[mm v2 0/3] Support memory cgroup hotplug

[Tejun Heo]

On Thu, Nov 24, 2016 at 12:05:12AM +1100, Balbir Singh wrote:
> On my desktop NODES_SHIFT is 6, many distro kernels have it a 9. I've known
> of solutions that use fake NUMA for partitioning and need as many nodes as
> possible.

It was a crude kludge that people used before memcg.  If people still
use it, that's fine but we don't want to optimize / make code
complicated for it, so let's please put away this part of
justification.

It's understandable that some kernels want to have large NODES_SHIFT
to support wide range of configurations but if that makes wastage too
high, the simpler solution is updating the users to use the rumtime
detected possible number / mask instead of the compile time
NODES_SHIFT.  Note that we do exactly the same thing for per-cpu
things - we configure high max but do all operations on what's
possible on the system.

NUMA code already has possible detection.  Why not simply make memcg
use those instead of MAX_NUMNODES like how we use nr_cpu_ids instead
of NR_CPUS?

Thanks.

-- 
tejun