On Tue, Sep 02, 2025 at 09:56:34AM +0200, "Gustavo A. R. Silva" <gustavo@embeddedor.com> wrote:
> If the increase in size is not a problem, then something like this
> works fine (unless there is a problem with moving those two members
> at the end of cgroup_root?):

Please don't forget to tackle cgroup_root allocators. IIUC, this move
towards the end shifts the burden to them.

There's only the rcu_head we care about.

(You seem to be well versed with flex arrays, I was wondering if
something like this could be rearranged to make it work (assuming the
union is at the end of its containers):

	union {
		struct cgroup *ancestors[];
		struct {
			struct cgroup *_root_ancestor;
			struct cgroup *_low_ancestors[];
		};
	};
)

Thanks,
Michal