discourse/app/controllers/admin/diagnostics_controller.rb

class Admin::DiagnosticsController < Admin::AdminController
  layout false
  skip_before_filter :check_xhr

  def memory_stats

    begin
      # ruby 2.1
      GC.start(full_mark: true)
    rescue
      GC.start
    end

    stats = GC.stat.map{|k,v| "#{k}: #{v}"}
    counts = ObjectSpace.count_objects.map{|k,v| "#{k}: #{v}"}

    render text: "GC STATS:\n#{stats.join("\n")} \n\nObjects:\n#{counts.join("\n")}",
      content_type: Mime::TEXT

  end
end