The original question had lots of speculation but it is all much simpler. See my own answer and this reported bug.
I leave the original question in case someone is having similar issues and helps them find this issue.
I have been working with a VirtualBox Ubuntu 14.04 VM hosted on Windows 7. The machine works ok but quite often the VirtualBox process suddenly starts to claim huge amounts of memory for no apparent reason. I have not been able to reproduce the error in a consistent manner, but it happens every few hours, or sometimes just after a few minutes. Here are some more details:
- I am using current VirtualBox version (4.3.16) but I have also tried older (4.3.12) and beta (4.3.17). I have the problem with all of them.
- I have tried assigning different amounts of RAM to the VM. I have the problems with all of them. I have tried assigning 512MB, 768MB and 1GB. My host has 4GB in total.
- The guest OS system monitor does not show significant changes in the amount of memory used.
- This can happen when I am working with the machine or when it is idle for hours. I can't find a single cause. Sometimes it happens when I open the Ubuntu Software Center, but I have used it many times without issues. Sometimes it happens when I just boot up the machine and don't do anything with it at all. Sometimes it happens after an hour developing with Eclipse. Sometimes it doesn't happen in the whole day.
- Sometimes the memory claimed by the VirtualBox process roughly doubles, all of the sudden. Usually I start with around 700 MB used, and suddenly it uses about 1.4 GB. Other times it grows slowly but steadly, and after a minute or so the process has more than 2 GB of memory and the system becomes really slow.
- I have tried different VM settings, different amounts of video memory, etc.
- I have created several VM to see if there's something wrong with my main one. It can happen before and after installing Ubuntu updates in all the 3 VMs I tried (different software installed in all of them).
Am I the only one with this problem?