Comp111 - Quiz 2 Answers

Dec 9, 2015 - closed book

Please fill in the blanks. Each blank is worth 5 points. There are several reasonable answers for some of the blanks; choose one. Blanks with the same number have the same answer.

  1. The structure of a linux filesystem is based upon a contractual arrangement between the ____filesystem driver____ and the ____pager____. The former determines the structure of disk, while the latter makes disk updates ____more efficient____.
  2. The ____least-recently-used____ reclamation strategy is commonly used to recover pages in the disk page table. This has one weakness; it does not deal efficiently with ____(long) loops____.
  3. Little's law relates arrival rate, time in system, and ____jobs in system____ for a queueing process. Little's law only requires that the system be ____in balance____. This is in contrast to all further results in queueing, which require some kind of assumption about the ____distribution____ of arrival times and/or service times.
  4. An M/M/1 queue is a device where job arrivals and service times conform to ____memoryless/exponential____ statistical distributions. Since real service times are not ____memoryless____, the theory of M/M/1 queues rather consistently ____underestimates____ the average time in system for a request.
  5. Every file in a linux filesystem is described by an ____inode____ that describes the owner, group, protection, and location of blocks in the file. The location of the first few blocks of the file are recorded directly inside the inode, while subsequent blocks are located by ____indirection____ in which a block is re-interpreted as an array of ____pointers____ to blocks. Thus a file is logically a list but physically very similar to a(n) ____array____, in the sense that access to any block is O(1).
  6. In assignment four, getting the very best score is extremely difficult, because seemingly small errors in code do not lead to crashes, but instead decrease ____efficiency/performance____.
  7. Long term scheduling, also called ____admission control_____ control, determines when a job should ____start____ rather than when it should continue.
  8. The completely fair scheduler attempts to give each process in the run queue the ____same____ time per scheduling epoch, while in the O(1) scheduler, processes get differing times based upon how much ____I/O____ they perform.
  9. The "systems monoculture" refers to the fact that several commonly available operating systems encourage all instances to have the same ____(attack) signature____ which means that any attack that compromises one of them compromises all of them.
  10. (EXTRA CREDIT ) In allocating a new block for a file, the filesystem driver first looks for blocks whose "used" descriptors are currently located in the ____page table cache____, to increase performance.