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Modern Operating Systems by Herbert Bos and Andrew S. Tanenb...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf
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Modern Operating Systems by Herbert Bos and Andrew...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Modern Operating Systems by Herbert...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Page 291
260
MEMORY MANAGEMENT
CHAP. 3
paged virtual memory system with virtual addresses that have a 4-bit page number, and
a 10-bit offset. The page tables and protection are as follows (all numbers in the table
are in decimal):
Segment 0
Segment 1
Read/Execute
Read/Write
Virtual Page #
Page frame #
Virtual Page #
Page frame #
0
2
0
On Disk
1
On Disk
1
14
2
11
2
9
3
5
3
6
4
On Disk
4
On Disk
5
On Disk
5
13
6
4
6
8
7
3
7
12
For each of the following cases, either give the real (actual) memory address which re-
sults from dynamic address translation or identify the type of fault which occurs (either
page or protection fault).
(a) Fetch from segment 1, page 1, offset 3
(b) Store into segment 0, page 0, offset 16
(c) Fetch from segment 1, page 4, offset 28
(d) Jump to location in segment 1, page 3, offset 32
48.
Can you think of any situations where supporting virtual memory would be a bad idea,
and what would be gained by not having to support virtual memory? Explain.
49.
Virtual memory provides a mechanism for isolating one process from another. What
memory management difficulties would be involved in allowing two operating systems
to run concurrently? How might these difficulties be addressed?
50.
Plot a histogram and calculate the mean and median of the sizes of executable binary
files on a computer to which you have access. On a Windows system, look at all .exe
and .dll files; on a UNIX system look at all executable files in
/bin
,
/usr/bin
, and
/local/bin
that are not scripts (or use the
file
utility to find all executables). Determine
the optimal page size for this computer just considering the code (not data).
Consider
internal fragmentation and page table size, making some reasonable assumption about
the size of a page table entry. Assume that all programs are equally likely to be run and
thus should be weighted equally.
51.
Write a program that simulates a paging system using the aging algorithm. The number
of page frames is a parameter. The sequence of page references should be read from a
file. For a given input file, plot the number of page faults per 1000 memory references
as a function of the number of page frames available.
52.
Write a program that simulates a toy paging system that uses the WSClock algorithm.
The system is a toy in that we will assume there are no write references (not very
Page 292
CHAP. 3
PROBLEMS
261
realistic), and process termination and creation are ignored (eternal life). The inputs
will be:
• The reclamation age threshhold
• The clock interrupt interval expressed as number of memory references
• A file containing the sequence of page references
(a) Describe the basic data structures and algorithms in your implementation.
(b) Show that your simulation behaves as expected for a simple (but nontrivial) input
example.
(c) Plot the number of page faults and working set size per 1000 memory references.
(d) Explain what is needed to extend the program to handle a page reference stream
that also includes writes.
53.
Write a program that demonstrates the effect of TLB misses on the effective memory
access time by measuring the per-access time it takes to stride through a large array.
(a) Explain the main concepts behind the program, and describe what you expect the
output to show for some practical virtual memory architecture.
(b) Run the program on some computer and explain how well the data fit your expecta-
tions.
(c) Repeat part (b) but for an older computer with a different architecture and explain
any major differences in the output.
54.
Write a program that will demonstrate the difference between using a local page re-
placement policy and a global one for the simple case of two processes. You will need
a routine that can generate a page reference string based on a statistical model.
This
model has
N
states numbered from 0 to
N
−
1 representing each of the possible page
references and a probability
p
i
associated with each state
i
representing the chance that
the next reference is to the same page.
Otherwise, the next page reference will be one
of the other pages with equal probability.
(a) Demonstrate that the page reference string-generation routine behaves properly for
some small
N
.
(b) Compute the page fault rate for a small example in which there is one process and a
fixed number of page frames. Explain why the behavior is correct.
(c) Repeat part (b) with two processes with independent page reference sequences and
twice as many page frames as in part (b).
(d) Repeat part (c) but using a global policy instead of a local one.
Also, contrast the
per-process page fault rate with that of the local policy approach.
55.
Write a program that can be used to compare the effectiveness of adding a tag field to
TLB entries when control is toggled between two programs. The tag field is used to ef-
fectively label each entry with the process id. Note that a nontagged TLB can be simu-
lated by requiring that all TLB entries have the same tag at any one time.
The inputs
will be:
• The number of TLB entries available
• The clock interrupt interval expressed as number of memory references
• A file containing a sequence of (process, page references) entries
• The cost to update one TLB entry
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