             host_metrics:
               # No `update`: `exit` then `enter` will be called instead.
               enter: (metrics) ->
-                {memory_free, memory_total} = metrics
-                @field.usage += +memory_total - memory_free
-                @field.size += +memory_total
+                free = +metrics.memory_free
+                total = +metrics.memory_total
+
+                @field.usage += total - free
+                @field.size += total
               exit: (metrics) ->
-                {memory_free, memory_total} = metrics
-                @field.usage -= +memory_total - memory_free
-                @field.size -= +memory_total
+                free = +metrics.memory_free
+                total = +metrics.memory_total
+
+                @field.usage -= total - free
+                @field.size -= total
 
       pool:
 

          # TODO: `0` should not be used when the value is unknown.
          memory: @dynamic {
            usage: null
            size: get 'memory_dynamic_min'
          }, {
            VM_metrics: {
              update: (metrics, UUID) ->


          SR_type: get('type')

          physical_usage: number get 'physical_utilization'

          usage: number get 'virtual_allocation'

          size: number get 'physical_size'

          $container: null # TODO

