I have attempted to install a swap file on the same disk that has a swap partition. However, this leads to severe thrashing and performance degradation. However it is desirable to have both a swap file and a swap partitition on the disk, as the swap partition is somewhat inadequate so sometimes an additional swap file is nice to be added, but we still want to use the space that has been allocated for the swap partition. There is no reason why we should not get good performance with such. FreeBSD needs to make sure performance is good in this situation. This is important for useability. The system should work well in ways that users need to use it.