What is Expansion swap?
At the time when any process needs more memory than it is currently allocated, the Kernel performs Expansion swap. To do this Kernel reserves enough space in the swap device. Then the address translation mapping is adjusted for the new virtual address space but the physical memory is not allocated. At last Kernel changes the process into the assigned space in the swap device. Later when the Kernel swaps the process into the main memory this allocates memory according to the new address translation mapping.