code: public String toHtml(MemoryUsage usage) {
          if(usage.availableSwapSpace==-1)
              return "N/A";
  
         String humanReadableSpace = Functions.humanReadableByteSize(usage.availableSwapSpace);
         
          long free = usage.availableSwapSpace;
          free/=1024L;   // convert to KB
          free/=1024L;   // convert to MB
          if(free>256 || usage.totalSwapSpace<usage.availableSwapSpace*5)
              return humanReadableSpace; // if we have more than 256MB free or less than 80% filled up, it's OK
  
          // Otherwise considered dangerously low.
          return Util.wrapToErrorSpan(humanReadableSpace);
      }
docs: Returns the HTML representation of the space.