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Re: GC & Virtual Memory

In article <1991Nov12.185801.1209@crl.dec.com> rwk@crl.dec.com (Bob Kerns) writes:
> In article <FERTIG.91Nov12095206@krypton.elements.rpal.com>, fertig@elements.rpal.com (Ken Fertig) writes:
>> I am currently developing an application (using CLIM v. 1.0) which
>> involves a significant amount of memory manipulating arrays.  When
>> running on the Symbolics fits in a world using about 80 Mb. of paging
>> area.  On the Macintosh under MCL 2.0b1p3 I initially tried running
>> under 5 Mb. of real memory (and failed).  I then turned on virtual
>> memory under system 7 and gave MCL 20 Mb.  The result has been GC
>> hell.
>> I am interested in heuristics and/or parameters for increasing
>> effectiveness of the MCL garbage collector.  Is the MCL garbage
>> collector unworkable with virtual memory?  Any and all thoughts on
>> this matter would be greatly appreciated.
> If you tried running your Symbolics machine with 5 Mb
> physical memory, you'd find *IT* was GC and paging hell,
> too.

> I'm sure the EGC (coming in MCL 2.0) will help a great
> deal, but trying to run a large Lisp with only 5 Mb of
> physical memory seems hopeless.  You should at least upgrade
> your system to 8Mb, which is pretty inexpensive, and will
> make an enourmous difference.

The mac I am running on is an fx with 16mb internal memory.  The 5mb
referred to above is the specific allocation I gave mcl, with virtual
memeroy turned off.

> ...
> Also, if you're just barely fitting into that 20 MB,
> you will be GCing very often, and taking a very long time
> to do those GC's.  If you've got 100K left over in that
> 20MB, and you add 1 more Mb, you might find that you only
> have to GC 1/11 as often, for an order of magnitude improvement
> in performance.

I am faily sure that the application fits easily into the 20mb i gave
it with virtual memory turned on. I'll try upping it to 30mb to see if
there is an effect. (I'll have to clean some old items off my disk to
make room...)  The real question remains, however: does anyone have
suggestions/heuristics as to how to tune the garbage collector. Are
there some interactions with virtual memory that I should take into


Palo Alto Laboratory, Rockwell International Science Center