Each task has counters PHYSICAL_MEMORY_BYTES and VIRTUAL_MEMORY_BYTES, which are snapshots of memory usage of that task. They are not sufficient for users to understand peak memory usage by that task, e.g. in order to diagnose task failures, tune job parameters or change application design. This new feature will add two more counters for each task: PHYSICAL_MEMORY_BYTES_MAX and VIRTUAL_MEMORY_BYTES_MAX.
This JIRA has the same feature from MAPREDUCE-4710. I file this new YARN JIRA since MAPREDUCE-4710 is pretty old one from MR 1.x era, it more or less assumes a branch-1 architecture, should be close at this point.