exec without replacing current process, posix_spawn kernel implementation

Question

Although the kernel marks pages (and page tables) as copy on write to make the fork syscall work efficiently, the creation and tear-down of page tables and related structures is still an expensive task.

Thus I wonder why the linux community has never managed to implement posix_spawn as a real kernel syscall that just spawns a new process, eliminating the need to call fork beforehand. Instead, posix_spawn is just a poor glibc wrapper around fork and exec.

The performance gains would be significantly for workloads that have to spawn thousands of new processes every second. The latency for launching new processes would be improved as well.

Answer 1

That's basically what posix_spawn is for. It is also a more flexible API. The real bug is that the Linux exec man page still doesn't include a cross-reference for it.