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461 lines
15 KiB
HTML
<html>
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<head>
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<title>Moss | Memory Management Simulator | User Guide</title>
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</head>
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<body bgcolor="#ffffff">
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<h1>
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MOSS
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Memory Management Simulator
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<br>User Guide</h1>
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<h2>Purpose</h2>
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<p>
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This document is a user guide for the MOSS
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Memory Management Simulator. It explains how to use the simulator and
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describes the display and the various input files used by and output files
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produced by the simulator. The MOSS software
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is designed for use with
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<a href="http://www.cs.vu.nl/~ast/">Andrew S. Tanenbaum</a>,
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<a href="http://vig.prenhall.com/catalog/academic/product/1,4096,0130313580,00.html">Modern Operating Systems, 2nd Edition</a>
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(<a href="http://www.prenhall.com/">Prentice Hall</a>, 2001).
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The Memory Management Simulator was written by
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<a href="http://www.cs.earlham.edu/~odo/">Alex Reeder</a>
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(<a href="mailto:alexr@e-sa.org"><i>alexr@e-sa.org</i></a>).
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This user guide was written by
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<a href="http://www.ontko.com/~rayo/">Ray Ontko</a>
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(<a href="mailto:rayo@ontko.com"><i>rayo@ontko.com</i></a>).
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<p>
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This user guide assumes that you have already installed and tested
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the simulator. If you are looking for installation information,
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please read the
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<a href="install_unix.html">Installation Guide for
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Unix/Linux/Solaris/HP-UX Systems</a> or the
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<a href="install_windows.html">Installation Guide for
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Win95/98/Me/NT/2000 Systems</a>.
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</p>
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<h2>Introduction</h2>
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<p>
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The memory management simulator illustrates page fault behavior
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in a paged virtual memory system. The program reads the initial
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state of the page table and a sequence of virtual memory
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instructions and writes a trace log indicating the effect of each
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instruction. It includes a graphical user interface so that
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students can observe page replacement algorithms at work. Students
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may be asked to implement a particular page replacement algorithm
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which the instructor can test by comparing the output from the
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student's algorithm to that produced by a working implementation.
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</p>
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<h2>Running the Simulator</h2>
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<p>
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The program reads a command file, optionally reads
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a configuration file, displays a GUI window which
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allows you to execute the command file, and optionally
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writes a trace file.
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<p>
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To run the program, enter the following command line.
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<blockquote><pre>
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$ java MemoryManagement commands memory.conf
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</pre></blockquote>
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<p>
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The program will display a window allowing you to run the
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simulator. You will notice a row of command buttons across
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the top, two columns of "page" buttons at the left, and an
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informational display at the right.
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</p>
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<IMG SRC="user_guide_1.gif">
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<p>
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Typically you will
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use the <tt>step</tt> button to execute a command from the
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input file, examine information about any pages by clicking
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on a <tt>page</tt> button, and when you're done, quit the
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simulation using the <tt>exit</tt> button.
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<p>
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The buttons:
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</p>
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<table border="1" cellspacing="0">
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<tr><th>Button
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<th>Description</th>
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<tr><td valign="top"><tt>run</tt>
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<td valign="top">runs the simulation to completion. Note that the simulation
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pauses and updates the screen between each step.
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<tr><td valign="top"><tt>step</tt>
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<td valign="top">runs a single setup of the simulation and updates the display.
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<tr><td valign="top"><tt>reset</tt>
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<td valign="top">initializes the simulator and starts from the beginning of
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the command file.
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<tr><td valign="top"><tt>exit</tt>
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<td valign="top">exits the simulation.
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<tr><td valign="top"><tt>page <i>n</i></tt>
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<td valign="top">display information about this virtual page in the display
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area at the right.
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</table>
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<p>
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The informational display:
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</p>
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<table border="1" cellspacing="0">
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<tr><th>Field
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<th>Description</th>
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<tr><td valign="top"><tt>status:</tt>
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<td valign="top">RUN, STEP, or STOP. This indicates whether the current
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run or step is completed.
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<tr><td valign="top"><tt>time:</tt>
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<td valign="top">number of "ns" since the start of the simulation.
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<tr><td valign="top"><tt>instruction:</tt>
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<td valign="top">READ or WRITE. The operation last performed.
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<tr><td valign="top"><tt>address:</tt>
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<td valign="top">the virtual memory address of the operation last performed.
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<tr><td valign="top"><tt>page fault:</tt>
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<td valign="top">whether the last operation caused a page fault to occur.
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<tr><td valign="top"><tt>virtual page:</tt>
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<td valign="top">the number of the virtual page being displayed in the
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fields below. This is the last virtual page accessed by the simulator,
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or the last <tt>page <i>n</i></tt> button pressed.
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<tr><td valign="top"><tt>physical page:</tt>
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<td valign="top">the physical page for this virtual page, if any. <tt>-1</tt>
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indicates that no physical page is associated with this virtual page.
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<tr><td valign="top"><tt>R:</tt>
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<td valign="top">whether this page has been read. (1=yes, 0=no)
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<tr><td valign="top"><tt>M:</tt>
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<td valign="top">whether this page has been modified. (1=yes, 0=no)
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<tr><td valign="top"><tt>inMemTime:</tt>
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<td valign="top">number of ns ago the physical page was allocated to this virtual
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page.
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<tr><td valign="top"><tt>lastTouchTime:</tt>
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<td valign="top">number of ns ago the physical page was last modified.
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<tr><td valign="top"><tt>low:</tt>
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<td valign="top">low virtual memory address of the virtual page.
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<tr><td valign="top"><tt>high:</tt>
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<td valign="top">high virtual memory address of the virtual page.
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</table>
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<h2>The Command File</h2>
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<p>
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The command file for the simulator specifies a sequence
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of memory instructions to be performed. Each instruction
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is either a memory READ or WRITE operation, and includes
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a virtual memory address to be read or written. Depending on whether
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the virtual page for the address is present in physical
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memory, the operation will succeed, or, if not, a page fault
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will occur.
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<h3>Operations on Virtual Memory</h3>
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<p>
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There are two operations one can carry out on pages in memory:
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READ and WRITE.
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<p>
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The format for each command is
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<blockquote><pre>
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<i>operation</i> <i>address</i>
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</pre></blockquote>
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or
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<blockquote><pre>
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<i>operation</i> random
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</pre></blockquote>
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where <i>operation</i> is <tt>READ</tt> or <tt>WRITE</tt>,
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and <i>address</i> is the numeric virtual memory address, optionally
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preceeded by one of the radix keywords <tt>bin</tt>, <tt>oct</tt>,
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or <tt>hex</tt>. If no radix is supplied, the number is assumed
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to be decimal.
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The keyword <tt>random</tt> will generate a random virtual
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memory address
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(for those who want to experiment quickly)
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rather than having to type an address.
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<p>
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For example, the sequence
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<blockquote><pre>
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READ bin 01010101
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WRITE bin 10101010
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READ random
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WRITE random
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</pre></blockquote>
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causes the virtual memory manager to:
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<ol>
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<li>read from virtual memory address 85
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<li>write to virtual memory address 170
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<li>read from some random virtual memory address
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<li>write to some random virtual memory address
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</ol>
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<h3>Sample Command File</h3>
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<p>
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The "commands" input file looks like this:
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<blockquote><pre>
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// Enter READ/WRITE commands into this file
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// READ <OPTIONAL number type: bin/hex/oct> <virtual memory address or random>
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// WRITE <OPTIONAL number type: bin/hex/oct> <virtual memory address or random>
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READ bin 100
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READ 19
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WRITE hex CC32
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READ bin 100000000000000
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READ bin 100000000000000
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WRITE bin 110000000000001
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WRITE random
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</pre></blockquote>
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<h2>The Configuration File</h2>
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The configuration file <tt>memory.conf</tt> is used to specify the
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the initial content of the virtual memory map
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(which pages of virtual
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memory are mapped to which pages in physical memory)
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and provide other configuration information, such
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as whether operation should be logged to a file.
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<h3>Setting Up the Virtual Memory Map</h3>
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<p>
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The <tt>memset</tt> command is used to initialize each
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entry in the virtual page map.
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<tt>memset</tt> is followed by six integer values:
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<ol>
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<li>The virtual page # to initialize
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<li>The physical page # associated with this virtual page
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(-1 if no page assigned)
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<li>If the page has been read from (R) (0=no, 1=yes)
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<li>If the page has been modified (M) (0=no, 1=yes)
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<li>The amount of time the page has been in memory (in ns)
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<li>The last time the page has been modified (in ns)
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</ol>
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The first two parameters define the mapping between
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the virtual page and a physical page, if any.
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The last four parameters are values that might be used
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by a page replacement algorithm.
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<p>
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For example,
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<blockquote><pre>
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memset 34 23 0 0 0 0
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</pre></blockquote>
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specifies that virtual page 34 maps to physical page 23,
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and that the page has not been read or modified.
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<p>
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Note:
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<ul>
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<li>Each physical page should be mapped to exactly one virtual page.
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<li>The number of virtual pages is fixed at 64 (0..63).
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<li>The number of physical pages cannot exceed 64 (0..63).
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<li>If a virtual page is not specified by any memset command,
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it is assumed that the page is not mapped.
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</ul>
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<h3>Other Configuration File Options</h3>
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<p>There are a number of other options which can
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be specified in the configuration file. These are
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summarized in the table below.
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</p>
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<table border="1" cellspacing="0">
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<tr><th>Keyword<th>Values<th>Description
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<tr><td valign="top"><tt>enable_logging</tt><td valign="top"><tt>true</tt><br><tt>false</tt>
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<td valign="top">Whether logging of the operations should be enabled. If logging
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is enabled, then the program writes a one-line message for each
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READ or WRITE operation. By default, no logging is enabled.
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See also the <tt>log_file</tt> option.
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<tr><td valign="top"><tt>log_file</tt>
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<td valign="top"><i>trace-file-name</i>
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<td valign="top">The name of the file to which log messages should be written.
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If no filename is given, then log messages are written to stdout.
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This option has no effect if <tt>enable_logging</tt> is <tt>false</tt>
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or not specified.
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<tr><td valign="top"><tt>pagesize</tt><td valign="top"><i>n</i><br>
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<tt>power</tt> <i>p</i>
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<td valign="top">The size of the page in bytes as a power of two.
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This can be given as a decimal number which is a
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power of two (1, 2, 4, 8, etc.) or as a power of two using
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the <tt>power</tt> keyword. The maximum page size is
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<tt>67108864</tt> or <tt>power 26</tt>. The default
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page size is <tt>power 26</tt>.
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<tr><td valign="top"><tt>addressradix</tt><td valign="top"><i>n</i>
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<td valign="top">The radix in which numerical values are displayed.
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The default radix is 2 (binary). You may prefer radix
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8 (octal), 10 (decimal), or 16 (hexadecimal).
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</table>
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<h3>Sample Configuration File</h3>
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<p>
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The "memory.conf" configuration file looks like this:
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<blockquote><pre>
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// memset virt page # physical page # R (read from) M (modified) inMemTime (ns) lastTouchTime (ns)
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memset 0 0 0 0 0 0
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memset 1 1 0 0 0 0
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memset 2 2 0 0 0 0
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memset 3 3 0 0 0 0
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memset 4 4 0 0 0 0
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memset 5 5 0 0 0 0
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memset 6 6 0 0 0 0
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memset 7 7 0 0 0 0
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memset 8 8 0 0 0 0
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memset 9 9 0 0 0 0
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memset 10 10 0 0 0 0
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memset 11 11 0 0 0 0
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memset 12 12 0 0 0 0
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memset 13 13 0 0 0 0
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memset 14 14 0 0 0 0
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memset 15 15 0 0 0 0
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memset 16 16 0 0 0 0
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memset 17 17 0 0 0 0
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memset 18 18 0 0 0 0
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memset 19 19 0 0 0 0
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memset 20 20 0 0 0 0
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memset 21 21 0 0 0 0
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memset 22 22 0 0 0 0
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memset 23 23 0 0 0 0
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memset 24 24 0 0 0 0
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memset 25 25 0 0 0 0
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memset 26 26 0 0 0 0
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memset 27 27 0 0 0 0
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memset 28 28 0 0 0 0
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memset 29 29 0 0 0 0
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memset 30 30 0 0 0 0
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memset 31 31 0 0 0 0
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// enable_logging 'true' or 'false'
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// When true specify a log_file or leave blank for stdout
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enable_logging true
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// log_file <FILENAME>
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// Where <FILENAME> is the name of the file you want output
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// to be print to.
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log_file tracefile
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// page size, defaults to 2^14 and cannot be greater than 2^26
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// pagesize <single page size (base 10)> or <'power' num (base 2)>
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pagesize 16384
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// addressradix sets the radix in which numerical values are displayed
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// 2 is the default value
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// addressradix <radix>
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addressradix 16
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// numpages sets the number of pages (physical and virtual)
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// 64 is the default value
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// numpages must be at least 2 and no more than 64
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// numpages <num>
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numpages 64
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</pre></blockquote>
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<h2>The Output File</h2>
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<p>
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The output file contains a log of the operations
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since the simulation started (or since the last reset).
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It lists the command that was attempted and what happened
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as a result. You can review this file after executing
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the simulation.
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<p>
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The output file contains one line per operation
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executed. The format of each line is:
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<blockquote><pre>
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<i>command</i> <i>address</i> ... <i>status</i>
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</pre></blockquote>
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where:
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<ul type="none">
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<li><i>command</i> is <tt>READ</tt> or <tt>WRITE</tt>,
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<li><i>address</i> is a number corresponding to a virtual memory address, and
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<li><i>status</i> is <tt>okay</tt> or <tt>page fault</tt>.
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</ul>
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<h3>Sample Output</h3>
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The output "tracefile" looks something like this:
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<blockquote><pre>
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READ 4 ... okay
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READ 13 ... okay
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WRITE 3acc32 ... okay
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READ 10000000 ... okay
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READ 10000000 ... okay
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WRITE c0001000 ... page fault
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WRITE 2aeea2ef ... okay
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</pre></blockquote>
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<h2>Suggested Exercises</h2>
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<ol>
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<li>Create a command file that maps any 8 pages of physical memory to
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the first 8 pages of virtual memory, and then reads from one virtual
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memory address on each
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of the 64 virtual pages. Step through
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the simulator one operation at a time and see if you can predict
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which virtual memory addresses cause page faults. What page replacement
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algorithm is being used?
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<p><!-- --></p>
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<li>Modify <tt>replacePage()</tt> in
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<tt>PageFault.java</tt> to implement a <em>round robin</em>
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page replacement algorithm
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(i.e., first page fault
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replaces page 0, next one replaces page 1, next one replaces page 2,
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etc.).
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<p><!-- --></p>
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<li>Modify <tt>replacePage()</tt> in
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<tt>PageFault.java</tt> to implement a <em>least recently used</em>
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(LRU) page replacement algorithm.
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<p><!-- --></p>
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</ol>
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<h2>To Do</h2>
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<ol>
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<li>
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The user guide should tell a little bit about how replacePage works, e.g.
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what data structures it uses, what the arguments are,
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how it operates, how it makes it choice known, etc.
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Add a section of documentation on how to implement a new
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page replacement algorithm. This should explain a little about
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what changes are needed in the GUI, what to call the page replacement
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class, what fields and methods it needs to provide, and what
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other changes might be needed.
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</ol>
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<h2>Copyright</h2>
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© Copyright 2001, Prentice-Hall, Inc.
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<p>
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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<p>
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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<p>
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You should have received a copy of the GNU General Public License
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along with this program (see <a href="copying.txt">copying.txt</a>);
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if not, write to the Free Software
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Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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<p>
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Please send suggestions, corrections, and comments to
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<a href="http://www.ontko.com/~rayo/">Ray Ontko</a>
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(<a href="mailto:rayo@ontko.com"><i>rayo@ontko.com</i></a>).
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<p>
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<i>Last updated: July 28, 2001</i>
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</body>
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</html>
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