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From: Pascal Zimmer <pzimmer@janestreet.com>
To: Jim Pryor <lists+caml@jimpryor.net>
Cc: "caml-list@inria.fr" <caml-list@inria.fr>
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Date: Thu, 06 Jan 2011 10:05:32 -0500
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Subject: Re: [Caml-list] memory leak in toplevel? or, how to implement
	sizeof

Because the overhead parameter can vary based on which version of OCaml
you are running, what the Gc module does, etc, I usually implement this
kind of measurements in this way:

# let sizeof maker arg =
    let first = Gc.((stat()).minor_words) in
    for i = 1 to 1000000 do
      ignore (maker arg)
    done;
    let second = Gc.((stat()).minor_words) in
    (second -. first) /. 1e6;;

# sizeof (fun x -> [x]) 1;;
- : float = 3.000022

The overhead gets amortized enough that is becomes negligible (you only
have to rely on the fact that the loop does not do any allocation).

Pascal


On Thu, 2011-01-06 at 09:44 -0500, Jim Pryor wrote:
> Thanks David. So does this look like a reasonable implementation of
> sizeof:
> 
>     # let sizeof maker arg =
>         let first = Gc.((stat()).minor_words) in
>         let res = maker arg in
>         let second = Gc.((stat()).minor_words) in
>         int_of_float (second -. first) - 23 ( *overhead *), res;;
> 
>     # sizeof (fun x -> [x]) 1;;
>     - : int * int list = (3, [1])
> 
>     # sizeof (fun x -> Some x) 1;;
>     - : int * int option = (2, Some 1)
> 
> It does give the right answers. ([1] is a block containing two non-blocks; Some 1 is a block containing one non-block.)
> 
> 
> -- 
> Jim Pryor
> profjim@jimpryor.net
>