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

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Message-ID: <20181203180008.GB31090@castle.DHCP.thefacebook.com>
Date:   Mon, 3 Dec 2018 18:00:11 +0000
From:   Roman Gushchin <guro@...com>
To:     Xunlei Pang <xlpang@...ux.alibaba.com>
CC:     Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH 1/3] mm/memcg: Fix min/low usage in
 propagate_protected_usage()

On Mon, Dec 03, 2018 at 04:01:17PM +0800, Xunlei Pang wrote:
> When usage exceeds min, min usage should be min other than 0.
> Apply the same for low.
> 
> 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);

This change makes sense in the combination with the patch 3, but not as a
standlone "fix". It's not a bug, it's a required thing unless you start scanning
proportionally to memory.low/min excess.

Please, reflect this in the commit message. Or, even better, merge it into
the patch 3.

Also, please, make sure that cgroup kselftests are passing after your changes.

Thanks!