Windows VM Shows 100% RAM in Proxmox: Ballooning or Static RAM?

When a Windows VM in Proxmox seems to use almost all of its assigned memory in the host UI while Task Manager shows normal usage, the usual cause is missing VirtIO drivers and a missing QEMU guest agent.

Windows does not ship with VirtIO drivers. Without the VirtIO balloon driver, Proxmox cannot properly track or reclaim memory from the guest, so the host may report close to 100% usage even when the guest is under no real memory pressure. Installing the VirtIO drivers from the ISO and enabling the QEMU guest agent usually brings the Proxmox memory figure in line with what Windows reports.

PCI passthrough and vGPU are an important exception. A VM with a PCI device attached often needs full access to its assigned memory, and Proxmox may keep showing high or full usage. That can be expected behavior and is not necessarily a problem.

On ballooning versus static RAM, opinions are split but lean pragmatic. Many people prefer to assign RAM statically to Windows Server VMs and avoid overcommitting, especially in smaller environments. Ballooning can work, but some users report confusing metrics or inconsistent behavior. If you have enough physical RAM and are not overallocating aggressively, static assignment keeps things simple and predictable.

In practice, install the VirtIO drivers and the guest agent in every Windows VM, keep in mind that passthrough devices can skew memory reporting, and pick ballooning only if you really need dynamic memory management.