Method: (FREE-SPACE HEAP)

Source

(defmethod free-space ((heap heap))
  ;; Returns an estimate of the number of octets that can be
  ;; allocated until the heap is full (i.e. heap-end >= heap-max-end).
  ;; For a copying collector, this number is very close to the truth.
  ;; But for mark-and-sweep collectorsestimate it is a very conservative
  ;; estimate, because we only count the heap space that hasn't been
  ;; reserved by one of the free lists (because you can't be sure that
  ;; a free list block can actually be used to allocate an arbitrary-sized
  ;; block).
  (- (max-heap-end heap) (heap-end heap)))