heroku GC settings generator for rails

heroku.rake

namespace :heroku do
  desc "generate GC settings"
  task gc: [:environment] do
    # https://discussion.heroku.com/t/tuning-rgengc-2-1-on-heroku/359/6
    # http://tmm1.net/ruby21-rgengc/
    # http://thorstenball.com/blog/2014/03/12/watching-understanding-ruby-2.1-garbage-collector/
    # http://collectiveidea.com/blog/archives/2015/02/19/optimizing-rails-for-memory-usage-part-1-before-you-optimize/
    settings = {
      RUBY_GC_HEAP_FREE_SLOTS:        600000,         # default is 4096,
      RUBY_GC_HEAP_GROWTH_FACTOR:     1.25,           # default is 1.8,
      RUBY_GC_HEAP_GROWTH_MAX_SLOTS:  300000,         # default is 0,
      RUBY_GC_HEAP_INIT_SLOTS:        600000,         # default is 10000,
      RUBY_GC_MALLOC_LIMIT:           16.megabyte,    # default is 16.megabyte,
      RUBY_GC_MALLOC_LIMIT_MAX:       32.megabyte,    # default is 32.megabyte,
      RUBY_GC_OLDMALLOC_LIMIT:        16.megabyte,    # default is 16.megabyte,
      RUBY_GC_OLDMALLOC_LIMIT_MAX:    32.megabyte,    # default is 32.megabyte,
    }

    puts "heroku config:add #{settings.map { |key, value| "#{key}=#{value}"}.join(' ') }"
  end
end