In addition to the Ruby under a Microscope (linked elsewhere), a lot of talks from Aaron Patterson (Tenderlove) are enlightening in this regard. I've learned a lot from them, and they also provided the inspiration to keep digging. Some highlights:
Memory:
- https://www.youtube.com/watch?v=ZfgxvNUfQdU&t=3s&ab_channel=...
- https://www.youtube.com/watch?v=1F3gXYhQsAY&ab_channel=Confr...
JIT and the Ruby VM:
- https://www.youtube.com/watch?v=FCjwSOlHqbY&ab_channel=hexde...
- https://www.youtube.com/watch?v=5QgQicKHmeU&ab_channel=RubyC...
And loads of others.