An administrator notices that 8 out of 10 virtual machines have memory ballooning and swapping. However, virtual machine 9 is not ballooning or swapping and virtual machine 10 is not ballooning but is

When a VM has a 100% memory reservation, ESXi guarantees all of that memory is backed by physical RAM and will not be reclaimed. Because the memory is fully reserved, the host bypasses both the balloon driver and host-level swap for that VM, explaining why VM9 experiences neither ballooning nor swapping.

A memory limit constrains the maximum memory a VM may consume but does not prevent ESXi from applying ballooning or swapping to that VM when the host is under memory pressure.

High memory shares give a VM scheduling priority during contention but do not create a complete exemption from ballooning - ESXi may still balloon the VM, just at a lower priority than VMs with fewer shares.

The VMware balloon driver is a component delivered by VMware Tools. Without VMware Tools installed, VM10 has no balloon driver, so the host cannot use ballooning to reclaim its guest memory. However, host-level memory swapping occurs at the hypervisor layer independent of VMware Tools, which is why VM10 is swapping but not ballooning.