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

On Fri, Apr 6, 2018 at 10:08 AM, Mark Johnston <markj_at_freebsd.org> wrote:
> 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.

Okay.  I latched onto the thread because it seemed similar.

> Threads being stuck in btalloc implies a KVA shortage. So:
> - What do you mean by "stuck in vmdaemon"?

The machine hangs, and my ssh sessions get killed.  I can't do
anything at the console except break into kdb.  When I do, the running
thread is always vmdaemon.

> - Which commits specifically cause problems? Does reverting r329882 fix the
>   hang?

I'll try reverting it and report back.  Thankfully I can buildkernel
successfully on the machine before it hangs.  Can't do more than that,
though.

> - Can you break to DDB and get "show page" output when the hang occurs?

I'll reproduce and get numbers today, but I do know the free_count was
high (6 digits), much higher than the free_min. when I checked
yesterday.  I'm surprised it's running out of KVA, I've never had the
problem before with the same workloads, and has ~7.5GB KVA (almost the
same size as the total RAM in the machine).

> - What is the system doing to cause the hang to occur?

Just a simple buildworld with 2 or 3 jobs (tried both).  It's 100% reproducible.

- Justin