what is memory_usage_byte in results?

[jtmoon79]

What exactly is the memory_usage_byte result within exported results?

In other words, for this output

{
  "results": [
    {
      "command": "my command",
      "mean": 0.042425522800000004,
      "stddev": 0.0012753653405051045,
      "median": 0.042866266,
      "user": 0.0436844,
      "system": 0.139675,
      "min": 0.040239074,
      "max": 0.043487722,
      "times": [
        0.042866266,
        0.042476109000000005,
        0.040239074,
        0.043487722,
        0.043058443
      ],
      "memory_usage_byte": [
        235024384,
        237850624,
        241963008,
        241963008,
        241963008
      ],
      "exit_codes": [
        0,
        0,
        0,
        0,
        0
      ]
    }
  ]
}

That result was from a run on a Ubuntu 24. I have some guesses but I wanted to confirm.

[jtmoon79]

It comes from

hyperfine/src/timer/unix_timer.rs

Line 46 in 975fe10

let success = getrusage(RUSAGE_CHILDREN, &mut buf);

    // Linux and *BSD return the value in KibiBytes, Darwin flavors in bytes
    let max_rss_byte = if cfg!(target_os = "macos") || cfg!(target_os = "ios") {
        result.ru_maxrss
    } else {
        result.ru_maxrss * 1024
    };

The result is from libc::getrusage which calls Linux getrusage.

The result has structure

   struct rusage {
       struct timeval ru_utime; /* user CPU time used */
       struct timeval ru_stime; /* system CPU time used */
       long   ru_maxrss;        /* maximum resident set size */
       long   ru_ixrss;         /* integral shared memory size */
       long   ru_idrss;         /* integral unshared data size */
       long   ru_isrss;         /* integral unshared stack size */
       long   ru_minflt;        /* page reclaims (soft page faults) */
       long   ru_majflt;        /* page faults (hard page faults) */
       long   ru_nswap;         /* swaps */
       long   ru_inblock;       /* block input operations */
       long   ru_oublock;       /* block output operations */
       long   ru_msgsnd;        /* IPC messages sent */
       long   ru_msgrcv;        /* IPC messages received */
       long   ru_nsignals;      /* signals received */
       long   ru_nvcsw;         /* voluntary context switches */
       long   ru_nivcsw;        /* involuntary context switches */
   };

So memory_usage_byte is field value ru_maxrss described as

ru_maxrss (since Linux 2.6.32)
This is the maximum resident set size used (in KiB). For
RUSAGE_CHILDREN, this is the resident set size of the
largest child, not the maximum resident set size of the
process tree.