CIS343|510
Chapter Eight Review w/ AnswersTwo characteristics of paging and segmentation are keys to a fundamental breakthrough in memory management. They are...
1-3. All memory references within a process are _____ that are dynamically
translated into _____ at run time. This means that a process may be
_____ such that it occupies different regions of main memory at
different times during the course of execution.
logical addresses; physical addresses;
swapped in and out of main memory
4-6. A process may be broken up into _____ and these need not be _____
in main memory during execution. The combination of dynamic
run-time _____ and the use of a page or segment table permits this.
a number of pieces; contiguously located; address translation
The breakthrough can be described this way:
7-10. If the preceding two characteristics are present, then it is _____ that
all of the pages or all of the segments of a process be _____ during
execution. If the piece that holds _____ and the piece that holds
_____ are in main memory, then at least for a time execution may
proceed.
not necessary; in main memory;
the next instruction to be fetched;
the next data location to be accessed
11. The portion of a process that is actually in memory at any given time is
called the _____ of the process.
resident set
The breakthrough mentioned above has two important implications.
12-16. More _____ may be _____. Because we are only going to load
some of the pieces of any particular process, there is _____. This leads
to more efficient utilization of _____ because it is more likely that at
least one of the more numerous processes will be _____ at any
particular time.
processes ; maintained in main memory;
room for more processes; the processor;in a Ready state
17. It is possible for a process to be _____.
larger than all of main memory
18. Because a process executes only in main memory, that memory is
referred to as ...
real memory
19. But a programmer or user perceives a potentially much larger memory -
that which is allocated on disk. This latter is referred to as...
virtual memory
20. When a processor spends most of its time swapping pieces rather than
executing instructions, this is known as...
thrashing
21-22. When virtual memory is implemented via paging, what two bits must
be present in the page table entry for each page?
resident bit; modified bit
23-27. In principle, every virtual memory reference can cause two physical
memory accesses: one to _____, and one to _____. This would have
the effect of doubling the memory access time. To overcome this
problem, most virtual memory systems make use of a special _____
for _____, usually called a _____. It contains those page table entries
that have been most recently used.
fetch the appropriate page table entry; fetch the desired data;
cache; page table entries; translation lookaside buffer
28. If the desired page is not in main memory when it is needed to continue
execution, this is called a ...
page fault
Listed below are considerations relevant to the choice of page size. Identify which are used to argue for larger, which for smaller page size.
Desire to...
29. ...decrease internal fragmentation.
smaller
30. ...decrease size of page tables
larger
31. ...increase the number of pages available in main memory for a process
smaller
32. Physical characteristics (rotational) of most secondary memory devices.
larger
33. Describe how a double page fault can occur for a single memory
reference.
Neither page referenced nor portion of page map table is in
memory
34-35. Describe two programming techniques used in large programs that
tend to decrease the locality of reference within a process.
OO techniques => many small program & data modules
scattered over a relatively large number of objects in
a relatively short period of time
Multithreaded applications => abrupt changes in instruction
stream & scattered memory references
Describe these fetch policies:
36. Demand paging
a page is brought into main memory only when a reference is
made to a location on that page
37. Prepaging
pages other than the one demanded are brought in
38-39. Choice of placement policy is an important issue for _____ but
relatively unimportant for _____.
pure segmentation systems;
pure paging or combined paging/segmentation systems
40. What is frame locking? Where may it be used?
specifying that the page contained in that frame may not be
replaced much of the kernel of the OS is held in locked frames
Identify the replacement policies described below:
41. Select that page for which the time to next reference is the longest.
optimal
42. Replace that page that has not been referenced for the longest time.
LRU = least recently used
43. Replace the page that has been in memory the longest.
FIFO = first in, first out
44. Using a use bit, replace the first page whose use bit = 0, resetting that
bit to 0 for each page passed over.
Clock
45. If there are 10 pages in the set to be considered for replacement, what is
the maximum number of pages, under Clock, that may be scanned before
a page is found to be replaced.
11
46. In the modification of Clock using two bits (u - used; m - modified), there
are 4 possible combinations of u & m: 0,0; 0,1; 1,0; 1,1. Which
combination is chosen during step 1 of this algorithm?
0,0
47. Which is chosen during step 2 of the algorithm?
0,1
48. If Step 2 fails, Step 3 involves
a. A repetition of Step 1 only.
b. A repetition of Step 1, and Step 2 (if necessary).
b
49. How is it possible for a page to be unused, but modified?
The used bit gets reset during Step #2 of 2nd Clock Alg.
Identify these resident set management policies:
50. Give a process a fixed number of pages within which to execute.
Fixed-allocation policy
51. Allow the number of page frames allocated to a process to change over
the lifetime of a process.
Variable-allocation policy
Identify these scope of replacement policies:
52. Choose only among the resident pages of the process that generated the
page fault to find a page to replace.
Local replacement policy
53. Choose all unlocked pages in memory are candidates for replacement,
regardless of which process they belong to.
Global replacement policy
54. Of the 4 combinations of resident set management and scope of
replacement policies, which one is not possible?
Fixed allocation, global scope
55. The set of pages that a process is accessing over a period of time is
known as its ...
working set
Describe how the working set of a process can be used to guide a strategy for determining resident set size:
56. Monitor the _____ of each process.
working set
57. Periodically _____ those pages that are not in its working set.
remove from the resident set of a process
58. A process may execute only if ...
its working set is in main memory
Give three problems with the working set strategy:
59. The past ...
does not always predict the future
60. A true measurement of the working set of each process ...
is impractical
61. The optimal value of delta ...
is unknown and would vary
62. What measurement may be used as an approximation for determining
whether or not the working set of a process is in main memory?
page-fault frequency
63. A problem with this approach is that during interlocality transitions, the
rapid succession of page faults causes _____ to swell.
the resident size of a process
64. An approach that attempts to deal with the phenomenon of interlocality
transition is the ...
variable-interval sampled working set (VSWS) policy
Identify these cleaning policies:
65. A page is written out to secondary memory only when it is selected for
replacement.
demand cleaning
66. Modified pages are written before page frames are needed, so that pages
can be written out in batches.
precleaning
67-71. The load control policy is critical in effective memory management.
If _____ are resident at any one time, then there will be many
occasions when all processes will be blocked, and much time will be
spent _____. On the other hand, if _____ are resident, then, on
average, the size of the resident set of each process will be inadequate
and _____ will occur.
too few processes; swapping; too many processes;
frequent faulting