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33.4. Overcommitting Resources
Most operating systems and applications do not use 100% of the available RAM all the time. This behavior can be exploited with KVM to use more memory for guests than what is physically available.
(0.5 * RAM) + (overcommit ratio * RAM) = Recommended swap size
The KVM hypervisor supports overcommitting virtualized CPUs. Virtualized CPUs can be overcommitted as far as load limits of guests allow. Use caution when overcommitting VCPUs as loads near 100% may cause dropped requests or unusable response times.