Determining how much memory a require uses

Here’s a quick little monkeypatch of the require method which will print out a tree showing how much memory each required file used:

# mem.rb
$require_level = 0
module MemTrackingRequire
  def require(name)
    $require_level += 1
    mem = lambda { GC.start; `ps -o rss= -p #$$`.to_i }
    before = mem.call

    required = super
  ensure
    after = mem.call
    $require_level -= 1
    if required
      puts "#{" "*$require_level}#{name} #{after - before}"
      puts "-------"  if $require_level.zero?
    end
  end
end

Object.class_eval { include MemTrackingRequire }

Here are some examples of how to use it (assuming it’s saved as mem.rb)

$ ruby -rmem -e 'require "rubygems"'
  rubygems/rubygems_version 0
  rubygems/defaults 0
   thread.so 24
  thread 28
  rbconfig 36

...

  rubygems/config_file 928
   rubygems 0
  rubygems/custom_require 0
 rubygems 1788  # <-- this is the number you are looking for, it represents the total amount of memory used by requiring 'rubygems'

$ ruby -rubygems -rmem -e 'gem "activerecord", "=2.2.2"; require "activerecord"'
...
   active_record/i18n_interpolation_deprecation 0
  active_record 5896
 activerecord 5896

$ ruby -rmem -e 'require "net/http"'
...
   uri/mailto 0
  uri 60
 net/http 800