linux-kernel - Re: [PATCH 1/3] mm/memcg: Fix min/low usage in propagate_protected

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Message-ID: <20181203115453.GO31738@dhcp22.suse.cz>
Date:   Mon, 3 Dec 2018 12:54:53 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Xunlei Pang <xlpang@...ux.alibaba.com>
Cc:     Roman Gushchin <guro@...com>, Johannes Weiner <hannes@...xchg.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 1/3] mm/memcg: Fix min/low usage in
 propagate_protected_usage()

On Mon 03-12-18 16:01:17, Xunlei Pang wrote:
> When usage exceeds min, min usage should be min other than 0.
> Apply the same for low.

Why? What is the actual problem.

> Signed-off-by: Xunlei Pang <xlpang@...ux.alibaba.com>
> ---
>  mm/page_counter.c | 12 ++----------
>  1 file changed, 2 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/page_counter.c b/mm/page_counter.c
> index de31470655f6..75d53f15f040 100644
> --- a/mm/page_counter.c
> +++ b/mm/page_counter.c
> @@ -23,11 +23,7 @@ static void propagate_protected_usage(struct page_counter *c,
>  		return;
>  
>  	if (c->min || atomic_long_read(&c->min_usage)) {
> -		if (usage <= c->min)
> -			protected = usage;
> -		else
> -			protected = 0;
> -
> +		protected = min(usage, c->min);
>  		old_protected = atomic_long_xchg(&c->min_usage, protected);
>  		delta = protected - old_protected;
>  		if (delta)
> @@ -35,11 +31,7 @@ static void propagate_protected_usage(struct page_counter *c,
>  	}
>  
>  	if (c->low || atomic_long_read(&c->low_usage)) {
> -		if (usage <= c->low)
> -			protected = usage;
> -		else
> -			protected = 0;
> -
> +		protected = min(usage, c->low);
>  		old_protected = atomic_long_xchg(&c->low_usage, protected);
>  		delta = protected - old_protected;
>  		if (delta)
> -- 
> 2.13.5 (Apple Git-94)
> 

-- 
Michal Hocko
SUSE Labs