I tend to think that Linus was right and microkernels are in reality a bad design.
Case in point: Minix 1.5 (which I hacked on before Linux came along).
Minix 1.5 has two "daemons" called mm and fs which run the memory management and filesystem respectively. Now consider process creation and loading (fork and exec). Creating and loading a process intimately involves both mm and fs, so in Minix 1.5 the program sends a message to mm [IIRC] which sends a message to fs and both daemons have to coordinate with each other. This makes it a lot more complex than if there was just one daemon (ie. a monolithic kernel).
Another example is that if mm or fs die, your OS dies. You can't restart one or the other because there's so much process state spread across the two daemons. So the claim that microkernels are more resilient because you can restart daemons seems to be nonsense (but I should say that QNX can apparently restart some(?) components transparently).
Nevertheless it's not all roses for monolithic kernels either. There's no process protection and they're usually written in deeply unsafe languages like C. Exokernels might be the answer to this because they have monolithic qualities (fast calls and shared state) but keep virtually everything running in userspace so you can use sane, safe programming techniques.
Case in point: Minix 1.5 (which I hacked on before Linux came along).
Minix 1.5 has two "daemons" called mm and fs which run the memory management and filesystem respectively. Now consider process creation and loading (fork and exec). Creating and loading a process intimately involves both mm and fs, so in Minix 1.5 the program sends a message to mm [IIRC] which sends a message to fs and both daemons have to coordinate with each other. This makes it a lot more complex than if there was just one daemon (ie. a monolithic kernel).
Another example is that if mm or fs die, your OS dies. You can't restart one or the other because there's so much process state spread across the two daemons. So the claim that microkernels are more resilient because you can restart daemons seems to be nonsense (but I should say that QNX can apparently restart some(?) components transparently).
Nevertheless it's not all roses for monolithic kernels either. There's no process protection and they're usually written in deeply unsafe languages like C. Exokernels might be the answer to this because they have monolithic qualities (fast calls and shared state) but keep virtually everything running in userspace so you can use sane, safe programming techniques.