By default, the swap file for each VM is created when you power it on, and it will be stored within the folder of the VM in a specific datastore.

The size of the VM's swap file equals the size of the VM's configured memory, unless you use reservations for the memory.

When no reservation is configured, the ESXi host cannot guarantee the amount of memory that will be served from physical memory and the size of memory that might be swapped due to contention.

When you reserve all memory for the VM, no swap file will be created because the ESXi hypervisor will ensure that the VM will always get the physical resources it needs.

If you set a partial reservation for the VM, the size of the swap file equals the configured memory size, minus the reservation.