Reworking Memory Management in CRuby: A Practitioner Report

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" summary

Reports integrating MMTk into CRuby by refactoring a non‑modular GC into a pluggable interface, implementing four stages: no-GC, non‑moving, copying (IMMIX/sticky IMMIX) and generational collection. Key engineering fixes are identifying PPP (potential pinning parents) to pin before scavenging, handling WB-unprotected legacy APIs by conservatively treating them as updated, and eliminating widespread finalizers by moving string/array/regexp payloads from malloc into the GC heap. The result runs Rails, upstreams a modular API (CRuby 3.4) and exposes remaining bottlenecks in finalization and parallel malloc.

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" chapters (12)

1. 0:00Introduction
2. 1:05CRuby GC history
3. 2:52Motivation for MMTK
4. 3:35Challenges with MMTK
5. 4:40No GC and allocation
6. 5:02Non-copying GC and stopping
7. 5:44Copying GC and forwarding
8. 9:00Generational GC and barriers
9. 10:45Performance bottlenecks
10. 13:38Refactoring finalizers
11. 15:02Lessons and future
12. 16:06Q&A

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