xmlns:ui="http://projectmallard.org/ui/1.0/"

      type="topic" style="task"

      id="memory-map-use">

  <info>

    <revision pkgversion="3.11" date="2014-01-28" status="candidate"/>

    <link type="guide" xref="index#memory" group="memory" />

    <include href="legal.xml" xmlns="http://www.w3.org/2001/XInclude"/>

    <credit type="author copyright">

      <name>Phil Bull</name>

      <email>philbull@gmail.com</email>

      <years>2011</years>

    </credit>

    <credit type="author copyright">

      <name>Michael Hill</name>

      <email>mdhillca@gmail.com</email>

      <years>2011, 2014</years>

    </credit>

    <desc>View the memory map of a process.</desc>

  </info>

  <title>Using memory maps</title>

  <comment>

    Phil Bull

    
Explain how to use the Memory Map feature.

  </comment>

  
<gui>Virtual memory</gui> is a representation of the combined

  <gui>physical memory</gui> and <link xref="mem-swap">swap space</link> in a

  system. It enables running processes to access more than the

  existing physical memory by <gui>mapping</gui> locations in physical memory

  to files on disk. When the system needs more pages of memory than are

  available, some of the existing pages will be paged out or written

  to the swap space.

  
The <gui>memory map</gui> displays the total virtual memory use of the

  process, and can be used to determine the memory cost of running a single or

  multiple instances of the program, to ensure the use of the correct shared

  libraries, to see the results of adjusting various performance tuning

  parameters the program may have, or to diagnose issues such as memory

  leaks.

  
To display the <link xref="memory-map-what">memory map</link> of a

  process:

  <steps>

    <item>
Click the <gui>Processes</gui> tab.
</item>

    <item>
Right click the desired process in the <gui>process list</gui>.
</item>

    <item>
Click <gui>Memory Maps</gui>.
</item>

  </steps>

<section id="read">

  <title>Reading the memory map</title>

  <list>

    <item>

      
Addresses are diplayed in hexadecimal (base 16).

    </item>

    <item>

      
Sizes are displayed in <link xref="units">IEC binary

      prefixes</link>.

    </item>

    <item>

      
At runtime the process can allocate more memory dynamically into an

      area called the heap, and store arguments and variables into

      another area called the stack.

    </item>

    <item>

      
The program itself and each of the shared libraries has three entries

      each, one for the read-execute text segment, one for the read-write data

      segment and one for a read-only data segment. Both data segments need to

      be paged out at swap time.

    </item>

  </list>

<title>Properties</title>

	  
Filename

	  
The location of a shared library that is currently used by the

    process. If this field is blank, the memory information in this row

    describes memory that is owned by the process whose name is displayed above

    the memory-map table.

	  
VM Start

	  
The address at which the memory segment begins. VM Start, VM End and

    VM Offset together specify the location on disk to which the shared library

    is mapped.

	  
VM End

	  
The address at which the memory segment ends.

	  
VM Size

	  
The size of the memory segment.

	  
Flags

	  
The following flags describe the different types of memory-segment

    access that the process can have:

    <terms>

      <item>

        <title><gui>p</gui></title>

        
The memory segment is private to the process, and is not accessible

        to other processes.

      </item>

      <item>

        <title><gui>r</gui></title>

        
The process has permission to read from the memory segment.

      </item>

      <item>

        <title><gui>s</gui></title>

        
The memory segment is shared with other processes.

      </item>

      <item>

        <title><gui>w</gui></title>

        
The process has permission to write into the memory segment.

      </item>

      <item>

        <title><gui>x</gui></title>

        
The process has permission to execute instructions that are

        contained within the memory segment.

      </item>

    </terms>

	  
VM Offset

	  
The location of the address within the memory segment,

    measured from VM Start.

	  
Private, Shared, Clean, Dirty

  be written to swap since they can be re-loaded from their original location

  on disk. Data pages have read-write permissions, and if modified when in

  memory, they are labeled dirty, and when designated for swapping,

  must be paged out.

-->

          <list><item>
private pages are accessed by one

  process
</item>

          <item>
shared pages can be accessed by more than

  one process
</item>

          <item>
clean pages have not yet been modified

  while in memory and can be discarded when designated to be swapped

  out
</item>

          <item>
dirty pages have been modified while in

  memory and must be written to disk when designated to be swapped

  out
</item></list>

	  
Device

	  
The major and minor numbers of the device on which the shared

    library filename is located. Together these specify a partition on the

    system.

	  
Inode

	  
The inode on the device from which the shared library location

    is loaded into memory. An inode is the structure the filesystem uses to

    store a file, and the number assigned to it is unique.

</section>

</page>