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Kevin Svetlitski cdb2c0e02f Implement C23's free_sized and free_aligned_sized 
[N2699 - Sized Memory Deallocation](https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2699.htm)
introduced two new functions which were incorporated into the C23
standard, `free_sized` and `free_aligned_sized`. Both already have
analogues in Jemalloc, all we are doing here is adding the appropriate
wrappers.
2023-07-20 15:06:41 -07:00

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<?xml version='1.0' encoding='UTF-8'?>
<?xml-stylesheet type="text/xsl"
href="http://docbook.sourceforge.net/release/xsl/current/manpages/docbook.xsl"?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd" [
]>
<refentry>
<refentryinfo>
<title>User Manual</title>
<productname>jemalloc</productname>
<releaseinfo role="version">@jemalloc_version@</releaseinfo>
<authorgroup>
<author>
<firstname>Jason</firstname>
<surname>Evans</surname>
<personblurb>Author</personblurb>
</author>
</authorgroup>
</refentryinfo>
<refmeta>
<refentrytitle>JEMALLOC</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refdescriptor>jemalloc</refdescriptor>
<refname>jemalloc</refname>
<!-- Each refname causes a man page file to be created. Only if this were
the system malloc(3) implementation would these files be appropriate.
<refname>malloc</refname>
<refname>calloc</refname>
<refname>posix_memalign</refname>
<refname>aligned_alloc</refname>
<refname>realloc</refname>
<refname>free</refname>
<refname>free_sized</refname>
<refname>free_aligned_sized</refname>
<refname>mallocx</refname>
<refname>rallocx</refname>
<refname>xallocx</refname>
<refname>sallocx</refname>
<refname>dallocx</refname>
<refname>sdallocx</refname>
<refname>nallocx</refname>
<refname>mallctl</refname>
<refname>mallctlnametomib</refname>
<refname>mallctlbymib</refname>
<refname>malloc_stats_print</refname>
<refname>malloc_usable_size</refname>
-->
<refpurpose>general purpose memory allocation functions</refpurpose>
</refnamediv>
<refsect1 id="library">
<title>LIBRARY</title>
<para>This manual describes jemalloc @jemalloc_version@. More information
can be found at the <ulink
url="http://jemalloc.net/">jemalloc website</ulink>.</para>
</refsect1>
<refsynopsisdiv>
<title>SYNOPSIS</title>
<funcsynopsis>
<funcsynopsisinfo>#include &lt;<filename class="headerfile">jemalloc/jemalloc.h</filename>&gt;</funcsynopsisinfo>
<refsect2>
<title>Standard API</title>
<funcprototype>
<funcdef>void *<function>malloc</function></funcdef>
<paramdef>size_t <parameter>size</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void *<function>calloc</function></funcdef>
<paramdef>size_t <parameter>number</parameter></paramdef>
<paramdef>size_t <parameter>size</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>posix_memalign</function></funcdef>
<paramdef>void **<parameter>ptr</parameter></paramdef>
<paramdef>size_t <parameter>alignment</parameter></paramdef>
<paramdef>size_t <parameter>size</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void *<function>aligned_alloc</function></funcdef>
<paramdef>size_t <parameter>alignment</parameter></paramdef>
<paramdef>size_t <parameter>size</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void *<function>realloc</function></funcdef>
<paramdef>void *<parameter>ptr</parameter></paramdef>
<paramdef>size_t <parameter>size</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void <function>free</function></funcdef>
<paramdef>void *<parameter>ptr</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void <function>free_sized</function></funcdef>
<paramdef>void *<parameter>ptr</parameter></paramdef>
<paramdef>size_t <parameter>size</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void <function>free_aligned_sized</function></funcdef>
<paramdef>void *<parameter>ptr</parameter></paramdef>
<paramdef>size_t <parameter>alignment</parameter></paramdef>
<paramdef>size_t <parameter>size</parameter></paramdef>
</funcprototype>
</refsect2>
<refsect2>
<title>Non-standard API</title>
<funcprototype>
<funcdef>void *<function>mallocx</function></funcdef>
<paramdef>size_t <parameter>size</parameter></paramdef>
<paramdef>int <parameter>flags</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void *<function>rallocx</function></funcdef>
<paramdef>void *<parameter>ptr</parameter></paramdef>
<paramdef>size_t <parameter>size</parameter></paramdef>
<paramdef>int <parameter>flags</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>size_t <function>xallocx</function></funcdef>
<paramdef>void *<parameter>ptr</parameter></paramdef>
<paramdef>size_t <parameter>size</parameter></paramdef>
<paramdef>size_t <parameter>extra</parameter></paramdef>
<paramdef>int <parameter>flags</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>size_t <function>sallocx</function></funcdef>
<paramdef>void *<parameter>ptr</parameter></paramdef>
<paramdef>int <parameter>flags</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void <function>dallocx</function></funcdef>
<paramdef>void *<parameter>ptr</parameter></paramdef>
<paramdef>int <parameter>flags</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void <function>sdallocx</function></funcdef>
<paramdef>void *<parameter>ptr</parameter></paramdef>
<paramdef>size_t <parameter>size</parameter></paramdef>
<paramdef>int <parameter>flags</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>size_t <function>nallocx</function></funcdef>
<paramdef>size_t <parameter>size</parameter></paramdef>
<paramdef>int <parameter>flags</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>mallctl</function></funcdef>
<paramdef>const char *<parameter>name</parameter></paramdef>
<paramdef>void *<parameter>oldp</parameter></paramdef>
<paramdef>size_t *<parameter>oldlenp</parameter></paramdef>
<paramdef>void *<parameter>newp</parameter></paramdef>
<paramdef>size_t <parameter>newlen</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>mallctlnametomib</function></funcdef>
<paramdef>const char *<parameter>name</parameter></paramdef>
<paramdef>size_t *<parameter>mibp</parameter></paramdef>
<paramdef>size_t *<parameter>miblenp</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>mallctlbymib</function></funcdef>
<paramdef>const size_t *<parameter>mib</parameter></paramdef>
<paramdef>size_t <parameter>miblen</parameter></paramdef>
<paramdef>void *<parameter>oldp</parameter></paramdef>
<paramdef>size_t *<parameter>oldlenp</parameter></paramdef>
<paramdef>void *<parameter>newp</parameter></paramdef>
<paramdef>size_t <parameter>newlen</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void <function>malloc_stats_print</function></funcdef>
<paramdef>void <parameter>(*write_cb)</parameter>
<funcparams>void *, const char *</funcparams>
</paramdef>
<paramdef>void *<parameter>cbopaque</parameter></paramdef>
<paramdef>const char *<parameter>opts</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>size_t <function>malloc_usable_size</function></funcdef>
<paramdef>const void *<parameter>ptr</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>void <function>(*malloc_message)</function></funcdef>
<paramdef>void *<parameter>cbopaque</parameter></paramdef>
<paramdef>const char *<parameter>s</parameter></paramdef>
</funcprototype>
<para><type>const char *</type><varname>malloc_conf</varname>;</para>
</refsect2>
</funcsynopsis>
</refsynopsisdiv>
<refsect1 id="description">
<title>DESCRIPTION</title>
<refsect2>
<title>Standard API</title>
<para>The <function>malloc()</function> function allocates
<parameter>size</parameter> bytes of uninitialized memory. The allocated
space is suitably aligned (after possible pointer coercion) for storage
of any type of object.</para>
<para>The <function>calloc()</function> function allocates
space for <parameter>number</parameter> objects, each
<parameter>size</parameter> bytes in length. The result is identical to
calling <function>malloc()</function> with an argument of
<parameter>number</parameter> * <parameter>size</parameter>, with the
exception that the allocated memory is explicitly initialized to zero
bytes.</para>
<para>The <function>posix_memalign()</function> function
allocates <parameter>size</parameter> bytes of memory such that the
allocation's base address is a multiple of
<parameter>alignment</parameter>, and returns the allocation in the value
pointed to by <parameter>ptr</parameter>. The requested
<parameter>alignment</parameter> must be a power of 2 at least as large as
<code language="C">sizeof(<type>void *</type>)</code>.</para>
<para>The <function>aligned_alloc()</function> function
allocates <parameter>size</parameter> bytes of memory such that the
allocation's base address is a multiple of
<parameter>alignment</parameter>. The requested
<parameter>alignment</parameter> must be a power of 2. Behavior is
undefined if <parameter>size</parameter> is not an integral multiple of
<parameter>alignment</parameter>.</para>
<para>The <function>realloc()</function> function changes the
size of the previously allocated memory referenced by
<parameter>ptr</parameter> to <parameter>size</parameter> 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 <parameter>ptr</parameter> is freed and a pointer to the newly
allocated memory is returned. Note that
<function>realloc()</function> may move the memory allocation,
resulting in a different return value than <parameter>ptr</parameter>.
If <parameter>ptr</parameter> is <constant>NULL</constant>, the
<function>realloc()</function> function behaves identically to
<function>malloc()</function> for the specified size.</para>
<para>The <function>free()</function> function causes the
allocated memory referenced by <parameter>ptr</parameter> to be made
available for future allocations. If <parameter>ptr</parameter> is
<constant>NULL</constant>, no action occurs.</para>
<para>The <function>free_sized()</function> function is an extension of
<function>free()</function> with a <parameter>size</parameter> parameter
to allow the caller to pass in the allocation size as an optimization.
</para>
<para>The <function>free_aligned_sized()</function> function accepts a
<parameter>ptr</parameter> which was allocated with a requested
<parameter>size</parameter> and <parameter>alignment</parameter>, causing
the allocated memory referenced by <parameter>ptr</parameter> to be made
available for future allocations.</para>
</refsect2>
<refsect2>
<title>Non-standard API</title>
<para>The <function>mallocx()</function>,
<function>rallocx()</function>,
<function>xallocx()</function>,
<function>sallocx()</function>,
<function>dallocx()</function>,
<function>sdallocx()</function>, and
<function>nallocx()</function> functions all have a
<parameter>flags</parameter> argument that can be used to specify
options. The functions only check the options that are contextually
relevant. Use bitwise or (<code language="C">|</code>) operations to
specify one or more of the following:
<variablelist>
<varlistentry id="MALLOCX_LG_ALIGN">
<term><constant>MALLOCX_LG_ALIGN(<parameter>la</parameter>)
</constant></term>
<listitem><para>Align the memory allocation to start at an address
that is a multiple of <code language="C">(1 &lt;&lt;
<parameter>la</parameter>)</code>. This macro does not validate
that <parameter>la</parameter> is within the valid
range.</para></listitem>
</varlistentry>
<varlistentry id="MALLOCX_ALIGN">
<term><constant>MALLOCX_ALIGN(<parameter>a</parameter>)
</constant></term>
<listitem><para>Align the memory allocation to start at an address
that is a multiple of <parameter>a</parameter>, where
<parameter>a</parameter> is a power of two. This macro does not
validate that <parameter>a</parameter> is a power of 2.
</para></listitem>
</varlistentry>
<varlistentry id="MALLOCX_ZERO">
<term><constant>MALLOCX_ZERO</constant></term>
<listitem><para>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.</para></listitem>
</varlistentry>
<varlistentry id="MALLOCX_TCACHE">
<term><constant>MALLOCX_TCACHE(<parameter>tc</parameter>)
</constant></term>
<listitem><para>Use the thread-specific cache (tcache) specified by
the identifier <parameter>tc</parameter>, which must have been
acquired via the <link
linkend="tcache.create"><mallctl>tcache.create</mallctl></link>
mallctl. This macro does not validate that
<parameter>tc</parameter> specifies a valid
identifier.</para></listitem>
</varlistentry>
<varlistentry id="MALLOC_TCACHE_NONE">
<term><constant>MALLOCX_TCACHE_NONE</constant></term>
<listitem><para>Do not use a thread-specific cache (tcache). Unless
<constant>MALLOCX_TCACHE(<parameter>tc</parameter>)</constant> or
<constant>MALLOCX_TCACHE_NONE</constant> is specified, an
automatically managed tcache will be used under many circumstances.
This macro cannot be used in the same <parameter>flags</parameter>
argument as
<constant>MALLOCX_TCACHE(<parameter>tc</parameter>)</constant>.</para></listitem>
</varlistentry>
<varlistentry id="MALLOCX_ARENA">
<term><constant>MALLOCX_ARENA(<parameter>a</parameter>)
</constant></term>
<listitem><para>Use the arena specified by the index
<parameter>a</parameter>. This macro has no effect for regions that
were allocated via an arena other than the one specified. This
macro does not validate that <parameter>a</parameter> specifies an
arena index in the valid range.</para></listitem>
</varlistentry>
</variablelist>
</para>
<para>The <function>mallocx()</function> function allocates at
least <parameter>size</parameter> bytes of memory, and returns a pointer
to the base address of the allocation. Behavior is undefined if
<parameter>size</parameter> is <constant>0</constant>.</para>
<para>The <function>rallocx()</function> function resizes the
allocation at <parameter>ptr</parameter> to be at least
<parameter>size</parameter> 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
<parameter>size</parameter> is <constant>0</constant>.</para>
<para>The <function>xallocx()</function> function resizes the
allocation at <parameter>ptr</parameter> in place to be at least
<parameter>size</parameter> bytes, and returns the real size of the
allocation. If <parameter>extra</parameter> is non-zero, an attempt is
made to resize the allocation to be at least <code
language="C">(<parameter>size</parameter> +
<parameter>extra</parameter>)</code> bytes, though inability to allocate
the extra byte(s) will not by itself result in failure to resize.
Behavior is undefined if <parameter>size</parameter> is
<constant>0</constant>, or if <code
language="C">(<parameter>size</parameter> + <parameter>extra</parameter>
&gt; <constant>SIZE_T_MAX</constant>)</code>.</para>
<para>The <function>sallocx()</function> function returns the
real size of the allocation at <parameter>ptr</parameter>.</para>
<para>The <function>dallocx()</function> function causes the
memory referenced by <parameter>ptr</parameter> to be made available for
future allocations.</para>
<para>The <function>sdallocx()</function> function is an
extension of <function>dallocx()</function> with a
<parameter>size</parameter> 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
<function>nallocx()</function> or
<function>sallocx()</function>.</para>
<para>The <function>nallocx()</function> function allocates no
memory, but it performs the same size computation as the
<function>mallocx()</function> function, and returns the real
size of the allocation that would result from the equivalent
<function>mallocx()</function> function call, or
<constant>0</constant> if the inputs exceed the maximum supported size
class and/or alignment. Behavior is undefined if
<parameter>size</parameter> is <constant>0</constant>.</para>
<para>The <function>mallctl()</function> function provides a
general interface for introspecting the memory allocator, as well as
setting modifiable parameters and triggering actions. The
period-separated <parameter>name</parameter> argument specifies a
location in a tree-structured namespace; see the <xref
linkend="mallctl_namespace" xrefstyle="template:%t"/> section for
documentation on the tree contents. To read a value, pass a pointer via
<parameter>oldp</parameter> to adequate space to contain the value, and a
pointer to its length via <parameter>oldlenp</parameter>; otherwise pass
<constant>NULL</constant> and <constant>NULL</constant>. Similarly, to
write a value, pass a pointer to the value via
<parameter>newp</parameter>, and its length via
<parameter>newlen</parameter>; otherwise pass <constant>NULL</constant>
and <constant>0</constant>.</para>
<para>The <function>mallctlnametomib()</function> 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 <quote>Management Information Base</quote> (MIB) that can be passed
repeatedly to <function>mallctlbymib()</function>. Upon
successful return from <function>mallctlnametomib()</function>,
<parameter>mibp</parameter> contains an array of
<parameter>*miblenp</parameter> integers, where
<parameter>*miblenp</parameter> is the lesser of the number of components
in <parameter>name</parameter> and the input value of
<parameter>*miblenp</parameter>. Thus it is possible to pass a
<parameter>*miblenp</parameter> 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
<link
linkend="arenas.bin.i.size"><mallctl>arenas.bin.2.size</mallctl></link>),
the corresponding MIB component will always be that integer. Therefore,
it is legitimate to construct code like the following: <programlisting
language="C"><![CDATA[
unsigned nbins, i;
size_t mib[4];
size_t len, miblen;
len = sizeof(nbins);
mallctl("arenas.nbins", &nbins, &len, NULL, 0);
miblen = 4;
mallctlnametomib("arenas.bin.0.size", mib, &miblen);
for (i = 0; i < nbins; i++) {
size_t bin_size;
mib[2] = i;
len = sizeof(bin_size);
mallctlbymib(mib, miblen, (void *)&bin_size, &len, NULL, 0);
/* Do something with bin_size... */
}]]></programlisting></para>
<varlistentry id="malloc_stats_print_opts">
</varlistentry>
<para>The <function>malloc_stats_print()</function> function writes
summary statistics via the <parameter>write_cb</parameter> callback
function pointer and <parameter>cbopaque</parameter> data passed to
<parameter>write_cb</parameter>, or <function>malloc_message()</function>
if <parameter>write_cb</parameter> is <constant>NULL</constant>. The
statistics are presented in human-readable form unless <quote>J</quote> is
specified as a character within the <parameter>opts</parameter> string, in
which case the statistics are presented in <ulink
url="http://www.json.org/">JSON format</ulink>. This function can be
called repeatedly. General information that never changes during
execution can be omitted by specifying <quote>g</quote> as a character
within the <parameter>opts</parameter> string. Note that
<function>malloc_stats_print()</function> uses the
<function>mallctl*()</function> functions internally, so inconsistent
statistics can be reported if multiple threads use these functions
simultaneously. If <option>--enable-stats</option> is specified during
configuration, <quote>m</quote>, <quote>d</quote>, and <quote>a</quote>
can be specified to omit merged arena, destroyed merged arena, and per
arena statistics, respectively; <quote>b</quote> and <quote>l</quote> can
be specified to omit per size class statistics for bins and large objects,
respectively; <quote>x</quote> can be specified to omit all mutex
statistics; <quote>e</quote> 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.</para>
<para>The <function>malloc_usable_size()</function> function
returns the usable size of the allocation pointed to by
<parameter>ptr</parameter>. The return value may be larger than the size
that was requested during allocation. The
<function>malloc_usable_size()</function> function is not a
mechanism for in-place <function>realloc()</function>; rather
it is provided solely as a tool for introspection purposes. Any
discrepancy between the requested allocation size and the size reported
by <function>malloc_usable_size()</function> should not be
depended on, since such behavior is entirely implementation-dependent.
</para>
</refsect2>
<refsect2>
<title>Interactions Between the Standard and Non-standard APIs</title>
<para>Generally speaking it is permissible to pass pointers obtained from
the standard API to the non-standard API and vice versa (e.g. calling
<function>free()</function> with a pointer returned by a call to
<function>mallocx()</function>, calling <function>sdallocx()</function>
with a pointer returned by a call to <function>calloc()</function>).
There are however a few exceptions. In keeping with the C23 standard –
which forbids calling <function>free_sized()</function> on a pointer
returned by <function>aligned_alloc()</function>, mandating that either
<function>free_aligned_sized()</function> or <function>free()</function>
be used instead – using any combination of the standard and non-standard
APIs in an equivalent fashion (i.e. taking a pointer which was allocated
with an explicitly requested alignment and attempting to free it via an
API that accepts a size hint, without also providing the alignment hint)
is likewise forbidden.
</para>
</refsect2>
</refsect1>
<refsect1 id="tuning">
<title>TUNING</title>
<para>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.</para>
<para>The string specified via <option>--with-malloc-conf</option>, the
string pointed to by the global variable <varname>malloc_conf</varname>, the
<quote>name</quote> of the file referenced by the symbolic link named
<filename class="symlink">/etc/malloc.conf</filename>, and the value of the
environment variable <envar>MALLOC_CONF</envar>, will be interpreted, in
that order, from left to right as options. Note that
<varname>malloc_conf</varname> may be read before
<function>main()</function> is entered, so the declaration of
<varname>malloc_conf</varname> should specify an initializer that contains
the final value to be read by jemalloc. <option>--with-malloc-conf</option>
and <varname>malloc_conf</varname> are compile-time mechanisms, whereas
<filename class="symlink">/etc/malloc.conf</filename> and
<envar>MALLOC_CONF</envar> can be safely set any time prior to program
invocation.</para>
<para>An options string is a comma-separated list of option:value pairs.
There is one key corresponding to each <link
linkend="opt.abort"><mallctl>opt.*</mallctl></link> mallctl (see the <xref
linkend="mallctl_namespace" xrefstyle="template:%t"/> section for options
documentation). For example, <literal>abort:true,narenas:1</literal> sets
the <link linkend="opt.abort"><mallctl>opt.abort</mallctl></link> and <link
linkend="opt.narenas"><mallctl>opt.narenas</mallctl></link> 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.</para>
</refsect1>
<refsect1 id="implementation_notes">
<title>IMPLEMENTATION NOTES</title>
<para>Traditionally, allocators have used
<citerefentry><refentrytitle>sbrk</refentrytitle>
<manvolnum>2</manvolnum></citerefentry> to obtain memory, which is
suboptimal for several reasons, including race conditions, increased
fragmentation, and artificial limitations on maximum usable memory. If
<citerefentry><refentrytitle>sbrk</refentrytitle>
<manvolnum>2</manvolnum></citerefentry> is supported by the operating
system, this allocator uses both
<citerefentry><refentrytitle>mmap</refentrytitle>
<manvolnum>2</manvolnum></citerefentry> and
<citerefentry><refentrytitle>sbrk</refentrytitle>
<manvolnum>2</manvolnum></citerefentry>, in that order of preference;
otherwise only <citerefentry><refentrytitle>mmap</refentrytitle>
<manvolnum>2</manvolnum></citerefentry> is used.</para>
<para>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.</para>
<para>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.</para>
<para>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.</para>
<para>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
language="C">sizeof(<type>double</type>)</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 <constant>PTRDIFF_MAX</constant>.</para>
<para>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.</para>
<para>The <function>realloc()</function>,
<function>rallocx()</function>, and
<function>xallocx()</function> functions may resize allocations
without moving them under limited circumstances. Unlike the
<function>*allocx()</function> 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
<function>realloc()</function> 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
<link
linkend="arena.i.extent_hooks"><mallctl>arena.&lt;i&gt;.extent_hooks</mallctl></link>).
Growth only succeeds if the trailing memory is currently available, and the
extent allocator supports merging.</para>
<para>Assuming 4 KiB pages and a 16-byte quantum on a 64-bit system, the
size classes in each category are as shown in <xref linkend="size_classes"
xrefstyle="template:Table %n"/>.</para>
<table xml:id="size_classes" frame="all">
<title>Size classes</title>
<tgroup cols="3" colsep="1" rowsep="1">
<colspec colname="c1" align="left"/>
<colspec colname="c2" align="right"/>
<colspec colname="c3" align="left"/>
<thead>
<row>
<entry>Category</entry>
<entry>Spacing</entry>
<entry>Size</entry>
</row>
</thead>
<tbody>
<row>
<entry morerows="8">Small</entry>
<entry>lg</entry>
<entry>[8]</entry>
</row>
<row>
<entry>16</entry>
<entry>[16, 32, 48, 64, 80, 96, 112, 128]</entry>
</row>
<row>
<entry>32</entry>
<entry>[160, 192, 224, 256]</entry>
</row>
<row>
<entry>64</entry>
<entry>[320, 384, 448, 512]</entry>
</row>
<row>
<entry>128</entry>
<entry>[640, 768, 896, 1024]</entry>
</row>
<row>
<entry>256</entry>
<entry>[1280, 1536, 1792, 2048]</entry>
</row>
<row>
<entry>512</entry>
<entry>[2560, 3072, 3584, 4096]</entry>
</row>
<row>
<entry>1 KiB</entry>
<entry>[5 KiB, 6 KiB, 7 KiB, 8 KiB]</entry>
</row>
<row>
<entry>2 KiB</entry>
<entry>[10 KiB, 12 KiB, 14 KiB]</entry>
</row>
<row>
<entry morerows="15">Large</entry>
<entry>2 KiB</entry>
<entry>[16 KiB]</entry>
</row>
<row>
<entry>4 KiB</entry>
<entry>[20 KiB, 24 KiB, 28 KiB, 32 KiB]</entry>
</row>
<row>
<entry>8 KiB</entry>
<entry>[40 KiB, 48 KiB, 56 KiB, 64 KiB]</entry>
</row>
<row>
<entry>16 KiB</entry>
<entry>[80 KiB, 96 KiB, 112 KiB, 128 KiB]</entry>
</row>
<row>
<entry>32 KiB</entry>
<entry>[160 KiB, 192 KiB, 224 KiB, 256 KiB]</entry>
</row>
<row>
<entry>64 KiB</entry>
<entry>[320 KiB, 384 KiB, 448 KiB, 512 KiB]</entry>
</row>
<row>
<entry>128 KiB</entry>
<entry>[640 KiB, 768 KiB, 896 KiB, 1 MiB]</entry>
</row>
<row>
<entry>256 KiB</entry>
<entry>[1280 KiB, 1536 KiB, 1792 KiB, 2 MiB]</entry>
</row>
<row>
<entry>512 KiB</entry>
<entry>[2560 KiB, 3 MiB, 3584 KiB, 4 MiB]</entry>
</row>
<row>
<entry>1 MiB</entry>
<entry>[5 MiB, 6 MiB, 7 MiB, 8 MiB]</entry>
</row>
<row>
<entry>2 MiB</entry>
<entry>[10 MiB, 12 MiB, 14 MiB, 16 MiB]</entry>
</row>
<row>
<entry>4 MiB</entry>
<entry>[20 MiB, 24 MiB, 28 MiB, 32 MiB]</entry>
</row>
<row>
<entry>8 MiB</entry>
<entry>[40 MiB, 48 MiB, 56 MiB, 64 MiB]</entry>
</row>
<row>
<entry>...</entry>
<entry>...</entry>
</row>
<row>
<entry>512 PiB</entry>
<entry>[2560 PiB, 3 EiB, 3584 PiB, 4 EiB]</entry>
</row>
<row>
<entry>1 EiB</entry>
<entry>[5 EiB, 6 EiB, 7 EiB]</entry>
</row>
</tbody>
</tgroup>
</table>
</refsect1>
<refsect1 id="mallctl_namespace">
<title>MALLCTL NAMESPACE</title>
<para>The following names are defined in the namespace accessible via the
<function>mallctl*()</function> functions. Value types are specified in
parentheses, their readable/writable statuses are encoded as
<literal>rw</literal>, <literal>r-</literal>, <literal>-w</literal>, or
<literal>--</literal>, and required build configuration flags follow, if
any. A name element encoded as <literal>&lt;i&gt;</literal> or
<literal>&lt;j&gt;</literal> indicates an integer component, where the
integer varies from 0 to some upper value that must be determined via
introspection. In the case of <mallctl>stats.arenas.&lt;i&gt;.*</mallctl>
and <mallctl>arena.&lt;i&gt;.{initialized,purge,decay,dss}</mallctl>,
<literal>&lt;i&gt;</literal> equal to
<constant>MALLCTL_ARENAS_ALL</constant> can be used to operate on all arenas
or access the summation of statistics from all arenas; similarly
<literal>&lt;i&gt;</literal> equal to
<constant>MALLCTL_ARENAS_DESTROYED</constant> can be used to access the
summation of statistics from all destroyed arenas. These constants can be
utilized either via <function>mallctlnametomib()</function> followed by
<function>mallctlbymib()</function>, or via code such as the following:
<programlisting language="C"><![CDATA[
#define STRINGIFY_HELPER(x) #x
#define STRINGIFY(x) STRINGIFY_HELPER(x)
mallctl("arena." STRINGIFY(MALLCTL_ARENAS_ALL) ".decay",
NULL, NULL, NULL, 0);]]></programlisting>
Take special note of the <link
linkend="epoch"><mallctl>epoch</mallctl></link> mallctl, which controls
refreshing of cached dynamic statistics.</para>
<variablelist>
<varlistentry id="version">
<term>
<mallctl>version</mallctl>
(<type>const char *</type>)
<literal>r-</literal>
</term>
<listitem><para>Return the jemalloc version string.</para></listitem>
</varlistentry>
<varlistentry id="epoch">
<term>
<mallctl>epoch</mallctl>
(<type>uint64_t</type>)
<literal>rw</literal>
</term>
<listitem><para>If a value is passed in, refresh the data from which
the <function>mallctl*()</function> functions report values,
and increment the epoch. Return the current epoch. This is useful for
detecting whether another thread caused a refresh.</para></listitem>
</varlistentry>
<varlistentry id="background_thread">
<term>
<mallctl>background_thread</mallctl>
(<type>bool</type>)
<literal>rw</literal>
</term>
<listitem><para>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 <link
linkend="arena.i.decay">purging</link> asynchronously. When switching
off, background threads are terminated synchronously. Note that after
<citerefentry><refentrytitle>fork</refentrytitle><manvolnum>2</manvolnum></citerefentry>
function, the state in the child process will be disabled regardless
the state in parent process. See <link
linkend="stats.background_thread.num_threads"><mallctl>stats.background_thread</mallctl></link>
for related stats. <link
linkend="opt.background_thread"><mallctl>opt.background_thread</mallctl></link>
can be used to set the default option. This option is only available on
selected pthread-based platforms.</para></listitem>
</varlistentry>
<varlistentry id="max_background_threads">
<term>
<mallctl>max_background_threads</mallctl>
(<type>size_t</type>)
<literal>rw</literal>
</term>
<listitem><para>Maximum number of background worker threads that will
be created. This value is capped at <link
linkend="opt.max_background_threads"><mallctl>opt.max_background_threads</mallctl></link> at
startup.</para></listitem>
</varlistentry>
<varlistentry id="config.cache_oblivious">
<term>
<mallctl>config.cache_oblivious</mallctl>
(<type>bool</type>)
<literal>r-</literal>
</term>
<listitem><para><option>--enable-cache-oblivious</option> was specified
during build configuration.</para></listitem>
</varlistentry>
<varlistentry id="config.debug">
<term>
<mallctl>config.debug</mallctl>
(<type>bool</type>)
<literal>r-</literal>
</term>
<listitem><para><option>--enable-debug</option> was specified during
build configuration.</para></listitem>
</varlistentry>
<varlistentry id="config.fill">
<term>
<mallctl>config.fill</mallctl>
(<type>bool</type>)
<literal>r-</literal>
</term>
<listitem><para><option>--enable-fill</option> was specified during
build configuration.</para></listitem>
</varlistentry>
<varlistentry id="config.lazy_lock">
<term>
<mallctl>config.lazy_lock</mallctl>
(<type>bool</type>)
<literal>r-</literal>
</term>
<listitem><para><option>--enable-lazy-lock</option> was specified
during build configuration.</para></listitem>
</varlistentry>
<varlistentry id="config.malloc_conf">
<term>
<mallctl>config.malloc_conf</mallctl>
(<type>const char *</type>)
<literal>r-</literal>
</term>
<listitem><para>Embedded configure-time-specified run-time options
string, empty unless <option>--with-malloc-conf</option> was specified
during build configuration.</para></listitem>
</varlistentry>
<varlistentry id="config.prof">
<term>
<mallctl>config.prof</mallctl>
(<type>bool</type>)
<literal>r-</literal>
</term>
<listitem><para><option>--enable-prof</option> was specified during
build configuration.</para></listitem>
</varlistentry>
<varlistentry id="config.prof_libgcc">
<term>
<mallctl>config.prof_libgcc</mallctl>
(<type>bool</type>)
<literal>r-</literal>
</term>
<listitem><para><option>--disable-prof-libgcc</option> was not
specified during build configuration.</para></listitem>
</varlistentry>
<varlistentry id="config.prof_libunwind">
<term>
<mallctl>config.prof_libunwind</mallctl>
(<type>bool</type>)
<literal>r-</literal>
</term>
<listitem><para><option>--enable-prof-libunwind</option> was specified
during build configuration.</para></listitem>
</varlistentry>
<varlistentry id="config.stats">
<term>
<mallctl>config.stats</mallctl>
(<type>bool</type>)
<literal>r-</literal>
</term>
<listitem><para><option>--enable-stats</option> was specified during
build configuration.</para></listitem>
</varlistentry>
<varlistentry id="config.utrace">
<term>
<mallctl>config.utrace</mallctl>
(<type>bool</type>)
<literal>r-</literal>
</term>
<listitem><para><option>--enable-utrace</option> was specified during
build configuration.</para></listitem>
</varlistentry>
<varlistentry id="config.xmalloc">
<term>
<mallctl>config.xmalloc</mallctl>
(<type>bool</type>)
<literal>r-</literal>
</term>
<listitem><para><option>--enable-xmalloc</option> was specified during
build configuration.</para></listitem>
</varlistentry>
<varlistentry id="opt.abort">
<term>
<mallctl>opt.abort</mallctl>
(<type>bool</type>)
<literal>r-</literal>
</term>
<listitem><para>Abort-on-warning enabled/disabled. If true, most
warnings are fatal. Note that runtime option warnings are not included
(see <link
linkend="opt.abort_conf"><mallctl>opt.abort_conf</mallctl></link> for
that). The process will call
<citerefentry><refentrytitle>abort</refentrytitle>
<manvolnum>3</manvolnum></citerefentry> in these cases. This option is
disabled by default unless <option>--enable-debug</option> is
specified during configuration, in which case it is enabled by default.
</para></listitem>
</varlistentry>
<varlistentry id="opt.confirm_conf">
<term>
<mallctl>opt.confirm_conf</mallctl>
(<type>bool</type>)
<literal>r-</literal>
</term>
<listitem><para>Confirm-runtime-options-when-program-starts
enabled/disabled. If true, the string specified via
<option>--with-malloc-conf</option>, the string pointed to by the
global variable <varname>malloc_conf</varname>, the <quote>name</quote>
of the file referenced by the symbolic link named
<filename class="symlink">/etc/malloc.conf</filename>, and the value of
the environment variable <envar>MALLOC_CONF</envar>, will be printed in
order. Then, each option being set will be individually printed. This
option is disabled by default.</para></listitem>
</varlistentry>
<varlistentry id="opt.abort_conf">
<term>
<mallctl>opt.abort_conf</mallctl>
(<type>bool</type>)
<literal>r-</literal>
</term>
<listitem><para>Abort-on-invalid-configuration enabled/disabled. If
true, invalid runtime options are fatal. The process will call
<citerefentry><refentrytitle>abort</refentrytitle>
<manvolnum>3</manvolnum></citerefentry> in these cases. This option is
disabled by default unless <option>--enable-debug</option> is
specified during configuration, in which case it is enabled by default.
</para></listitem>
</varlistentry>
<varlistentry id="opt.cache_oblivious">
<term>
<mallctl>opt.cache_oblivious</mallctl>
(<type>bool</type>)
<literal>r-</literal>
</term>
<listitem><para>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.</para></listitem>
</varlistentry>
<varlistentry id="opt.metadata_thp">
<term>
<mallctl>opt.metadata_thp</mallctl>
(<type>const char *</type>)
<literal>r-</literal>
</term>
<listitem><para>Controls whether to allow jemalloc to use transparent
huge page (THP) for internal metadata (see <link
linkend="stats.metadata">stats.metadata</link>). <quote>always</quote>
allows such usage. <quote>auto</quote> uses no THP initially, but may
begin to do so when metadata usage reaches certain level. The default
is <quote>disabled</quote>.</para></listitem>
</varlistentry>
<varlistentry id="opt.trust_madvise">
<term>
<mallctl>opt.trust_madvise</mallctl>
(<type>bool</type>)
<literal>r-</literal>
</term>
<listitem><para>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.</para></listitem>
</varlistentry>
<varlistentry id="opt.retain">
<term>
<mallctl>opt.retain</mallctl>
(<type>bool</type>)
<literal>r-</literal>
</term>
<listitem><para>If true, retain unused virtual memory for later reuse
rather than discarding it by calling
<citerefentry><refentrytitle>munmap</refentrytitle>
<manvolnum>2</manvolnum></citerefentry> or equivalent (see <link
linkend="stats.retained">stats.retained</link> for related details).
It also makes jemalloc use <citerefentry>
<refentrytitle>mmap</refentrytitle><manvolnum>2</manvolnum>
</citerefentry> 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
<parameter><constant>MEM_RELEASE</constant></parameter>. 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. </para></listitem>
</varlistentry>
<varlistentry id="opt.dss">
<term>
<mallctl>opt.dss</mallctl>
(<type>const char *</type>)
<literal>r-</literal>
</term>
<listitem><para>dss (<citerefentry><refentrytitle>sbrk</refentrytitle>
<manvolnum>2</manvolnum></citerefentry>) allocation precedence as
related to <citerefentry><refentrytitle>mmap</refentrytitle>
<manvolnum>2</manvolnum></citerefentry> allocation. The following
settings are supported if
<citerefentry><refentrytitle>sbrk</refentrytitle>
<manvolnum>2</manvolnum></citerefentry> is supported by the operating
system: <quote>disabled</quote>, <quote>primary</quote>, and
<quote>secondary</quote>; otherwise only <quote>disabled</quote> is
supported. The default is <quote>secondary</quote> if
<citerefentry><refentrytitle>sbrk</refentrytitle>
<manvolnum>2</manvolnum></citerefentry> is supported by the operating
system; <quote>disabled</quote> otherwise.
</para></listitem>
</varlistentry>
<varlistentry id="opt.narenas">
<term>
<mallctl>opt.narenas</mallctl>
(<type>unsigned</type>)
<literal>r-</literal>
</term>
<listitem><para>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.</para></listitem>
</varlistentry>
<varlistentry id="opt.oversize_threshold">
<term>
<mallctl>opt.oversize_threshold</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
</term>
<listitem><para>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
<literal>narenas</literal>), 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
<constant>MALLOCX_ARENA</constant>, or threads associated with explicit
arenas will not be considered. The default threshold is 8MiB. Values
not within large size classes disables this feature.</para></listitem>
</varlistentry>
<varlistentry id="opt.percpu_arena">
<term>
<mallctl>opt.percpu_arena</mallctl>
(<type>const char *</type>)
<literal>r-</literal>
</term>
<listitem><para>Per CPU arena mode. Use the <quote>percpu</quote>
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. <quote>phycpu</quote> 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
<quote>disabled</quote>, narenas and thread to arena association will
not be impacted by this option. The default is <quote>disabled</quote>.
</para></listitem>
</varlistentry>
<varlistentry id="opt.background_thread">
<term>
<mallctl>opt.background_thread</mallctl>
(<type>bool</type>)
<literal>r-</literal>
</term>
<listitem><para>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 <link
linkend="background_thread">background_thread</link> for dynamic control
options and details. This option is disabled by
default.</para></listitem>
</varlistentry>
<varlistentry id="opt.max_background_threads">
<term>
<mallctl>opt.max_background_threads</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
</term>
<listitem><para>Maximum number of background threads that will be created
if <link linkend="background_thread">background_thread</link> is set.
Defaults to number of cpus.</para></listitem>
</varlistentry>
<varlistentry id="opt.dirty_decay_ms">
<term>
<mallctl>opt.dirty_decay_ms</mallctl>
(<type>ssize_t</type>)
<literal>r-</literal>
</term>
<listitem><para>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.
<function>madvise(<parameter>...</parameter><parameter><constant>MADV_FREE</constant></parameter>)</function>
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 <link
linkend="arenas.dirty_decay_ms"><mallctl>arenas.dirty_decay_ms</mallctl></link>
and <link
linkend="arena.i.dirty_decay_ms"><mallctl>arena.&lt;i&gt;.dirty_decay_ms</mallctl></link>
for related dynamic control options. See <link
linkend="opt.muzzy_decay_ms"><mallctl>opt.muzzy_decay_ms</mallctl></link>
for a description of muzzy pages. Note that when the <link linkend="opt.oversize_threshold"><mallctl>oversize_threshold</mallctl></link>
feature is enabled, the arenas reserved for oversize requests may have
its own default decay settings.</para></listitem>
</varlistentry>
<varlistentry id="opt.muzzy_decay_ms">
<term>
<mallctl>opt.muzzy_decay_ms</mallctl>
(<type>ssize_t</type>)
<literal>r-</literal>
</term>
<listitem><para>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.
<function>madvise(<parameter>...</parameter><parameter><constant>MADV_FREE</constant></parameter>)</function>),
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 <link
linkend="arenas.muzzy_decay_ms"><mallctl>arenas.muzzy_decay_ms</mallctl></link>
and <link
linkend="arena.i.muzzy_decay_ms"><mallctl>arena.&lt;i&gt;.muzzy_decay_ms</mallctl></link>
for related dynamic control options.</para></listitem>
</varlistentry>
<varlistentry id="opt.lg_extent_max_active_fit">
<term>
<mallctl>opt.lg_extent_max_active_fit</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
</term>
<listitem><para>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).</para></listitem>
</varlistentry>
<varlistentry id="opt.stats_print">
<term>
<mallctl>opt.stats_print</mallctl>
(<type>bool</type>)
<literal>r-</literal>
</term>
<listitem><para>Enable/disable statistics printing at exit. If
enabled, the <function>malloc_stats_print()</function>
function is called at program exit via an
<citerefentry><refentrytitle>atexit</refentrytitle>
<manvolnum>3</manvolnum></citerefentry> function. <link
linkend="opt.stats_print_opts"><mallctl>opt.stats_print_opts</mallctl></link>
can be combined to specify output options. If
<option>--enable-stats</option> 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, <function>atexit()</function> may
allocate memory during application initialization and then deadlock
internally when jemalloc in turn calls
<function>atexit()</function>, so this option is not
universally usable (though the application can register its own
<function>atexit()</function> 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.</para></listitem>
</varlistentry>
<varlistentry id="opt.stats_print_opts">
<term>
<mallctl>opt.stats_print_opts</mallctl>
(<type>const char *</type>)
<literal>r-</literal>
</term>
<listitem><para>Options (the <parameter>opts</parameter> string) to pass
to the <function>malloc_stats_print()</function> at exit (enabled
through <link
linkend="opt.stats_print"><mallctl>opt.stats_print</mallctl></link>). See
available options in <link
linkend="malloc_stats_print_opts"><function>malloc_stats_print()</function></link>.
Has no effect unless <link
linkend="opt.stats_print"><mallctl>opt.stats_print</mallctl></link> is
enabled. The default is <quote></quote>.</para></listitem>
</varlistentry>
<varlistentry id="opt.stats_interval">
<term>
<mallctl>opt.stats_interval</mallctl>
(<type>int64_t</type>)
<literal>r-</literal>
</term>
<listitem><para>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 <function>malloc_stats_print()</function>. <link
linkend="opt.stats_interval_opts"><mallctl>opt.stats_interval_opts</mallctl></link>
can be combined to specify output options. By default,
interval-triggered stats output is disabled (encoded as
-1).</para></listitem>
</varlistentry>
<varlistentry id="opt.stats_interval_opts">
<term>
<mallctl>opt.stats_interval_opts</mallctl>
(<type>const char *</type>)
<literal>r-</literal>
</term>
<listitem><para>Options (the <parameter>opts</parameter> string) to pass
to the <function>malloc_stats_print()</function> for interval based
statistics printing (enabled
through <link
linkend="opt.stats_interval"><mallctl>opt.stats_interval</mallctl></link>). See
available options in <link
linkend="malloc_stats_print_opts"><function>malloc_stats_print()</function></link>.
Has no effect unless <link
linkend="opt.stats_interval"><mallctl>opt.stats_interval</mallctl></link> is
enabled. The default is <quote></quote>.</para></listitem>
</varlistentry>
<varlistentry id="opt.junk">
<term>
<mallctl>opt.junk</mallctl>
(<type>const char *</type>)
<literal>r-</literal>
[<option>--enable-fill</option>]
</term>
<listitem><para>Junk filling. If set to <quote>alloc</quote>, each byte
of uninitialized allocated memory will be initialized to
<literal>0xa5</literal>. If set to <quote>free</quote>, all deallocated
memory will be initialized to <literal>0x5a</literal>. If set to
<quote>true</quote>, both allocated and deallocated memory will be
initialized, and if set to <quote>false</quote>, junk filling be
disabled entirely. This is intended for debugging and will impact
performance negatively. This option is <quote>false</quote> by default
unless <option>--enable-debug</option> is specified during
configuration, in which case it is <quote>true</quote> by
default.</para></listitem>
</varlistentry>
<varlistentry id="opt.zero">
<term>
<mallctl>opt.zero</mallctl>
(<type>bool</type>)
<literal>r-</literal>
[<option>--enable-fill</option>]
</term>
<listitem><para>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
<function>realloc()</function> and
<function>rallocx()</function> 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.
</para></listitem>
</varlistentry>
<varlistentry id="opt.utrace">
<term>
<mallctl>opt.utrace</mallctl>
(<type>bool</type>)
<literal>r-</literal>
[<option>--enable-utrace</option>]
</term>
<listitem><para>Allocation tracing based on
<citerefentry><refentrytitle>utrace</refentrytitle>
<manvolnum>2</manvolnum></citerefentry> enabled/disabled. This option
is disabled by default.</para></listitem>
</varlistentry>
<varlistentry id="opt.xmalloc">
<term>
<mallctl>opt.xmalloc</mallctl>
(<type>bool</type>)
<literal>r-</literal>
[<option>--enable-xmalloc</option>]
</term>
<listitem><para>Abort-on-out-of-memory enabled/disabled. If enabled,
rather than returning failure for any allocation function, display a
diagnostic message on <constant>STDERR_FILENO</constant> and cause the
program to drop core (using
<citerefentry><refentrytitle>abort</refentrytitle>
<manvolnum>3</manvolnum></citerefentry>). If an application is
designed to depend on this behavior, set the option at compile time by
including the following in the source code:
<programlisting language="C"><![CDATA[
malloc_conf = "xmalloc:true";]]></programlisting>
This option is disabled by default.</para></listitem>
</varlistentry>
<varlistentry id="opt.tcache">
<term>
<mallctl>opt.tcache</mallctl>
(<type>bool</type>)
<literal>r-</literal>
</term>
<listitem><para>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 <link
linkend="opt.tcache_max"><mallctl>opt.tcache_max</mallctl></link>
option for related tuning information. This option is enabled by
default.</para></listitem>
</varlistentry>
<varlistentry id="opt.tcache_max">
<term>
<mallctl>opt.tcache_max</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
</term>
<listitem><para>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.</para></listitem>
</varlistentry>
<varlistentry id="opt.thp">
<term>
<mallctl>opt.thp</mallctl>
(<type>const char *</type>)
<literal>r-</literal>
</term>
<listitem><para>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
<parameter><constant>MADV_HUGEPAGE</constant></parameter>; "never"
ensures no transparent hugepage with
<parameter><constant>MADV_NOHUGEPAGE</constant></parameter>; the default
setting "default" makes no changes. Note that: this option does not
affect THP for jemalloc internal metadata (see <link
linkend="opt.metadata_thp"><mallctl>opt.metadata_thp</mallctl></link>);
in addition, for arenas with customized <link
linkend="arena.i.extent_hooks"><mallctl>extent_hooks</mallctl></link>,
this option is bypassed as it is implemented as part of the default
extent hooks.</para></listitem>
</varlistentry>
<varlistentry id="opt.prof">
<term>
<mallctl>opt.prof</mallctl>
(<type>bool</type>)
<literal>r-</literal>
[<option>--enable-prof</option>]
</term>
<listitem><para>Memory profiling enabled/disabled. If enabled, profile
memory allocation activity. See the <link
linkend="opt.prof_active"><mallctl>opt.prof_active</mallctl></link>
option for on-the-fly activation/deactivation. See the <link
linkend="opt.lg_prof_sample"><mallctl>opt.lg_prof_sample</mallctl></link>
option for probabilistic sampling control. See the <link
linkend="opt.prof_accum"><mallctl>opt.prof_accum</mallctl></link>
option for control of cumulative sample reporting. See the <link
linkend="opt.lg_prof_interval"><mallctl>opt.lg_prof_interval</mallctl></link>
option for information on interval-triggered profile dumping, the <link
linkend="opt.prof_gdump"><mallctl>opt.prof_gdump</mallctl></link>
option for information on high-water-triggered profile dumping, and the
<link linkend="opt.prof_final"><mallctl>opt.prof_final</mallctl></link>
option for final profile dumping. Profile output is compatible with
the <command>jeprof</command> command, which is based on the
<command>pprof</command> that is developed as part of the <ulink
url="http://code.google.com/p/gperftools/">gperftools
package</ulink>. See <link linkend="heap_profile_format">HEAP PROFILE
FORMAT</link> for heap profile format documentation.</para></listitem>
</varlistentry>
<varlistentry id="opt.prof_prefix">
<term>
<mallctl>opt.prof_prefix</mallctl>
(<type>const char *</type>)
<literal>r-</literal>
[<option>--enable-prof</option>]
</term>
<listitem><para>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
<filename>jeprof</filename>. This prefix value can be overridden by
<link linkend="prof.prefix"><mallctl>prof.prefix</mallctl></link>.
</para></listitem>
</varlistentry>
<varlistentry id="opt.prof_active">
<term>
<mallctl>opt.prof_active</mallctl>
(<type>bool</type>)
<literal>r-</literal>
[<option>--enable-prof</option>]
</term>
<listitem><para>Profiling activated/deactivated. This is a secondary
control mechanism that makes it possible to start the application with
profiling enabled (see the <link
linkend="opt.prof"><mallctl>opt.prof</mallctl></link> option) but
inactive, then toggle profiling at any time during program execution
with the <link
linkend="prof.active"><mallctl>prof.active</mallctl></link> mallctl.
This option is enabled by default.</para></listitem>
</varlistentry>
<varlistentry id="opt.prof_thread_active_init">
<term>
<mallctl>opt.prof_thread_active_init</mallctl>
(<type>bool</type>)
<literal>r-</literal>
[<option>--enable-prof</option>]
</term>
<listitem><para>Initial setting for <link
linkend="thread.prof.active"><mallctl>thread.prof.active</mallctl></link>
in newly created threads. The initial setting for newly created threads
can also be changed during execution via the <link
linkend="prof.thread_active_init"><mallctl>prof.thread_active_init</mallctl></link>
mallctl. This option is enabled by default.</para></listitem>
</varlistentry>
<varlistentry id="opt.lg_prof_sample">
<term>
<mallctl>opt.lg_prof_sample</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
[<option>--enable-prof</option>]
</term>
<listitem><para>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).</para></listitem>
</varlistentry>
<varlistentry id="opt.prof_accum">
<term>
<mallctl>opt.prof_accum</mallctl>
(<type>bool</type>)
<literal>r-</literal>
[<option>--enable-prof</option>]
</term>
<listitem><para>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.</para></listitem>
</varlistentry>
<varlistentry id="opt.lg_prof_interval">
<term>
<mallctl>opt.lg_prof_interval</mallctl>
(<type>ssize_t</type>)
<literal>r-</literal>
[<option>--enable-prof</option>]
</term>
<listitem><para>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
<filename>&lt;prefix&gt;.&lt;pid&gt;.&lt;seq&gt;.i&lt;iseq&gt;.heap</filename>,
where <literal>&lt;prefix&gt;</literal> is controlled by the
<link
linkend="opt.prof_prefix"><mallctl>opt.prof_prefix</mallctl></link> and
<link linkend="prof.prefix"><mallctl>prof.prefix</mallctl></link>
options. By default, interval-triggered profile dumping is disabled
(encoded as -1).
</para></listitem>
</varlistentry>
<varlistentry id="opt.prof_gdump">
<term>
<mallctl>opt.prof_gdump</mallctl>
(<type>bool</type>)
<literal>r-</literal>
[<option>--enable-prof</option>]
</term>
<listitem><para>Set the initial state of <link
linkend="prof.gdump"><mallctl>prof.gdump</mallctl></link>, which when
enabled triggers a memory profile dump every time the total virtual
memory exceeds the previous maximum. This option is disabled by
default.</para></listitem>
</varlistentry>
<varlistentry id="opt.prof_final">
<term>
<mallctl>opt.prof_final</mallctl>
(<type>bool</type>)
<literal>r-</literal>
[<option>--enable-prof</option>]
</term>
<listitem><para>Use an
<citerefentry><refentrytitle>atexit</refentrytitle>
<manvolnum>3</manvolnum></citerefentry> function to dump final memory
usage to a file named according to the pattern
<filename>&lt;prefix&gt;.&lt;pid&gt;.&lt;seq&gt;.f.heap</filename>,
where <literal>&lt;prefix&gt;</literal> is controlled by the <link
linkend="opt.prof_prefix"><mallctl>opt.prof_prefix</mallctl></link> and
<link linkend="prof.prefix"><mallctl>prof.prefix</mallctl></link>
options. Note that <function>atexit()</function> may allocate
memory during application initialization and then deadlock internally
when jemalloc in turn calls <function>atexit()</function>, so
this option is not universally usable (though the application can
register its own <function>atexit()</function> function with
equivalent functionality). This option is disabled by
default.</para></listitem>
</varlistentry>
<varlistentry id="opt.prof_leak">
<term>
<mallctl>opt.prof_leak</mallctl>
(<type>bool</type>)
<literal>r-</literal>
[<option>--enable-prof</option>]
</term>
<listitem><para>Leak reporting enabled/disabled. If enabled, use an
<citerefentry><refentrytitle>atexit</refentrytitle>
<manvolnum>3</manvolnum></citerefentry> function to report memory leaks
detected by allocation sampling. See the
<link linkend="opt.prof"><mallctl>opt.prof</mallctl></link> option for
information on analyzing heap profile output. Works only when combined
with <link linkend="opt.prof_final"><mallctl>opt.prof_final</mallctl>
</link>, otherwise does nothing. This option is disabled by default.
</para></listitem>
</varlistentry>
<varlistentry id="opt.prof_leak_error">
<term>
<mallctl>opt.prof_leak_error</mallctl>
(<type>bool</type>)
<literal>r-</literal>
[<option>--enable-prof</option>]
</term>
<listitem><para>Similar to <link linkend="opt.prof_leak"><mallctl>
opt.prof_leak</mallctl></link>, but makes the process exit with error
code 1 if a memory leak is detected. This option supersedes
<link linkend="opt.prof_leak"><mallctl>opt.prof_leak</mallctl></link>,
meaning that if both are specified, this option takes precedence. When
enabled, also enables <link linkend="opt.prof_leak"><mallctl>
opt.prof_leak</mallctl></link>. Works only when combined with
<link linkend="opt.prof_final"><mallctl>opt.prof_final</mallctl></link>,
otherwise does nothing. This option is disabled by default.
</para></listitem>
</varlistentry>
<varlistentry id="opt.zero_realloc">
<term>
<mallctl>opt.zero_realloc</mallctl>
(<type>const char *</type>)
<literal>r-</literal>
</term>
<listitem><para> Determines the behavior of
<function>realloc()</function> when passed a value of zero for the new
size. <quote>alloc</quote> treats this as an allocation of size zero
(and returns a non-null result except in case of resource exhaustion).
<quote>free</quote> treats this as a deallocation of the pointer, and
returns <constant>NULL</constant> without setting
<varname>errno</varname>. <quote>abort</quote> aborts the process if
zero is passed. The default is <quote>free</quote> on Linux and
Windows, and <quote>alloc</quote> elsewhere.</para>
<para>There is considerable divergence of behaviors across
implementations in handling this case. Many have the behavior of
<quote>free</quote>. This can introduce security vulnerabilities, since
a <constant>NULL</constant> return value indicates failure, and the
continued validity of the passed-in pointer (per POSIX and C11).
<quote>alloc</quote> 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 <quote>abort</quote> option enables these
testing this behavior.</para></listitem>
</varlistentry>
<varlistentry id="thread.arena">
<term>
<mallctl>thread.arena</mallctl>
(<type>unsigned</type>)
<literal>rw</literal>
</term>
<listitem><para>Get or set the arena associated with the calling
thread. If the specified arena was not initialized beforehand (see the
<link
linkend="arena.i.initialized"><mallctl>arena.i.initialized</mallctl></link>
mallctl), it will be automatically initialized as a side effect of
calling this interface.</para></listitem>
</varlistentry>
<varlistentry id="thread.allocated">
<term>
<mallctl>thread.allocated</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>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.</para></listitem>
</varlistentry>
<varlistentry id="thread.allocatedp">
<term>
<mallctl>thread.allocatedp</mallctl>
(<type>uint64_t *</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Get a pointer to the the value that is returned by the
<link
linkend="thread.allocated"><mallctl>thread.allocated</mallctl></link>
mallctl. This is useful for avoiding the overhead of repeated
<function>mallctl*()</function> calls. Note that the underlying counter
should not be modified by the application.</para></listitem>
</varlistentry>
<varlistentry id="thread.deallocated">
<term>
<mallctl>thread.deallocated</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>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.</para></listitem>
</varlistentry>
<varlistentry id="thread.deallocatedp">
<term>
<mallctl>thread.deallocatedp</mallctl>
(<type>uint64_t *</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Get a pointer to the the value that is returned by the
<link
linkend="thread.deallocated"><mallctl>thread.deallocated</mallctl></link>
mallctl. This is useful for avoiding the overhead of repeated
<function>mallctl*()</function> calls. Note that the underlying counter
should not be modified by the application.</para></listitem>
</varlistentry>
<varlistentry id="thread.peak.read">
<term>
<mallctl>thread.peak.read</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>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 <link
linkend="thread.peak.reset"><mallctl>thread.peak.reset</mallctl></link>,
or since the thread's creation if it has not called <link
linkend="thread.peak.reset"><mallctl>thread.peak.reset</mallctl></link>.
No guarantees are made about the quality of the approximation, but
jemalloc currently endeavors to maintain accuracy to within one hundred
kilobytes.
</para></listitem>
</varlistentry>
<varlistentry id="thread.peak.reset">
<term>
<mallctl>thread.peak.reset</mallctl>
(<type>void</type>)
<literal>--</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Resets the counter for net bytes allocated in the calling
thread to zero. This affects subsequent calls to <link
linkend="thread.peak.read"><mallctl>thread.peak.read</mallctl></link>,
but not the values returned by <link
linkend="thread.allocated"><mallctl>thread.allocated</mallctl></link>
or <link
linkend="thread.deallocated"><mallctl>thread.deallocated</mallctl></link>.
</para></listitem>
</varlistentry>
<varlistentry id="thread.tcache.enabled">
<term>
<mallctl>thread.tcache.enabled</mallctl>
(<type>bool</type>)
<literal>rw</literal>
</term>
<listitem><para>Enable/disable calling thread's tcache. The tcache is
implicitly flushed as a side effect of becoming
disabled (see <link
linkend="thread.tcache.flush"><mallctl>thread.tcache.flush</mallctl></link>).
</para></listitem>
</varlistentry>
<varlistentry id="thread.tcache.flush">
<term>
<mallctl>thread.tcache.flush</mallctl>
(<type>void</type>)
<literal>--</literal>
</term>
<listitem><para>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.</para></listitem>
</varlistentry>
<varlistentry id="thread.prof.name">
<term>
<mallctl>thread.prof.name</mallctl>
(<type>const char *</type>)
<literal>r-</literal> or
<literal>-w</literal>
[<option>--enable-prof</option>]
</term>
<listitem><para>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 <citerefentry><refentrytitle>isgraph</refentrytitle>
<manvolnum>3</manvolnum></citerefentry> and
<citerefentry><refentrytitle>isblank</refentrytitle>
<manvolnum>3</manvolnum></citerefentry>.</para></listitem>
</varlistentry>
<varlistentry id="thread.prof.active">
<term>
<mallctl>thread.prof.active</mallctl>
(<type>bool</type>)
<literal>rw</literal>
[<option>--enable-prof</option>]
</term>
<listitem><para>Control whether sampling is currently active for the
calling thread. This is an activation mechanism in addition to <link
linkend="prof.active"><mallctl>prof.active</mallctl></link>; both must
be active for the calling thread to sample. This flag is enabled by
default.</para></listitem>
</varlistentry>
<varlistentry id="thread.idle">
<term>
<mallctl>thread.idle</mallctl>
(<type>void</type>)
<literal>--</literal>
</term>
<listitem><para>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.</para>
<para>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 <link linkend="thread.idle"><mallctl>thread.idle</mallctl></link>
if no task appears in the timeout interval, and then do an untimed wait.
For such a background activity mechanism, see
<link linkend="background_thread"><mallctl>background_thread</mallctl></link>.
</para></listitem>
</varlistentry>
<varlistentry id="tcache.create">
<term>
<mallctl>tcache.create</mallctl>
(<type>unsigned</type>)
<literal>r-</literal>
</term>
<listitem><para>Create an explicit thread-specific cache (tcache) and
return an identifier that can be passed to the <link
linkend="MALLOCX_TCACHE"><constant>MALLOCX_TCACHE(<parameter>tc</parameter>)</constant></link>
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.
</para>
<para>If the amount of space supplied for storing the thread-specific
cache identifier does not equal
<code language="C">sizeof(<type>unsigned</type>)</code>, no
thread-specific cache will be created, no data will be written to the
space pointed by <parameter>oldp</parameter>, and
<parameter>*oldlenp</parameter> will be set to 0.
</para></listitem>
</varlistentry>
<varlistentry id="tcache.flush">
<term>
<mallctl>tcache.flush</mallctl>
(<type>unsigned</type>)
<literal>-w</literal>
</term>
<listitem><para>Flush the specified thread-specific cache (tcache). The
same considerations apply to this interface as to <link
linkend="thread.tcache.flush"><mallctl>thread.tcache.flush</mallctl></link>,
except that the tcache will never be automatically discarded.
</para></listitem>
</varlistentry>
<varlistentry id="tcache.destroy">
<term>
<mallctl>tcache.destroy</mallctl>
(<type>unsigned</type>)
<literal>-w</literal>
</term>
<listitem><para>Flush the specified thread-specific cache (tcache) and
make the identifier available for use during a future tcache creation.
</para></listitem>
</varlistentry>
<varlistentry id="arena.i.initialized">
<term>
<mallctl>arena.&lt;i&gt;.initialized</mallctl>
(<type>bool</type>)
<literal>r-</literal>
</term>
<listitem><para>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 <constant>MALLCTL_ARENAS_ALL</constant> are
initialized (always true).</para></listitem>
</varlistentry>
<varlistentry id="arena.i.decay">
<term>
<mallctl>arena.&lt;i&gt;.decay</mallctl>
(<type>void</type>)
<literal>--</literal>
</term>
<listitem><para>Trigger decay-based purging of unused dirty/muzzy pages
for arena &lt;i&gt;, or for all arenas if &lt;i&gt; equals
<constant>MALLCTL_ARENAS_ALL</constant>. The proportion of unused
dirty/muzzy pages to be purged depends on the current time; see <link
linkend="opt.dirty_decay_ms"><mallctl>opt.dirty_decay_ms</mallctl></link>
and <link
linkend="opt.muzzy_decay_ms"><mallctl>opt.muzy_decay_ms</mallctl></link>
for details.</para></listitem>
</varlistentry>
<varlistentry id="arena.i.purge">
<term>
<mallctl>arena.&lt;i&gt;.purge</mallctl>
(<type>void</type>)
<literal>--</literal>
</term>
<listitem><para>Purge all unused dirty pages for arena &lt;i&gt;, or for
all arenas if &lt;i&gt; equals <constant>MALLCTL_ARENAS_ALL</constant>.
</para></listitem>
</varlistentry>
<varlistentry id="arena.i.reset">
<term>
<mallctl>arena.&lt;i&gt;.reset</mallctl>
(<type>void</type>)
<literal>--</literal>
</term>
<listitem><para>Discard all of the arena's extant allocations. This
interface can only be used with arenas explicitly created via <link
linkend="arenas.create"><mallctl>arenas.create</mallctl></link>. 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.</para></listitem>
</varlistentry>
<varlistentry id="arena.i.destroy">
<term>
<mallctl>arena.&lt;i&gt;.destroy</mallctl>
(<type>void</type>)
<literal>--</literal>
</term>
<listitem><para>Destroy the arena. Discard all of the arena's extant
allocations using the same mechanism as for <link
linkend="arena.i.reset"><mallctl>arena.&lt;i&gt;.reset</mallctl></link>
(with all the same constraints and side effects), merge the arena stats
into those accessible at arena index
<constant>MALLCTL_ARENAS_DESTROYED</constant>, and then completely
discard all metadata associated with the arena. Future calls to <link
linkend="arenas.create"><mallctl>arenas.create</mallctl></link> may
recycle the arena index. Destruction will fail if any threads are
currently associated with the arena as a result of calls to <link
linkend="thread.arena"><mallctl>thread.arena</mallctl></link>.</para></listitem>
</varlistentry>
<varlistentry id="arena.i.dss">
<term>
<mallctl>arena.&lt;i&gt;.dss</mallctl>
(<type>const char *</type>)
<literal>rw</literal>
</term>
<listitem><para>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
<constant>MALLCTL_ARENAS_ALL</constant>. See <link
linkend="opt.dss"><mallctl>opt.dss</mallctl></link> for supported
settings.</para></listitem>
</varlistentry>
<varlistentry id="arena.i.dirty_decay_ms">
<term>
<mallctl>arena.&lt;i&gt;.dirty_decay_ms</mallctl>
(<type>ssize_t</type>)
<literal>rw</literal>
</term>
<listitem><para>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 <link
linkend="opt.dirty_decay_ms"><mallctl>opt.dirty_decay_ms</mallctl></link>
for additional information.</para></listitem>
</varlistentry>
<varlistentry id="arena.i.muzzy_decay_ms">
<term>
<mallctl>arena.&lt;i&gt;.muzzy_decay_ms</mallctl>
(<type>ssize_t</type>)
<literal>rw</literal>
</term>
<listitem><para>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 <link
linkend="opt.muzzy_decay_ms"><mallctl>opt.muzzy_decay_ms</mallctl></link>
for additional information.</para></listitem>
</varlistentry>
<varlistentry id="arena.i.retain_grow_limit">
<term>
<mallctl>arena.&lt;i&gt;.retain_grow_limit</mallctl>
(<type>size_t</type>)
<literal>rw</literal>
</term>
<listitem><para>Maximum size to grow retained region (only relevant when
<link linkend="opt.retain"><mallctl>opt.retain</mallctl></link> is
enabled). This controls the maximum increment to expand virtual memory,
or allocation through <link
linkend="arena.i.extent_hooks"><mallctl>arena.&lt;i&gt;extent_hooks</mallctl></link>.
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.</para></listitem>
</varlistentry>
<varlistentry id="arena.i.extent_hooks">
<term>
<mallctl>arena.&lt;i&gt;.extent_hooks</mallctl>
(<type>extent_hooks_t *</type>)
<literal>rw</literal>
</term>
<listitem><para>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 <link
linkend="arenas.create"><mallctl>arenas.create</mallctl></link> 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.</para>
<programlisting language="C"><![CDATA[
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;
};]]></programlisting>
<para>The <type>extent_hooks_t</type> 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 <constant>NULL</constant>, 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.</para>
<funcsynopsis><funcprototype>
<funcdef>typedef void *<function>(extent_alloc_t)</function></funcdef>
<paramdef>extent_hooks_t *<parameter>extent_hooks</parameter></paramdef>
<paramdef>void *<parameter>new_addr</parameter></paramdef>
<paramdef>size_t <parameter>size</parameter></paramdef>
<paramdef>size_t <parameter>alignment</parameter></paramdef>
<paramdef>bool *<parameter>zero</parameter></paramdef>
<paramdef>bool *<parameter>commit</parameter></paramdef>
<paramdef>unsigned <parameter>arena_ind</parameter></paramdef>
</funcprototype></funcsynopsis>
<literallayout></literallayout>
<para>An extent allocation function conforms to the
<type>extent_alloc_t</type> type and upon success returns a pointer to
<parameter>size</parameter> bytes of mapped memory on behalf of arena
<parameter>arena_ind</parameter> such that the extent's base address is
a multiple of <parameter>alignment</parameter>, as well as setting
<parameter>*zero</parameter> to indicate whether the extent is zeroed
and <parameter>*commit</parameter> to indicate whether the extent is
committed. Upon error the function returns <constant>NULL</constant>
and leaves <parameter>*zero</parameter> and
<parameter>*commit</parameter> unmodified. The
<parameter>size</parameter> parameter is always a multiple of the page
size. The <parameter>alignment</parameter> parameter is always a power
of two at least as large as the page size. Zeroing is mandatory if
<parameter>*zero</parameter> is true upon function entry. Committing is
mandatory if <parameter>*commit</parameter> is true upon function entry.
If <parameter>new_addr</parameter> is not <constant>NULL</constant>, the
returned pointer must be <parameter>new_addr</parameter> on success or
<constant>NULL</constant> 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 <link
linkend="arena.i.dss"><mallctl>arena.&lt;i&gt;.dss</mallctl></link>
setting irrelevant.</para>
<funcsynopsis><funcprototype>
<funcdef>typedef bool <function>(extent_dalloc_t)</function></funcdef>
<paramdef>extent_hooks_t *<parameter>extent_hooks</parameter></paramdef>
<paramdef>void *<parameter>addr</parameter></paramdef>
<paramdef>size_t <parameter>size</parameter></paramdef>
<paramdef>bool <parameter>committed</parameter></paramdef>
<paramdef>unsigned <parameter>arena_ind</parameter></paramdef>
</funcprototype></funcsynopsis>
<literallayout></literallayout>
<para>
An extent deallocation function conforms to the
<type>extent_dalloc_t</type> type and deallocates an extent at given
<parameter>addr</parameter> and <parameter>size</parameter> with
<parameter>committed</parameter>/decommited memory as indicated, on
behalf of arena <parameter>arena_ind</parameter>, 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.</para>
<funcsynopsis><funcprototype>
<funcdef>typedef void <function>(extent_destroy_t)</function></funcdef>
<paramdef>extent_hooks_t *<parameter>extent_hooks</parameter></paramdef>
<paramdef>void *<parameter>addr</parameter></paramdef>
<paramdef>size_t <parameter>size</parameter></paramdef>
<paramdef>bool <parameter>committed</parameter></paramdef>
<paramdef>unsigned <parameter>arena_ind</parameter></paramdef>
</funcprototype></funcsynopsis>
<literallayout></literallayout>
<para>
An extent destruction function conforms to the
<type>extent_destroy_t</type> type and unconditionally destroys an
extent at given <parameter>addr</parameter> and
<parameter>size</parameter> with
<parameter>committed</parameter>/decommited memory as indicated, on
behalf of arena <parameter>arena_ind</parameter>. This function may be
called to destroy retained extents during arena destruction (see <link
linkend="arena.i.destroy"><mallctl>arena.&lt;i&gt;.destroy</mallctl></link>).</para>
<funcsynopsis><funcprototype>
<funcdef>typedef bool <function>(extent_commit_t)</function></funcdef>
<paramdef>extent_hooks_t *<parameter>extent_hooks</parameter></paramdef>
<paramdef>void *<parameter>addr</parameter></paramdef>
<paramdef>size_t <parameter>size</parameter></paramdef>
<paramdef>size_t <parameter>offset</parameter></paramdef>
<paramdef>size_t <parameter>length</parameter></paramdef>
<paramdef>unsigned <parameter>arena_ind</parameter></paramdef>
</funcprototype></funcsynopsis>
<literallayout></literallayout>
<para>An extent commit function conforms to the
<type>extent_commit_t</type> type and commits zeroed physical memory to
back pages within an extent at given <parameter>addr</parameter> and
<parameter>size</parameter> at <parameter>offset</parameter> bytes,
extending for <parameter>length</parameter> on behalf of arena
<parameter>arena_ind</parameter>, 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.</para>
<funcsynopsis><funcprototype>
<funcdef>typedef bool <function>(extent_decommit_t)</function></funcdef>
<paramdef>extent_hooks_t *<parameter>extent_hooks</parameter></paramdef>
<paramdef>void *<parameter>addr</parameter></paramdef>
<paramdef>size_t <parameter>size</parameter></paramdef>
<paramdef>size_t <parameter>offset</parameter></paramdef>
<paramdef>size_t <parameter>length</parameter></paramdef>
<paramdef>unsigned <parameter>arena_ind</parameter></paramdef>
</funcprototype></funcsynopsis>
<literallayout></literallayout>
<para>An extent decommit function conforms to the
<type>extent_decommit_t</type> type and decommits any physical memory
that is backing pages within an extent at given
<parameter>addr</parameter> and <parameter>size</parameter> at
<parameter>offset</parameter> bytes, extending for
<parameter>length</parameter> on behalf of arena
<parameter>arena_ind</parameter>, 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.</para>
<funcsynopsis><funcprototype>
<funcdef>typedef bool <function>(extent_purge_t)</function></funcdef>
<paramdef>extent_hooks_t *<parameter>extent_hooks</parameter></paramdef>
<paramdef>void *<parameter>addr</parameter></paramdef>
<paramdef>size_t <parameter>size</parameter></paramdef>
<paramdef>size_t <parameter>offset</parameter></paramdef>
<paramdef>size_t <parameter>length</parameter></paramdef>
<paramdef>unsigned <parameter>arena_ind</parameter></paramdef>
</funcprototype></funcsynopsis>
<literallayout></literallayout>
<para>An extent purge function conforms to the
<type>extent_purge_t</type> type and discards physical pages
within the virtual memory mapping associated with an extent at given
<parameter>addr</parameter> and <parameter>size</parameter> at
<parameter>offset</parameter> bytes, extending for
<parameter>length</parameter> on behalf of arena
<parameter>arena_ind</parameter>. A lazy extent purge function (e.g.
implemented via
<function>madvise(<parameter>...</parameter><parameter><constant>MADV_FREE</constant></parameter>)</function>)
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.</para>
<funcsynopsis><funcprototype>
<funcdef>typedef bool <function>(extent_split_t)</function></funcdef>
<paramdef>extent_hooks_t *<parameter>extent_hooks</parameter></paramdef>
<paramdef>void *<parameter>addr</parameter></paramdef>
<paramdef>size_t <parameter>size</parameter></paramdef>
<paramdef>size_t <parameter>size_a</parameter></paramdef>
<paramdef>size_t <parameter>size_b</parameter></paramdef>
<paramdef>bool <parameter>committed</parameter></paramdef>
<paramdef>unsigned <parameter>arena_ind</parameter></paramdef>
</funcprototype></funcsynopsis>
<literallayout></literallayout>
<para>An extent split function conforms to the
<type>extent_split_t</type> type and optionally splits an extent at
given <parameter>addr</parameter> and <parameter>size</parameter> into
two adjacent extents, the first of <parameter>size_a</parameter> bytes,
and the second of <parameter>size_b</parameter> bytes, operating on
<parameter>committed</parameter>/decommitted memory as indicated, on
behalf of arena <parameter>arena_ind</parameter>, 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.</para>
<funcsynopsis><funcprototype>
<funcdef>typedef bool <function>(extent_merge_t)</function></funcdef>
<paramdef>extent_hooks_t *<parameter>extent_hooks</parameter></paramdef>
<paramdef>void *<parameter>addr_a</parameter></paramdef>
<paramdef>size_t <parameter>size_a</parameter></paramdef>
<paramdef>void *<parameter>addr_b</parameter></paramdef>
<paramdef>size_t <parameter>size_b</parameter></paramdef>
<paramdef>bool <parameter>committed</parameter></paramdef>
<paramdef>unsigned <parameter>arena_ind</parameter></paramdef>
</funcprototype></funcsynopsis>
<literallayout></literallayout>
<para>An extent merge function conforms to the
<type>extent_merge_t</type> type and optionally merges adjacent extents,
at given <parameter>addr_a</parameter> and <parameter>size_a</parameter>
with given <parameter>addr_b</parameter> and
<parameter>size_b</parameter> into one contiguous extent, operating on
<parameter>committed</parameter>/decommitted memory as indicated, on
behalf of arena <parameter>arena_ind</parameter>, 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.</para>
</listitem>
</varlistentry>
<varlistentry id="arenas.narenas">
<term>
<mallctl>arenas.narenas</mallctl>
(<type>unsigned</type>)
<literal>r-</literal>
</term>
<listitem><para>Current limit on number of arenas.</para></listitem>
</varlistentry>
<varlistentry id="arenas.dirty_decay_ms">
<term>
<mallctl>arenas.dirty_decay_ms</mallctl>
(<type>ssize_t</type>)
<literal>rw</literal>
</term>
<listitem><para>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 <link
linkend="arena.i.dirty_decay_ms"><mallctl>arena.&lt;i&gt;.dirty_decay_ms</mallctl></link>
during arena creation. See <link
linkend="opt.dirty_decay_ms"><mallctl>opt.dirty_decay_ms</mallctl></link>
for additional information.</para></listitem>
</varlistentry>
<varlistentry id="arenas.muzzy_decay_ms">
<term>
<mallctl>arenas.muzzy_decay_ms</mallctl>
(<type>ssize_t</type>)
<literal>rw</literal>
</term>
<listitem><para>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 <link
linkend="arena.i.muzzy_decay_ms"><mallctl>arena.&lt;i&gt;.muzzy_decay_ms</mallctl></link>
during arena creation. See <link
linkend="opt.muzzy_decay_ms"><mallctl>opt.muzzy_decay_ms</mallctl></link>
for additional information.</para></listitem>
</varlistentry>
<varlistentry id="arenas.quantum">
<term>
<mallctl>arenas.quantum</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
</term>
<listitem><para>Quantum size.</para></listitem>
</varlistentry>
<varlistentry id="arenas.page">
<term>
<mallctl>arenas.page</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
</term>
<listitem><para>Page size.</para></listitem>
</varlistentry>
<varlistentry id="arenas.tcache_max">
<term>
<mallctl>arenas.tcache_max</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
</term>
<listitem><para>Maximum thread-cached size class.</para></listitem>
</varlistentry>
<varlistentry id="arenas.nbins">
<term>
<mallctl>arenas.nbins</mallctl>
(<type>unsigned</type>)
<literal>r-</literal>
</term>
<listitem><para>Number of bin size classes.</para></listitem>
</varlistentry>
<varlistentry id="arenas.nhbins">
<term>
<mallctl>arenas.nhbins</mallctl>
(<type>unsigned</type>)
<literal>r-</literal>
</term>
<listitem><para>Total number of thread cache bin size
classes.</para></listitem>
</varlistentry>
<varlistentry id="arenas.bin.i.size">
<term>
<mallctl>arenas.bin.&lt;i&gt;.size</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
</term>
<listitem><para>Maximum size supported by size class.</para></listitem>
</varlistentry>
<varlistentry id="arenas.bin.i.nregs">
<term>
<mallctl>arenas.bin.&lt;i&gt;.nregs</mallctl>
(<type>uint32_t</type>)
<literal>r-</literal>
</term>
<listitem><para>Number of regions per slab.</para></listitem>
</varlistentry>
<varlistentry id="arenas.bin.i.slab_size">
<term>
<mallctl>arenas.bin.&lt;i&gt;.slab_size</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
</term>
<listitem><para>Number of bytes per slab.</para></listitem>
</varlistentry>
<varlistentry id="arenas.nlextents">
<term>
<mallctl>arenas.nlextents</mallctl>
(<type>unsigned</type>)
<literal>r-</literal>
</term>
<listitem><para>Total number of large size classes.</para></listitem>
</varlistentry>
<varlistentry id="arenas.lextent.i.size">
<term>
<mallctl>arenas.lextent.&lt;i&gt;.size</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
</term>
<listitem><para>Maximum size supported by this large size
class.</para></listitem>
</varlistentry>
<varlistentry id="arenas.create">
<term>
<mallctl>arenas.create</mallctl>
(<type>unsigned</type>, <type>extent_hooks_t *</type>)
<literal>rw</literal>
</term>
<listitem><para>Explicitly create a new arena outside the range of
automatically managed arenas, with optionally specified extent hooks,
and return the new arena index.</para>
<para>If the amount of space supplied for storing the arena index does
not equal <code language="C">sizeof(<type>unsigned</type>)</code>, no
arena will be created, no data will be written to the space pointed by
<parameter>oldp</parameter>, and <parameter>*oldlenp</parameter> will
be set to 0.
</para></listitem>
</varlistentry>
<varlistentry id="arenas.lookup">
<term>
<mallctl>arenas.lookup</mallctl>
(<type>unsigned</type>, <type>void*</type>)
<literal>rw</literal>
</term>
<listitem><para>Index of the arena to which an allocation belongs to.</para></listitem>
</varlistentry>
<varlistentry id="prof.thread_active_init">
<term>
<mallctl>prof.thread_active_init</mallctl>
(<type>bool</type>)
<literal>rw</literal>
[<option>--enable-prof</option>]
</term>
<listitem><para>Control the initial setting for <link
linkend="thread.prof.active"><mallctl>thread.prof.active</mallctl></link>
in newly created threads. See the <link
linkend="opt.prof_thread_active_init"><mallctl>opt.prof_thread_active_init</mallctl></link>
option for additional information.</para></listitem>
</varlistentry>
<varlistentry id="prof.active">
<term>
<mallctl>prof.active</mallctl>
(<type>bool</type>)
<literal>rw</literal>
[<option>--enable-prof</option>]
</term>
<listitem><para>Control whether sampling is currently active. See the
<link
linkend="opt.prof_active"><mallctl>opt.prof_active</mallctl></link>
option for additional information, as well as the interrelated <link
linkend="thread.prof.active"><mallctl>thread.prof.active</mallctl></link>
mallctl.</para></listitem>
</varlistentry>
<varlistentry id="prof.dump">
<term>
<mallctl>prof.dump</mallctl>
(<type>const char *</type>)
<literal>-w</literal>
[<option>--enable-prof</option>]
</term>
<listitem><para>Dump a memory profile to the specified file, or if NULL
is specified, to a file according to the pattern
<filename>&lt;prefix&gt;.&lt;pid&gt;.&lt;seq&gt;.m&lt;mseq&gt;.heap</filename>,
where <literal>&lt;prefix&gt;</literal> is controlled by the
<link linkend="opt.prof_prefix"><mallctl>opt.prof_prefix</mallctl></link>
and <link linkend="prof.prefix"><mallctl>prof.prefix</mallctl></link>
options.</para></listitem>
</varlistentry>
<varlistentry id="prof.prefix">
<term>
<mallctl>prof.prefix</mallctl>
(<type>const char *</type>)
<literal>-w</literal>
[<option>--enable-prof</option>]
</term>
<listitem><para>Set the filename prefix for profile dumps. See
<link
linkend="opt.prof_prefix"><mallctl>opt.prof_prefix</mallctl></link>
for the default setting. This can be useful to differentiate profile
dumps such as from forked processes.
</para></listitem>
</varlistentry>
<varlistentry id="prof.gdump">
<term>
<mallctl>prof.gdump</mallctl>
(<type>bool</type>)
<literal>rw</literal>
[<option>--enable-prof</option>]
</term>
<listitem><para>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
<filename>&lt;prefix&gt;.&lt;pid&gt;.&lt;seq&gt;.u&lt;useq&gt;.heap</filename>,
where <literal>&lt;prefix&gt;</literal> is controlled by the <link
linkend="opt.prof_prefix"><mallctl>opt.prof_prefix</mallctl></link> and
<link linkend="prof.prefix"><mallctl>prof.prefix</mallctl></link>
options.</para></listitem>
</varlistentry>
<varlistentry id="prof.reset">
<term>
<mallctl>prof.reset</mallctl>
(<type>size_t</type>)
<literal>-w</literal>
[<option>--enable-prof</option>]
</term>
<listitem><para>Reset all memory profile statistics, and optionally
update the sample rate (see <link
linkend="opt.lg_prof_sample"><mallctl>opt.lg_prof_sample</mallctl></link>
and <link
linkend="prof.lg_sample"><mallctl>prof.lg_sample</mallctl></link>).
</para></listitem>
</varlistentry>
<varlistentry id="prof.lg_sample">
<term>
<mallctl>prof.lg_sample</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
[<option>--enable-prof</option>]
</term>
<listitem><para>Get the current sample rate (see <link
linkend="opt.lg_prof_sample"><mallctl>opt.lg_prof_sample</mallctl></link>).
</para></listitem>
</varlistentry>
<varlistentry id="prof.interval">
<term>
<mallctl>prof.interval</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-prof</option>]
</term>
<listitem><para>Average number of bytes allocated between
interval-based profile dumps. See the
<link
linkend="opt.lg_prof_interval"><mallctl>opt.lg_prof_interval</mallctl></link>
option for additional information.</para></listitem>
</varlistentry>
<varlistentry id="stats.allocated">
<term>
<mallctl>stats.allocated</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Total number of bytes allocated by the
application.</para></listitem>
</varlistentry>
<varlistentry id="stats.active">
<term>
<mallctl>stats.active</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>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 <link
linkend="stats.allocated"><mallctl>stats.allocated</mallctl></link>.
This does not include <link linkend="stats.arenas.i.pdirty">
<mallctl>stats.arenas.&lt;i&gt;.pdirty</mallctl></link>,
<link linkend="stats.arenas.i.pmuzzy">
<mallctl>stats.arenas.&lt;i&gt;.pmuzzy</mallctl></link>, nor pages
entirely devoted to allocator metadata.</para></listitem>
</varlistentry>
<varlistentry id="stats.metadata">
<term>
<mallctl>stats.metadata</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Total number of bytes dedicated to metadata, which
comprise base allocations used for bootstrap-sensitive allocator
metadata structures (see <link
linkend="stats.arenas.i.base"><mallctl>stats.arenas.&lt;i&gt;.base</mallctl></link>)
and internal allocations (see <link
linkend="stats.arenas.i.internal"><mallctl>stats.arenas.&lt;i&gt;.internal</mallctl></link>).
Transparent huge page (enabled with <link
linkend="opt.metadata_thp">opt.metadata_thp</link>) usage is not
considered.</para></listitem>
</varlistentry>
<varlistentry id="stats.metadata_thp">
<term>
<mallctl>stats.metadata_thp</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Number of transparent huge pages (THP) used for
metadata. See <link
linkend="stats.metadata"><mallctl>stats.metadata</mallctl></link> and
<link linkend="opt.metadata_thp">opt.metadata_thp</link>) for
details.</para></listitem>
</varlistentry>
<varlistentry id="stats.resident">
<term>
<mallctl>stats.resident</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>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 <link
linkend="stats.active"><mallctl>stats.active</mallctl></link>.</para></listitem>
</varlistentry>
<varlistentry id="stats.mapped">
<term>
<mallctl>stats.mapped</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Total number of bytes in active extents mapped by the
allocator. This is larger than <link
linkend="stats.active"><mallctl>stats.active</mallctl></link>. This
does not include inactive extents, even those that contain unused dirty
pages, which means that there is no strict ordering between this and
<link
linkend="stats.resident"><mallctl>stats.resident</mallctl></link>.</para></listitem>
</varlistentry>
<varlistentry id="stats.retained">
<term>
<mallctl>stats.retained</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Total number of bytes in virtual memory mappings that
were retained rather than being returned to the operating system via
e.g. <citerefentry><refentrytitle>munmap</refentrytitle>
<manvolnum>2</manvolnum></citerefentry> or similar. Retained virtual
memory is typically untouched, decommitted, or purged, so it has no
strongly associated physical memory (see <link
linkend="arena.i.extent_hooks">extent hooks</link> for details).
Retained memory is excluded from mapped memory statistics, e.g. <link
linkend="stats.mapped"><mallctl>stats.mapped</mallctl></link>.
</para></listitem>
</varlistentry>
<varlistentry id="stats.zero_reallocs">
<term>
<mallctl>stats.zero_reallocs</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Number of times that the <function>realloc()</function>
was called with a non-<constant>NULL</constant> pointer argument and a
<constant>0</constant> size argument. This is a fundamentally unsafe
pattern in portable programs; see <link linkend="opt.zero_realloc">
<mallctl>opt.zero_realloc</mallctl></link> for details.
</para></listitem>
</varlistentry>
<varlistentry id="stats.background_thread.num_threads">
<term>
<mallctl>stats.background_thread.num_threads</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para> Number of <link linkend="background_thread">background
threads</link> running currently.</para></listitem>
</varlistentry>
<varlistentry id="stats.background_thread.num_runs">
<term>
<mallctl>stats.background_thread.num_runs</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para> Total number of runs from all <link
linkend="background_thread">background threads</link>.</para></listitem>
</varlistentry>
<varlistentry id="stats.background_thread.run_interval">
<term>
<mallctl>stats.background_thread.run_interval</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para> Average run interval in nanoseconds of <link
linkend="background_thread">background threads</link>.</para></listitem>
</varlistentry>
<varlistentry id="stats.mutexes.ctl">
<term>
<mallctl>stats.mutexes.ctl.{counter};</mallctl>
(<type>counter specific type</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Statistics on <varname>ctl</varname> mutex (global
scope; mallctl related). <mallctl>{counter}</mallctl> is one of the
counters below:</para>
<varlistentry id="mutex_counters">
<listitem><para><varname>num_ops</varname> (<type>uint64_t</type>):
Total number of lock acquisition operations on this mutex.</para>
<para><varname>num_spin_acq</varname> (<type>uint64_t</type>): 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.</para>
<para><varname>num_wait</varname> (<type>uint64_t</type>): 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.</para>
<para><varname>max_wait_time</varname> (<type>uint64_t</type>):
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.</para>
<para><varname>total_wait_time</varname> (<type>uint64_t</type>):
Cumulative time in nanoseconds spent on wait-acquired lock operations.
Similarly, spin-acquired cases are not considered.</para>
<para><varname>max_num_thds</varname> (<type>uint32_t</type>): Maximum
number of threads waiting on this mutex simultaneously. Similarly,
spin-acquired cases are not considered.</para>
<para><varname>num_owner_switch</varname> (<type>uint64_t</type>):
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.
</para>
</listitem>
</varlistentry>
</listitem>
</varlistentry>
<varlistentry id="stats.mutexes.background_thread">
<term>
<mallctl>stats.mutexes.background_thread.{counter}</mallctl>
(<type>counter specific type</type>) <literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Statistics on <varname>background_thread</varname> mutex
(global scope; <link
linkend="background_thread"><mallctl>background_thread</mallctl></link>
related). <mallctl>{counter}</mallctl> is one of the counters in <link
linkend="mutex_counters">mutex profiling
counters</link>.</para></listitem>
</varlistentry>
<varlistentry id="stats.mutexes.prof">
<term>
<mallctl>stats.mutexes.prof.{counter}</mallctl>
(<type>counter specific type</type>) <literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Statistics on <varname>prof</varname> mutex (global
scope; profiling related). <mallctl>{counter}</mallctl> is one of the
counters in <link linkend="mutex_counters">mutex profiling
counters</link>.</para></listitem>
</varlistentry>
<varlistentry id="stats.mutexes.prof_thds_data">
<term>
<mallctl>stats.mutexes.prof_thds_data.{counter}</mallctl>
(<type>counter specific type</type>) <literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Statistics on <varname>prof</varname> threads data mutex
(global scope; profiling related). <mallctl>{counter}</mallctl> is one
of the counters in <link linkend="mutex_counters">mutex profiling
counters</link>.</para></listitem>
</varlistentry>
<varlistentry id="stats.mutexes.prof_dump">
<term>
<mallctl>stats.mutexes.prof_dump.{counter}</mallctl>
(<type>counter specific type</type>) <literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Statistics on <varname>prof</varname> dumping mutex
(global scope; profiling related). <mallctl>{counter}</mallctl> is one
of the counters in <link linkend="mutex_counters">mutex profiling
counters</link>.</para></listitem>
</varlistentry>
<varlistentry id="stats.mutexes.reset">
<term>
<mallctl>stats.mutexes.reset</mallctl>
(<type>void</type>) <literal>--</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Reset all mutex profile statistics, including global
mutexes, arena mutexes and bin mutexes.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.dss">
<term>
<mallctl>stats.arenas.&lt;i&gt;.dss</mallctl>
(<type>const char *</type>)
<literal>r-</literal>
</term>
<listitem><para>dss (<citerefentry><refentrytitle>sbrk</refentrytitle>
<manvolnum>2</manvolnum></citerefentry>) allocation precedence as
related to <citerefentry><refentrytitle>mmap</refentrytitle>
<manvolnum>2</manvolnum></citerefentry> allocation. See <link
linkend="opt.dss"><mallctl>opt.dss</mallctl></link> for details.
</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.dirty_decay_ms">
<term>
<mallctl>stats.arenas.&lt;i&gt;.dirty_decay_ms</mallctl>
(<type>ssize_t</type>)
<literal>r-</literal>
</term>
<listitem><para>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 <link
linkend="opt.dirty_decay_ms"><mallctl>opt.dirty_decay_ms</mallctl></link>
for details.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.muzzy_decay_ms">
<term>
<mallctl>stats.arenas.&lt;i&gt;.muzzy_decay_ms</mallctl>
(<type>ssize_t</type>)
<literal>r-</literal>
</term>
<listitem><para>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 <link
linkend="opt.muzzy_decay_ms"><mallctl>opt.muzzy_decay_ms</mallctl></link>
for details.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.nthreads">
<term>
<mallctl>stats.arenas.&lt;i&gt;.nthreads</mallctl>
(<type>unsigned</type>)
<literal>r-</literal>
</term>
<listitem><para>Number of threads currently assigned to
arena.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.uptime">
<term>
<mallctl>stats.arenas.&lt;i&gt;.uptime</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
</term>
<listitem><para>Time elapsed (in nanoseconds) since the arena was
created. If &lt;i&gt; equals <constant>0</constant> or
<constant>MALLCTL_ARENAS_ALL</constant>, this is the uptime since malloc
initialization.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.pactive">
<term>
<mallctl>stats.arenas.&lt;i&gt;.pactive</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
</term>
<listitem><para>Number of pages in active extents.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.pdirty">
<term>
<mallctl>stats.arenas.&lt;i&gt;.pdirty</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
</term>
<listitem><para>Number of pages within unused extents that are
potentially dirty, and for which <function>madvise()</function> or
similar has not been called. See <link
linkend="opt.dirty_decay_ms"><mallctl>opt.dirty_decay_ms</mallctl></link>
for a description of dirty pages.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.pmuzzy">
<term>
<mallctl>stats.arenas.&lt;i&gt;.pmuzzy</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
</term>
<listitem><para>Number of pages within unused extents that are muzzy.
See <link
linkend="opt.muzzy_decay_ms"><mallctl>opt.muzzy_decay_ms</mallctl></link>
for a description of muzzy pages.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.mapped">
<term>
<mallctl>stats.arenas.&lt;i&gt;.mapped</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Number of mapped bytes.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.retained">
<term>
<mallctl>stats.arenas.&lt;i&gt;.retained</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Number of retained bytes. See <link
linkend="stats.retained"><mallctl>stats.retained</mallctl></link> for
details.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.extent_avail">
<term>
<mallctl>stats.arenas.&lt;i&gt;.extent_avail</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Number of allocated (but unused) extent structs in this
arena.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.base">
<term>
<mallctl>stats.arenas.&lt;i&gt;.base</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>
Number of bytes dedicated to bootstrap-sensitive allocator metadata
structures.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.internal">
<term>
<mallctl>stats.arenas.&lt;i&gt;.internal</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>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.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.metadata_thp">
<term>
<mallctl>stats.arenas.&lt;i&gt;.metadata_thp</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Number of transparent huge pages (THP) used for
metadata. See <link linkend="opt.metadata_thp">opt.metadata_thp</link>
for details.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.resident">
<term>
<mallctl>stats.arenas.&lt;i&gt;.resident</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>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.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.dirty_npurge">
<term>
<mallctl>stats.arenas.&lt;i&gt;.dirty_npurge</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Number of dirty page purge sweeps performed.
</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.dirty_nmadvise">
<term>
<mallctl>stats.arenas.&lt;i&gt;.dirty_nmadvise</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Number of <function>madvise()</function> or similar
calls made to purge dirty pages.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.dirty_purged">
<term>
<mallctl>stats.arenas.&lt;i&gt;.dirty_purged</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Number of dirty pages purged.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.muzzy_npurge">
<term>
<mallctl>stats.arenas.&lt;i&gt;.muzzy_npurge</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Number of muzzy page purge sweeps performed.
</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.muzzy_nmadvise">
<term>
<mallctl>stats.arenas.&lt;i&gt;.muzzy_nmadvise</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Number of <function>madvise()</function> or similar
calls made to purge muzzy pages.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.muzzy_purged">
<term>
<mallctl>stats.arenas.&lt;i&gt;.muzzy_purged</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Number of muzzy pages purged.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.small.allocated">
<term>
<mallctl>stats.arenas.&lt;i&gt;.small.allocated</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Number of bytes currently allocated by small objects.
</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.small.nmalloc">
<term>
<mallctl>stats.arenas.&lt;i&gt;.small.nmalloc</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Cumulative number of times a small allocation was
requested from the arena's bins, whether to fill the relevant tcache if
<link linkend="opt.tcache"><mallctl>opt.tcache</mallctl></link> is
enabled, or to directly satisfy an allocation request
otherwise.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.small.ndalloc">
<term>
<mallctl>stats.arenas.&lt;i&gt;.small.ndalloc</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Cumulative number of times a small allocation was
returned to the arena's bins, whether to flush the relevant tcache if
<link linkend="opt.tcache"><mallctl>opt.tcache</mallctl></link> is
enabled, or to directly deallocate an allocation
otherwise.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.small.nrequests">
<term>
<mallctl>stats.arenas.&lt;i&gt;.small.nrequests</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Cumulative number of allocation requests satisfied by
all bin size classes.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.small.nfills">
<term>
<mallctl>stats.arenas.&lt;i&gt;.small.nfills</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Cumulative number of tcache fills by all small size
classes.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.small.nflushes">
<term>
<mallctl>stats.arenas.&lt;i&gt;.small.nflushes</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Cumulative number of tcache flushes by all small size
classes.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.large.allocated">
<term>
<mallctl>stats.arenas.&lt;i&gt;.large.allocated</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Number of bytes currently allocated by large objects.
</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.large.nmalloc">
<term>
<mallctl>stats.arenas.&lt;i&gt;.large.nmalloc</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Cumulative number of times a large extent was allocated
from the arena, whether to fill the relevant tcache if <link
linkend="opt.tcache"><mallctl>opt.tcache</mallctl></link> is enabled and
the size class is within the range being cached, or to directly satisfy
an allocation request otherwise.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.large.ndalloc">
<term>
<mallctl>stats.arenas.&lt;i&gt;.large.ndalloc</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Cumulative number of times a large extent was returned
to the arena, whether to flush the relevant tcache if <link
linkend="opt.tcache"><mallctl>opt.tcache</mallctl></link> is enabled and
the size class is within the range being cached, or to directly
deallocate an allocation otherwise.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.large.nrequests">
<term>
<mallctl>stats.arenas.&lt;i&gt;.large.nrequests</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Cumulative number of allocation requests satisfied by
all large size classes.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.large.nfills">
<term>
<mallctl>stats.arenas.&lt;i&gt;.large.nfills</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Cumulative number of tcache fills by all large size
classes.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.large.nflushes">
<term>
<mallctl>stats.arenas.&lt;i&gt;.large.nflushes</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Cumulative number of tcache flushes by all large size
classes.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.bins.j.nmalloc">
<term>
<mallctl>stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.nmalloc</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Cumulative number of times a bin region of the
corresponding size class was allocated from the arena, whether to fill
the relevant tcache if <link
linkend="opt.tcache"><mallctl>opt.tcache</mallctl></link> is enabled, or
to directly satisfy an allocation request otherwise.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.bins.j.ndalloc">
<term>
<mallctl>stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.ndalloc</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Cumulative number of times a bin region of the
corresponding size class was returned to the arena, whether to flush the
relevant tcache if <link
linkend="opt.tcache"><mallctl>opt.tcache</mallctl></link> is enabled, or
to directly deallocate an allocation otherwise.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.bins.j.nrequests">
<term>
<mallctl>stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.nrequests</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Cumulative number of allocation requests satisfied by
bin regions of the corresponding size class.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.bins.j.curregs">
<term>
<mallctl>stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.curregs</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Current number of regions for this size
class.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.bins.j.nfills">
<term>
<mallctl>stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.nfills</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
</term>
<listitem><para>Cumulative number of tcache fills.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.bins.j.nflushes">
<term>
<mallctl>stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.nflushes</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
</term>
<listitem><para>Cumulative number of tcache flushes.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.bins.j.nslabs">
<term>
<mallctl>stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.nslabs</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Cumulative number of slabs created.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.bins.j.nreslabs">
<term>
<mallctl>stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.nreslabs</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Cumulative number of times the current slab from which
to allocate changed.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.bins.j.curslabs">
<term>
<mallctl>stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.curslabs</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Current number of slabs.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.bins.j.nonfull_slabs">
<term>
<mallctl>stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.nonfull_slabs</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Current number of nonfull slabs.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.bins.mutex">
<term>
<mallctl>stats.arenas.&lt;i&gt;.bins.&lt;j&gt;.mutex.{counter}</mallctl>
(<type>counter specific type</type>) <literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Statistics on
<varname>arena.&lt;i&gt;.bins.&lt;j&gt;</varname> mutex (arena bin
scope; bin operation related). <mallctl>{counter}</mallctl> is one of
the counters in <link linkend="mutex_counters">mutex profiling
counters</link>.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.extents.n">
<term>
<mallctl>stats.arenas.&lt;i&gt;.extents.&lt;j&gt;.n{extent_type}</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para> 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.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.extents.bytes">
<term>
<mallctl>stats.arenas.&lt;i&gt;.extents.&lt;j&gt;.{extent_type}_bytes</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para> 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.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.lextents.j.nmalloc">
<term>
<mallctl>stats.arenas.&lt;i&gt;.lextents.&lt;j&gt;.nmalloc</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Cumulative number of times a large extent of the
corresponding size class was allocated from the arena, whether to fill
the relevant tcache if <link
linkend="opt.tcache"><mallctl>opt.tcache</mallctl></link> is enabled and
the size class is within the range being cached, or to directly satisfy
an allocation request otherwise.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.lextents.j.ndalloc">
<term>
<mallctl>stats.arenas.&lt;i&gt;.lextents.&lt;j&gt;.ndalloc</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Cumulative number of times a large extent of the
corresponding size class was returned to the arena, whether to flush the
relevant tcache if <link
linkend="opt.tcache"><mallctl>opt.tcache</mallctl></link> is enabled and
the size class is within the range being cached, or to directly
deallocate an allocation otherwise.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.lextents.j.nrequests">
<term>
<mallctl>stats.arenas.&lt;i&gt;.lextents.&lt;j&gt;.nrequests</mallctl>
(<type>uint64_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Cumulative number of allocation requests satisfied by
large extents of the corresponding size class.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.lextents.j.curlextents">
<term>
<mallctl>stats.arenas.&lt;i&gt;.lextents.&lt;j&gt;.curlextents</mallctl>
(<type>size_t</type>)
<literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Current number of large allocations for this size class.
</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.mutexes.large">
<term>
<mallctl>stats.arenas.&lt;i&gt;.mutexes.large.{counter}</mallctl>
(<type>counter specific type</type>) <literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Statistics on <varname>arena.&lt;i&gt;.large</varname>
mutex (arena scope; large allocation related).
<mallctl>{counter}</mallctl> is one of the counters in <link
linkend="mutex_counters">mutex profiling
counters</link>.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.mutexes.extent_avail">
<term>
<mallctl>stats.arenas.&lt;i&gt;.mutexes.extent_avail.{counter}</mallctl>
(<type>counter specific type</type>) <literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Statistics on <varname>arena.&lt;i&gt;.extent_avail
</varname> mutex (arena scope; extent avail related).
<mallctl>{counter}</mallctl> is one of the counters in <link
linkend="mutex_counters">mutex profiling
counters</link>.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.mutexes.extents_dirty">
<term>
<mallctl>stats.arenas.&lt;i&gt;.mutexes.extents_dirty.{counter}</mallctl>
(<type>counter specific type</type>) <literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Statistics on <varname>arena.&lt;i&gt;.extents_dirty
</varname> mutex (arena scope; dirty extents related).
<mallctl>{counter}</mallctl> is one of the counters in <link
linkend="mutex_counters">mutex profiling
counters</link>.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.mutexes.extents_muzzy">
<term>
<mallctl>stats.arenas.&lt;i&gt;.mutexes.extents_muzzy.{counter}</mallctl>
(<type>counter specific type</type>) <literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Statistics on <varname>arena.&lt;i&gt;.extents_muzzy
</varname> mutex (arena scope; muzzy extents related).
<mallctl>{counter}</mallctl> is one of the counters in <link
linkend="mutex_counters">mutex profiling
counters</link>.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.mutexes.extents_retained">
<term>
<mallctl>stats.arenas.&lt;i&gt;.mutexes.extents_retained.{counter}</mallctl>
(<type>counter specific type</type>) <literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Statistics on <varname>arena.&lt;i&gt;.extents_retained
</varname> mutex (arena scope; retained extents related).
<mallctl>{counter}</mallctl> is one of the counters in <link
linkend="mutex_counters">mutex profiling
counters</link>.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.mutexes.decay_dirty">
<term>
<mallctl>stats.arenas.&lt;i&gt;.mutexes.decay_dirty.{counter}</mallctl>
(<type>counter specific type</type>) <literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Statistics on <varname>arena.&lt;i&gt;.decay_dirty
</varname> mutex (arena scope; decay for dirty pages related).
<mallctl>{counter}</mallctl> is one of the counters in <link
linkend="mutex_counters">mutex profiling
counters</link>.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.mutexes.decay_muzzy">
<term>
<mallctl>stats.arenas.&lt;i&gt;.mutexes.decay_muzzy.{counter}</mallctl>
(<type>counter specific type</type>) <literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Statistics on <varname>arena.&lt;i&gt;.decay_muzzy
</varname> mutex (arena scope; decay for muzzy pages related).
<mallctl>{counter}</mallctl> is one of the counters in <link
linkend="mutex_counters">mutex profiling
counters</link>.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.mutexes.base">
<term>
<mallctl>stats.arenas.&lt;i&gt;.mutexes.base.{counter}</mallctl>
(<type>counter specific type</type>) <literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Statistics on <varname>arena.&lt;i&gt;.base</varname>
mutex (arena scope; base allocator related).
<mallctl>{counter}</mallctl> is one of the counters in <link
linkend="mutex_counters">mutex profiling
counters</link>.</para></listitem>
</varlistentry>
<varlistentry id="stats.arenas.i.mutexes.tcache_list">
<term>
<mallctl>stats.arenas.&lt;i&gt;.mutexes.tcache_list.{counter}</mallctl>
(<type>counter specific type</type>) <literal>r-</literal>
[<option>--enable-stats</option>]
</term>
<listitem><para>Statistics on
<varname>arena.&lt;i&gt;.tcache_list</varname> mutex (arena scope;
tcache to arena association related). This mutex is expected to be
accessed less often. <mallctl>{counter}</mallctl> is one of the
counters in <link linkend="mutex_counters">mutex profiling
counters</link>.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1 id="heap_profile_format">
<title>HEAP PROFILE FORMAT</title>
<para>Although the heap profiling functionality was originally designed to
be compatible with the
<command>pprof</command> command that is developed as part of the <ulink
url="http://code.google.com/p/gperftools/">gperftools
package</ulink>, the addition of per thread heap profiling functionality
required a different heap profile format. The <command>jeprof</command>
command is derived from <command>pprof</command>, with enhancements to
support the heap profile format described here.</para>
<para>In the following hypothetical heap profile, <constant>[...]</constant>
indicates elision for the sake of compactness. <programlisting><![CDATA[
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:
[...]]]></programlisting> The following matches the above heap profile, but most
tokens are replaced with <constant>&lt;description&gt;</constant> to indicate
descriptions of the corresponding fields. <programlisting><![CDATA[
<heap_profile_format_version>/<mean_sample_interval>
<aggregate>: <curobjs>: <curbytes> [<cumobjs>: <cumbytes>]
[...]
<thread_3_aggregate>: <curobjs>: <curbytes> [<cumobjs>: <cumbytes>]
[...]
<thread_99_aggregate>: <curobjs>: <curbytes> [<cumobjs>: <cumbytes>]
[...]
@ <top_frame> <frame> [...] <frame> <frame> <frame> [...]
<backtrace_aggregate>: <curobjs>: <curbytes> [<cumobjs>: <cumbytes>]
<backtrace_thread_3>: <curobjs>: <curbytes> [<cumobjs>: <cumbytes>]
<backtrace_thread_99>: <curobjs>: <curbytes> [<cumobjs>: <cumbytes>]
[...]
MAPPED_LIBRARIES:
</proc/<pid>/maps>]]></programlisting></para>
</refsect1>
<refsect1 id="debugging_malloc_problems">
<title>DEBUGGING MALLOC PROBLEMS</title>
<para>When debugging, it is a good idea to configure/build jemalloc with
the <option>--enable-debug</option> and <option>--enable-fill</option>
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.</para>
<para>Programs often accidentally depend on <quote>uninitialized</quote>
memory actually being filled with zero bytes. Junk filling
(see the <link linkend="opt.junk"><mallctl>opt.junk</mallctl></link>
option) tends to expose such bugs in the form of obviously incorrect
results and/or coredumps. Conversely, zero
filling (see the <link
linkend="opt.zero"><mallctl>opt.zero</mallctl></link> option) eliminates
the symptoms of such bugs. Between these two options, it is usually
possible to quickly detect, diagnose, and eliminate such bugs.</para>
<para>This implementation does not provide much detail about the problems
it detects, because the performance impact for storing such information
would be prohibitive.</para>
</refsect1>
<refsect1 id="diagnostic_messages">
<title>DIAGNOSTIC MESSAGES</title>
<para>If any of the memory allocation/deallocation functions detect an
error or warning condition, a message will be printed to file descriptor
<constant>STDERR_FILENO</constant>. Errors will result in the process
dumping core. If the <link
linkend="opt.abort"><mallctl>opt.abort</mallctl></link> option is set, most
warnings are treated as errors.</para>
<para>The <varname>malloc_message</varname> variable allows the programmer
to override the function which emits the text strings forming the errors
and warnings if for some reason the <constant>STDERR_FILENO</constant> file
descriptor is not suitable for this.
<function>malloc_message()</function> takes the
<parameter>cbopaque</parameter> pointer argument that is
<constant>NULL</constant> unless overridden by the arguments in a call to
<function>malloc_stats_print()</function>, 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.</para>
<para>All messages are prefixed by
<quote><computeroutput>&lt;jemalloc&gt;: </computeroutput></quote>.</para>
</refsect1>
<refsect1 id="return_values">
<title>RETURN VALUES</title>
<refsect2>
<title>Standard API</title>
<para>The <function>malloc()</function> and
<function>calloc()</function> functions return a pointer to the
allocated memory if successful; otherwise a <constant>NULL</constant>
pointer is returned and <varname>errno</varname> is set to
<errorname>ENOMEM</errorname>.</para>
<para>The <function>posix_memalign()</function> function
returns the value 0 if successful; otherwise it returns an error value.
The <function>posix_memalign()</function> function will fail
if:
<variablelist>
<varlistentry>
<term><errorname>EINVAL</errorname></term>
<listitem><para>The <parameter>alignment</parameter> parameter is
not a power of 2 at least as large as
<code language="C">sizeof(<type>void *</type>)</code>.
</para></listitem>
</varlistentry>
<varlistentry>
<term><errorname>ENOMEM</errorname></term>
<listitem><para>Memory allocation error.</para></listitem>
</varlistentry>
</variablelist>
</para>
<para>The <function>aligned_alloc()</function> function returns
a pointer to the allocated memory if successful; otherwise a
<constant>NULL</constant> pointer is returned and
<varname>errno</varname> is set. The
<function>aligned_alloc()</function> function will fail if:
<variablelist>
<varlistentry>
<term><errorname>EINVAL</errorname></term>
<listitem><para>The <parameter>alignment</parameter> parameter is
not a power of 2.
</para></listitem>
</varlistentry>
<varlistentry>
<term><errorname>ENOMEM</errorname></term>
<listitem><para>Memory allocation error.</para></listitem>
</varlistentry>
</variablelist>
</para>
<para>The <function>realloc()</function> function returns a
pointer, possibly identical to <parameter>ptr</parameter>, to the
allocated memory if successful; otherwise a <constant>NULL</constant>
pointer is returned, and <varname>errno</varname> is set to
<errorname>ENOMEM</errorname> if the error was the result of an
allocation failure. The <function>realloc()</function>
function always leaves the original buffer intact when an error occurs.
</para>
<para>The <function>free()</function> function returns no
value.</para>
</refsect2>
<refsect2>
<title>Non-standard API</title>
<para>The <function>mallocx()</function> and
<function>rallocx()</function> functions return a pointer to
the allocated memory if successful; otherwise a <constant>NULL</constant>
pointer is returned to indicate insufficient contiguous memory was
available to service the allocation request. </para>
<para>The <function>xallocx()</function> function returns the
real size of the resulting resized allocation pointed to by
<parameter>ptr</parameter>, which is a value less than
<parameter>size</parameter> if the allocation could not be adequately
grown in place. </para>
<para>The <function>sallocx()</function> function returns the
real size of the allocation pointed to by <parameter>ptr</parameter>.
</para>
<para>The <function>nallocx()</function> returns the real size
that would result from a successful equivalent
<function>mallocx()</function> function call, or zero if
insufficient memory is available to perform the size computation. </para>
<para>The <function>mallctl()</function>,
<function>mallctlnametomib()</function>, and
<function>mallctlbymib()</function> functions return 0 on
success; otherwise they return an error value. The functions will fail
if:
<variablelist>
<varlistentry>
<term><errorname>EINVAL</errorname></term>
<listitem><para><parameter>newp</parameter> is not
<constant>NULL</constant>, and <parameter>newlen</parameter> is too
large or too small. Alternatively, <parameter>*oldlenp</parameter>
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 <parameter>*oldlenp</parameter>.</para></listitem>
</varlistentry>
<varlistentry>
<term><errorname>ENOENT</errorname></term>
<listitem><para><parameter>name</parameter> or
<parameter>mib</parameter> specifies an unknown/invalid
value.</para></listitem>
</varlistentry>
<varlistentry>
<term><errorname>EPERM</errorname></term>
<listitem><para>Attempt to read or write void value, or attempt to
write read-only value.</para></listitem>
</varlistentry>
<varlistentry>
<term><errorname>EAGAIN</errorname></term>
<listitem><para>A memory allocation failure
occurred.</para></listitem>
</varlistentry>
<varlistentry>
<term><errorname>EFAULT</errorname></term>
<listitem><para>An interface with side effects failed in some way
not directly related to <function>mallctl*()</function>
read/write processing.</para></listitem>
</varlistentry>
</variablelist>
</para>
<para>The <function>malloc_usable_size()</function> function
returns the usable size of the allocation pointed to by
<parameter>ptr</parameter>. </para>
</refsect2>
</refsect1>
<refsect1 id="environment">
<title>ENVIRONMENT</title>
<para>The following environment variable affects the execution of the
allocation functions:
<variablelist>
<varlistentry>
<term><envar>MALLOC_CONF</envar></term>
<listitem><para>If the environment variable
<envar>MALLOC_CONF</envar> is set, the characters it contains
will be interpreted as options.</para></listitem>
</varlistentry>
</variablelist>
</para>
</refsect1>
<refsect1 id="examples">
<title>EXAMPLES</title>
<para>To dump core whenever a problem occurs:
<screen>ln -s 'abort:true' /etc/malloc.conf</screen>
</para>
<para>To specify in the source that only one arena should be automatically
created:
<programlisting language="C"><![CDATA[
malloc_conf = "narenas:1";]]></programlisting></para>
</refsect1>
<refsect1 id="see_also">
<title>SEE ALSO</title>
<para><citerefentry><refentrytitle>madvise</refentrytitle>
<manvolnum>2</manvolnum></citerefentry>,
<citerefentry><refentrytitle>mmap</refentrytitle>
<manvolnum>2</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sbrk</refentrytitle>
<manvolnum>2</manvolnum></citerefentry>,
<citerefentry><refentrytitle>utrace</refentrytitle>
<manvolnum>2</manvolnum></citerefentry>,
<citerefentry><refentrytitle>alloca</refentrytitle>
<manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>atexit</refentrytitle>
<manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>getpagesize</refentrytitle>
<manvolnum>3</manvolnum></citerefentry></para>
</refsect1>
<refsect1 id="standards">
<title>STANDARDS</title>
<para>The <function>malloc()</function>,
<function>calloc()</function>,
<function>realloc()</function>, and
<function>free()</function> functions conform to ISO/IEC
9899:1990 (<quote>ISO C90</quote>).</para>
<para>The <function>posix_memalign()</function> function conforms
to IEEE Std 1003.1-2001 (<quote>POSIX.1</quote>).</para>
</refsect1>
</refentry>
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