import Foreign.ForeignPtr
import Foreign.Ptr
import Foreign.Marshal
import Control.Monad

bufsize  = 4096    -- or 2^20
bufcount = 10^4    -- and 50, correspondingly

main = m 1
m i  = do fptr <- mallocForeignPtrBytes bufsize
          withForeignPtr fptr $ \ptr -> do
          copyBytes ptr (ptr `plusPtr` 1) (bufsize-1)
          when (i==bufcount) $ do
              putStrLn$ show(bufcount*bufsize)++" bytes allocated"
              getLine
              return ()
          m (i+1)