Which of the following descriptions about memory bubbles is wrong?

Question

Options

• AThe virtualization layer can reclaim the physical memory temporarily unused by the virtual machine
• BMultiple virtual machines can share the same memory space using data
• CThe operation of the memory bubble is automatically implemented by the virtualization layer, and
• DThe total memory allocated for virtual machines on the server cannot exceed the total physical

• A
  9% (3)
• B
  76% (26)
• C
  3% (1)
• D
  12% (4)

Explanation

Option B describes memory sharing/deduplication - a technique where identical memory pages across VMs are consolidated - not memory ballooning. Memory bubbles work by installing a balloon driver inside the guest OS; when the hypervisor needs memory back, it inflates the balloon, forcing the guest to release pages the hypervisor then redistributes. There is no shared memory space between VMs involved.

• A is correct: Ballooning's core purpose is exactly this - the hypervisor inflates the balloon to reclaim pages the guest isn't actively using, then deflates it when the VM needs memory back.
• C is correct (as implied): The balloon driver operates transparently through the virtualization layer; the guest OS handles it automatically without user intervention.
• D is correct: Memory ballooning redistributes existing physical memory more efficiently but does not create new memory - total VM allocations are still bounded by the server's physical RAM unless separate overcommitment mechanisms are in use.

Memory tip: Think of a balloon inside a room (the VM). Inflating the balloon (hypervisor reclaiming memory) pushes air (unused pages) out of the room - it's about reclaiming, not sharing. Whenever you see "VMs sharing memory space," that's a different technology (page deduplication/KSM), not ballooning.

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