Ah, got it, you only ended up at wanting namespace labels because
there was no other way to carve up device-dax. That's changing as part
of the efi_fake_mem= enabling and I have a patch set in the works to
allow discontiguous sub-divisions of a device-dax range. Note that is
this branch rebases frequently:
https://git.kernel.org/pub/scm/linux/kernel/git/djbw/nvdimm.git/log/?h=libnvdimm-pending