Try the following code. that should give you the results you are after (especially the Pss field). You can read more about it here
Debug.MemoryInfo memoryInfo = new Debug.MemoryInfo();
Debug.getMemoryInfo(memoryInfo);
String memMessage = String.format(
"Memory: Pss=%.2f MB, Private=%.2f MB, Shared=%.2f MB",
memoryInfo.getTotalPss() / 1024.0,
memoryInfo.getTotalPrivateDirty() / 1024.0,
memoryInfo.getTotalSharedDirty() / 1024.0);