In a virtualized server environment, which technique allows the hypervisor to reclaim memory from non-critical VMs so a critical VM can continue running with the required memory?

• A. Ballooning
• B. Snapshotting
• C. Page sharing
• D. CPU pinning

Answer: (A)

Memory ballooning is a reclamation technique where the hypervisor uses a balloon driver inside non-critical VMs to force them to release memory. When memory is tight, the balloon inflates inside those VMs, causing the guest OS to reclaim or free pages. Those freed physical pages are then returned to the hypervisor and can be allocated to the critical VM that needs more memory, allowing it to continue running smoothly. This approach directly addresses memory pressure by reallocating existing resources rather than creating new ones.

Snapshotting saves the current state of a VM and does not free or reallocate memory for another VM. Page sharing can reduce overall memory use by deduplicating identical pages across VMs, but it doesn’t guarantee reclaiming memory from one VM to satisfy another. CPU pinning ties virtual CPUs to specific physical CPUs for performance reasons and has no effect on reclaiming memory.