From mboxrd@z Thu Jan  1 00:00:00 1970
From: Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org>
Subject: Re: [PATCH 3/3] memcg: increase MEMCG_CHARGE_BATCH to 64
Date: Mon, 22 Aug 2022 21:34:59 +0200
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To: Roman Gushchin <roman.gushchin-fxUVXftIFDnyG1zEObXtfA@public.gmane.org>
Cc: Shakeel Butt <shakeelb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>, Muchun Song <songmuchun-EC8Uxl6Npydl57MIdRCFDg@public.gmane.org>, Michal =?iso-8859-1?Q?Koutn=FD?= <mkoutny-IBi9RG/b67k@public.gmane.org>, Eric Dumazet <edumazet-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Soheil Hassas Yeganeh <soheil-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Feng Tang <feng.tang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>, Oliver Sang <oliver.sang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, lkp-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org

On Mon 22-08-22 11:37:30, Roman Gushchin wrote:
[...]
> I wonder only if we want to make it configurable (Idk a sysctl or maybe
> a config option) and close the topic.

I do not think this is a good idea. We have other examples where we have
outsourced internal tunning to the userspace and it has mostly proven
impractical and long term more problematic than useful (e.g.
lowmem_reserve_ratio, percpu_pagelist_high_fraction, swappiness just to
name some that come to my mind). I have seen more often these to be used
incorrectly than useful.

In this case, I guess we should consider either moving to per memcg
charge batching and see whether the pcp overhead x memcg_count is worth
that or some automagic tuning of the batch size depending on how
effectively the batch is used. Certainly a lot of room for
experimenting.

-- 
Michal Hocko
SUSE Labs