More Ram for Guest on Linix Mint Host

[JowivK]

Hi,
I am running Virtualbox 5.2.10 as available in the Linux Mint App Store. I want to run a Win7 client, which needs a lot of RAM.
In my desktop computer, I have 12 GB available, which is recognized by Mint System Info.
However, in the setup menu for the guest the maximum RAM I can make available is 3584 MB. Why? Where does this Value come from? How can I get Virtualbox to recognize the real environment?
I have tried:
Uninstall VB and Install from a downloaded DEB. does not work because some depenency is missing.
dpkg-reconfigure virtualbox-dkms which worked and sudo dpkg-reconfigure virtualbox which did not work.
So I reinstalled from the appsore in order to have at least something.
But the restriction to 3584 is still there.
What now?

[mpack]

The most likely reason for the RAM limit is that the host OS and/or guest OS is 32bit.

Provide a VM log file. With the VM fully shut down, right click it in the GUI. Select "Show Log" and save "VBox.log" (no other file) to a zip file. Attach the zip here.

[JowivK]

Well, your suspicion is correct. Both the host (the real machine) and the Virtual Win7 Machine are only 32 bit. That's all I have.
So there is no way to go beyond that RAM barrier on 32bit level? Or is there some workaround?
Do you need the logfile beyond this?
Thanks!

[mpack]

So there is no way to go beyond that RAM barrier on 32bit level? Or is there some workaround?

No, there is no way around it.

A VM is hardware simulation created by an application running on the host. Like any app, almost all resources are requested from the host OS. The host app can't make anything available to the guest that isn't available to the host.

[JowivK]

Thanks for your response Of course I understand the logic. But I am not requesting a different processor. I only want to use the RAM, which is definitely available. Or can a 32bit processor not really make use of the additional RAM I installed? Please pardon my ignorance…

[JowivK]

Hi again,
now Ive a bit of reading and I understand that 32bit processors cannot handle more than 4GB Ram - in principle. However, there seems to be the PAE technology that does provide a workaround for the operating system. PAE is enabled in my BIOS, so the Linux Mint host should be able to address up to 64GB. In the Virtualbox setup I also see the PAE option, which I can activate. But that does not take away the RAM restriction. Is that because WIN7 does not use PAE? Or oes my virtual PAE use the available RAM better if I activate the PAE switch? Or is that precluded by the 3584 setup barrier anyway?
Sorry, I never really worried about hardware issues, seems I should have....
Thanks again
Jowi

[mpack]

Windows 7 does not use PAE, so no amount of messing will allow a 32bit install of Win7 to use more than 4GB.

The only way to get a Win7 VM to use more than 4GB is to install Win7-64bit on a 64bit host. AFAIK PAE enabled on the host will not allow a Win7-64bit guest to have more than 4GB either.

[socratis]

AFAIK PAE enabled on the host will not allow a Win7-64bit guest to have more than 4GB either.

Isn't that simply because the per-process RAM cannot exceed the 4 GB limit? Isn't PAE only for the kernel to be able to address/see more than 4 GB, but not the per-process one? Or do I have it wrong?

[mpack]

I can't speak with certainty about the memory allocation strategies of Linux apps on Linux hosts. If the model was similar to Windows hosts (which I assume will be the case) then yes, single allocations of RAM from a 32bit allocator cannot be larger than 4GB. I.e. RAM is allocated using a "flat" memory model, subject to the maximum segment size 2^32 (4G) bytes.

A single app might be able to allocate more than one global memory segment, but it would be very impractical. Each segment would be its own address space, so data could only be copied from one to another with a great deal of care. My understanding is that VirtualBox requires a single flat allocation for the VM, though I've not dug into how ballooning works: I assume the flat allocation is paged, pages will be mapped to physical RAM on a memory exception (I'm not talking about disk paged RAM).

[JowivK]

Well, you guys are taking the discussion to another level. All I understand is that I will have to live with my virtual Win7 running on slightly less that 4GB ram. The lesson I have learnt is that it will not make sense to purchase more RAM, which saves me the investment.
But I have switched on the PAE option in the VB setup for this machine and it does seem to run a bit better. In addition I increased the "virtual ram" in Windows (funny, is that "virtual to the square" then, the whole Windows is virtual… ), ie. the size of the swapfile. It also improved my perceived performance a little. With that, having a pretty well running system I will leave it. Dishing out more money for a better processor will be an option for the future.
Thanks again for your help and patience!