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

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Message-Id: <91D2E468-B89A-4DD7-B1B0-B892FA4482E3@linux.dev>
Date: Thu, 6 Feb 2025 11:30:10 +0800
From: Muchun Song <muchun.song@...ux.dev>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Johannes Weiner <hannes@...xchg.org>,
 Hamza Mahfooz <hamzamahfooz@...ux.microsoft.com>,
 linux-mm@...ck.org,
 Roman Gushchin <roman.gushchin@...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>,
 Allen Pais <apais@...ux.microsoft.com>,
 Yosry Ahmed <yosryahmed@...gle.com>
Subject: Re: A path forward to cleaning up dying cgroups?

> On Feb 6, 2025, at 02:46, Shakeel Butt <shakeel.butt@...ux.dev> wrote:
> 
> On Wed, Feb 05, 2025 at 01:08:42PM -0500, Johannes Weiner wrote:
>> 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?
> 
> I think the recharging (or whatever the alternative) can be a followup
> to this. I agree this is a good change.

I agree with you. We've been encountering dying memory issues for years
on our servers. As Roman said, I need to refresh my patches. So I need
some time for refreshing.

Muchun,
Thanks.