mem() added writeback and dirty (linux)

lib/index.d.ts

@@ -126,6 +126,8 @@ export namespace Systeminformation {
     swaptotal: number;
     swapused: number;
     swapfree: number;
+    writeback: number | null;
+    dirty: number | null;
   }
 
   interface MemLayoutData {

lib/memory.js

@@ -162,7 +162,9 @@ function mem(callback) {
 
         swaptotal: 0,
         swapused: 0,
-        swapfree: 0
+        swapfree: 0,
+        writeback: null,
+        dirty: null
       };
 
       if (_linux) {
@@ -193,6 +195,10 @@ function mem(callback) {
               result.swapfree = parseInt(util.getValue(lines, 'swapfree'), 10);
               result.swapfree = result.swapfree ? result.swapfree * 1024 : 0;
               result.swapused = result.swaptotal - result.swapfree;
+              result.writeback = parseInt(util.getValue(lines, 'writeback'), 10);
+              result.writeback = result.writeback ? result.writeback * 1024 : 0;
+              result.dirty = parseInt(util.getValue(lines, 'dirty'), 10);
+              result.dirty = result.dirty ? result.dirty * 1024 : 0;
             }
             if (callback) { callback(result); }
             resolve(result);