G1Policy::logged_cards_processing_time approximates the time spent processing logged cards (used as an input to concurrent refinement) using the total card processing time, the number of logged cards, and the total number of cards processed. As written, if both card counts are zero it will perform a divide by zero operation. This is particularly likely during early GCs.

This isn't causing crashes (it's a floating point division), but may be messing up early estimations.