> Compare this to the API of FreeBSD's kqueue - it is another solution to avoid the linear costs of select()/poll(), but instead of making a syscall for registe

> Compare this to the API of FreeBSD's kqueue - it is another solution to avoid the linear costs of select()/poll(), but instead of making a syscall for registering/unregistering each new FD, kevent() is called with a list of FDs that you want to change. So an event loop using kqueue consists of just one syscall per loop. It would be simple enough to add a version of epoll_ctl that took array arguments, but the existing epoll_ctl makes a lot of sense for the most common use cases. You either know all the descriptors ahead of time or you don't. If you do then you can add them all on startup and never touch it again, and one-time costs usually aren't worth optimizing. If you don't then you're usually modifying them one at a time anyway. And if the syscall takes them one at a time then you don't have to worry about maintaining the state yourself or memory management based on how many descriptors you have or anything like that.