Reasons of ignoring these argument is permanent generation has been removed in HotSpot for JDK8 because of following drawbacks
Fixed size at startup – difficult to tune.
Internal Hotspot types were Java objects : Could move with full GC, opaque, not strongly typed and hard to debug, needed meta-metadata.
Simplify full collections : Special iterators for metadata for each collector
Want to deallocate class data concurrently and not during GC pause
Enable future improvements that were limited by PermGen.
The Permanent Generation (PermGen) space has completely been removed and is kind of replaced by a new space called Metaspace. The consequences of the PermGen removal is that obviously the PermSize and MaxPermSize JVM arguments are ignored and you will never get a java.lang.OutOfMemoryError: PermGen error.
Advantages of MetaSpace
Take advantage of Java Language Specification property : Classes and associated metadata lifetimes match class loader’s
Per loader storage area – Metaspace
Linear allocation only
No individual reclamation (except for RedefineClasses and class loading failure)
No GC scan or compaction
No relocation for metaspace objects
Metaspace Tuning
The maximum metaspace size can be set using the -XX:MaxMetaspaceSize flag, and the default is unlimited, which means that only your system memory is the limit. The -XX:MetaspaceSize tuning flag defines the initial size of metaspace If you don’t specify this flag, the Metaspace will dynamically re-size depending of the application demand at runtime.
Change enables other optimizations and features in the future
Application class data sharing
Young collection optimizations, G1 class unloading
Metadata size reductions and internal JVM footprint projects
There is improved GC performace also. More detail
http://*.com/questions/18339707/permgen-elimination-in-jdk-8/22509753#22509753