perf-test.js

var fs = require('fs')

for (var i = 0; i < 10000; i++) {
  printLength(__filename)
}

function printLength (filename) {
  fs.readFile(filename, foo)

  function foo (err, buf)  {
    if (err) return // ignore error - probably just too many fds
    console.error(filename + ' has length ' + buf.length)
  }
}

foo is marked for optimization, but never optimized.

$ node --trace-opt perf-test.js
...
[marking 0x37192dd8fd79 <JS Function foo (SharedFunctionInfo 0xde0e275bcd1)> for optimized recompilation, reason: small function, ICs with typeinfo: 1/1 (100%), generic ICs: 0/1 (0%)]