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Date: Thu, 1 Feb 2024 14:57:22 +0100
From: Michal =?utf-8?Q?Koutn=C3=BD?= <mkoutny@suse.com>
To: "T.J. Mercier" <tjmercier@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@kernel.org>, 
	Roman Gushchin <roman.gushchin@linux.dev>, Shakeel Butt <shakeelb@google.com>, 
	Muchun Song <muchun.song@linux.dev>, Andrew Morton <akpm@linux-foundation.org>, 
	Efly Young <yangyifei03@kuaishou.com>, android-mm@google.com, yuzhao@google.com, 
	cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: memcg: Use larger chunks for proactive reclaim
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Hello.

On Wed, Jan 31, 2024 at 04:24:41PM +0000, "T.J. Mercier" <tjmercier@google.=
com> wrote:
>  		reclaimed =3D try_to_free_mem_cgroup_pages(memcg,
> -					min(nr_to_reclaim - nr_reclaimed, SWAP_CLUSTER_MAX),
> +					max((nr_to_reclaim - nr_reclaimed) / 4,
> +					    (nr_to_reclaim - nr_reclaimed) % 4),

The 1/4 factor looks like magic.=20

Commit 0388536ac291 says:
| In theory, the amount of reclaimed would be in [request, 2 * request).

Doesn't this suggest 1/2 as a better option? (I didn't pursue the
theory.)

Also IMO importantly, when nr_to_reclaim - nr_reclaimed is less than 8,
the formula gives arbitrary (unrelated to delta's magnitude) values.

Regards,
Michal

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