Smart paging is an advanced version of memory paging in Windows Server 2012 Hyper-V.
Smart paging allows a virtual machine (VM) to temporarily use hard disk space to supplement shortages of non-volatile memory. Smart paging is only used during VM restarts when there is no available physical memory.
VMs often require more memory during startups. Smart paging reduces the need to over-provision solid state memory while preventing the VM from crashing due to lack of memory. Because hard disk I/O speed is slower than solid-state memory however, smart paging will stop once the VM is up and running.
Smart paging is not used when memory is oversubscribed or when the VM fails over in a Hyper-V cluster. It is also not used if a VM is started from an off state, as opposed to being restarted.