How is kbmemused calculated in sar?

Issue

• Explanation of kbmemused in man sar has changed in RHEL9.
• How is the value calculated? What is the difference compared with the older version?

RHEL8 and older version
# man sar
...
              kbmemused
                     Amount of used memory in kilobytes. This does not take into account memory used by  the  kernel
                     itself.

RHEL9
# man sar
...
              kbmemused
                     Amount of used memory in kilobytes (calculated as total installed  memory  -  kbmemfree  -  kb‐
                     buffers - kbcached - kbslab).