Advanced Operating Systems   COMP9242 2002/S2

UNSW

Printer-Friendly Version Administration                - Notices - Course Intro - Consultations # On-line Survey (closed) - Survey Results   Work - Lectures - Milestone 0 - Project Admin - Project Spec - Project FAQ - Exam   Documentation - ASysT Lab - L4 source browser - Sulima ISA Simulator - R4x00 ISA Summary  - MIPS R4700 Reference - MIPS R4000 User Manual  - Network Driver - GT64111   Related Info - Aurema OS Prize - OS Hall of Fame   History - 2000 - 1999 - 1998   Staff - Gernot Heiser (LiC)

Resource Management in Mungi A major design aspect of Mungi is to make the system as unintrusive as possible. This means: no restrictions whatsoever on pointer/capability use, presentation of a valid capability at any time should guarantee access, object persistence is under full control of users (as traditional files) The system should also not rely on ``sensible'' users, like asking users to register/de-register ``interest'' in an object. How do we deal with garbage? Resource Management ... Automatic garbage collection is impossible because: reference counting is impossible as system cannot track references, scanning schemes cannot work as system cannot find pointers. Quota: require checking whenever an object is allocated ==> overhead, cannot distinguish between used and unused space. What else? Resource Management Using Bank Accounts Every object is associated with a bank account. ``Rent'' is periodically collected from account for associated objects. Regular ``income'' is periodically deposited into bank accounts. Overdrawn accounts prevent further creation of persistent objects ==> forces users to clean up. ``Tax'' on high balances prevents excessive accumulation of funds. Based on similar ideas in Amoeba [MT86] and the Monash Password Capability System [APW86]. Graceful degradation Q: How stop system from brickwalling when disk is full? A: Market approach: adjust rent to demand!       Fairness Q: How stop someone from accumulating large amounts of money enabling them to ``buy the whole world''? A: Taxation: limit balance by imposing a progressive tax!       Resource management issues: Secondary memory -- solved Primary memory -- have a model, work to be done Kernel memory (TCBs) -- to be done CPU time, scheduling -- to be done Lottery scheduling[WW94] worth looking at Network bandwidth -- to be done ???