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Step-by-Step Explanation of Ballooning, Compression & Swapping in VMware

 ðŸ”¹ Step-by-Step Explanation of Ballooning, Compression & Swapping in VMware


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1️⃣ Memory Ballooning (vmmemctl)


Ballooning is the first memory reclamation technique used when ESXi detects memory pressure.


➤ Step-by-Step: How Ballooning Works

 1. VMware Tools installs the balloon driver (vmmemctl) inside the guest OS.

 2. ESXi detects low free memory on the host.

 3. ESXi inflates the balloon in selected VMs.

 4. Balloon driver occupies guest memory, making the OS think RAM is full.

 5. Guest OS frees idle / unused pages (because it believes memory is needed).

 6. ESXi reclaims those freed pages and makes them available to other VMs.


Why Ballooning Happens?

 • Host free memory is very low.

 • ESXi wants the VM to release unused pages before resorting to swapping.


Example

 • Host memory: 64 GB

 • VMs used: 62 GB

 • Free: 2 GB → ESXi triggers ballooning

 • VM1 (8 GB RAM): Balloon inflates to 2 GB → OS frees 2 GB → ESXi reclaims.

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