| JEMALLOC(3) | User Manual | JEMALLOC(3) |
.SH "NAME" jemalloc - general purpose memory allocation
functions
.SH "LIBRARY"
.PP This manual describes jemalloc
5.4.0-0-g7a34f18502e7b222724097cdcd499b437d189acc. More information can be
found at the jemalloc website[1].
.SH "SYNOPSIS"
#include <jemalloc/jemalloc.h>
.SS "Standard API"
.HP 312u void *malloc(size_t size);
.HP 312u void *calloc(size_t number,
size_t size);
.HP 456u int posix_memalign(void **ptr,
size_t alignment,
size_t size);
.HP 480u void *aligned_alloc(size_t alignment,
size_t size);
.HP 336u void *realloc(void *ptr,
size_t size);
.HP 240u void free(void *ptr);
.HP 384u void free_sized(void *ptr,
size_t size);
.HP 576u void free_aligned_sized(void *ptr,
size_t alignment,
size_t size);
.SS "Non-standard API"
.HP 336u void *mallocx(size_t size,
int flags);
.HP 336u void *rallocx(void *ptr,
size_t size, int flags);
.HP 360u size_t xallocx(void *ptr,
size_t size, size_t extra,
int flags);
.HP 360u size_t sallocx(void *ptr,
int flags);
.HP 312u void dallocx(void *ptr,
int flags);
.HP 336u void sdallocx(void *ptr,
size_t size, int flags);
.HP 360u size_t nallocx(size_t size,
int flags);
.HP 288u int mallctl(const char *name,
void *oldp, size_t *oldlenp,
void *newp,
size_t newlen);
.HP 504u int
mallctlnametomib(const char *name,
size_t *mibp,
size_t *miblenp);
.HP 408u int mallctlbymib(const size_t *mib,
size_t miblen, void *oldp,
size_t *oldlenp, void *newp,
size_t newlen);
.HP 576u void
malloc_stats_print(void (*write_cb) (void *, const char *),
void *cbopaque,
const char *opts);
.HP 624u size_t
malloc_usable_size(const void *ptr);
.HP 552u void (*malloc_message)(void *cbopaque,
const char *s);
.PP const char *malloc_conf;
.SH "DESCRIPTION"
.SS "Standard API"
.PP The malloc() function allocates size bytes of uninitialized
memory. The allocated space is suitably aligned (after possible pointer
coercion) for storage of any type of object.
.PP The calloc() function allocates space for number objects,
each size bytes in length. The result is identical to calling
malloc() with an argument of number * size, with the
exception that the allocated memory is explicitly initialized to zero
bytes.
.PP The posix_memalign() function allocates size bytes of
memory such that the allocation's base address is a multiple of
alignment, and returns the allocation in the value pointed to by
ptr. The requested alignment must be a power of 2 at least as
large as sizeof(void *).
.PP The aligned_alloc() function allocates size bytes of memory
such that the allocation's base address is a multiple of alignment.
The requested alignment must be a power of 2. Behavior is undefined
if size is not an integral multiple of alignment.
.PP The realloc() function changes the size of the previously
allocated memory referenced by ptr to size 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 ptr is
freed and a pointer to the newly allocated memory is returned. Note that
realloc() may move the memory allocation, resulting in a different
return value than ptr. If ptr is NULL, the
realloc() function behaves identically to malloc() for the
specified size.
.PP The free() function causes the allocated memory referenced by
ptr to be made available for future allocations. If ptr is
NULL, no action occurs.
.PP The free_sized() function is an extension of free() with a
size parameter to allow the caller to pass in the allocation size as
an optimization.
.PP The free_aligned_sized() function accepts a ptr which was
allocated with a requested size and alignment, causing the
allocated memory referenced by ptr to be made available for future
allocations.
.SS "Non-standard API"
.PP The mallocx(), rallocx(), xallocx(),
sallocx(), dallocx(), sdallocx(), and nallocx()
functions all have a flags argument that can be used to specify
options. The functions only check the options that are contextually
relevant. Use bitwise or (|) operations to specify one or more of the
following:
.PP MALLOCX_LG_ALIGN(la)
Align the memory allocation to start at an address that is a multiple of (1
<< la). This macro does not validate that la is within
the valid range.
.RE
.PP MALLOCX_ALIGN(a)
Align the memory allocation to start at an address that is a multiple of
a, where a is a power of two. This macro does not validate
that a is a power of 2.
.RE
.PP MALLOCX_ZERO
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.
.RE
.PP MALLOCX_TCACHE(tc)
Use the thread-specific cache (tcache) specified by the identifier tc,
which must have been acquired via the
<mallctl>tcache.create</mallctl> mallctl. This macro does not
validate that tc specifies a valid identifier.
.RE
.PP MALLOCX_TCACHE_NONE
Do not use a thread-specific cache (tcache). Unless
MALLOCX_TCACHE(tc) or MALLOCX_TCACHE_NONE
is specified, an automatically managed tcache will be used under many
circumstances. This macro cannot be used in the same flags argument
as MALLOCX_TCACHE(tc).
.RE
.PP MALLOCX_ARENA(a)
Use the arena specified by the index a. This macro has no effect for
regions that were allocated via an arena other than the one specified. This
macro does not validate that a specifies an arena index in the valid
range.
.RE
.PP The mallocx() function allocates at least size bytes of
memory, and returns a pointer to the base address of the allocation.
Behavior is undefined if size is 0.
.PP The rallocx() function resizes the allocation at ptr to be
at least size 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 size is 0.
.PP The xallocx() function resizes the allocation at ptr in
place to be at least size bytes, and returns the real size of the
allocation. If extra is non-zero, an attempt is made to resize the
allocation to be at least (size + extra) bytes, though
inability to allocate the extra byte(s) will not by itself result in failure
to resize. Behavior is undefined if size is 0, or if
(size + extra > SIZE_T_MAX).
.PP The sallocx() function returns the real size of the allocation at
ptr.
.PP The dallocx() function causes the memory referenced by ptr
to be made available for future allocations.
.PP The sdallocx() function is an extension of dallocx() with a
size 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 nallocx() or sallocx().
.PP The nallocx() function allocates no memory, but it performs the
same size computation as the mallocx() function, and returns the real
size of the allocation that would result from the equivalent
mallocx() function call, or 0 if the inputs exceed the maximum
supported size class and/or alignment. Behavior is undefined if size
is 0.
.PP The mallctl() function provides a general interface for
introspecting the memory allocator, as well as setting modifiable parameters
and triggering actions. The period-separated name argument specifies
a location in a tree-structured namespace; see the MALLCTL NAMESPACE section
for documentation on the tree contents. To read a value, pass a pointer via
oldp to adequate space to contain the value, and a pointer to its
length via oldlenp; otherwise pass NULL and NULL.
Similarly, to write a value, pass a pointer to the value via newp,
and its length via newlen; otherwise pass NULL and
0.
.PP The mallctlnametomib() function provides a way to avoid repeated
name lookups for applications that repeatedly query the same portion of the
namespace, by translating a name to a “Management Information
Base” (MIB) that can be passed repeatedly to mallctlbymib().
Upon successful return from mallctlnametomib(), mibp contains
an array of *miblenp integers, where *miblenp is the lesser of
the number of components in name and the input value of
*miblenp. Thus it is possible to pass a *miblenp 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
<mallctl>arenas.bin.2.size</mallctl>), the corresponding MIB
component will always be that integer. Therefore, it is legitimate to
construct code like the following:
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... */
}
.PP
.RE
.PP The malloc_stats_print() function writes summary statistics via
the write_cb callback function pointer and cbopaque data
passed to write_cb, or malloc_message() if write_cb is
NULL. The statistics are presented in human-readable form unless
“J” is specified as a character within the opts string,
in which case the statistics are presented in JSON format[2]. This
function can be called repeatedly. General information that never changes
during execution can be omitted by specifying “g” as a
character within the opts string. Note that
malloc_stats_print() uses the mallctl*() functions internally,
so inconsistent statistics can be reported if multiple threads use these
functions simultaneously. If --enable-stats is specified during
configuration, “m”, “d”, and “a”
can be specified to omit merged arena, destroyed merged arena, and per arena
statistics, respectively; “b” and “l” can be
specified to omit per size class statistics for bins and large objects,
respectively; “x” can be specified to omit all mutex
statistics; “e” can be used to omit extent statistics.
Unrecognized characters are silently ignored. Note that thread caching may
prevent some statistics from being completely up to date, since extra
locking would be required to merge counters that track thread cache
operations.
.PP The malloc_usable_size() function returns the usable size of the
allocation pointed to by ptr. The return value may be larger than the
size that was requested during allocation. The malloc_usable_size()
function is not a mechanism for in-place realloc(); rather it is
provided solely as a tool for introspection purposes. Any discrepancy
between the requested allocation size and the size reported by
malloc_usable_size() should not be depended on, since such behavior
is entirely implementation-dependent.
.SS "Interactions Between the Standard and Non-standard APIs"
.PP Generally speaking it is permissible to pass pointers obtained from the
standard API to the non-standard API and vice versa (e.g. calling
free() with a pointer returned by a call to mallocx(), calling
sdallocx() with a pointer returned by a call to calloc()).
There are however a few exceptions. In keeping with the C23 standard
– which forbids calling free_sized() on a pointer returned by
aligned_alloc(), mandating that either free_aligned_sized() or
free() 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.
.SH "TUNING"
.PP 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.
.PP The string specified via --with-malloc-conf, the string pointed to
by the global variable malloc_conf, the “name” of the
file referenced by the symbolic link named /etc/malloc.conf, and the value
of the environment variable MALLOC_CONF, will be interpreted, in that
order, from left to right as options. Note that malloc_conf may be
read before main() is entered, so the declaration of
malloc_conf should specify an initializer that contains the final
value to be read by jemalloc. --with-malloc-conf and
malloc_conf are compile-time mechanisms, whereas /etc/malloc.conf and
MALLOC_CONF can be safely set any time prior to program
invocation.
.PP An options string is a comma-separated list of option:value pairs. There
is one key corresponding to each <mallctl>opt.*</mallctl>
mallctl (see the MALLCTL NAMESPACE section for options documentation). For
example, abort:true,narenas:1 sets the
<mallctl>opt.abort</mallctl> and
<mallctl>opt.narenas</mallctl> 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.
.SH "IMPLEMENTATION NOTES"
.PP Traditionally, allocators have used sbrk(2) to obtain memory,
which is suboptimal for several reasons, including race conditions,
increased fragmentation, and artificial limitations on maximum usable
memory. If sbrk(2) is supported by the operating system, this
allocator uses both mmap(2) and sbrk(2), in that order of
preference; otherwise only mmap(2) is used.
.PP 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.
.PP 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.
.PP 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.
.PP 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 sizeof(double). 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 PTRDIFF_MAX.
.PP 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.
.PP The realloc(), rallocx(), and xallocx() functions
may resize allocations without moving them under limited circumstances.
Unlike the *allocx() 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 realloc() 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 <mallctl>arena.<i>.extent_hooks</mallctl>).
Growth only succeeds if the trailing memory is currently available, and the
extent allocator supports merging.
.PP Assuming 4 KiB pages and a 16-byte quantum on a 64-bit system, the size
classes in each category are as shown in Table 1.
.sp
Table 1. Size classes
| Category | Spacing | Size |
| Small | lg | [8] |
| 16 | [16, 32, 48, 64, 80, 96, 112, 128] | |
| 32 | [160, 192, 224, 256] | |
| 64 | [320, 384, 448, 512] | |
| 128 | [640, 768, 896, 1024] | |
| 256 | [1280, 1536, 1792, 2048] | |
| 512 | [2560, 3072, 3584, 4096] | |
| 1 KiB | [5 KiB, 6 KiB, 7 KiB, 8 KiB] | |
| 2 KiB | [10 KiB, 12 KiB, 14 KiB] | |
| Large | 2 KiB | [16 KiB] |
| 4 KiB | [20 KiB, 24 KiB, 28 KiB, 32 KiB] | |
| 8 KiB | [40 KiB, 48 KiB, 56 KiB, 64 KiB] | |
| 16 KiB | [80 KiB, 96 KiB, 112 KiB, 128 KiB] | |
| 32 KiB | [160 KiB, 192 KiB, 224 KiB, 256 KiB] | |
| 64 KiB | [320 KiB, 384 KiB, 448 KiB, 512 KiB] | |
| 128 KiB | [640 KiB, 768 KiB, 896 KiB, 1 MiB] | |
| 256 KiB | [1280 KiB, 1536 KiB, 1792 KiB, 2 MiB] | |
| 512 KiB | [2560 KiB, 3 MiB, 3584 KiB, 4 MiB] | |
| 1 MiB | [5 MiB, 6 MiB, 7 MiB, 8 MiB] | |
| 2 MiB | [10 MiB, 12 MiB, 14 MiB, 16 MiB] | |
| 4 MiB | [20 MiB, 24 MiB, 28 MiB, 32 MiB] | |
| 8 MiB | [40 MiB, 48 MiB, 56 MiB, 64 MiB] | |
| ... | ... | |
| 512 PiB | [2560 PiB, 3 EiB, 3584 PiB, 4 EiB] | |
| 1 EiB | [5 EiB, 6 EiB, 7 EiB] |
.SH "MALLCTL NAMESPACE"
.PP The following names are defined in the namespace accessible via the
mallctl*() functions. Value types are specified in parentheses, their
readable/writable statuses are encoded as rw, r-, -w, or --, and required
build configuration flags follow, if any. A name element encoded as
<i> or <j> 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.<i>.*</mallctl> and
<mallctl>arena.<i>.{initialized,purge,decay,dss}</mallctl>,
<i> equal to MALLCTL_ARENAS_ALL can be used to operate on all
arenas or access the summation of statistics from all arenas; similarly
<i> equal to MALLCTL_ARENAS_DESTROYED can be used to access the
summation of statistics from all destroyed arenas. These constants can be
utilized either via mallctlnametomib() followed by
mallctlbymib(), or via code such as the following:
#define STRINGIFY_HELPER(x) #x
#define STRINGIFY(x) STRINGIFY_HELPER(x)
mallctl("arena." STRINGIFY(MALLCTL_ARENAS_ALL) ".decay",
NULL, NULL, NULL, 0);
Take special note of the <mallctl>epoch</mallctl> mallctl, which controls refreshing of cached dynamic statistics.
.PP <mallctl>version</mallctl> (const char *) r-
Return the jemalloc version string.
.RE
.PP <mallctl>epoch</mallctl> (uint64_t) rw
If a value is passed in, refresh the data from which the mallctl*()
functions report values, and increment the epoch. Return the current epoch.
This is useful for detecting whether another thread caused a refresh.
.RE
.PP <mallctl>background_thread</mallctl> (bool) rw
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 purging asynchronously. When switching off,
background threads are terminated synchronously. Note that after
fork(2) function, the state in the child process will be disabled
regardless the state in parent process. See
<mallctl>stats.background_thread</mallctl> for related stats.
<mallctl>opt.background_thread</mallctl> can be used to set the
default option. This option is only available on selected pthread-based
platforms.
.RE
.PP <mallctl>max_background_threads</mallctl> (size_t)
rw
Maximum number of background worker threads that will be created. This value
is capped at <mallctl>opt.max_background_threads</mallctl> at
startup.
.RE
.PP <mallctl>config.cache_oblivious</mallctl> (bool)
r-
--enable-cache-oblivious was specified during build configuration.
.RE
.PP <mallctl>config.debug</mallctl> (bool) r-
--enable-debug was specified during build configuration.
.RE
.PP <mallctl>config.fill</mallctl> (bool) r-
--enable-fill was specified during build configuration.
.RE
.PP <mallctl>config.infallible_new</mallctl> (bool) r-
--enable-cxx-infallible-new was specified during build
configuration.
.RE
.PP <mallctl>config.lazy_lock</mallctl> (bool) r-
--enable-lazy-lock was specified during build configuration.
.RE
.PP <mallctl>config.malloc_conf</mallctl> (const char *)
r-
Embedded configure-time-specified run-time options string, empty unless
--with-malloc-conf was specified during build configuration.
.RE
.PP <mallctl>config.prof</mallctl> (bool) r-
--enable-prof was specified during build configuration.
.RE
.PP <mallctl>config.prof_libgcc</mallctl> (bool) r-
--disable-prof-libgcc was not specified during build
configuration.
.RE
.PP <mallctl>config.prof_libunwind</mallctl> (bool) r-
--enable-prof-libunwind was specified during build configuration.
.RE
.PP <mallctl>config.stats</mallctl> (bool) r-
--enable-stats was specified during build configuration.
.RE
.PP <mallctl>config.utrace</mallctl> (bool) r-
--enable-utrace was specified during build configuration.
.RE
.PP <mallctl>config.xmalloc</mallctl> (bool) r-
--enable-xmalloc was specified during build configuration.
.RE
.PP <mallctl>opt.abort</mallctl> (bool) r-
Abort-on-warning enabled/disabled. If true, most warnings are fatal. Note
that runtime option warnings are not included (see
<mallctl>opt.abort_conf</mallctl> for that). The process will
call abort(3) in these cases. This option is disabled by default
unless --enable-debug is specified during configuration, in which
case it is enabled by default.
.RE
.PP <mallctl>opt.confirm_conf</mallctl> (bool) r-
Confirm-runtime-options-when-program-starts enabled/disabled. If true, the string specified via --with-malloc-conf, the string pointed to by the global variable malloc_conf, the “name” of the file referenced by the symbolic link named /etc/malloc.conf, and the value of the environment variable MALLOC_CONF, will be printed in order. Then, each option being set will be individually printed. This option is disabled by default.
.RE
.PP <mallctl>opt.abort_conf</mallctl> (bool) r-
Abort-on-invalid-configuration enabled/disabled. If true, invalid runtime
options are fatal. The process will call abort(3) in these cases.
This option is disabled by default unless --enable-debug is specified
during configuration, in which case it is enabled by default.
.RE
.PP <mallctl>opt.cache_oblivious</mallctl> (bool) r-
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.
.RE
.PP <mallctl>opt.metadata_thp</mallctl> (const char *)
r-
Controls whether to allow jemalloc to use transparent huge page (THP) for
internal metadata (see stats.metadata). “always” allows such
usage. “auto” uses no THP initially, but may begin to do so
when metadata usage reaches certain level. The default is
“disabled”.
.RE
.PP <mallctl>opt.trust_madvise</mallctl> (bool) r-
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.
.RE
.PP <mallctl>opt.retain</mallctl> (bool) r-
If true, retain unused virtual memory for later reuse rather than discarding
it by calling munmap(2) or equivalent (see stats.retained for related
details). It also makes jemalloc use mmap(2) or equivalent in a more
greedy way, mapping larger chunks in one go. This option is disabled by
default unless discarding virtual memory is known to trigger
platform-specific performance problems, namely 1) for [64-bit] Linux, which
has a quirk in its virtual memory allocation algorithm that causes
semi-permanent VM map holes under normal jemalloc operation; and 2) for
[64-bit] Windows, which disallows split / merged regions with
MEM_RELEASE. 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.
.RE
.PP <mallctl>opt.dss</mallctl> (const char *) r-
dss (sbrk(2)) allocation precedence as related to mmap(2)
allocation. The following settings are supported if sbrk(2) is
supported by the operating system: “disabled”,
“primary”, and “secondary”; otherwise only
“disabled” is supported. The default is
“secondary” if sbrk(2) is supported by the operating
system; “disabled” otherwise.
.RE
.PP <mallctl>opt.narenas</mallctl> (unsigned) r-
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.
.RE
.PP <mallctl>opt.oversize_threshold</mallctl> (size_t)
r-
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 narenas), 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
MALLOCX_ARENA, or threads associated with explicit arenas will not be
considered. The default threshold is 8MiB. Values not within large size
classes disables this feature.
.RE
.PP <mallctl>opt.percpu_arena</mallctl> (const char *)
r-
Per CPU arena mode. Use the “percpu” setting to enable this
feature, which uses number of CPUs to determine number of arenas, and bind
threads to arenas dynamically based on the CPU the thread runs on currently.
“phycpu” setting uses one arena per physical CPU, which means
the two hyper threads on the same CPU share one arena. Note that no runtime
checking regarding the availability of hyper threading is done at the
moment. When set to “disabled”, narenas and thread to arena
association will not be impacted by this option. The default is
“disabled”.
.RE
.PP <mallctl>opt.background_thread</mallctl> (bool) r-
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 background_thread for dynamic control options and details.
This option is disabled by default.
.RE
.PP <mallctl>opt.max_background_threads</mallctl> (size_t)
r-
Maximum number of background threads that will be created if
background_thread is set. Defaults to 4.
.RE
.PP <mallctl>opt.dirty_decay_ms</mallctl> (ssize_t) r-
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.
madvise(...MADV_FREE) 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 <mallctl>arenas.dirty_decay_ms</mallctl> and
<mallctl>arena.<i>.dirty_decay_ms</mallctl> for related
dynamic control options. See
<mallctl>opt.muzzy_decay_ms</mallctl> for a description of muzzy
pages. Note that when the <mallctl>oversize_threshold</mallctl>
feature is enabled, the arenas reserved for oversize requests may have its
own default decay settings.
.RE
.PP <mallctl>opt.muzzy_decay_ms</mallctl> (ssize_t) r-
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.
madvise(...MADV_FREE)), 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. Muzzy decay
is disabled by default (with decay time 0). See
<mallctl>arenas.muzzy_decay_ms</mallctl> and
<mallctl>arena.<i>.muzzy_decay_ms</mallctl> for related
dynamic control options.
.RE
.PP <mallctl>opt.lg_extent_max_active_fit</mallctl>
(size_t) r-
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).
.RE
.PP <mallctl>opt.stats_print</mallctl> (bool) r-
Enable/disable statistics printing at exit. If enabled, the
malloc_stats_print() function is called at program exit via an
atexit(3) function.
<mallctl>opt.stats_print_opts</mallctl> can be combined to
specify output options. If --enable-stats 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, atexit() may allocate memory
during application initialization and then deadlock internally when jemalloc
in turn calls atexit(), so this option is not universally usable
(though the application can register its own atexit() 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.
.RE
.PP <mallctl>opt.stats_print_opts</mallctl> (const char *)
r-
Options (the opts string) to pass to the malloc_stats_print()
at exit (enabled through <mallctl>opt.stats_print</mallctl>).
See available options in malloc_stats_print(). Has no effect unless
<mallctl>opt.stats_print</mallctl> is enabled. The default is
“”.
.RE
.PP <mallctl>opt.stats_interval</mallctl> (int64_t) r-
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
malloc_stats_print().
<mallctl>opt.stats_interval_opts</mallctl> can be combined to
specify output options. By default, interval-triggered stats output is
disabled (encoded as -1).
.RE
.PP <mallctl>opt.stats_interval_opts</mallctl> (const char
*) r-
Options (the opts string) to pass to the malloc_stats_print()
for interval based statistics printing (enabled through
<mallctl>opt.stats_interval</mallctl>). See available options in
malloc_stats_print(). Has no effect unless
<mallctl>opt.stats_interval</mallctl> is enabled. The default is
“”.
.RE
.PP <mallctl>opt.junk</mallctl> (const char *) r-
[--enable-fill]
Junk filling. If set to “alloc”, each byte of uninitialized
allocated memory will be initialized to 0xa5. If set to
“free”, all deallocated memory will be initialized to 0x5a. If
set to “true”, both allocated and deallocated memory will be
initialized, and if set to “false”, junk filling be disabled
entirely. This is intended for debugging and will impact performance
negatively. This option is “false” by default unless
--enable-debug is specified during configuration, in which case it is
“true” by default.
.RE
.PP <mallctl>opt.zero</mallctl> (bool) r-
[--enable-fill]
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 realloc() and rallocx()
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.
.RE
.PP <mallctl>opt.utrace</mallctl> (bool) r-
[--enable-utrace]
Allocation tracing based on utrace(2) enabled/disabled. This option is
disabled by default.
.RE
.PP <mallctl>opt.xmalloc</mallctl> (bool) r-
[--enable-xmalloc]
Abort-on-out-of-memory enabled/disabled. If enabled, rather than returning
failure for any allocation function, display a diagnostic message on
STDERR_FILENO and cause the program to drop core (using
abort(3)). If an application is designed to depend on this behavior,
set the option at compile time by including the following in the source
code:
malloc_conf = "xmalloc:true";
This option is disabled by default.
.RE
.PP <mallctl>opt.tcache</mallctl> (bool) r-
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 <mallctl>opt.tcache_max</mallctl> option for related
tuning information. This option is enabled by default.
.RE
.PP <mallctl>opt.tcache_max</mallctl> (size_t) r-
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.
.RE
.PP <mallctl>opt.thp</mallctl> (const char *) r-
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 MADV_HUGEPAGE;
"never" ensures no transparent hugepage with
MADV_NOHUGEPAGE; the default setting "default" makes
no changes. Note that: this option does not affect THP for jemalloc internal
metadata (see <mallctl>opt.metadata_thp</mallctl>); in addition,
for arenas with customized <mallctl>extent_hooks</mallctl>, this
option is bypassed as it is implemented as part of the default extent
hooks.
.RE
.PP <mallctl>opt.prof_bt_max</mallctl> (unsigned) r-
[--enable-prof]
Maximum number of stack frames to record in profiling backtraces. The default
is 128.
.RE
.PP <mallctl>opt.prof</mallctl> (bool) r-
[--enable-prof]
Memory profiling enabled/disabled. If enabled, profile memory allocation
activity. See the <mallctl>opt.prof_active</mallctl> option for
on-the-fly activation/deactivation. See the
<mallctl>opt.lg_prof_sample</mallctl> option for probabilistic
sampling control. See the <mallctl>opt.prof_accum</mallctl>
option for control of cumulative sample reporting. See the
<mallctl>opt.lg_prof_interval</mallctl> option for information
on interval-triggered profile dumping, the
<mallctl>opt.prof_gdump</mallctl> option for information on
high-water-triggered profile dumping, and the
<mallctl>opt.prof_final</mallctl> option for final profile
dumping. Profile output is compatible with the jeprof command, which
is based on the pprof that is developed as part of the gperftools
package[3]. See HEAP PROFILE FORMAT for heap profile format
documentation.
.RE
.PP <mallctl>opt.prof_prefix</mallctl> (const char *) r-
[--enable-prof]
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 jeprof. This prefix value can be overridden by
<mallctl>prof.prefix</mallctl>.
.RE
.PP <mallctl>opt.prof_active</mallctl> (bool) r-
[--enable-prof]
Profiling activated/deactivated. This is a secondary control mechanism that
makes it possible to start the application with profiling enabled (see the
<mallctl>opt.prof</mallctl> option) but inactive, then toggle
profiling at any time during program execution with the
<mallctl>prof.active</mallctl> mallctl. This option is enabled
by default.
.RE
.PP <mallctl>opt.prof_thread_active_init</mallctl> (bool)
r- [--enable-prof]
Initial setting for <mallctl>thread.prof.active</mallctl> in
newly created threads. The initial setting for newly created threads can
also be changed during execution via the
<mallctl>prof.thread_active_init</mallctl> mallctl. This option
is enabled by default.
.RE
.PP <mallctl>opt.lg_prof_sample</mallctl> (size_t) r-
[--enable-prof]
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).
.RE
.PP <mallctl>opt.prof_accum</mallctl> (bool) r-
[--enable-prof]
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.
.RE
.PP <mallctl>opt.prof_pid_namespace</mallctl> (bool) r-
[--enable-prof]
Enable adding the pid namespace to the profile filename. Profiles are dumped
to files named according to the pattern
<prefix>.<pid_namespace>.<pid>.<seq>.i<iseq>.heap,
where <prefix> is controlled by the
<mallctl>opt.prof_prefix</mallctl> and
<mallctl>prof.prefix</mallctl> options.
.RE
.PP <mallctl>opt.lg_prof_interval</mallctl> (ssize_t) r-
[--enable-prof]
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 <prefix>.<pid>.<seq>.i<iseq>.heap, where
<prefix> is controlled by the
<mallctl>opt.prof_prefix</mallctl> and
<mallctl>prof.prefix</mallctl> options. By default,
interval-triggered profile dumping is disabled (encoded as -1).
.RE
.PP <mallctl>opt.prof_gdump</mallctl> (bool) r-
[--enable-prof]
Set the initial state of <mallctl>prof.gdump</mallctl>, which
when enabled triggers a memory profile dump every time the total virtual
memory exceeds the previous maximum. This option is disabled by default.
.RE
.PP <mallctl>opt.prof_final</mallctl> (bool) r-
[--enable-prof]
Use an atexit(3) function to dump final memory usage to a file named
according to the pattern <prefix>.<pid>.<seq>.f.heap,
where <prefix> is controlled by the
<mallctl>opt.prof_prefix</mallctl> and
<mallctl>prof.prefix</mallctl> options. Note that
atexit() may allocate memory during application initialization and
then deadlock internally when jemalloc in turn calls atexit(), so
this option is not universally usable (though the application can register
its own atexit() function with equivalent functionality). This option
is disabled by default.
.RE
.PP <mallctl>opt.prof_leak</mallctl> (bool) r-
[--enable-prof]
Leak reporting enabled/disabled. If enabled, use an atexit(3) function
to report memory leaks detected by allocation sampling. See the
<mallctl>opt.prof</mallctl> option for information on analyzing
heap profile output. Works only when combined with
<mallctl>opt.prof_final</mallctl>, otherwise does nothing. This
option is disabled by default.
.RE
.PP <mallctl>opt.prof_leak_error</mallctl> (bool) r-
[--enable-prof]
Similar to <mallctl> opt.prof_leak</mallctl>, but makes the
process exit with error code 1 if a memory leak is detected. This option
supersedes <mallctl>opt.prof_leak</mallctl>, meaning that if
both are specified, this option takes precedence. When enabled, also enables
<mallctl> opt.prof_leak</mallctl>. Works only when combined with
<mallctl>opt.prof_final</mallctl>, otherwise does nothing. This
option is disabled by default.
.RE
.PP <mallctl>opt.zero_realloc</mallctl> (const char *)
r-
Determines the behavior of realloc() when passed a value of zero for
the new size. “alloc” treats this as an allocation of size
zero (and returns a non-null result except in case of resource exhaustion).
“free” treats this as a deallocation of the pointer, and
returns NULL without setting errno. “abort”
aborts the process if zero is passed. The default is “free” on
Linux and Windows, and “alloc” elsewhere.
There is considerable divergence of behaviors across implementations in handling this case. Many have the behavior of “free”. This can introduce security vulnerabilities, since a NULL return value indicates failure, and the continued validity of the passed-in pointer (per POSIX and C11). “alloc” is safe, but can cause leaks in programs that expect the common behavior. Programs intended to be portable and leak-free cannot assume either behavior, and must therefore never call realloc with a size of 0. The “abort” option enables these testing this behavior.
.RE
.PP <mallctl>opt.debug_double_free_max_scan</mallctl>
(unsigned) r- [--enable-debug]
Maximum number of cached pointers to scan in the thread cache when checking
for double-free errors on deallocation. When debug is enabled, each
deallocation into the tcache scans up to this many recently cached pointers
to detect whether the same pointer is being freed twice. Setting this to 0
disables the check. This option is set to 0 and has no effect when debug is
not enabled. The default is 32.
.RE
.PP <mallctl>opt.disable_large_size_classes</mallctl>
(bool) r-
When enabled (the default), large allocations (i.e. allocations of size >=
SC_LARGE_MINCLASS) are rounded up to the nearest page boundary rather
than the nearest large size class. This minimizes memory overhead,
especially when using hugepages, at the cost of disabling the standard large
size class hierarchy.
.RE
.PP <mallctl>opt.process_madvise_max_batch</mallctl>
(size_t) r-
Maximum number of memory regions to include in each process_madvise(2)
batch call. When set to 0 (the default), process_madvise is not used, and
the standard madvise(2) is used instead. Setting this to a positive
value enables batched purging via process_madvise, which can reduce the
number of system calls needed for purging.
.RE
.PP <mallctl>thread.arena</mallctl> (unsigned) rw
Get or set the arena associated with the calling thread. If the specified
arena was not initialized beforehand (see the
<mallctl>arena.i.initialized</mallctl> mallctl), it will be
automatically initialized as a side effect of calling this interface.
.RE
.PP <mallctl>thread.allocated</mallctl> (uint64_t) r-
[--enable-stats]
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.
.RE
.PP <mallctl>thread.allocatedp</mallctl> (uint64_t *) r-
[--enable-stats]
Get a pointer to the the value that is returned by the
<mallctl>thread.allocated</mallctl> mallctl. This is useful for
avoiding the overhead of repeated mallctl*() calls. Note that the
underlying counter should not be modified by the application.
.RE
.PP <mallctl>thread.deallocated</mallctl> (uint64_t) r-
[--enable-stats]
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.
.RE
.PP <mallctl>thread.deallocatedp</mallctl> (uint64_t *) r-
[--enable-stats]
Get a pointer to the the value that is returned by the
<mallctl>thread.deallocated</mallctl> mallctl. This is useful
for avoiding the overhead of repeated mallctl*() calls. Note that the
underlying counter should not be modified by the application.
.RE
.PP <mallctl>thread.peak.read</mallctl> (uint64_t) r-
[--enable-stats]
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
<mallctl>thread.peak.reset</mallctl>, or since the thread's
creation if it has not called
<mallctl>thread.peak.reset</mallctl>. No guarantees are made
about the quality of the approximation, but jemalloc currently endeavors to
maintain accuracy to within one hundred kilobytes.
.RE
.PP <mallctl>thread.peak.reset</mallctl> (void) --
[--enable-stats]
Resets the counter for net bytes allocated in the calling thread to zero.
This affects subsequent calls to
<mallctl>thread.peak.read</mallctl>, but not the values returned
by <mallctl>thread.allocated</mallctl> or
<mallctl>thread.deallocated</mallctl>.
.RE
.PP <mallctl>thread.tcache.enabled</mallctl> (bool) rw
Enable/disable calling thread's tcache. The tcache is implicitly flushed as a
side effect of becoming disabled (see
<mallctl>thread.tcache.flush</mallctl>).
.RE
.PP <mallctl>thread.tcache.flush</mallctl> (void) --
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.
.RE
.PP <mallctl>thread.tcache.max</mallctl> (size_t) rw
Get or set the maximum cached size class (tcache_max) for the calling
thread's tcache. The value is clamped to the maximum allowed limit and
rounded up to the nearest size class boundary. Changing this value will
resize the thread cache accordingly.
.RE
.PP <mallctl>thread.tcache.ncached_max.read_sizeclass</mallctl>
(size_t) rw
Query the maximum number of cached objects (ncached_max) for a given
size class in the calling thread's tcache. The size class is passed in via
newp, and the corresponding ncached_max is returned via
oldp.
.RE
.PP <mallctl>thread.tcache.ncached_max.write</mallctl> (char
*) -w
Set the maximum number of cached objects (ncached_max) for size
classes in the calling thread's tcache. The input is a string of
pipe-separated settings, where each setting specifies a size range and a
count, in the same format as the
<mallctl>opt.tcache_ncached_max</mallctl> runtime option.
.RE
.PP <mallctl>thread.prof.name</mallctl> (const char *) r-
or -w [--enable-prof]
Get/set the descriptive name associated with the calling thread in memory
profile dumps. An internal copy of the name string is created, so the input
string need not be maintained after this interface completes execution. The
output string of this interface should be copied for non-ephemeral uses,
because multiple implementation details can cause asynchronous string
deallocation. Furthermore, each invocation of this interface can only read
or write; simultaneous read/write is not supported due to string lifetime
limitations. The name string must be nil-terminated and comprised only of
characters in the sets recognized by isgraph(3) and
isblank(3).
.RE
.PP <mallctl>thread.prof.active</mallctl> (bool) rw
[--enable-prof]
Control whether sampling is currently active for the calling thread. This is
an activation mechanism in addition to
<mallctl>prof.active</mallctl>; both must be active for the
calling thread to sample. This flag is enabled by default.
.RE
.PP <mallctl>thread.idle</mallctl> (void) --
Hints to jemalloc that the calling thread will be idle for some nontrivial
period of time (say, on the order of seconds), and that doing some cleanup
operations may be beneficial. There are no guarantees as to what specific
operations will be performed; currently this flushes the caller's tcache and
may (according to some heuristic) purge its associated arena.
This is not intended to be a general-purpose background activity mechanism, and threads should not wake up multiple times solely to call it. Rather, a thread waiting for a task should do a timed wait first, call <mallctl>thread.idle</mallctl> if no task appears in the timeout interval, and then do an untimed wait. For such a background activity mechanism, see <mallctl>background_thread</mallctl>.
.RE
.PP <mallctl>tcache.create</mallctl> (unsigned) r-
Create an explicit thread-specific cache (tcache) and return an identifier
that can be passed to the MALLOCX_TCACHE(tc)
macro to explicitly use the specified cache rather than the automatically
managed one that is used by default. Each explicit cache can be used by only
one thread at a time; the application must assure that this constraint
holds.
If the amount of space supplied for storing the thread-specific cache
identifier does not equal sizeof(unsigned), no thread-specific cache
will be created, no data will be written to the space pointed by
oldp, and *oldlenp will be set to 0.
.RE
.PP <mallctl>tcache.flush</mallctl> (unsigned) -w
Flush the specified thread-specific cache (tcache). The same considerations
apply to this interface as to
<mallctl>thread.tcache.flush</mallctl>, except that the tcache
will never be automatically discarded.
.RE
.PP <mallctl>tcache.destroy</mallctl> (unsigned) -w
Flush the specified thread-specific cache (tcache) and make the identifier
available for use during a future tcache creation.
.RE
.PP <mallctl>arena.<i>.initialized</mallctl> (bool)
r-
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
MALLCTL_ARENAS_ALL are initialized (always true).
.RE
.PP <mallctl>arena.<i>.decay</mallctl> (void) --
Trigger decay-based purging of unused dirty/muzzy pages for arena <i>,
or for all arenas if <i> equals MALLCTL_ARENAS_ALL. The
proportion of unused dirty/muzzy pages to be purged depends on the current
time; see <mallctl>opt.dirty_decay_ms</mallctl> and
<mallctl>opt.muzy_decay_ms</mallctl> for details.
.RE
.PP <mallctl>arena.<i>.purge</mallctl> (void) --
Purge all unused dirty pages for arena <i>, or for all arenas if
<i> equals MALLCTL_ARENAS_ALL.
.RE
.PP <mallctl>arena.<i>.reset</mallctl> (void) --
Discard all of the arena's extant allocations. This interface can only be
used with arenas explicitly created via
<mallctl>arenas.create</mallctl>. 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.
.RE
.PP <mallctl>arena.<i>.destroy</mallctl> (void)
--
Destroy the arena. Discard all of the arena's extant allocations using the
same mechanism as for <mallctl>arena.<i>.reset</mallctl>
(with all the same constraints and side effects), merge the arena stats into
those accessible at arena index MALLCTL_ARENAS_DESTROYED, and then
completely discard all metadata associated with the arena. Future calls to
<mallctl>arenas.create</mallctl> may recycle the arena index.
Destruction will fail if any threads are currently associated with the arena
as a result of calls to <mallctl>thread.arena</mallctl>.
.RE
.PP <mallctl>arena.<i>.name</mallctl> (char *)
rw
Get or set a descriptive name for arena <i>. Arena names can be up to
32 characters long (including the null terminator); longer names are
truncated. When reading, the caller passes a pointer to a pre-allocated
buffer (of at least 32 bytes) via oldp, and *oldlenp must be
sizeof(char *). Arena names are also included in the output of
malloc_stats_print().
.RE
.PP <mallctl>arena.<i>.dss</mallctl> (const char *)
rw
Set the precedence of dss allocation as related to mmap allocation for arena
<i>, or for all arenas if <i> equals MALLCTL_ARENAS_ALL.
See <mallctl>opt.dss</mallctl> for supported settings.
.RE
.PP <mallctl>arena.<i>.dirty_decay_ms</mallctl>
(ssize_t) rw
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 <mallctl>opt.dirty_decay_ms</mallctl> for
additional information.
.RE
.PP <mallctl>arena.<i>.muzzy_decay_ms</mallctl>
(ssize_t) rw
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 <mallctl>opt.muzzy_decay_ms</mallctl> for
additional information.
.RE
.PP <mallctl>arena.<i>.retain_grow_limit</mallctl>
(size_t) rw
Maximum size to grow retained region (only relevant when
<mallctl>opt.retain</mallctl> is enabled). This controls the
maximum increment to expand virtual memory, or allocation through
<mallctl>arena.<i>extent_hooks</mallctl>. 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.
.RE
.PP <mallctl>arena.<i>.extent_hooks</mallctl>
(extent_hooks_t *) rw
Get or set the extent management hook functions for arena <i>. The
functions must be capable of operating on all extant extents associated with
arena <i>, usually by passing unknown extents to the replaced
functions. In practice, it is feasible to control allocation for arenas
explicitly created via <mallctl>arenas.create</mallctl> 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.
An extent must be operated on (dalloc, destroy, commit, decommit, purge,
split, merge) by a hook capable of handling it, normally the hook that
allocated it. Replacing hooks on a live arena is tricky and thus
discouraged. If the hook is replaced anyway, the new hook should forward
operations on extents it did not allocate to the previous hook (e.g., the
new dalloc dispatches to the previous dalloc for an old-hook-allocated
extent). The new hook should also avoid merging extents allocated by
different hooks.
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;
};
The extent_hooks_t structure comprises function pointers which are
described individually below. jemalloc uses these functions to manage extent
lifetime, which starts off with allocation of mapped committed memory, in
the simplest case followed by deallocation. However, there are performance
and platform reasons to retain extents for later reuse. Cleanup attempts
cascade from deallocation to decommit to forced purging to lazy purging,
which gives the extent management functions opportunities to reject the most
permanent cleanup operations in favor of less permanent (and often less
costly) operations. All operations except allocation can be universally
opted out of by setting the hook pointers to NULL, 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.
.HP 744u typedef void
*(extent_alloc_t)(extent_hooks_t *extent_hooks,
void *new_addr, size_t size,
size_t alignment, bool *zero,
bool *commit,
unsigned arena_ind);
An extent allocation function conforms to the extent_alloc_t type and
upon success returns a pointer to size bytes of mapped memory on
behalf of arena arena_ind such that the extent's base address is a
multiple of alignment, as well as setting *zero to indicate
whether the extent is zeroed and *commit to indicate whether the
extent is committed. Upon error the function returns NULL and leaves
*zero and *commit unmodified. The size parameter is
always a multiple of the page size. The alignment parameter is always
a power of two at least as large as the page size. Zeroing is mandatory if
*zero is true upon function entry. Committing is mandatory if
*commit is true upon function entry. If new_addr is not
NULL, the returned pointer must be new_addr on success or
NULL 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 <mallctl>arena.<i>.dss</mallctl> setting
irrelevant.
The alloc hook may bitwise-OR EXTENT_ALLOC_FLAG_PINNED into the low
bits of the returned pointer to indicate that the backing memory is
non-reclaimable (e.g. HugeTLB pages) and should be reused preferentially; in
that case *commit must also be set to true. jemalloc strips the low
byte before use. The pinned attribute is per-extent rather than per-hook: a
single alloc hook may return pinned and non-pinned extents in different
calls. Pinned-ness is set at allocation, inherited through splits, and never
changes after that. Pinned and non-pinned extents are never merged
together.
.HP 744u typedef bool
(extent_dalloc_t)(extent_hooks_t *extent_hooks,
void *addr, size_t size,
bool committed,
unsigned arena_ind);
An extent deallocation function conforms to the extent_dalloc_t type
and deallocates an extent at given addr and size with
committed/decommited memory as indicated, on behalf of arena
arena_ind, 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.
.HP 768u typedef void
(extent_destroy_t)(extent_hooks_t *extent_hooks,
void *addr, size_t size,
bool committed,
unsigned arena_ind);
An extent destruction function conforms to the extent_destroy_t type
and unconditionally destroys an extent at given addr and size
with committed/decommited memory as indicated, on behalf of arena
arena_ind. This function may be called to destroy retained extents
during arena destruction (see
<mallctl>arena.<i>.destroy</mallctl>).
.HP 744u typedef bool
(extent_commit_t)(extent_hooks_t *extent_hooks,
void *addr, size_t size,
size_t offset, size_t length,
unsigned arena_ind);
An extent commit function conforms to the extent_commit_t type and
commits zeroed physical memory to back pages within an extent at given
addr and size at offset bytes, extending for
length on behalf of arena arena_ind, 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.
.HP 792u typedef bool
(extent_decommit_t)(extent_hooks_t *extent_hooks,
void *addr, size_t size,
size_t offset, size_t length,
unsigned arena_ind);
An extent decommit function conforms to the extent_decommit_t type and
decommits any physical memory that is backing pages within an extent at
given addr and size at offset bytes, extending for
length on behalf of arena arena_ind, 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.
.HP 720u typedef bool
(extent_purge_t)(extent_hooks_t *extent_hooks,
void *addr, size_t size,
size_t offset, size_t length,
unsigned arena_ind);
An extent purge function conforms to the extent_purge_t type and
discards physical pages within the virtual memory mapping associated with an
extent at given addr and size at offset bytes,
extending for length on behalf of arena arena_ind. A lazy
extent purge function (e.g. implemented via
madvise(...MADV_FREE)) 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.
.HP 720u typedef bool
(extent_split_t)(extent_hooks_t *extent_hooks,
void *addr, size_t size,
size_t size_a, size_t size_b,
bool committed,
unsigned arena_ind);
An extent split function conforms to the extent_split_t type and
optionally splits an extent at given addr and size into two
adjacent extents, the first of size_a bytes, and the second of
size_b bytes, operating on committed/decommitted memory as
indicated, on behalf of arena arena_ind, 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.
.HP 720u typedef bool
(extent_merge_t)(extent_hooks_t *extent_hooks,
void *addr_a, size_t size_a,
void *addr_b, size_t size_b,
bool committed,
unsigned arena_ind);
An extent merge function conforms to the extent_merge_t type and
optionally merges adjacent extents, at given addr_a and size_a
with given addr_b and size_b into one contiguous extent,
operating on committed/decommitted memory as indicated, on behalf of
arena arena_ind, 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.
.RE
.PP <mallctl>arenas.narenas</mallctl> (unsigned) r-
Current limit on number of arenas.
.RE
.PP <mallctl>arenas.dirty_decay_ms</mallctl> (ssize_t)
rw
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
<mallctl>arena.<i>.dirty_decay_ms</mallctl> during arena
creation. See <mallctl>opt.dirty_decay_ms</mallctl> for
additional information.
.RE
.PP <mallctl>arenas.muzzy_decay_ms</mallctl> (ssize_t)
rw
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
<mallctl>arena.<i>.muzzy_decay_ms</mallctl> during arena
creation. See <mallctl>opt.muzzy_decay_ms</mallctl> for
additional information.
.RE
.PP <mallctl>arenas.quantum</mallctl> (size_t) r-
Quantum size.
.RE
.PP <mallctl>arenas.page</mallctl> (size_t) r-
Page size.
.RE
.PP <mallctl>arenas.hugepage</mallctl> (size_t) r-
Hugepage size. This value is also reported in the output of
malloc_stats_print().
.RE
.PP <mallctl>arenas.tcache_max</mallctl> (size_t) r-
Maximum thread-cached size class.
.RE
.PP <mallctl>arenas.nbins</mallctl> (unsigned) r-
Number of bin size classes.
.RE
.PP <mallctl>arenas.nhbins</mallctl> (unsigned) r-
Total number of thread cache bin size classes.
.RE
.PP <mallctl>arenas.bin.<i>.size</mallctl> (size_t)
r-
Maximum size supported by size class.
.RE
.PP <mallctl>arenas.bin.<i>.nregs</mallctl>
(uint32_t) r-
Number of regions per slab.
.RE
.PP <mallctl>arenas.bin.<i>.slab_size</mallctl>
(size_t) r-
Number of bytes per slab.
.RE
.PP <mallctl>arenas.nlextents</mallctl> (unsigned) r-
Total number of large size classes.
.RE
.PP <mallctl>arenas.lextent.<i>.size</mallctl>
(size_t) r-
Maximum size supported by this large size class.
.RE
.PP <mallctl>arenas.create</mallctl> (unsigned,
extent_hooks_t *) rw
Explicitly create a new arena outside the range of automatically managed
arenas, with optionally specified extent hooks, and return the new arena
index.
If the amount of space supplied for storing the arena index does not equal
sizeof(unsigned), no arena will be created, no data will be written
to the space pointed by oldp, and *oldlenp will be set to
0.
.RE
.PP <mallctl>arenas.lookup</mallctl> (unsigned,
void*) rw
Index of the arena to which an allocation belongs to.
.RE
.PP <mallctl>prof.thread_active_init</mallctl> (bool) rw
[--enable-prof]
Control the initial setting for
<mallctl>thread.prof.active</mallctl> in newly created threads.
See the <mallctl>opt.prof_thread_active_init</mallctl> option
for additional information.
.RE
.PP <mallctl>prof.active</mallctl> (bool) rw
[--enable-prof]
Control whether sampling is currently active. See the
<mallctl>opt.prof_active</mallctl> option for additional
information, as well as the interrelated
<mallctl>thread.prof.active</mallctl> mallctl.
.RE
.PP <mallctl>prof.dump</mallctl> (const char *) -w
[--enable-prof]
Dump a memory profile to the specified file, or if NULL is specified, to a
file according to the pattern
<prefix>.<pid>.<seq>.m<mseq>.heap, where
<prefix> is controlled by the
<mallctl>opt.prof_prefix</mallctl> and
<mallctl>prof.prefix</mallctl> options.
.RE
.PP <mallctl>prof.prefix</mallctl> (const char *) -w
[--enable-prof]
Set the filename prefix for profile dumps. See
<mallctl>opt.prof_prefix</mallctl> for the default setting. This
can be useful to differentiate profile dumps such as from forked
processes.
.RE
.PP <mallctl>prof.gdump</mallctl> (bool) rw
[--enable-prof]
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
<prefix>.<pid>.<seq>.u<useq>.heap, where
<prefix> is controlled by the
<mallctl>opt.prof_prefix</mallctl> and
<mallctl>prof.prefix</mallctl> options.
.RE
.PP <mallctl>prof.reset</mallctl> (size_t) -w
[--enable-prof]
Reset all memory profile statistics, and optionally update the sample rate
(see <mallctl>opt.lg_prof_sample</mallctl> and
<mallctl>prof.lg_sample</mallctl>).
.RE
.PP <mallctl>prof.lg_sample</mallctl> (size_t) r-
[--enable-prof]
Get the current sample rate (see
<mallctl>opt.lg_prof_sample</mallctl>).
.RE
.PP <mallctl>prof.interval</mallctl> (uint64_t) r-
[--enable-prof]
Average number of bytes allocated between interval-based profile dumps. See
the <mallctl>opt.lg_prof_interval</mallctl> option for
additional information.
.RE
.PP <mallctl>approximate_stats.active</mallctl> (size_t)
r-
Return the total number of bytes in active pages collected in an
unsynchronized manner, without requiring an
<mallctl>epoch</mallctl> update. As a result, this value should
NOT be compared with other stats. For example, the relative ordering between
<mallctl>approximate_stats.active</mallctl> and
<mallctl>stats.active</mallctl> or
<mallctl>stats.resident</mallctl> is not guaranteed. This
interface is intended for lightweight monitoring where an approximate value
is sufficient.
.RE
.PP <mallctl>stats.allocated</mallctl> (size_t) r-
[--enable-stats]
Total number of bytes allocated by the application.
.RE
.PP <mallctl>stats.active</mallctl> (size_t) r-
[--enable-stats]
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
<mallctl>stats.allocated</mallctl>. This does not include
<mallctl>stats.arenas.<i>.pdirty</mallctl>,
<mallctl>stats.arenas.<i>.pmuzzy</mallctl>, nor pages
entirely devoted to allocator metadata.
.RE
.PP <mallctl>stats.metadata</mallctl> (size_t) r-
[--enable-stats]
Total number of bytes dedicated to metadata, which comprise base allocations
used for bootstrap-sensitive allocator metadata structures (see
<mallctl>stats.arenas.<i>.base</mallctl>) and internal
allocations (see
<mallctl>stats.arenas.<i>.internal</mallctl>). Transparent
huge page (enabled with opt.metadata_thp) usage is not considered.
.RE
.PP <mallctl>stats.metadata_thp</mallctl> (size_t) r-
[--enable-stats]
Number of transparent huge pages (THP) used for metadata. See
<mallctl>stats.metadata</mallctl> and opt.metadata_thp) for
details.
.RE
.PP <mallctl>stats.resident</mallctl> (size_t) r-
[--enable-stats]
Maximum number of bytes in physically resident data pages mapped by the
allocator, comprising all pages dedicated to allocator metadata, pages
backing active allocations, unused dirty pages, and pinned 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
<mallctl>stats.active</mallctl>.
.RE
.PP <mallctl>stats.mapped</mallctl> (size_t) r-
[--enable-stats]
Total number of bytes in active extents mapped by the allocator. This is
larger than <mallctl>stats.active</mallctl>. This does not
include inactive extents, even those that contain unused dirty pages, which
means that there is no strict ordering between this and
<mallctl>stats.resident</mallctl>.
.RE
.PP <mallctl>stats.retained</mallctl> (size_t) r-
[--enable-stats]
Total number of bytes in virtual memory mappings that were retained rather
than being returned to the operating system via e.g. munmap(2) or
similar. Retained virtual memory is typically untouched, decommitted, or
purged, so it has no strongly associated physical memory (see extent hooks
for details). Retained memory is excluded from mapped memory statistics,
e.g. <mallctl>stats.mapped</mallctl>.
.RE
.PP <mallctl>stats.pinned</mallctl> (size_t) r-
[--enable-stats]
Total number of bytes in unused extents backed by non-reclaimable memory.
Pinned extents are tracked separately from dirty, muzzy, and retained
extents because they are excluded from decay and purging; unlike
<mallctl>stats.retained</mallctl>, pinned bytes are included in
<mallctl>stats.mapped</mallctl>.
.RE
.PP <mallctl>stats.zero_reallocs</mallctl> (size_t) r-
[--enable-stats]
Number of times that the realloc() was called with a non-NULL
pointer argument and a 0 size argument. This is a fundamentally
unsafe pattern in portable programs; see
<mallctl>opt.zero_realloc</mallctl> for details.
.RE
.PP <mallctl>stats.background_thread.num_threads</mallctl>
(size_t) r- [--enable-stats]
Number of background threads running currently.
.RE
.PP <mallctl>stats.background_thread.num_runs</mallctl>
(uint64_t) r- [--enable-stats]
Total number of runs from all background threads.
.RE
.PP <mallctl>stats.background_thread.run_interval</mallctl>
(uint64_t) r- [--enable-stats]
Average run interval in nanoseconds of background threads.
.RE
.PP <mallctl>stats.mutexes.ctl.{counter};</mallctl> (counter
specific type) r- [--enable-stats]
Statistics on ctl mutex (global scope; mallctl related).
<mallctl>{counter}</mallctl> is one of the counters below:
.PP
num_ops (uint64_t): Total number of lock acquisition operations
on this mutex.
num_spin_acq (uint64_t): Number of times the mutex was spin-acquired. When the mutex is currently locked and cannot be acquired immediately, a short period of spin-retry within jemalloc will be performed. Acquired through spin generally means the contention was lightweight and not causing context switches.
num_wait (uint64_t): Number of times the mutex was wait-acquired, which means the mutex contention was not solved by spin-retry, and blocking operation was likely involved in order to acquire the mutex. This event generally implies higher cost / longer delay, and should be investigated if it happens often.
max_wait_time (uint64_t): Maximum length of time in nanoseconds spent on a single wait-acquired lock operation. Note that to avoid profiling overhead on the common path, this does not consider spin-acquired cases.
total_wait_time (uint64_t): Cumulative time in nanoseconds spent on wait-acquired lock operations. Similarly, spin-acquired cases are not considered.
max_num_thds (uint32_t): Maximum number of threads waiting on this mutex simultaneously. Similarly, spin-acquired cases are not considered.
num_owner_switch (uint64_t): Number of times the current mutex owner is different from the previous one. This event does not generally imply an issue; rather it is an indicator of how often the protected data are accessed by different threads.
.RE
.RE
.PP <mallctl>stats.mutexes.background_thread.{counter}</mallctl>
(counter specific type) r- [--enable-stats]
Statistics on background_thread mutex (global scope;
<mallctl>background_thread</mallctl> related).
<mallctl>{counter}</mallctl> is one of the counters in mutex
profiling counters.
.RE
.PP <mallctl>stats.mutexes.prof.{counter}</mallctl> (counter
specific type) r- [--enable-stats]
Statistics on prof mutex (global scope; profiling related).
<mallctl>{counter}</mallctl> is one of the counters in mutex
profiling counters.
.RE
.PP <mallctl>stats.mutexes.prof_thds_data.{counter}</mallctl>
(counter specific type) r- [--enable-stats]
Statistics on prof threads data mutex (global scope; profiling related). <mallctl>{counter}</mallctl> is one of the counters in mutex profiling counters.
.RE
.PP <mallctl>stats.mutexes.prof_dump.{counter}</mallctl>
(counter specific type) r- [--enable-stats]
Statistics on prof dumping mutex (global scope; profiling related). <mallctl>{counter}</mallctl> is one of the counters in mutex profiling counters.
.RE
.PP <mallctl>stats.mutexes.reset</mallctl> (void) --
[--enable-stats]
Reset all mutex profile statistics, including global mutexes, arena mutexes
and bin mutexes.
.RE
.PP <mallctl>stats.arenas.<i>.dss</mallctl> (const char
*) r-
dss (sbrk(2)) allocation precedence as related to mmap(2)
allocation. See <mallctl>opt.dss</mallctl> for details.
.RE
.PP <mallctl>stats.arenas.<i>.dirty_decay_ms</mallctl>
(ssize_t) r-
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 <mallctl>opt.dirty_decay_ms</mallctl> for details.
.RE
.PP <mallctl>stats.arenas.<i>.muzzy_decay_ms</mallctl>
(ssize_t) r-
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 <mallctl>opt.muzzy_decay_ms</mallctl> for details.
.RE
.PP <mallctl>stats.arenas.<i>.nthreads</mallctl>
(unsigned) r-
Number of threads currently assigned to arena.
.RE
.PP <mallctl>stats.arenas.<i>.uptime</mallctl>
(uint64_t) r-
Time elapsed (in nanoseconds) since the arena was created. If <i>
equals 0 or MALLCTL_ARENAS_ALL, this is the uptime since
malloc initialization.
.RE
.PP <mallctl>stats.arenas.<i>.pactive</mallctl>
(size_t) r-
Number of pages in active extents.
.RE
.PP <mallctl>stats.arenas.<i>.pdirty</mallctl>
(size_t) r-
Number of pages within unused extents that are potentially dirty, and for
which madvise() or similar has not been called. See
<mallctl>opt.dirty_decay_ms</mallctl> for a description of dirty
pages.
.RE
.PP <mallctl>stats.arenas.<i>.pmuzzy</mallctl>
(size_t) r-
Number of pages within unused extents that are muzzy. See
<mallctl>opt.muzzy_decay_ms</mallctl> for a description of muzzy
pages.
.RE
.PP <mallctl>stats.arenas.<i>.mapped</mallctl>
(size_t) r- [--enable-stats]
Number of mapped bytes.
.RE
.PP <mallctl>stats.arenas.<i>.retained</mallctl>
(size_t) r- [--enable-stats]
Number of retained bytes. See <mallctl>stats.retained</mallctl>
for details.
.RE
.PP <mallctl>stats.arenas.<i>.pinned</mallctl>
(size_t) r- [--enable-stats]
Number of pinned bytes. See <mallctl>stats.pinned</mallctl> for
details.
.RE
.PP <mallctl>stats.arenas.<i>.extent_avail</mallctl>
(size_t) r- [--enable-stats]
Number of allocated (but unused) extent structs in this arena.
.RE
.PP <mallctl>stats.arenas.<i>.base</mallctl>
(size_t) r- [--enable-stats]
Number of bytes dedicated to bootstrap-sensitive allocator metadata
structures.
.RE
.PP <mallctl>stats.arenas.<i>.internal</mallctl>
(size_t) r- [--enable-stats]
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.
.RE
.PP <mallctl>stats.arenas.<i>.metadata_thp</mallctl>
(size_t) r- [--enable-stats]
Number of transparent huge pages (THP) used for metadata. See
opt.metadata_thp for details.
.RE
.PP <mallctl>stats.arenas.<i>.resident</mallctl>
(size_t) r- [--enable-stats]
Maximum number of bytes in physically resident data pages mapped by the
arena, comprising all pages dedicated to allocator metadata, pages backing
active allocations, unused dirty pages, and pinned 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.
.RE
.PP <mallctl>stats.arenas.<i>.dirty_npurge</mallctl>
(uint64_t) r- [--enable-stats]
Number of dirty page purge sweeps performed.
.RE
.PP <mallctl>stats.arenas.<i>.dirty_nmadvise</mallctl>
(uint64_t) r- [--enable-stats]
Number of madvise() or similar calls made to purge dirty pages.
.RE
.PP <mallctl>stats.arenas.<i>.dirty_purged</mallctl>
(uint64_t) r- [--enable-stats]
Number of dirty pages purged.
.RE
.PP <mallctl>stats.arenas.<i>.muzzy_npurge</mallctl>
(uint64_t) r- [--enable-stats]
Number of muzzy page purge sweeps performed.
.RE
.PP <mallctl>stats.arenas.<i>.muzzy_nmadvise</mallctl>
(uint64_t) r- [--enable-stats]
Number of madvise() or similar calls made to purge muzzy pages.
.RE
.PP <mallctl>stats.arenas.<i>.muzzy_purged</mallctl>
(uint64_t) r- [--enable-stats]
Number of muzzy pages purged.
.RE
.PP <mallctl>stats.arenas.<i>.small.allocated</mallctl>
(size_t) r- [--enable-stats]
Number of bytes currently allocated by small objects.
.RE
.PP <mallctl>stats.arenas.<i>.small.nmalloc</mallctl>
(uint64_t) r- [--enable-stats]
Cumulative number of times a small allocation was requested from the arena's
bins, whether to fill the relevant tcache if
<mallctl>opt.tcache</mallctl> is enabled, or to directly satisfy
an allocation request otherwise.
.RE
.PP <mallctl>stats.arenas.<i>.small.ndalloc</mallctl>
(uint64_t) r- [--enable-stats]
Cumulative number of times a small allocation was returned to the arena's
bins, whether to flush the relevant tcache if
<mallctl>opt.tcache</mallctl> is enabled, or to directly
deallocate an allocation otherwise.
.RE
.PP <mallctl>stats.arenas.<i>.small.nrequests</mallctl>
(uint64_t) r- [--enable-stats]
Cumulative number of allocation requests satisfied by all bin size
classes.
.RE
.PP <mallctl>stats.arenas.<i>.small.nfills</mallctl>
(uint64_t) r- [--enable-stats]
Cumulative number of tcache fills by all small size classes.
.RE
.PP <mallctl>stats.arenas.<i>.small.nflushes</mallctl>
(uint64_t) r- [--enable-stats]
Cumulative number of tcache flushes by all small size classes.
.RE
.PP <mallctl>stats.arenas.<i>.large.allocated</mallctl>
(size_t) r- [--enable-stats]
Number of bytes currently allocated by large objects.
.RE
.PP <mallctl>stats.arenas.<i>.large.nmalloc</mallctl>
(uint64_t) r- [--enable-stats]
Cumulative number of times a large extent was allocated from the arena,
whether to fill the relevant tcache if
<mallctl>opt.tcache</mallctl> is enabled and the size class is
within the range being cached, or to directly satisfy an allocation request
otherwise.
.RE
.PP <mallctl>stats.arenas.<i>.large.ndalloc</mallctl>
(uint64_t) r- [--enable-stats]
Cumulative number of times a large extent was returned to the arena, whether
to flush the relevant tcache if <mallctl>opt.tcache</mallctl> is
enabled and the size class is within the range being cached, or to directly
deallocate an allocation otherwise.
.RE
.PP <mallctl>stats.arenas.<i>.large.nrequests</mallctl>
(uint64_t) r- [--enable-stats]
Cumulative number of allocation requests satisfied by all large size
classes.
.RE
.PP <mallctl>stats.arenas.<i>.large.nfills</mallctl>
(uint64_t) r- [--enable-stats]
Cumulative number of tcache fills by all large size classes.
.RE
.PP <mallctl>stats.arenas.<i>.large.nflushes</mallctl>
(uint64_t) r- [--enable-stats]
Cumulative number of tcache flushes by all large size classes.
.RE
.PP
<mallctl>stats.arenas.<i>.bins.<j>.nmalloc</mallctl>
(uint64_t) r- [--enable-stats]
Cumulative number of times a bin region of the corresponding size class was
allocated from the arena, whether to fill the relevant tcache if
<mallctl>opt.tcache</mallctl> is enabled, or to directly satisfy
an allocation request otherwise.
.RE
.PP
<mallctl>stats.arenas.<i>.bins.<j>.ndalloc</mallctl>
(uint64_t) r- [--enable-stats]
Cumulative number of times a bin region of the corresponding size class was
returned to the arena, whether to flush the relevant tcache if
<mallctl>opt.tcache</mallctl> is enabled, or to directly
deallocate an allocation otherwise.
.RE
.PP
<mallctl>stats.arenas.<i>.bins.<j>.nrequests</mallctl>
(uint64_t) r- [--enable-stats]
Cumulative number of allocation requests satisfied by bin regions of the
corresponding size class.
.RE
.PP
<mallctl>stats.arenas.<i>.bins.<j>.curregs</mallctl>
(size_t) r- [--enable-stats]
Current number of regions for this size class.
.RE
.PP
<mallctl>stats.arenas.<i>.bins.<j>.nfills</mallctl>
(uint64_t) r-
Cumulative number of tcache fills.
.RE
.PP
<mallctl>stats.arenas.<i>.bins.<j>.nflushes</mallctl>
(uint64_t) r-
Cumulative number of tcache flushes.
.RE
.PP
<mallctl>stats.arenas.<i>.bins.<j>.nslabs</mallctl>
(uint64_t) r- [--enable-stats]
Cumulative number of slabs created.
.RE
.PP
<mallctl>stats.arenas.<i>.bins.<j>.nreslabs</mallctl>
(uint64_t) r- [--enable-stats]
Cumulative number of times the current slab from which to allocate
changed.
.RE
.PP
<mallctl>stats.arenas.<i>.bins.<j>.curslabs</mallctl>
(size_t) r- [--enable-stats]
Current number of slabs.
.RE
.PP
<mallctl>stats.arenas.<i>.bins.<j>.nonfull_slabs</mallctl>
(size_t) r- [--enable-stats]
Current number of nonfull slabs.
.RE
.PP
<mallctl>stats.arenas.<i>.bins.<j>.mutex.{counter}</mallctl>
(counter specific type) r- [--enable-stats]
Statistics on arena.<i>.bins.<j> mutex (arena bin scope;
bin operation related). <mallctl>{counter}</mallctl> is one of
the counters in mutex profiling counters.
.RE
.PP
<mallctl>stats.arenas.<i>.extents.<j>.n{extent_type}</mallctl>
(size_t) r- [--enable-stats]
Number of extents of the given type in this arena in the bucket corresponding
to page size index <j>. The extent type is one of dirty, muzzy,
retained, or pinned.
.RE
.PP
<mallctl>stats.arenas.<i>.extents.<j>.{extent_type}_bytes</mallctl>
(size_t) r- [--enable-stats]
Sum of the bytes managed by extents of the given type in this arena in the bucket corresponding to page size index <j>. The extent type is one of dirty, muzzy, retained, or pinned.
.RE
.PP
<mallctl>stats.arenas.<i>.lextents.<j>.nmalloc</mallctl>
(uint64_t) r- [--enable-stats]
Cumulative number of times a large extent of the corresponding size class was
allocated from the arena, whether to fill the relevant tcache if
<mallctl>opt.tcache</mallctl> is enabled and the size class is
within the range being cached, or to directly satisfy an allocation request
otherwise.
.RE
.PP
<mallctl>stats.arenas.<i>.lextents.<j>.ndalloc</mallctl>
(uint64_t) r- [--enable-stats]
Cumulative number of times a large extent of the corresponding size class was
returned to the arena, whether to flush the relevant tcache if
<mallctl>opt.tcache</mallctl> is enabled and the size class is
within the range being cached, or to directly deallocate an allocation
otherwise.
.RE
.PP
<mallctl>stats.arenas.<i>.lextents.<j>.nrequests</mallctl>
(uint64_t) r- [--enable-stats]
Cumulative number of allocation requests satisfied by large extents of the
corresponding size class.
.RE
.PP
<mallctl>stats.arenas.<i>.lextents.<j>.curlextents</mallctl>
(size_t) r- [--enable-stats]
Current number of large allocations for this size class.
.RE
.PP
<mallctl>stats.arenas.<i>.mutexes.large.{counter}</mallctl>
(counter specific type) r- [--enable-stats]
Statistics on arena.<i>.large mutex (arena scope; large
allocation related). <mallctl>{counter}</mallctl> is one of the
counters in mutex profiling counters.
.RE
.PP
<mallctl>stats.arenas.<i>.mutexes.extent_avail.{counter}</mallctl>
(counter specific type) r- [--enable-stats]
Statistics on arena.<i>.extent_avail mutex (arena scope; extent
avail related). <mallctl>{counter}</mallctl> is one of the
counters in mutex profiling counters.
.RE
.PP
<mallctl>stats.arenas.<i>.mutexes.extents_dirty.{counter}</mallctl>
(counter specific type) r- [--enable-stats]
Statistics on arena.<i>.extents_dirty mutex (arena scope; dirty
extents related). <mallctl>{counter}</mallctl> is one of the
counters in mutex profiling counters.
.RE
.PP
<mallctl>stats.arenas.<i>.mutexes.extents_muzzy.{counter}</mallctl>
(counter specific type) r- [--enable-stats]
Statistics on arena.<i>.extents_muzzy mutex (arena scope; muzzy
extents related). <mallctl>{counter}</mallctl> is one of the
counters in mutex profiling counters.
.RE
.PP
<mallctl>stats.arenas.<i>.mutexes.extents_retained.{counter}</mallctl>
(counter specific type) r- [--enable-stats]
Statistics on arena.<i>.extents_retained mutex (arena scope;
retained extents related). <mallctl>{counter}</mallctl> is one
of the counters in mutex profiling counters.
.RE
.PP
<mallctl>stats.arenas.<i>.mutexes.extents_pinned.{counter}</mallctl>
(counter specific type) r- [--enable-stats]
Statistics on arena.<i>.extents_pinned mutex (arena scope;
pinned extents related). <mallctl>{counter}</mallctl> is one of
the counters in mutex profiling counters.
.RE
.PP
<mallctl>stats.arenas.<i>.mutexes.decay_dirty.{counter}</mallctl>
(counter specific type) r- [--enable-stats]
Statistics on arena.<i>.decay_dirty mutex (arena scope; decay
for dirty pages related). <mallctl>{counter}</mallctl> is one of
the counters in mutex profiling counters.
.RE
.PP
<mallctl>stats.arenas.<i>.mutexes.decay_muzzy.{counter}</mallctl>
(counter specific type) r- [--enable-stats]
Statistics on arena.<i>.decay_muzzy mutex (arena scope; decay
for muzzy pages related). <mallctl>{counter}</mallctl> is one of
the counters in mutex profiling counters.
.RE
.PP
<mallctl>stats.arenas.<i>.mutexes.base.{counter}</mallctl>
(counter specific type) r- [--enable-stats]
Statistics on arena.<i>.base mutex (arena scope; base allocator
related). <mallctl>{counter}</mallctl> is one of the counters in
mutex profiling counters.
.RE
.PP
<mallctl>stats.arenas.<i>.mutexes.tcache_list.{counter}</mallctl>
(counter specific type) r- [--enable-stats]
Statistics on arena.<i>.tcache_list 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
mutex profiling counters.
.RE
.SH "HEAP PROFILE FORMAT"
.PP Although the heap profiling functionality was originally designed to be
compatible with the pprof command that is developed as part of the
gperftools package[3], the addition of per thread heap profiling
functionality required a different heap profile format. The jeprof
command is derived from pprof, with enhancements to support the heap
profile format described here.
.PP In the following hypothetical heap profile, [...] indicates
elision for the sake of compactness.
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: [...]
The following matches the above heap profile, but most tokens are replaced with <description> to indicate descriptions of the corresponding fields.
<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>
.SH "DEBUGGING MALLOC PROBLEMS"
.PP When debugging, it is a good idea to configure/build jemalloc with the
--enable-debug and --enable-fill 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.
.PP Programs often accidentally depend on “uninitialized”
memory actually being filled with zero bytes. Junk filling (see the
<mallctl>opt.junk</mallctl> option) tends to expose such bugs in
the form of obviously incorrect results and/or coredumps. Conversely, zero
filling (see the <mallctl>opt.zero</mallctl> option) eliminates
the symptoms of such bugs. Between these two options, it is usually possible
to quickly detect, diagnose, and eliminate such bugs.
.PP This implementation does not provide much detail about the problems it
detects, because the performance impact for storing such information would
be prohibitive.
.SH "DIAGNOSTIC MESSAGES"
.PP If any of the memory allocation/deallocation functions detect an error or
warning condition, a message will be printed to file descriptor
STDERR_FILENO. Errors will result in the process dumping core. If the
<mallctl>opt.abort</mallctl> option is set, most warnings are
treated as errors.
.PP The malloc_message variable allows the programmer to override the
function which emits the text strings forming the errors and warnings if for
some reason the STDERR_FILENO file descriptor is not suitable for
this. malloc_message() takes the cbopaque pointer argument
that is NULL unless overridden by the arguments in a call to
malloc_stats_print(), 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.
.PP All messages are prefixed by “<jemalloc>: ”.
.SH "RETURN VALUES"
.SS "Standard API"
.PP The malloc() and calloc() functions return a pointer to the
allocated memory if successful; otherwise a NULL pointer is returned
and errno is set to ENOMEM.
.PP The posix_memalign() function returns the value 0 if successful;
otherwise it returns an error value. The posix_memalign() function
will fail if:
.PP EINVAL
The alignment parameter is not a power of 2 at least as large as
sizeof(void *).
.RE
.PP ENOMEM
Memory allocation error.
.RE
.PP The aligned_alloc() function returns a pointer to the allocated
memory if successful; otherwise a NULL pointer is returned and
errno is set. The aligned_alloc() function will fail if:
.PP EINVAL
The alignment parameter is not a power of 2.
.RE
.PP ENOMEM
Memory allocation error.
.RE
.PP The realloc() function returns a pointer, possibly identical to
ptr, to the allocated memory if successful; otherwise a NULL
pointer is returned, and errno is set to ENOMEM if the error was the
result of an allocation failure. The realloc() function always leaves
the original buffer intact when an error occurs.
.PP The free() function returns no value.
.SS "Non-standard API"
.PP The mallocx() and rallocx() functions return a pointer to
the allocated memory if successful; otherwise a NULL pointer is
returned to indicate insufficient contiguous memory was available to service
the allocation request.
.PP The xallocx() function returns the real size of the resulting
resized allocation pointed to by ptr, which is a value less than
size if the allocation could not be adequately grown in place.
.PP The sallocx() function returns the real size of the allocation
pointed to by ptr.
.PP The nallocx() returns the real size that would result from a
successful equivalent mallocx() function call, or zero if
insufficient memory is available to perform the size computation.
.PP The mallctl(), mallctlnametomib(), and
mallctlbymib() functions return 0 on success; otherwise they return
an error value. The functions will fail if:
.PP EINVAL
newp is not NULL, and newlen is too large or too small.
Alternatively, *oldlenp 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 *oldlenp.
.RE
.PP ENOENT
name or mib specifies an unknown/invalid value.
.RE
.PP EPERM
Attempt to read or write void value, or attempt to write read-only value.
.RE
.PP EAGAIN
A memory allocation failure occurred.
.RE
.PP EFAULT
An interface with side effects failed in some way not directly related to
mallctl*() read/write processing.
.RE
.PP The malloc_usable_size() function returns the usable size of the
allocation pointed to by ptr.
.SH "ENVIRONMENT"
.PP The following environment variable affects the execution of the
allocation functions:
.PP MALLOC_CONF
If the environment variable MALLOC_CONF is set, the characters it
contains will be interpreted as options.
.RE
.SH "EXAMPLES"
.PP To dump core whenever a problem occurs:
ln -s 'abort:true' /etc/malloc.conf
.PP To specify in the source that only one arena should be automatically
created:
malloc_conf = "narenas:1";
.SH "SEE ALSO"
.PP madvise(2), mmap(2), sbrk(2), utrace(2),
alloca(3), atexit(3), getpagesize(3)
.SH "STANDARDS"
.PP The malloc(), calloc(), realloc(), and free()
functions conform to ISO/IEC 9899:1990 (“ISO C90”).
.PP The posix_memalign() function conforms to IEEE Std 1003.1-2001
(“POSIX.1”).
AUTHOR
Jason Evans
NOTES
- 1.
- jemalloc website
- 2.
- JSON format
- 3.
- gperftools package
| 09/23/2026 | jemalloc 5.4.0-0-g7a34f18502e7 |