ROOT CAUSE: YARN UI shows total memory vs used memory wrong when there are reserved resources. The memory total shown when there is no reserved resources will be the correct one.
We can also compare that with sum of all NodeManager memory resource. This won't have any impact on YARN scheduler logic. This behavior has been reported in bug in YARN UI and got fixed by https://issues.apache.org/jira/browse/YARN-3432 and https://issues.apache.org/jira/browse/YARN-3243