ratio of heap size to live data in Caml GC?

ratio of heap size to live data in Caml GC?

[Norman Ramsey]

Can anybody tell me what ratio of heap size to live data the OCaml collector
needs to perform well?  The default ratio appears to be 2.4.  I assume
this means the collector is a mark-and-sweep collector?


Norman

Re: ratio of heap size to live data in Caml GC?

[David Mentré]

Norman Ramsey <nr@eecs.harvard.edu> writes:

>  I assume this means the collector is a mark-and-sweep collector?

As far as I have understood, the collector is a combination of a
mark&sweep (at major collection) and of a generation (at minor
collection) collectors.

You'll find a description of this collector, unfortunatly in french, on
this web pages :
 http://www.pps.jussieu.fr/Livres/ora/DA-OCAML/book-ora088.html


I *think* you'll find a close description of the actual GC in the
following paper. As I haven't read thise papers, you are on your own :

Damien Doligez, Xavier Leroy. "A concurrent, generational garbage
collector for a multithreaded implementation of ML". Proceedings POPL
93.
http://pauillac.inria.fr/~xleroy/publi/concurrent-gc.ps.gz

      This paper presents the design and implementation of a ``quasi
      real-time'' garbage collector for Concurrent Caml Light, an
      implementation of ML with threads. This two-generation system
      combines a fast, asynchronous copying collector on the young
      generation with a non-disruptive concurrent marking collector on
      the old generation. This design crucially relies on the ML
      compile-time distinction between mutable and immutable
      objects. (BibTeX reference.)

Hope it helps,
d.
-- 
 David.Mentre@irisa.fr -- http://www.irisa.fr/prive/dmentre/
 Opinions expressed here are only mine.

Re: ratio of heap size to live data in Caml GC?

[Chris Quinn]

David Mentré wrote:
> 
> 
> Damien Doligez, Xavier Leroy. "A concurrent, generational garbage
> collector for a multithreaded implementation of ML". Proceedings POPL
> 93.
> http://pauillac.inria.fr/~xleroy/publi/concurrent-gc.ps.gz
> 

While the multiprocessor version went into in Caml Light 0.4 in '93, it does mention in passing the cut-down uniprocessor algorithm as implemented in Ocaml. 
I found no mention of concurrency through the hump link to Caml Light, so now I'm 
wondering whether it still lives on in some other guise.
It would be great to have it as a compilation option to Ocaml.
So how about it...?  :o)

regards,
chris

Re: ratio of heap size to live data in Caml GC?

[Damien Doligez]

>From: Norman Ramsey <nr@eecs.harvard.edu>

>Can anybody tell me what ratio of heap size to live data the OCaml collector
>needs to perform well?  The default ratio appears to be 2.4.  I assume
>this means the collector is a mark-and-sweep collector?

The collector is generational, with the young generation managed by a
stop-and-copy collector, and the old generation by a mark-and-sweep.

The default ratio of heap size to live data for the old heap is
supposed to be about 1.42, assuming that your program uses a constant
amount of live data.

-- Damien