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<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="id2968890"></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 2.2.5-0-gfc1bb70e5f0d9a58b39efa39cc549b5af5104760. More information
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;
#include &lt;<code class="filename">jemalloc/jemalloc.h</code>&gt;</pre><div class="refsect2" title="Standard API"><a name="id2992781"></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="id2998350"></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>
<code>(</code>void *, const char *<code>)</code>
, </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="id3014125"></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="id3014924"></a><h3>Standard API</h3><p>The <code class="function">malloc</code>(<em class="parameter"><code></code></em>) function allocates
<em class="parameter"><code>size</code></em> bytes of uninitialized memory. The allocated
space is suitably aligned (after possible pointer coercion) for storage
of any type of object.</p><p>The <code class="function">calloc</code>(<em class="parameter"><code></code></em>) function allocates
space for <em class="parameter"><code>number</code></em> objects, each
<em class="parameter"><code>size</code></em> bytes in length. The result is identical to
calling <code class="function">malloc</code>(<em class="parameter"><code></code></em>) with an argument of
<em class="parameter"><code>number</code></em> * <em class="parameter"><code>size</code></em>, with the
exception that the allocated memory is explicitly initialized to zero
bytes.</p><p>The <code class="function">posix_memalign</code>(<em class="parameter"><code></code></em>) function
allocates <em class="parameter"><code>size</code></em> bytes of memory such that the
allocation's base address is an even multiple of
<em class="parameter"><code>alignment</code></em>, and returns the allocation in the value
pointed to by <em class="parameter"><code>ptr</code></em>. The requested
<em class="parameter"><code>alignment</code></em> must be a power of 2 at least as large
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
size of the previously allocated memory referenced by
<em class="parameter"><code>ptr</code></em> to <em class="parameter"><code>size</code></em> bytes. The
contents of the memory are unchanged up to the lesser of the new and old
sizes. If the new size is larger, the contents of the newly allocated
portion of the memory are undefined. Upon success, the memory referenced
by <em class="parameter"><code>ptr</code></em> is freed and a pointer to the newly
allocated memory is returned. Note that
<code class="function">realloc</code>(<em class="parameter"><code></code></em>) may move the memory allocation,
resulting in a different return value than <em class="parameter"><code>ptr</code></em>.
If <em class="parameter"><code>ptr</code></em> is <code class="constant">NULL</code>, the
<code class="function">realloc</code>(<em class="parameter"><code></code></em>) function behaves identically to
<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
allocated memory referenced by <em class="parameter"><code>ptr</code></em> to be made
available for future allocations. If <em class="parameter"><code>ptr</code></em> is
<code class="constant">NULL</code>, no action occurs.</p></div><div class="refsect2" title="Non-standard API"><a name="id3025603"></a><h3>Non-standard API</h3><p>The <code class="function">malloc_usable_size</code>(<em class="parameter"><code></code></em>) function
returns the usable size of the allocation pointed to by
<em class="parameter"><code>ptr</code></em>. The return value may be larger than the size
that was requested during allocation. The
<code class="function">malloc_usable_size</code>(<em class="parameter"><code></code></em>) function is not a
mechanism for in-place <code class="function">realloc</code>(<em class="parameter"><code></code></em>); rather
it is provided solely as a tool for introspection purposes. Any
discrepancy between the requested allocation size and the size reported
by <code class="function">malloc_usable_size</code>(<em class="parameter"><code></code></em>) should not be
depended on, since such behavior is entirely implementation-dependent.
</p><p>The <code class="function">malloc_stats_print</code>(<em class="parameter"><code></code></em>) function
writes human-readable summary statistics via the
<em class="parameter"><code>write_cb</code></em> callback function pointer and
<em class="parameter"><code>cbopaque</code></em> data passed to
<em class="parameter"><code>write_cb</code></em>, or
<code class="function">malloc_message</code>(<em class="parameter"><code></code></em>) if
<em class="parameter"><code>write_cb</code></em> is <code class="constant">NULL</code>. This
function can be called repeatedly. General information that never
changes during execution can be omitted by specifying "g" as a character
within the <em class="parameter"><code>opts</code></em> string. Note that
<code class="function">malloc_message</code>(<em class="parameter"><code></code></em>) uses the
<code class="function">mallctl*</code>(<em class="parameter"><code></code></em>) functions internally, so
inconsistent statistics can be reported if multiple threads use these
functions simultaneously. If <code class="option">--enable-stats</code> is
specified during configuration, &#8220;m&#8221; and &#8220;a&#8221; can
be specified to omit merged arena and per arena statistics, respectively;
&#8220;b&#8221; and &#8220;l&#8221; can be specified to omit per size
class statistics for bins and large objects, respectively. Unrecognized
characters are silently ignored. Note that thread caching may prevent
some statistics from being completely up to date, since extra locking
would be required to merge counters that track thread cache operations.
</p><p>The <code class="function">mallctl</code>(<em class="parameter"><code></code></em>) function provides a
general interface for introspecting the memory allocator, as well as
setting modifiable parameters and triggering actions. The
period-separated <em class="parameter"><code>name</code></em> argument specifies a
location in a tree-structured namespace; see the <a class="xref" href="#mallctl_namespace" title="MALLCTL NAMESPACE">MALLCTL NAMESPACE</a> section for
documentation on the tree contents. To read a value, pass a pointer via
<em class="parameter"><code>oldp</code></em> to adequate space to contain the value, and a
pointer to its length via <em class="parameter"><code>oldlenp</code></em>; otherwise pass
<code class="constant">NULL</code> and <code class="constant">NULL</code>. Similarly, to
write a value, pass a pointer to the value via
<em class="parameter"><code>newp</code></em>, and its length via
<em class="parameter"><code>newlen</code></em>; otherwise pass <code class="constant">NULL</code>
and <code class="constant">0</code>.</p><p>The <code class="function">mallctlnametomib</code>(<em class="parameter"><code></code></em>) function
provides a way to avoid repeated name lookups for applications that
repeatedly query the same portion of the namespace, by translating a name
to a &#8220;Management Information Base&#8221; (MIB) that can be passed
repeatedly to <code class="function">mallctlbymib</code>(<em class="parameter"><code></code></em>). Upon
successful return from <code class="function">mallctlnametomib</code>(<em class="parameter"><code></code></em>),
<em class="parameter"><code>mibp</code></em> contains an array of
<em class="parameter"><code>*miblenp</code></em> integers, where
<em class="parameter"><code>*miblenp</code></em> is the lesser of the number of components
in <em class="parameter"><code>name</code></em> and the input value of
<em class="parameter"><code>*miblenp</code></em>. Thus it is possible to pass a
<em class="parameter"><code>*miblenp</code></em> that is smaller than the number of
period-separated name components, which results in a partial MIB that can
be used as the basis for constructing a complete MIB. For name
components that are integers (e.g. the 2 in
<a class="link" href="#arenas.bin.i.size">
"<code class="mallctl">arenas.bin.2.size</code>"
</a>),
the corresponding MIB component will always be that integer. Therefore,
it is legitimate to construct code like the following: </p><pre class="programlisting">
unsigned nbins, i;
int mib[4];
size_t len, miblen;
len = sizeof(nbins);
mallctl("arenas.nbins", &amp;nbins, &amp;len, NULL, 0);
miblen = 4;
mallnametomib("arenas.bin.0.size", mib, &amp;miblen);
for (i = 0; i &lt; nbins; i++) {
size_t bin_size;
mib[2] = i;
len = sizeof(bin_size);
mallctlbymib(mib, miblen, &amp;bin_size, &amp;len, NULL, 0);
/* Do something with bin_size... */
}</pre></div><div class="refsect2" title="Experimental API"><a name="id3013809"></a><h3>Experimental API</h3><p>The experimental API is subject to change or removal without regard
for backward compatibility.</p><p>The <code class="function">allocm</code>(<em class="parameter"><code></code></em>),
<code class="function">rallocm</code>(<em class="parameter"><code></code></em>),
<code class="function">sallocm</code>(<em class="parameter"><code></code></em>), and
<code class="function">dallocm</code>(<em class="parameter"><code></code></em>) functions all have a
<em class="parameter"><code>flags</code></em> argument that can be used to specify
options. The functions only check the options that are contextually
relevant. Use bitwise or (<code class="code">|</code>) operations to
specify one or more of the following:
</p><div class="variablelist"><dl><dt><span class="term"><code class="constant">ALLOCM_LG_ALIGN(<em class="parameter"><code>la</code></em>)
</code></span></dt><dd><p>Align the memory allocation to start at an address
that is a multiple of <code class="code">(1 &lt;&lt;
<em class="parameter"><code>la</code></em>)</code>. This macro does not validate
that <em class="parameter"><code>la</code></em> is within the valid
range.</p></dd><dt><span class="term"><code class="constant">ALLOCM_ALIGN(<em class="parameter"><code>a</code></em>)
</code></span></dt><dd><p>Align the memory allocation to start at an address
that is a multiple of <em class="parameter"><code>a</code></em>, where
<em class="parameter"><code>a</code></em> is a power of two. This macro does not
validate that <em class="parameter"><code>a</code></em> is a power of 2.
</p></dd><dt><span class="term"><code class="constant">ALLOCM_ZERO</code></span></dt><dd><p>Initialize newly allocated memory to contain zero
bytes. In the growing reallocation case, the real size prior to
reallocation defines the boundary between untouched bytes and those
that are initialized to contain zero bytes. If this option is
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
object. This constraint can apply to both growth and
shrinkage.</p></dd></dl></div><p>
</p><p>The <code class="function">allocm</code>(<em class="parameter"><code></code></em>) function allocates at
least <em class="parameter"><code>size</code></em> bytes of memory, sets
<em class="parameter"><code>*ptr</code></em> to the base address of the allocation, and
sets <em class="parameter"><code>*rsize</code></em> to the real size of the allocation if
<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
allocation at <em class="parameter"><code>*ptr</code></em> to be at least
<em class="parameter"><code>size</code></em> bytes, sets <em class="parameter"><code>*ptr</code></em> to
the base address of the allocation if it moved, and sets
<em class="parameter"><code>*rsize</code></em> to the real size of the allocation if
<em class="parameter"><code>rsize</code></em> is not <code class="constant">NULL</code>. If
<em class="parameter"><code>extra</code></em> is non-zero, an attempt is made to resize
the allocation to be at least <code class="code"><em class="parameter"><code>size</code></em> +
<em class="parameter"><code>extra</code></em>)</code> bytes, though inability to allocate
the extra byte(s) will not by itself result in failure. Behavior is
undefined if <code class="code">(<em class="parameter"><code>size</code></em> +
<em class="parameter"><code>extra</code></em> &gt;
<code class="constant">SIZE_T_MAX</code>)</code>.</p><p>The <code class="function">sallocm</code>(<em class="parameter"><code></code></em>) function sets
<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
memory referenced by <em class="parameter"><code>ptr</code></em> to be made available for
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
routines, the allocator initializes its internals based in part on various
options that can be specified at compile- or run-time.</p><p>The string pointed to by the global variable
<code class="varname">malloc_conf</code>, the &#8220;name&#8221; of the file
referenced by the symbolic link named <code class="filename">/etc/malloc.conf</code>, and the value of the
environment variable <code class="envar">MALLOC_CONF</code>, will be interpreted, in
that order, from left to right as options.</p><p>An options string is a comma-separated list of option:value pairs.
There is one key corresponding to each <a class="link" href="#opt.abort">
"<code class="mallctl">opt.*</code>"
</a> mallctl (see the <a class="xref" href="#mallctl_namespace" title="MALLCTL NAMESPACE">MALLCTL NAMESPACE</a> section for options
documentation). For example, <code class="literal">abort:true,narenas:1</code> sets
the <a class="link" href="#opt.abort">
"<code class="mallctl">opt.abort</code>"
</a> and <a class="link" href="#opt.narenas">
"<code class="mallctl">opt.narenas</code>"
</a> options. Some
options have boolean values (true/false), others have integer values (base
8, 10, or 16, depending on prefix), and yet others have raw string
values.</p></div><div class="refsect1" title="IMPLEMENTATION NOTES"><a name="implementation_notes"></a><h2>IMPLEMENTATION NOTES</h2><p>Traditionally, allocators have used
<span class="citerefentry"><span class="refentrytitle">sbrk</span>(2)</span> to obtain memory, which is
suboptimal for several reasons, including race conditions, increased
fragmentation, and artificial limitations on maximum usable memory. If
<code class="option">--enable-dss</code> is specified during configuration, this
allocator uses both <span class="citerefentry"><span class="refentrytitle">sbrk</span>(2)</span> and
<span class="citerefentry"><span class="refentrytitle">mmap</span>(2)</span>, in that order of preference;
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
contention for threaded programs on multi-processor systems. This works
well with regard to threading scalability, but incurs some costs. There is
a small fixed per-arena overhead, and additionally, arenas manage memory
completely independently of each other, which means a small fixed increase
in overall memory fragmentation. These overheads are not generally an
issue, given the number of arenas normally used. Note that using
substantially more arenas than the default is not likely to improve
performance, mainly due to reduced cache performance. However, it may make
sense to reduce the number of arenas if an application does not make much
use of the allocation functions.</p><p>In addition to multiple arenas, unless
<code class="option">--disable-tcache</code> is specified during configuration, this
allocator supports thread-specific caching for small and large objects, in
order to make it possible to completely avoid synchronization for most
allocation requests. Such caching allows very fast allocation in the
common case, but it increases memory usage and fragmentation, since a
bounded number of objects can remain allocated in each thread cache.</p><p>Memory is conceptually broken into equal-sized chunks, where the
chunk size is a power of two that is greater than the page size. Chunks
are always aligned to multiples of the chunk size. This alignment makes it
possible to find metadata for user objects very quickly.</p><p>User objects are broken into three categories according to size:
small, large, and huge. Small objects are smaller than one page. Large
objects are smaller than the chunk size. Huge objects are a multiple of
the chunk size. Small and large objects are managed by arenas; huge
objects are managed separately in a single data structure that is shared by
all threads. Huge objects are used by applications infrequently enough
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
contiguous pages (unused, backing a set of small objects, or backing one
large object). The combination of chunk alignment and chunk page maps
makes it possible to determine all metadata regarding small and large
allocations in constant time.</p><p>Small objects are managed in groups by page runs. Each run maintains
a frontier and free list to track which regions are in use. Unless
<code class="option">--disable-tiny</code> is specified during configuration,
allocation requests that are no more than half the quantum (8 or 16,
depending on architecture) are rounded up to the nearest power of two that
is at least <code class="code">sizeof(<span class="type">void *</span>)</code>.
Allocation requests that are more than half the quantum, but no more than
the minimum cacheline-multiple size class (see the <a class="link" href="#opt.lg_qspace_max">
"<code class="mallctl">opt.lg_qspace_max</code>"
</a>
option) are rounded up to the nearest multiple of the quantum. Allocation
requests that are more than the minimum cacheline-multiple size class, but
no more than the minimum subpage-multiple size class (see the <a class="link" href="#opt.lg_cspace_max">
"<code class="mallctl">opt.lg_cspace_max</code>"
</a>
option) are rounded up to the nearest multiple of the cacheline size (64).
Allocation requests that are more than the minimum subpage-multiple size
class, but no more than the maximum subpage-multiple size class are rounded
up to the nearest multiple of the subpage size (256). Allocation requests
that are more than the maximum subpage-multiple size class, but small
enough to fit in an arena-managed chunk (see the <a class="link" href="#opt.lg_chunk">
"<code class="mallctl">opt.lg_chunk</code>"
</a> option), are
rounded up to the nearest run size. Allocation requests that are too large
to fit in an arena-managed chunk are rounded up to the nearest multiple of
the chunk size.</p><p>Allocations are packed tightly together, which can be an issue for
multi-threaded applications. If you need to assure that allocations do not
suffer from cacheline sharing, round your allocation requests up to the
nearest multiple of the cacheline size, or specify cacheline alignment when
allocating.</p><p>Assuming 4 MiB chunks, 4 KiB pages, and a 16-byte quantum on a 64-bit
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
<code class="function">mallctl*</code>(<em class="parameter"><code></code></em>) functions. Value types are
specified in parentheses, their readable/writable statuses are encoded as
<code class="literal">rw</code>, <code class="literal">r-</code>, <code class="literal">-w</code>, or
<code class="literal">--</code>, and required build configuration flags follow, if
any. A name element encoded as <code class="literal">&lt;i&gt;</code> or
<code class="literal">&lt;j&gt;</code> indicates an integer component, where the
integer varies from 0 to some upper value that must be determined via
introspection. In the case of
"<code class="mallctl">stats.arenas.&lt;i&gt;.*</code>"
,
<code class="literal">&lt;i&gt;</code> equal to <a class="link" href="#arenas.narenas">
"<code class="mallctl">arenas.narenas</code>"
</a> can be
used to access the summation of statistics from all arenas. Take special
note of the <a class="link" href="#epoch">
"<code class="mallctl">epoch</code>"
</a> mallctl,
which controls refreshing of cached dynamic statistics.</p><div class="variablelist"><dl><dt><span class="term">
"<code class="mallctl">version</code>"
(<span class="type">const char *</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Return the jemalloc version string.</p></dd><dt><a name="epoch"></a><span class="term">
"<code class="mallctl">epoch</code>"
(<span class="type">uint64_t</span>)
<code class="literal">rw</code>
</span></dt><dd><p>If a value is passed in, refresh the data from which
the <code class="function">mallctl*</code>(<em class="parameter"><code></code></em>) functions report values,
and increment the epoch. Return the current epoch. This is useful for
detecting whether another thread caused a refresh.</p></dd><dt><span class="term">
"<code class="mallctl">config.debug</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
</span></dt><dd><p><code class="option">--enable-debug</code> was specified during
build configuration.</p></dd><dt><span class="term">
"<code class="mallctl">config.dss</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
</span></dt><dd><p><code class="option">--enable-dss</code> was specified during
build configuration.</p></dd><dt><span class="term">
"<code class="mallctl">config.dynamic_page_shift</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
</span></dt><dd><p><code class="option">--enable-dynamic-page-shift</code> was
specified during build configuration.</p></dd><dt><span class="term">
"<code class="mallctl">config.fill</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
</span></dt><dd><p><code class="option">--enable-fill</code> was specified during
build configuration.</p></dd><dt><span class="term">
"<code class="mallctl">config.lazy_lock</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
</span></dt><dd><p><code class="option">--enable-lazy-lock</code> was specified
during build configuration.</p></dd><dt><span class="term">
"<code class="mallctl">config.prof</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
</span></dt><dd><p><code class="option">--enable-prof</code> was specified during
build configuration.</p></dd><dt><span class="term">
"<code class="mallctl">config.prof_libgcc</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
</span></dt><dd><p><code class="option">--disable-prof-libgcc</code> was not
specified during build configuration.</p></dd><dt><span class="term">
"<code class="mallctl">config.prof_libunwind</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
</span></dt><dd><p><code class="option">--enable-prof-libunwind</code> was specified
during build configuration.</p></dd><dt><span class="term">
"<code class="mallctl">config.stats</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
</span></dt><dd><p><code class="option">--enable-stats</code> was specified during
build configuration.</p></dd><dt><span class="term">
"<code class="mallctl">config.swap</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
</span></dt><dd><p><code class="option">--enable-swap</code> was specified during
build configuration.</p></dd><dt><span class="term">
"<code class="mallctl">config.sysv</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
</span></dt><dd><p><code class="option">--enable-sysv</code> was specified during
build configuration.</p></dd><dt><span class="term">
"<code class="mallctl">config.tcache</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
</span></dt><dd><p><code class="option">--disable-tcache</code> was not specified
during build configuration.</p></dd><dt><span class="term">
"<code class="mallctl">config.tiny</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
</span></dt><dd><p><code class="option">--disable-tiny</code> was not specified
during build configuration.</p></dd><dt><span class="term">
"<code class="mallctl">config.tls</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
</span></dt><dd><p><code class="option">--disable-tls</code> was not specified during
build configuration.</p></dd><dt><span class="term">
"<code class="mallctl">config.xmalloc</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
</span></dt><dd><p><code class="option">--enable-xmalloc</code> was specified during
build configuration.</p></dd><dt><a name="opt.abort"></a><span class="term">
"<code class="mallctl">opt.abort</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Abort-on-warning enabled/disabled. If true, most
warnings are fatal. The process will call
<span class="citerefentry"><span class="refentrytitle">abort</span>(3)</span> in these cases. This option is
disabled by default unless <code class="option">--enable-debug</code> is
specified during configuration, in which case it is enabled by default.
</p></dd><dt><a name="opt.lg_qspace_max"></a><span class="term">
"<code class="mallctl">opt.lg_qspace_max</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Size (log base 2) of the maximum size class that is a
multiple of the quantum (8 or 16 bytes, depending on architecture).
Above this size, cacheline spacing is used for size classes. The
default value is 128 bytes (2^7).</p></dd><dt><a name="opt.lg_cspace_max"></a><span class="term">
"<code class="mallctl">opt.lg_cspace_max</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Size (log base 2) of the maximum size class that is a
multiple of the cacheline size (64). Above this size, subpage spacing
(256 bytes) is used for size classes. The default value is 512 bytes
(2^9).</p></dd><dt><a name="opt.lg_chunk"></a><span class="term">
"<code class="mallctl">opt.lg_chunk</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Virtual memory chunk size (log base 2). The default
chunk size is 4 MiB (2^22).</p></dd><dt><a name="opt.narenas"></a><span class="term">
"<code class="mallctl">opt.narenas</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Maximum number of arenas to use. The default maximum
number of arenas is four times the number of CPUs, or one if there is a
single CPU.</p></dd><dt><a name="opt.lg_dirty_mult"></a><span class="term">
"<code class="mallctl">opt.lg_dirty_mult</code>"
(<span class="type">ssize_t</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Per-arena minimum ratio (log base 2) of active to dirty
pages. Some dirty unused pages may be allowed to accumulate, within
the limit set by the ratio (or one chunk worth of dirty pages,
whichever is greater), before informing the kernel about some of those
pages via <span class="citerefentry"><span class="refentrytitle">madvise</span>(2)</span> or a similar system call. This
provides the kernel with sufficient information to recycle dirty pages
if physical memory becomes scarce and the pages remain unused. The
default minimum ratio is 32:1 (2^5:1); an option value of -1 will
disable dirty page purging.</p></dd><dt><a name="opt.stats_print"></a><span class="term">
"<code class="mallctl">opt.stats_print</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Enable/disable statistics printing at exit. If
enabled, the <code class="function">malloc_stats_print</code>(<em class="parameter"><code></code></em>)
function is called at program exit via an
<span class="citerefentry"><span class="refentrytitle">atexit</span>(3)</span> function. If
<code class="option">--enable-stats</code> is specified during configuration, this
has the potential to cause deadlock for a multi-threaded process that
exits while one or more threads are executing in the memory allocation
functions. Therefore, this option should only be used with care; it is
primarily intended as a performance tuning aid during application
development. This option is disabled by default.</p></dd><dt><a name="opt.junk"></a><span class="term">
"<code class="mallctl">opt.junk</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
[<code class="option">--enable-fill</code>]
</span></dt><dd><p>Junk filling enabled/disabled. If enabled, each byte
of uninitialized allocated memory will be initialized to
<code class="literal">0xa5</code>. All deallocated memory will be initialized to
<code class="literal">0x5a</code>. This is intended for debugging and will
impact performance negatively. This option is disabled by default
unless <code class="option">--enable-debug</code> is specified during
configuration, in which case it is enabled by default.</p></dd><dt><a name="opt.zero"></a><span class="term">
"<code class="mallctl">opt.zero</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
[<code class="option">--enable-fill</code>]
</span></dt><dd><p>Zero filling enabled/disabled. If enabled, each byte
of uninitialized allocated memory will be initialized to 0. Note that
this initialization only happens once for each byte, so
<code class="function">realloc</code>(<em class="parameter"><code></code></em>) and
<code class="function">rallocm</code>(<em class="parameter"><code></code></em>) calls do not zero memory that
was previously allocated. This is intended for debugging and will
impact performance negatively. This option is disabled by default.
</p></dd><dt><a name="opt.sysv"></a><span class="term">
"<code class="mallctl">opt.sysv</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
[<code class="option">--enable-sysv</code>]
</span></dt><dd><p>If enabled, attempting to allocate zero bytes will
return a <code class="constant">NULL</code> pointer instead of a valid pointer.
(The default behavior is to make a minimal allocation and return a
pointer to it.) This option is provided for System V compatibility.
This option is incompatible with the <a class="link" href="#opt.xmalloc">
"<code class="mallctl">opt.xmalloc</code>"
</a> option.
This option is disabled by default.</p></dd><dt><a name="opt.xmalloc"></a><span class="term">
"<code class="mallctl">opt.xmalloc</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
[<code class="option">--enable-xmalloc</code>]
</span></dt><dd><p>Abort-on-out-of-memory enabled/disabled. If enabled,
rather than returning failure for any allocation function, display a
diagnostic message on <code class="constant">STDERR_FILENO</code> and cause the
program to drop core (using
<span class="citerefentry"><span class="refentrytitle">abort</span>(3)</span>). If an application is
designed to depend on this behavior, set the option at compile time by
including the following in the source code:
</p><pre class="programlisting">
malloc_conf = "xmalloc:true";</pre><p>
This option is disabled by default.</p></dd><dt><a name="opt.tcache"></a><span class="term">
"<code class="mallctl">opt.tcache</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
[<code class="option">--enable-tcache</code>]
</span></dt><dd><p>Thread-specific caching enabled/disabled. When there
are multiple threads, each thread uses a thread-specific cache for
objects up to a certain size. Thread-specific caching allows many
allocations to be satisfied without performing any thread
synchronization, at the cost of increased memory use. See the
<a class="link" href="#opt.lg_tcache_gc_sweep">
"<code class="mallctl">opt.lg_tcache_gc_sweep</code>"
</a>
and <a class="link" href="#opt.lg_tcache_max">
"<code class="mallctl">opt.lg_tcache_max</code>"
</a>
options for related tuning information. This option is enabled by
default.</p></dd><dt><a name="opt.lg_tcache_gc_sweep"></a><span class="term">
"<code class="mallctl">opt.lg_tcache_gc_sweep</code>"
(<span class="type">ssize_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-tcache</code>]
</span></dt><dd><p>Approximate interval (log base 2) between full
thread-specific cache garbage collection sweeps, counted in terms of
thread-specific cache allocation/deallocation events. Garbage
collection is actually performed incrementally, one size class at a
time, in order to avoid large collection pauses. The default sweep
interval is 8192 (2^13); setting this option to -1 will disable garbage
collection.</p></dd><dt><a name="opt.lg_tcache_max"></a><span class="term">
"<code class="mallctl">opt.lg_tcache_max</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-tcache</code>]
</span></dt><dd><p>Maximum size class (log base 2) to cache in the
thread-specific cache. At a minimum, all small size classes are
cached, and at a maximum all large size classes are cached. The
default maximum is 32 KiB (2^15).</p></dd><dt><a name="opt.prof"></a><span class="term">
"<code class="mallctl">opt.prof</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
[<code class="option">--enable-prof</code>]
</span></dt><dd><p>Memory profiling enabled/disabled. If enabled, profile
memory allocation activity, and use an
<span class="citerefentry"><span class="refentrytitle">atexit</span>(3)</span> function to dump final memory
usage to a file named according to the pattern
<code class="filename">&lt;prefix&gt;.&lt;pid&gt;.&lt;seq&gt;.f.heap</code>,
where <code class="literal">&lt;prefix&gt;</code> is controlled by the <a class="link" href="#opt.prof_prefix">
"<code class="mallctl">opt.prof_prefix</code>"
</a>
option. See the <a class="link" href="#opt.lg_prof_bt_max">
"<code class="mallctl">opt.lg_prof_bt_max</code>"
</a>
option for backtrace depth control. See the <a class="link" href="#opt.prof_active">
"<code class="mallctl">opt.prof_active</code>"
</a>
option for on-the-fly activation/deactivation. See the <a class="link" href="#opt.lg_prof_sample">
"<code class="mallctl">opt.lg_prof_sample</code>"
</a>
option for probabilistic sampling control. See the <a class="link" href="#opt.prof_accum">
"<code class="mallctl">opt.prof_accum</code>"
</a>
option for control of cumulative sample reporting. See the <a class="link" href="#opt.lg_prof_tcmax">
"<code class="mallctl">opt.lg_prof_tcmax</code>"
</a>
option for control of per thread backtrace caching. See the <a class="link" href="#opt.lg_prof_interval">
"<code class="mallctl">opt.lg_prof_interval</code>"
</a>
option for information on interval-triggered profile dumping, and the
<a class="link" href="#opt.prof_gdump">
"<code class="mallctl">opt.prof_gdump</code>"
</a>
option for information on high-water-triggered profile dumping.
Profile output is compatible with the included <span class="command"><strong>pprof</strong></span>
Perl script, which originates from the <a class="ulink" href="http://code.google.com/p/google-perftools/" target="_top">google-perftools
package</a>.</p></dd><dt><a name="opt.prof_prefix"></a><span class="term">
"<code class="mallctl">opt.prof_prefix</code>"
(<span class="type">const char *</span>)
<code class="literal">r-</code>
[<code class="option">--enable-prof</code>]
</span></dt><dd><p>Filename prefix for profile dumps. If the prefix is
set to the empty string, no automatic dumps will occur; this is
primarily useful for disabling the automatic final heap dump (which
also disables leak reporting, if enabled). The default prefix is
<code class="filename">jeprof</code>.</p></dd><dt><a name="opt.lg_prof_bt_max"></a><span class="term">
"<code class="mallctl">opt.lg_prof_bt_max</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-prof</code>]
</span></dt><dd><p>Maximum backtrace depth (log base 2) when profiling
memory allocation activity. The default is 128 (2^7).</p></dd><dt><a name="opt.prof_active"></a><span class="term">
"<code class="mallctl">opt.prof_active</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
[<code class="option">--enable-prof</code>]
</span></dt><dd><p>Profiling activated/deactivated. This is a secondary
control mechanism that makes it possible to start the application with
profiling enabled (see the <a class="link" href="#opt.prof">
"<code class="mallctl">opt.prof</code>"
</a> option) but
inactive, then toggle profiling at any time during program execution
with the <a class="link" href="#prof.active">
"<code class="mallctl">prof.active</code>"
</a> mallctl.
This option is enabled by default.</p></dd><dt><a name="opt.lg_prof_sample"></a><span class="term">
"<code class="mallctl">opt.lg_prof_sample</code>"
(<span class="type">ssize_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-prof</code>]
</span></dt><dd><p>Average interval (log base 2) between allocation
samples, as measured in bytes of allocation activity. Increasing the
sampling interval decreases profile fidelity, but also decreases the
computational overhead. The default sample interval is 1 (2^0) (i.e.
all allocations are sampled).</p></dd><dt><a name="opt.prof_accum"></a><span class="term">
"<code class="mallctl">opt.prof_accum</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
[<code class="option">--enable-prof</code>]
</span></dt><dd><p>Reporting of cumulative object/byte counts in profile
dumps enabled/disabled. If this option is enabled, every unique
backtrace must be stored for the duration of execution. Depending on
the application, this can impose a large memory overhead, and the
cumulative counts are not always of interest. See the
<a class="link" href="#opt.lg_prof_tcmax">
"<code class="mallctl">opt.lg_prof_tcmax</code>"
</a>
option for control of per thread backtrace caching, which has important
interactions. This option is enabled by default.</p></dd><dt><a name="opt.lg_prof_tcmax"></a><span class="term">
"<code class="mallctl">opt.lg_prof_tcmax</code>"
(<span class="type">ssize_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-prof</code>]
</span></dt><dd><p>Maximum per thread backtrace cache (log base 2) used
for heap profiling. A backtrace can only be discarded if the
<a class="link" href="#opt.prof_accum">
"<code class="mallctl">opt.prof_accum</code>"
</a>
option is disabled, and no thread caches currently refer to the
backtrace. Therefore, a backtrace cache limit should be imposed if the
intention is to limit how much memory is used by backtraces. By
default, no limit is imposed (encoded as -1).
</p></dd><dt><a name="opt.lg_prof_interval"></a><span class="term">
"<code class="mallctl">opt.lg_prof_interval</code>"
(<span class="type">ssize_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-prof</code>]
</span></dt><dd><p>Average interval (log base 2) between memory profile
dumps, as measured in bytes of allocation activity. The actual
interval between dumps may be sporadic because decentralized allocation
counters are used to avoid synchronization bottlenecks. Profiles are
dumped to files named according to the pattern
<code class="filename">&lt;prefix&gt;.&lt;pid&gt;.&lt;seq&gt;.i&lt;iseq&gt;.heap</code>,
where <code class="literal">&lt;prefix&gt;</code> is controlled by the
<a class="link" href="#opt.prof_prefix">
"<code class="mallctl">opt.prof_prefix</code>"
</a>
option. By default, interval-triggered profile dumping is disabled
(encoded as -1).
</p></dd><dt><a name="opt.prof_gdump"></a><span class="term">
"<code class="mallctl">opt.prof_gdump</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
[<code class="option">--enable-prof</code>]
</span></dt><dd><p>Trigger a memory profile dump every time the total
virtual memory exceeds the previous maximum. Profiles are dumped to
files named according to the pattern
<code class="filename">&lt;prefix&gt;.&lt;pid&gt;.&lt;seq&gt;.u&lt;useq&gt;.heap</code>,
where <code class="literal">&lt;prefix&gt;</code> is controlled by the <a class="link" href="#opt.prof_prefix">
"<code class="mallctl">opt.prof_prefix</code>"
</a>
option. This option is disabled by default.</p></dd><dt><a name="opt.prof_leak"></a><span class="term">
"<code class="mallctl">opt.prof_leak</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
[<code class="option">--enable-prof</code>]
</span></dt><dd><p>Leak reporting enabled/disabled. If enabled, use an
<span class="citerefentry"><span class="refentrytitle">atexit</span>(3)</span> function to report memory leaks
detected by allocation sampling. See the
<a class="link" href="#opt.lg_prof_bt_max">
"<code class="mallctl">opt.lg_prof_bt_max</code>"
</a>
option for backtrace depth control. See the
<a class="link" href="#opt.prof">
"<code class="mallctl">opt.prof</code>"
</a> option for
information on analyzing heap profile output. This option is disabled
by default.</p></dd><dt><a name="opt.overcommit"></a><span class="term">
"<code class="mallctl">opt.overcommit</code>"
(<span class="type">bool</span>)
<code class="literal">r-</code>
[<code class="option">--enable-swap</code>]
</span></dt><dd><p>Over-commit enabled/disabled. If enabled, over-commit
memory as a side effect of using anonymous
<span class="citerefentry"><span class="refentrytitle">mmap</span>(2)</span> or
<span class="citerefentry"><span class="refentrytitle">sbrk</span>(2)</span> for virtual memory allocation.
In order for overcommit to be disabled, the <a class="link" href="#swap.fds">
"<code class="mallctl">swap.fds</code>"
</a> mallctl must have
been successfully written to. This option is enabled by
default.</p></dd><dt><span class="term">
"<code class="mallctl">tcache.flush</code>"
(<span class="type">void</span>)
<code class="literal">--</code>
[<code class="option">--enable-tcache</code>]
</span></dt><dd><p>Flush calling thread's tcache. This interface releases
all cached objects and internal data structures associated with the
calling thread's thread-specific cache. Ordinarily, this interface
need not be called, since automatic periodic incremental garbage
collection occurs, and the thread cache is automatically discarded when
a thread exits. However, garbage collection is triggered by allocation
activity, so it is possible for a thread that stops
allocating/deallocating to retain its cache indefinitely, in which case
the developer may find manual flushing useful.</p></dd><dt><span class="term">
"<code class="mallctl">thread.arena</code>"
(<span class="type">unsigned</span>)
<code class="literal">rw</code>
</span></dt><dd><p>Get or set the arena associated with the calling
thread. The arena index must be less than the maximum number of arenas
(see the <a class="link" href="#arenas.narenas">
"<code class="mallctl">arenas.narenas</code>"
</a>
mallctl). If the specified arena was not initialized beforehand (see
the <a class="link" href="#arenas.initialized">
"<code class="mallctl">arenas.initialized</code>"
</a>
mallctl), it will be automatically initialized as a side effect of
calling this interface.</p></dd><dt><a name="thread.allocated"></a><span class="term">
"<code class="mallctl">thread.allocated</code>"
(<span class="type">uint64_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Get the total number of bytes ever allocated by the
calling thread. This counter has the potential to wrap around; it is
up to the application to appropriately interpret the counter in such
cases.</p></dd><dt><span class="term">
"<code class="mallctl">thread.allocatedp</code>"
(<span class="type">uint64_t *</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Get a pointer to the the value that is returned by the
<a class="link" href="#thread.allocated">
"<code class="mallctl">thread.allocated</code>"
</a>
mallctl. This is useful for avoiding the overhead of repeated
<code class="function">mallctl*</code>(<em class="parameter"><code></code></em>) calls.</p></dd><dt><a name="thread.deallocated"></a><span class="term">
"<code class="mallctl">thread.deallocated</code>"
(<span class="type">uint64_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Get the total number of bytes ever deallocated by the
calling thread. This counter has the potential to wrap around; it is
up to the application to appropriately interpret the counter in such
cases.</p></dd><dt><span class="term">
"<code class="mallctl">thread.deallocatedp</code>"
(<span class="type">uint64_t *</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Get a pointer to the the value that is returned by the
<a class="link" href="#thread.deallocated">
"<code class="mallctl">thread.deallocated</code>"
</a>
mallctl. This is useful for avoiding the overhead of repeated
<code class="function">mallctl*</code>(<em class="parameter"><code></code></em>) calls.</p></dd><dt><a name="arenas.narenas"></a><span class="term">
"<code class="mallctl">arenas.narenas</code>"
(<span class="type">unsigned</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Maximum number of arenas.</p></dd><dt><a name="arenas.initialized"></a><span class="term">
"<code class="mallctl">arenas.initialized</code>"
(<span class="type">bool *</span>)
<code class="literal">r-</code>
</span></dt><dd><p>An array of <a class="link" href="#arenas.narenas">
"<code class="mallctl">arenas.narenas</code>"
</a>
booleans. Each boolean indicates whether the corresponding arena is
initialized.</p></dd><dt><span class="term">
"<code class="mallctl">arenas.quantum</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Quantum size.</p></dd><dt><span class="term">
"<code class="mallctl">arenas.cacheline</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Assumed cacheline size.</p></dd><dt><span class="term">
"<code class="mallctl">arenas.subpage</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Subpage size class interval.</p></dd><dt><span class="term">
"<code class="mallctl">arenas.pagesize</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Page size.</p></dd><dt><span class="term">
"<code class="mallctl">arenas.chunksize</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Chunk size.</p></dd><dt><span class="term">
"<code class="mallctl">arenas.tspace_min</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Minimum tiny size class. Tiny size classes are powers
of two.</p></dd><dt><span class="term">
"<code class="mallctl">arenas.tspace_max</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Maximum tiny size class. Tiny size classes are powers
of two.</p></dd><dt><span class="term">
"<code class="mallctl">arenas.qspace_min</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Minimum quantum-spaced size class.</p></dd><dt><span class="term">
"<code class="mallctl">arenas.qspace_max</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Maximum quantum-spaced size class.</p></dd><dt><span class="term">
"<code class="mallctl">arenas.cspace_min</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Minimum cacheline-spaced size class.</p></dd><dt><span class="term">
"<code class="mallctl">arenas.cspace_max</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Maximum cacheline-spaced size class.</p></dd><dt><span class="term">
"<code class="mallctl">arenas.sspace_min</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Minimum subpage-spaced size class.</p></dd><dt><span class="term">
"<code class="mallctl">arenas.sspace_max</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Maximum subpage-spaced size class.</p></dd><dt><span class="term">
"<code class="mallctl">arenas.tcache_max</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-tcache</code>]
</span></dt><dd><p>Maximum thread-cached size class.</p></dd><dt><span class="term">
"<code class="mallctl">arenas.ntbins</code>"
(<span class="type">unsigned</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Number of tiny bin size classes.</p></dd><dt><span class="term">
"<code class="mallctl">arenas.nqbins</code>"
(<span class="type">unsigned</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Number of quantum-spaced bin size
classes.</p></dd><dt><span class="term">
"<code class="mallctl">arenas.ncbins</code>"
(<span class="type">unsigned</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Number of cacheline-spaced bin size
classes.</p></dd><dt><span class="term">
"<code class="mallctl">arenas.nsbins</code>"
(<span class="type">unsigned</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Number of subpage-spaced bin size
classes.</p></dd><dt><span class="term">
"<code class="mallctl">arenas.nbins</code>"
(<span class="type">unsigned</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Total number of bin size classes.</p></dd><dt><span class="term">
"<code class="mallctl">arenas.nhbins</code>"
(<span class="type">unsigned</span>)
<code class="literal">r-</code>
[<code class="option">--enable-tcache</code>]
</span></dt><dd><p>Total number of thread cache bin size
classes.</p></dd><dt><a name="arenas.bin.i.size"></a><span class="term">
"<code class="mallctl">arenas.bin.&lt;i&gt;.size</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Maximum size supported by size class.</p></dd><dt><span class="term">
"<code class="mallctl">arenas.bin.&lt;i&gt;.nregs</code>"
(<span class="type">uint32_t</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Number of regions per page run.</p></dd><dt><span class="term">
"<code class="mallctl">arenas.bin.&lt;i&gt;.run_size</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Number of bytes per page run.</p></dd><dt><span class="term">
"<code class="mallctl">arenas.nlruns</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Total number of large size classes.</p></dd><dt><span class="term">
"<code class="mallctl">arenas.lrun.&lt;i&gt;.size</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Maximum size supported by this large size
class.</p></dd><dt><span class="term">
"<code class="mallctl">arenas.purge</code>"
(<span class="type">unsigned</span>)
<code class="literal">-w</code>
</span></dt><dd><p>Purge unused dirty pages for the specified arena, or
for all arenas if none is specified.</p></dd><dt><a name="prof.active"></a><span class="term">
"<code class="mallctl">prof.active</code>"
(<span class="type">bool</span>)
<code class="literal">rw</code>
[<code class="option">--enable-prof</code>]
</span></dt><dd><p>Control whether sampling is currently active. See the
<a class="link" href="#opt.prof_active">
"<code class="mallctl">opt.prof_active</code>"
</a>
option for additional information.
</p></dd><dt><span class="term">
"<code class="mallctl">prof.dump</code>"
(<span class="type">const char *</span>)
<code class="literal">-w</code>
[<code class="option">--enable-prof</code>]
</span></dt><dd><p>Dump a memory profile to the specified file, or if NULL
is specified, to a file according to the pattern
<code class="filename">&lt;prefix&gt;.&lt;pid&gt;.&lt;seq&gt;.m&lt;mseq&gt;.heap</code>,
where <code class="literal">&lt;prefix&gt;</code> is controlled by the
<a class="link" href="#opt.prof_prefix">
"<code class="mallctl">opt.prof_prefix</code>"
</a>
option.</p></dd><dt><span class="term">
"<code class="mallctl">prof.interval</code>"
(<span class="type">uint64_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-prof</code>]
</span></dt><dd><p>Average number of bytes allocated between
inverval-based profile dumps. See the
<a class="link" href="#opt.lg_prof_interval">
"<code class="mallctl">opt.lg_prof_interval</code>"
</a>
option for additional information.</p></dd><dt><a name="stats.cactive"></a><span class="term">
"<code class="mallctl">stats.cactive</code>"
(<span class="type">size_t *</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Pointer to a counter that contains an approximate count
of the current number of bytes in active pages. The estimate may be
high, but never low, because each arena rounds up to the nearest
multiple of the chunk size when computing its contribution to the
counter. Note that the <a class="link" href="#epoch">
"<code class="mallctl">epoch</code>"
</a> mallctl has no bearing
on this counter. Furthermore, counter consistency is maintained via
atomic operations, so it is necessary to use an atomic operation in
order to guarantee a consistent read when dereferencing the pointer.
</p></dd><dt><a name="stats.allocated"></a><span class="term">
"<code class="mallctl">stats.allocated</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Total number of bytes allocated by the
application.</p></dd><dt><a name="stats.active"></a><span class="term">
"<code class="mallctl">stats.active</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Total number of bytes in active pages allocated by the
application. This is a multiple of the page size, and greater than or
equal to <a class="link" href="#stats.allocated">
"<code class="mallctl">stats.allocated</code>"
</a>.
</p></dd><dt><span class="term">
"<code class="mallctl">stats.mapped</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Total number of bytes in chunks mapped on behalf of the
application. This is a multiple of the chunk size, and is at least as
large as <a class="link" href="#stats.active">
"<code class="mallctl">stats.active</code>"
</a>. This
does not include inactive chunks backed by swap files. his does not
include inactive chunks embedded in the DSS.</p></dd><dt><span class="term">
"<code class="mallctl">stats.chunks.current</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Total number of chunks actively mapped on behalf of the
application. This does not include inactive chunks backed by swap
files. This does not include inactive chunks embedded in the DSS.
</p></dd><dt><span class="term">
"<code class="mallctl">stats.chunks.total</code>"
(<span class="type">uint64_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Cumulative number of chunks allocated.</p></dd><dt><span class="term">
"<code class="mallctl">stats.chunks.high</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Maximum number of active chunks at any time thus far.
</p></dd><dt><span class="term">
"<code class="mallctl">stats.huge.allocated</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Number of bytes currently allocated by huge objects.
</p></dd><dt><span class="term">
"<code class="mallctl">stats.huge.nmalloc</code>"
(<span class="type">uint64_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Cumulative number of huge allocation requests.
</p></dd><dt><span class="term">
"<code class="mallctl">stats.huge.ndalloc</code>"
(<span class="type">uint64_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Cumulative number of huge deallocation requests.
</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.nthreads</code>"
(<span class="type">unsigned</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Number of threads currently assigned to
arena.</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.pactive</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Number of pages in active runs.</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.pdirty</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
</span></dt><dd><p>Number of pages within unused runs that are potentially
dirty, and for which <code class="function">madvise</code>(<em class="parameter"><code>...</code></em>,
<em class="parameter"><code><code class="constant">MADV_DONTNEED</code></code></em>) or
similar has not been called.</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.mapped</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Number of mapped bytes.</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.npurge</code>"
(<span class="type">uint64_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Number of dirty page purge sweeps performed.
</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.nmadvise</code>"
(<span class="type">uint64_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Number of <code class="function">madvise</code>(<em class="parameter"><code>...</code></em>,
<em class="parameter"><code><code class="constant">MADV_DONTNEED</code></code></em>) or
similar calls made to purge dirty pages.</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.npurged</code>"
(<span class="type">uint64_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Number of pages purged.</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.small.allocated</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Number of bytes currently allocated by small objects.
</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.small.nmalloc</code>"
(<span class="type">uint64_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Cumulative number of allocation requests served by
small bins.</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.small.ndalloc</code>"
(<span class="type">uint64_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Cumulative number of small objects returned to bins.
</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.small.nrequests</code>"
(<span class="type">uint64_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Cumulative number of small allocation requests.
</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.large.allocated</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Number of bytes currently allocated by large objects.
</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.large.nmalloc</code>"
(<span class="type">uint64_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Cumulative number of large allocation requests served
directly by the arena.</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.large.ndalloc</code>"
(<span class="type">uint64_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Cumulative number of large deallocation requests served
directly by the arena.</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.large.nrequests</code>"
(<span class="type">uint64_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Cumulative number of large allocation requests.
</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.allocated</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Current number of bytes allocated by
bin.</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.nmalloc</code>"
(<span class="type">uint64_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Cumulative number of allocations served by bin.
</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.ndalloc</code>"
(<span class="type">uint64_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Cumulative number of allocations returned to bin.
</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.nrequests</code>"
(<span class="type">uint64_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Cumulative number of allocation
requests.</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.nfills</code>"
(<span class="type">uint64_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code> <code class="option">--enable-tcache</code>]
</span></dt><dd><p>Cumulative number of tcache fills.</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.nflushes</code>"
(<span class="type">uint64_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code> <code class="option">--enable-tcache</code>]
</span></dt><dd><p>Cumulative number of tcache flushes.</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.nruns</code>"
(<span class="type">uint64_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Cumulative number of runs created.</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.nreruns</code>"
(<span class="type">uint64_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Cumulative number of times the current run from which
to allocate changed.</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.highruns</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Maximum number of runs at any time thus far.
</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.curruns</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Current number of runs.</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.lruns.&lt;j&gt;.nmalloc</code>"
(<span class="type">uint64_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Cumulative number of allocation requests for this size
class served directly by the arena.</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.lruns.&lt;j&gt;.ndalloc</code>"
(<span class="type">uint64_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Cumulative number of deallocation requests for this
size class served directly by the arena.</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.lruns.&lt;j&gt;.nrequests</code>"
(<span class="type">uint64_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Cumulative number of allocation requests for this size
class.</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.lruns.&lt;j&gt;.highruns</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Maximum number of runs at any time thus far for this
size class.</p></dd><dt><span class="term">
"<code class="mallctl">stats.arenas.&lt;i&gt;.lruns.&lt;j&gt;.curruns</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats</code>]
</span></dt><dd><p>Current number of runs for this size class.
</p></dd><dt><span class="term">
"<code class="mallctl">swap.avail</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-stats --enable-swap</code>]
</span></dt><dd><p>Number of swap file bytes that are currently not
associated with any chunk (i.e. mapped, but otherwise completely
unmanaged).</p></dd><dt><a name="swap.prezeroed"></a><span class="term">
"<code class="mallctl">swap.prezeroed</code>"
(<span class="type">bool</span>)
<code class="literal">rw</code>
[<code class="option">--enable-swap</code>]
</span></dt><dd><p>If true, the allocator assumes that the swap file(s)
contain nothing but nil bytes. If this assumption is violated,
allocator behavior is undefined. This value becomes read-only after
<a class="link" href="#swap.fds">
"<code class="mallctl">swap.fds</code>"
</a> is
successfully written to.</p></dd><dt><span class="term">
"<code class="mallctl">swap.nfds</code>"
(<span class="type">size_t</span>)
<code class="literal">r-</code>
[<code class="option">--enable-swap</code>]
</span></dt><dd><p>Number of file descriptors in use for swap.
</p></dd><dt><a name="swap.fds"></a><span class="term">
"<code class="mallctl">swap.fds</code>"
(<span class="type">int *</span>)
<code class="literal">rw</code>
[<code class="option">--enable-swap</code>]
</span></dt><dd><p>When written to, the files associated with the
specified file descriptors are contiguously mapped via
<span class="citerefentry"><span class="refentrytitle">mmap</span>(2)</span>. The resulting virtual memory
region is preferred over anonymous
<span class="citerefentry"><span class="refentrytitle">mmap</span>(2)</span> and
<span class="citerefentry"><span class="refentrytitle">sbrk</span>(2)</span> memory. Note that if a file's
size is not a multiple of the page size, it is automatically truncated
to the nearest page size multiple. See the
<a class="link" href="#swap.prezeroed">
"<code class="mallctl">swap.prezeroed</code>"
</a>
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
the <code class="option">--enable-debug</code> and <code class="option">--enable-fill</code>
options, and recompile the program with suitable options and symbols for
debugger support. When so configured, jemalloc incorporates a wide variety
of run-time assertions that catch application errors such as double-free,
write-after-free, etc.</p><p>Programs often accidentally depend on &#8220;uninitialized&#8221;
memory actually being filled with zero bytes. Junk filling
(see the <a class="link" href="#opt.junk">
"<code class="mallctl">opt.junk</code>"
</a>
option) tends to expose such bugs in the form of obviously incorrect
results and/or coredumps. Conversely, zero
filling (see the <a class="link" href="#opt.zero">
"<code class="mallctl">opt.zero</code>"
</a> option) eliminates
the symptoms of such bugs. Between these two options, it is usually
possible to quickly detect, diagnose, and eliminate such bugs.</p><p>This implementation does not provide much detail about the problems
it detects, because the performance impact for storing such information
would be prohibitive. There are a number of allocator implementations
available on the Internet which focus on detecting and pinpointing problems
by trading performance for extra sanity checks and detailed
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
error or warning condition, a message will be printed to file descriptor
<code class="constant">STDERR_FILENO</code>. Errors will result in the process
dumping core. If the <a class="link" href="#opt.abort">
"<code class="mallctl">opt.abort</code>"
</a> option is set, most
warnings are treated as errors.</p><p>The <code class="varname">malloc_message</code> variable allows the programmer
to override the function which emits the text strings forming the errors
and warnings if for some reason the <code class="constant">STDERR_FILENO</code> file
descriptor is not suitable for this.
<code class="function">malloc_message</code>(<em class="parameter"><code></code></em>) takes the
<em class="parameter"><code>cbopaque</code></em> pointer argument that is
<code class="constant">NULL</code> unless overridden by the arguments in a call to
<code class="function">malloc_stats_print</code>(<em class="parameter"><code></code></em>), followed by a string
pointer. Please note that doing anything which tries to allocate memory in
this function is likely to result in a crash or deadlock.</p><p>All messages are prefixed by
&#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="id3029250"></a><h3>Standard API</h3><p>The <code class="function">malloc</code>(<em class="parameter"><code></code></em>) and
<code class="function">calloc</code>(<em class="parameter"><code></code></em>) functions return a pointer to the
allocated memory if successful; otherwise a <code class="constant">NULL</code>
pointer is returned and <code class="varname">errno</code> is set to
<span class="errorname">ENOMEM</span>.</p><p>The <code class="function">posix_memalign</code>(<em class="parameter"><code></code></em>) function
returns the value 0 if successful; otherwise it returns an error value.
The <code class="function">posix_memalign</code>(<em class="parameter"><code></code></em>) function will fail
if:
</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
not a power of 2 at least as large as
<code class="code">sizeof(<span class="type">void *</span>)</code>.
</p></dd><dt><span class="term"><span class="errorname">ENOMEM</span></span></dt><dd><p>Memory allocation error.</p></dd></dl></div><p>
</p><p>The <code class="function">realloc</code>(<em class="parameter"><code></code></em>) function returns a
pointer, possibly identical to <em class="parameter"><code>ptr</code></em>, to the
allocated memory if successful; otherwise a <code class="constant">NULL</code>
pointer is returned, and <code class="varname">errno</code> is set to
<span class="errorname">ENOMEM</span> if the error was the result of an
allocation failure. The <code class="function">realloc</code>(<em class="parameter"><code></code></em>)
function always leaves the original buffer intact when an error occurs.
</p><p>The <code class="function">free</code>(<em class="parameter"><code></code></em>) function returns no
value.</p></div><div class="refsect2" title="Non-standard API"><a name="id3029403"></a><h3>Non-standard API</h3><p>The <code class="function">malloc_usable_size</code>(<em class="parameter"><code></code></em>) function
returns the usable size of the allocation pointed to by
<em class="parameter"><code>ptr</code></em>. </p><p>The <code class="function">mallctl</code>(<em class="parameter"><code></code></em>),
<code class="function">mallctlnametomib</code>(<em class="parameter"><code></code></em>), and
<code class="function">mallctlbymib</code>(<em class="parameter"><code></code></em>) functions return 0 on
success; otherwise they return an error value. The functions will fail
if:
</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
<code class="constant">NULL</code>, and <em class="parameter"><code>newlen</code></em> is too
large or too small. Alternatively, <em class="parameter"><code>*oldlenp</code></em>
is too large or too small; in this case as much data as possible
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
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
<em class="parameter"><code>mib</code></em> specifies an unknown/invalid
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
write read-only value.</p></dd><dt><span class="term"><span class="errorname">EAGAIN</span></span></dt><dd><p>A memory allocation failure
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
not directly related to <code class="function">mallctl*</code>(<em class="parameter"><code></code></em>)
read/write processing.</p></dd></dl></div><p>
</p></div><div class="refsect2" title="Experimental API"><a name="id3029581"></a><h3>Experimental API</h3><p>The <code class="function">allocm</code>(<em class="parameter"><code></code></em>),
<code class="function">rallocm</code>(<em class="parameter"><code></code></em>),
<code class="function">sallocm</code>(<em class="parameter"><code></code></em>), and
<code class="function">dallocm</code>(<em class="parameter"><code></code></em>) functions return
<code class="constant">ALLOCM_SUCCESS</code> on success; otherwise they return an
error value. The <code class="function">allocm</code>(<em class="parameter"><code></code></em>) and
<code class="function">rallocm</code>(<em class="parameter"><code></code></em>) functions will fail if:
</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
available to service the allocation request. The
<code class="function">allocm</code>(<em class="parameter"><code></code></em>) function additionally sets
<em class="parameter"><code>*ptr</code></em> to <code class="constant">NULL</code>, whereas
the <code class="function">rallocm</code>(<em class="parameter"><code></code></em>) function leaves
<code class="constant">*ptr</code> unmodified.</p></dd></dl></div><p>
The <code class="function">rallocm</code>(<em class="parameter"><code></code></em>) function will also
fail if:
</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,
but the reallocation request could not be serviced without moving
the object.</p></dd></dl></div><p>
</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
allocation functions:
</p><div class="variablelist"><dl><dt><span class="term"><code class="envar">MALLOC_CONF</code></span></dt><dd><p>If the environment variable
<code class="envar">MALLOC_CONF</code> is set, the characters it contains
will be interpreted as options.</p></dd></dl></div><p>
</p></div><div class="refsect1" title="EXAMPLES"><a name="examples"></a><h2>EXAMPLES</h2><p>To dump core whenever a problem occurs:
</p><pre class="screen">ln -s 'abort:true' /etc/malloc.conf</pre><p>
</p><p>To specify in the source a chunk size that is 16 MiB:
</p><pre class="programlisting">
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>,
<span class="citerefentry"><span class="refentrytitle">mmap</span>(2)</span>,
<span class="citerefentry"><span class="refentrytitle">sbrk</span>(2)</span>,
<span class="citerefentry"><span class="refentrytitle">alloca</span>(3)</span>,
<span class="citerefentry"><span class="refentrytitle">atexit</span>(3)</span>,
<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>),
<code class="function">calloc</code>(<em class="parameter"><code></code></em>),
<code class="function">realloc</code>(<em class="parameter"><code></code></em>), and
<code class="function">free</code>(<em class="parameter"><code></code></em>) functions conform to ISO/IEC
9899:1990 (&#8220;ISO C90&#8221;).</p><p>The <code class="function">posix_memalign</code>(<em class="parameter"><code></code></em>) function conforms
to IEEE Std 1003.1-2001 (&#8220;POSIX.1&#8221;).</p></div></div></body></html>
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