Source code question - about the logic of calculating network buffer

[徐涛]

Hi Experts,
        I am debugging the WordCount Flink streaming program in local mode. 
Flink version is 1.7.2
        I saw the following calculation logic about network buffer in class 
TaskManagerServices.        
        jvmHeapNoNet is equal to -xmx amount in Java.
        why the networkBufBytes = xmx / (1-networkBufFraction) * 
networkBufFraction, it is a bit strange.
        why it is not calculated by xmx * networkBufFraction?
 
final long networkBufBytes = Math.min(networkBufMax, Math.max(networkBufMin,
   (long) (jvmHeapNoNet / (1.0 - networkBufFraction) * networkBufFraction)));

Best 
Henry