Thousands of open /dev/zero

[joshbeard]

I'm running VirtualBox 4.2.4-81684 on Ubuntu 12.04 with FreeBSD 9.1 guests and Ubuntu 12.04 guests, both 64-bit.

I've noticed thousands of open /dev/zero by VBoxHeadless, which grows fairly rapidly:

sudo lsof|grep -e "VBoxHead.*zero"|wc -l
6448

That's with a host uptime of 32 minutes with 4 guests - two FreeBSD 9.1 and two Ubuntu 12.04.

I have two nearly identical host machines with the same sort of guests - about half FreeBSD 9.1 and half Ubuntu 12.04 and both seem to have this issue. One seems slightly worse, but that may just be due to the busier guests.

Unfortunately, I don't have a previous version to compare to, as VirtualBox on these hosts is a new experiment, so it's only been installed for a week or two.

I haven't seen any serious consequences from this, but I haven't had a lot of uptime on the host or guests.

https://www.virtualbox.org/ticket/8806 (closed; from last year) looks similar.

Is this expected behavior? I'd be happy to provide any other details as needed.

Attached is an aggregated log from one of the hosts with four guests.

[Frank Mehnert]

I don't think this is a problem at all. The /dev/zero regions you mention are just mmap regions for anonymous memory, that's the way VirtualBox allocates memory for his guests. And the amount of memory for your VMs can of course grow as long as your guests didn't touch the complete memory. Note that VirtualBox does lazy guest memory allocation. As long as a guest does not touch a physical memory page, the memory is not allocated on the host. This works pretty nice with Linux guests but, for instance, Windows guests require the complete memory during boot.

That said it should be completely normal that your guests require only a part of the RAM you assigned to them (5GB, 7GB, 3GB, 4GB) for the first time. The memory allocation will continue to grow -- up to the amount of memory you assigned plus some overhead VirtualBox needs to maintain the guests.

Therefore I doubt this is a bug at all.