
> Cc: <stable@vger.kernel.org> # 5.8.x
> Reported-by: Sonny Rao <sonnyrao@chromium.org>
> Signed-off-by: Baoquan He <bhe@redhat.com>
> ---
>  mm/vmstat.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 5b35c0eb8c57..62376dc66ec0 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1644,12 +1644,6 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
>  		   zone->present_pages,
>  		   zone_managed_pages(zone));
>  
> -	/* If unpopulated, no other information is useful */
> -	if (!populated_zone(zone)) {
> -		seq_putc(m, '\n');
> -		return;
> -	}
> -
>  	seq_printf(m,
>  		   "\n        protection: (%ld",
>  		   zone->lowmem_reserve[0]);
> @@ -1657,6 +1651,12 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
>  		seq_printf(m, ", %ld", zone->lowmem_reserve[i]);
>  	seq_putc(m, ')');
>  
> +	/* If unpopulated, no other information is useful */
> +	if (!populated_zone(zone)) {
> +		seq_putc(m, '\n');
> +		return;
> +	}
> +
>  	for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
>  		seq_printf(m, "\n      %-12s %lu", zone_stat_name(i),
>  			   zone_page_state(zone, i));
> 

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb