Physical memory shows high usage in Management Center >> Administration >> Hardware Diagnostics
Physical memory on Management center can be filled up. When physical memory gets filled up it borrows space out of the swap memory.
The problem would be if the high memory is reported in the virtual memory (sum of physical + swap) and the swap space is low.
If enough swap space is available then though physical memory is filled up it does not create an issue.
Swap space is the portion of virtual memory on the hard disk. It is a substitute for physical memory. It is used as virtual memory, which contains process memory images. Whenever MC runs short of physical memory, it uses its virtual memory and stores information in memory on a disk.
Incase the swap space is free and physical memory is full the MC will allocate additional space on physical memory by borrowing space from the swap space.