From mboxrd@z Thu Jan  1 00:00:00 1970
From: Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org>
Subject: Re: [RFC] Add swappiness argument to memory.reclaim
Date: Thu, 19 May 2022 10:51:53 +0200
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To: Wei Xu <weixugc-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
Cc: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>, Yosry Ahmed <yosryahmed-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Shakeel Butt <shakeelb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, David Rientjes <rientjes-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Roman Gushchin <roman.gushchin-fxUVXftIFDnyG1zEObXtfA@public.gmane.org>, Cgroups <cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Linux-MM <linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org>, Yu Zhao <yuzhao-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Greg Thelen <gthelen-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Chen Wandun <chenwandun-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>

On Wed 18-05-22 22:44:13, Wei Xu wrote:
> On Tue, May 17, 2022 at 1:06 PM Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org> wrote:
[...]
> > But I don't think an anon/file bias will capture this coefficient?
> 
> It essentially provides the userspace proactive reclaimer an ability
> to define its own reclaim policy by adding an argument to specify
> which type of pages to reclaim via memory.reclaim.

I am not sure the swappiness is really a proper interface for that.
Historically this tunable has changed behavior several times and the
reclaim algorithm is free to ignore it completely in many cases. If you
want to build a userspace reclaim policy, then it really has to have a
predictable and stable behavior. That would mean that the semantic would
have to be much stronger than the global vm_swappiness.
-- 
Michal Hocko
SUSE Labs