In vSphere 6, what is the role of the hypervisor in the context of Ballooning?

In the context of vSphere 6, the hypervisor plays a critical role in managing memory allocation through a process known as ballooning. The ballooning mechanism is initiated to reclaim memory from virtual machines when the host system is under memory pressure.

When this situation arises, the hypervisor communicates with the balloon driver, which is installed in the guest operating system, to instruct it to "inflate" or activate. This action causes the guest OS to allocate memory pages back to the hypervisor. By doing so, the hypervisor is able to free up memory resources that can then be reallocated to other virtual machines on the host, ensuring better overall performance and stability during times of memory strain.

This process is vital for maintaining efficiency and responsiveness in a virtualized environment, particularly when running multiple virtual machines that may have fluctuating memory demands. The balloon driver acts as an intermediary, allowing for the controlled reclamation of memory without the need for abrupt changes or shutdowns of the virtual machines.