  We present the design and implementation details of a geometric multigrid
method on adaptively refined meshes for massively parallel computations. The
method uses local smoothing on the refined part of the mesh. Partitioning is
achieved by using a space filling curve for the leaf mesh and distributing
ancestors in the hierarchy based on the leaves. We present a model of the
efficiency of mesh hierarchy distribution and compare its predictions to
runtime measurements. The algorithm is implemented as part of the deal.II
finite element library and as such available to the public.
