10.0 interaction with vmware

[Paul Koch]

Curious if anyone has an understanding of what actually goes on
with VMWare memory control of a FreeBSD 10 guest when open-vm-tools
is installed and how it could affect performance.

Our typical customer environment is a largish VMWare server with
an appropriate amount of RAM allocated to the guest, which currently
runs FreeBSD 10.0p7 + our software, UFS root, and data stored on a
ZFS partition.  Our software mmaps large database files, does rather
largish data collection (ping, snmp, netflow, syslog, etc) and
mostly cruises along, but performance drops off a cliff in low
memory situations.

We don't install open-vm-tools at the moment, therefore we have a known
amount of memory to work with (ie. what the customer initially 
configured the guest for), but our customers (or in particular, their
VM guys) would really like vmware tools or open-vm-tools by default.

From what we gather, many sites choose to "over provision" the memory
in the VM setups, and when memory gets low, the host takes back 
some of the RAM allocated to the guest.

How does this work actually work ?  Does it only take back what
FreeBSD considers to be "free" memory or can the host start taking
back "inactive", "wired", "zfs arc" memory ?  We tend to rely on
stuff being in inactive and zfs arc.  If we start swapping, we
are dead.

Also, is there much of a performance hit if the host steals back
free memory, and then gives it back ?  We'd assume all memory
the host gives to the guest is pre-bzero'ed so the FreeBSD wouldn't
need to also bzero it.

	Paul.
-- 
Paul Koch | Founder, CEO
AKIPS Network Monitor
http://www.akips.com
Brisbane, Australia