linux-kernel - Re: A path forward to cleaning up dying cgroups?

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Message-ID: <20250205180842.GC1183495@cmpxchg.org>
Date: Wed, 5 Feb 2025 13:08:42 -0500
From: Johannes Weiner <hannes@...xchg.org>
To: Hamza Mahfooz <hamzamahfooz@...ux.microsoft.com>
Cc: linux-mm@...ck.org, Roman Gushchin <roman.gushchin@...ux.dev>,
	Shakeel Butt <shakeel.butt@...ux.dev>,
	Andrew Morton <akpm@...ux-foundation.org>, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>,
	Michal Koutný <mkoutny@...e.com>,
	Michal Hocko <mhocko@...nel.org>,
	Muchun Song <muchun.song@...ux.dev>,
	Allen Pais <apais@...ux.microsoft.com>,
	Yosry Ahmed <yosryahmed@...gle.com>
Subject: Re: A path forward to cleaning up dying cgroups?

On Wed, Feb 05, 2025 at 12:50:19PM -0500, Hamza Mahfooz wrote:
> Cc: Shakeel Butt <shakeel.butt@...ux.dev>
> 
> On 2/5/25 12:48, Hamza Mahfooz wrote:
> > I was just curious as to what the status of the issue described in [1]
> > is. It appears that the last time someone took a stab at it was in [2].

If memory serves, the sticking point was whether pages should indeed
be reparented on cgroup death, or whether they could be moved
arbitrarily to other cgroups that are still using them.

It's a bit unfortunate, because the reparenting patches were tested
and reviewed, and the arbitrary recharging was just an idea that
ttbomk nobody seriously followed up on afterwards.

We also recently removed the charge moving code from cgroup1, along
with the subtle page access/locking/accounting rules it imposed on the
rest of the MM. I'm doubtful there is much appetite in either camp for
bringing this back.

So I would still love to see Muchun's patches merged. They fix a
seemingly universally experienced operational issue in memcg, and we
shouldn't hold it up unless somebody actually posts alternative code.

Thoughts?