Overwriting closures without indirections

[Simon Marlow]

On 26/03/2010 17:50, Chris Nicholls wrote:
>     Sure.  Inside the RTS you would call recordMutableCap() after
>     checking which generation the closure belongs to.  I've just cleaned
>     this up and added recordMutated(Capability *, StgClosure *) which
>     does the generation check too, but that's part of some other work I
>     haven't committed yet.
>
>
> Thanks! That works fine now, though it has a pretty negative effect on
> performance...
>
>     I'd be interested to hear how you get on with closure overwriting:
>     typically approaches like that have not been terribly successful in
>     the past, and we tend to favour just allocating new objects these
>     days because it's simpler.  Also overwriting interacts badly with
>     generational GC, as you've discovered.  I suspect that
>     update-in-place and generational GC might be mutually exclusive.
>
>
> Do you know of any work on GGC/update-in-place that you could point me
> to? Or, more generally, any papers on updating in-place are always
> interesting.

Typically when using generational GC with a language that does a lot of 
mutation, you want to use a cheaper write barrier - this is what the 
Java folks focus on.  In GHC, because mutation is rare, we opted for a 
relatively more expensive, but more accurate, write barrier.  If you're 
doing a lot of overwriting of old closures, that might tip the balance 
towards a cheaper but less accurate write barrier.

Look at papers on write barriers, e.g.

@inproceedings{hosk92,
author = {Antony L. Hosking and J. Eliot B. Moss and Darko Stefanovi\'{c}},
title = "A Comparative Performance Evaluation of Write Barrier 
Implementations",
crossref = "OOPSLA92",
pages = "92--109",
URL = "ftp://ftp.cs.umass.edu/pub/osl/papers/oopsla92.ps.Z"
}

@inproceedings{blac04b,
   author =	 {Stephen M. Blackburn and Tony Hosking},
   title =	 {Barriers: Friend or Foe?},
   crossref =	 {ISMM04},
   pages =	 {143--151},
   doi =		 {10.1145/1029873.1029891}
}

@techreport{zorn90b,
author = "Zorn, Benjamin",
title = "Barrier Methods for Garbage Collection",
institution = "University of Colorado, Boulder",
year = 1990,
number = "CU-CS-494-90",
URL = "ftp://ftp.cs.colorado.edu/pub/cs/techreports/zorn/CU-CS-494-90.ps.Z",
month = Nov,
}

@inproceedings{wils92c,
title = "Uniprocessor Garbage Collection Techniques",
author = "Paul R. Wilson",
address = "University of Texas, USA",
crossref = "IWMM92",
URL = "ftp://ftp.cs.utexas.edu/pub/garbage/gcsurvey.ps",
}

Cheers,
	Simon