> To add to this, unless you are compiling your kernel specifically for your machine, your kernel is going to be a bloated compromise of the set of drivers that your system is most likely to see. That means that you will have dozens, if not hundreds of drivers compiled into your kernel which will never need to be used.
These days most Linux distros build pretty much any driver as a module that can be built as one. Boot-critical modules (like NVMe drivers) are included in the initramfs so they're available before the disk is mounted.
I agree that Linux is still larger than a microkernel, but very few users have a bloated kernel in RAM due to lack of customizations.
Which distribution kernel specifically? If you're running on a VM, you get a cloud kernel in many distros, which is very stripped down for example. On other systems - the modules part still applies - how much are you actually trying to save on the kernel RAM usage? I've got a very average kernel from a distro at 20MB and initramfs at 35MB. They could be twice the size and I would never notice. I appreciate they could be smaller, but we're running a minimum of 8GB these days.
The rest is in the modules and they're not loaded unless they're actually used. The parts baked into the kernel are mostly display, storage and various buses, which you would need to have immediately loaded in Hurd anyway to load the rest of services.
It would be great if they didn't of course. But historically, I've never had issues with kernel patches. In large enough deployments you get everything rolled ahead of the publication, or care enough to run grsec and custom profiles. In smaller ones, the kernel side is far down the list of things you care about.
So yeah, in the ideal world, let's have everything isolated. For now it would be great if they worked at all.
Also... There's a bit of practical limitation to how useful the isolation is. It's cool that the FS module runs in the userspace. But if it can create a suid-equivalent file and point an arbitrary config at it, you're not gaining much.
These days most Linux distros build pretty much any driver as a module that can be built as one. Boot-critical modules (like NVMe drivers) are included in the initramfs so they're available before the disk is mounted.
I agree that Linux is still larger than a microkernel, but very few users have a bloated kernel in RAM due to lack of customizations.