deps/jemalloc/doc/jemalloc.html

   1 <html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>JEMALLOC</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="refentry" title="JEMALLOC"><a name="id2783946"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>jemalloc &#8212; general purpose memory allocation functions</p></div><div class="refsect1" title="LIBRARY"><a name="library"></a><h2>LIBRARY</h2><p>This manual describes jemalloc 2.2.1-0-g5ef7abf6d846720fb3fb8c737861c99b5ad1d862.  More information
   2     can be found at the <a class="ulink" href="http://www.canonware.com/jemalloc/" target="_top">jemalloc website</a>.</p></div><div class="refsynopsisdiv" title="SYNOPSIS"><h2>SYNOPSIS</h2><div class="funcsynopsis"><pre class="funcsynopsisinfo">#include &lt;<code class="filename">stdlib.h</code>&gt;
   3 #include &lt;<code class="filename">jemalloc/jemalloc.h</code>&gt;</pre><div class="refsect2" title="Standard API"><a name="id2830421"></a><h3>Standard API</h3><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" class="funcprototype-table"><tr><td><code class="funcdef">void *<b class="fsfunc">malloc</b>(</code></td><td>size_t <var class="pdparam">size</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" class="funcprototype-table"><tr><td><code class="funcdef">void *<b class="fsfunc">calloc</b>(</code></td><td>size_t <var class="pdparam">number</var>, </td></tr><tr><td> </td><td>size_t <var class="pdparam">size</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" class="funcprototype-table"><tr><td><code class="funcdef">int <b class="fsfunc">posix_memalign</b>(</code></td><td>void **<var class="pdparam">ptr</var>, </td></tr><tr><td> </td><td>size_t <var class="pdparam">alignment</var>, </td></tr><tr><td> </td><td>size_t <var class="pdparam">size</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" class="funcprototype-table"><tr><td><code class="funcdef">void *<b class="fsfunc">realloc</b>(</code></td><td>void *<var class="pdparam">ptr</var>, </td></tr><tr><td> </td><td>size_t <var class="pdparam">size</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" class="funcprototype-table"><tr><td><code class="funcdef">void <b class="fsfunc">free</b>(</code></td><td>void *<var class="pdparam">ptr</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div><div class="refsect2" title="Non-standard API"><a name="id2837717"></a><h3>Non-standard API</h3><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" class="funcprototype-table"><tr><td><code class="funcdef">size_t <b class="fsfunc">malloc_usable_size</b>(</code></td><td>const void *<var class="pdparam">ptr</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" class="funcprototype-table"><tr><td><code class="funcdef">void <b class="fsfunc">malloc_stats_print</b>(</code></td><td>void <var class="pdparam">(*write_cb)</var>
   4             <code>(</code>void *, const char *<code>)</code>
   5           , </td></tr><tr><td> </td><td>void *<var class="pdparam">cbopaque</var>, </td></tr><tr><td> </td><td>const char *<var class="pdparam">opts</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" class="funcprototype-table"><tr><td><code class="funcdef">int <b class="fsfunc">mallctl</b>(</code></td><td>const char *<var class="pdparam">name</var>, </td></tr><tr><td> </td><td>void *<var class="pdparam">oldp</var>, </td></tr><tr><td> </td><td>size_t *<var class="pdparam">oldlenp</var>, </td></tr><tr><td> </td><td>void *<var class="pdparam">newp</var>, </td></tr><tr><td> </td><td>size_t <var class="pdparam">newlen</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" class="funcprototype-table"><tr><td><code class="funcdef">int <b class="fsfunc">mallctlnametomib</b>(</code></td><td>const char *<var class="pdparam">name</var>, </td></tr><tr><td> </td><td>size_t *<var class="pdparam">mibp</var>, </td></tr><tr><td> </td><td>size_t *<var class="pdparam">miblenp</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" class="funcprototype-table"><tr><td><code class="funcdef">int <b class="fsfunc">mallctlbymib</b>(</code></td><td>const size_t *<var class="pdparam">mib</var>, </td></tr><tr><td> </td><td>size_t <var class="pdparam">miblen</var>, </td></tr><tr><td> </td><td>void *<var class="pdparam">oldp</var>, </td></tr><tr><td> </td><td>size_t *<var class="pdparam">oldlenp</var>, </td></tr><tr><td> </td><td>void *<var class="pdparam">newp</var>, </td></tr><tr><td> </td><td>size_t <var class="pdparam">newlen</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" class="funcprototype-table"><tr><td><code class="funcdef">void <b class="fsfunc">(*malloc_message)</b>(</code></td><td>void *<var class="pdparam">cbopaque</var>, </td></tr><tr><td> </td><td>const char *<var class="pdparam">s</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><p><span class="type">const char *</span><code class="varname">malloc_conf</code>;</p></div><div class="refsect2" title="Experimental API"><a name="id2830042"></a><h3>Experimental API</h3><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" class="funcprototype-table"><tr><td><code class="funcdef">int <b class="fsfunc">allocm</b>(</code></td><td>void **<var class="pdparam">ptr</var>, </td></tr><tr><td> </td><td>size_t *<var class="pdparam">rsize</var>, </td></tr><tr><td> </td><td>size_t <var class="pdparam">size</var>, </td></tr><tr><td> </td><td>int <var class="pdparam">flags</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" class="funcprototype-table"><tr><td><code class="funcdef">int <b class="fsfunc">rallocm</b>(</code></td><td>void **<var class="pdparam">ptr</var>, </td></tr><tr><td> </td><td>size_t *<var class="pdparam">rsize</var>, </td></tr><tr><td> </td><td>size_t <var class="pdparam">size</var>, </td></tr><tr><td> </td><td>size_t <var class="pdparam">extra</var>, </td></tr><tr><td> </td><td>int <var class="pdparam">flags</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" class="funcprototype-table"><tr><td><code class="funcdef">int <b class="fsfunc">sallocm</b>(</code></td><td>const void *<var class="pdparam">ptr</var>, </td></tr><tr><td> </td><td>size_t *<var class="pdparam">rsize</var>, </td></tr><tr><td> </td><td>int <var class="pdparam">flags</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" summary="Function synopsis" cellspacing="0" cellpadding="0" class="funcprototype-table"><tr><td><code class="funcdef">int <b class="fsfunc">dallocm</b>(</code></td><td>void *<var class="pdparam">ptr</var>, </td></tr><tr><td> </td><td>int <var class="pdparam">flags</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div></div><div class="refsect1" title="DESCRIPTION"><a name="description"></a><h2>DESCRIPTION</h2><div class="refsect2" title="Standard API"><a name="id2840968"></a><h3>Standard API</h3><p>The <code class="function">malloc</code>(<em class="parameter"><code></code></em>) function allocates
   6       <em class="parameter"><code>size</code></em> bytes of uninitialized memory.  The allocated
   7       space is suitably aligned (after possible pointer coercion) for storage
   8       of any type of object.</p><p>The <code class="function">calloc</code>(<em class="parameter"><code></code></em>) function allocates
   9       space for <em class="parameter"><code>number</code></em> objects, each
  10       <em class="parameter"><code>size</code></em> bytes in length.  The result is identical to
  11       calling <code class="function">malloc</code>(<em class="parameter"><code></code></em>) with an argument of
  12       <em class="parameter"><code>number</code></em> * <em class="parameter"><code>size</code></em>, with the
  13       exception that the allocated memory is explicitly initialized to zero
  14       bytes.</p><p>The <code class="function">posix_memalign</code>(<em class="parameter"><code></code></em>) function
  15       allocates <em class="parameter"><code>size</code></em> bytes of memory such that the
  16       allocation's base address is an even multiple of
  17       <em class="parameter"><code>alignment</code></em>, and returns the allocation in the value
  18       pointed to by <em class="parameter"><code>ptr</code></em>.  The requested
  19       <em class="parameter"><code>alignment</code></em> must be a power of 2 at least as large
  20       as <code class="code">sizeof(<span class="type">void *</span>)</code>.</p><p>The <code class="function">realloc</code>(<em class="parameter"><code></code></em>) function changes the
  21       size of the previously allocated memory referenced by
  22       <em class="parameter"><code>ptr</code></em> to <em class="parameter"><code>size</code></em> bytes.  The
  23       contents of the memory are unchanged up to the lesser of the new and old
  24       sizes.  If the new size is larger, the contents of the newly allocated
  25       portion of the memory are undefined.  Upon success, the memory referenced
  26       by <em class="parameter"><code>ptr</code></em> is freed and a pointer to the newly
  27       allocated memory is returned.  Note that
  28       <code class="function">realloc</code>(<em class="parameter"><code></code></em>) may move the memory allocation,
  29       resulting in a different return value than <em class="parameter"><code>ptr</code></em>.
  30       If <em class="parameter"><code>ptr</code></em> is <code class="constant">NULL</code>, the
  31       <code class="function">realloc</code>(<em class="parameter"><code></code></em>) function behaves identically to
  32       <code class="function">malloc</code>(<em class="parameter"><code></code></em>) for the specified size.</p><p>The <code class="function">free</code>(<em class="parameter"><code></code></em>) function causes the
  33       allocated memory referenced by <em class="parameter"><code>ptr</code></em> to be made
  34       available for future allocations.  If <em class="parameter"><code>ptr</code></em> is
  35       <code class="constant">NULL</code>, no action occurs.</p></div><div class="refsect2" title="Non-standard API"><a name="id2827225"></a><h3>Non-standard API</h3><p>The <code class="function">malloc_usable_size</code>(<em class="parameter"><code></code></em>) function
  36       returns the usable size of the allocation pointed to by
  37       <em class="parameter"><code>ptr</code></em>.  The return value may be larger than the size
  38       that was requested during allocation.  The
  39       <code class="function">malloc_usable_size</code>(<em class="parameter"><code></code></em>) function is not a
  40       mechanism for in-place <code class="function">realloc</code>(<em class="parameter"><code></code></em>); rather
  41       it is provided solely as a tool for introspection purposes.  Any
  42       discrepancy between the requested allocation size and the size reported
  43       by <code class="function">malloc_usable_size</code>(<em class="parameter"><code></code></em>) should not be
  44       depended on, since such behavior is entirely implementation-dependent.
  45       </p><p>The <code class="function">malloc_stats_print</code>(<em class="parameter"><code></code></em>) function
  46       writes human-readable summary statistics via the
  47       <em class="parameter"><code>write_cb</code></em> callback function pointer and
  48       <em class="parameter"><code>cbopaque</code></em> data passed to
  49       <em class="parameter"><code>write_cb</code></em>, or
  50       <code class="function">malloc_message</code>(<em class="parameter"><code></code></em>) if
  51       <em class="parameter"><code>write_cb</code></em> is <code class="constant">NULL</code>.  This
  52       function can be called repeatedly.  General information that never
  53       changes during execution can be omitted by specifying "g" as a character
  54       within the <em class="parameter"><code>opts</code></em> string.  Note that
  55       <code class="function">malloc_message</code>(<em class="parameter"><code></code></em>) uses the
  56       <code class="function">mallctl*</code>(<em class="parameter"><code></code></em>) functions internally, so
  57       inconsistent statistics can be reported if multiple threads use these
  58       functions simultaneously.  If <code class="option">--enable-stats</code> is
  59       specified during configuration, &#8220;m&#8221; and &#8220;a&#8221; can
  60       be specified to omit merged arena and per arena statistics, respectively;
  61       &#8220;b&#8221; and &#8220;l&#8221; can be specified to omit per size
  62       class statistics for bins and large objects, respectively.  Unrecognized
  63       characters are silently ignored.  Note that thread caching may prevent
  64       some statistics from being completely up to date, since extra locking
  65       would be required to merge counters that track thread cache operations.
  66       </p><p>The <code class="function">mallctl</code>(<em class="parameter"><code></code></em>) function provides a
  67       general interface for introspecting the memory allocator, as well as
  68       setting modifiable parameters and triggering actions.  The
  69       period-separated <em class="parameter"><code>name</code></em> argument specifies a
  70       location in a tree-structured namespace; see the <a class="xref" href="#mallctl_namespace" title="MALLCTL NAMESPACE">MALLCTL NAMESPACE</a> section for
  71       documentation on the tree contents.  To read a value, pass a pointer via
  72       <em class="parameter"><code>oldp</code></em> to adequate space to contain the value, and a
  73       pointer to its length via <em class="parameter"><code>oldlenp</code></em>; otherwise pass
  74       <code class="constant">NULL</code> and <code class="constant">NULL</code>.  Similarly, to
  75       write a value, pass a pointer to the value via
  76       <em class="parameter"><code>newp</code></em>, and its length via
  77       <em class="parameter"><code>newlen</code></em>; otherwise pass <code class="constant">NULL</code>
  78       and <code class="constant">0</code>.</p><p>The <code class="function">mallctlnametomib</code>(<em class="parameter"><code></code></em>) function
  79       provides a way to avoid repeated name lookups for applications that
  80       repeatedly query the same portion of the namespace, by translating a name
  81       to a &#8220;Management Information Base&#8221; (MIB) that can be passed
  82       repeatedly to <code class="function">mallctlbymib</code>(<em class="parameter"><code></code></em>).  Upon
  83       successful return from <code class="function">mallctlnametomib</code>(<em class="parameter"><code></code></em>),
  84       <em class="parameter"><code>mibp</code></em> contains an array of
  85       <em class="parameter"><code>*miblenp</code></em> integers, where
  86       <em class="parameter"><code>*miblenp</code></em> is the lesser of the number of components
  87       in <em class="parameter"><code>name</code></em> and the input value of
  88       <em class="parameter"><code>*miblenp</code></em>.  Thus it is possible to pass a
  89       <em class="parameter"><code>*miblenp</code></em> that is smaller than the number of
  90       period-separated name components, which results in a partial MIB that can
  91       be used as the basis for constructing a complete MIB.  For name
  92       components that are integers (e.g. the 2 in
  93       <a class="link" href="#arenas.bin.i.size">
  94     "<code class="mallctl">arenas.bin.2.size</code>"
  95   </a>),
  96       the corresponding MIB component will always be that integer.  Therefore,
  97       it is legitimate to construct code like the following: </p><pre class="programlisting">
  98 unsigned nbins, i;
  99
 100 int mib[4];
 101 size_t len, miblen;
 102
 103 len = sizeof(nbins);
 104 mallctl("arenas.nbins", &amp;nbins, &amp;len, NULL, 0);
 105
 106 miblen = 4;
 107 mallnametomib("arenas.bin.0.size", mib, &amp;miblen);
 108 for (i = 0; i &lt; nbins; i++) {
 109         size_t bin_size;
 110
 111         mib[2] = i;
 112         len = sizeof(bin_size);
 113         mallctlbymib(mib, miblen, &amp;bin_size, &amp;len, NULL, 0);
 114         /* Do something with bin_size... */
 115 }</pre></div><div class="refsect2" title="Experimental API"><a name="id2807945"></a><h3>Experimental API</h3><p>The experimental API is subject to change or removal without regard
 116       for backward compatibility.</p><p>The <code class="function">allocm</code>(<em class="parameter"><code></code></em>),
 117       <code class="function">rallocm</code>(<em class="parameter"><code></code></em>),
 118       <code class="function">sallocm</code>(<em class="parameter"><code></code></em>), and
 119       <code class="function">dallocm</code>(<em class="parameter"><code></code></em>) functions all have a
 120       <em class="parameter"><code>flags</code></em> argument that can be used to specify
 121       options.  The functions only check the options that are contextually
 122       relevant.  Use bitwise or (<code class="code">|</code>) operations to
 123       specify one or more of the following:
 124         </p><div class="variablelist"><dl><dt><span class="term"><code class="constant">ALLOCM_LG_ALIGN(<em class="parameter"><code>la</code></em>)
 125             </code></span></dt><dd><p>Align the memory allocation to start at an address
 126             that is a multiple of <code class="code">(1 &lt;&lt;
 127             <em class="parameter"><code>la</code></em>)</code>.  This macro does not validate
 128             that <em class="parameter"><code>la</code></em> is within the valid
 129             range.</p></dd><dt><span class="term"><code class="constant">ALLOCM_ALIGN(<em class="parameter"><code>a</code></em>)
 130             </code></span></dt><dd><p>Align the memory allocation to start at an address
 131             that is a multiple of <em class="parameter"><code>a</code></em>, where
 132             <em class="parameter"><code>a</code></em> is a power of two.  This macro does not
 133             validate that <em class="parameter"><code>a</code></em> is a power of 2.
 134             </p></dd><dt><span class="term"><code class="constant">ALLOCM_ZERO</code></span></dt><dd><p>Initialize newly allocated memory to contain zero
 135             bytes.  In the growing reallocation case, the real size prior to
 136             reallocation defines the boundary between untouched bytes and those
 137             that are initialized to contain zero bytes.  If this option is
 138             absent, newly allocated memory is uninitialized.</p></dd><dt><span class="term"><code class="constant">ALLOCM_NO_MOVE</code></span></dt><dd><p>For reallocation, fail rather than moving the
 139             object.  This constraint can apply to both growth and
 140             shrinkage.</p></dd></dl></div><p>
 141       </p><p>The <code class="function">allocm</code>(<em class="parameter"><code></code></em>) function allocates at
 142       least <em class="parameter"><code>size</code></em> bytes of memory, sets
 143       <em class="parameter"><code>*ptr</code></em> to the base address of the allocation, and
 144       sets <em class="parameter"><code>*rsize</code></em> to the real size of the allocation if
 145       <em class="parameter"><code>rsize</code></em> is not <code class="constant">NULL</code>.</p><p>The <code class="function">rallocm</code>(<em class="parameter"><code></code></em>) function resizes the
 146       allocation at <em class="parameter"><code>*ptr</code></em> to be at least
 147       <em class="parameter"><code>size</code></em> bytes, sets <em class="parameter"><code>*ptr</code></em> to
 148       the base address of the allocation if it moved, and sets
 149       <em class="parameter"><code>*rsize</code></em> to the real size of the allocation if
 150       <em class="parameter"><code>rsize</code></em> is not <code class="constant">NULL</code>.  If
 151       <em class="parameter"><code>extra</code></em> is non-zero, an attempt is made to resize
 152       the allocation to be at least <code class="code"><em class="parameter"><code>size</code></em> +
 153       <em class="parameter"><code>extra</code></em>)</code> bytes, though inability to allocate
 154       the extra byte(s) will not by itself result in failure.  Behavior is
 155       undefined if <code class="code">(<em class="parameter"><code>size</code></em> +
 156       <em class="parameter"><code>extra</code></em> &gt;
 157       <code class="constant">SIZE_T_MAX</code>)</code>.</p><p>The <code class="function">sallocm</code>(<em class="parameter"><code></code></em>) function sets
 158       <em class="parameter"><code>*rsize</code></em> to the real size of the allocation.</p><p>The <code class="function">dallocm</code>(<em class="parameter"><code></code></em>) function causes the
 159       memory referenced by <em class="parameter"><code>ptr</code></em> to be made available for
 160       future allocations.</p></div></div><div class="refsect1" title="TUNING"><a name="tuning"></a><h2>TUNING</h2><p>Once, when the first call is made to one of the memory allocation
 161     routines, the allocator initializes its internals based in part on various
 162     options that can be specified at compile- or run-time.</p><p>The string pointed to by the global variable
 163     <code class="varname">malloc_conf</code>, the &#8220;name&#8221; of the file
 164     referenced by the symbolic link named <code class="filename">/etc/malloc.conf</code>, and the value of the
 165     environment variable <code class="envar">MALLOC_CONF</code>, will be interpreted, in
 166     that order, from left to right as options.</p><p>An options string is a comma-separated list of option:value pairs.
 167     There is one key corresponding to each <a class="link" href="#opt.abort">
 168     "<code class="mallctl">opt.*</code>"
 169   </a> mallctl (see the <a class="xref" href="#mallctl_namespace" title="MALLCTL NAMESPACE">MALLCTL NAMESPACE</a> section for options
 170     documentation).  For example, <code class="literal">abort:true,narenas:1</code> sets
 171     the <a class="link" href="#opt.abort">
 172     "<code class="mallctl">opt.abort</code>"
 173   </a> and <a class="link" href="#opt.narenas">
 174     "<code class="mallctl">opt.narenas</code>"
 175   </a> options.  Some
 176     options have boolean values (true/false), others have integer values (base
 177     8, 10, or 16, depending on prefix), and yet others have raw string
 178     values.</p></div><div class="refsect1" title="IMPLEMENTATION NOTES"><a name="implementation_notes"></a><h2>IMPLEMENTATION NOTES</h2><p>Traditionally, allocators have used
 179     <span class="citerefentry"><span class="refentrytitle">sbrk</span>(2)</span> to obtain memory, which is
 180     suboptimal for several reasons, including race conditions, increased
 181     fragmentation, and artificial limitations on maximum usable memory.  If
 182     <code class="option">--enable-dss</code> is specified during configuration, this
 183     allocator uses both <span class="citerefentry"><span class="refentrytitle">sbrk</span>(2)</span> and
 184     <span class="citerefentry"><span class="refentrytitle">mmap</span>(2)</span>, in that order of preference;
 185     otherwise only <span class="citerefentry"><span class="refentrytitle">mmap</span>(2)</span> is used.</p><p>This allocator uses multiple arenas in order to reduce lock
 186     contention for threaded programs on multi-processor systems.  This works
 187     well with regard to threading scalability, but incurs some costs.  There is
 188     a small fixed per-arena overhead, and additionally, arenas manage memory
 189     completely independently of each other, which means a small fixed increase
 190     in overall memory fragmentation.  These overheads are not generally an
 191     issue, given the number of arenas normally used.  Note that using
 192     substantially more arenas than the default is not likely to improve
 193     performance, mainly due to reduced cache performance.  However, it may make
 194     sense to reduce the number of arenas if an application does not make much
 195     use of the allocation functions.</p><p>In addition to multiple arenas, unless
 196     <code class="option">--disable-tcache</code> is specified during configuration, this
 197     allocator supports thread-specific caching for small and large objects, in
 198     order to make it possible to completely avoid synchronization for most
 199     allocation requests.  Such caching allows very fast allocation in the
 200     common case, but it increases memory usage and fragmentation, since a
 201     bounded number of objects can remain allocated in each thread cache.</p><p>Memory is conceptually broken into equal-sized chunks, where the
 202     chunk size is a power of two that is greater than the page size.  Chunks
 203     are always aligned to multiples of the chunk size.  This alignment makes it
 204     possible to find metadata for user objects very quickly.</p><p>User objects are broken into three categories according to size:
 205     small, large, and huge.  Small objects are smaller than one page.  Large
 206     objects are smaller than the chunk size.  Huge objects are a multiple of
 207     the chunk size.  Small and large objects are managed by arenas; huge
 208     objects are managed separately in a single data structure that is shared by
 209     all threads.  Huge objects are used by applications infrequently enough
 210     that this single data structure is not a scalability issue.</p><p>Each chunk that is managed by an arena tracks its contents as runs of
 211     contiguous pages (unused, backing a set of small objects, or backing one
 212     large object).  The combination of chunk alignment and chunk page maps
 213     makes it possible to determine all metadata regarding small and large
 214     allocations in constant time.</p><p>Small objects are managed in groups by page runs.  Each run maintains
 215     a frontier and free list to track which regions are in use.  Unless
 216     <code class="option">--disable-tiny</code> is specified during configuration,
 217     allocation requests that are no more than half the quantum (8 or 16,
 218     depending on architecture) are rounded up to the nearest power of two that
 219     is at least <code class="code">sizeof(<span class="type">void *</span>)</code>.
 220     Allocation requests that are more than half the quantum, but no more than
 221     the minimum cacheline-multiple size class (see the <a class="link" href="#opt.lg_qspace_max">
 222     "<code class="mallctl">opt.lg_qspace_max</code>"
 223   </a>
 224     option) are rounded up to the nearest multiple of the quantum.  Allocation
 225     requests that are more than the minimum cacheline-multiple size class, but
 226     no more than the minimum subpage-multiple size class (see the <a class="link" href="#opt.lg_cspace_max">
 227     "<code class="mallctl">opt.lg_cspace_max</code>"
 228   </a>
 229     option) are rounded up to the nearest multiple of the cacheline size (64).
 230     Allocation requests that are more than the minimum subpage-multiple size
 231     class, but no more than the maximum subpage-multiple size class are rounded
 232     up to the nearest multiple of the subpage size (256).  Allocation requests
 233     that are more than the maximum subpage-multiple size class, but small
 234     enough to fit in an arena-managed chunk (see the <a class="link" href="#opt.lg_chunk">
 235     "<code class="mallctl">opt.lg_chunk</code>"
 236   </a> option), are
 237     rounded up to the nearest run size.  Allocation requests that are too large
 238     to fit in an arena-managed chunk are rounded up to the nearest multiple of
 239     the chunk size.</p><p>Allocations are packed tightly together, which can be an issue for
 240     multi-threaded applications.  If you need to assure that allocations do not
 241     suffer from cacheline sharing, round your allocation requests up to the
 242     nearest multiple of the cacheline size, or specify cacheline alignment when
 243     allocating.</p><p>Assuming 4 MiB chunks, 4 KiB pages, and a 16-byte quantum on a 64-bit
 244     system, the size classes in each category are as shown in <a class="xref" href="#size_classes" title="Table 1. Size classes">Table 1</a>.</p><div class="table"><a name="size_classes"></a><p class="title"><b>Table 1. Size classes</b></p><div class="table-contents"><table summary="Size classes" border="1"><colgroup><col align="left"><col align="left"><col align="left"></colgroup><thead><tr><th align="left">Category</th><th align="left">Subcategory</th><th align="left">Size</th></tr></thead><tbody><tr><td rowspan="4" align="left">Small</td><td align="left">Tiny</td><td align="left">[8]</td></tr><tr><td align="left">Quantum-spaced</td><td align="left">[16, 32, 48, ..., 128]</td></tr><tr><td align="left">Cacheline-spaced</td><td align="left">[192, 256, 320, ..., 512]</td></tr><tr><td align="left">Subpage-spaced</td><td align="left">[768, 1024, 1280, ..., 3840]</td></tr><tr><td colspan="2" align="left">Large</td><td align="left">[4 KiB, 8 KiB, 12 KiB, ..., 4072 KiB]</td></tr><tr><td colspan="2" align="left">Huge</td><td align="left">[4 MiB, 8 MiB, 12 MiB, ...]</td></tr></tbody></table></div></div><br class="table-break"></div><div class="refsect1" title="MALLCTL NAMESPACE"><a name="mallctl_namespace"></a><h2>MALLCTL NAMESPACE</h2><p>The following names are defined in the namespace accessible via the
 245     <code class="function">mallctl*</code>(<em class="parameter"><code></code></em>) functions.  Value types are
 246     specified in parentheses, their readable/writable statuses are encoded as
 247     <code class="literal">rw</code>, <code class="literal">r-</code>, <code class="literal">-w</code>, or
 248     <code class="literal">--</code>, and required build configuration flags follow, if
 249     any.  A name element encoded as <code class="literal">&lt;i&gt;</code> or
 250     <code class="literal">&lt;j&gt;</code> indicates an integer component, where the
 251     integer varies from 0 to some upper value that must be determined via
 252     introspection.  In the case of
 253     "<code class="mallctl">stats.arenas.&lt;i&gt;.*</code>"
 254   ,
 255     <code class="literal">&lt;i&gt;</code> equal to <a class="link" href="#arenas.narenas">
 256     "<code class="mallctl">arenas.narenas</code>"
 257   </a> can be
 258     used to access the summation of statistics from all arenas.  Take special
 259     note of the <a class="link" href="#epoch">
 260     "<code class="mallctl">epoch</code>"
 261   </a> mallctl,
 262     which controls refreshing of cached dynamic statistics.</p><div class="variablelist"><dl><dt><span class="term">
 263
 264     "<code class="mallctl">version</code>"
 265
 266           (<span class="type">const char *</span>)
 267           <code class="literal">r-</code>
 268         </span></dt><dd><p>Return the jemalloc version string.</p></dd><dt><a name="epoch"></a><span class="term">
 269
 270     "<code class="mallctl">epoch</code>"
 271
 272           (<span class="type">uint64_t</span>)
 273           <code class="literal">rw</code>
 274         </span></dt><dd><p>If a value is passed in, refresh the data from which
 275         the <code class="function">mallctl*</code>(<em class="parameter"><code></code></em>) functions report values,
 276         and increment the epoch.  Return the current epoch.  This is useful for
 277         detecting whether another thread caused a refresh.</p></dd><dt><span class="term">
 278
 279     "<code class="mallctl">config.debug</code>"
 280
 281           (<span class="type">bool</span>)
 282           <code class="literal">r-</code>
 283         </span></dt><dd><p><code class="option">--enable-debug</code> was specified during
 284         build configuration.</p></dd><dt><span class="term">
 285
 286     "<code class="mallctl">config.dss</code>"
 287
 288           (<span class="type">bool</span>)
 289           <code class="literal">r-</code>
 290         </span></dt><dd><p><code class="option">--enable-dss</code> was specified during
 291         build configuration.</p></dd><dt><span class="term">
 292
 293     "<code class="mallctl">config.dynamic_page_shift</code>"
 294
 295           (<span class="type">bool</span>)
 296           <code class="literal">r-</code>
 297         </span></dt><dd><p><code class="option">--enable-dynamic-page-shift</code> was
 298         specified during build configuration.</p></dd><dt><span class="term">
 299
 300     "<code class="mallctl">config.fill</code>"
 301
 302           (<span class="type">bool</span>)
 303           <code class="literal">r-</code>
 304         </span></dt><dd><p><code class="option">--enable-fill</code> was specified during
 305         build configuration.</p></dd><dt><span class="term">
 306
 307     "<code class="mallctl">config.lazy_lock</code>"
 308
 309           (<span class="type">bool</span>)
 310           <code class="literal">r-</code>
 311         </span></dt><dd><p><code class="option">--enable-lazy-lock</code> was specified
 312         during build configuration.</p></dd><dt><span class="term">
 313
 314     "<code class="mallctl">config.prof</code>"
 315
 316           (<span class="type">bool</span>)
 317           <code class="literal">r-</code>
 318         </span></dt><dd><p><code class="option">--enable-prof</code> was specified during
 319         build configuration.</p></dd><dt><span class="term">
 320
 321     "<code class="mallctl">config.prof_libgcc</code>"
 322
 323           (<span class="type">bool</span>)
 324           <code class="literal">r-</code>
 325         </span></dt><dd><p><code class="option">--disable-prof-libgcc</code> was not
 326         specified during build configuration.</p></dd><dt><span class="term">
 327
 328     "<code class="mallctl">config.prof_libunwind</code>"
 329
 330           (<span class="type">bool</span>)
 331           <code class="literal">r-</code>
 332         </span></dt><dd><p><code class="option">--enable-prof-libunwind</code> was specified
 333         during build configuration.</p></dd><dt><span class="term">
 334
 335     "<code class="mallctl">config.stats</code>"
 336
 337           (<span class="type">bool</span>)
 338           <code class="literal">r-</code>
 339         </span></dt><dd><p><code class="option">--enable-stats</code> was specified during
 340         build configuration.</p></dd><dt><span class="term">
 341
 342     "<code class="mallctl">config.swap</code>"
 343
 344           (<span class="type">bool</span>)
 345           <code class="literal">r-</code>
 346         </span></dt><dd><p><code class="option">--enable-swap</code> was specified during
 347         build configuration.</p></dd><dt><span class="term">
 348
 349     "<code class="mallctl">config.sysv</code>"
 350
 351           (<span class="type">bool</span>)
 352           <code class="literal">r-</code>
 353         </span></dt><dd><p><code class="option">--enable-sysv</code> was specified during
 354         build configuration.</p></dd><dt><span class="term">
 355
 356     "<code class="mallctl">config.tcache</code>"
 357
 358           (<span class="type">bool</span>)
 359           <code class="literal">r-</code>
 360         </span></dt><dd><p><code class="option">--disable-tcache</code> was not specified
 361         during build configuration.</p></dd><dt><span class="term">
 362
 363     "<code class="mallctl">config.tiny</code>"
 364
 365           (<span class="type">bool</span>)
 366           <code class="literal">r-</code>
 367         </span></dt><dd><p><code class="option">--disable-tiny</code> was not specified
 368         during build configuration.</p></dd><dt><span class="term">
 369
 370     "<code class="mallctl">config.tls</code>"
 371
 372           (<span class="type">bool</span>)
 373           <code class="literal">r-</code>
 374         </span></dt><dd><p><code class="option">--disable-tls</code> was not specified during
 375         build configuration.</p></dd><dt><span class="term">
 376
 377     "<code class="mallctl">config.xmalloc</code>"
 378
 379           (<span class="type">bool</span>)
 380           <code class="literal">r-</code>
 381         </span></dt><dd><p><code class="option">--enable-xmalloc</code> was specified during
 382         build configuration.</p></dd><dt><a name="opt.abort"></a><span class="term">
 383
 384     "<code class="mallctl">opt.abort</code>"
 385
 386           (<span class="type">bool</span>)
 387           <code class="literal">r-</code>
 388         </span></dt><dd><p>Abort-on-warning enabled/disabled.  If true, most
 389         warnings are fatal.  The process will call
 390         <span class="citerefentry"><span class="refentrytitle">abort</span>(3)</span> in these cases.  This option is
 391         disabled by default unless <code class="option">--enable-debug</code> is
 392         specified during configuration, in which case it is enabled by default.
 393         </p></dd><dt><a name="opt.lg_qspace_max"></a><span class="term">
 394
 395     "<code class="mallctl">opt.lg_qspace_max</code>"
 396
 397           (<span class="type">size_t</span>)
 398           <code class="literal">r-</code>
 399         </span></dt><dd><p>Size (log base 2) of the maximum size class that is a
 400         multiple of the quantum (8 or 16 bytes, depending on architecture).
 401         Above this size, cacheline spacing is used for size classes.  The
 402         default value is 128 bytes (2^7).</p></dd><dt><a name="opt.lg_cspace_max"></a><span class="term">
 403
 404     "<code class="mallctl">opt.lg_cspace_max</code>"
 405
 406           (<span class="type">size_t</span>)
 407           <code class="literal">r-</code>
 408         </span></dt><dd><p>Size (log base 2) of the maximum size class that is a
 409         multiple of the cacheline size (64).  Above this size, subpage spacing
 410         (256 bytes) is used for size classes.  The default value is 512 bytes
 411         (2^9).</p></dd><dt><a name="opt.lg_chunk"></a><span class="term">
 412
 413     "<code class="mallctl">opt.lg_chunk</code>"
 414
 415           (<span class="type">size_t</span>)
 416           <code class="literal">r-</code>
 417         </span></dt><dd><p>Virtual memory chunk size (log base 2).  The default
 418         chunk size is 4 MiB (2^22).</p></dd><dt><a name="opt.narenas"></a><span class="term">
 419
 420     "<code class="mallctl">opt.narenas</code>"
 421
 422           (<span class="type">size_t</span>)
 423           <code class="literal">r-</code>
 424         </span></dt><dd><p>Maximum number of arenas to use.  The default maximum
 425         number of arenas is four times the number of CPUs, or one if there is a
 426         single CPU.</p></dd><dt><a name="opt.lg_dirty_mult"></a><span class="term">
 427
 428     "<code class="mallctl">opt.lg_dirty_mult</code>"
 429
 430           (<span class="type">ssize_t</span>)
 431           <code class="literal">r-</code>
 432         </span></dt><dd><p>Per-arena minimum ratio (log base 2) of active to dirty
 433         pages.  Some dirty unused pages may be allowed to accumulate, within
 434         the limit set by the ratio (or one chunk worth of dirty pages,
 435         whichever is greater), before informing the kernel about some of those
 436         pages via <span class="citerefentry"><span class="refentrytitle">madvise</span>(2)</span> or a similar system call.  This
 437         provides the kernel with sufficient information to recycle dirty pages
 438         if physical memory becomes scarce and the pages remain unused.  The
 439         default minimum ratio is 32:1 (2^5:1); an option value of -1 will
 440         disable dirty page purging.</p></dd><dt><a name="opt.stats_print"></a><span class="term">
 441
 442     "<code class="mallctl">opt.stats_print</code>"
 443
 444           (<span class="type">bool</span>)
 445           <code class="literal">r-</code>
 446         </span></dt><dd><p>Enable/disable statistics printing at exit.  If
 447         enabled, the <code class="function">malloc_stats_print</code>(<em class="parameter"><code></code></em>)
 448         function is called at program exit via an
 449         <span class="citerefentry"><span class="refentrytitle">atexit</span>(3)</span> function.  If
 450         <code class="option">--enable-stats</code> is specified during configuration, this
 451         has the potential to cause deadlock for a multi-threaded process that
 452         exits while one or more threads are executing in the memory allocation
 453         functions.  Therefore, this option should only be used with care; it is
 454         primarily intended as a performance tuning aid during application
 455         development.  This option is disabled by default.</p></dd><dt><a name="opt.junk"></a><span class="term">
 456
 457     "<code class="mallctl">opt.junk</code>"
 458
 459           (<span class="type">bool</span>)
 460           <code class="literal">r-</code>
 461           [<code class="option">--enable-fill</code>]
 462         </span></dt><dd><p>Junk filling enabled/disabled.  If enabled, each byte
 463         of uninitialized allocated memory will be initialized to
 464         <code class="literal">0xa5</code>.  All deallocated memory will be initialized to
 465         <code class="literal">0x5a</code>.  This is intended for debugging and will
 466         impact performance negatively.  This option is disabled by default
 467         unless <code class="option">--enable-debug</code> is specified during
 468         configuration, in which case it is enabled by default.</p></dd><dt><a name="opt.zero"></a><span class="term">
 469
 470     "<code class="mallctl">opt.zero</code>"
 471
 472           (<span class="type">bool</span>)
 473           <code class="literal">r-</code>
 474           [<code class="option">--enable-fill</code>]
 475         </span></dt><dd><p>Zero filling enabled/disabled.  If enabled, each byte
 476         of uninitialized allocated memory will be initialized to 0.  Note that
 477         this initialization only happens once for each byte, so
 478         <code class="function">realloc</code>(<em class="parameter"><code></code></em>) and
 479         <code class="function">rallocm</code>(<em class="parameter"><code></code></em>) calls do not zero memory that
 480         was previously allocated.  This is intended for debugging and will
 481         impact performance negatively.  This option is disabled by default.
 482         </p></dd><dt><a name="opt.sysv"></a><span class="term">
 483
 484     "<code class="mallctl">opt.sysv</code>"
 485
 486           (<span class="type">bool</span>)
 487           <code class="literal">r-</code>
 488           [<code class="option">--enable-sysv</code>]
 489         </span></dt><dd><p>If enabled, attempting to allocate zero bytes will
 490         return a <code class="constant">NULL</code> pointer instead of a valid pointer.
 491         (The default behavior is to make a minimal allocation and return a
 492         pointer to it.) This option is provided for System V compatibility.
 493         This option is incompatible with the <a class="link" href="#opt.xmalloc">
 494     "<code class="mallctl">opt.xmalloc</code>"
 495   </a> option.
 496         This option is disabled by default.</p></dd><dt><a name="opt.xmalloc"></a><span class="term">
 497
 498     "<code class="mallctl">opt.xmalloc</code>"
 499
 500           (<span class="type">bool</span>)
 501           <code class="literal">r-</code>
 502           [<code class="option">--enable-xmalloc</code>]
 503         </span></dt><dd><p>Abort-on-out-of-memory enabled/disabled.  If enabled,
 504         rather than returning failure for any allocation function, display a
 505         diagnostic message on <code class="constant">STDERR_FILENO</code> and cause the
 506         program to drop core (using
 507         <span class="citerefentry"><span class="refentrytitle">abort</span>(3)</span>).  If an application is
 508         designed to depend on this behavior, set the option at compile time by
 509         including the following in the source code:
 510         </p><pre class="programlisting">
 511 malloc_conf = "xmalloc:true";</pre><p>
 512         This option is disabled by default.</p></dd><dt><a name="opt.tcache"></a><span class="term">
 513
 514     "<code class="mallctl">opt.tcache</code>"
 515
 516           (<span class="type">bool</span>)
 517           <code class="literal">r-</code>
 518           [<code class="option">--enable-tcache</code>]
 519         </span></dt><dd><p>Thread-specific caching enabled/disabled.  When there
 520         are multiple threads, each thread uses a thread-specific cache for
 521         objects up to a certain size.  Thread-specific caching allows many
 522         allocations to be satisfied without performing any thread
 523         synchronization, at the cost of increased memory use.  See the
 524         <a class="link" href="#opt.lg_tcache_gc_sweep">
 525     "<code class="mallctl">opt.lg_tcache_gc_sweep</code>"
 526   </a>
 527         and <a class="link" href="#opt.lg_tcache_max">
 528     "<code class="mallctl">opt.lg_tcache_max</code>"
 529   </a>
 530         options for related tuning information.  This option is enabled by
 531         default.</p></dd><dt><a name="opt.lg_tcache_gc_sweep"></a><span class="term">
 532
 533     "<code class="mallctl">opt.lg_tcache_gc_sweep</code>"
 534
 535           (<span class="type">ssize_t</span>)
 536           <code class="literal">r-</code>
 537           [<code class="option">--enable-tcache</code>]
 538         </span></dt><dd><p>Approximate interval (log base 2) between full
 539         thread-specific cache garbage collection sweeps, counted in terms of
 540         thread-specific cache allocation/deallocation events.  Garbage
 541         collection is actually performed incrementally, one size class at a
 542         time, in order to avoid large collection pauses.  The default sweep
 543         interval is 8192 (2^13); setting this option to -1 will disable garbage
 544         collection.</p></dd><dt><a name="opt.lg_tcache_max"></a><span class="term">
 545
 546     "<code class="mallctl">opt.lg_tcache_max</code>"
 547
 548           (<span class="type">size_t</span>)
 549           <code class="literal">r-</code>
 550           [<code class="option">--enable-tcache</code>]
 551         </span></dt><dd><p>Maximum size class (log base 2) to cache in the
 552         thread-specific cache.  At a minimum, all small size classes are
 553         cached, and at a maximum all large size classes are cached.  The
 554         default maximum is 32 KiB (2^15).</p></dd><dt><a name="opt.prof"></a><span class="term">
 555
 556     "<code class="mallctl">opt.prof</code>"
 557
 558           (<span class="type">bool</span>)
 559           <code class="literal">r-</code>
 560           [<code class="option">--enable-prof</code>]
 561         </span></dt><dd><p>Memory profiling enabled/disabled.  If enabled, profile
 562         memory allocation activity, and use an
 563         <span class="citerefentry"><span class="refentrytitle">atexit</span>(3)</span> function to dump final memory
 564         usage to a file named according to the pattern
 565         <code class="filename">&lt;prefix&gt;.&lt;pid&gt;.&lt;seq&gt;.f.heap</code>,
 566         where <code class="literal">&lt;prefix&gt;</code> is controlled by the <a class="link" href="#opt.prof_prefix">
 567     "<code class="mallctl">opt.prof_prefix</code>"
 568   </a>
 569         option.  See the <a class="link" href="#opt.lg_prof_bt_max">
 570     "<code class="mallctl">opt.lg_prof_bt_max</code>"
 571   </a>
 572         option for backtrace depth control.  See the <a class="link" href="#opt.prof_active">
 573     "<code class="mallctl">opt.prof_active</code>"
 574   </a>
 575         option for on-the-fly activation/deactivation.  See the <a class="link" href="#opt.lg_prof_sample">
 576     "<code class="mallctl">opt.lg_prof_sample</code>"
 577   </a>
 578         option for probabilistic sampling control.  See the <a class="link" href="#opt.prof_accum">
 579     "<code class="mallctl">opt.prof_accum</code>"
 580   </a>
 581         option for control of cumulative sample reporting.  See the <a class="link" href="#opt.lg_prof_tcmax">
 582     "<code class="mallctl">opt.lg_prof_tcmax</code>"
 583   </a>
 584         option for control of per thread backtrace caching.  See the <a class="link" href="#opt.lg_prof_interval">
 585     "<code class="mallctl">opt.lg_prof_interval</code>"
 586   </a>
 587         option for information on interval-triggered profile dumping, and the
 588         <a class="link" href="#opt.prof_gdump">
 589     "<code class="mallctl">opt.prof_gdump</code>"
 590   </a>
 591         option for information on high-water-triggered profile dumping.
 592         Profile output is compatible with the included <span class="command"><strong>pprof</strong></span>
 593         Perl script, which originates from the <a class="ulink" href="http://code.google.com/p/google-perftools/" target="_top">google-perftools
 594         package</a>.</p></dd><dt><a name="opt.prof_prefix"></a><span class="term">
 595
 596     "<code class="mallctl">opt.prof_prefix</code>"
 597
 598           (<span class="type">const char *</span>)
 599           <code class="literal">r-</code>
 600           [<code class="option">--enable-prof</code>]
 601         </span></dt><dd><p>Filename prefix for profile dumps.  If the prefix is
 602         set to the empty string, no automatic dumps will occur; this is
 603         primarily useful for disabling the automatic final heap dump (which
 604         also disables leak reporting, if enabled).  The default prefix is
 605         <code class="filename">jeprof</code>.</p></dd><dt><a name="opt.lg_prof_bt_max"></a><span class="term">
 606
 607     "<code class="mallctl">opt.lg_prof_bt_max</code>"
 608
 609           (<span class="type">size_t</span>)
 610           <code class="literal">r-</code>
 611           [<code class="option">--enable-prof</code>]
 612         </span></dt><dd><p>Maximum backtrace depth (log base 2) when profiling
 613         memory allocation activity.  The default is 128 (2^7).</p></dd><dt><a name="opt.prof_active"></a><span class="term">
 614
 615     "<code class="mallctl">opt.prof_active</code>"
 616
 617           (<span class="type">bool</span>)
 618           <code class="literal">r-</code>
 619           [<code class="option">--enable-prof</code>]
 620         </span></dt><dd><p>Profiling activated/deactivated.  This is a secondary
 621         control mechanism that makes it possible to start the application with
 622         profiling enabled (see the <a class="link" href="#opt.prof">
 623     "<code class="mallctl">opt.prof</code>"
 624   </a> option) but
 625         inactive, then toggle profiling at any time during program execution
 626         with the <a class="link" href="#prof.active">
 627     "<code class="mallctl">prof.active</code>"
 628   </a> mallctl.
 629         This option is enabled by default.</p></dd><dt><a name="opt.lg_prof_sample"></a><span class="term">
 630
 631     "<code class="mallctl">opt.lg_prof_sample</code>"
 632
 633           (<span class="type">ssize_t</span>)
 634           <code class="literal">r-</code>
 635           [<code class="option">--enable-prof</code>]
 636         </span></dt><dd><p>Average interval (log base 2) between allocation
 637         samples, as measured in bytes of allocation activity.  Increasing the
 638         sampling interval decreases profile fidelity, but also decreases the
 639         computational overhead.  The default sample interval is 1 (2^0) (i.e.
 640         all allocations are sampled).</p></dd><dt><a name="opt.prof_accum"></a><span class="term">
 641
 642     "<code class="mallctl">opt.prof_accum</code>"
 643
 644           (<span class="type">bool</span>)
 645           <code class="literal">r-</code>
 646           [<code class="option">--enable-prof</code>]
 647         </span></dt><dd><p>Reporting of cumulative object/byte counts in profile
 648         dumps enabled/disabled.  If this option is enabled, every unique
 649         backtrace must be stored for the duration of execution.  Depending on
 650         the application, this can impose a large memory overhead, and the
 651         cumulative counts are not always of interest.  See the
 652         <a class="link" href="#opt.lg_prof_tcmax">
 653     "<code class="mallctl">opt.lg_prof_tcmax</code>"
 654   </a>
 655         option for control of per thread backtrace caching, which has important
 656         interactions.  This option is enabled by default.</p></dd><dt><a name="opt.lg_prof_tcmax"></a><span class="term">
 657
 658     "<code class="mallctl">opt.lg_prof_tcmax</code>"
 659
 660           (<span class="type">ssize_t</span>)
 661           <code class="literal">r-</code>
 662           [<code class="option">--enable-prof</code>]
 663         </span></dt><dd><p>Maximum per thread backtrace cache (log base 2) used
 664         for heap profiling.  A backtrace can only be discarded if the
 665         <a class="link" href="#opt.prof_accum">
 666     "<code class="mallctl">opt.prof_accum</code>"
 667   </a>
 668         option is disabled, and no thread caches currently refer to the
 669         backtrace.  Therefore, a backtrace cache limit should be imposed if the
 670         intention is to limit how much memory is used by backtraces.  By
 671         default, no limit is imposed (encoded as -1).
 672         </p></dd><dt><a name="opt.lg_prof_interval"></a><span class="term">
 673
 674     "<code class="mallctl">opt.lg_prof_interval</code>"
 675
 676           (<span class="type">ssize_t</span>)
 677           <code class="literal">r-</code>
 678           [<code class="option">--enable-prof</code>]
 679         </span></dt><dd><p>Average interval (log base 2) between memory profile
 680         dumps, as measured in bytes of allocation activity.  The actual
 681         interval between dumps may be sporadic because decentralized allocation
 682         counters are used to avoid synchronization bottlenecks.  Profiles are
 683         dumped to files named according to the pattern
 684         <code class="filename">&lt;prefix&gt;.&lt;pid&gt;.&lt;seq&gt;.i&lt;iseq&gt;.heap</code>,
 685         where <code class="literal">&lt;prefix&gt;</code> is controlled by the
 686         <a class="link" href="#opt.prof_prefix">
 687     "<code class="mallctl">opt.prof_prefix</code>"
 688   </a>
 689         option.  By default, interval-triggered profile dumping is disabled
 690         (encoded as -1).
 691         </p></dd><dt><a name="opt.prof_gdump"></a><span class="term">
 692
 693     "<code class="mallctl">opt.prof_gdump</code>"
 694
 695           (<span class="type">bool</span>)
 696           <code class="literal">r-</code>
 697           [<code class="option">--enable-prof</code>]
 698         </span></dt><dd><p>Trigger a memory profile dump every time the total
 699         virtual memory exceeds the previous maximum.  Profiles are dumped to
 700         files named according to the pattern
 701         <code class="filename">&lt;prefix&gt;.&lt;pid&gt;.&lt;seq&gt;.u&lt;useq&gt;.heap</code>,
 702         where <code class="literal">&lt;prefix&gt;</code> is controlled by the <a class="link" href="#opt.prof_prefix">
 703     "<code class="mallctl">opt.prof_prefix</code>"
 704   </a>
 705         option.  This option is disabled by default.</p></dd><dt><a name="opt.prof_leak"></a><span class="term">
 706
 707     "<code class="mallctl">opt.prof_leak</code>"
 708
 709           (<span class="type">bool</span>)
 710           <code class="literal">r-</code>
 711           [<code class="option">--enable-prof</code>]
 712         </span></dt><dd><p>Leak reporting enabled/disabled.  If enabled, use an
 713         <span class="citerefentry"><span class="refentrytitle">atexit</span>(3)</span> function to report memory leaks
 714         detected by allocation sampling.  See the
 715         <a class="link" href="#opt.lg_prof_bt_max">
 716     "<code class="mallctl">opt.lg_prof_bt_max</code>"
 717   </a>
 718         option for backtrace depth control.  See the
 719         <a class="link" href="#opt.prof">
 720     "<code class="mallctl">opt.prof</code>"
 721   </a> option for
 722         information on analyzing heap profile output.  This option is disabled
 723         by default.</p></dd><dt><a name="opt.overcommit"></a><span class="term">
 724
 725     "<code class="mallctl">opt.overcommit</code>"
 726
 727           (<span class="type">bool</span>)
 728           <code class="literal">r-</code>
 729           [<code class="option">--enable-swap</code>]
 730         </span></dt><dd><p>Over-commit enabled/disabled.  If enabled, over-commit
 731         memory as a side effect of using anonymous
 732         <span class="citerefentry"><span class="refentrytitle">mmap</span>(2)</span> or
 733         <span class="citerefentry"><span class="refentrytitle">sbrk</span>(2)</span> for virtual memory allocation.
 734         In order for overcommit to be disabled, the <a class="link" href="#swap.fds">
 735     "<code class="mallctl">swap.fds</code>"
 736   </a> mallctl must have
 737         been successfully written to.  This option is enabled by
 738         default.</p></dd><dt><span class="term">
 739
 740     "<code class="mallctl">tcache.flush</code>"
 741
 742           (<span class="type">void</span>)
 743           <code class="literal">--</code>
 744           [<code class="option">--enable-tcache</code>]
 745         </span></dt><dd><p>Flush calling thread's tcache.  This interface releases
 746         all cached objects and internal data structures associated with the
 747         calling thread's thread-specific cache.  Ordinarily, this interface
 748         need not be called, since automatic periodic incremental garbage
 749         collection occurs, and the thread cache is automatically discarded when
 750         a thread exits.  However, garbage collection is triggered by allocation
 751         activity, so it is possible for a thread that stops
 752         allocating/deallocating to retain its cache indefinitely, in which case
 753         the developer may find manual flushing useful.</p></dd><dt><span class="term">
 754
 755     "<code class="mallctl">thread.arena</code>"
 756
 757           (<span class="type">unsigned</span>)
 758           <code class="literal">rw</code>
 759         </span></dt><dd><p>Get or set the arena associated with the calling
 760         thread.  The arena index must be less than the maximum number of arenas
 761         (see the <a class="link" href="#arenas.narenas">
 762     "<code class="mallctl">arenas.narenas</code>"
 763   </a>
 764         mallctl).  If the specified arena was not initialized beforehand (see
 765         the <a class="link" href="#arenas.initialized">
 766     "<code class="mallctl">arenas.initialized</code>"
 767   </a>
 768         mallctl), it will be automatically initialized as a side effect of
 769         calling this interface.</p></dd><dt><a name="thread.allocated"></a><span class="term">
 770
 771     "<code class="mallctl">thread.allocated</code>"
 772
 773           (<span class="type">uint64_t</span>)
 774           <code class="literal">r-</code>
 775           [<code class="option">--enable-stats</code>]
 776         </span></dt><dd><p>Get the total number of bytes ever allocated by the
 777         calling thread.  This counter has the potential to wrap around; it is
 778         up to the application to appropriately interpret the counter in such
 779         cases.</p></dd><dt><span class="term">
 780
 781     "<code class="mallctl">thread.allocatedp</code>"
 782
 783           (<span class="type">uint64_t *</span>)
 784           <code class="literal">r-</code>
 785           [<code class="option">--enable-stats</code>]
 786         </span></dt><dd><p>Get a pointer to the the value that is returned by the
 787         <a class="link" href="#thread.allocated">
 788     "<code class="mallctl">thread.allocated</code>"
 789   </a>
 790         mallctl.  This is useful for avoiding the overhead of repeated
 791         <code class="function">mallctl*</code>(<em class="parameter"><code></code></em>) calls.</p></dd><dt><a name="thread.deallocated"></a><span class="term">
 792
 793     "<code class="mallctl">thread.deallocated</code>"
 794
 795           (<span class="type">uint64_t</span>)
 796           <code class="literal">r-</code>
 797           [<code class="option">--enable-stats</code>]
 798         </span></dt><dd><p>Get the total number of bytes ever deallocated by the
 799         calling thread.  This counter has the potential to wrap around; it is
 800         up to the application to appropriately interpret the counter in such
 801         cases.</p></dd><dt><span class="term">
 802
 803     "<code class="mallctl">thread.deallocatedp</code>"
 804
 805           (<span class="type">uint64_t *</span>)
 806           <code class="literal">r-</code>
 807           [<code class="option">--enable-stats</code>]
 808         </span></dt><dd><p>Get a pointer to the the value that is returned by the
 809         <a class="link" href="#thread.deallocated">
 810     "<code class="mallctl">thread.deallocated</code>"
 811   </a>
 812         mallctl.  This is useful for avoiding the overhead of repeated
 813         <code class="function">mallctl*</code>(<em class="parameter"><code></code></em>) calls.</p></dd><dt><a name="arenas.narenas"></a><span class="term">
 814
 815     "<code class="mallctl">arenas.narenas</code>"
 816
 817           (<span class="type">unsigned</span>)
 818           <code class="literal">r-</code>
 819         </span></dt><dd><p>Maximum number of arenas.</p></dd><dt><a name="arenas.initialized"></a><span class="term">
 820
 821     "<code class="mallctl">arenas.initialized</code>"
 822
 823           (<span class="type">bool *</span>)
 824           <code class="literal">r-</code>
 825         </span></dt><dd><p>An array of <a class="link" href="#arenas.narenas">
 826     "<code class="mallctl">arenas.narenas</code>"
 827   </a>
 828         booleans.  Each boolean indicates whether the corresponding arena is
 829         initialized.</p></dd><dt><span class="term">
 830
 831     "<code class="mallctl">arenas.quantum</code>"
 832
 833           (<span class="type">size_t</span>)
 834           <code class="literal">r-</code>
 835         </span></dt><dd><p>Quantum size.</p></dd><dt><span class="term">
 836
 837     "<code class="mallctl">arenas.cacheline</code>"
 838
 839           (<span class="type">size_t</span>)
 840           <code class="literal">r-</code>
 841         </span></dt><dd><p>Assumed cacheline size.</p></dd><dt><span class="term">
 842
 843     "<code class="mallctl">arenas.subpage</code>"
 844
 845           (<span class="type">size_t</span>)
 846           <code class="literal">r-</code>
 847         </span></dt><dd><p>Subpage size class interval.</p></dd><dt><span class="term">
 848
 849     "<code class="mallctl">arenas.pagesize</code>"
 850
 851           (<span class="type">size_t</span>)
 852           <code class="literal">r-</code>
 853         </span></dt><dd><p>Page size.</p></dd><dt><span class="term">
 854
 855     "<code class="mallctl">arenas.chunksize</code>"
 856
 857           (<span class="type">size_t</span>)
 858           <code class="literal">r-</code>
 859         </span></dt><dd><p>Chunk size.</p></dd><dt><span class="term">
 860
 861     "<code class="mallctl">arenas.tspace_min</code>"
 862
 863           (<span class="type">size_t</span>)
 864           <code class="literal">r-</code>
 865         </span></dt><dd><p>Minimum tiny size class.  Tiny size classes are powers
 866         of two.</p></dd><dt><span class="term">
 867
 868     "<code class="mallctl">arenas.tspace_max</code>"
 869
 870           (<span class="type">size_t</span>)
 871           <code class="literal">r-</code>
 872         </span></dt><dd><p>Maximum tiny size class.  Tiny size classes are powers
 873         of two.</p></dd><dt><span class="term">
 874
 875     "<code class="mallctl">arenas.qspace_min</code>"
 876
 877           (<span class="type">size_t</span>)
 878           <code class="literal">r-</code>
 879         </span></dt><dd><p>Minimum quantum-spaced size class.</p></dd><dt><span class="term">
 880
 881     "<code class="mallctl">arenas.qspace_max</code>"
 882
 883           (<span class="type">size_t</span>)
 884           <code class="literal">r-</code>
 885         </span></dt><dd><p>Maximum quantum-spaced size class.</p></dd><dt><span class="term">
 886
 887     "<code class="mallctl">arenas.cspace_min</code>"
 888
 889           (<span class="type">size_t</span>)
 890           <code class="literal">r-</code>
 891         </span></dt><dd><p>Minimum cacheline-spaced size class.</p></dd><dt><span class="term">
 892
 893     "<code class="mallctl">arenas.cspace_max</code>"
 894
 895           (<span class="type">size_t</span>)
 896           <code class="literal">r-</code>
 897         </span></dt><dd><p>Maximum cacheline-spaced size class.</p></dd><dt><span class="term">
 898
 899     "<code class="mallctl">arenas.sspace_min</code>"
 900
 901           (<span class="type">size_t</span>)
 902           <code class="literal">r-</code>
 903         </span></dt><dd><p>Minimum subpage-spaced size class.</p></dd><dt><span class="term">
 904
 905     "<code class="mallctl">arenas.sspace_max</code>"
 906
 907           (<span class="type">size_t</span>)
 908           <code class="literal">r-</code>
 909         </span></dt><dd><p>Maximum subpage-spaced size class.</p></dd><dt><span class="term">
 910
 911     "<code class="mallctl">arenas.tcache_max</code>"
 912
 913           (<span class="type">size_t</span>)
 914           <code class="literal">r-</code>
 915           [<code class="option">--enable-tcache</code>]
 916         </span></dt><dd><p>Maximum thread-cached size class.</p></dd><dt><span class="term">
 917
 918     "<code class="mallctl">arenas.ntbins</code>"
 919
 920           (<span class="type">unsigned</span>)
 921           <code class="literal">r-</code>
 922         </span></dt><dd><p>Number of tiny bin size classes.</p></dd><dt><span class="term">
 923
 924     "<code class="mallctl">arenas.nqbins</code>"
 925
 926           (<span class="type">unsigned</span>)
 927           <code class="literal">r-</code>
 928         </span></dt><dd><p>Number of quantum-spaced bin size
 929         classes.</p></dd><dt><span class="term">
 930
 931     "<code class="mallctl">arenas.ncbins</code>"
 932
 933           (<span class="type">unsigned</span>)
 934           <code class="literal">r-</code>
 935         </span></dt><dd><p>Number of cacheline-spaced bin size
 936         classes.</p></dd><dt><span class="term">
 937
 938     "<code class="mallctl">arenas.nsbins</code>"
 939
 940           (<span class="type">unsigned</span>)
 941           <code class="literal">r-</code>
 942         </span></dt><dd><p>Number of subpage-spaced bin size
 943         classes.</p></dd><dt><span class="term">
 944
 945     "<code class="mallctl">arenas.nbins</code>"
 946
 947           (<span class="type">unsigned</span>)
 948           <code class="literal">r-</code>
 949         </span></dt><dd><p>Total number of bin size classes.</p></dd><dt><span class="term">
 950
 951     "<code class="mallctl">arenas.nhbins</code>"
 952
 953           (<span class="type">unsigned</span>)
 954           <code class="literal">r-</code>
 955           [<code class="option">--enable-tcache</code>]
 956         </span></dt><dd><p>Total number of thread cache bin size
 957         classes.</p></dd><dt><a name="arenas.bin.i.size"></a><span class="term">
 958
 959     "<code class="mallctl">arenas.bin.&lt;i&gt;.size</code>"
 960
 961           (<span class="type">size_t</span>)
 962           <code class="literal">r-</code>
 963         </span></dt><dd><p>Maximum size supported by size class.</p></dd><dt><span class="term">
 964
 965     "<code class="mallctl">arenas.bin.&lt;i&gt;.nregs</code>"
 966
 967           (<span class="type">uint32_t</span>)
 968           <code class="literal">r-</code>
 969         </span></dt><dd><p>Number of regions per page run.</p></dd><dt><span class="term">
 970
 971     "<code class="mallctl">arenas.bin.&lt;i&gt;.run_size</code>"
 972
 973           (<span class="type">size_t</span>)
 974           <code class="literal">r-</code>
 975         </span></dt><dd><p>Number of bytes per page run.</p></dd><dt><span class="term">
 976
 977     "<code class="mallctl">arenas.nlruns</code>"
 978
 979           (<span class="type">size_t</span>)
 980           <code class="literal">r-</code>
 981         </span></dt><dd><p>Total number of large size classes.</p></dd><dt><span class="term">
 982
 983     "<code class="mallctl">arenas.lrun.&lt;i&gt;.size</code>"
 984
 985           (<span class="type">size_t</span>)
 986           <code class="literal">r-</code>
 987         </span></dt><dd><p>Maximum size supported by this large size
 988         class.</p></dd><dt><span class="term">
 989
 990     "<code class="mallctl">arenas.purge</code>"
 991
 992           (<span class="type">unsigned</span>)
 993           <code class="literal">-w</code>
 994         </span></dt><dd><p>Purge unused dirty pages for the specified arena, or
 995         for all arenas if none is specified.</p></dd><dt><a name="prof.active"></a><span class="term">
 996
 997     "<code class="mallctl">prof.active</code>"
 998
 999           (<span class="type">bool</span>)
1000           <code class="literal">rw</code>
1001           [<code class="option">--enable-prof</code>]
1002         </span></dt><dd><p>Control whether sampling is currently active.  See the
1003         <a class="link" href="#opt.prof_active">
1004     "<code class="mallctl">opt.prof_active</code>"
1005   </a>
1006         option for additional information.
1007         </p></dd><dt><span class="term">
1008
1009     "<code class="mallctl">prof.dump</code>"
1010
1011           (<span class="type">const char *</span>)
1012           <code class="literal">-w</code>
1013           [<code class="option">--enable-prof</code>]
1014         </span></dt><dd><p>Dump a memory profile to the specified file, or if NULL
1015         is specified, to a file according to the pattern
1016         <code class="filename">&lt;prefix&gt;.&lt;pid&gt;.&lt;seq&gt;.m&lt;mseq&gt;.heap</code>,
1017         where <code class="literal">&lt;prefix&gt;</code> is controlled by the
1018         <a class="link" href="#opt.prof_prefix">
1019     "<code class="mallctl">opt.prof_prefix</code>"
1020   </a>
1021         option.</p></dd><dt><span class="term">
1022
1023     "<code class="mallctl">prof.interval</code>"
1024
1025           (<span class="type">uint64_t</span>)
1026           <code class="literal">r-</code>
1027           [<code class="option">--enable-prof</code>]
1028         </span></dt><dd><p>Average number of bytes allocated between
1029         inverval-based profile dumps.  See the
1030         <a class="link" href="#opt.lg_prof_interval">
1031     "<code class="mallctl">opt.lg_prof_interval</code>"
1032   </a>
1033         option for additional information.</p></dd><dt><a name="stats.cactive"></a><span class="term">
1034
1035     "<code class="mallctl">stats.cactive</code>"
1036
1037           (<span class="type">size_t *</span>)
1038           <code class="literal">r-</code>
1039           [<code class="option">--enable-stats</code>]
1040         </span></dt><dd><p>Pointer to a counter that contains an approximate count
1041         of the current number of bytes in active pages.  The estimate may be
1042         high, but never low, because each arena rounds up to the nearest
1043         multiple of the chunk size when computing its contribution to the
1044         counter.  Note that the <a class="link" href="#epoch">
1045     "<code class="mallctl">epoch</code>"
1046   </a> mallctl has no bearing
1047         on this counter.  Furthermore, counter consistency is maintained via
1048         atomic operations, so it is necessary to use an atomic operation in
1049         order to guarantee a consistent read when dereferencing the pointer.
1050         </p></dd><dt><a name="stats.allocated"></a><span class="term">
1051
1052     "<code class="mallctl">stats.allocated</code>"
1053
1054           (<span class="type">size_t</span>)
1055           <code class="literal">r-</code>
1056           [<code class="option">--enable-stats</code>]
1057         </span></dt><dd><p>Total number of bytes allocated by the
1058         application.</p></dd><dt><a name="stats.active"></a><span class="term">
1059
1060     "<code class="mallctl">stats.active</code>"
1061
1062           (<span class="type">size_t</span>)
1063           <code class="literal">r-</code>
1064           [<code class="option">--enable-stats</code>]
1065         </span></dt><dd><p>Total number of bytes in active pages allocated by the
1066         application.  This is a multiple of the page size, and greater than or
1067         equal to <a class="link" href="#stats.allocated">
1068     "<code class="mallctl">stats.allocated</code>"
1069   </a>.
1070         </p></dd><dt><span class="term">
1071
1072     "<code class="mallctl">stats.mapped</code>"
1073
1074           (<span class="type">size_t</span>)
1075           <code class="literal">r-</code>
1076           [<code class="option">--enable-stats</code>]
1077         </span></dt><dd><p>Total number of bytes in chunks mapped on behalf of the
1078         application.  This is a multiple of the chunk size, and is at least as
1079         large as <a class="link" href="#stats.active">
1080     "<code class="mallctl">stats.active</code>"
1081   </a>.  This
1082         does not include inactive chunks backed by swap files.  his does not
1083         include inactive chunks embedded in the DSS.</p></dd><dt><span class="term">
1084
1085     "<code class="mallctl">stats.chunks.current</code>"
1086
1087           (<span class="type">size_t</span>)
1088           <code class="literal">r-</code>
1089           [<code class="option">--enable-stats</code>]
1090         </span></dt><dd><p>Total number of chunks actively mapped on behalf of the
1091         application.  This does not include inactive chunks backed by swap
1092         files.  This does not include inactive chunks embedded in the DSS.
1093         </p></dd><dt><span class="term">
1094
1095     "<code class="mallctl">stats.chunks.total</code>"
1096
1097           (<span class="type">uint64_t</span>)
1098           <code class="literal">r-</code>
1099           [<code class="option">--enable-stats</code>]
1100         </span></dt><dd><p>Cumulative number of chunks allocated.</p></dd><dt><span class="term">
1101
1102     "<code class="mallctl">stats.chunks.high</code>"
1103
1104           (<span class="type">size_t</span>)
1105           <code class="literal">r-</code>
1106           [<code class="option">--enable-stats</code>]
1107         </span></dt><dd><p>Maximum number of active chunks at any time thus far.
1108         </p></dd><dt><span class="term">
1109
1110     "<code class="mallctl">stats.huge.allocated</code>"
1111
1112           (<span class="type">size_t</span>)
1113           <code class="literal">r-</code>
1114           [<code class="option">--enable-stats</code>]
1115         </span></dt><dd><p>Number of bytes currently allocated by huge objects.
1116         </p></dd><dt><span class="term">
1117
1118     "<code class="mallctl">stats.huge.nmalloc</code>"
1119
1120           (<span class="type">uint64_t</span>)
1121           <code class="literal">r-</code>
1122           [<code class="option">--enable-stats</code>]
1123         </span></dt><dd><p>Cumulative number of huge allocation requests.
1124         </p></dd><dt><span class="term">
1125
1126     "<code class="mallctl">stats.huge.ndalloc</code>"
1127
1128           (<span class="type">uint64_t</span>)
1129           <code class="literal">r-</code>
1130           [<code class="option">--enable-stats</code>]
1131         </span></dt><dd><p>Cumulative number of huge deallocation requests.
1132         </p></dd><dt><span class="term">
1133
1134     "<code class="mallctl">stats.arenas.&lt;i&gt;.nthreads</code>"
1135
1136           (<span class="type">unsigned</span>)
1137           <code class="literal">r-</code>
1138         </span></dt><dd><p>Number of threads currently assigned to
1139         arena.</p></dd><dt><span class="term">
1140
1141     "<code class="mallctl">stats.arenas.&lt;i&gt;.pactive</code>"
1142
1143           (<span class="type">size_t</span>)
1144           <code class="literal">r-</code>
1145         </span></dt><dd><p>Number of pages in active runs.</p></dd><dt><span class="term">
1146
1147     "<code class="mallctl">stats.arenas.&lt;i&gt;.pdirty</code>"
1148
1149           (<span class="type">size_t</span>)
1150           <code class="literal">r-</code>
1151         </span></dt><dd><p>Number of pages within unused runs that are potentially
1152         dirty, and for which <code class="function">madvise</code>(<em class="parameter"><code>...</code></em>,
1153         <em class="parameter"><code><code class="constant">MADV_DONTNEED</code></code></em>) or
1154         similar has not been called.</p></dd><dt><span class="term">
1155
1156     "<code class="mallctl">stats.arenas.&lt;i&gt;.mapped</code>"
1157
1158           (<span class="type">size_t</span>)
1159           <code class="literal">r-</code>
1160           [<code class="option">--enable-stats</code>]
1161         </span></dt><dd><p>Number of mapped bytes.</p></dd><dt><span class="term">
1162
1163     "<code class="mallctl">stats.arenas.&lt;i&gt;.npurge</code>"
1164
1165           (<span class="type">uint64_t</span>)
1166           <code class="literal">r-</code>
1167           [<code class="option">--enable-stats</code>]
1168         </span></dt><dd><p>Number of dirty page purge sweeps performed.
1169         </p></dd><dt><span class="term">
1170
1171     "<code class="mallctl">stats.arenas.&lt;i&gt;.nmadvise</code>"
1172
1173           (<span class="type">uint64_t</span>)
1174           <code class="literal">r-</code>
1175           [<code class="option">--enable-stats</code>]
1176         </span></dt><dd><p>Number of <code class="function">madvise</code>(<em class="parameter"><code>...</code></em>,
1177         <em class="parameter"><code><code class="constant">MADV_DONTNEED</code></code></em>) or
1178         similar calls made to purge dirty pages.</p></dd><dt><span class="term">
1179
1180     "<code class="mallctl">stats.arenas.&lt;i&gt;.npurged</code>"
1181
1182           (<span class="type">uint64_t</span>)
1183           <code class="literal">r-</code>
1184           [<code class="option">--enable-stats</code>]
1185         </span></dt><dd><p>Number of pages purged.</p></dd><dt><span class="term">
1186
1187     "<code class="mallctl">stats.arenas.&lt;i&gt;.small.allocated</code>"
1188
1189           (<span class="type">size_t</span>)
1190           <code class="literal">r-</code>
1191           [<code class="option">--enable-stats</code>]
1192         </span></dt><dd><p>Number of bytes currently allocated by small objects.
1193         </p></dd><dt><span class="term">
1194
1195     "<code class="mallctl">stats.arenas.&lt;i&gt;.small.nmalloc</code>"
1196
1197           (<span class="type">uint64_t</span>)
1198           <code class="literal">r-</code>
1199           [<code class="option">--enable-stats</code>]
1200         </span></dt><dd><p>Cumulative number of allocation requests served by
1201         small bins.</p></dd><dt><span class="term">
1202
1203     "<code class="mallctl">stats.arenas.&lt;i&gt;.small.ndalloc</code>"
1204
1205           (<span class="type">uint64_t</span>)
1206           <code class="literal">r-</code>
1207           [<code class="option">--enable-stats</code>]
1208         </span></dt><dd><p>Cumulative number of small objects returned to bins.
1209         </p></dd><dt><span class="term">
1210
1211     "<code class="mallctl">stats.arenas.&lt;i&gt;.small.nrequests</code>"
1212
1213           (<span class="type">uint64_t</span>)
1214           <code class="literal">r-</code>
1215           [<code class="option">--enable-stats</code>]
1216         </span></dt><dd><p>Cumulative number of small allocation requests.
1217         </p></dd><dt><span class="term">
1218
1219     "<code class="mallctl">stats.arenas.&lt;i&gt;.large.allocated</code>"
1220
1221           (<span class="type">size_t</span>)
1222           <code class="literal">r-</code>
1223           [<code class="option">--enable-stats</code>]
1224         </span></dt><dd><p>Number of bytes currently allocated by large objects.
1225         </p></dd><dt><span class="term">
1226
1227     "<code class="mallctl">stats.arenas.&lt;i&gt;.large.nmalloc</code>"
1228
1229           (<span class="type">uint64_t</span>)
1230           <code class="literal">r-</code>
1231           [<code class="option">--enable-stats</code>]
1232         </span></dt><dd><p>Cumulative number of large allocation requests served
1233         directly by the arena.</p></dd><dt><span class="term">
1234
1235     "<code class="mallctl">stats.arenas.&lt;i&gt;.large.ndalloc</code>"
1236
1237           (<span class="type">uint64_t</span>)
1238           <code class="literal">r-</code>
1239           [<code class="option">--enable-stats</code>]
1240         </span></dt><dd><p>Cumulative number of large deallocation requests served
1241         directly by the arena.</p></dd><dt><span class="term">
1242
1243     "<code class="mallctl">stats.arenas.&lt;i&gt;.large.nrequests</code>"
1244
1245           (<span class="type">uint64_t</span>)
1246           <code class="literal">r-</code>
1247           [<code class="option">--enable-stats</code>]
1248         </span></dt><dd><p>Cumulative number of large allocation requests.
1249         </p></dd><dt><span class="term">
1250
1251     "<code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.allocated</code>"
1252
1253           (<span class="type">size_t</span>)
1254           <code class="literal">r-</code>
1255           [<code class="option">--enable-stats</code>]
1256         </span></dt><dd><p>Current number of bytes allocated by
1257         bin.</p></dd><dt><span class="term">
1258
1259     "<code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.nmalloc</code>"
1260
1261           (<span class="type">uint64_t</span>)
1262           <code class="literal">r-</code>
1263           [<code class="option">--enable-stats</code>]
1264         </span></dt><dd><p>Cumulative number of allocations served by bin.
1265         </p></dd><dt><span class="term">
1266
1267     "<code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.ndalloc</code>"
1268
1269           (<span class="type">uint64_t</span>)
1270           <code class="literal">r-</code>
1271           [<code class="option">--enable-stats</code>]
1272         </span></dt><dd><p>Cumulative number of allocations returned to bin.
1273         </p></dd><dt><span class="term">
1274
1275     "<code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.nrequests</code>"
1276
1277           (<span class="type">uint64_t</span>)
1278           <code class="literal">r-</code>
1279           [<code class="option">--enable-stats</code>]
1280         </span></dt><dd><p>Cumulative number of allocation
1281         requests.</p></dd><dt><span class="term">
1282
1283     "<code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.nfills</code>"
1284
1285           (<span class="type">uint64_t</span>)
1286           <code class="literal">r-</code>
1287           [<code class="option">--enable-stats</code> <code class="option">--enable-tcache</code>]
1288         </span></dt><dd><p>Cumulative number of tcache fills.</p></dd><dt><span class="term">
1289
1290     "<code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.nflushes</code>"
1291
1292           (<span class="type">uint64_t</span>)
1293           <code class="literal">r-</code>
1294           [<code class="option">--enable-stats</code> <code class="option">--enable-tcache</code>]
1295         </span></dt><dd><p>Cumulative number of tcache flushes.</p></dd><dt><span class="term">
1296
1297     "<code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.nruns</code>"
1298
1299           (<span class="type">uint64_t</span>)
1300           <code class="literal">r-</code>
1301           [<code class="option">--enable-stats</code>]
1302         </span></dt><dd><p>Cumulative number of runs created.</p></dd><dt><span class="term">
1303
1304     "<code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.nreruns</code>"
1305
1306           (<span class="type">uint64_t</span>)
1307           <code class="literal">r-</code>
1308           [<code class="option">--enable-stats</code>]
1309         </span></dt><dd><p>Cumulative number of times the current run from which
1310         to allocate changed.</p></dd><dt><span class="term">
1311
1312     "<code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.highruns</code>"
1313
1314           (<span class="type">size_t</span>)
1315           <code class="literal">r-</code>
1316           [<code class="option">--enable-stats</code>]
1317         </span></dt><dd><p>Maximum number of runs at any time thus far.
1318         </p></dd><dt><span class="term">
1319
1320     "<code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.curruns</code>"
1321
1322           (<span class="type">size_t</span>)
1323           <code class="literal">r-</code>
1324           [<code class="option">--enable-stats</code>]
1325         </span></dt><dd><p>Current number of runs.</p></dd><dt><span class="term">
1326
1327     "<code class="mallctl">stats.arenas.&lt;i&gt;.lruns.&lt;j&gt;.nmalloc</code>"
1328
1329           (<span class="type">uint64_t</span>)
1330           <code class="literal">r-</code>
1331           [<code class="option">--enable-stats</code>]
1332         </span></dt><dd><p>Cumulative number of allocation requests for this size
1333         class served directly by the arena.</p></dd><dt><span class="term">
1334
1335     "<code class="mallctl">stats.arenas.&lt;i&gt;.lruns.&lt;j&gt;.ndalloc</code>"
1336
1337           (<span class="type">uint64_t</span>)
1338           <code class="literal">r-</code>
1339           [<code class="option">--enable-stats</code>]
1340         </span></dt><dd><p>Cumulative number of deallocation requests for this
1341         size class served directly by the arena.</p></dd><dt><span class="term">
1342
1343     "<code class="mallctl">stats.arenas.&lt;i&gt;.lruns.&lt;j&gt;.nrequests</code>"
1344
1345           (<span class="type">uint64_t</span>)
1346           <code class="literal">r-</code>
1347           [<code class="option">--enable-stats</code>]
1348         </span></dt><dd><p>Cumulative number of allocation requests for this size
1349         class.</p></dd><dt><span class="term">
1350
1351     "<code class="mallctl">stats.arenas.&lt;i&gt;.lruns.&lt;j&gt;.highruns</code>"
1352
1353           (<span class="type">size_t</span>)
1354           <code class="literal">r-</code>
1355           [<code class="option">--enable-stats</code>]
1356         </span></dt><dd><p>Maximum number of runs at any time thus far for this
1357         size class.</p></dd><dt><span class="term">
1358
1359     "<code class="mallctl">stats.arenas.&lt;i&gt;.lruns.&lt;j&gt;.curruns</code>"
1360
1361           (<span class="type">size_t</span>)
1362           <code class="literal">r-</code>
1363           [<code class="option">--enable-stats</code>]
1364         </span></dt><dd><p>Current number of runs for this size class.
1365         </p></dd><dt><span class="term">
1366
1367     "<code class="mallctl">swap.avail</code>"
1368
1369           (<span class="type">size_t</span>)
1370           <code class="literal">r-</code>
1371           [<code class="option">--enable-stats --enable-swap</code>]
1372         </span></dt><dd><p>Number of swap file bytes that are currently not
1373         associated with any chunk (i.e. mapped, but otherwise completely
1374         unmanaged).</p></dd><dt><a name="swap.prezeroed"></a><span class="term">
1375
1376     "<code class="mallctl">swap.prezeroed</code>"
1377
1378           (<span class="type">bool</span>)
1379           <code class="literal">rw</code>
1380           [<code class="option">--enable-swap</code>]
1381         </span></dt><dd><p>If true, the allocator assumes that the swap file(s)
1382         contain nothing but nil bytes.  If this assumption is violated,
1383         allocator behavior is undefined.  This value becomes read-only after
1384         <a class="link" href="#swap.fds">
1385     "<code class="mallctl">swap.fds</code>"
1386   </a> is
1387         successfully written to.</p></dd><dt><span class="term">
1388
1389     "<code class="mallctl">swap.nfds</code>"
1390
1391           (<span class="type">size_t</span>)
1392           <code class="literal">r-</code>
1393           [<code class="option">--enable-swap</code>]
1394         </span></dt><dd><p>Number of file descriptors in use for swap.
1395         </p></dd><dt><a name="swap.fds"></a><span class="term">
1396
1397     "<code class="mallctl">swap.fds</code>"
1398
1399           (<span class="type">int *</span>)
1400           <code class="literal">r-</code>
1401           [<code class="option">--enable-swap</code>]
1402         </span></dt><dd><p>When written to, the files associated with the
1403         specified file descriptors are contiguously mapped via
1404         <span class="citerefentry"><span class="refentrytitle">mmap</span>(2)</span>.  The resulting virtual memory
1405         region is preferred over anonymous
1406         <span class="citerefentry"><span class="refentrytitle">mmap</span>(2)</span> and
1407         <span class="citerefentry"><span class="refentrytitle">sbrk</span>(2)</span> memory.  Note that if a file's
1408         size is not a multiple of the page size, it is automatically truncated
1409         to the nearest page size multiple.  See the
1410         <a class="link" href="#swap.prezeroed">
1411     "<code class="mallctl">swap.prezeroed</code>"
1412   </a>
1413         mallctl for specifying that the files are pre-zeroed.</p></dd></dl></div></div><div class="refsect1" title="DEBUGGING MALLOC PROBLEMS"><a name="debugging_malloc_problems"></a><h2>DEBUGGING MALLOC PROBLEMS</h2><p>When debugging, it is a good idea to configure/build jemalloc with
1414     the <code class="option">--enable-debug</code> and <code class="option">--enable-fill</code>
1415     options, and recompile the program with suitable options and symbols for
1416     debugger support.  When so configured, jemalloc incorporates a wide variety
1417     of run-time assertions that catch application errors such as double-free,
1418     write-after-free, etc.</p><p>Programs often accidentally depend on &#8220;uninitialized&#8221;
1419     memory actually being filled with zero bytes.  Junk filling
1420     (see the <a class="link" href="#opt.junk">
1421     "<code class="mallctl">opt.junk</code>"
1422   </a>
1423     option) tends to expose such bugs in the form of obviously incorrect
1424     results and/or coredumps.  Conversely, zero
1425     filling (see the <a class="link" href="#opt.zero">
1426     "<code class="mallctl">opt.zero</code>"
1427   </a> option) eliminates
1428     the symptoms of such bugs.  Between these two options, it is usually
1429     possible to quickly detect, diagnose, and eliminate such bugs.</p><p>This implementation does not provide much detail about the problems
1430     it detects, because the performance impact for storing such information
1431     would be prohibitive.  There are a number of allocator implementations
1432     available on the Internet which focus on detecting and pinpointing problems
1433     by trading performance for extra sanity checks and detailed
1434     diagnostics.</p></div><div class="refsect1" title="DIAGNOSTIC MESSAGES"><a name="diagnostic_messages"></a><h2>DIAGNOSTIC MESSAGES</h2><p>If any of the memory allocation/deallocation functions detect an
1435     error or warning condition, a message will be printed to file descriptor
1436     <code class="constant">STDERR_FILENO</code>.  Errors will result in the process
1437     dumping core.  If the <a class="link" href="#opt.abort">
1438     "<code class="mallctl">opt.abort</code>"
1439   </a> option is set, most
1440     warnings are treated as errors.</p><p>The <code class="varname">malloc_message</code> variable allows the programmer
1441     to override the function which emits the text strings forming the errors
1442     and warnings if for some reason the <code class="constant">STDERR_FILENO</code> file
1443     descriptor is not suitable for this.
1444     <code class="function">malloc_message</code>(<em class="parameter"><code></code></em>) takes the
1445     <em class="parameter"><code>cbopaque</code></em> pointer argument that is
1446     <code class="constant">NULL</code> unless overridden by the arguments in a call to
1447     <code class="function">malloc_stats_print</code>(<em class="parameter"><code></code></em>), followed by a string
1448     pointer.  Please note that doing anything which tries to allocate memory in
1449     this function is likely to result in a crash or deadlock.</p><p>All messages are prefixed by
1450     &#8220;<code class="computeroutput">&lt;jemalloc&gt;: </code>&#8221;.</p></div><div class="refsect1" title="RETURN VALUES"><a name="return_values"></a><h2>RETURN VALUES</h2><div class="refsect2" title="Standard API"><a name="id2844722"></a><h3>Standard API</h3><p>The <code class="function">malloc</code>(<em class="parameter"><code></code></em>) and
1451       <code class="function">calloc</code>(<em class="parameter"><code></code></em>) functions return a pointer to the
1452       allocated memory if successful; otherwise a <code class="constant">NULL</code>
1453       pointer is returned and <code class="varname">errno</code> is set to
1454       <span class="errorname">ENOMEM</span>.</p><p>The <code class="function">posix_memalign</code>(<em class="parameter"><code></code></em>) function
1455       returns the value 0 if successful; otherwise it returns an error value.
1456       The <code class="function">posix_memalign</code>(<em class="parameter"><code></code></em>) function will fail
1457       if:
1458         </p><div class="variablelist"><dl><dt><span class="term"><span class="errorname">EINVAL</span></span></dt><dd><p>The <em class="parameter"><code>alignment</code></em> parameter is
1459             not a power of 2 at least as large as
1460             <code class="code">sizeof(<span class="type">void *</span>)</code>.
1461             </p></dd><dt><span class="term"><span class="errorname">ENOMEM</span></span></dt><dd><p>Memory allocation error.</p></dd></dl></div><p>
1462       </p><p>The <code class="function">realloc</code>(<em class="parameter"><code></code></em>) function returns a
1463       pointer, possibly identical to <em class="parameter"><code>ptr</code></em>, to the
1464       allocated memory if successful; otherwise a <code class="constant">NULL</code>
1465       pointer is returned, and <code class="varname">errno</code> is set to
1466       <span class="errorname">ENOMEM</span> if the error was the result of an
1467       allocation failure.  The <code class="function">realloc</code>(<em class="parameter"><code></code></em>)
1468       function always leaves the original buffer intact when an error occurs.
1469       </p><p>The <code class="function">free</code>(<em class="parameter"><code></code></em>) function returns no
1470       value.</p></div><div class="refsect2" title="Non-standard API"><a name="id2844875"></a><h3>Non-standard API</h3><p>The <code class="function">malloc_usable_size</code>(<em class="parameter"><code></code></em>) function
1471       returns the usable size of the allocation pointed to by
1472       <em class="parameter"><code>ptr</code></em>.  </p><p>The <code class="function">mallctl</code>(<em class="parameter"><code></code></em>),
1473       <code class="function">mallctlnametomib</code>(<em class="parameter"><code></code></em>), and
1474       <code class="function">mallctlbymib</code>(<em class="parameter"><code></code></em>) functions return 0 on
1475       success; otherwise they return an error value.  The functions will fail
1476       if:
1477         </p><div class="variablelist"><dl><dt><span class="term"><span class="errorname">EINVAL</span></span></dt><dd><p><em class="parameter"><code>newp</code></em> is not
1478             <code class="constant">NULL</code>, and <em class="parameter"><code>newlen</code></em> is too
1479             large or too small.  Alternatively, <em class="parameter"><code>*oldlenp</code></em>
1480             is too large or too small; in this case as much data as possible
1481             are read despite the error.</p></dd><dt><span class="term"><span class="errorname">ENOMEM</span></span></dt><dd><p><em class="parameter"><code>*oldlenp</code></em> is too short to
1482             hold the requested value.</p></dd><dt><span class="term"><span class="errorname">ENOENT</span></span></dt><dd><p><em class="parameter"><code>name</code></em> or
1483             <em class="parameter"><code>mib</code></em> specifies an unknown/invalid
1484             value.</p></dd><dt><span class="term"><span class="errorname">EPERM</span></span></dt><dd><p>Attempt to read or write void value, or attempt to
1485             write read-only value.</p></dd><dt><span class="term"><span class="errorname">EAGAIN</span></span></dt><dd><p>A memory allocation failure
1486             occurred.</p></dd><dt><span class="term"><span class="errorname">EFAULT</span></span></dt><dd><p>An interface with side effects failed in some way
1487             not directly related to <code class="function">mallctl*</code>(<em class="parameter"><code></code></em>)
1488             read/write processing.</p></dd></dl></div><p>
1489       </p></div><div class="refsect2" title="Experimental API"><a name="id2845053"></a><h3>Experimental API</h3><p>The <code class="function">allocm</code>(<em class="parameter"><code></code></em>),
1490       <code class="function">rallocm</code>(<em class="parameter"><code></code></em>),
1491       <code class="function">sallocm</code>(<em class="parameter"><code></code></em>), and
1492       <code class="function">dallocm</code>(<em class="parameter"><code></code></em>) functions return
1493       <code class="constant">ALLOCM_SUCCESS</code> on success; otherwise they return an
1494       error value.  The <code class="function">allocm</code>(<em class="parameter"><code></code></em>) and
1495       <code class="function">rallocm</code>(<em class="parameter"><code></code></em>) functions will fail if:
1496         </p><div class="variablelist"><dl><dt><span class="term"><span class="errorname">ALLOCM_ERR_OOM</span></span></dt><dd><p>Out of memory.  Insufficient contiguous memory was
1497             available to service the allocation request.  The
1498             <code class="function">allocm</code>(<em class="parameter"><code></code></em>) function additionally sets
1499             <em class="parameter"><code>*ptr</code></em> to <code class="constant">NULL</code>, whereas
1500             the <code class="function">rallocm</code>(<em class="parameter"><code></code></em>) function leaves
1501             <code class="constant">*ptr</code> unmodified.</p></dd></dl></div><p>
1502       The <code class="function">rallocm</code>(<em class="parameter"><code></code></em>) function will also
1503       fail if:
1504         </p><div class="variablelist"><dl><dt><span class="term"><span class="errorname">ALLOCM_ERR_NOT_MOVED</span></span></dt><dd><p><code class="constant">ALLOCM_NO_MOVE</code> was specified,
1505             but the reallocation request could not be serviced without moving
1506             the object.</p></dd></dl></div><p>
1507       </p></div></div><div class="refsect1" title="ENVIRONMENT"><a name="environment"></a><h2>ENVIRONMENT</h2><p>The following environment variable affects the execution of the
1508     allocation functions:
1509       </p><div class="variablelist"><dl><dt><span class="term"><code class="envar">MALLOC_CONF</code></span></dt><dd><p>If the environment variable
1510           <code class="envar">MALLOC_CONF</code> is set, the characters it contains
1511           will be interpreted as options.</p></dd></dl></div><p>
1512     </p></div><div class="refsect1" title="EXAMPLES"><a name="examples"></a><h2>EXAMPLES</h2><p>To dump core whenever a problem occurs:
1513       </p><pre class="screen">ln -s 'abort:true' /etc/malloc.conf</pre><p>
1514     </p><p>To specify in the source a chunk size that is 16 MiB:
1515       </p><pre class="programlisting">
1516 malloc_conf = "lg_chunk:24";</pre></div><div class="refsect1" title="SEE ALSO"><a name="see_also"></a><h2>SEE ALSO</h2><p><span class="citerefentry"><span class="refentrytitle">madvise</span>(2)</span>,
1517     <span class="citerefentry"><span class="refentrytitle">mmap</span>(2)</span>,
1518     <span class="citerefentry"><span class="refentrytitle">sbrk</span>(2)</span>,
1519     <span class="citerefentry"><span class="refentrytitle">alloca</span>(3)</span>,
1520     <span class="citerefentry"><span class="refentrytitle">atexit</span>(3)</span>,
1521     <span class="citerefentry"><span class="refentrytitle">getpagesize</span>(3)</span></p></div><div class="refsect1" title="STANDARDS"><a name="standards"></a><h2>STANDARDS</h2><p>The <code class="function">malloc</code>(<em class="parameter"><code></code></em>),
1522     <code class="function">calloc</code>(<em class="parameter"><code></code></em>),
1523     <code class="function">realloc</code>(<em class="parameter"><code></code></em>), and
1524     <code class="function">free</code>(<em class="parameter"><code></code></em>) functions conform to ISO/IEC
1525     9899:1990 (&#8220;ISO C90&#8221;).</p><p>The <code class="function">posix_memalign</code>(<em class="parameter"><code></code></em>) function conforms
1526     to IEEE Std 1003.1-2001 (&#8220;POSIX.1&#8221;).</p></div></div></body></html>