Pre-allocating RAM on a Virtualbox guest

One of the problems with guest VMs in Virtualbox is that RAM is dynamically allocated by the host as the guest uses an increasing quantity of memory.  This is fine if you run many VMs which do not always need all the memory allocated to them at once; but you will find it inconvenient if you really need to allocate specific (read: large) amounts of memory to a VM.  This is especially true when running a guest on a host like windows 7, where superfetch has already allocated chunks of memory to different applications.  When the guest requests more memory, the OS does not give it, because it is only available to other programs which may not necessarily need it.

-- The solution then...

Forcing VirtualBox to "grab" all of the guest's memory at startup is possible.  This will attempt to allocate the entire guest memory from the host.  If that memory isn't really free, then the guest will not start at all.

There is a boolean flag which can be set as follows:

VBoxManage setextradata <VM NAME> VBoxInternal/RamPreAlloc 1

That's all.

Documentation: Unfortunately there is very poor documentation on the "VBoxInternal" keyset; probably because it is mainly used for development purposes and not necessarily "real" day-to-day use.  Consider this then, a hack.

The possible variables that can be set using VBoxInternal seem to be defined in the following C++ header file:

http://www.virtualbox.org/svn/vbox/trunk/src/VBox/VMM/include/PGMInternal.h

Here is another interesting file worth reading:

http://www.virtualbox.org/svn/vbox/trunk/include/VBox/err.h

I would be very careful with attempting to set any of these without a good understanding of the VirtualBox codebase.