ZFS stability in netbsd-11 is great

[Greg Troxel <gdt%lexort.com@localhost>]

I had been having ZFS lockups for a long time, and there are a lot of
fixes also pulled up to netbsd-11 (and in 11.0).  Mostly it's about
properly writing/freeing dirty mmap'd pages; before they weren't and it
led to lockups.

I have not been seeing problems, but still wondered.  Recently, I've
been suffering from the "modesetting X11 glx wired pages leak", and even
when the machine was unusuably slow, it did not crash/lockup.  The
silver lining was a great ZFS stress test, and it passed.

So personally I consider the ZFS deadlocks all fixed.  As always,
contrary evidence welcome.

(The fixes are not on netbsd-10.   If you are running ZFS, run do not
walk to the nearest 11 upgrade.  But seriously, take the time to do it
right, but find that time.)