YJIT tech lead here.

On the flip side, YJIT is probably one of the most memory-efficient JIT compilers out there (for any language). I say this having spoken to other JIT implementers.

We've worked really hard to reduce the memory overhead and at Shopify it's now down to less than 10% in our flagship production deployment.

Regardless, if memory usage is a legitimate concern for you, you can very easily remove the Rails initializer that turns on YJIT. You can choose between memory usage and response time. The choice is yours.