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While smart paging is a temporary reallocation of memory between VMs and disk swap files, hypervisor swapping is more of a long-term measure. This VMware ESXi feature provides page swap support for a certain amount of memory reclamation. Because the hypervisor isn't aware of which VM memory pages are being used and which ones aren't, the data that is swapped out may need to be swapped back again. When the hypervisor does swap pages that are needed (indicated by B), the performance of the VM could be negatively affected. This technique can also interfere with memory ballooning, which is when the OS determines what pages to swap, further affecting performance. As such, hypervisor swapping should only be used if all other memory management techniques have been attempted.