A página atop man ajuda a explicar o que os números realmente indicam.
Memory
If the committed virtual memory exceeds the limit ('vmcom' and 'vmlim' in the SWP-line), the SWP-line is colored due to overcommitting the system.
SWP
Swap occupation and overcommit info.
This line contains the total amount of swap space on disk ('tot') and the amount of free swap space ('free').
Furthermore the committed virtual memory space ('vmcom') and the maximum limit of the committed space ('vmlim', which is by default swap size plus 50% of memory size) is shown. The committed space is the reserved virtual space for all allocations of private memory space for processes. The kernel only verifies whether the committed space exceeds the limit if strict overcommit handling is configured (vm.overcommit_memory is 2).
Parece que esse aviso não é nada crítico, mas apenas um aviso de que a pressão da memória está aumentando: link