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diff --git a/help/C/memory-map-use.page b/help/C/memory-map-use.page new file mode 100644 index 0000000..b2f03e4 --- /dev/null +++ b/help/C/memory-map-use.page @@ -0,0 +1,174 @@ +<page xmlns="http://projectmallard.org/1.0/" + 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> + <cite date="2011-06-18" href="mailto:philbull@gmail.com">Phil Bull</cite> + <p>Explain how to use the Memory Map feature.</p> + </comment> + + <p><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 <em>more</em> 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 <em>paged out</em> or written + to the swap space.</p> + + <p>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.</p> + + <p>To display the <link xref="memory-map-what">memory map</link> of a + process:</p> + + <steps> + <item><p>Click the <gui>Processes</gui> tab.</p></item> + <item><p>Right click the desired process in the <gui>process list</gui>.</p></item> + <item><p>Click <gui>Memory Maps</gui>.</p></item> + </steps> + +<section id="read"> + <title>Reading the memory map</title> + + <list> + <item> + <p>Addresses are displayed in hexadecimal (base 16).</p> + </item> + <item> + <p>Sizes are displayed in <link xref="units">IEC binary + prefixes</link>.</p> + </item> + <item> + <p>At runtime the process can allocate more memory dynamically into an + area called the <em>heap</em>, and store arguments and variables into + another area called the <em>stack</em>.</p> + </item> + <item> + <p>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.</p> + </item> + </list> + +<table shade="rows" ui:expanded="false"> +<title>Properties</title> + <tr> + <td><p>Filename</p></td> + <td><p>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.</p></td> + </tr> + <tr> + <td><p>VM Start</p></td> + <td><p>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.</p></td> + </tr> + <tr> + <td><p>VM End</p></td> + <td><p>The address at which the memory segment ends.</p></td> + </tr> + <tr> + <td><p>VM Size</p></td> + <td><p>The size of the memory segment.</p></td> + </tr> + <tr> + <td><p>Flags</p></td> + <td><p>The following flags describe the different types of memory-segment + access that the process can have:</p> + <terms> + <item> + <title><gui>p</gui></title> + <p>The memory segment is private to the process, and is not accessible + to other processes.</p> + </item> + <item> + <title><gui>r</gui></title> + <p>The process has permission to read from the memory segment.</p> + </item> + <item> + <title><gui>s</gui></title> + <p>The memory segment is shared with other processes.</p> + </item> + <item> + <title><gui>w</gui></title> + <p>The process has permission to write into the memory segment.</p> + </item> + <item> + <title><gui>x</gui></title> + <p>The process has permission to execute instructions that are + contained within the memory segment.</p> + </item> + </terms> + </td> + </tr> + <tr> + <td><p>VM Offset</p></td> + <td><p>The location of the address within the memory segment, + measured from VM Start.</p></td> + </tr> + <tr> + <td><p>Private, Shared, Clean, Dirty</p></td> +<!-- <td><p>Text pages are flagged read-execute in memory and don't need to + 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 <em>dirty</em>, and when designated for swapping, + must be paged out.</p></td> +--> + <td><list><item><p><em>private</em> pages are accessed by one + process</p></item> + <item><p><em>shared</em> pages can be accessed by more than + one process</p></item> + <item><p><em>clean</em> pages have not yet been modified + while in memory and can be discarded when designated to be swapped + out</p></item> + <item><p><em>dirty</em> pages have been modified while in + memory and must be written to disk when designated to be swapped + out</p></item></list></td> + </tr> + <tr> + <td><p>Device</p></td> + <td><p>The major and minor numbers of the device on which the shared + library filename is located. Together these specify a partition on the + system.</p></td> + </tr> + <tr> + <td><p>Inode</p></td> + <td><p>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.</p></td> + </tr> +</table> + +</section> +</page> |