[Openmcl-devel] Memory usage on 64-bits

Gary Byers gb at clozure.com
Sun Oct 19 19:33:09 PDT 2008

On Sun, 19 Oct 2008, Lengyel, Florian wrote:

> A group at my university is about to port a large lisp AI program to CCL;
> I'd like to ask two rather general questions that pertain to this effort.
> Does CCL have a limitation on the RAM it can access on a 64-bit system?
> Will it use the available RAM? (The program generates a lot of garbage,
> I'm told.)

When CCL starts up, it "reserves" a large contiguous chunk of its address
space.  The size of this chunk depends on the OS, but on x86-64 Darwin
and Linux it's currently 512GB.  (I don't know of anyone who's run into
that limit, but we do have users running on machines with ~150GB of
RAM today, and it's not unreasonable to think that the 512GB limit
will be a real problem for at least some users in the relatively
near future.

Generating lots of garbage is generally something that GCs like;
it's the non-garbage that can have higher costs associated with

> Also, they would like to run CCL on one of the newer MacBook Pros. These
> use either the E7000 or E8000 Intel Core 2 Duo CPU. Is there an issue
> with this
> processor or the chipset?

I'd need to borrow one for an extended period to be sure, but I think
that it's likely that the newer implementations are architecturally
identical to older ones (or may offer architectural extensions). In
most respects, it's the same chip designed to run the same instruction
set as its predecessors, and the fact that it may be the result
of a different manufacturing process and/or have different power/
thermal/performance characteristics than those predecessors usually
isn't too visible to user-level code.

> Thanks,
> FL
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