Transcript MacOSX-by-Tomomi-Kotera-2003

Mac OS X Panther
Operating System
Tomomi Kotera
CS 550 Section 3
Fall 2003
Presentation Overview
• Overview of Mac OS X
– System Architecture
• Key technologies
– CPU scheduling
– Symmetric Multiprocessing
– Memory Management
• Conclusion
Overview of Mac OS X
• UNIX-based Operating System with the
intuitive user interface called Aqua
• “Classic” Mac OS vs. Newer Mac OS
• Four major successes of Mac OS X
– Preemptive Multitasking
– Symmetric Multiprocessing
– Memory Protection
– Virtual Memory
System Architecture
• Four layers of system software
–
–
–
–
Application Environments
Application Services
Core Services
Kernel Environments
Preemptive Multiprocessing
• Cooperative multitasking (Classic Mac
OS) vs. Preemptive Multiprocessing
(Mac OS X)
• Preemptive Multiprocessing
– Multilevel Feedback Queue Scheduling
Algorithm
– Round Robin Scheduling Algorithm
Preemptive Multiprocessing (cont.)
• Multilevel Feedback Queue Scheduling
Algorithm
– 128 priority levels are divided into four bands
•
•
•
•
Normal (0-51)
System High Priority (52-79)
Kernel Mode Only (80-95)
Real-Time Threads (96-127)
– Real-Time Threads are treated differently
– Avoid Starvation
– Threads migrate within a given band
Symmetric Multiprocessing
• Dual processor capabilities
• Share Memory and I/O bus
• Kernel can execute on any processor
Memory Protection
• Crush Resistant
– Processes are isolated in own memory
spaces
– Cannot interfere one another
– If one applications crashes, the system, and
other applications are unaffected - no
restarts
Virtual Memory
• Classic Mac OS uses Segmentation
• Mac OS X adopts Demand Paging
– Large, sparse virtual address spaces
– Mapping a page reference to a physical address
application
Page
fault
resume
pager
Address space
Function call
Virtual Memory (cont.)
• VM Object (Virtual Memory Object)
– Object-oriented nature of Mach
– Contiguous repository for data
indexed by byte
– All data in an address space is
provided through VM objects
– Track and manage the resident
and nonresident pages
• Memory Sharing
– Inheritance (shared, copy, none)
– Copy-on-Write
Virtual Memory (cont.)
• Content of a VM object
Field
Description
Resident
pages
List of resident pages in physical memory
Size
The size of the region, in bytes
Pager
Shadow
The pager responsible for tracking and handling the
pages of this region in backing store
Used for copy-on-write optimizations
Copy
Used for copy-on-write optimizations
Attributes
Flags indicating the state of various implementation
details
Virtual Memory (cont.)
• Second-chance first in, first out (FIFO)
Algorithm
• Three lists of physical memory pages
List
Active
list
Inactive
list
Free list
Description
pages that are currently mapped into memory and
have been recently accessed
pages that are currently resident in physical memory
pages of physical memory that are not associated with
any address space of the page table
Virtual Memory (cont.)
•
•
•
•
•
Continuously check the free list
When the number of pages in the free list dips
below this threshold, remove pages from the
inactive list to place them on the free list
Always maintains a few pages on the inactive
list
Once the free list size exceeds the target
threshold, the pager rests
FIFO-like page replacement
•
The inactive list serves as a second chance
Conclusion
• Technical Success of Mac OS X
– Marriage of stability, reliability and security of
UNIX, with the ease of use of the Macintosh
GUI
– Benefits from UNIX features
• Preemptive Scheduling
• Symmetric Multiprocessing
• Memory Management
– Target both home users and IT professionals