QEMU models 'RAMBlocks' which used to mostly actually be RAM or ROM; over time they've slowly got more complex. We've got huge pages, non volatile storage, devices, shared memory. I'll talk about the different types, and talk about some of the problems they can cause from migrations point of view.
I work on Red Hat's QEMU/KVM team on live migration. I've previously spoken at KVM Forum on how to avoid migration failures, and with Andrea Arcangeli on Postcopy migration.