linux-kernel - Re: [PATCH] mm/page_alloc: fix counting of managed

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Date:   Fri, 28 May 2021 07:47:50 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Liu Shixin <liushixin2@...wei.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        yangerkun <yangerkun@...wei.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/page_alloc: fix counting of managed_pages

On 05/27/21 at 08:57pm, 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.

Right, this is a good catch. Thanks for the fixing. 

Is it worth adding words in Documentation/admin-guide/sysctl/vm.rst
to notice this?

Reviewed-by: Baoquan He <bhe@...hat.com>

Thanks
Baoquan

> 
> Fixes: f63661566fad ("mm/page_alloc.c: clear out zone->lowmem_reserve[] if the zone is empty")
> Reported-by: yangerkun <yangerkun@...wei.com>
> Signed-off-by: Liu Shixin <liushixin2@...wei.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;
> -				}
>  			}
>  		}
>  	}
> -- 
> 2.18.0.huawei.25
> 
>