Inside Mesos Web UI I can see memory usage of my Spark executors in a table
Agents -> Framework -> Executors
There is a table listing all exe
The memory usage of executors in fact is related with mesos task, means for every task how many memory the executors will consume.
If above is what you need, you can use following rest api to get a json and then parse the memory used from it.
http://mesos_ip:5050/master/tasks
FYI.