In a different article, he said he had issues with the ext4 maintainer who was acting high and mighty about C despite being responsible for a number of huge CVEs from code that he wrote.

That being said, I don't really see the benefit of rewriting modules in Rust.

Technically, it's still not a 1:1 replacement because Rust will many times not generate the exact same machine code as C, which does result in a small loss of speed (and in some small cases, vice versa).

It's acceptable for anything new, but unless there's a notoriously painful part of the kernel, there's no pont in redoing existing parts and even core userspace binaries.

C quite literally makes you manipulate memory like a caveman holding a machine gun, but that's important because it's exactly what the machine is doing, which is required when you need to maximize efficiency. In Rust, you'd have to abstract some of that to the compiler to handle your logic which doesn't match what a machine is doing. There is no such thing as "borrowing" and "ownership" in machine code.