[Haskell-cafe] Memory usage with TVar?

Johan Brinch brinchj at gmail.com
Wed Feb 1 16:29:14 CET 2012

Here's the example program:

When I run the program (which maintains a list inside an STM TVar), I
get the following statistics:
> ./Test +RTS -s
     176,041,728 bytes allocated in the heap
     386,794,976 bytes copied during GC
      69,180,224 bytes maximum residency (7 sample(s))
      42,651,080 bytes maximum slop
             179 MB total memory in use (0 MB lost due to fragmentation)

                                    Tot time (elapsed)  Avg pause  Max pause
  Gen  0       336 colls,     0 par    0.44s    0.44s     0.0013s    0.0033s
  Gen  1         7 colls,     0 par    0.39s    0.40s     0.0570s    0.1968s

  INIT    time    0.00s  (  0.00s elapsed)
  MUT     time    0.23s  (  0.23s elapsed)
  GC      time    0.83s  (  0.84s elapsed)
  EXIT    time    0.00s  (  0.00s elapsed)
  Total   time    1.06s  (  1.07s elapsed)

  %GC     time      77.9%  (78.3% elapsed)

  Alloc rate    749,153,093 bytes per MUT second

  Productivity  22.1% of total user, 22.0% of total elapsed

How come this program uses 179 MB of memory? I'm on a 64-bit machine
where 2'000'000 integers uses 32 MB. Where does the overhead come

Johan Brinch

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