tailieunhanh - Lecture Operating system concepts - Lecture 15

Chapter 16 looks at the current major research and development in distributed-file systems (DFS). The purpose of a DFS is to support the same kind of sharing when the files are physically dispersed among the various sites of a distributed system. | CSC 322 Operating Systems Concepts Lecture - 16: by Ahmed Mumtaz Mustehsan Special Thanks To: Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. (Chapter-3) Ahmed Mumtaz Mustehsan, CIIT, Islamabad 1 Chapter 3 Memory Management Virtual Memory Design Issues for Paging System Lecture-16 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 2 Need to take into account a number of design issues in order to get a working algorithm Design Issues for Paging System Lecture-16 3 Ahmed Mumtaz Mustehsan, CIIT, Islamabad Working sets grow and shrink over time Processes have different sizes Assign equal number of pages to each process or proportional to its size ? Start with allocation based on size and use page fault frequency (PFF) to modify allocation size for each process Global is better for the memory Lecture-16 4 Ahmed Mumtaz Mustehsan, CIIT, Islamabad Local-take into account just the process which faulted. Local replacement : from only its own set of allocated frames. Global-take . | CSC 322 Operating Systems Concepts Lecture - 16: by Ahmed Mumtaz Mustehsan Special Thanks To: Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. (Chapter-3) Ahmed Mumtaz Mustehsan, CIIT, Islamabad 1 Chapter 3 Memory Management Virtual Memory Design Issues for Paging System Lecture-16 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 2 Need to take into account a number of design issues in order to get a working algorithm Design Issues for Paging System Lecture-16 3 Ahmed Mumtaz Mustehsan, CIIT, Islamabad Working sets grow and shrink over time Processes have different sizes Assign equal number of pages to each process or proportional to its size ? Start with allocation based on size and use page fault frequency (PFF) to modify allocation size for each process Global is better for the memory Lecture-16 4 Ahmed Mumtaz Mustehsan, CIIT, Islamabad Local-take into account just the process which faulted. Local replacement : from only its own set of allocated frames. Global-take into account all of the processes. Global replacement : process selects a replacement frame from the set of all frames; one process can take a frame from another Local versus Global choice of page Original configuration. Local page replacement. Global page replacement. Lecture-16 5 Ahmed Mumtaz Mustehsan, CIIT, Islamabad Maintain upper (A) and lower (B) bounds for PFF Try to keep process in between bounds PFF used to determine page allocation Lecture-16 6 Ahmed Mumtaz Mustehsan, CIIT, Islamabad PFF is global component; determines page allocation Replacement algorithm Is local component; determines which page to kick out Can use combination of algorithms Local Versus Global Lecture-16 7 Ahmed Mumtaz Mustehsan, CIIT, Islamabad Thrashing If a process does not have “enough” pages, the page-fault rate is very high. This leads to: low CPU utilization operating system thinks that it needs to increase the degree of multiprogramming another process added to the system Thrashing a process is .