virtio-devices: mark a possible improvement

This would be a good opportunity to optimize another pointless vector
away, but I don't have a good way to test this at the moment. But
maybe someone else gives it a shot.

On-behalf-of: SAP julian.stecklina@sap.com
Signed-off-by: Julian Stecklina <julian.stecklina@cyberus-technology.de>

virtio-devices/src/mem.rs

@@ -391,6 +391,8 @@ impl BlocksState {
             }
         }
 
+        // TODO We can avoid creating a new bitmap here, if we switch the code
+        // to use Vec<u64> to keep dirty bits and just pass it as is.
         MemoryRangeTable::from_bitmap(bitmap, start_addr, VIRTIO_MEM_DEFAULT_BLOCK_SIZE)
     }
 }