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@@ -9,9 +9,10 @@ H3 {font-family: Verdana,Arial,Helvetica}
 A:link, A:visited, A:active { text-decoration: underline }
 </style><title>Memory Management</title></head><body bgcolor="#8b7765" text="#000000" link="#a06060" vlink="#000000"><table border="0" width="100%" cellpadding="5" cellspacing="0" align="center"><tr><td width="120"><a href="http://swpat.ffii.org/"><img src="epatents.png" alt="Action against software patents" /></a></td><td width="180"><a href="http://www.gnome.org/"><img src="gnome2.png" alt="Gnome2 Logo" /></a><a href="http://www.w3.org/Status"><img src="w3c.png" alt="W3C Logo" /></a><a href="http://www.redhat.com/"><img src="redhat.gif" alt="Red Hat Logo" /></a><div align="left"><a href="http://xmlsoft.org/"><img src="Libxml2-Logo-180x168.gif" alt="Made with Libxml2 Logo" /></a></div></td><td><table border="0" width="90%" cellpadding="2" cellspacing="0" align="center" bgcolor="#000000"><tr><td><table width="100%" border="0" cellspacing="1" cellpadding="3" bgcolor="#fffacd"><tr><td align="center"><h1>The XML C parser and toolkit of Gnome</h1><h2>Memory 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border="0" cellspacing="0" cellpadding="1" width="100%"><tr><td><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td><table border="0" cellpadding="3" cellspacing="1" width="100%"><tr><td bgcolor="#fffacd"><p>Table of Content:</p><ol><li><a href="#General3">General overview</a></li>
   <li><a href="#setting">Setting libxml2 set of memory routines</a></li>
-  <li><a href="#cleanup">Cleaning up after parsing</a></li>
+  <li><a href="#cleanup">Cleaning up after using the library</a></li>
   <li><a href="#Debugging">Debugging routines</a></li>
   <li><a href="#General4">General memory requirements</a></li>
+  <li><a href="#Compacting">Returning memory to the kernel</a></li>
 </ol><h3><a name="General3" id="General3">General overview</a></h3><p>The module <code><a href="http://xmlsoft.org/html/libxml-xmlmemory.html">xmlmemory.h</a></code>
 provides the interfaces to the libxml2 memory system:</p><ul><li>libxml2 does not use the libc memory allocator directly but xmlFree(),
     xmlMalloc() and xmlRealloc()</li>
@@ -26,21 +27,23 @@ debugging, analysis or to implement a specific behaviour on memory management
     which allow to set up a new set of memory allocation functions</li>
 </ul><p>Of course a call to xmlMemSetup() should probably be done before calling
 any other libxml2 routines (unless you are sure your allocations routines are
-compatibles).</p><h3><a name="cleanup" id="cleanup">Cleaning up after parsing</a></h3><p>Libxml2 is not stateless, there is a few set of memory structures needing
+compatibles).</p><h3><a name="cleanup" id="cleanup">Cleaning up after using the library</a></h3><p>Libxml2 is not stateless, there is a few set of memory structures needing
 allocation before the parser is fully functional (some encoding structures
 for example). This also mean that once parsing is finished there is a tiny
 amount of memory (a few hundred bytes) which can be recollected if you don't
-reuse the parser immediately:</p><ul><li><a href="http://xmlsoft.org/html/libxml-parser.html">xmlCleanupParser
-    ()</a> is a centralized routine to free the parsing states. Note that it
-    won't deallocate any produced tree if any (use the xmlFreeDoc() and
-    related routines for this).</li>
+reuse the library or any document built with it:</p><ul><li><a href="http://xmlsoft.org/html/libxml-parser.html">xmlCleanupParser
+    ()</a> is a centralized routine to free the library state and data. Note
+    that it won't deallocate any produced tree if any (use the xmlFreeDoc()
+    and related routines for this). This should be called only when the library
+    is not used anymore.</li>
   <li><a href="http://xmlsoft.org/html/libxml-parser.html">xmlInitParser
     ()</a> is the dual routine allowing to preallocate the parsing state
     which can be useful for example to avoid initialization reentrancy
     problems when using libxml2 in multithreaded applications</li>
-</ul><p>Generally xmlCleanupParser() is safe, if needed the state will be rebuild
-at the next invocation of parser routines, but be careful of the consequences
-in multithreaded applications.</p><h3><a name="Debugging" id="Debugging">Debugging routines</a></h3><p>When configured using --with-mem-debug flag (off by default), libxml2 uses
+</ul><p>Generally xmlCleanupParser() is safe assuming no parsing is ongoing and
+no document is still being used, if needed the state will be rebuild at the
+next invocation of parser routines (or by xmlInitParser()), but be careful
+of the consequences in multithreaded applications.</p><h3><a name="Debugging" id="Debugging">Debugging routines</a></h3><p>When configured using --with-mem-debug flag (off by default), libxml2 uses
 a set of memory allocation debugging routines keeping track of all allocated
 blocks and the location in the code where the routine was called. A couple of
 other debugging routines allow to dump the memory allocated infos to a file
@@ -99,4 +102,14 @@ of a number of things:</p><ul><li>the parser itself should work  in a fixed amou
     validation, DOM, XPath or XPointer, don't use entities, need to work with
     fixed memory requirements, and try to get the fastest parsing possible
     then the SAX interface should be used, but it has known restrictions.</li>
-</ul><p></p><p><a href="bugs.html">Daniel Veillard</a></p></td></tr></table></td></tr></table></td></tr></table></td></tr></table></td></tr></table></body></html>
+</ul><p></p><h3><a name="Compacting" id="Compacting">Returning memory to the kernel</a></h3><p>You may encounter that your process using libxml2 does not have a
+reduced memory usage although you freed the trees. This is because
+libxml2 allocates memory in a number of small chunks. When freeing one
+of those chunks, the OS may decide that giving this little memory back
+to the kernel will cause too much overhead and delay the operation. As
+all chunks are this small, they get actually freed but not returned to
+the kernel. On systems using glibc, there is a function call
+"malloc_trim" from malloc.h which does this missing operation (note that
+it is allowed to fail). Thus, after freeing your tree you may simply try
+"malloc_trim(0);" to really get the memory back. If your OS does not
+provide malloc_trim, try searching for a similar function.</p><p></p><p><a href="bugs.html">Daniel Veillard</a></p></td></tr></table></td></tr></table></td></tr></table></td></tr></table></td></tr></table></body></html>