3 ms·

I'm not aware of any other industrial-strength GC using this strategy. Are there any? If not, is there something about OCaml that makes this strategy more suit

by twic 7y ago

I'm not aware of any other industrial-strength GC using this strategy. Are there any? If not, is there something about OCaml that makes this strategy more suitable than it is for other languages? If not, is this a case of this being the best strategy they have the resources to implement, rather than the best possible strategy?

the8472 7y ago
I think the hotspot's CMS old gen allocator used best-fit strategy since its collector didn't compact. But CMS has been deprecated because newer, compacting low pause collectors have taken over its use-cases while being less fragile.
- hinkley 7y ago
  If memory serves, the new one uses an extra object header that points from the old object to the new one during move operations, and any reads of the old object get forwarded to the new one. I'm pretty sure that would have not performed well without the aggressive prediction logic in modern processors. Java 1's object accesses always read through an indirect pointer, but that went away in the name of performance, either when Hotspot was introduced, or on the next round of GC impromevents.
  - _old_dude_ 7y ago
    They are two new GCs Shenandoah and ZGC. Indirect pointers or Brooks pointers has it is called were used in Shenandoah v1 to allow an application thread that perform a read to not move the object during the evacuation phase. This strategy has been removed in Shenandoah v2 to have a better throughput so now both read and write by the application move the object during the evacuation phase. ZGC has never used Brooks pointers.
    - MaxBarraclough 7y ago
      I had to look up 'Brooks pointers'. For anyone else in this position, these two blog posts seem a good place to start: https://rkennke.wordpress.com/2013/10/23/shenandoah-gc-brooks-pointers/ https://rkennke.wordpress.com/2013/10/23/shenandoah-gc-brook... , https://blog.plan99.net/modern-garbage-collection-part-2-1c88847abcfd https://blog.plan99.net/modern-garbage-collection-part-2-1c8...
dfox 7y ago
I feel that it is mostly about nobody else explicitly calling the strategy best-fit. For example BIBOP-derived GCs (which for purposes of this discussion includes BDW GC) are inherently best(-ish)-fit and in fact traditional unix malloc is also mostly best-fit.
rlp 7y ago
It's not exactly an industrial-strength GC, but Nim uses TLSF to reduce fragmentation: http://www.gii.upv.es/tlsf/ http://www.gii.upv.es/tlsf/. I'm not sure how that compares to the strategy in the article, though.

by twic 7y ago

the8472 7y ago

I think the hotspot's CMS old gen allocator used best-fit strategy since its collector didn't compact. But CMS has been deprecated because newer, compacting low pause collectors have taken over its use-cases while being less fragile.

hinkley 7y ago
If memory serves, the new one uses an extra object header that points from the old object to the new one during move operations, and any reads of the old object get forwarded to the new one. I'm pretty sure that would have not performed well without the aggressive prediction logic in modern processors. Java 1's object accesses always read through an indirect pointer, but that went away in the name of performance, either when Hotspot was introduced, or on the next round of GC impromevents.
- _old_dude_ 7y ago
  They are two new GCs Shenandoah and ZGC. Indirect pointers or Brooks pointers has it is called were used in Shenandoah v1 to allow an application thread that perform a read to not move the object during the evacuation phase. This strategy has been removed in Shenandoah v2 to have a better throughput so now both read and write by the application move the object during the evacuation phase. ZGC has never used Brooks pointers.
  - MaxBarraclough 7y ago
    I had to look up 'Brooks pointers'. For anyone else in this position, these two blog posts seem a good place to start: https://rkennke.wordpress.com/2013/10/23/shenandoah-gc-brooks-pointers/ https://rkennke.wordpress.com/2013/10/23/shenandoah-gc-brook... , https://blog.plan99.net/modern-garbage-collection-part-2-1c88847abcfd https://blog.plan99.net/modern-garbage-collection-part-2-1c8...

dfox 7y ago

I feel that it is mostly about nobody else explicitly calling the strategy best-fit. For example BIBOP-derived GCs (which for purposes of this discussion includes BDW GC) are inherently best(-ish)-fit and in fact traditional unix malloc is also mostly best-fit.

rlp 7y ago

It's not exactly an industrial-strength GC, but Nim uses TLSF to reduce fragmentation: http://www.gii.upv.es/tlsf/ http://www.gii.upv.es/tlsf/. I'm not sure how that compares to the strategy in the article, though.