http://209.85.129.132/search?q=cache:FWEPvRwqiIYJ:sapbasis-security.blogspot.com/2008/04/monitoring-system-work-processes-sm50.html+process+stopped+reason+priv+sap+basis&hl=en&ct=clnk&cd=4&gl=uk
Useful link on processes.
It says
If the reason columns display Priv, it means that a work process has been reserved for a private use in a particular ABAP transaction requiring a large paging storage. This mechanism prevents the rolling in and out of the user contexts and the ABAP paging.
Useful topic on this http://sap.ittoolbox.com/groups/technical-functional/sap-basis/re-re-in-sm50-ststus-stopped-reason-priv-110313
which suggests a memory management problem
http://www.sapsecurityonline.com/sap_security_interview_questions/sap_basis_performance_analysis.htm
Shows a diagram of whole process
