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Date:   Fri, 15 Oct 2021 13:00:35 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Huangzhaoyang <huangzhaoyang@gmail.com>
Cc:     Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Zhaoyang Huang <zhaoyang.huang@unisoc.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: skip current when memcg reclaim
Message-Id: <20211015130035.aacc18a4d1ee141b306c2272@linux-foundation.org>
In-Reply-To: <1634278529-16983-1-git-send-email-huangzhaoyang@gmail.com>
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On Fri, 15 Oct 2021 14:15:29 +0800 Huangzhaoyang <huangzhaoyang@gmail.com> wrote:

> From: Zhaoyang Huang <zhaoyang.huang@unisoc.com>
> 
> Sibling thread of the same process could refault the reclaimed pages
> in the same time, which would be typical in None global reclaim and
> introduce thrashing.

"None" -> "node", I assume?

> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2841,6 +2841,11 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
>  				sc->memcg_low_skipped = 1;
>  				continue;
>  			}
> +			/*
> +			 * Don't bother current when its memcg is below low
> +			 */

The comment explains what the code is doing, but the code itself
already does this.  Please can we have a comment that explains *why*
the code is doing this?


> +			if (get_mem_cgroup_from_mm(current->mm) == memcg)
> +				continue;
>  			memcg_memory_event(memcg, MEMCG_LOW);
>  		}