[1] https://gist.github.com/stedolan/52c13d6b1a30276db31ca98683c8db16
Stephen Dolan suggested that we count only live data as sweeping work for the purpose of GC pacing. In other words, the work counter for sweeping is only incremented when we sweep a live block, not when we sweep a free block or a garbage block.
This is to improve the stability of the system by removing a feedback loop. If we count the whole heap size as sweeping work, then the GC speed depends on the heap size, which