OCaml write barrier

[Stephen Weeks]

> I'm  curious that the `write barrior' in OCaml GC is SO expensive (Leroy says
> that 70% of the time in the simple example is in `cross-generation  checks'.)
> The  sum  loop isn't doing any writes at all.

Yeah, there was a post that explained the slowdown (3X relative to MLton) for
the sum loop as being because of boxing integer arrays.

> Do you know OCaml uses a Chez-
> style byte vector of possible cross-space pointers, or does  it  use  a  MUCH
> more  expensive store list.  The latter never made any real sense to me since
> every store cons's onto the list.

I would be surprised if it did the latter, but I don't know.  There's a few
papers on their GC at http://pauillac.inria.fr/ocaml/papers.html.