linux-kernel - Re: [PATCH v2] memcg: Only record foreign writebacks with dirty pages when memcg is not disabled

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Message-ID: <20190924122747.GQ23050@dhcp22.suse.cz>
Date:   Tue, 24 Sep 2019 14:27:47 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Baoquan He <bhe@...hat.com>
Cc:     akpm@...ux-foundation.org, tj@...nel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2] memcg: Only record foreign writebacks with dirty
 pages when memcg is not disabled

On Tue 24-09-19 19:11:51, Baoquan He wrote:
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index f3c15bb07cce..84e3fdb1ccb4 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4317,6 +4317,9 @@ void mem_cgroup_track_foreign_dirty_slowpath(struct page *page,
>  
>  	trace_track_foreign_dirty(page, wb);
>  
> +	if (mem_cgroup_disabled())
> +		return;
> +

This doesn't seem correct. We shouldn't even enter the slowpath with
memcg disabled AFAIC. The check should be done at mem_cgroup_track_foreign_dirty
level.
-- 
Michal Hocko
SUSE Labs