stress_mem.rb

@retained = []

MAX_STRING_SIZE = 100

def stress(allocate_count, retain_count, chunk_size)
  chunk = []
  while retain_count > 0 || allocate_count > 0
    if retain_count == 0 || (Random.rand < 0.5 && allocate_count > 0)
      chunk << " " * (Random.rand * MAX_STRING_SIZE).to_i
      allocate_count -= 1
      if chunk.length > chunk_size
        chunk = []
      end
    else
      @retained << " " * (Random.rand * MAX_STRING_SIZE).to_i
      retain_count -= 1
    end
  end
end

start = Time.now
stress(10_000_000, 600_000, 200_000)
puts "Duration: #{(Time.now - start).to_f}"
# GC.start
# p GC.stat

puts `ps aux | grep #{Process.pid} | grep -v grep`

Ruby 2.0: 151120 RSS
Ruby 2.1.0 : 267076 RSS

WITHOUT THREEGEN

sam@ubuntu ~ % ruby stress_mem.rb
Duration: 5.355337084
sam 18567 89.6 3.8 267532 238356 pts/14 Sl+ 16:20 0:05 ruby stress_mem.rb

WITH THREEGEN

sam@ubuntu ~ % ruby stress_mem.rb
Duration: 4.468102349
sam 18612 112 2.4 178928 148624 pts/14 Sl+ 16:21 0:04 ruby stress_mem.rb

RSS reduced from 238mb to 148mb