Why co use too many memory

var co = require("co");
var urllib = require("urllib");

var count = 0;
co(function* () {
  while (true) {
    try {
      yield urllib.request("http://www.baidu.com");
    } catch (err) {
      console.error(err.message);
    }
    yield sleep(10);
    // global.gc();
    console.log("run %d, %smb", count++, process.memoryUsage().rss / 1024 / 1024);
  }
}).catch(function (err) {
  throw err;
});

function sleep(ms) {
  return function (callback) {
    setTimeout(callback, ms);
  };
}

var co = require("co");
var urllib = require("urllib");

var count = 0;
var running = false;

function* start() {
  if (running) {
    return;
  }
  running = true;
  var r;
  try {
    r = yield urllib.requestThunk("http://www.baidu.com");
  } catch (err) {
    console.error(err.message);
  } finally {
    running = false;
  }
  count++;
  if (count % 10 === 0) {
    console.log("run %d, %j, %smb", count, r && r.status, process.memoryUsage().rss / 1024 / 1024);
  }
}

var fn = co.wrap(start);

setInterval(function () {
  fn.call(null).catch(function (err) {
    throw err;
  });
}, 10);

var http = require("http");
var co = require("co");
var urllib = require("urllib");

var counts = {
  0: 0,
  1: 0,
  2: 0,
  3: 0,
  4: 0,
  5: 0,
  6: 0,
  7: 0,
};
var running = false;

function get(url) {
  return function (callback) {
    http
      .get(url, function (res) {
        var size = 0;
        res
          .on("data", function (data) {
            size += data.length;
          })
          .on("end", function () {
            callback(null, {
              size: size,
              statusCode: res.statusCode,
            });
          });
      })
      .on("error", callback);
  };
}

function getPromise(url) {
  return new Promise(function (resolve, reject) {
    http
      .get(url, function (res) {
        var size = 0;
        res
          .on("data", function (data) {
            size += data.length;
          })
          .on("end", function () {
            resolve({
              size: size,
              statusCode: res.statusCode,
            });
          });
      })
      .on("error", reject);
  });
}

function* start(index) {
  if (running) {
    return;
  }
  running = true;
  var r;
  try {
    r = yield urllib.request("http://127.0.0.1:7001");
    // r = yield get('http://127.0.0.1:7001/');
    // r = yield getPromise('http://127.0.0.1:7001/');
  } catch (err) {
    console.error(err.message);
  } finally {
    running = false;
  }
  counts[index]++;
  if (counts[index] % 100 === 0) {
    console.log(
      "[#%d] run %d, %s:%s, %smb",
      index,
      counts[index],
      r && r.status,
      r && r.size,
      process.memoryUsage().rss / 1024 / 1024,
    );
  }
}

var fn = co.wrap(start);

setInterval(function () {
  fn.call(null, 1).catch(function (err) {
    throw err;
  });
}, 10);
setInterval(function () {
  fn.call(null, 2).catch(function (err) {
    throw err;
  });
}, 10);
setInterval(function () {
  fn.call(null, 3).catch(function (err) {
    throw err;
  });
}, 10);
setInterval(function () {
  fn.call(null, 4).catch(function (err) {
    throw err;
  });
}, 10);
setInterval(function () {
  fn.call(null, 5).catch(function (err) {
    throw err;
  });
}, 10);
setInterval(function () {
  fn.call(null, 6).catch(function (err) {
    throw err;
  });
}, 10);