Perf comparision for MMapDirectory Vs NIOFSDirectory

As per Lucene documentation there is not much difference between these 2
implementations and users should use the Open() method and Lucene choses
the best implementation based on the system.

https://lucene.apache.org/core/9_7_0/core/org/apache/lucene/store/FSDirectory.html


Is there any perf impact on choosing one of the options on a 64 bit linux
system ? Do we have any comparison numbers? What is the advantage of using
MMapDirectory when we already have a system buffer cache (on linux) for
file access ?


Thanks
Ashwini