linux-kernel - Re: [PATCH 2/2 RESEND] mm: vmpressure: fix sending wrong events on underflow

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Message-ID: <20170206124037.GA10298@dhcp22.suse.cz>
Date:   Mon, 6 Feb 2017 13:40:37 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Vinayak Menon <vinmenon@...eaurora.org>
Cc:     akpm@...ux-foundation.org, hannes@...xchg.org,
        mgorman@...hsingularity.net, vbabka@...e.cz, riel@...hat.com,
        vdavydov.dev@...il.com, anton.vorontsov@...aro.org,
        minchan@...nel.org, shashim@...eaurora.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2 RESEND] mm: vmpressure: fix sending wrong events on
 underflow

On Mon 06-02-17 17:54:10, Vinayak Menon wrote:
[...]
> diff --git a/mm/vmpressure.c b/mm/vmpressure.c
> index 149fdf6..3281b34 100644
> --- a/mm/vmpressure.c
> +++ b/mm/vmpressure.c
> @@ -112,8 +112,10 @@ static enum vmpressure_levels vmpressure_calc_level(unsigned long scanned,
>  						    unsigned long reclaimed)
>  {
>  	unsigned long scale = scanned + reclaimed;
> -	unsigned long pressure;
> +	unsigned long pressure = 0;
>  
> +	if (reclaimed >= scanned)
> +		goto out;

This deserves a comment IMHO. Besides that, why shouldn't we normalize
the result already in vmpressure()? Please note that the tree == true
path will aggregate both scanned and reclaimed and that already skews
numbers.
-- 
Michal Hocko
SUSE Labs