linux-kernel - Re: [PATCH -next] mm: introduce per-node proactive reclaim interface

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Message-ID: <ZuE9fSvWzlUdY5z2@tiehlicka>
Date: Wed, 11 Sep 2024 08:49:33 +0200
From: Michal Hocko <mhocko@...e.com>
To: Davidlohr Bueso <dave@...olabs.net>
Cc: linux-mm@...ck.org, akpm@...ux-foundation.org, rientjes@...gle.com,
	yosryahmed@...gle.com, hannes@...xchg.org, almasrymina@...gle.com,
	roman.gushchin@...ux.dev, gthelen@...gle.com, dseo3@....edu,
	a.manzanares@...sung.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next] mm: introduce per-node proactive reclaim interface

On Tue 10-09-24 09:31:15, Davidlohr Bueso wrote:
> On Mon, 09 Sep 2024, Michal Hocko wrote:
> 
> > On Wed 04-09-24 09:27:40, Davidlohr Bueso wrote:
> > > 1. Users who do not use memcg can benefit from proactive reclaim.
> > 
> > It would be great to have some specific examples here. Is there a
> > specific reason memcg is not used?
> 
> I know cases of people wanting to use this to free up fast memory
> without incurring in extra latency spikes before a promotion occurs.

Please give us more information about those because this might have an
impact on how the interface is shaped. E.g. we might need to plan for 
future extension.

> I do not have details as to why memcg is not used.

I am not saying this is crucial to clarify but it is a natural question.
We have a ready interface to achieve preemptive reclaim, why not use
that and introduce something new. A plausible argument could be that
memcg interface is not NUMA aware and there are usecases that are
focusing on NUMA balancing rather than workload memory footprint.

> I can also see
> this for virtual machines running on specific nodes, reclaiming "extra"
> memory based on wss and qos, as well as potential hibernation optimizations.

Do not virtual solutions have own ways to manage overcommit/memory
balancing (memory balooning etc.)? Does such interface fall into the
existing picture?

-- 
Michal Hocko
SUSE Labs