2nd class support for me means a feature that is not enabled by default
but that can be enabled in order to increase performance. The 2nd class
support is there because we are not yet sure about the maturity of the
memory allocation methods.
Nor does mine for the low orders that we are considering. For order >
MAX_ORDER this is unavoidable since the page allocator cannot manage such
large pages. It can be used for lower order if there are issues (that I
have not seen yet).