old_contents: import psutil
  from django              import template
  from django.conf         import settings
  
  try:
      path = settings.DISK_USAGE_PATH
  except:
      path = "/"
  register = template.Library()
  @register.inclusion_tag('system_monitor/donut.html', takes_context=True)
  def disk_donut(context):
      disk_usage = psutil.disk_usage(path)
      return {
          'disk_usage_free':disk_usage.percent,
      }
  @register.simple_tag
  def disk_text():
      disk_usage = psutil.disk_usage(path)
      return 'free space left (%): {}'.format(disk_usage.percent)
  
new_contents: import psutil
  from django              import template
  from django.conf         import settings
  
  try:
      path = settings.DISK_USAGE_PATH
  except:
      path = "/"
  register = template.Library()
  @register.inclusion_tag('system_monitor/donut.html', takes_context=True)
  def disk_donut(context):
      disk_usage = psutil.disk_usage(path)
      return {
          'disk_usage_free':disk_usage.percent,
      }
  @register.simple_tag
  def disk_text():
      disk_usage = psutil.disk_usage(path)
      return 'free space left (%): {}'.format(100 - disk_usage.percent)
  
subject: fix the meaning of disk usage