[Feature]: Dynamic RAM allocation for Windows VM

[MopigamesYT]

Is your proposal related to a problem?

I'm always frustrated when the Windows VM uses all the allocated RAM even when it doesn't need it. For example, if I allocate 4GB of RAM to the VM, it uses all 4GB even if Windows only needs 2GB, wasting resources that could be used by other processes on my host system.

Describe the solution you'd like.

I'd like the RAM_SIZE parameter to act as a maximum limit rather than a fixed allocation. The VM should only use the amount of RAM it actually needs, up to the RAM_SIZE limit. Unused RAM should be released back to the host system. For instance, if RAM_SIZE is set to 4GB and Windows only needs 2GB, it should only use 2GB, leaving the other 2GB available for the host system.

Describe alternatives you've considered.

1. Manually adjusting RAM_SIZE: This requires constant monitoring and container restarts, which is inconvenient.
2. Using a smaller fixed RAM size: This could lead to performance issues when the VM occasionally needs more RAM.

Additional context

This feature would allow users to set a higher RAM_SIZE for peak usage without constantly reserving that amount, leading to more efficient use of system resources and improved overall system performance. It might involve changes to how QEMU and virtio-balloon are configured and managed within the container.

[ornago]

I'm running five of these windows containers simultaneously and it would be really nice, if they would share the RAM. With my Server having 32G of RAM installed, I can only allocate 10G for my containers. Is there a workaround?

[lmargit]

About the " ...RAM_SIZE parameter to act as a maximum limit rather than a fixed allocation".
I think this is one of the features built-in of using windows in a docker instead of windows in the traditional VM. Right?
You may compare the use of memory RAM in your Linux instance (host) using windows the traditional VM method vs the Dockur/windows method (Docker). Of course, same amount of RAM memory allocated to the Windows VM.

Or it is referring to change the amount of RAM memory inside the windows VM itself (on-the-fly)?

[Hi-Angel]

To have some keywords for searches: the feature being requested is called "memory ballooning".

[lukakama]

Hi, I recently opened a pull request (#1688) for an experimental Python implementation of a memory balloon controller. It was originally made to handle a single WinBoat-managed Windows VM, by adding the needed QEMU parameters and running the controller as an additional compose service. It was working reasonably well on my Ubuntu 25.10, so I decided to improve it for direct integration into the main dockur image and opened the pull request.

The implementation isn't the simplest, and as far as I can tell, doing the same in a pure bash script would be quite complex, so the added Python dependency could be a good trade-off. Probably the best would be to externalize the controller into a separate project written in Go and then integrate it into the image, but my Go skills are limited for now.

Let me know your thoughts.

[Hi-Angel]

and as far as I can tell, doing the same in a pure bash script would be quite complex

Not a project member so my opinion doesn't really matter, but I'd concur with you — "please no bash". Having lots of job experience with shell scripts, I came at some point to conclusion bash is never worth it, not even for simple cases. You always happen to think "Ah, c'mon, I'd just run a few commands and have a single if, what's gonna happen", and after a few more changes all hell breaks loose, with no typing, syntactic nuances, odd error-propagation in places…

At work we're now mostly using python-sh library — allows to write similarly short code as in bash, but with all Python features.