Method: (EXPAND-FREE-LIST T FREE-LIST-HEAP)

Source

(defmethod expand-free-list (size-class (heap free-list-heap))
  ;; Try to find a block that's at least EXPANSION-SIZE big on
  ;; one of the bigger free lists.  If there is such a block,
  ;; carve it up.  If there isn't, expand the heap if possible.
  (let ((min-size
         (if (< (1+ size-class) (nr-free-lists heap))
             (max (expansion-size heap)
                  ;; Make sure we only try bigger free lists than
                  ;; the current one.
                  (size-class-block-size (1+ size-class) heap))
           (expansion-size heap))))
    (multiple-value-bind (block size)
        (find-block min-size heap)
      (unless block
        (setq size (max (expansion-size heap)
                        (size-class-block-size size-class heap))
              block (expand-heap heap size)))
      (carve-up-block-for-free-list size-class block size heap)
      ;; Return the first new block.
      block)))