Re: [PATCH v3 net-next 01/12] mptcp: Fix up subflow's memcg when CONFIG_SOCK_CGROUP_DATA=n.

Hello.

On Tue, Aug 12, 2025 at 05:58:19PM +0000, Kuniyuki Iwashima [off-list ref] wrote:

When sk_alloc() allocates a socket, mem_cgroup_sk_alloc() sets
sk->sk_memcg based on the current task.

MPTCP subflow socket creation is triggered from userspace or
an in-kernel worker.

I somewhat remembered
d752a4986532c ("net: memcg: late association of sock to memcg")

but IIUC this MPTCP codepath, the socket would never be visible to
userspace nor manipulated from a proper process context, so there is no
option to defer the association in similar fashion, correct?

Then, I wonder whether this isn't a scenario for
	o = set_active_memcg(sk->sk_memcg);
	newsk =  sk_alloc();
	...
	set_active_memcg(o);

i.e. utilize the existing remote charging infra instead of introducing
specific mem_cgroup_sk_inherit() helper.

Regards,
Michal