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Date:   Wed, 1 Apr 2020 18:23:06 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Chris Down <chris@chrisdown.name>
Cc:     Johannes Weiner <hannes@cmpxchg.org>, Tejun Heo <tj@kernel.org>,
        linux-mm@kvack.org, cgroups@vger.kernel.org,
        linux-kernel@vger.kernel.org, kernel-team@fb.com,
        Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCH] mm, memcg: Bypass high reclaim iteration for cgroup
 hierarchy root
Message-Id: <20200401182306.724698b74692b5d31f66ad10@linux-foundation.org>
In-Reply-To: <20200312164137.GA1753625@chrisdown.name>
References: <20200312164137.GA1753625@chrisdown.name>
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On Thu, 12 Mar 2020 16:41:37 +0000 Chris Down <chris@chrisdown.name> wrote:

> The root of the hierarchy cannot have high set, so we will never reclaim
> based on it. This makes that clearer and avoids another entry.
> 
> ...
>
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2232,7 +2232,8 @@ static void reclaim_high(struct mem_cgroup *memcg,
>  			continue;
>  		memcg_memory_event(memcg, MEMCG_HIGH);
>  		try_to_free_mem_cgroup_pages(memcg, nr_pages, gfp_mask, true);
> -	} while ((memcg = parent_mem_cgroup(memcg)));
> +	} while ((memcg = parent_mem_cgroup(memcg)) &&
> +		 !mem_cgroup_is_root(memcg));
>  }
>  
>  static void high_work_func(struct work_struct *work)

Does someone have time to review this one?

Thanks.