when chunk size was a already multiple of the page size, the
resulting size would be one page too much

This was neccessary in order to make the memory available via GDRcopy
when multiple small allocations were made. cudaMalloc() would return
multiple memory chunks located in the same GPU page, which GDRcopy
pretty much dislikes (`gdrdrv:offset != 0 is not supported`).
As a side effect, this will keep the number of BAR-mappings done
via GDRcopy low, because they seem to be quite limited.

Using CUDA, memory can be allocated on the GPU and shared to peers on
the PCIe bus such as the FPGA. Furthermore, the DMA on the GPU can also
be used to read and write to/from other memory on the PCIe bus, such as
BRAM on the FPGA.