[kbumsik]

I took a OS class with Xv6. As a Linux kernel dev I can tell you Xv6 is great for teaching OS than Linux.

1. I remember the first assignment if the class was adding a new syscall. It was quite trivial task for Xv6 because Xv6 syscall layers is thin and it implements only < 30 simple syscalls. Imagine you are going to add a Linux syscall out of > 300 syscalls.

2. Production grade kernels like Linux is very hard to read for students because they support additional configurations which, for example, are wrapped by a lot of #ifdef macros. Also there are overwhelming number of Arch/hardware support that are not needed for teaching.