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Subject: Re: [PATCH] mm/page_alloc: fix counting of managed_pages
To:     Liu Shixin <liushixin2@huawei.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        yangerkun <yangerkun@huawei.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org
References: <20210527125707.3760259-1-liushixin2@huawei.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
Message-ID: <24751c12-b43e-7860-015b-09d204e6e397@redhat.com>
Date:   Wed, 9 Jun 2021 12:29:45 +0200
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On 27.05.21 14:57, Liu Shixin wrote:
> The commit f63661566fad (mm/page_alloc.c: clear out zone->lowmem_reserve[]
> if the zone is empty) clear out zone->lowmem_reserve[] if zone is empty.
> But when zone is not empty and sysctl_lowmem_reserve_ratio[i] is set to zero,
> zone_managed_pages(zone) is not counted in the managed_pages either. This is
> inconsistent with the description of lowmen_reserve, so fix it.
> 
> Fixes: f63661566fad ("mm/page_alloc.c: clear out zone->lowmem_reserve[] if the zone is empty")
> Reported-by: yangerkun <yangerkun@huawei.com>
> Signed-off-by: Liu Shixin <liushixin2@huawei.com>
> ---
>   mm/page_alloc.c | 12 ++++++------
>   1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index aaa1655cf682..49a2efce5a84 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -8061,14 +8061,14 @@ static void setup_per_zone_lowmem_reserve(void)
>   			unsigned long managed_pages = 0;
>   
>   			for (j = i + 1; j < MAX_NR_ZONES; j++) {
> -				if (clear) {
> -					zone->lowmem_reserve[j] = 0;
> -				} else {
> -					struct zone *upper_zone = &pgdat->node_zones[j];
> +				struct zone *upper_zone = &pgdat->node_zones[j];
> +
> +				managed_pages += zone_managed_pages(upper_zone);
>   
> -					managed_pages += zone_managed_pages(upper_zone);
> +				if (clear)
> +					zone->lowmem_reserve[j] = 0;
> +				else
>   					zone->lowmem_reserve[j] = managed_pages / ratio;
> -				}
>   			}
>   		}
>   	}
> 

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

-- 
Thanks,

David / dhildenb