Re: [RFC PATCH 0/4] memcg_ext: memcg policy through cgroup-attached struct_ops

[Shakeel Butt <shakeel.butt@linux.dev>]

Hi Yafang,

On Wed, Sep 23, 2026 at 09:07:40PM +0800, Yafang Shao wrote:
> On Tue, Sep 22, 2026 at 3:30 AM Shakeel Butt <shakeel.butt@linux.dev> wrote:
> >
[...]
> >
> > Known open questions
> > ====================
> >
> > The semantics of memory.high for remote chargers or kernel threads is a
> > grey area and this series does not aim to resolve that.
> >
> > Another open question is whether a bound on debt deferral is needed. At
> > the moment, we think that rather than putting a limit on deferral for
> > memory.high, it will be better to handle that through an async worker like
> > memcg->high_work.  We aim to introduce that later, along with the right CPU
> > accounting for that async work.
> 
> Hello Shakeel,
> 
> On the open question of how deferred debt eventually gets paid: would
> it make sense for the policy to also notify userspace (e.g. via
> ringbuf) when it defers,

I think the notification through bpf programs is already possible and a bpf
program deciding to bypass memory.high can already do notification via ringbuf.

> and have a userspace reclaimer do the reclaim
> through memory.reclaim?
> 
> I understand one of the concerns for the async worker is CPU
> accounting. If the concern is that the kworker's CPU usage is not
> charged to the target cgroup, the userspace reclaimer could instead be
> spawned with clone3(CLONE_INTO_CGROUP) so it runs inside the target
> cgroup, and both its CPU and memory usage get charged there.
> 
> One caveat: intermediate cgroups with the no-internal-process
> constraint cannot take processes, so this would only work for leaf
> cgroups.
> 
> What do you think?

I think all of this is possible without additional code and with this series.
With AI, should be very easy to prototype it. Please take a stab and I will look
into it as well (time permitting).

Thanks for taking a look and also please let me know what other ways you think
memcg can be customized through BPF in a beneficial way.