operf evil memory consumption

I was surprised to see this:

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
 1968 aph       20   0 7657600 1.675g  13184 S 754.0 10.5  73:01.82 java
 1970 aph       20   0 7533760 7.180g   4288 S  36.8 45.1   3:28.73 operf

The RSS of operf really is extreme.  Is it that it keeps all samples
in memory, or somesuch?

Thanks,
Andrew.

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