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Systems & Data Center · Advanced

Memory Ballooning

A memory reclamation technique where a driver inside the guest inflates to make the guest OS release memory back to the hypervisor.

Definition

The balloon driver (part of VMware Tools) requests memory from the guest, which pages out its least valuable pages, letting the hypervisor reallocate them. It is more efficient than hypervisor-level swapping because the guest chooses what to page.

Example

esxtop's MCTLSZ column shows how much memory has been ballooned from each VM.

Exam tip

Ballooning requires VMware Tools; it indicates host memory pressure.

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