mps VS mark-sweep

I have a library which has an extremely slow free, around 2m for large files, because of unnaturally scattered allocation patterns, but this old conservative GC didn't help at all. It was about 40% slower with libgc. mimalloc was a bit better. Best would be a properly fast GC, like mps https://github.com/Ravenbrook/mps, but this would be too much work.

The first thing you should look at is MPS (see https://github.com/Ravenbrook/mps and https://www.ravenbrook.com/project/mps/). It's open source, professionally maintained and very powerful, and it was used e.g. in Dylan and LispWorks.

I wonder how the MMTK compares to the venerable Ravenbrook MPS https://www.ravenbrook.com/project/mps/ which originated in Harlequin’s programming language implementations, particularly Dylan.

I am trying to implement garbage collection for my language because I want memory management for arrays/lists and strings. I am looking through LLVM's garbage collection page but the documentation isn't great. Are there any other resources that offer more concrete steps to implement garbage collection? Would it be wise to circumvent LLVM all together for garbage collection and only use something like the Memory Pool System? Thanks!

This post seems related to the authors of MPS (1) that seems to be a general garbage-collector to use with various languages.

Many GC'd languages really didn't bother with stack-allocating variable-size entities, and regardless of if they did then _precicely_ scanning the stack would be complicated without compiler help.

If the compiler doesn't leave any info to the GC, then it can't know if it's scanning a pointer or a float and if your GC strategy relies on compacting memory (ie moving objects) then trying to guess between a float or a pointer can become fatal.

(1) https://github.com/Ravenbrook/mps

Never forget:

https://journal.stuffwithstuff.com/2013/12/08/babys-first-ga...

> Let me stress here that while this collector is simple, it isn’t a toy.

> There are a ton of optimizations you can build on top of this—in GCs and programming languages, optimization is 90% of the effort—but the core code here is a legitimate real GC.

> It’s very similar to the collectors that were in Ruby and Lua until recently.

> You can ship production code that uses something exactly like this.

> Now go build something awesome!

Bob Nystrom also has a blog, and his articles are really well written (see his post on Pratt parsers / garbage collectors). I'd also recommend going through the source code for Wren, it shares a lot of code with Lox. Despite the deceptive simplicity of the implementation, it (like Lox) is incredibly fast - it's a great way to learn how to build production grade compilers in general.

Bob Nystrom (of Game Programming Patterns, Crafting Interpreters, and dartfmt fame) also wrote a tutorial[1], of a precise as opposed to a conservative garbage collector.

Regarding register scanning, Andreas Kling has made (or at least quoted) an amusing observation[2] that your C runtime already has a primitive to dump all callee-save registers onto the stack: setjmp(). So all you have to do to scan registers is to put a jmp_buf onto the stack, setjmp() to it, then scan the stack normally starting from its address.

[1] https://journal.stuffwithstuff.com/2013/12/08/babys-first-ga...

[2] https://youtu.be/IzB6iTeo8kk

- http://journal.stuffwithstuff.com/2013/12/08/babys-first-gar...

Might not be that hard: https://journal.stuffwithstuff.com/2013/12/08/babys-first-garbage-collector/

To better understand garbage collection, nothing better than implementation. This article is such a joy to read:

https://journal.stuffwithstuff.com/2013/12/08/babys-first-ga...