[plt-scheme] asking mzscheme and DrScheme to GC less to get speedups at the expense of memory usage?

This is perhaps obvious, but if you wrap (time ...) around the entry
point, you'll get back times that include gc time and that might also
tell us if it garbage collecting a lot. Or, if you are running from
mzscheme, you can run like this:

mzscheme -W debug

and you'll see when garbage collections happen.

Robby

On Wed, Dec 30, 2009 at 12:06 PM, Lee Spector <lspector at hampshire.edu> wrote:
>
> Under DrScheme the green recycle icon flashes about 3 or 4 times per second.
>
> If I understand correctly I should add something like this to my code:
>
> (define wasted-memory-to-trick-GC
>  (make-string 100000000 #\x))
>
> I've just tried that for a new Linux/mzscheme run, but it will take some time to tell if it's having an effect. I don't see anything dramatic, however. I'll try in DrScheme, where I may notice different behavior of the recycle icon, when my current run completes (which may be a day or so).
>
> Thanks,
>
>  -Lee
>
> On Dec 30, 2009, at 12:36 PM, Matthew Flatt wrote:
>
>> There's currently no such control, but
>>
>> * Do you know how much time is being spent by the GC? When you run in
>>   DrScheme, does it spend a lot of time with the green recycle icon
>>   on or flashing very quickly?
>>
>> * You can partially simulate a request to use more memory by
>>   allocating a big byte string and holding onto it. A GC is triggered
>>   based on current memory use versus the memory use after the most
>>   recent garbage collection. So, if you hold onto a bunch of data,
>>   more data will be used before another GC. (Be sure to allocate a big
>>   byte string or character string, and not a big vector, because you
>>   don't want the GC to have to traverse the big object.)
>>
>>
>> At Wed, 30 Dec 2009 12:20:18 -0500, Lee Spector wrote:
>>>
>>> I have some memory-hungry and compute-intensive programs that I'm running in
>>> DrScheme under Mac OS X and in mzscheme under Linux. Under DrScheme I set the
>>> memory limit to something fairly high, while under Linux, if I understand
>>> correctly, there is no limit.
>>>
>>> In both cases, however, less memory is actually being used than I would
>>> expect. I suppose this means that a lot of the memory turns quickly to garbage
>>> and is being quickly collected, which is nice in some respects, but in the
>>> current case I want maximum execution speed and would be happy for the thing
>>> to eat several GB more memory if that would help things to run faster.
>>>
>>> The reason I suspect this might be possible is that I used to experience
>>> similar things in various Lisps, and I could get substantial speedups by
>>> telling them to GC less. For example, in CMUCL the default GC parameters would
>>> always cause my programs (which are often genetic programming systems with
>>> large populations) to thrash in GC and run very slowly overall, but if I
>>> launched CMUCL with a command-line argument that told it not to GC until a
>>> particular (high) threshold of allocation was reached then it would run much
>>> faster. This makes a big difference for runs that can take hours or days.
>>>
>>> Is there a way to do something similar with mzscheme and/or DrScheme? Or would
>>> it not help for some reason? I'm currently conducting a run that I would
>>> expect to eat lots of RAM and it's using a measly 1.9% of my system memory.
>>> I'd be happy for it to use 99% if that would improve the runtime.
>>>
>>> I've browsed the reference and found a number of sections related to GC but
>>> nothing addressing this issue specifically.
>>>
>>> Thanks for any help you can provide,
>>>
>>> -Lee
>>>
>>> --
>>> Lee Spector, Professor of Computer Science
>>> School of Cognitive Science, Hampshire College
>>> 893 West Street, Amherst, MA 01002-3359
>>> lspector at hampshire.edu, http://hampshire.edu/lspector/
>>> Phone: 413-559-5352, Fax: 413-559-5438
>>>
>>> Check out Genetic Programming and Evolvable Machines:
>>> http://www.springer.com/10710 - http://gpemjournal.blogspot.com/
>>>
>>> _________________________________________________
>>>  For list-related administrative tasks:
>>>  http://list.cs.brown.edu/mailman/listinfo/plt-scheme
>
> --
> Lee Spector, Professor of Computer Science
> School of Cognitive Science, Hampshire College
> 893 West Street, Amherst, MA 01002-3359
> lspector at hampshire.edu, http://hampshire.edu/lspector/
> Phone: 413-559-5352, Fax: 413-559-5438
>
> Check out Genetic Programming and Evolvable Machines:
> http://www.springer.com/10710 - http://gpemjournal.blogspot.com/
>
> _________________________________________________
>  For list-related administrative tasks:
>  http://list.cs.brown.edu/mailman/listinfo/plt-scheme
>