Gecko [ edgpens.lpkmn.gov.my ]

Name	Size	Permission	Action
jemalloc.html	178.91 KB	-rw-rw-rw-

Code Editor : jemalloc.html

<?xml version="1.0" encoding="utf-8"?>
<html><head><title>JEMALLOC</title><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot"/></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="refentry"><a name="idm46057389671552"/><div class="titlepage"/><div class="refnamediv"><h2>Name</h2>jemalloc — general purpose memory allocation functions</div><div class="refsect1"><a name="library"/><h2>LIBRARY</h2>This manual describes jemalloc 5.3.0-0-g54eaed1d8b56b1aa528be3bdd1877e59c56fa90c. More information
 can be found at the <a class="ulink" href="http://jemalloc.net/" target="_top">jemalloc website</a>.</div><div class="refsynopsisdiv"><h2>SYNOPSIS</h2><div class="funcsynopsis"><pre class="funcsynopsisinfo">#include &lt;<code class="filename">jemalloc/jemalloc.h</code>&gt;</pre><div class="refsect2"><a name="idm46057388074960"/><h3>Standard API</h3><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">void *malloc(</code></td><td>size_t <var class="pdparam">size</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">void *calloc(</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" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int posix_memalign(</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" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">void *aligned_alloc(</code></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" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">void *realloc(</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" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">void free(</code></td><td>void *<var class="pdparam">ptr</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div><div class="refsect2"><a name="idm46057391291888"/><h3>Non-standard API</h3><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">void *mallocx(</code></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" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">void *rallocx(</code></td><td>void *<var class="pdparam">ptr</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" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">size_t xallocx(</code></td><td>void *<var class="pdparam">ptr</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" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">size_t sallocx(</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><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">void dallocx(</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><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">void sdallocx(</code></td><td>void *<var class="pdparam">ptr</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" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">size_t nallocx(</code></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" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int mallctl(</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" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int mallctlnametomib(</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" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int mallctlbymib(</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" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">void malloc_stats_print(</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" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">size_t malloc_usable_size(</code></td><td>const void *<var class="pdparam">ptr</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">void (*malloc_message)(</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>const char *<code class="varname">malloc_conf</code>;</div></div></div><div class="refsect1"><a name="description"/><h2>DESCRIPTION</h2><div class="refsect2"><a name="idm46057386032448"/><h3>Standard API</h3>The <code class="function">malloc()</code> function allocates
 <code>size</code> bytes of uninitialized memory. The allocated
 space is suitably aligned (after possible pointer coercion) for storage
 of any type of object.The <code class="function">calloc()</code> function allocates
 space for <code>number</code> objects, each
 <code>size</code> bytes in length. The result is identical to
 calling <code class="function">malloc()</code> with an argument of
 <code>number</code> * <code>size</code>, with the
 exception that the allocated memory is explicitly initialized to zero
 bytes.The <code class="function">posix_memalign()</code> function
 allocates <code>size</code> bytes of memory such that the
 allocation's base address is a multiple of
 <code>alignment</code>, and returns the allocation in the value
 pointed to by <code>ptr</code>. The requested
 <code>alignment</code> must be a power of 2 at least as large as
 <code class="code">sizeof(void *)</code>.The <code class="function">aligned_alloc()</code> function
 allocates <code>size</code> bytes of memory such that the
 allocation's base address is a multiple of
 <code>alignment</code>. The requested
 <code>alignment</code> must be a power of 2. Behavior is
 undefined if <code>size</code> is not an integral multiple of
 <code>alignment</code>.The <code class="function">realloc()</code> function changes the
 size of the previously allocated memory referenced by
 <code>ptr</code> to <code>size</code> 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 <code>ptr</code> is freed and a pointer to the newly
 allocated memory is returned. Note that
 <code class="function">realloc()</code> may move the memory allocation,
 resulting in a different return value than <code>ptr</code>.
 If <code>ptr</code> is <code class="constant">NULL</code>, the
 <code class="function">realloc()</code> function behaves identically to
 <code class="function">malloc()</code> for the specified size.The <code class="function">free()</code> function causes the
 allocated memory referenced by <code>ptr</code> to be made
 available for future allocations. If <code>ptr</code> is
 <code class="constant">NULL</code>, no action occurs.</div><div class="refsect2"><a name="idm46057386007648"/><h3>Non-standard API</h3>The <code class="function">mallocx()</code>,
 <code class="function">rallocx()</code>,
 <code class="function">xallocx()</code>,
 <code class="function">sallocx()</code>,
 <code class="function">dallocx()</code>,
 <code class="function">sdallocx()</code>, and
 <code class="function">nallocx()</code> functions all have a
 <code>flags</code> 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:
 <div class="variablelist"><dl class="variablelist"><dt><a name="MALLOCX_LG_ALIGN"/><code class="constant">MALLOCX_LG_ALIGN(<code>la</code>)
 </code></dt><dd>Align the memory allocation to start at an address
 that is a multiple of <code class="code">(1 &lt;&lt;
 <code>la</code>)</code>. This macro does not validate
 that <code>la</code> is within the valid
 range.</dd><dt><a name="MALLOCX_ALIGN"/><code class="constant">MALLOCX_ALIGN(<code>a</code>)
 </code></dt><dd>Align the memory allocation to start at an address
 that is a multiple of <code>a</code>, where
 <code>a</code> is a power of two. This macro does not
 validate that <code>a</code> is a power of 2.
 </dd><dt><a name="MALLOCX_ZERO"/><code class="constant">MALLOCX_ZERO</code></dt><dd>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 macro is
 absent, newly allocated memory is uninitialized.</dd><dt><a name="MALLOCX_TCACHE"/><code class="constant">MALLOCX_TCACHE(<code>tc</code>)
 </code></dt><dd>Use the thread-specific cache (tcache) specified by
 the identifier <code>tc</code>, which must have been
 acquired via the <a class="link" href="#tcache.create"><quote><code class="mallctl">tcache.create</code></quote></a>
 mallctl. This macro does not validate that
 <code>tc</code> specifies a valid
 identifier.</dd><dt><a name="MALLOC_TCACHE_NONE"/><code class="constant">MALLOCX_TCACHE_NONE</code></dt><dd>Do not use a thread-specific cache (tcache). Unless
 <code class="constant">MALLOCX_TCACHE(<code>tc</code>)</code> or
 <code class="constant">MALLOCX_TCACHE_NONE</code> is specified, an
 automatically managed tcache will be used under many circumstances.
 This macro cannot be used in the same <code>flags</code>
 argument as
 <code class="constant">MALLOCX_TCACHE(<code>tc</code>)</code>.</dd><dt><a name="MALLOCX_ARENA"/><code class="constant">MALLOCX_ARENA(<code>a</code>)
 </code></dt><dd>Use the arena specified by the index
 <code>a</code>. This macro has no effect for regions that
 were allocated via an arena other than the one specified. This
 macro does not validate that <code>a</code> specifies an
 arena index in the valid range.</dd></dl></div>
 The <code class="function">mallocx()</code> function allocates at
 least <code>size</code> bytes of memory, and returns a pointer
 to the base address of the allocation. Behavior is undefined if
 <code>size</code> is <code class="constant">0</code>.The <code class="function">rallocx()</code> function resizes the
 allocation at <code>ptr</code> to be at least
 <code>size</code> bytes, and returns a pointer to the base
 address of the resulting allocation, which may or may not have moved from
 its original location. Behavior is undefined if
 <code>size</code> is <code class="constant">0</code>.The <code class="function">xallocx()</code> function resizes the
 allocation at <code>ptr</code> in place to be at least
 <code>size</code> bytes, and returns the real size of the
 allocation. If <code>extra</code> is non-zero, an attempt is
 made to resize the allocation to be at least <code class="code">(<code>size</code> +
 <code>extra</code>)</code> bytes, though inability to allocate
 the extra byte(s) will not by itself result in failure to resize.
 Behavior is undefined if <code>size</code> is
 <code class="constant">0</code>, or if <code class="code">(<code>size</code> + <code>extra</code>
 &gt; <code class="constant">SIZE_T_MAX</code>)</code>.The <code class="function">sallocx()</code> function returns the
 real size of the allocation at <code>ptr</code>.The <code class="function">dallocx()</code> function causes the
 memory referenced by <code>ptr</code> to be made available for
 future allocations.The <code class="function">sdallocx()</code> function is an
 extension of <code class="function">dallocx()</code> with a
 <code>size</code> parameter to allow the caller to pass in the
 allocation size as an optimization. The minimum valid input size is the
 original requested size of the allocation, and the maximum valid input
 size is the corresponding value returned by
 <code class="function">nallocx()</code> or
 <code class="function">sallocx()</code>.The <code class="function">nallocx()</code> function allocates no
 memory, but it performs the same size computation as the
 <code class="function">mallocx()</code> function, and returns the real
 size of the allocation that would result from the equivalent
 <code class="function">mallocx()</code> function call, or
 <code class="constant">0</code> if the inputs exceed the maximum supported size
 class and/or alignment. Behavior is undefined if
 <code>size</code> is <code class="constant">0</code>.The <code class="function">mallctl()</code> function provides a
 general interface for introspecting the memory allocator, as well as
 setting modifiable parameters and triggering actions. The
 period-separated <code>name</code> 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
 <code>oldp</code> to adequate space to contain the value, and a
 pointer to its length via <code>oldlenp</code>; 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
 <code>newp</code>, and its length via
 <code>newlen</code>; otherwise pass <code class="constant">NULL</code>
 and <code class="constant">0</code>.The <code class="function">mallctlnametomib()</code> 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 “Management Information Base” (MIB) that can be passed
 repeatedly to <code class="function">mallctlbymib()</code>. Upon
 successful return from <code class="function">mallctlnametomib()</code>,
 <code>mibp</code> contains an array of
 <code>*miblenp</code> integers, where
 <code>*miblenp</code> is the lesser of the number of components
 in <code>name</code> and the input value of
 <code>*miblenp</code>. Thus it is possible to pass a
 <code>*miblenp</code> 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"><quote><code class="mallctl">arenas.bin.2.size</code></quote></a>),
 the corresponding MIB component will always be that integer. Therefore,
 it is legitimate to construct code like the following: <pre class="programlisting">
unsigned nbins, i;
size_t mib[4];
size_t len, miblen;

len = sizeof(nbins);
mallctl("arenas.nbins", &amp;nbins, &amp;len, NULL, 0);

miblen = 4;
mallctlnametomib("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, (void *)&amp;bin_size, &amp;len, NULL, 0);
	/* Do something with bin_size... */
}</pre><dt><a name="malloc_stats_print_opts"/></dt><dd/>The <code class="function">malloc_stats_print()</code> function writes
 summary statistics via the <code>write_cb</code> callback
 function pointer and <code>cbopaque</code> data passed to
 <code>write_cb</code>, or <code class="function">malloc_message()</code>
 if <code>write_cb</code> is <code class="constant">NULL</code>. The
 statistics are presented in human-readable form unless “J” is
 specified as a character within the <code>opts</code> string, in
 which case the statistics are presented in <a class="ulink" href="http://www.json.org/" target="_top">JSON format</a>. This function can be
 called repeatedly. General information that never changes during
 execution can be omitted by specifying “g” as a character
 within the <code>opts</code> string. Note that
 <code class="function">malloc_stats_print()</code> uses the
 <code class="function">mallctl*()</code> 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, “m”, “d”, and “a”
 can be specified to omit merged arena, destroyed merged arena, and per
 arena statistics, respectively; “b” and “l” can
 be specified to omit per size class statistics for bins and large objects,
 respectively; “x” can be specified to omit all mutex
 statistics; “e” can be used to omit extent statistics.
 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.The <code class="function">malloc_usable_size()</code> function
 returns the usable size of the allocation pointed to by
 <code>ptr</code>. The return value may be larger than the size
 that was requested during allocation. The
 <code class="function">malloc_usable_size()</code> function is not a
 mechanism for in-place <code class="function">realloc()</code>; 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> should not be
 depended on, since such behavior is entirely implementation-dependent.
 </div></div><div class="refsect1"><a name="tuning"/><h2>TUNING</h2>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.The string specified via <code class="option">--with-malloc-conf</code>, the
 string pointed to by the global variable <code class="varname">malloc_conf</code>, the
 “name” 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. Note that
 <code class="varname">malloc_conf</code> may be read before
 <code class="function">main()</code> is entered, so the declaration of
 <code class="varname">malloc_conf</code> should specify an initializer that contains
 the final value to be read by jemalloc. <code class="option">--with-malloc-conf</code>
 and <code class="varname">malloc_conf</code> are compile-time mechanisms, whereas
 <code class="filename">/etc/malloc.conf</code> and
 <code class="envar">MALLOC_CONF</code> can be safely set any time prior to program
 invocation.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"><quote><code class="mallctl">opt.*</code></quote></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"><quote><code class="mallctl">opt.abort</code></quote></a> and <a class="link" href="#opt.narenas"><quote><code class="mallctl">opt.narenas</code></quote></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.</div><div class="refsect1"><a name="implementation_notes"/><h2>IMPLEMENTATION NOTES</h2>Traditionally, allocators have used
 sbrk(2) to obtain memory, which is
 suboptimal for several reasons, including race conditions, increased
 fragmentation, and artificial limitations on maximum usable memory. If
 sbrk(2) is supported by the operating
 system, this allocator uses both
 mmap(2) and
 sbrk(2), in that order of preference;
 otherwise only mmap(2) is used.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.In addition to multiple arenas, this allocator supports
 thread-specific caching, 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.Memory is conceptually broken into extents. Extents are always
 aligned to multiples of the page size. This alignment makes it possible to
 find metadata for user objects quickly. User objects are broken into two
 categories according to size: small and large. Contiguous small objects
 comprise a slab, which resides within a single extent, whereas large objects
 each have their own extents backing them.Small objects are managed in groups by slabs. Each slab maintains
 a bitmap to track which regions are in use. 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(double)</code>. All other object size
 classes are multiples of the quantum, spaced such that there are four size
 classes for each doubling in size, which limits internal fragmentation to
 approximately 20% for all but the smallest size classes. Small size classes
 are smaller than four times the page size, and large size classes extend
 from four times the page size up to the largest size class that does not
 exceed <code class="constant">PTRDIFF_MAX</code>.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.The <code class="function">realloc()</code>,
 <code class="function">rallocx()</code>, and
 <code class="function">xallocx()</code> functions may resize allocations
 without moving them under limited circumstances. Unlike the
 <code class="function">*allocx()</code> API, the standard API does not
 officially round up the usable size of an allocation to the nearest size
 class, so technically it is necessary to call
 <code class="function">realloc()</code> to grow e.g. a 9-byte allocation to
 16 bytes, or shrink a 16-byte allocation to 9 bytes. Growth and shrinkage
 trivially succeeds in place as long as the pre-size and post-size both round
 up to the same size class. No other API guarantees are made regarding
 in-place resizing, but the current implementation also tries to resize large
 allocations in place, as long as the pre-size and post-size are both large.
 For shrinkage to succeed, the extent allocator must support splitting (see
 <a class="link" href="#arena.i.extent_hooks"><quote><code class="mallctl">arena.&lt;i&gt;.extent_hooks</code></quote></a>).
 Growth only succeeds if the trailing memory is currently available, and the
 extent allocator supports merging.Assuming 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>.<div class="table"><a name="size_classes"/>Table 1. Size classes<div class="table-contents"><table class="table" summary="Size classes" border="1"><colgroup><col align="left" class="c1"/><col align="right" class="c2"/><col align="left" class="c3"/></colgroup><thead><tr><th align="left">Category</th><th align="right">Spacing</th><th align="left">Size</th></tr></thead><tbody><tr><td rowspan="9" align="left">Small</td><td align="right">lg</td><td align="left">[8]</td></tr><tr><td align="right">16</td><td align="left">[16, 32, 48, 64, 80, 96, 112, 128]</td></tr><tr><td align="right">32</td><td align="left">[160, 192, 224, 256]</td></tr><tr><td align="right">64</td><td align="left">[320, 384, 448, 512]</td></tr><tr><td align="right">128</td><td align="left">[640, 768, 896, 1024]</td></tr><tr><td align="right">256</td><td align="left">[1280, 1536, 1792, 2048]</td></tr><tr><td align="right">512</td><td align="left">[2560, 3072, 3584, 4096]</td></tr><tr><td align="right">1 KiB</td><td align="left">[5 KiB, 6 KiB, 7 KiB, 8 KiB]</td></tr><tr><td align="right">2 KiB</td><td align="left">[10 KiB, 12 KiB, 14 KiB]</td></tr><tr><td rowspan="16" align="left">Large</td><td align="right">2 KiB</td><td align="left">[16 KiB]</td></tr><tr><td align="right">4 KiB</td><td align="left">[20 KiB, 24 KiB, 28 KiB, 32 KiB]</td></tr><tr><td align="right">8 KiB</td><td align="left">[40 KiB, 48 KiB, 56 KiB, 64 KiB]</td></tr><tr><td align="right">16 KiB</td><td align="left">[80 KiB, 96 KiB, 112 KiB, 128 KiB]</td></tr><tr><td align="right">32 KiB</td><td align="left">[160 KiB, 192 KiB, 224 KiB, 256 KiB]</td></tr><tr><td align="right">64 KiB</td><td align="left">[320 KiB, 384 KiB, 448 KiB, 512 KiB]</td></tr><tr><td align="right">128 KiB</td><td align="left">[640 KiB, 768 KiB, 896 KiB, 1 MiB]</td></tr><tr><td align="right">256 KiB</td><td align="left">[1280 KiB, 1536 KiB, 1792 KiB, 2 MiB]</td></tr><tr><td align="right">512 KiB</td><td align="left">[2560 KiB, 3 MiB, 3584 KiB, 4 MiB]</td></tr><tr><td align="right">1 MiB</td><td align="left">[5 MiB, 6 MiB, 7 MiB, 8 MiB]</td></tr><tr><td align="right">2 MiB</td><td align="left">[10 MiB, 12 MiB, 14 MiB, 16 MiB]</td></tr><tr><td align="right">4 MiB</td><td align="left">[20 MiB, 24 MiB, 28 MiB, 32 MiB]</td></tr><tr><td align="right">8 MiB</td><td align="left">[40 MiB, 48 MiB, 56 MiB, 64 MiB]</td></tr><tr><td align="right">...</td><td align="left">...</td></tr><tr><td align="right">512 PiB</td><td align="left">[2560 PiB, 3 EiB, 3584 PiB, 4 EiB]</td></tr><tr><td align="right">1 EiB</td><td align="left">[5 EiB, 6 EiB, 7 EiB]</td></tr></tbody></table></div></div> </div><div class="refsect1"><a name="mallctl_namespace"/><h2>MALLCTL NAMESPACE</h2>The following names are defined in the namespace accessible via the
 <code class="function">mallctl*()</code> 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 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.*</code></quote>
 and <quote><code class="mallctl">arena.&lt;i&gt;.{initialized,purge,decay,dss}</code></quote>,
 <code class="literal">&lt;i&gt;</code> equal to
 <code class="constant">MALLCTL_ARENAS_ALL</code> can be used to operate on all arenas
 or access the summation of statistics from all arenas; similarly
 <code class="literal">&lt;i&gt;</code> equal to
 <code class="constant">MALLCTL_ARENAS_DESTROYED</code> can be used to access the
 summation of statistics from all destroyed arenas. These constants can be
 utilized either via <code class="function">mallctlnametomib()</code> followed by
 <code class="function">mallctlbymib()</code>, or via code such as the following:
 <pre class="programlisting">
#define STRINGIFY_HELPER(x) #x
#define STRINGIFY(x) STRINGIFY_HELPER(x)

mallctl("arena." STRINGIFY(MALLCTL_ARENAS_ALL) ".decay",
 NULL, NULL, NULL, 0);</pre>
 Take special note of the <a class="link" href="#epoch"><quote><code class="mallctl">epoch</code></quote></a> mallctl, which controls
 refreshing of cached dynamic statistics.<div class="variablelist"><dl class="variablelist"><dt><a name="version"/>
 <quote><code class="mallctl">version</code></quote>
 (const char *)
 <code class="literal">r-</code>
 </dt><dd>Return the jemalloc version string.</dd><dt><a name="epoch"/>
 <quote><code class="mallctl">epoch</code></quote>
 (uint64_t)
 <code class="literal">rw</code>
 </dt><dd>If a value is passed in, refresh the data from which
 the <code class="function">mallctl*()</code> functions report values,
 and increment the epoch. Return the current epoch. This is useful for
 detecting whether another thread caused a refresh.</dd><dt><a name="background_thread"/>
 <quote><code class="mallctl">background_thread</code></quote>
 (bool)
 <code class="literal">rw</code>
 </dt><dd>Enable/disable internal background worker threads. When
 set to true, background threads are created on demand (the number of
 background threads will be no more than the number of CPUs or active
 arenas). Threads run periodically, and handle <a class="link" href="#arena.i.decay">purging</a> asynchronously. When switching
 off, background threads are terminated synchronously. Note that after
 fork(2)
 function, the state in the child process will be disabled regardless
 the state in parent process. See <a class="link" href="#stats.background_thread.num_threads"><quote><code class="mallctl">stats.background_thread</code></quote></a>
 for related stats. <a class="link" href="#opt.background_thread"><quote><code class="mallctl">opt.background_thread</code></quote></a>
 can be used to set the default option. This option is only available on
 selected pthread-based platforms.</dd><dt><a name="max_background_threads"/>
 <quote><code class="mallctl">max_background_threads</code></quote>
 (size_t)
 <code class="literal">rw</code>
 </dt><dd>Maximum number of background worker threads that will
 be created. This value is capped at <a class="link" href="#opt.max_background_threads"><quote><code class="mallctl">opt.max_background_threads</code></quote></a> at
 startup.</dd><dt><a name="config.cache_oblivious"/>
 <quote><code class="mallctl">config.cache_oblivious</code></quote>
 (bool)
 <code class="literal">r-</code>
 </dt><dd><code class="option">--enable-cache-oblivious</code> was specified
 during build configuration.</dd><dt><a name="config.debug"/>
 <quote><code class="mallctl">config.debug</code></quote>
 (bool)
 <code class="literal">r-</code>
 </dt><dd><code class="option">--enable-debug</code> was specified during
 build configuration.</dd><dt><a name="config.fill"/>
 <quote><code class="mallctl">config.fill</code></quote>
 (bool)
 <code class="literal">r-</code>
 </dt><dd><code class="option">--enable-fill</code> was specified during
 build configuration.</dd><dt><a name="config.lazy_lock"/>
 <quote><code class="mallctl">config.lazy_lock</code></quote>
 (bool)
 <code class="literal">r-</code>
 </dt><dd><code class="option">--enable-lazy-lock</code> was specified
 during build configuration.</dd><dt><a name="config.malloc_conf"/>
 <quote><code class="mallctl">config.malloc_conf</code></quote>
 (const char *)
 <code class="literal">r-</code>
 </dt><dd>Embedded configure-time-specified run-time options
 string, empty unless <code class="option">--with-malloc-conf</code> was specified
 during build configuration.</dd><dt><a name="config.prof"/>
 <quote><code class="mallctl">config.prof</code></quote>
 (bool)
 <code class="literal">r-</code>
 </dt><dd><code class="option">--enable-prof</code> was specified during
 build configuration.</dd><dt><a name="config.prof_libgcc"/>
 <quote><code class="mallctl">config.prof_libgcc</code></quote>
 (bool)
 <code class="literal">r-</code>
 </dt><dd><code class="option">--disable-prof-libgcc</code> was not
 specified during build configuration.</dd><dt><a name="config.prof_libunwind"/>
 <quote><code class="mallctl">config.prof_libunwind</code></quote>
 (bool)
 <code class="literal">r-</code>
 </dt><dd><code class="option">--enable-prof-libunwind</code> was specified
 during build configuration.</dd><dt><a name="config.stats"/>
 <quote><code class="mallctl">config.stats</code></quote>
 (bool)
 <code class="literal">r-</code>
 </dt><dd><code class="option">--enable-stats</code> was specified during
 build configuration.</dd><dt><a name="config.utrace"/>
 <quote><code class="mallctl">config.utrace</code></quote>
 (bool)
 <code class="literal">r-</code>
 </dt><dd><code class="option">--enable-utrace</code> was specified during
 build configuration.</dd><dt><a name="config.xmalloc"/>
 <quote><code class="mallctl">config.xmalloc</code></quote>
 (bool)
 <code class="literal">r-</code>
 </dt><dd><code class="option">--enable-xmalloc</code> was specified during
 build configuration.</dd><dt><a name="opt.abort"/>
 <quote><code class="mallctl">opt.abort</code></quote>
 (bool)
 <code class="literal">r-</code>
 </dt><dd>Abort-on-warning enabled/disabled. If true, most
 warnings are fatal. Note that runtime option warnings are not included
 (see <a class="link" href="#opt.abort_conf"><quote><code class="mallctl">opt.abort_conf</code></quote></a> for
 that). The process will call
 abort(3) 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.
 </dd><dt><a name="opt.confirm_conf"/>
 <quote><code class="mallctl">opt.confirm_conf</code></quote>
 (bool)
 <code class="literal">r-</code>
 </dt><dd>Confirm-runtime-options-when-program-starts
	enabled/disabled. If true, the string specified via
	<code class="option">--with-malloc-conf</code>, the string pointed to by the
	global variable <code class="varname">malloc_conf</code>, the “name”
	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 printed in
	order. Then, each option being set will be individually printed. This
	option is disabled by default.</dd><dt><a name="opt.abort_conf"/>
 <quote><code class="mallctl">opt.abort_conf</code></quote>
 (bool)
 <code class="literal">r-</code>
 </dt><dd>Abort-on-invalid-configuration enabled/disabled. If
 true, invalid runtime options are fatal. The process will call
 abort(3) 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.
 </dd><dt><a name="opt.cache_oblivious"/>
 <quote><code class="mallctl">opt.cache_oblivious</code></quote>
 (bool)
 <code class="literal">r-</code>
 </dt><dd>Enable / Disable cache-oblivious large allocation
 alignment, for large requests with no alignment constraints. If this
 feature is disabled, all large allocations are page-aligned as an
 implementation artifact, which can severely harm CPU cache utilization.
 However, the cache-oblivious layout comes at the cost of one extra page
 per large allocation, which in the most extreme case increases physical
 memory usage for the 16 KiB size class to 20 KiB. This option is enabled
 by default.</dd><dt><a name="opt.metadata_thp"/>
 <quote><code class="mallctl">opt.metadata_thp</code></quote>
 (const char *)
 <code class="literal">r-</code>
 </dt><dd>Controls whether to allow jemalloc to use transparent
 huge page (THP) for internal metadata (see <a class="link" href="#stats.metadata">stats.metadata</a>). “always”
 allows such usage. “auto” uses no THP initially, but may
 begin to do so when metadata usage reaches certain level. The default
 is “disabled”.</dd><dt><a name="opt.trust_madvise"/>
 <quote><code class="mallctl">opt.trust_madvise</code></quote>
 (bool)
 <code class="literal">r-</code>
 </dt><dd>If true, do not perform runtime check for MADV_DONTNEED,
 to check that it actually zeros pages. The default is disabled on Linux
 and enabled elsewhere.</dd><dt><a name="opt.retain"/>
 <quote><code class="mallctl">opt.retain</code></quote>
 (bool)
 <code class="literal">r-</code>
 </dt><dd>If true, retain unused virtual memory for later reuse
 rather than discarding it by calling
 munmap(2) or equivalent (see <a class="link" href="#stats.retained">stats.retained</a> for related details).
 It also makes jemalloc use mmap(2) or equivalent in a more greedy way, mapping larger
 chunks in one go. This option is disabled by default unless discarding
 virtual memory is known to trigger platform-specific performance
 problems, namely 1) for [64-bit] Linux, which has a quirk in its virtual
 memory allocation algorithm that causes semi-permanent VM map holes
 under normal jemalloc operation; and 2) for [64-bit] Windows, which
 disallows split / merged regions with
 <code><code class="constant">MEM_RELEASE</code></code>. Although the
 same issues may present on 32-bit platforms as well, retaining virtual
 memory for 32-bit Linux and Windows is disabled by default due to the
 practical possibility of address space exhaustion. </dd><dt><a name="opt.dss"/>
 <quote><code class="mallctl">opt.dss</code></quote>
 (const char *)
 <code class="literal">r-</code>
 </dt><dd>dss (sbrk(2)) allocation precedence as
 related to mmap(2) allocation. The following
 settings are supported if
 sbrk(2) is supported by the operating
 system: “disabled”, “primary”, and
 “secondary”; otherwise only “disabled” is
 supported. The default is “secondary” if
 sbrk(2) is supported by the operating
 system; “disabled” otherwise.
 </dd><dt><a name="opt.narenas"/>
 <quote><code class="mallctl">opt.narenas</code></quote>
 (unsigned)
 <code class="literal">r-</code>
 </dt><dd>Maximum number of arenas to use for automatic
 multiplexing of threads and arenas. The default is four times the
 number of CPUs, or one if there is a single CPU.</dd><dt><a name="opt.oversize_threshold"/>
 <quote><code class="mallctl">opt.oversize_threshold</code></quote>
 (size_t)
 <code class="literal">r-</code>
 </dt><dd>The threshold in bytes of which requests are considered
 oversize. Allocation requests with greater sizes are fulfilled from a
 dedicated arena (automatically managed, however not within
 <code class="literal">narenas</code>), in order to reduce fragmentation by not
 mixing huge allocations with small ones. In addition, the decay API
 guarantees on the extents greater than the specified threshold may be
 overridden. Note that requests with arena index specified via
 <code class="constant">MALLOCX_ARENA</code>, or threads associated with explicit
 arenas will not be considered. The default threshold is 8MiB. Values
 not within large size classes disables this feature.</dd><dt><a name="opt.percpu_arena"/>
 <quote><code class="mallctl">opt.percpu_arena</code></quote>
 (const char *)
 <code class="literal">r-</code>
 </dt><dd>Per CPU arena mode. Use the “percpu”
 setting to enable this feature, which uses number of CPUs to determine
 number of arenas, and bind threads to arenas dynamically based on the
 CPU the thread runs on currently. “phycpu” setting uses
 one arena per physical CPU, which means the two hyper threads on the
 same CPU share one arena. Note that no runtime checking regarding the
 availability of hyper threading is done at the moment. When set to
 “disabled”, narenas and thread to arena association will
 not be impacted by this option. The default is “disabled”.
 </dd><dt><a name="opt.background_thread"/>
 <quote><code class="mallctl">opt.background_thread</code></quote>
 (bool)
 <code class="literal">r-</code>
 </dt><dd>Internal background worker threads enabled/disabled.
 Because of potential circular dependencies, enabling background thread
 using this option may cause crash or deadlock during initialization. For
 a reliable way to use this feature, see <a class="link" href="#background_thread">background_thread</a> for dynamic control
 options and details. This option is disabled by
 default.</dd><dt><a name="opt.max_background_threads"/>
 <quote><code class="mallctl">opt.max_background_threads</code></quote>
 (size_t)
 <code class="literal">r-</code>
 </dt><dd>Maximum number of background threads that will be created
 if <a class="link" href="#background_thread">background_thread</a> is set.
 Defaults to number of cpus.</dd><dt><a name="opt.dirty_decay_ms"/>
 <quote><code class="mallctl">opt.dirty_decay_ms</code></quote>
 (ssize_t)
 <code class="literal">r-</code>
 </dt><dd>Approximate time in milliseconds from the creation of a
 set of unused dirty pages until an equivalent set of unused dirty pages
 is purged (i.e. converted to muzzy via e.g.
 <code class="function">madvise(<code>...</code><code><code class="constant">MADV_FREE</code></code>)</code>
 if supported by the operating system, or converted to clean otherwise)
 and/or reused. Dirty pages are defined as previously having been
 potentially written to by the application, and therefore consuming
 physical memory, yet having no current use. The pages are incrementally
 purged according to a sigmoidal decay curve that starts and ends with
 zero purge rate. A decay time of 0 causes all unused dirty pages to be
 purged immediately upon creation. A decay time of -1 disables purging.
 The default decay time is 10 seconds. See <a class="link" href="#arenas.dirty_decay_ms"><quote><code class="mallctl">arenas.dirty_decay_ms</code></quote></a>
 and <a class="link" href="#arena.i.dirty_decay_ms"><quote><code class="mallctl">arena.&lt;i&gt;.dirty_decay_ms</code></quote></a>
 for related dynamic control options. See <a class="link" href="#opt.muzzy_decay_ms"><quote><code class="mallctl">opt.muzzy_decay_ms</code></quote></a>
 for a description of muzzy pages.for a description of muzzy pages. Note
 that when the <a class="link" href="#opt.oversize_threshold"><quote><code class="mallctl">oversize_threshold</code></quote></a>
 feature is enabled, the arenas reserved for oversize requests may have
 its own default decay settings.</dd><dt><a name="opt.muzzy_decay_ms"/>
 <quote><code class="mallctl">opt.muzzy_decay_ms</code></quote>
 (ssize_t)
 <code class="literal">r-</code>
 </dt><dd>Approximate time in milliseconds from the creation of a
 set of unused muzzy pages until an equivalent set of unused muzzy pages
 is purged (i.e. converted to clean) and/or reused. Muzzy pages are
 defined as previously having been unused dirty pages that were
 subsequently purged in a manner that left them subject to the
 reclamation whims of the operating system (e.g.
 <code class="function">madvise(<code>...</code><code><code class="constant">MADV_FREE</code></code>)</code>),
 and therefore in an indeterminate state. The pages are incrementally
 purged according to a sigmoidal decay curve that starts and ends with
 zero purge rate. A decay time of 0 causes all unused muzzy pages to be
 purged immediately upon creation. A decay time of -1 disables purging.
 The default decay time is 10 seconds. See <a class="link" href="#arenas.muzzy_decay_ms"><quote><code class="mallctl">arenas.muzzy_decay_ms</code></quote></a>
 and <a class="link" href="#arena.i.muzzy_decay_ms"><quote><code class="mallctl">arena.&lt;i&gt;.muzzy_decay_ms</code></quote></a>
 for related dynamic control options.</dd><dt><a name="opt.lg_extent_max_active_fit"/>
 <quote><code class="mallctl">opt.lg_extent_max_active_fit</code></quote>
 (size_t)
 <code class="literal">r-</code>
 </dt><dd>When reusing dirty extents, this determines the (log
 base 2 of the) maximum ratio between the size of the active extent
 selected (to split off from) and the size of the requested allocation.
 This prevents the splitting of large active extents for smaller
 allocations, which can reduce fragmentation over the long run
 (especially for non-active extents). Lower value may reduce
 fragmentation, at the cost of extra active extents. The default value
 is 6, which gives a maximum ratio of 64 (2^6).</dd><dt><a name="opt.stats_print"/>
 <quote><code class="mallctl">opt.stats_print</code></quote>
 (bool)
 <code class="literal">r-</code>
 </dt><dd>Enable/disable statistics printing at exit. If
 enabled, the <code class="function">malloc_stats_print()</code>
 function is called at program exit via an
 atexit(3) function. <a class="link" href="#opt.stats_print_opts"><quote><code class="mallctl">opt.stats_print_opts</code></quote></a>
 can be combined to specify output options. 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. Furthermore, <code class="function">atexit()</code> may
 allocate memory during application initialization and then deadlock
 internally when jemalloc in turn calls
 <code class="function">atexit()</code>, so this option is not
 universally usable (though the application can register its own
 <code class="function">atexit()</code> function with equivalent
 functionality). 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.</dd><dt><a name="opt.stats_print_opts"/>
 <quote><code class="mallctl">opt.stats_print_opts</code></quote>
 (const char *)
 <code class="literal">r-</code>
 </dt><dd>Options (the <code>opts</code> string) to pass
 to the <code class="function">malloc_stats_print()</code> at exit (enabled
 through <a class="link" href="#opt.stats_print"><quote><code class="mallctl">opt.stats_print</code></quote></a>). See
 available options in <a class="link" href="#malloc_stats_print_opts"><code class="function">malloc_stats_print()</code></a>.
 Has no effect unless <a class="link" href="#opt.stats_print"><quote><code class="mallctl">opt.stats_print</code></quote></a> is
 enabled. The default is “”.</dd><dt><a name="opt.stats_interval"/>
 <quote><code class="mallctl">opt.stats_interval</code></quote>
 (int64_t)
 <code class="literal">r-</code>
 </dt><dd>Average interval between statistics outputs, as measured
 in bytes of allocation activity. The actual interval may be sporadic
 because decentralized event counters are used to avoid synchronization
 bottlenecks. The output may be triggered on any thread, which then
 calls <code class="function">malloc_stats_print()</code>. <a class="link" href="#opt.stats_interval_opts"><quote><code class="mallctl">opt.stats_interval_opts</code></quote></a>
 can be combined to specify output options. By default,
 interval-triggered stats output is disabled (encoded as
 -1).</dd><dt><a name="opt.stats_interval_opts"/>
 <quote><code class="mallctl">opt.stats_interval_opts</code></quote>
 (const char *)
 <code class="literal">r-</code>
 </dt><dd>Options (the <code>opts</code> string) to pass
 to the <code class="function">malloc_stats_print()</code> for interval based
	statistics printing (enabled
 through <a class="link" href="#opt.stats_interval"><quote><code class="mallctl">opt.stats_interval</code></quote></a>). See
 available options in <a class="link" href="#malloc_stats_print_opts"><code class="function">malloc_stats_print()</code></a>.
 Has no effect unless <a class="link" href="#opt.stats_interval"><quote><code class="mallctl">opt.stats_interval</code></quote></a> is
 enabled. The default is “”.</dd><dt><a name="opt.junk"/>
 <quote><code class="mallctl">opt.junk</code></quote>
 (const char *)
 <code class="literal">r-</code>
 [<code class="option">--enable-fill</code>]
 </dt><dd>Junk filling. If set to “alloc”, each byte
 of uninitialized allocated memory will be initialized to
 <code class="literal">0xa5</code>. If set to “free”, all deallocated
 memory will be initialized to <code class="literal">0x5a</code>. If set to
 “true”, both allocated and deallocated memory will be
 initialized, and if set to “false”, junk filling be
 disabled entirely. This is intended for debugging and will impact
 performance negatively. This option is “false” by default
 unless <code class="option">--enable-debug</code> is specified during
 configuration, in which case it is “true” by
 default.</dd><dt><a name="opt.zero"/>
 <quote><code class="mallctl">opt.zero</code></quote>
 (bool)
 <code class="literal">r-</code>
 [<code class="option">--enable-fill</code>]
 </dt><dd>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> and
 <code class="function">rallocx()</code> 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.
 </dd><dt><a name="opt.utrace"/>
 <quote><code class="mallctl">opt.utrace</code></quote>
 (bool)
 <code class="literal">r-</code>
 [<code class="option">--enable-utrace</code>]
 </dt><dd>Allocation tracing based on
 utrace(2) enabled/disabled. This option
 is disabled by default.</dd><dt><a name="opt.xmalloc"/>
 <quote><code class="mallctl">opt.xmalloc</code></quote>
 (bool)
 <code class="literal">r-</code>
 [<code class="option">--enable-xmalloc</code>]
 </dt><dd>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
 abort(3)). If an application is
 designed to depend on this behavior, set the option at compile time by
 including the following in the source code:
 <pre class="programlisting">
malloc_conf = "xmalloc:true";</pre>
 This option is disabled by default.</dd><dt><a name="opt.tcache"/>
 <quote><code class="mallctl">opt.tcache</code></quote>
 (bool)
 <code class="literal">r-</code>
 </dt><dd>Thread-specific caching (tcache) enabled/disabled. When
 there are multiple threads, each thread uses a tcache 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.tcache_max"><quote><code class="mallctl">opt.tcache_max</code></quote></a>
 option for related tuning information. This option is enabled by
 default.</dd><dt><a name="opt.tcache_max"/>
 <quote><code class="mallctl">opt.tcache_max</code></quote>
 (size_t)
 <code class="literal">r-</code>
 </dt><dd>Maximum size class to cache in the thread-specific cache
 (tcache). At a minimum, the first size class is cached; and at a
 maximum, size classes up to 8 MiB can be cached. The default maximum is
 32 KiB (2^15). As a convenience, this may also be set by specifying
 lg_tcache_max, which will be taken to be the base-2 logarithm of the
 setting of tcache_max.</dd><dt><a name="opt.thp"/>
 <quote><code class="mallctl">opt.thp</code></quote>
 (const char *)
 <code class="literal">r-</code>
 </dt><dd>Transparent hugepage (THP) mode. Settings "always",
 "never" and "default" are available if THP is supported by the operating
 system. The "always" setting enables transparent hugepage for all user
 memory mappings with
 <code><code class="constant">MADV_HUGEPAGE</code></code>; "never"
 ensures no transparent hugepage with
 <code><code class="constant">MADV_NOHUGEPAGE</code></code>; the default
 setting "default" makes no changes. Note that: this option does not
 affect THP for jemalloc internal metadata (see <a class="link" href="#opt.metadata_thp"><quote><code class="mallctl">opt.metadata_thp</code></quote></a>);
 in addition, for arenas with customized <a class="link" href="#arena.i.extent_hooks"><quote><code class="mallctl">extent_hooks</code></quote></a>,
 this option is bypassed as it is implemented as part of the default
 extent hooks.</dd><dt><a name="opt.prof"/>
 <quote><code class="mallctl">opt.prof</code></quote>
 (bool)
 <code class="literal">r-</code>
 [<code class="option">--enable-prof</code>]
 </dt><dd>Memory profiling enabled/disabled. If enabled, profile
 memory allocation activity. See the <a class="link" href="#opt.prof_active"><quote><code class="mallctl">opt.prof_active</code></quote></a>
 option for on-the-fly activation/deactivation. See the <a class="link" href="#opt.lg_prof_sample"><quote><code class="mallctl">opt.lg_prof_sample</code></quote></a>
 option for probabilistic sampling control. See the <a class="link" href="#opt.prof_accum"><quote><code class="mallctl">opt.prof_accum</code></quote></a>
 option for control of cumulative sample reporting. See the <a class="link" href="#opt.lg_prof_interval"><quote><code class="mallctl">opt.lg_prof_interval</code></quote></a>
 option for information on interval-triggered profile dumping, the <a class="link" href="#opt.prof_gdump"><quote><code class="mallctl">opt.prof_gdump</code></quote></a>
 option for information on high-water-triggered profile dumping, and the
 <a class="link" href="#opt.prof_final"><quote><code class="mallctl">opt.prof_final</code></quote></a>
 option for final profile dumping. Profile output is compatible with
 the jeprof command, which is based on the
 pprof that is developed as part of the <a class="ulink" href="http://code.google.com/p/gperftools/" target="_top">gperftools
 package</a>. See <a class="link" href="#heap_profile_format" title="HEAP PROFILE FORMAT">HEAP PROFILE
 FORMAT</a> for heap profile format documentation.</dd><dt><a name="opt.prof_prefix"/>
 <quote><code class="mallctl">opt.prof_prefix</code></quote>
 (const char *)
 <code class="literal">r-</code>
 [<code class="option">--enable-prof</code>]
 </dt><dd>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>. This prefix value can be overridden by
 <a class="link" href="#prof.prefix"><quote><code class="mallctl">prof.prefix</code></quote></a>.
 </dd><dt><a name="opt.prof_active"/>
 <quote><code class="mallctl">opt.prof_active</code></quote>
 (bool)
 <code class="literal">r-</code>
 [<code class="option">--enable-prof</code>]
 </dt><dd>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"><quote><code class="mallctl">opt.prof</code></quote></a> option) but
 inactive, then toggle profiling at any time during program execution
 with the <a class="link" href="#prof.active"><quote><code class="mallctl">prof.active</code></quote></a> mallctl.
 This option is enabled by default.</dd><dt><a name="opt.prof_thread_active_init"/>
 <quote><code class="mallctl">opt.prof_thread_active_init</code></quote>
 (bool)
 <code class="literal">r-</code>
 [<code class="option">--enable-prof</code>]
 </dt><dd>Initial setting for <a class="link" href="#thread.prof.active"><quote><code class="mallctl">thread.prof.active</code></quote></a>
 in newly created threads. The initial setting for newly created threads
 can also be changed during execution via the <a class="link" href="#prof.thread_active_init"><quote><code class="mallctl">prof.thread_active_init</code></quote></a>
 mallctl. This option is enabled by default.</dd><dt><a name="opt.lg_prof_sample"/>
 <quote><code class="mallctl">opt.lg_prof_sample</code></quote>
 (size_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-prof</code>]
 </dt><dd>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 512 KiB (2^19
 B).</dd><dt><a name="opt.prof_accum"/>
 <quote><code class="mallctl">opt.prof_accum</code></quote>
 (bool)
 <code class="literal">r-</code>
 [<code class="option">--enable-prof</code>]
 </dt><dd>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. This option is disabled
 by default.</dd><dt><a name="opt.lg_prof_interval"/>
 <quote><code class="mallctl">opt.lg_prof_interval</code></quote>
 (ssize_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-prof</code>]
 </dt><dd>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"><quote><code class="mallctl">opt.prof_prefix</code></quote></a> and
 <a class="link" href="#prof.prefix"><quote><code class="mallctl">prof.prefix</code></quote></a>
 options. By default, interval-triggered profile dumping is disabled
 (encoded as -1).
 </dd><dt><a name="opt.prof_gdump"/>
 <quote><code class="mallctl">opt.prof_gdump</code></quote>
 (bool)
 <code class="literal">r-</code>
 [<code class="option">--enable-prof</code>]
 </dt><dd>Set the initial state of <a class="link" href="#prof.gdump"><quote><code class="mallctl">prof.gdump</code></quote></a>, which when
 enabled triggers a memory profile dump every time the total virtual
 memory exceeds the previous maximum. This option is disabled by
 default.</dd><dt><a name="opt.prof_final"/>
 <quote><code class="mallctl">opt.prof_final</code></quote>
 (bool)
 <code class="literal">r-</code>
 [<code class="option">--enable-prof</code>]
 </dt><dd>Use an
 atexit(3) 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"><quote><code class="mallctl">opt.prof_prefix</code></quote></a> and
 <a class="link" href="#prof.prefix"><quote><code class="mallctl">prof.prefix</code></quote></a>
 options. Note that <code class="function">atexit()</code> may allocate
 memory during application initialization and then deadlock internally
 when jemalloc in turn calls <code class="function">atexit()</code>, so
 this option is not universally usable (though the application can
 register its own <code class="function">atexit()</code> function with
 equivalent functionality). This option is disabled by
 default.</dd><dt><a name="opt.prof_leak"/>
 <quote><code class="mallctl">opt.prof_leak</code></quote>
 (bool)
 <code class="literal">r-</code>
 [<code class="option">--enable-prof</code>]
 </dt><dd>Leak reporting enabled/disabled. If enabled, use an
 atexit(3) function to report memory leaks
 detected by allocation sampling. See the
 <a class="link" href="#opt.prof"><quote><code class="mallctl">opt.prof</code></quote></a> option for
 information on analyzing heap profile output. Works only when combined
 with <a class="link" href="#opt.prof_final"><quote><code class="mallctl">opt.prof_final</code></quote>
 </a>, otherwise does nothing. This option is disabled by default.
 </dd><dt><a name="opt.prof_leak_error"/>
 <quote><code class="mallctl">opt.prof_leak_error</code></quote>
 (bool)
 <code class="literal">r-</code>
 [<code class="option">--enable-prof</code>]
 </dt><dd>Similar to <a class="link" href="#opt.prof_leak"><quote><code class="mallctl">
 opt.prof_leak</code></quote></a>, but makes the process exit with error
 code 1 if a memory leak is detected. This option supersedes
 <a class="link" href="#opt.prof_leak"><quote><code class="mallctl">opt.prof_leak</code></quote></a>,
 meaning that if both are specified, this option takes precedence. When
 enabled, also enables <a class="link" href="#opt.prof_leak"><quote><code class="mallctl">
 opt.prof_leak</code></quote></a>. Works only when combined with
 <a class="link" href="#opt.prof_final"><quote><code class="mallctl">opt.prof_final</code></quote></a>,
 otherwise does nothing. This option is disabled by default.
 </dd><dt><a name="opt.zero_realloc"/>
 <quote><code class="mallctl">opt.zero_realloc</code></quote>
 (const char *)
 <code class="literal">r-</code>
 </dt><dd> Determines the behavior of
 <code class="function">realloc()</code> when passed a value of zero for the new
 size. “alloc” treats this as an allocation of size zero
 (and returns a non-null result except in case of resource exhaustion).
 “free” treats this as a deallocation of the pointer, and
 returns <code class="constant">NULL</code> without setting
 <code class="varname">errno</code>. “abort” aborts the process if
 zero is passed. The default is “free” on Linux and
 Windows, and “alloc” elsewhere.There is considerable divergence of behaviors across
	implementations in handling this case. Many have the behavior of
	“free”. This can introduce security vulnerabilities, since
	a <code class="constant">NULL</code> return value indicates failure, and the
	continued validity of the passed-in pointer (per POSIX and C11).
	“alloc” is safe, but can cause leaks in programs that
	expect the common behavior. Programs intended to be portable and
	leak-free cannot assume either behavior, and must therefore never call
	realloc with a size of 0. The “abort” option enables these
	testing this behavior.</dd><dt><a name="thread.arena"/>
 <quote><code class="mallctl">thread.arena</code></quote>
 (unsigned)
 <code class="literal">rw</code>
 </dt><dd>Get or set the arena associated with the calling
 thread. If the specified arena was not initialized beforehand (see the
 <a class="link" href="#arena.i.initialized"><quote><code class="mallctl">arena.i.initialized</code></quote></a>
 mallctl), it will be automatically initialized as a side effect of
 calling this interface.</dd><dt><a name="thread.allocated"/>
 <quote><code class="mallctl">thread.allocated</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>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.</dd><dt><a name="thread.allocatedp"/>
 <quote><code class="mallctl">thread.allocatedp</code></quote>
 (uint64_t *)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Get a pointer to the the value that is returned by the
 <a class="link" href="#thread.allocated"><quote><code class="mallctl">thread.allocated</code></quote></a>
 mallctl. This is useful for avoiding the overhead of repeated
 <code class="function">mallctl*()</code> calls. Note that the underlying counter
 should not be modified by the application.</dd><dt><a name="thread.deallocated"/>
 <quote><code class="mallctl">thread.deallocated</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>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.</dd><dt><a name="thread.deallocatedp"/>
 <quote><code class="mallctl">thread.deallocatedp</code></quote>
 (uint64_t *)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Get a pointer to the the value that is returned by the
 <a class="link" href="#thread.deallocated"><quote><code class="mallctl">thread.deallocated</code></quote></a>
 mallctl. This is useful for avoiding the overhead of repeated
 <code class="function">mallctl*()</code> calls. Note that the underlying counter
 should not be modified by the application.</dd><dt><a name="thread.peak.read"/>
 <quote><code class="mallctl">thread.peak.read</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Get an approximation of the maximum value of the
 difference between the number of bytes allocated and the number of bytes
 deallocated by the calling thread since the last call to <a class="link" href="#thread.peak.reset"><quote><code class="mallctl">thread.peak.reset</code></quote></a>,
 or since the thread's creation if it has not called <a class="link" href="#thread.peak.reset"><quote><code class="mallctl">thread.peak.reset</code></quote></a>.
 No guarantees are made about the quality of the approximation, but
 jemalloc currently endeavors to maintain accuracy to within one hundred
 kilobytes.
 </dd><dt><a name="thread.peak.reset"/>
 <quote><code class="mallctl">thread.peak.reset</code></quote>
 (void)
 <code class="literal">--</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Resets the counter for net bytes allocated in the calling
 thread to zero. This affects subsequent calls to <a class="link" href="#thread.peak.read"><quote><code class="mallctl">thread.peak.read</code></quote></a>,
 but not the values returned by <a class="link" href="#thread.allocated"><quote><code class="mallctl">thread.allocated</code></quote></a>
 or <a class="link" href="#thread.deallocated"><quote><code class="mallctl">thread.deallocated</code></quote></a>.
 </dd><dt><a name="thread.tcache.enabled"/>
 <quote><code class="mallctl">thread.tcache.enabled</code></quote>
 (bool)
 <code class="literal">rw</code>
 </dt><dd>Enable/disable calling thread's tcache. The tcache is
 implicitly flushed as a side effect of becoming
 disabled (see <a class="link" href="#thread.tcache.flush"><quote><code class="mallctl">thread.tcache.flush</code></quote></a>).
 </dd><dt><a name="thread.tcache.flush"/>
 <quote><code class="mallctl">thread.tcache.flush</code></quote>
 (void)
 <code class="literal">--</code>
 </dt><dd>Flush calling thread's thread-specific cache (tcache).
 This interface releases all cached objects and internal data structures
 associated with the calling thread's tcache. 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.</dd><dt><a name="thread.prof.name"/>
 <quote><code class="mallctl">thread.prof.name</code></quote>
 (const char *)
 <code class="literal">r-</code> or
 <code class="literal">-w</code>
 [<code class="option">--enable-prof</code>]
 </dt><dd>Get/set the descriptive name associated with the calling
 thread in memory profile dumps. An internal copy of the name string is
 created, so the input string need not be maintained after this interface
 completes execution. The output string of this interface should be
 copied for non-ephemeral uses, because multiple implementation details
 can cause asynchronous string deallocation. Furthermore, each
 invocation of this interface can only read or write; simultaneous
 read/write is not supported due to string lifetime limitations. The
 name string must be nil-terminated and comprised only of characters in
 the sets recognized
 by isgraph(3) and
 isblank(3).</dd><dt><a name="thread.prof.active"/>
 <quote><code class="mallctl">thread.prof.active</code></quote>
 (bool)
 <code class="literal">rw</code>
 [<code class="option">--enable-prof</code>]
 </dt><dd>Control whether sampling is currently active for the
 calling thread. This is an activation mechanism in addition to <a class="link" href="#prof.active"><quote><code class="mallctl">prof.active</code></quote></a>; both must
 be active for the calling thread to sample. This flag is enabled by
 default.</dd><dt><a name="thread.idle"/>
 <quote><code class="mallctl">thread.idle</code></quote>
 (void)
 <code class="literal">--</code>
 </dt><dd>Hints to jemalloc that the calling thread will be idle
	for some nontrivial period of time (say, on the order of seconds), and
	that doing some cleanup operations may be beneficial. There are no
	guarantees as to what specific operations will be performed; currently
	this flushes the caller's tcache and may (according to some heuristic)
	purge its associated arena.This is not intended to be a general-purpose background activity
	mechanism, and threads should not wake up multiple times solely to call
	it. Rather, a thread waiting for a task should do a timed wait first,
	call <a class="link" href="#thread.idle"><quote><code class="mallctl">thread.idle</code></quote></a>
	if no task appears in the timeout interval, and then do an untimed wait.
	For such a background activity mechanism, see
	<a class="link" href="#background_thread"><quote><code class="mallctl">background_thread</code></quote></a>.
	</dd><dt><a name="tcache.create"/>
 <quote><code class="mallctl">tcache.create</code></quote>
 (unsigned)
 <code class="literal">r-</code>
 </dt><dd>Create an explicit thread-specific cache (tcache) and
 return an identifier that can be passed to the <a class="link" href="#MALLOCX_TCACHE"><code class="constant">MALLOCX_TCACHE(<code>tc</code>)</code></a>
 macro to explicitly use the specified cache rather than the
 automatically managed one that is used by default. Each explicit cache
 can be used by only one thread at a time; the application must assure
 that this constraint holds.
 If the amount of space supplied for storing the thread-specific
 cache identifier does not equal
 <code class="code">sizeof(unsigned)</code>, no
 thread-specific cache will be created, no data will be written to the
 space pointed by <code>oldp</code>, and
 <code>*oldlenp</code> will be set to 0.
 </dd><dt><a name="tcache.flush"/>
 <quote><code class="mallctl">tcache.flush</code></quote>
 (unsigned)
 <code class="literal">-w</code>
 </dt><dd>Flush the specified thread-specific cache (tcache). The
 same considerations apply to this interface as to <a class="link" href="#thread.tcache.flush"><quote><code class="mallctl">thread.tcache.flush</code></quote></a>,
 except that the tcache will never be automatically discarded.
 </dd><dt><a name="tcache.destroy"/>
 <quote><code class="mallctl">tcache.destroy</code></quote>
 (unsigned)
 <code class="literal">-w</code>
 </dt><dd>Flush the specified thread-specific cache (tcache) and
 make the identifier available for use during a future tcache creation.
 </dd><dt><a name="arena.i.initialized"/>
 <quote><code class="mallctl">arena.&lt;i&gt;.initialized</code></quote>
 (bool)
 <code class="literal">r-</code>
 </dt><dd>Get whether the specified arena's statistics are
 initialized (i.e. the arena was initialized prior to the current epoch).
 This interface can also be nominally used to query whether the merged
 statistics corresponding to <code class="constant">MALLCTL_ARENAS_ALL</code> are
 initialized (always true).</dd><dt><a name="arena.i.decay"/>
 <quote><code class="mallctl">arena.&lt;i&gt;.decay</code></quote>
 (void)
 <code class="literal">--</code>
 </dt><dd>Trigger decay-based purging of unused dirty/muzzy pages
 for arena &lt;i&gt;, or for all arenas if &lt;i&gt; equals
 <code class="constant">MALLCTL_ARENAS_ALL</code>. The proportion of unused
 dirty/muzzy pages to be purged depends on the current time; see <a class="link" href="#opt.dirty_decay_ms"><quote><code class="mallctl">opt.dirty_decay_ms</code></quote></a>
 and <a class="link" href="#opt.muzzy_decay_ms"><quote><code class="mallctl">opt.muzy_decay_ms</code></quote></a>
 for details.</dd><dt><a name="arena.i.purge"/>
 <quote><code class="mallctl">arena.&lt;i&gt;.purge</code></quote>
 (void)
 <code class="literal">--</code>
 </dt><dd>Purge all unused dirty pages for arena &lt;i&gt;, or for
 all arenas if &lt;i&gt; equals <code class="constant">MALLCTL_ARENAS_ALL</code>.
 </dd><dt><a name="arena.i.reset"/>
 <quote><code class="mallctl">arena.&lt;i&gt;.reset</code></quote>
 (void)
 <code class="literal">--</code>
 </dt><dd>Discard all of the arena's extant allocations. This
 interface can only be used with arenas explicitly created via <a class="link" href="#arenas.create"><quote><code class="mallctl">arenas.create</code></quote></a>. None
 of the arena's discarded/cached allocations may accessed afterward. As
 part of this requirement, all thread caches which were used to
 allocate/deallocate in conjunction with the arena must be flushed
 beforehand.</dd><dt><a name="arena.i.destroy"/>
 <quote><code class="mallctl">arena.&lt;i&gt;.destroy</code></quote>
 (void)
 <code class="literal">--</code>
 </dt><dd>Destroy the arena. Discard all of the arena's extant
 allocations using the same mechanism as for <a class="link" href="#arena.i.reset"><quote><code class="mallctl">arena.&lt;i&gt;.reset</code></quote></a>
 (with all the same constraints and side effects), merge the arena stats
 into those accessible at arena index
 <code class="constant">MALLCTL_ARENAS_DESTROYED</code>, and then completely
 discard all metadata associated with the arena. Future calls to <a class="link" href="#arenas.create"><quote><code class="mallctl">arenas.create</code></quote></a> may
 recycle the arena index. Destruction will fail if any threads are
 currently associated with the arena as a result of calls to <a class="link" href="#thread.arena"><quote><code class="mallctl">thread.arena</code></quote></a>.</dd><dt><a name="arena.i.dss"/>
 <quote><code class="mallctl">arena.&lt;i&gt;.dss</code></quote>
 (const char *)
 <code class="literal">rw</code>
 </dt><dd>Set the precedence of dss allocation as related to mmap
 allocation for arena &lt;i&gt;, or for all arenas if &lt;i&gt; equals
 <code class="constant">MALLCTL_ARENAS_ALL</code>. See <a class="link" href="#opt.dss"><quote><code class="mallctl">opt.dss</code></quote></a> for supported
 settings.</dd><dt><a name="arena.i.dirty_decay_ms"/>
 <quote><code class="mallctl">arena.&lt;i&gt;.dirty_decay_ms</code></quote>
 (ssize_t)
 <code class="literal">rw</code>
 </dt><dd>Current per-arena approximate time in milliseconds from
 the creation of a set of unused dirty pages until an equivalent set of
 unused dirty pages is purged and/or reused. Each time this interface is
 set, all currently unused dirty pages are considered to have fully
 decayed, which causes immediate purging of all unused dirty pages unless
 the decay time is set to -1 (i.e. purging disabled). See <a class="link" href="#opt.dirty_decay_ms"><quote><code class="mallctl">opt.dirty_decay_ms</code></quote></a>
 for additional information.</dd><dt><a name="arena.i.muzzy_decay_ms"/>
 <quote><code class="mallctl">arena.&lt;i&gt;.muzzy_decay_ms</code></quote>
 (ssize_t)
 <code class="literal">rw</code>
 </dt><dd>Current per-arena approximate time in milliseconds from
 the creation of a set of unused muzzy pages until an equivalent set of
 unused muzzy pages is purged and/or reused. Each time this interface is
 set, all currently unused muzzy pages are considered to have fully
 decayed, which causes immediate purging of all unused muzzy pages unless
 the decay time is set to -1 (i.e. purging disabled). See <a class="link" href="#opt.muzzy_decay_ms"><quote><code class="mallctl">opt.muzzy_decay_ms</code></quote></a>
 for additional information.</dd><dt><a name="arena.i.retain_grow_limit"/>
 <quote><code class="mallctl">arena.&lt;i&gt;.retain_grow_limit</code></quote>
 (size_t)
 <code class="literal">rw</code>
 </dt><dd>Maximum size to grow retained region (only relevant when
 <a class="link" href="#opt.retain"><quote><code class="mallctl">opt.retain</code></quote></a> is
 enabled). This controls the maximum increment to expand virtual memory,
 or allocation through <a class="link" href="#arena.i.extent_hooks"><quote><code class="mallctl">arena.&lt;i&gt;extent_hooks</code></quote></a>.
 In particular, if customized extent hooks reserve physical memory
 (e.g. 1G huge pages), this is useful to control the allocation hook's
 input size. The default is no limit.</dd><dt><a name="arena.i.extent_hooks"/>
 <quote><code class="mallctl">arena.&lt;i&gt;.extent_hooks</code></quote>
 (extent_hooks_t *)
 <code class="literal">rw</code>
 </dt><dd>Get or set the extent management hook functions for
 arena &lt;i&gt;. The functions must be capable of operating on all
 extant extents associated with arena &lt;i&gt;, usually by passing
 unknown extents to the replaced functions. In practice, it is feasible
 to control allocation for arenas explicitly created via <a class="link" href="#arenas.create"><quote><code class="mallctl">arenas.create</code></quote></a> such
 that all extents originate from an application-supplied extent allocator
 (by specifying the custom extent hook functions during arena creation).
 However, the API guarantees for the automatically created arenas may be
 relaxed -- hooks set there may be called in a "best effort" fashion; in
 addition there may be extents created prior to the application having an
 opportunity to take over extent allocation.<pre class="programlisting">
typedef extent_hooks_s extent_hooks_t;
struct extent_hooks_s {
	extent_alloc_t		*alloc;
	extent_dalloc_t		*dalloc;
	extent_destroy_t	*destroy;
	extent_commit_t		*commit;
	extent_decommit_t	*decommit;
	extent_purge_t		*purge_lazy;
	extent_purge_t		*purge_forced;
	extent_split_t		*split;
	extent_merge_t		*merge;
};</pre>The extent_hooks_t structure comprises function
 pointers which are described individually below. jemalloc uses these
 functions to manage extent lifetime, which starts off with allocation of
 mapped committed memory, in the simplest case followed by deallocation.
 However, there are performance and platform reasons to retain extents
 for later reuse. Cleanup attempts cascade from deallocation to decommit
 to forced purging to lazy purging, which gives the extent management
 functions opportunities to reject the most permanent cleanup operations
 in favor of less permanent (and often less costly) operations. All
 operations except allocation can be universally opted out of by setting
 the hook pointers to <code class="constant">NULL</code>, or selectively opted out
 of by returning failure. Note that once the extent hook is set, the
 structure is accessed directly by the associated arenas, so it must
 remain valid for the entire lifetime of the arenas.<div class="funcsynopsis"><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">typedef void *(extent_alloc_t)(</code></td><td>extent_hooks_t *<var class="pdparam">extent_hooks</var>, </td></tr><tr><td> </td><td>void *<var class="pdparam">new_addr</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">alignment</var>, </td></tr><tr><td> </td><td>bool *<var class="pdparam">zero</var>, </td></tr><tr><td> </td><td>bool *<var class="pdparam">commit</var>, </td></tr><tr><td> </td><td>unsigned <var class="pdparam">arena_ind</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div><div class="literallayout"></div>An extent allocation function conforms to the
 extent_alloc_t type and upon success returns a pointer to
 <code>size</code> bytes of mapped memory on behalf of arena
 <code>arena_ind</code> such that the extent's base address is
 a multiple of <code>alignment</code>, as well as setting
 <code>*zero</code> to indicate whether the extent is zeroed
 and <code>*commit</code> to indicate whether the extent is
 committed. Upon error the function returns <code class="constant">NULL</code>
 and leaves <code>*zero</code> and
 <code>*commit</code> unmodified. The
 <code>size</code> parameter is always a multiple of the page
 size. The <code>alignment</code> parameter is always a power
 of two at least as large as the page size. Zeroing is mandatory if
 <code>*zero</code> is true upon function entry. Committing is
 mandatory if <code>*commit</code> is true upon function entry.
 If <code>new_addr</code> is not <code class="constant">NULL</code>, the
 returned pointer must be <code>new_addr</code> on success or
 <code class="constant">NULL</code> on error. Committed memory may be committed
 in absolute terms as on a system that does not overcommit, or in
 implicit terms as on a system that overcommits and satisfies physical
 memory needs on demand via soft page faults. Note that replacing the
 default extent allocation function makes the arena's <a class="link" href="#arena.i.dss"><quote><code class="mallctl">arena.&lt;i&gt;.dss</code></quote></a>
 setting irrelevant.<div class="funcsynopsis"><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">typedef bool (extent_dalloc_t)(</code></td><td>extent_hooks_t *<var class="pdparam">extent_hooks</var>, </td></tr><tr><td> </td><td>void *<var class="pdparam">addr</var>, </td></tr><tr><td> </td><td>size_t <var class="pdparam">size</var>, </td></tr><tr><td> </td><td>bool <var class="pdparam">committed</var>, </td></tr><tr><td> </td><td>unsigned <var class="pdparam">arena_ind</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div><div class="literallayout"></div>
 An extent deallocation function conforms to the
 extent_dalloc_t type and deallocates an extent at given
 <code>addr</code> and <code>size</code> with
 <code>committed</code>/decommited memory as indicated, on
 behalf of arena <code>arena_ind</code>, returning false upon
 success. If the function returns true, this indicates opt-out from
 deallocation; the virtual memory mapping associated with the extent
 remains mapped, in the same commit state, and available for future use,
 in which case it will be automatically retained for later reuse.<div class="funcsynopsis"><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">typedef void (extent_destroy_t)(</code></td><td>extent_hooks_t *<var class="pdparam">extent_hooks</var>, </td></tr><tr><td> </td><td>void *<var class="pdparam">addr</var>, </td></tr><tr><td> </td><td>size_t <var class="pdparam">size</var>, </td></tr><tr><td> </td><td>bool <var class="pdparam">committed</var>, </td></tr><tr><td> </td><td>unsigned <var class="pdparam">arena_ind</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div><div class="literallayout"></div>
 An extent destruction function conforms to the
 extent_destroy_t type and unconditionally destroys an
 extent at given <code>addr</code> and
 <code>size</code> with
 <code>committed</code>/decommited memory as indicated, on
 behalf of arena <code>arena_ind</code>. This function may be
 called to destroy retained extents during arena destruction (see <a class="link" href="#arena.i.destroy"><quote><code class="mallctl">arena.&lt;i&gt;.destroy</code></quote></a>).<div class="funcsynopsis"><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">typedef bool (extent_commit_t)(</code></td><td>extent_hooks_t *<var class="pdparam">extent_hooks</var>, </td></tr><tr><td> </td><td>void *<var class="pdparam">addr</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">offset</var>, </td></tr><tr><td> </td><td>size_t <var class="pdparam">length</var>, </td></tr><tr><td> </td><td>unsigned <var class="pdparam">arena_ind</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div><div class="literallayout"></div>An extent commit function conforms to the
 extent_commit_t type and commits zeroed physical memory to
 back pages within an extent at given <code>addr</code> and
 <code>size</code> at <code>offset</code> bytes,
 extending for <code>length</code> on behalf of arena
 <code>arena_ind</code>, returning false upon success.
 Committed memory may be committed in absolute terms as on a system that
 does not overcommit, or in implicit terms as on a system that
 overcommits and satisfies physical memory needs on demand via soft page
 faults. If the function returns true, this indicates insufficient
 physical memory to satisfy the request.<div class="funcsynopsis"><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">typedef bool (extent_decommit_t)(</code></td><td>extent_hooks_t *<var class="pdparam">extent_hooks</var>, </td></tr><tr><td> </td><td>void *<var class="pdparam">addr</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">offset</var>, </td></tr><tr><td> </td><td>size_t <var class="pdparam">length</var>, </td></tr><tr><td> </td><td>unsigned <var class="pdparam">arena_ind</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div><div class="literallayout"></div>An extent decommit function conforms to the
 extent_decommit_t type and decommits any physical memory
 that is backing pages within an extent at given
 <code>addr</code> and <code>size</code> at
 <code>offset</code> bytes, extending for
 <code>length</code> on behalf of arena
 <code>arena_ind</code>, returning false upon success, in which
 case the pages will be committed via the extent commit function before
 being reused. If the function returns true, this indicates opt-out from
 decommit; the memory remains committed and available for future use, in
 which case it will be automatically retained for later reuse.<div class="funcsynopsis"><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">typedef bool (extent_purge_t)(</code></td><td>extent_hooks_t *<var class="pdparam">extent_hooks</var>, </td></tr><tr><td> </td><td>void *<var class="pdparam">addr</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">offset</var>, </td></tr><tr><td> </td><td>size_t <var class="pdparam">length</var>, </td></tr><tr><td> </td><td>unsigned <var class="pdparam">arena_ind</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div><div class="literallayout"></div>An extent purge function conforms to the
 extent_purge_t type and discards physical pages
 within the virtual memory mapping associated with an extent at given
 <code>addr</code> and <code>size</code> at
 <code>offset</code> bytes, extending for
 <code>length</code> on behalf of arena
 <code>arena_ind</code>. A lazy extent purge function (e.g.
 implemented via
 <code class="function">madvise(<code>...</code><code><code class="constant">MADV_FREE</code></code>)</code>)
 can delay purging indefinitely and leave the pages within the purged
 virtual memory range in an indeterminite state, whereas a forced extent
 purge function immediately purges, and the pages within the virtual
 memory range will be zero-filled the next time they are accessed. If
 the function returns true, this indicates failure to purge.<div class="funcsynopsis"><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">typedef bool (extent_split_t)(</code></td><td>extent_hooks_t *<var class="pdparam">extent_hooks</var>, </td></tr><tr><td> </td><td>void *<var class="pdparam">addr</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">size_a</var>, </td></tr><tr><td> </td><td>size_t <var class="pdparam">size_b</var>, </td></tr><tr><td> </td><td>bool <var class="pdparam">committed</var>, </td></tr><tr><td> </td><td>unsigned <var class="pdparam">arena_ind</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div><div class="literallayout"></div>An extent split function conforms to the
 extent_split_t type and optionally splits an extent at
 given <code>addr</code> and <code>size</code> into
 two adjacent extents, the first of <code>size_a</code> bytes,
 and the second of <code>size_b</code> bytes, operating on
 <code>committed</code>/decommitted memory as indicated, on
 behalf of arena <code>arena_ind</code>, returning false upon
 success. If the function returns true, this indicates that the extent
 remains unsplit and therefore should continue to be operated on as a
 whole.<div class="funcsynopsis"><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">typedef bool (extent_merge_t)(</code></td><td>extent_hooks_t *<var class="pdparam">extent_hooks</var>, </td></tr><tr><td> </td><td>void *<var class="pdparam">addr_a</var>, </td></tr><tr><td> </td><td>size_t <var class="pdparam">size_a</var>, </td></tr><tr><td> </td><td>void *<var class="pdparam">addr_b</var>, </td></tr><tr><td> </td><td>size_t <var class="pdparam">size_b</var>, </td></tr><tr><td> </td><td>bool <var class="pdparam">committed</var>, </td></tr><tr><td> </td><td>unsigned <var class="pdparam">arena_ind</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div><div class="literallayout"></div>An extent merge function conforms to the
 extent_merge_t type and optionally merges adjacent extents,
 at given <code>addr_a</code> and <code>size_a</code>
 with given <code>addr_b</code> and
 <code>size_b</code> into one contiguous extent, operating on
 <code>committed</code>/decommitted memory as indicated, on
 behalf of arena <code>arena_ind</code>, returning false upon
 success. If the function returns true, this indicates that the extents
 remain distinct mappings and therefore should continue to be operated on
 independently.</dd><dt><a name="arenas.narenas"/>
 <quote><code class="mallctl">arenas.narenas</code></quote>
 (unsigned)
 <code class="literal">r-</code>
 </dt><dd>Current limit on number of arenas.</dd><dt><a name="arenas.dirty_decay_ms"/>
 <quote><code class="mallctl">arenas.dirty_decay_ms</code></quote>
 (ssize_t)
 <code class="literal">rw</code>
 </dt><dd>Current default per-arena approximate time in
 milliseconds from the creation of a set of unused dirty pages until an
 equivalent set of unused dirty pages is purged and/or reused, used to
 initialize <a class="link" href="#arena.i.dirty_decay_ms"><quote><code class="mallctl">arena.&lt;i&gt;.dirty_decay_ms</code></quote></a>
 during arena creation. See <a class="link" href="#opt.dirty_decay_ms"><quote><code class="mallctl">opt.dirty_decay_ms</code></quote></a>
 for additional information.</dd><dt><a name="arenas.muzzy_decay_ms"/>
 <quote><code class="mallctl">arenas.muzzy_decay_ms</code></quote>
 (ssize_t)
 <code class="literal">rw</code>
 </dt><dd>Current default per-arena approximate time in
 milliseconds from the creation of a set of unused muzzy pages until an
 equivalent set of unused muzzy pages is purged and/or reused, used to
 initialize <a class="link" href="#arena.i.muzzy_decay_ms"><quote><code class="mallctl">arena.&lt;i&gt;.muzzy_decay_ms</code></quote></a>
 during arena creation. See <a class="link" href="#opt.muzzy_decay_ms"><quote><code class="mallctl">opt.muzzy_decay_ms</code></quote></a>
 for additional information.</dd><dt><a name="arenas.quantum"/>
 <quote><code class="mallctl">arenas.quantum</code></quote>
 (size_t)
 <code class="literal">r-</code>
 </dt><dd>Quantum size.</dd><dt><a name="arenas.page"/>
 <quote><code class="mallctl">arenas.page</code></quote>
 (size_t)
 <code class="literal">r-</code>
 </dt><dd>Page size.</dd><dt><a name="arenas.tcache_max"/>
 <quote><code class="mallctl">arenas.tcache_max</code></quote>
 (size_t)
 <code class="literal">r-</code>
 </dt><dd>Maximum thread-cached size class.</dd><dt><a name="arenas.nbins"/>
 <quote><code class="mallctl">arenas.nbins</code></quote>
 (unsigned)
 <code class="literal">r-</code>
 </dt><dd>Number of bin size classes.</dd><dt><a name="arenas.nhbins"/>
 <quote><code class="mallctl">arenas.nhbins</code></quote>
 (unsigned)
 <code class="literal">r-</code>
 </dt><dd>Total number of thread cache bin size
 classes.</dd><dt><a name="arenas.bin.i.size"/>
 <quote><code class="mallctl">arenas.bin.&lt;i&gt;.size</code></quote>
 (size_t)
 <code class="literal">r-</code>
 </dt><dd>Maximum size supported by size class.</dd><dt><a name="arenas.bin.i.nregs"/>
 <quote><code class="mallctl">arenas.bin.&lt;i&gt;.nregs</code></quote>
 (uint32_t)
 <code class="literal">r-</code>
 </dt><dd>Number of regions per slab.</dd><dt><a name="arenas.bin.i.slab_size"/>
 <quote><code class="mallctl">arenas.bin.&lt;i&gt;.slab_size</code></quote>
 (size_t)
 <code class="literal">r-</code>
 </dt><dd>Number of bytes per slab.</dd><dt><a name="arenas.nlextents"/>
 <quote><code class="mallctl">arenas.nlextents</code></quote>
 (unsigned)
 <code class="literal">r-</code>
 </dt><dd>Total number of large size classes.</dd><dt><a name="arenas.lextent.i.size"/>
 <quote><code class="mallctl">arenas.lextent.&lt;i&gt;.size</code></quote>
 (size_t)
 <code class="literal">r-</code>
 </dt><dd>Maximum size supported by this large size
 class.</dd><dt><a name="arenas.create"/>
 <quote><code class="mallctl">arenas.create</code></quote>
 (unsigned, extent_hooks_t *)
 <code class="literal">rw</code>
 </dt><dd>Explicitly create a new arena outside the range of
 automatically managed arenas, with optionally specified extent hooks,
 and return the new arena index.If the amount of space supplied for storing the arena index does
 not equal <code class="code">sizeof(unsigned)</code>, no
 arena will be created, no data will be written to the space pointed by
 <code>oldp</code>, and <code>*oldlenp</code> will
 be set to 0.
 </dd><dt><a name="arenas.lookup"/>
 <quote><code class="mallctl">arenas.lookup</code></quote>
 (unsigned, void*)
 <code class="literal">rw</code>
 </dt><dd>Index of the arena to which an allocation belongs to.</dd><dt><a name="prof.thread_active_init"/>
 <quote><code class="mallctl">prof.thread_active_init</code></quote>
 (bool)
 <code class="literal">rw</code>
 [<code class="option">--enable-prof</code>]
 </dt><dd>Control the initial setting for <a class="link" href="#thread.prof.active"><quote><code class="mallctl">thread.prof.active</code></quote></a>
 in newly created threads. See the <a class="link" href="#opt.prof_thread_active_init"><quote><code class="mallctl">opt.prof_thread_active_init</code></quote></a>
 option for additional information.</dd><dt><a name="prof.active"/>
 <quote><code class="mallctl">prof.active</code></quote>
 (bool)
 <code class="literal">rw</code>
 [<code class="option">--enable-prof</code>]
 </dt><dd>Control whether sampling is currently active. See the
 <a class="link" href="#opt.prof_active"><quote><code class="mallctl">opt.prof_active</code></quote></a>
 option for additional information, as well as the interrelated <a class="link" href="#thread.prof.active"><quote><code class="mallctl">thread.prof.active</code></quote></a>
 mallctl.</dd><dt><a name="prof.dump"/>
 <quote><code class="mallctl">prof.dump</code></quote>
 (const char *)
 <code class="literal">-w</code>
 [<code class="option">--enable-prof</code>]
 </dt><dd>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"><quote><code class="mallctl">opt.prof_prefix</code></quote></a>
 and <a class="link" href="#prof.prefix"><quote><code class="mallctl">prof.prefix</code></quote></a>
 options.</dd><dt><a name="prof.prefix"/>
 <quote><code class="mallctl">prof.prefix</code></quote>
 (const char *)
 <code class="literal">-w</code>
 [<code class="option">--enable-prof</code>]
 </dt><dd>Set the filename prefix for profile dumps. See
 <a class="link" href="#opt.prof_prefix"><quote><code class="mallctl">opt.prof_prefix</code></quote></a>
 for the default setting. This can be useful to differentiate profile
 dumps such as from forked processes.
 </dd><dt><a name="prof.gdump"/>
 <quote><code class="mallctl">prof.gdump</code></quote>
 (bool)
 <code class="literal">rw</code>
 [<code class="option">--enable-prof</code>]
 </dt><dd>When enabled, 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"><quote><code class="mallctl">opt.prof_prefix</code></quote></a> and
 <a class="link" href="#prof.prefix"><quote><code class="mallctl">prof.prefix</code></quote></a>
 options.</dd><dt><a name="prof.reset"/>
 <quote><code class="mallctl">prof.reset</code></quote>
 (size_t)
 <code class="literal">-w</code>
 [<code class="option">--enable-prof</code>]
 </dt><dd>Reset all memory profile statistics, and optionally
 update the sample rate (see <a class="link" href="#opt.lg_prof_sample"><quote><code class="mallctl">opt.lg_prof_sample</code></quote></a>
 and <a class="link" href="#prof.lg_sample"><quote><code class="mallctl">prof.lg_sample</code></quote></a>).
 </dd><dt><a name="prof.lg_sample"/>
 <quote><code class="mallctl">prof.lg_sample</code></quote>
 (size_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-prof</code>]
 </dt><dd>Get the current sample rate (see <a class="link" href="#opt.lg_prof_sample"><quote><code class="mallctl">opt.lg_prof_sample</code></quote></a>).
 </dd><dt><a name="prof.interval"/>
 <quote><code class="mallctl">prof.interval</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-prof</code>]
 </dt><dd>Average number of bytes allocated between
 interval-based profile dumps. See the
 <a class="link" href="#opt.lg_prof_interval"><quote><code class="mallctl">opt.lg_prof_interval</code></quote></a>
 option for additional information.</dd><dt><a name="stats.allocated"/>
 <quote><code class="mallctl">stats.allocated</code></quote>
 (size_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Total number of bytes allocated by the
 application.</dd><dt><a name="stats.active"/>
 <quote><code class="mallctl">stats.active</code></quote>
 (size_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>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"><quote><code class="mallctl">stats.allocated</code></quote></a>.
 This does not include <a class="link" href="#stats.arenas.i.pdirty">
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.pdirty</code></quote></a>,
 <a class="link" href="#stats.arenas.i.pmuzzy">
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.pmuzzy</code></quote></a>, nor pages
 entirely devoted to allocator metadata.</dd><dt><a name="stats.metadata"/>
 <quote><code class="mallctl">stats.metadata</code></quote>
 (size_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Total number of bytes dedicated to metadata, which
 comprise base allocations used for bootstrap-sensitive allocator
 metadata structures (see <a class="link" href="#stats.arenas.i.base"><quote><code class="mallctl">stats.arenas.&lt;i&gt;.base</code></quote></a>)
 and internal allocations (see <a class="link" href="#stats.arenas.i.internal"><quote><code class="mallctl">stats.arenas.&lt;i&gt;.internal</code></quote></a>).
 Transparent huge page (enabled with <a class="link" href="#opt.metadata_thp">opt.metadata_thp</a>) usage is not
 considered.</dd><dt><a name="stats.metadata_thp"/>
 <quote><code class="mallctl">stats.metadata_thp</code></quote>
 (size_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Number of transparent huge pages (THP) used for
 metadata. See <a class="link" href="#stats.metadata"><quote><code class="mallctl">stats.metadata</code></quote></a> and
 <a class="link" href="#opt.metadata_thp">opt.metadata_thp</a>) for
 details.</dd><dt><a name="stats.resident"/>
 <quote><code class="mallctl">stats.resident</code></quote>
 (size_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Maximum number of bytes in physically resident data
 pages mapped by the allocator, comprising all pages dedicated to
 allocator metadata, pages backing active allocations, and unused dirty
 pages. This is a maximum rather than precise because pages may not
 actually be physically resident if they correspond to demand-zeroed
 virtual memory that has not yet been touched. This is a multiple of the
 page size, and is larger than <a class="link" href="#stats.active"><quote><code class="mallctl">stats.active</code></quote></a>.</dd><dt><a name="stats.mapped"/>
 <quote><code class="mallctl">stats.mapped</code></quote>
 (size_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Total number of bytes in active extents mapped by the
 allocator. This is larger than <a class="link" href="#stats.active"><quote><code class="mallctl">stats.active</code></quote></a>. This
 does not include inactive extents, even those that contain unused dirty
 pages, which means that there is no strict ordering between this and
 <a class="link" href="#stats.resident"><quote><code class="mallctl">stats.resident</code></quote></a>.</dd><dt><a name="stats.retained"/>
 <quote><code class="mallctl">stats.retained</code></quote>
 (size_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Total number of bytes in virtual memory mappings that
 were retained rather than being returned to the operating system via
 e.g. munmap(2) or similar. Retained virtual
 memory is typically untouched, decommitted, or purged, so it has no
 strongly associated physical memory (see <a class="link" href="#arena.i.extent_hooks">extent hooks</a> for details).
 Retained memory is excluded from mapped memory statistics, e.g. <a class="link" href="#stats.mapped"><quote><code class="mallctl">stats.mapped</code></quote></a>.
 </dd><dt><a name="stats.zero_reallocs"/>
 <quote><code class="mallctl">stats.zero_reallocs</code></quote>
 (size_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Number of times that the <code class="function">realloc()</code>
 was called with a non-<code class="constant">NULL</code> pointer argument and a
 <code class="constant">0</code> size argument. This is a fundamentally unsafe
 pattern in portable programs; see <a class="link" href="#opt.zero_realloc">
 <quote><code class="mallctl">opt.zero_realloc</code></quote></a> for details.
 </dd><dt><a name="stats.background_thread.num_threads"/>
 <quote><code class="mallctl">stats.background_thread.num_threads</code></quote>
 (size_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd> Number of <a class="link" href="#background_thread">background
 threads</a> running currently.</dd><dt><a name="stats.background_thread.num_runs"/>
 <quote><code class="mallctl">stats.background_thread.num_runs</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd> Total number of runs from all <a class="link" href="#background_thread">background threads</a>.</dd><dt><a name="stats.background_thread.run_interval"/>
 <quote><code class="mallctl">stats.background_thread.run_interval</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd> Average run interval in nanoseconds of <a class="link" href="#background_thread">background threads</a>.</dd><dt><a name="stats.mutexes.ctl"/>
 <quote><code class="mallctl">stats.mutexes.ctl.{counter};</code></quote>
 (counter specific type)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Statistics on <code class="varname">ctl</code> mutex (global
 scope; mallctl related). <quote><code class="mallctl">{counter}</code></quote> is one of the
 counters below:<dt><a name="mutex_counters"/></dt><dd><code class="varname">num_ops</code> (uint64_t):
 Total number of lock acquisition operations on this mutex.<code class="varname">num_spin_acq</code> (uint64_t): Number
	 of times the mutex was spin-acquired. When the mutex is currently
	 locked and cannot be acquired immediately, a short period of
	 spin-retry within jemalloc will be performed. Acquired through spin
	 generally means the contention was lightweight and not causing context
	 switches.<code class="varname">num_wait</code> (uint64_t): Number of
	 times the mutex was wait-acquired, which means the mutex contention
	 was not solved by spin-retry, and blocking operation was likely
	 involved in order to acquire the mutex. This event generally implies
	 higher cost / longer delay, and should be investigated if it happens
	 often.<code class="varname">max_wait_time</code> (uint64_t):
	 Maximum length of time in nanoseconds spent on a single wait-acquired
	 lock operation. Note that to avoid profiling overhead on the common
	 path, this does not consider spin-acquired cases.<code class="varname">total_wait_time</code> (uint64_t):
	 Cumulative time in nanoseconds spent on wait-acquired lock operations.
	 Similarly, spin-acquired cases are not considered.<code class="varname">max_num_thds</code> (uint32_t): Maximum
	 number of threads waiting on this mutex simultaneously. Similarly,
	 spin-acquired cases are not considered.<code class="varname">num_owner_switch</code> (uint64_t):
	 Number of times the current mutex owner is different from the previous
	 one. This event does not generally imply an issue; rather it is an
	 indicator of how often the protected data are accessed by different
	 threads.
	 </dd></dd><dt><a name="stats.mutexes.background_thread"/>
 <quote><code class="mallctl">stats.mutexes.background_thread.{counter}</code></quote>
	 (counter specific type) <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Statistics on <code class="varname">background_thread</code> mutex
 (global scope; <a class="link" href="#background_thread"><quote><code class="mallctl">background_thread</code></quote></a>
 related). <quote><code class="mallctl">{counter}</code></quote> is one of the counters in <a class="link" href="#mutex_counters">mutex profiling
 counters</a>.</dd><dt><a name="stats.mutexes.prof"/>
 <quote><code class="mallctl">stats.mutexes.prof.{counter}</code></quote>
	 (counter specific type) <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Statistics on <code class="varname">prof</code> mutex (global
 scope; profiling related). <quote><code class="mallctl">{counter}</code></quote> is one of the
 counters in <a class="link" href="#mutex_counters">mutex profiling
 counters</a>.</dd><dt><a name="stats.mutexes.prof_thds_data"/>
 <quote><code class="mallctl">stats.mutexes.prof_thds_data.{counter}</code></quote>
	 (counter specific type) <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Statistics on <code class="varname">prof</code> threads data mutex
	(global scope; profiling related). <quote><code class="mallctl">{counter}</code></quote> is one
	of the counters in <a class="link" href="#mutex_counters">mutex profiling
 counters</a>.</dd><dt><a name="stats.mutexes.prof_dump"/>
 <quote><code class="mallctl">stats.mutexes.prof_dump.{counter}</code></quote>
	 (counter specific type) <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Statistics on <code class="varname">prof</code> dumping mutex
	(global scope; profiling related). <quote><code class="mallctl">{counter}</code></quote> is one
	of the counters in <a class="link" href="#mutex_counters">mutex profiling
 counters</a>.</dd><dt><a name="stats.mutexes.reset"/>
 <quote><code class="mallctl">stats.mutexes.reset</code></quote>
	 (void) <code class="literal">--</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Reset all mutex profile statistics, including global
 mutexes, arena mutexes and bin mutexes.</dd><dt><a name="stats.arenas.i.dss"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.dss</code></quote>
 (const char *)
 <code class="literal">r-</code>
 </dt><dd>dss (sbrk(2)) allocation precedence as
 related to mmap(2) allocation. See <a class="link" href="#opt.dss"><quote><code class="mallctl">opt.dss</code></quote></a> for details.
 </dd><dt><a name="stats.arenas.i.dirty_decay_ms"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.dirty_decay_ms</code></quote>
 (ssize_t)
 <code class="literal">r-</code>
 </dt><dd>Approximate time in milliseconds from the creation of a
 set of unused dirty pages until an equivalent set of unused dirty pages
 is purged and/or reused. See <a class="link" href="#opt.dirty_decay_ms"><quote><code class="mallctl">opt.dirty_decay_ms</code></quote></a>
 for details.</dd><dt><a name="stats.arenas.i.muzzy_decay_ms"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.muzzy_decay_ms</code></quote>
 (ssize_t)
 <code class="literal">r-</code>
 </dt><dd>Approximate time in milliseconds from the creation of a
 set of unused muzzy pages until an equivalent set of unused muzzy pages
 is purged and/or reused. See <a class="link" href="#opt.muzzy_decay_ms"><quote><code class="mallctl">opt.muzzy_decay_ms</code></quote></a>
 for details.</dd><dt><a name="stats.arenas.i.nthreads"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.nthreads</code></quote>
 (unsigned)
 <code class="literal">r-</code>
 </dt><dd>Number of threads currently assigned to
 arena.</dd><dt><a name="stats.arenas.i.uptime"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.uptime</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 </dt><dd>Time elapsed (in nanoseconds) since the arena was
 created. If &lt;i&gt; equals <code class="constant">0</code> or
 <code class="constant">MALLCTL_ARENAS_ALL</code>, this is the uptime since malloc
 initialization.</dd><dt><a name="stats.arenas.i.pactive"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.pactive</code></quote>
 (size_t)
 <code class="literal">r-</code>
 </dt><dd>Number of pages in active extents.</dd><dt><a name="stats.arenas.i.pdirty"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.pdirty</code></quote>
 (size_t)
 <code class="literal">r-</code>
 </dt><dd>Number of pages within unused extents that are
 potentially dirty, and for which <code class="function">madvise()</code> or
 similar has not been called. See <a class="link" href="#opt.dirty_decay_ms"><quote><code class="mallctl">opt.dirty_decay_ms</code></quote></a>
 for a description of dirty pages.</dd><dt><a name="stats.arenas.i.pmuzzy"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.pmuzzy</code></quote>
 (size_t)
 <code class="literal">r-</code>
 </dt><dd>Number of pages within unused extents that are muzzy.
 See <a class="link" href="#opt.muzzy_decay_ms"><quote><code class="mallctl">opt.muzzy_decay_ms</code></quote></a>
 for a description of muzzy pages.</dd><dt><a name="stats.arenas.i.mapped"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.mapped</code></quote>
 (size_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Number of mapped bytes.</dd><dt><a name="stats.arenas.i.retained"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.retained</code></quote>
 (size_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Number of retained bytes. See <a class="link" href="#stats.retained"><quote><code class="mallctl">stats.retained</code></quote></a> for
 details.</dd><dt><a name="stats.arenas.i.extent_avail"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.extent_avail</code></quote>
 (size_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Number of allocated (but unused) extent structs in this
	arena.</dd><dt><a name="stats.arenas.i.base"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.base</code></quote>
 (size_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>
 Number of bytes dedicated to bootstrap-sensitive allocator metadata
 structures.</dd><dt><a name="stats.arenas.i.internal"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.internal</code></quote>
 (size_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Number of bytes dedicated to internal allocations.
 Internal allocations differ from application-originated allocations in
 that they are for internal use, and that they are omitted from heap
 profiles.</dd><dt><a name="stats.arenas.i.metadata_thp"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.metadata_thp</code></quote>
 (size_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Number of transparent huge pages (THP) used for
 metadata. See <a class="link" href="#opt.metadata_thp">opt.metadata_thp</a>
 for details.</dd><dt><a name="stats.arenas.i.resident"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.resident</code></quote>
 (size_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Maximum number of bytes in physically resident data
 pages mapped by the arena, comprising all pages dedicated to allocator
 metadata, pages backing active allocations, and unused dirty pages.
 This is a maximum rather than precise because pages may not actually be
 physically resident if they correspond to demand-zeroed virtual memory
 that has not yet been touched. This is a multiple of the page
 size.</dd><dt><a name="stats.arenas.i.dirty_npurge"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.dirty_npurge</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Number of dirty page purge sweeps performed.
 </dd><dt><a name="stats.arenas.i.dirty_nmadvise"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.dirty_nmadvise</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Number of <code class="function">madvise()</code> or similar
 calls made to purge dirty pages.</dd><dt><a name="stats.arenas.i.dirty_purged"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.dirty_purged</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Number of dirty pages purged.</dd><dt><a name="stats.arenas.i.muzzy_npurge"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.muzzy_npurge</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Number of muzzy page purge sweeps performed.
 </dd><dt><a name="stats.arenas.i.muzzy_nmadvise"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.muzzy_nmadvise</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Number of <code class="function">madvise()</code> or similar
 calls made to purge muzzy pages.</dd><dt><a name="stats.arenas.i.muzzy_purged"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.muzzy_purged</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Number of muzzy pages purged.</dd><dt><a name="stats.arenas.i.small.allocated"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.small.allocated</code></quote>
 (size_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Number of bytes currently allocated by small objects.
 </dd><dt><a name="stats.arenas.i.small.nmalloc"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.small.nmalloc</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Cumulative number of times a small allocation was
 requested from the arena's bins, whether to fill the relevant tcache if
 <a class="link" href="#opt.tcache"><quote><code class="mallctl">opt.tcache</code></quote></a> is
 enabled, or to directly satisfy an allocation request
 otherwise.</dd><dt><a name="stats.arenas.i.small.ndalloc"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.small.ndalloc</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Cumulative number of times a small allocation was
 returned to the arena's bins, whether to flush the relevant tcache if
 <a class="link" href="#opt.tcache"><quote><code class="mallctl">opt.tcache</code></quote></a> is
 enabled, or to directly deallocate an allocation
 otherwise.</dd><dt><a name="stats.arenas.i.small.nrequests"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.small.nrequests</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Cumulative number of allocation requests satisfied by
 all bin size classes.</dd><dt><a name="stats.arenas.i.small.nfills"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.small.nfills</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Cumulative number of tcache fills by all small size
	classes.</dd><dt><a name="stats.arenas.i.small.nflushes"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.small.nflushes</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Cumulative number of tcache flushes by all small size
 classes.</dd><dt><a name="stats.arenas.i.large.allocated"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.large.allocated</code></quote>
 (size_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Number of bytes currently allocated by large objects.
 </dd><dt><a name="stats.arenas.i.large.nmalloc"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.large.nmalloc</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Cumulative number of times a large extent was allocated
 from the arena, whether to fill the relevant tcache if <a class="link" href="#opt.tcache"><quote><code class="mallctl">opt.tcache</code></quote></a> is enabled and
 the size class is within the range being cached, or to directly satisfy
 an allocation request otherwise.</dd><dt><a name="stats.arenas.i.large.ndalloc"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.large.ndalloc</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Cumulative number of times a large extent was returned
 to the arena, whether to flush the relevant tcache if <a class="link" href="#opt.tcache"><quote><code class="mallctl">opt.tcache</code></quote></a> is enabled and
 the size class is within the range being cached, or to directly
 deallocate an allocation otherwise.</dd><dt><a name="stats.arenas.i.large.nrequests"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.large.nrequests</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Cumulative number of allocation requests satisfied by
 all large size classes.</dd><dt><a name="stats.arenas.i.large.nfills"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.large.nfills</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Cumulative number of tcache fills by all large size
	classes.</dd><dt><a name="stats.arenas.i.large.nflushes"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.large.nflushes</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Cumulative number of tcache flushes by all large size
 classes.</dd><dt><a name="stats.arenas.i.bins.j.nmalloc"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.nmalloc</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Cumulative number of times a bin region of the
 corresponding size class was allocated from the arena, whether to fill
 the relevant tcache if <a class="link" href="#opt.tcache"><quote><code class="mallctl">opt.tcache</code></quote></a> is enabled, or
 to directly satisfy an allocation request otherwise.</dd><dt><a name="stats.arenas.i.bins.j.ndalloc"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.ndalloc</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Cumulative number of times a bin region of the
 corresponding size class was returned to the arena, whether to flush the
 relevant tcache if <a class="link" href="#opt.tcache"><quote><code class="mallctl">opt.tcache</code></quote></a> is enabled, or
 to directly deallocate an allocation otherwise.</dd><dt><a name="stats.arenas.i.bins.j.nrequests"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.nrequests</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Cumulative number of allocation requests satisfied by
 bin regions of the corresponding size class.</dd><dt><a name="stats.arenas.i.bins.j.curregs"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.curregs</code></quote>
 (size_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Current number of regions for this size
 class.</dd><dt><a name="stats.arenas.i.bins.j.nfills"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.nfills</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 </dt><dd>Cumulative number of tcache fills.</dd><dt><a name="stats.arenas.i.bins.j.nflushes"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.nflushes</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 </dt><dd>Cumulative number of tcache flushes.</dd><dt><a name="stats.arenas.i.bins.j.nslabs"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.nslabs</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Cumulative number of slabs created.</dd><dt><a name="stats.arenas.i.bins.j.nreslabs"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.nreslabs</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Cumulative number of times the current slab from which
 to allocate changed.</dd><dt><a name="stats.arenas.i.bins.j.curslabs"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.curslabs</code></quote>
 (size_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Current number of slabs.</dd><dt><a name="stats.arenas.i.bins.j.nonfull_slabs"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.nonfull_slabs</code></quote>
 (size_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Current number of nonfull slabs.</dd><dt><a name="stats.arenas.i.bins.mutex"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.mutex.{counter}</code></quote>
 (counter specific type) <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Statistics on
 <code class="varname">arena.&lt;i&gt;.bins.&lt;j&gt;</code> mutex (arena bin
 scope; bin operation related). <quote><code class="mallctl">{counter}</code></quote> is one of
 the counters in <a class="link" href="#mutex_counters">mutex profiling
 counters</a>.</dd><dt><a name="stats.arenas.i.extents.n"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.extents.&lt;j&gt;.n{extent_type}</code></quote>
 (size_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd> Number of extents of the given type in this arena in
	the bucket corresponding to page size index &lt;j&gt;. The extent type
	is one of dirty, muzzy, or retained.</dd><dt><a name="stats.arenas.i.extents.bytes"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.extents.&lt;j&gt;.{extent_type}_bytes</code></quote>
 (size_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd> Sum of the bytes managed by extents of the given type
	in this arena in the bucket corresponding to page size index &lt;j&gt;.
	The extent type is one of dirty, muzzy, or retained.</dd><dt><a name="stats.arenas.i.lextents.j.nmalloc"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.lextents.&lt;j&gt;.nmalloc</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Cumulative number of times a large extent of the
 corresponding size class was allocated from the arena, whether to fill
 the relevant tcache if <a class="link" href="#opt.tcache"><quote><code class="mallctl">opt.tcache</code></quote></a> is enabled and
 the size class is within the range being cached, or to directly satisfy
 an allocation request otherwise.</dd><dt><a name="stats.arenas.i.lextents.j.ndalloc"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.lextents.&lt;j&gt;.ndalloc</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Cumulative number of times a large extent of the
 corresponding size class was returned to the arena, whether to flush the
 relevant tcache if <a class="link" href="#opt.tcache"><quote><code class="mallctl">opt.tcache</code></quote></a> is enabled and
 the size class is within the range being cached, or to directly
 deallocate an allocation otherwise.</dd><dt><a name="stats.arenas.i.lextents.j.nrequests"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.lextents.&lt;j&gt;.nrequests</code></quote>
 (uint64_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Cumulative number of allocation requests satisfied by
 large extents of the corresponding size class.</dd><dt><a name="stats.arenas.i.lextents.j.curlextents"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.lextents.&lt;j&gt;.curlextents</code></quote>
 (size_t)
 <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Current number of large allocations for this size class.
 </dd><dt><a name="stats.arenas.i.mutexes.large"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.mutexes.large.{counter}</code></quote>
 (counter specific type) <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Statistics on <code class="varname">arena.&lt;i&gt;.large</code>
 mutex (arena scope; large allocation related).
 <quote><code class="mallctl">{counter}</code></quote> is one of the counters in <a class="link" href="#mutex_counters">mutex profiling
 counters</a>.</dd><dt><a name="stats.arenas.i.mutexes.extent_avail"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.mutexes.extent_avail.{counter}</code></quote>
 (counter specific type) <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Statistics on <code class="varname">arena.&lt;i&gt;.extent_avail
 </code> mutex (arena scope; extent avail related).
 <quote><code class="mallctl">{counter}</code></quote> is one of the counters in <a class="link" href="#mutex_counters">mutex profiling
 counters</a>.</dd><dt><a name="stats.arenas.i.mutexes.extents_dirty"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.mutexes.extents_dirty.{counter}</code></quote>
 (counter specific type) <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Statistics on <code class="varname">arena.&lt;i&gt;.extents_dirty
 </code> mutex (arena scope; dirty extents related).
 <quote><code class="mallctl">{counter}</code></quote> is one of the counters in <a class="link" href="#mutex_counters">mutex profiling
 counters</a>.</dd><dt><a name="stats.arenas.i.mutexes.extents_muzzy"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.mutexes.extents_muzzy.{counter}</code></quote>
 (counter specific type) <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Statistics on <code class="varname">arena.&lt;i&gt;.extents_muzzy
 </code> mutex (arena scope; muzzy extents related).
 <quote><code class="mallctl">{counter}</code></quote> is one of the counters in <a class="link" href="#mutex_counters">mutex profiling
 counters</a>.</dd><dt><a name="stats.arenas.i.mutexes.extents_retained"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.mutexes.extents_retained.{counter}</code></quote>
 (counter specific type) <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Statistics on <code class="varname">arena.&lt;i&gt;.extents_retained
 </code> mutex (arena scope; retained extents related).
 <quote><code class="mallctl">{counter}</code></quote> is one of the counters in <a class="link" href="#mutex_counters">mutex profiling
 counters</a>.</dd><dt><a name="stats.arenas.i.mutexes.decay_dirty"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.mutexes.decay_dirty.{counter}</code></quote>
 (counter specific type) <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Statistics on <code class="varname">arena.&lt;i&gt;.decay_dirty
 </code> mutex (arena scope; decay for dirty pages related).
 <quote><code class="mallctl">{counter}</code></quote> is one of the counters in <a class="link" href="#mutex_counters">mutex profiling
 counters</a>.</dd><dt><a name="stats.arenas.i.mutexes.decay_muzzy"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.mutexes.decay_muzzy.{counter}</code></quote>
 (counter specific type) <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Statistics on <code class="varname">arena.&lt;i&gt;.decay_muzzy
 </code> mutex (arena scope; decay for muzzy pages related).
 <quote><code class="mallctl">{counter}</code></quote> is one of the counters in <a class="link" href="#mutex_counters">mutex profiling
 counters</a>.</dd><dt><a name="stats.arenas.i.mutexes.base"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.mutexes.base.{counter}</code></quote>
 (counter specific type) <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Statistics on <code class="varname">arena.&lt;i&gt;.base</code>
 mutex (arena scope; base allocator related).
 <quote><code class="mallctl">{counter}</code></quote> is one of the counters in <a class="link" href="#mutex_counters">mutex profiling
 counters</a>.</dd><dt><a name="stats.arenas.i.mutexes.tcache_list"/>
 <quote><code class="mallctl">stats.arenas.&lt;i&gt;.mutexes.tcache_list.{counter}</code></quote>
 (counter specific type) <code class="literal">r-</code>
 [<code class="option">--enable-stats</code>]
 </dt><dd>Statistics on
 <code class="varname">arena.&lt;i&gt;.tcache_list</code> mutex (arena scope;
 tcache to arena association related). This mutex is expected to be
 accessed less often. <quote><code class="mallctl">{counter}</code></quote> is one of the
 counters in <a class="link" href="#mutex_counters">mutex profiling
 counters</a>.</dd></dl></div></div><div class="refsect1"><a name="heap_profile_format"/><h2>HEAP PROFILE FORMAT</h2>Although the heap profiling functionality was originally designed to
 be compatible with the
 pprof command that is developed as part of the <a class="ulink" href="http://code.google.com/p/gperftools/" target="_top">gperftools
 package</a>, the addition of per thread heap profiling functionality
 required a different heap profile format. The jeprof
 command is derived from pprof, with enhancements to
 support the heap profile format described here.In the following hypothetical heap profile, <code class="constant">[...]</code>
 indicates elision for the sake of compactness. <pre class="programlisting">
heap_v2/524288
 t*: 28106: 56637512 [0: 0]
 [...]
 t3: 352: 16777344 [0: 0]
 [...]
 t99: 17754: 29341640 [0: 0]
 [...]
@ 0x5f86da8 0x5f5a1dc [...] 0x29e4d4e 0xa200316 0xabb2988 [...]
 t*: 13: 6688 [0: 0]
 t3: 12: 6496 [0: 0]
 t99: 1: 192 [0: 0]
[...]

MAPPED_LIBRARIES:
[...]</pre> The following matches the above heap profile, but most
tokens are replaced with <code class="constant">&lt;description&gt;</code> to indicate
descriptions of the corresponding fields. <pre class="programlisting">
&lt;heap_profile_format_version&gt;/&lt;mean_sample_interval&gt;
 &lt;aggregate&gt;: &lt;curobjs&gt;: &lt;curbytes&gt; [&lt;cumobjs&gt;: &lt;cumbytes&gt;]
 [...]
 &lt;thread_3_aggregate&gt;: &lt;curobjs&gt;: &lt;curbytes&gt; [&lt;cumobjs&gt;: &lt;cumbytes&gt;]
 [...]
 &lt;thread_99_aggregate&gt;: &lt;curobjs&gt;: &lt;curbytes&gt; [&lt;cumobjs&gt;: &lt;cumbytes&gt;]
 [...]
@ &lt;top_frame&gt; &lt;frame&gt; [...] &lt;frame&gt; &lt;frame&gt; &lt;frame&gt; [...]
 &lt;backtrace_aggregate&gt;: &lt;curobjs&gt;: &lt;curbytes&gt; [&lt;cumobjs&gt;: &lt;cumbytes&gt;]
 &lt;backtrace_thread_3&gt;: &lt;curobjs&gt;: &lt;curbytes&gt; [&lt;cumobjs&gt;: &lt;cumbytes&gt;]
 &lt;backtrace_thread_99&gt;: &lt;curobjs&gt;: &lt;curbytes&gt; [&lt;cumobjs&gt;: &lt;cumbytes&gt;]
[...]

MAPPED_LIBRARIES:
&lt;/proc/&lt;pid&gt;/maps&gt;</pre></div><div class="refsect1"><a name="debugging_malloc_problems"/><h2>DEBUGGING MALLOC PROBLEMS</h2>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.Programs often accidentally depend on “uninitialized”
 memory actually being filled with zero bytes. Junk filling
 (see the <a class="link" href="#opt.junk"><quote><code class="mallctl">opt.junk</code></quote></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"><quote><code class="mallctl">opt.zero</code></quote></a> option) eliminates
 the symptoms of such bugs. Between these two options, it is usually
 possible to quickly detect, diagnose, and eliminate such bugs.This implementation does not provide much detail about the problems
 it detects, because the performance impact for storing such information
 would be prohibitive.</div><div class="refsect1"><a name="diagnostic_messages"/><h2>DIAGNOSTIC MESSAGES</h2>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"><quote><code class="mallctl">opt.abort</code></quote></a> option is set, most
 warnings are treated as errors.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> takes the
 <code>cbopaque</code> 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>, 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.All messages are prefixed by
 “<code class="computeroutput">&lt;jemalloc&gt;: </code>”.</div><div class="refsect1"><a name="return_values"/><h2>RETURN VALUES</h2><div class="refsect2"><a name="idm46057384902176"/><h3>Standard API</h3>The <code class="function">malloc()</code> and
 <code class="function">calloc()</code> 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
 ENOMEM.The <code class="function">posix_memalign()</code> function
 returns the value 0 if successful; otherwise it returns an error value.
 The <code class="function">posix_memalign()</code> function will fail
 if:
 <div class="variablelist"><dl class="variablelist"><dt>EINVAL</dt><dd>The <code>alignment</code> parameter is
 not a power of 2 at least as large as
 <code class="code">sizeof(void *)</code>.
 </dd><dt>ENOMEM</dt><dd>Memory allocation error.</dd></dl></div>
 The <code class="function">aligned_alloc()</code> function returns
 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. The
 <code class="function">aligned_alloc()</code> function will fail if:
 <div class="variablelist"><dl class="variablelist"><dt>EINVAL</dt><dd>The <code>alignment</code> parameter is
 not a power of 2.
 </dd><dt>ENOMEM</dt><dd>Memory allocation error.</dd></dl></div>
 The <code class="function">realloc()</code> function returns a
 pointer, possibly identical to <code>ptr</code>, 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
 ENOMEM if the error was the result of an
 allocation failure. The <code class="function">realloc()</code>
 function always leaves the original buffer intact when an error occurs.
 The <code class="function">free()</code> function returns no
 value.</div><div class="refsect2"><a name="idm46057384880688"/><h3>Non-standard API</h3>The <code class="function">mallocx()</code> and
 <code class="function">rallocx()</code> functions return a pointer to
 the allocated memory if successful; otherwise a <code class="constant">NULL</code>
 pointer is returned to indicate insufficient contiguous memory was
 available to service the allocation request. The <code class="function">xallocx()</code> function returns the
 real size of the resulting resized allocation pointed to by
 <code>ptr</code>, which is a value less than
 <code>size</code> if the allocation could not be adequately
 grown in place. The <code class="function">sallocx()</code> function returns the
 real size of the allocation pointed to by <code>ptr</code>.
 The <code class="function">nallocx()</code> returns the real size
 that would result from a successful equivalent
 <code class="function">mallocx()</code> function call, or zero if
 insufficient memory is available to perform the size computation. The <code class="function">mallctl()</code>,
 <code class="function">mallctlnametomib()</code>, and
 <code class="function">mallctlbymib()</code> functions return 0 on
 success; otherwise they return an error value. The functions will fail
 if:
 <div class="variablelist"><dl class="variablelist"><dt>EINVAL</dt><dd><code>newp</code> is not
 <code class="constant">NULL</code>, and <code>newlen</code> is too
 large or too small. Alternatively, <code>*oldlenp</code>
 is too large or too small; when it happens, except for a very few
 cases explicitly documented otherwise, as much data as possible
 are read despite the error, with the amount of data read being
 recorded in <code>*oldlenp</code>.</dd><dt>ENOENT</dt><dd><code>name</code> or
 <code>mib</code> specifies an unknown/invalid
 value.</dd><dt>EPERM</dt><dd>Attempt to read or write void value, or attempt to
 write read-only value.</dd><dt>EAGAIN</dt><dd>A memory allocation failure
 occurred.</dd><dt>EFAULT</dt><dd>An interface with side effects failed in some way
 not directly related to <code class="function">mallctl*()</code>
 read/write processing.</dd></dl></div>
 The <code class="function">malloc_usable_size()</code> function
 returns the usable size of the allocation pointed to by
 <code>ptr</code>. </div></div><div class="refsect1"><a name="environment"/><h2>ENVIRONMENT</h2>The following environment variable affects the execution of the
 allocation functions:
 <div class="variablelist"><dl class="variablelist"><dt><code class="envar">MALLOC_CONF</code></dt><dd>If the environment variable
 <code class="envar">MALLOC_CONF</code> is set, the characters it contains
 will be interpreted as options.</dd></dl></div>
 </div><div class="refsect1"><a name="examples"/><h2>EXAMPLES</h2>To dump core whenever a problem occurs:
 <pre class="screen">ln -s 'abort:true' /etc/malloc.conf</pre>
 To specify in the source that only one arena should be automatically
 created:
 <pre class="programlisting">
malloc_conf = "narenas:1";</pre></div><div class="refsect1"><a name="see_also"/><h2>SEE ALSO</h2>madvise(2),
 mmap(2),
 sbrk(2),
 utrace(2),
 alloca(3),
 atexit(3),
 getpagesize(3)</div><div class="refsect1"><a name="standards"/><h2>STANDARDS</h2>The <code class="function">malloc()</code>,
 <code class="function">calloc()</code>,
 <code class="function">realloc()</code>, and
 <code class="function">free()</code> functions conform to ISO/IEC
 9899:1990 (“ISO C90”).The <code class="function">posix_memalign()</code> function conforms
 to IEEE Std 1003.1-2001 (“POSIX.1”).</div></div></body></html>

${this.title}

Code Editor : jemalloc.html