linux-kernel - Re: [PATCH] mm: skip current when memcg reclaim

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Date:   Fri, 15 Oct 2021 13:00:35 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Huangzhaoyang <huangzhaoyang@...il.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Zhaoyang Huang <zhaoyang.huang@...soc.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: skip current when memcg reclaim

On Fri, 15 Oct 2021 14:15:29 +0800 Huangzhaoyang <huangzhaoyang@...il.com> wrote:

> From: Zhaoyang Huang <zhaoyang.huang@...soc.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);
>  		}