Why the size of swap space is always 4KiB less than size of actual swap device?

Issue

• Why the size of swap space is always 4KiB less than size of actual swap device?

# lvs --units k
  LV   VG                 Attr       LSize         Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  home rhel_dell-per630-5 -wi-ao---- 514908160.00k                                                    
  root rhel_dell-per630-5 -wi-ao----  52428800.00k                                                    
  swp1 rhel_dell-per630-5 -wi-a-----   4194304.00k    <<-----                                                    
  swp2 rhel_dell-per630-5 -wi-a-----   4194304.00k    <<-----   


# mkswap /dev/mapper/rhel_dell--per630--5-swp1 
Setting up swapspace version 1, size = 4194300 KiB    <<-----


# mkswap /dev/mapper/rhel_dell--per630--5-swp2
Setting up swapspace version 1, size = 4194300 KiB    <<-----


# cat /proc/swaps 
Filename                Type        Size    Used    Priority
/dev/dm-1                               partition   4194300 0   -2    <<-----
/dev/dm-3                               partition   4194300 0   -3    <<-----