Re: A path forward to cleaning up dying cgroups?

[Yosry Ahmed <yosry.ahmed@linux.dev>]

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@linux.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.

There was an RFC series [1] for the recharging, but all memcg
maintainers hated it :P

https://lore.kernel.org/lkml/20230720070825.992023-1-yosryahmed@google.com/

> 
> 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.

Yeah with the charge moving code gone the case for recharging grows
weaker.

> 
> 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?

Adding Zach and Kinsey who were recently looking into this from the
Google side.