You're assuming RC requires atomics. Just like GCs have been improving so have RCs. There are several designs for modern non-atomic RCs with various solutions f

You're assuming RC requires atomics. Just like GCs have been improving so have RCs. There are several designs for modern non-atomic RCs with various solutions for passing data between threads. It generally improves performance significantly better than atomic RCs, for the cache reasons you point out. Though yes reference counting does increase the size of small objects. I find the performance edge depends on the use case. In some scenarios tracing GCs can be faster than non-atomic RCs, but sometimes they're slower. Sometimes I swap between the two just to see. Generally though RCs tend to use less RAM which can be very valuable.