freebsd stable - Aug 2019 - Memory management changes after kernel update on 6-Aug

Since I updated my 12.0-STABLE system on 6-Aug I have been seeing issues
resuming my Win7 VM on VirtualBox. My prior kernel was built on 24-Jul. If
there is not sufficient memory available to reload the system (4 Meg.), the
resume fails with a message that memory was exhausted. Usually I can try
resuming again and it will work. Sometimes I get the error two or three
times before the system resumes.

Since I have not touched VirtualBox other than to rebuild the kmod after
the kernel build, it looks like something in the OS triggered this. Since
the system frees up some memory each time so that the VM eventually
resumes, it looks like the memory request is made to the OS, but VB is not
waiting or not enough memory is freed to allow the VB to complete the
resume.

Any clue what might have changed over those 13 days? I am running GENERIC
except that I run the 4BSD scheduler.
--
Kevin Oberman, Part time kid herder and retired Network Engineer
E-mail: rkoberman at gmail.com
PGP Fingerprint: D03FB98AFA78E3B78C1694B318AB39EF1B055683

On Fri, Aug 09, 2019 at 11:09:24AM -0700, Kevin Oberman
wrote:
> Since I updated my 12.0-STABLE system on 6-Aug I have been seeing issues
> resuming my Win7 VM on VirtualBox. My prior kernel was built on 24-Jul. If
> there is not sufficient memory available to reload the system (4 Meg.), the
Where does this number come from?  What memory usage stats do you see in
top(1) when the error occurs?
> resume fails with a message that memory was exhausted. Usually I can try
> resuming again and it will work. Sometimes I get the error two or three
> times before the system resumes.
What exactly is the error message?
> Since I have not touched VirtualBox other than to rebuild the kmod after
> the kernel build, it looks like something in the OS triggered this. Since
> the system frees up some memory each time so that the VM eventually
> resumes, it looks like the memory request is made to the OS, but VB is not
> waiting or not enough memory is freed to allow the VB to complete the
> resume.
> 
> Any clue what might have changed over those 13 days? I am running GENERIC
> except that I run the 4BSD scheduler.
Possible culprits are r350374 and r350375, but I can't really see how.