System low on memory+swap shortage message

Hi.

One of my DragonFly box keeps eating memory and eventually it starts
killing some random processes, and I need to reboot it every two
weeks because of this.  This is a swap-less system running AMD C60
and 8G bytes of RAM, which is much more than the sum of the virtual
memory of all processes, which is less than 1G bytes.  I had no problem
before upgrading from 4.0-RELEASE to 4.2.  The kernel has been built
from source as of 5f93900a, and the kernel config file X86_64_GENERIC.
Do I have anywhere else to look at?

Best Regards,
YONETANI Tomokazu.