Feature request: support more than 3.584 MB guest RAM (64 bits hosts)

[Patrick Julien]

Even when running the 64-bit version of VirtualBox on a 64 bit version of Windows Vista, it's not possible to allocate more than 3GB of memory to the guess operating system.

[Sander van Leeuwen]

Which method are you using for running the VMs? My VirtualBox.exe has the LARGE_ADDRESS_AWARE flag set and I can use up to the max (3.584 MB). Vista 64 host with 16 GB ram.

[Patrick Julien]

I too, can set the maximum to 3.584MB with a Vista 64 bit host with 32GB of RAM.

However, it's possible for the process to access up to 8TB of virtual address space. Looking at the article that I posted, the testlimit64 tool was able to reserve(not commit) 8TB of virtual memory before running out.

I am trying to find the switch that makes this possible.

[Patrick Julien]

According to the information I have found, IMAGE_FILE_LARGE_ADDRESS_AWARE is all that is needed on a 64-bit host to have access to an 8TB address space on 64 bit.

So why is virtual box limiting the memory limit of a guest to 3.584MB then?

[Sander van Leeuwen]

Because we don't allow more at the moment. That has nothing to do with executable image flags. We will allow for more in the near future.

[Patrick Julien]

Replying to sandervl73:

Because we don't allow more at the moment. That has nothing to do with executable image flags. We will allow for more in the near future.

OK then, sounds good.

[Sander van Leeuwen]

Note that we'll probably not implement this on 32 bits *hosts*.

[Patrick Julien]

Replying to pjulien:

Replying to sandervl73:

Note that we'll probably not implement this on 32 bits *hosts*.

I wouldn't expect you too, this is a feature request for 64 bit hosts only.

[Patrick Julien]

However, I have to ask why did you close this "worksforme"? Shouldn't this ticket be left open and turned into a RFE?

[Sander van Leeuwen]

Of course. Forgot :)

[bqbauer]

2.1.2 says you can now have up to 75% of host memory in new guests. I've tried creating a new 64-bit guest on my 64-bit OpenSolaris host with 8GB memory, and the limit is still 3584. Also tried a larger number using VBoxManage, and it also says the limit is 3584.

[Nikolay Igotti]

More than 3.5G RAM limitation for guests not yet lifted - it's hypervisor limitation. Mentioned feature is only UI enhancement.

[Scott Pakin]

I just want to chime in that enabling 64-bit guests to access more than 3584 MB of memory on a 64-bit (Linux) host containing gobs and gobs of memory is highly desirable to me as well. Any chance the hypervisor limitation will go away sometime soon? (I have no idea how much effort is involved in getting the hypervisor to handle large memory spaces.)

[Frank Mehnert]

Fixed with version 2.2.0, make sure to check the latest release 2.2.2. VirtualBox can now maintain up to 16GB on a 64-bit host.

[Scott Pakin]

Thanks, but why is there any limitation other than what the CPU can address? Can't VirtualBox be modified to support an "infinite" amount of guest RAM?

[Frank Mehnert]

The guest RAM has to be maintained somehow. The larger the amount of guest RAM to maintain, the larger the maintenance structures and the bigger the maintenance overhead. VirtualBox maps all memory of the guest into the VM process. This could be changed but this would induce more overhead and this would require a rewrite of a big part of the VMM. Therefore the limitation for 32-Bit hosts.

[Scott Pakin]

I'm confused by your comment, "Therefore the limitation for 32-Bit hosts", in relation to your prior comment, "VirtualBox can now maintain up to 16GB on a 64-bit host." If I have a 64-bit host with significantly more than 16GB of RAM, then can't VirtualBox let me create a guest with whatever my RAM size is minus the size of the VirtualBox maintenance structures? I don't see why there needs to be an arbitrary limit on guest memory capacity.

[Frank Mehnert]

Sorry for the confusion, I told you the reason for the 64-bit limit with the first two sentences of my last comment. Only the lines starting with VirtualBox maps all ... were the reason for the 32-bit limit.

[sseidel]

I cannot assign more than 8GB to my Linux guest on Windows Server 2008 R2. This is a host with 24GB RAM, 64bit, VirtualBox 4.1.20. Has the guest memory limit been reduced in the more recent versions?

[Frank Mehnert]

What do you mean be 'cannot assign more than 8GB' -- what happens if you try to? Does the GUI not allow you to assign more than 8GB or do you experience a Guru Meditation when the guest starts? The latter is another bug which is reported elsewhere.

[sseidel]

Whenever I assign more than 8GB I can save the settings and start the VM. But the started VM will only receive 8GB and when I re-check the settings page it is reset to 8GB. I also tried setting the RAM size with VBoxManage and by editing the vbox XML file to no avail.

[sseidel]

Ok it works now. I must shut down the VBoxVmService for the change to work. I had always shut down (powered off) the VM itself, but VBoxVmService leaves VBoxSVC running which seems to prevent any changes to this VM configuration.

[Frank Mehnert]

Leaving VBoxSVC running should not be a problem but running VirtualBox together with VBoxVmService might be a problem as we don't support the latter.

[ag987654321]

Just checking in on the latest state of play on Max Ram that can be allocated to Guest (both Guest and Host are running 64b windows) and whether the 16GB limit​https://forums.virtualbox.org/viewtopic.php?f=24&t=41211 is still in place?

[Klaus Espenlaub]

No, this limit has been raised significantly in VirtualBox 4.1. The officially supported maximum is now 1TB (see changelog of 4.1.0), but this only means that we tested it up to this point because we couldn't quickly get access to a system with more memory. The theoretical maximum is 2TB.

Reading the previous comment makes me think that there was no problem with VirtualBox as such, closing.