Functions and memory usage

[Basile STARYNKEVITCH <basile@...>]

>>>>> "John" == John Donovan <JohnD@MagentaSoftware.com> writes:

    John> Hi, I'm new to the list, and normally I'd just lurk for a
    John> couple of weeks getting the feel for the list. However, time
    John> is of the essence at the moment.  We're developing a game on
    John> a couple of well-known games consoles, and I've been given
    John> the task of implementing a scripting system. After looking
    John> at various options, I picked Lua. Now I'm trying to convince
    John> my boss that Lua is A Good Thing. He's worried about memory
    John> fragmentation.  As most of you will be aware, consoles have
    John> a very limited amount of memory, [...]

In my opinion the only real tool against memory fragmentation is a
moving (or copying, or compacting) garbage collector. The LUA GC is a
mark&sweep one, so it does not compact memory and neither does the
ordinary manual malloc+free (as in C) or new+delete (as in C++) memory
management. Fragmentation issues do appear in C or C++. There are lots
of literature on compacting or moving garbage collection (and there is
a GC mailing list, even if it is a bit quiet these days).

I am not sure that fragmentation is really an issue for game scripting
(I really don't know what these are exactly - I don't play games on my
computer, and never coded any game).

However, if you feel that fragmentation is an issue:

1. you cannot use traditional manual memory management (ie malloc+free
   or new+delete) because it has the same fragmentation problem.

2. you should consider compacting or moving garbage collection
   techniques, which do have some drawbacks (in particular, real-time
   or interactive-time constraints may require tricky tradeoffs or
   tuning with such moving GCs).

3. you could perhaps change Lua GC to be compacting. The simple case
   would be to compact the memory once in a while, in your idle loop,
   when the Lua call stack is nearly empty. If you do this, please
   contribute (if possible) your compacting GC to the Lua community.

4. you might consider alternative scripting languages (or virtual
   machines). I feel that Ocaml is a good scripting language, and its
   garbage collection can be tuned to perform very well in an
   interactive setting (like a game). Ocaml garbage collection is one
   of the finest I know (it is generational, copying for new objects,
   and marking & compacting for old ones). See www.ocaml.org 

5. You might use a copying GC in C. This is painful but doable. My
Qish runtime is actually such a beast. See my home page and/or send me
email.

[Sorry for mentionning another language on the Lua mailing list, but I
think that there are cases where Lua might not be the best solution]

Regards.


-- 

Basile STARYNKEVITCH         http://starynkevitch.net/Basile/ 
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