* Memory is basically reserved on the host on VM start. KVM and XEN reserve the whole memory by default and do not allow memory overcommitment. As a result you can't run more then 15 VMs with 1GB RAM on 16Gb box. ESX, being the most advanced hypervisor, uses page sharing and ballooning technologies to introduce memory overcommitment. However, on practice it allows to get only about 2x times overcommitment on the guests of the same type. Our experiments tell that half of the improvement is due to page sharing, and half is due to ballooning.

* Multiple kernels and their system data structures in memory. RAM pages sharing and ballooning help a bit here, too.

* what happens when CT is above it's limit

* what happens when node RAM is exhausted

* plots and examples. Kir had http_load plot in the past. We will have LAMP results as well.