Here is the corresponding mm_free:

    1   void mm_free(void *bp)
    2   {
    3       size_t size = GET_SIZE(HDRP(bp));
    4   
    5       PUT(HDRP(bp), PACK(size, 0));
    6       PUT(FTRP(bp), PACK(size, 0));
    7       coalesce(bp);
    8   }