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I was in his FOSDEM GC talk about whippet and found out that he doesn't know anything about the really good GC strategies. He only knows and implemented about d

by rurban 2y ago

I was in his FOSDEM GC talk about whippet and found out that he doesn't know anything about the really good GC strategies. He only knows and implemented about dirt-slow mark-sweep, which is only needed for pointer stability from C callbacks, and then inmix which is the slow variant of a copying GC, just without the double heap requirement. But a conventional Cheney copying collector with 1-2 generations for minor sweeps is far better than those. Until he adds a proper GC to whippet I don't trust anything he says about GC's. He even has the luxury for a precise GC because scheme carries the types along with its values. And he doesn't know about colored pointers, using 2-5 bits for the GC state, nor nan-tagging. Probably neither about forwarding pointers.

naasking 2y ago
Immix is not a slow variant of a copying GC. It's pretty state of the art for copying GCs in fact, do claiming he doesn't know anything and hasn't implemented a "proper" GC is just incorrect.
NeutralForest 2y ago
I was at his talk as well and I found it interesting. Maybe you could open an issue in the Whippet repo to point at possible improvements?
milesrout 2y ago
You can see from his blog archives (and this post) that the author is well aware of GC strategies other than mark-sweep including Cheney copying. He has posted about conservative GC (contrary to your implication he has only implemented precise GC). Maybe "forwarding pointers" is overloaded but given he has a post about a semispace collectors which uses something he refers to as forwarding pointers I don't see how he can be said not to know about it. He also has posts referring to NaN-tagging and pointer tagging unless my memory betrays me. https://wingolog.org/tags/garbage%20collection https://wingolog.org/tags/garbage%20collection
- rurban 2y ago
  Well, that would be good, because when we asked him in the Q&A at FOSDEM he had no idea about colored pointers and did not mention semi-space collectors at all, and had no plan to add it. I initially thought about using whippet, but I will stay clear and rather use MPS https://memory-pool-system.readthedocs.io/en/latest/ https://memory-pool-system.readthedocs.io/en/latest/
  - milesrout 2y ago
    That is baffling because in July he wrote "One of Whippet’s collectors is a semi-space collector." (https://wingolog.org/archives/2024/07/10/copying-collectors-with-block-structured-heaps-are-unreliable https://wingolog.org/archives/2024/07/10/copying-collectors-...) I didn't attend the talk and don't know him at all so wouldn't want to speak for him but from personal experience one can find oneself saying some bizarre things under stress/pressure when giving a presentation in front of lots of people. And then one looks back and goes: "why did I say that??"

by rurban 2y ago

naasking 2y ago

Immix is not a slow variant of a copying GC. It's pretty state of the art for copying GCs in fact, do claiming he doesn't know anything and hasn't implemented a "proper" GC is just incorrect.

NeutralForest 2y ago

I was at his talk as well and I found it interesting. Maybe you could open an issue in the Whippet repo to point at possible improvements?

milesrout 2y ago

You can see from his blog archives (and this post) that the author is well aware of GC strategies other than mark-sweep including Cheney copying. He has posted about conservative GC (contrary to your implication he has only implemented precise GC). Maybe "forwarding pointers" is overloaded but given he has a post about a semispace collectors which uses something he refers to as forwarding pointers I don't see how he can be said not to know about it. He also has posts referring to NaN-tagging and pointer tagging unless my memory betrays me. https://wingolog.org/tags/garbage%20collection https://wingolog.org/tags/garbage%20collection

rurban 2y ago
Well, that would be good, because when we asked him in the Q&A at FOSDEM he had no idea about colored pointers and did not mention semi-space collectors at all, and had no plan to add it. I initially thought about using whippet, but I will stay clear and rather use MPS https://memory-pool-system.readthedocs.io/en/latest/ https://memory-pool-system.readthedocs.io/en/latest/
- milesrout 2y ago
  That is baffling because in July he wrote "One of Whippet’s collectors is a semi-space collector." (https://wingolog.org/archives/2024/07/10/copying-collectors-with-block-structured-heaps-are-unreliable https://wingolog.org/archives/2024/07/10/copying-collectors-...) I didn't attend the talk and don't know him at all so wouldn't want to speak for him but from personal experience one can find oneself saying some bizarre things under stress/pressure when giving a presentation in front of lots of people. And then one looks back and goes: "why did I say that??"