[jhj]

For performance, it's always better to explicitly manage GPU memory and host/device copies for performance than to depend upon the unified memory paging mechanism, if it's possible to go the extra effort.

My feeling is that unified memory and on-demand paging introduced with Pascal? was mainly about making it easier to onboard existing applications (e.g., HPC codes etc) to the GPU a bit at a time with less problem. For writing a GPU application from scratch, I don't think it makes much sense (unless the granluarity of the data that you are moving around is really tiny and/or you can't predict what you would need in advance on CPU or GPU).