As per hortonwork documentation Young Generation Size should be 1/8 of heap memory size .But I can see in below link data is not matching i.e. (5-10 million file heap size is 5376 and Young Generation Size is 768 which is not matching as 1/8 of 5376 is 672) .
It's not mandatory to have 1/8. It's current recommendation is to set this to 1/8 to 1/6 of the total heap size.
These control the minimum and maximum size of the new generation in the generational garbage collector architecture. We’ve found that for large heaps, the JVM defaults are too small for this. Our current recommendation is to set this to 1/8 to 1/6 of the total heap size. We recommend setting each of these to the same value for stability reasons, similar to the above discussion of total heap size.
This controls the minimum and maximum size of the permanent generation, which is a portion of the heap dedicated to application metadata, such as Java class definitions and interned string variables. If this is too small, then you’ll see errors like:
java.lang.OutOfMemoryError: PermGen space
These settings are our current recommendation for what works well for our usage patterns.