3000 Test2 Notes PDF

Questions: DEFINITIONS/TERMS, APPLICATION/CALCULATION, GENERALISATION Material Covered: Lectures: From Lecture 8, slide 8.32 (Deadlock Detection) to Lecture 15, slide 15.13 (Client-Server Model) inclusive. Tutorials: From Tutorial 6 to Tutorial 10 (inclusive), and all supplementary material that w...

Questions: DEFINITIONS/TERMS, APPLICATION/CALCULATION, GENERALISATION Material Covered: Lectures: From Lecture 8, slide 8.32 (Deadlock Detection) to Lecture 15, slide 15.13 (Client-Server Model) inclusive. Tutorials: From Tutorial 6 to Tutorial 10 (inclusive), and all supplementary material that was delivered with them (e.g., Journaling File Systems). Self-Study Assignments: From Assignment 4 to Assignment 6 (inclusive) THINGS TO LOOK UP AND UNDERSTAND: NFS Mounting, Data/(Metadata) Journaling, Demand Paging, Deadlocks, Detection Algorithm, Intel Architectures, LRU Algorithm, FIFO algorithm, Page and Frame replacement algorithm, RAID, Storage Device Management, C-SCAN, Disk Attachment, Nonvolatile Memory Devices, Mass Storage Structure, Power Management, I/O Subsystems, Graph Directories, WAFL, Free Space Management, Linked Allocation, File Systems Layers, DEFINITIONS/TERMS: Root Partition: contains the OS, other partitions can hold other OSes, other file systems Domain Name System (DNS): Provides host-name-to-network address translations Network Information Service (NIS): provide username, password, userID, etc. Common Internet File System (CIFS): Used with user auth to create network logins File Session: Series of accesses between file open and closed Sun Network File System (NFS): Implementation and specification of a software system accessing remote files across LANS Virtual File System (VFS) layer: distinguishes local files from remote ones Journaling: Before overwriting on-disk structures, write note on the disk, describing what you’re doing. Writing this note is the “write ahead”. Journal write: write the contents of the transaction to the log Journal commit: write the transaction commit block Checkpoint: write the contents of the update to their locations. File control block (FCB): storage structure consisting of information about a file Device drivers: manage I/O devices at the I/O control layer Mount table: storing file system mounts, mount points, filesystem types System-wide open-file table: contains a copy of the FCB of each file and other info Per-process open-file table: contains pointers to appropriate entries in system-wide open-file table as well as other info Collisions: situations where two file names hash to the same location Buffer cache: separate section of main memory for frequently used blocks Free-behind and read-ahead: techniques to optimize sequential access Page cache: caches pages rather than disk blocks using virtual memory techniques and addresses File Attributes: - Name – only information kept in human-readable form - Identifier – unique tag (number) identifies file within file system - Type – needed for systems that support different types - Location – pointer to file location on device - Size – current file size - Protection – controls who can do reading, writing, executing - Time, date, and user identification – data for protection, security, and usage monitoring File Operations: - Create - Write – at write pointer location - Read – at read pointer location - Reposition within file - seek - Delete - Truncate - Open (Fi) – search the directory structure on disk for entry Fi, and - move the content of entry to memory - Close (Fi) – move the content of entry Fi in memory to directory - structure on disk Open-file table: tracks open files File-open count: counter of number of times a file is open – to allow removal of data from open-file table when last processes closes it Shared lock: similar to reader lock – several processes can acquire concurrently Exclusive lock: similar to writer lock Transfer rate: is rate at which data flow between drive and computer Positioning time (random-access time): is time to move disk arm to desired cylinder (seek time) and time for desired sector to rotate under the disk head (rotational latency) Head crash: results from disk head making contact with the disk surface Access Latency = Average access time = average seek time + average latency RAM drives: present as raw block devices, commonly file system formatted Error-correction code (ECC): not only detects, but can correct some errors Mean time to repair: exposure time when another failure could cause data loss Mean time to data loss: based on above factors RAID (redundant array of inexpensive disks): multiple disk drives provides reliability via redundancy Mirroring or shadowing (RAID 1): keeps duplicate of each disk Striped mirrors (RAID 1+0) or mirrored stripes (RAID 0+1): provides high performance and high reliability Block interleaved parity (RAID 4, 5, 6): uses much less redundancy Virtual memory: separation of user logical memory from physical memory Virtual address space: logical view of how process is stored in memory Lazy swapper: never swaps a page into memory unless page will be needed Copy-on-Write (COW): allows both parent and child processes to initially share the same pages in memory Lease Frequently Used (LFU) Algorithm: Replaces page with smallest count Most Frequently Used (MFU) Algorithm: Based on the argument that the page with the smallest count, was probably just brought in and has yet to be used Global replacement: process selects a replacement frame from the set of all frames; one process can take a frame from another Local replacement: each process selects from only its own set of allocated frames page address extension (PAE): allowing 32-bit apps access to more than 4GB of memory space Resource Type: - Available: A vector of length m indicates the number of available resources of each type - Allocation: An n x m matrix defines the number of resources of each type currently allocated to each thread. - Request: An n x m matrix indicates the current request of each thread. If Request [i][j] = k, then thread Ti is requesting k more instances of resource type R TUTORIALS / STUDY ASSIGNMENTS: A4: - FIFO: - In FIFO the producer can give multiple words before they are processed - Read, write, sleep - Rendezvous: - Waits for the producer to give a word - Futex, and Close, Rendezvous has longer strace log - Max queue size in place - uses many mutexes - pipefd A5: - ioctl: system call that maniupulates the device parameters of files - used to change physical to virtual address - sync, echo, buf A6: - docker.io T6: - memory allocation schemes that have internal fragmentation: Fixed partitioning, paging - why memory compaction cannot be performed if absolute address (binding) is used in the code: The code and data can’t be moved in the memory. Compaction requires moving code and data.’ T7: - LRU: LEAST RECENTLY USED - Second Chance: SKIPS IF RECENCY BIT - FIFO: First in first out Help CPU utilisation: - Decrease the degree of multiprogramming - Install more main memory disk scheduling discipline - No improvement under light loads Key Concepts: “Turnaround time” in scheduling. Major and minor numbers used in special (device) files. Mandatory vs. Discretionary Access Control “Bare metal” hypervisor Four necessary conditions for a deadlock: mutual exclusion, no preemption, hold and wait and circular set Demand Paging Banker’s Algorithm