child_process memory issue local reproduction attempt

local.js

// use to attempt to reproduce locally like so:
// docker run --rm=true -v $(pwd)/local.js:/local.js node:6.11.0 node -e "require('./local').reproduce_sync_exec()"

const child_process = require('child_process');
const os = require('os');

function debug() {
  const free = os.freemem();
  const total = os.totalmem();

  console.log('process: ', process.memoryUsage(), 'os: ', {
    free, total,
    usedMiB: (total - free) / (1024 * 1024)
  });
}

function spawn(command, args, options = {}) {
  return new Promise((resolve, reject) => {
    const child = child_process.spawn(command, args, options);
    child.on('error', err => {
      reject(err);
    });

    child.on('close', code => {
      if (code === 0) {
        resolve(code);
      } else {
        reject(code);
      }
    });
  });
}

function spawn_child() {
  return spawn('ls', ['/']).then(() => {
    debug();
  });
}

function reproduce_async_spawn() {
  spawn_child()
      .then(spawn_child)
      .then(spawn_child)
      .then(spawn_child)
      .then(spawn_child)
      .then(spawn_child)
      .then(spawn_child)
      .then(spawn_child)
      .then(spawn_child)
      .then(spawn_child)
      .then(() => {
        console.log('done');
      })
      .catch(err => {
        console.log(err);
      });
}

function reproduce_sync_exec() {
  for (let i = 0; i < 10; i++) {
    child_process.execSync('ls /');
    debug();
  }

  console.log('done');
}

function reproduce_sync_spawn() {
  for (let i = 0; i < 10; i++) {
    child_process.spawnSync('ls' ['/']);
    debug();
  }

  console.log('done');
}

module.exports = {
  reproduce_async_spawn,
  reproduce_sync_exec,
  reproduce_sync_spawn
};