Strange ARC/Swap/CPU on yesterday's -CURRENT

[Mark Johnston]

On Fri, Apr 06, 2018 at 12:47:14AM +0000, Justin Hibbits wrote:
> My powerpc64 embedded machine is virtually unusable since these vm changes.
> I tried setting vfs.zfs.arc_free_target as suggested, and that didn't help
> at all. Eventually the machine hangs and just gets stuck in vmdaemon, with
> many processes in wait channel btalloc.

You don't really have the same symptoms that Don is reporting.
Threads being stuck in btalloc implies a KVA shortage. So:
- What do you mean by "stuck in vmdaemon"?
- Which commits specifically cause problems? Does reverting r329882 fix the
  hang?
- Can you break to DDB and get "show page" output when the hang occurs?
- What is the system doing to cause the hang to occur?