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
Found the answer myself. For each worker/agent on which executors may run, direct access to memory info is here:
http://IP_of_worker1:5051/slave(1)/monitor/statistics
http://IP_of_worker2:5051/slave(1)/monitor/statistics
etc
The content is in the form of a json and framework_id allows to find the related executors and their memory consumption, cpu usage etc what is given in the table.