linux-kernel - Re: [PATCH] mm: correct the comment when reclaimed pages exceed the scanned pages

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Date:   Thu, 8 Jun 2017 15:46:58 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     zhongjiang <zhongjiang@...wei.com>
Cc:     akpm@...ux-foundation.org, vinayakm.list@...il.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: correct the comment when reclaimed pages exceed the
 scanned pages

On Wed, Jun 07, 2017 at 04:31:06PM +0800, zhongjiang wrote:
> The commit e1587a494540 ("mm: vmpressure: fix sending wrong events on
> underflow") declare that reclaimed pages exceed the scanned pages due
> to the thp reclaim. it is incorrect because THP will be spilt to normal
> page and loop again. which will result in the scanned pages increment.
> 
> Signed-off-by: zhongjiang <zhongjiang@...wei.com>
> ---
>  mm/vmpressure.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/vmpressure.c b/mm/vmpressure.c
> index 6063581..0e91ba3 100644
> --- a/mm/vmpressure.c
> +++ b/mm/vmpressure.c
> @@ -116,8 +116,9 @@ static enum vmpressure_levels vmpressure_calc_level(unsigned long scanned,
>  
>  	/*
>  	 * reclaimed can be greater than scanned in cases
> -	 * like THP, where the scanned is 1 and reclaimed
> -	 * could be 512
> +	 * like reclaimed slab pages, shrink_node just add
> +	 * reclaimed page without a related increment to
> +	 * scanned pages.
>  	 */
>  	if (reclaimed >= scanned)
>  		goto out;

Thanks for the fixing my fault!

Acked-by: Minchan Kim <minchan@...nel.org>

Frankly speaking, I'm not sure we need such comment in there at the cost
of maintainance because it would be fragile but easy to fix by above simple
condition so I think it would be better to remove that comment but others
might be different. So, don't have any objection.