linux-kernel - Re: [PATCH] disable demotion during memory reclamation

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Message-ID: <20250910063643.2323-1-cuishw@inspur.com>
Date: Wed, 10 Sep 2025 14:36:40 +0800
From: cuishiwei <cuishw@...pur.com>
To: Johannes Weiner <hannes@...xchg.org>
CC: cuishiwei <cuishw@...pur.com>, Michal Hocko <mhocko@...e.com>,
	<akpm@...ux-foundation.org>, <axelrasmussen@...gle.com>,
	<yuanchu@...gle.com>, <weixugc@...gle.com>, <david@...hat.com>,
	<zhengqi.arch@...edance.com>, <shakeel.butt@...ux.dev>,
	<lorenzo.stoakes@...cle.com>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] disable demotion during memory reclamation

On Tue, 9 Sep 2025 15:45:31 +0100 Johannes Weiner <hannes@...xchg.org> wrote:

> On Tue, Sep 09, 2025 at 09:40:51AM +0200, Michal Hocko wrote:
> > On Tue 09-09-25 09:21:41, cuishiwei wrote:
> > > When a memory cgroup exceeds its memory limit, the system reclaims
> > > its cold memory.However, if /sys/kernel/mm/numa/demotion_enabled is
> > > set to 1, memory on fast memory nodes will also be demoted to slow 
> > > memory nodes.
> > > 
> > > This demotion contradicts the goal of reclaiming cold memory within
> > > the memcg.At this point, demoting cold memory from fast to slow nodes
> > > is pointless;it doesn't reduce the memcg's memory usage. Therefore, 
> > > we should set no_demotion when reclaiming memory in a memcg.
> > 
> > We have discussed this in the past and it is my recollection that we
> > have concluded that demotion is a part of proper aging and therefore it
> > should be done during the limit reclaim.
> 
> Yes, thanks. This is intentional. Please see 3f1509c57b1b ("Revert
> "mm/vmscan: never demote for memcg reclaim"") for more details.
Thank you for the guidance. It seems the original processing logic was sound.

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