Xperf actions are trace processing components that format trace files to produce text reports, csv files and xml files. Actions are designed to produce summarized reports that are specific to a set of events, in this case, heap events.
Actions are all invoked with the same command line pattern:
xperf -I input.etl -o output.txt -a action name [action parameters]...
Where <action name> is the name of the action. This is always preceded by the '-a' command line switch. The action name can be followed by one or more action specific parameters.