Transferring data from a HDL to the Nios II processor

It really depends on your case.

Ie, if I assume that your component always holds all the status and measurement data, then it may be simpler to simply expose that in the MM slave interface as separate addresses.

This would avoid the need to copy the selected data into the FIFO.

It also depends on your performance needs.

In an extreme case, you may want your component to be have a MM master interface and write data directly into RAM.