Reworking Memory Management in CRuby

Summary

This blog post was adapted from our paper and talk at the International Symposium on Memory Management 2025. Click here to read the paper This browser does not support displaying PDFs. Please download the PDF to view it: Download PDF. We would first like to acknowledge the late Chris Seaton, who initiated our collaboration with the Australian National University on this project. We are thankful for his contribution, vision, and leadership. Without him, none of this would have been possible. Background The Australian National University (ANU) and Shopify are collaborating on integrating the Memory Management Toolkit (MMTk) with Ruby. We are supporting the project and working alongside ANU researchers to explore how to build a next-generation garbage collector for Ruby. If you’re not familiar with MMTk, it offers a highly modular, VM-neutral framework for rapidly building high-performance garbage collectors. Once a language plugs into MMTk, it can leverage a wide range of built-in garbage collection algorithms, ranging from canonical collectors such as NoGC, Mark and Sweep, and Immix to more performant collectors such as Generational Immix and Sticky Immix. Many of these algorithms are considerably more sophisticated than the Mark and Sweep algorithm used in Ruby and have the potential to deliver significant performance gains. There are currently two implementations of MMTk in Ruby: one is maintained by the MMTk team and is a fork of Ruby (in the mmtk/ruby and mmtk/mmtk-ruby repositories), the other lives inside Ruby using the modular GC framework (in the ruby/mmtk repository). You might be wondering, why are there two implementations? The MMTk team’s implementation is much more advanced, with around 5 years of development. They continue to use it to experiment and develop new techniques to further leverage MMTk’s powers and improve performance. The implementation upstreamed to Ruby uses the modular GC framework and is designed to be part of an ecosystem of garbage co...