test +RTS -stest2fs.stat 
412,700,712 bytes allocated in the heap
6,411,611,864 bytes copied during GC (scavenged)
     38,864 bytes copied during GC (not scavenged)
 96,029,672 bytes maximum residency (8 sample(s))

        762 collections in generation 0 (169.31s)
          8 collections in generation 1 (  2.87s)

        189 Mb total memory in use

  INIT  time    0.01s  (  0.00s elapsed)
  MUT   time    3.69s  (  3.58s elapsed)
  GC    time  172.18s  (171.91s elapsed)
  EXIT  time    0.00s  (  0.00s elapsed)
  Total time  175.88s  (175.49s elapsed)

  %GC time      97.9%  (98.0% elapsed)

  Alloc rate    111,450,367 bytes per MUT second

  Productivity   2.1% of total user, 2.1% of total elapsed