Re: [Caml-list] Regarding SMP computing

[Damien Doligez <damien.doligez@inria.fr>]

On 2006-09-25, at 21:41, Richard Jones wrote:

> On a related note, is/could there be a way in OCaml to tell the GC not
> to bother going "into" a particular data structure to check if it part
> of it has become unreachable?

The GC doesn't work by checking whether something has become
unreachable.  It works by marking all reachable data, then deallocating
everything else.  There is no way to do what you want in OCaml, and
I don't think it can be done without a major rework of the runtime
system.

> Otherwise every time we do a major
> collection it's going to be uselessly iterating over the whole lot,
> and that appears to have particularly bad consequences as soon as we
> start to go into swap.

The OCaml GC is not designed to work well when the heap becomes larger
than physical memory.  As soon as you start going to swap you'll see
a huge performance hit, and there's not much we can do about it.

-- Damien