Pulling slabs out of struct page

>It depends on what we call successful and operating system, doesn't it.

Don't forget various RTOSes and other embedded stuff -- C (and to a lesser extent, C++) overwhelmingly dominate.

Rust has some promise to supplant things there, but the amount of unsafe boilerplate needed to drive a modern MCU is staggering. Some of that can be automated away but it results in a much steeper curve to being productive.