What is the maximum memory allowed for w3wp worker process on 64 bit IIS 7

What is the maximum memory allowed for w3wp worker process on 64 bit IIS 7.

There are 16 Gigs on the web server and the w3wp worker process is using over 6 Gigs of memory (mostly session stora开发者_开发知识库ge). We suddenly began experiencing high cpu and seeing much more garbage collection. Could we have reached the limits of the w3wp process and that is causing more garbage collection cycles?

Additional note: We are using 64 bit classic mode on .Net 3.5 on Windows Server 2008.