By the way, did anybody succesfully applied a different
GC to OCaml?

I've tried to add parallelism -- more specifically, to collect
major heap in a separate thread -- but failed to do so:
as usually with parallel programs, I've got lots of bugs that
were just nightmare to track down.

So, after two weeks of trying, I just abandoned this, with hope
to return to this some day. 

Regards,
Dmitri