prelude: |
  class C
    attr_accessor :foo
  end
  long_lived = C.new

  if RUBY_VERSION >= "2.2.0"
    3.times{ GC.start(full_mark: false, immediate_mark: true, immediate_sweep: true) }
  elsif
    GC.start
  end

  short_lived = ''
benchmark:
  vm_gc_wb_obj_promoted: |
    long_lived.foo = short_lived # write barrier
loop_count: 30000000