During Concurrent Marking, G1 increases the marking stack size in bytes, starting from a minimum and potentially reaching a maximum as defined by the -XX:MarkStackSize and -XX:MarkStackSizeMax options.

Previously, G1 was unable to grow the marking stack during Reference Processing, which could result in a mark stack overflow error before reaching the MarkStackSizeMax limit. With this update, the marking stack is allowed to expand even during Reference Processing, preventing such overflow errors.