jemalloc — general purpose memory allocation functions
This manual describes jemalloc 2.2.1-0-g5ef7abf6d846720fb3fb8c737861c99b5ad1d862. More information can be found at the jemalloc website.
#include <stdlib.h> #include <jemalloc/jemalloc.h>
void *malloc( | size_t size); |
void *calloc( | size_t number, |
size_t size); |
int posix_memalign( | void **ptr, |
| size_t alignment, | |
size_t size); |
void *realloc( | void *ptr, |
size_t size); |
void free( | void *ptr); |
size_t malloc_usable_size( | const void *ptr); |
void malloc_stats_print( | void (*write_cb)
(void *, const char *)
, |
| void *cbopaque, | |
const char *opts); |
int mallctl( | const char *name, |
| void *oldp, | |
| size_t *oldlenp, | |
| void *newp, | |
size_t newlen); |
int mallctlnametomib( | const char *name, |
| size_t *mibp, | |
size_t *miblenp); |
int mallctlbymib( | const size_t *mib, |
| size_t miblen, | |
| void *oldp, | |
| size_t *oldlenp, | |
| void *newp, | |
size_t newlen); |
void (*malloc_message)( | void *cbopaque, |
const char *s); |
const char *malloc_conf;
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.
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.
The posix_memalign() function
allocates size bytes of memory such that the
allocation's base address is an even 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 *).
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.
The free() function causes the
allocated memory referenced by ptr to be made
available for future allocations. If ptr is
NULL, no action occurs.
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.
The malloc_stats_print() function
writes human-readable summary statistics via the
write_cb callback function pointer and
cbopaque data passed to
write_cb, or
malloc_message() if
write_cb is NULL. 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_message() 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” and “a” can
be specified to omit 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. Unrecognized
characters are silently ignored. Note that thread caching may prevent
some statistics from being completely up to date, since extra locking
would be required to merge counters that track thread cache operations.
The 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.
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
"arenas.bin.2.size"
),
the corresponding MIB component will always be that integer. Therefore,
it is legitimate to construct code like the following:
unsigned nbins, i;
int mib[4];
size_t len, miblen;
len = sizeof(nbins);
mallctl("arenas.nbins", &nbins, &len, NULL, 0);
miblen = 4;
mallnametomib("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, &bin_size, &len, NULL, 0);
/* Do something with bin_size... */
}The experimental API is subject to change or removal without regard for backward compatibility.
The allocm(),
rallocm(),
sallocm(), and
dallocm() 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:
ALLOCM_LG_ALIGN(la)
Align the memory allocation to start at an address
that is a multiple of (1 <<
. This macro does not validate
that la)la is within the valid
range.
ALLOCM_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.
ALLOCM_ZEROInitialize newly allocated memory to contain zero bytes. In the growing reallocation case, the real size prior to reallocation defines the boundary between untouched bytes and those that are initialized to contain zero bytes. If this option is absent, newly allocated memory is uninitialized.
ALLOCM_NO_MOVEFor reallocation, fail rather than moving the object. This constraint can apply to both growth and shrinkage.
The allocm() function allocates at
least size bytes of memory, sets
*ptr to the base address of the allocation, and
sets *rsize to the real size of the allocation if
rsize is not NULL.
The rallocm() function resizes the
allocation at *ptr to be at least
size bytes, sets *ptr to
the base address of the allocation if it moved, and sets
*rsize to the real size of the allocation if
rsize is not NULL. If
extra is non-zero, an attempt is made to resize
the allocation to be at least size +
extra)(.size +
extra >
SIZE_T_MAX)
The sallocm() function sets
*rsize to the real size of the allocation.
The dallocm() function causes the
memory referenced by ptr to be made available for
future allocations.
Once, when the first call is made to one of the memory allocation routines, the allocator initializes its internals based in part on various options that can be specified at compile- or run-time.
The string 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.
An options string is a comma-separated list of option:value pairs.
There is one key corresponding to each
"opt.*"
mallctl (see the MALLCTL NAMESPACE section for options
documentation). For example, abort:true,narenas:1 sets
the
"opt.abort"
and
"opt.narenas"
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.
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
--enable-dss is specified during configuration, this
allocator uses both sbrk(2) and
mmap(2), in that order of preference;
otherwise only mmap(2) is used.
This allocator uses multiple arenas in order to reduce lock contention for threaded programs on multi-processor systems. This works well with regard to threading scalability, but incurs some costs. There is a small fixed per-arena overhead, and additionally, arenas manage memory completely independently of each other, which means a small fixed increase in overall memory fragmentation. These overheads are not generally an issue, given the number of arenas normally used. Note that using substantially more arenas than the default is not likely to improve performance, mainly due to reduced cache performance. However, it may make sense to reduce the number of arenas if an application does not make much use of the allocation functions.
In addition to multiple arenas, unless
--disable-tcache is specified during configuration, this
allocator supports thread-specific caching for small and large objects, in
order to make it possible to completely avoid synchronization for most
allocation requests. Such caching allows very fast allocation in the
common case, but it increases memory usage and fragmentation, since a
bounded number of objects can remain allocated in each thread cache.
Memory is conceptually broken into equal-sized chunks, where the chunk size is a power of two that is greater than the page size. Chunks are always aligned to multiples of the chunk size. This alignment makes it possible to find metadata for user objects very quickly.
User objects are broken into three categories according to size: small, large, and huge. Small objects are smaller than one page. Large objects are smaller than the chunk size. Huge objects are a multiple of the chunk size. Small and large objects are managed by arenas; huge objects are managed separately in a single data structure that is shared by all threads. Huge objects are used by applications infrequently enough that this single data structure is not a scalability issue.
Each chunk that is managed by an arena tracks its contents as runs of contiguous pages (unused, backing a set of small objects, or backing one large object). The combination of chunk alignment and chunk page maps makes it possible to determine all metadata regarding small and large allocations in constant time.
Small objects are managed in groups by page runs. Each run maintains
a frontier and free list to track which regions are in use. Unless
--disable-tiny is specified during configuration,
allocation requests that are no more than half the quantum (8 or 16,
depending on architecture) are rounded up to the nearest power of two that
is at least sizeof(void *).
Allocation requests that are more than half the quantum, but no more than
the minimum cacheline-multiple size class (see the
"opt.lg_qspace_max"
option) are rounded up to the nearest multiple of the quantum. Allocation
requests that are more than the minimum cacheline-multiple size class, but
no more than the minimum subpage-multiple size class (see the
"opt.lg_cspace_max"
option) are rounded up to the nearest multiple of the cacheline size (64).
Allocation requests that are more than the minimum subpage-multiple size
class, but no more than the maximum subpage-multiple size class are rounded
up to the nearest multiple of the subpage size (256). Allocation requests
that are more than the maximum subpage-multiple size class, but small
enough to fit in an arena-managed chunk (see the
"opt.lg_chunk"
option), are
rounded up to the nearest run size. Allocation requests that are too large
to fit in an arena-managed chunk are rounded up to the nearest multiple of
the chunk size.
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.
Assuming 4 MiB chunks, 4 KiB pages, and a 16-byte quantum on a 64-bit system, the size classes in each category are as shown in Table 1.
Table 1. Size classes
| Category | Subcategory | Size |
|---|---|---|
| Small | Tiny | [8] |
| Quantum-spaced | [16, 32, 48, ..., 128] | |
| Cacheline-spaced | [192, 256, 320, ..., 512] | |
| Subpage-spaced | [768, 1024, 1280, ..., 3840] | |
| Large | [4 KiB, 8 KiB, 12 KiB, ..., 4072 KiB] | |
| Huge | [4 MiB, 8 MiB, 12 MiB, ...] | |
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
"stats.arenas.<i>.*"
,
<i> equal to
"arenas.narenas"
can be
used to access the summation of statistics from all arenas. Take special
note of the
"epoch"
mallctl,
which controls refreshing of cached dynamic statistics.
version"
(const char *)
r-
Return the jemalloc version string.
epoch"
(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.
config.debug"
(bool)
r-
--enable-debug was specified during
build configuration.
config.dss"
(bool)
r-
--enable-dss was specified during
build configuration.
config.dynamic_page_shift"
(bool)
r-
--enable-dynamic-page-shift was
specified during build configuration.
config.fill"
(bool)
r-
--enable-fill was specified during
build configuration.
config.lazy_lock"
(bool)
r-
--enable-lazy-lock was specified
during build configuration.
config.prof"
(bool)
r-
--enable-prof was specified during
build configuration.
config.prof_libgcc"
(bool)
r-
--disable-prof-libgcc was not
specified during build configuration.
config.prof_libunwind"
(bool)
r-
--enable-prof-libunwind was specified
during build configuration.
config.stats"
(bool)
r-
--enable-stats was specified during
build configuration.
config.swap"
(bool)
r-
--enable-swap was specified during
build configuration.
config.sysv"
(bool)
r-
--enable-sysv was specified during
build configuration.
config.tcache"
(bool)
r-
--disable-tcache was not specified
during build configuration.
config.tiny"
(bool)
r-
--disable-tiny was not specified
during build configuration.
config.tls"
(bool)
r-
--disable-tls was not specified during
build configuration.
config.xmalloc"
(bool)
r-
--enable-xmalloc was specified during
build configuration.
opt.abort"
(bool)
r-
Abort-on-warning enabled/disabled. If true, most
warnings 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.
opt.lg_qspace_max"
(size_t)
r-
Size (log base 2) of the maximum size class that is a multiple of the quantum (8 or 16 bytes, depending on architecture). Above this size, cacheline spacing is used for size classes. The default value is 128 bytes (2^7).
opt.lg_cspace_max"
(size_t)
r-
Size (log base 2) of the maximum size class that is a multiple of the cacheline size (64). Above this size, subpage spacing (256 bytes) is used for size classes. The default value is 512 bytes (2^9).
opt.lg_chunk"
(size_t)
r-
Virtual memory chunk size (log base 2). The default chunk size is 4 MiB (2^22).
opt.narenas"
(size_t)
r-
Maximum number of arenas to use. The default maximum number of arenas is four times the number of CPUs, or one if there is a single CPU.
opt.lg_dirty_mult"
(ssize_t)
r-
Per-arena minimum ratio (log base 2) of active to dirty pages. Some dirty unused pages may be allowed to accumulate, within the limit set by the ratio (or one chunk worth of dirty pages, whichever is greater), before informing the kernel about some of those pages via madvise(2) or a similar system call. This provides the kernel with sufficient information to recycle dirty pages if physical memory becomes scarce and the pages remain unused. The default minimum ratio is 32:1 (2^5:1); an option value of -1 will disable dirty page purging.
opt.stats_print"
(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. 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. 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.
opt.junk"
(bool)
r-
[--enable-fill]
Junk filling enabled/disabled. If enabled, each byte
of uninitialized allocated memory will be initialized to
0xa5. All deallocated memory will be initialized to
0x5a. This is intended for debugging and will
impact performance negatively. This option is disabled by default
unless --enable-debug is specified during
configuration, in which case it is enabled by default.
opt.zero"
(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
rallocm() 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.
opt.sysv"
(bool)
r-
[--enable-sysv]
If enabled, attempting to allocate zero bytes will
return a NULL pointer instead of a valid pointer.
(The default behavior is to make a minimal allocation and return a
pointer to it.) This option is provided for System V compatibility.
This option is incompatible with the
"opt.xmalloc"
option.
This option is disabled by default.
opt.xmalloc"
(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.
opt.tcache"
(bool)
r-
[--enable-tcache]
Thread-specific caching enabled/disabled. When there
are multiple threads, each thread uses a thread-specific cache for
objects up to a certain size. Thread-specific caching allows many
allocations to be satisfied without performing any thread
synchronization, at the cost of increased memory use. See the
"opt.lg_tcache_gc_sweep"
and
"opt.lg_tcache_max"
options for related tuning information. This option is enabled by
default.
opt.lg_tcache_gc_sweep"
(ssize_t)
r-
[--enable-tcache]
Approximate interval (log base 2) between full thread-specific cache garbage collection sweeps, counted in terms of thread-specific cache allocation/deallocation events. Garbage collection is actually performed incrementally, one size class at a time, in order to avoid large collection pauses. The default sweep interval is 8192 (2^13); setting this option to -1 will disable garbage collection.
opt.lg_tcache_max"
(size_t)
r-
[--enable-tcache]
Maximum size class (log base 2) to cache in the thread-specific cache. At a minimum, all small size classes are cached, and at a maximum all large size classes are cached. The default maximum is 32 KiB (2^15).
opt.prof"
(bool)
r-
[--enable-prof]
Memory profiling enabled/disabled. If enabled, profile
memory allocation activity, and 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
"opt.prof_prefix"
option. See the
"opt.lg_prof_bt_max"
option for backtrace depth control. See the
"opt.prof_active"
option for on-the-fly activation/deactivation. See the
"opt.lg_prof_sample"
option for probabilistic sampling control. See the
"opt.prof_accum"
option for control of cumulative sample reporting. See the
"opt.lg_prof_tcmax"
option for control of per thread backtrace caching. See the
"opt.lg_prof_interval"
option for information on interval-triggered profile dumping, and the
"opt.prof_gdump"
option for information on high-water-triggered profile dumping.
Profile output is compatible with the included pprof
Perl script, which originates from the google-perftools
package.
opt.prof_prefix"
(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.
opt.lg_prof_bt_max"
(size_t)
r-
[--enable-prof]
Maximum backtrace depth (log base 2) when profiling memory allocation activity. The default is 128 (2^7).
opt.prof_active"
(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
"opt.prof"
option) but
inactive, then toggle profiling at any time during program execution
with the
"prof.active"
mallctl.
This option is enabled by default.
opt.lg_prof_sample"
(ssize_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 1 (2^0) (i.e. all allocations are sampled).
opt.prof_accum"
(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. See the
"opt.lg_prof_tcmax"
option for control of per thread backtrace caching, which has important
interactions. This option is enabled by default.
opt.lg_prof_tcmax"
(ssize_t)
r-
[--enable-prof]
Maximum per thread backtrace cache (log base 2) used
for heap profiling. A backtrace can only be discarded if the
"opt.prof_accum"
option is disabled, and no thread caches currently refer to the
backtrace. Therefore, a backtrace cache limit should be imposed if the
intention is to limit how much memory is used by backtraces. By
default, no limit is imposed (encoded as -1).
opt.lg_prof_interval"
(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
"opt.prof_prefix"
option. By default, interval-triggered profile dumping is disabled
(encoded as -1).
opt.prof_gdump"
(bool)
r-
[--enable-prof]
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
"opt.prof_prefix"
option. This option is disabled by default.
opt.prof_leak"
(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
"opt.lg_prof_bt_max"
option for backtrace depth control. See the
"opt.prof"
option for
information on analyzing heap profile output. This option is disabled
by default.
opt.overcommit"
(bool)
r-
[--enable-swap]
Over-commit enabled/disabled. If enabled, over-commit
memory as a side effect of using anonymous
mmap(2) or
sbrk(2) for virtual memory allocation.
In order for overcommit to be disabled, the
"swap.fds"
mallctl must have
been successfully written to. This option is enabled by
default.
tcache.flush"
(void)
--
[--enable-tcache]
Flush calling thread's tcache. This interface releases all cached objects and internal data structures associated with the calling thread's thread-specific cache. Ordinarily, this interface need not be called, since automatic periodic incremental garbage collection occurs, and the thread cache is automatically discarded when a thread exits. However, garbage collection is triggered by allocation activity, so it is possible for a thread that stops allocating/deallocating to retain its cache indefinitely, in which case the developer may find manual flushing useful.
thread.arena"
(unsigned)
rw
Get or set the arena associated with the calling
thread. The arena index must be less than the maximum number of arenas
(see the
"arenas.narenas"
mallctl). If the specified arena was not initialized beforehand (see
the
"arenas.initialized"
mallctl), it will be automatically initialized as a side effect of
calling this interface.
thread.allocated"
(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.
thread.allocatedp"
(uint64_t *)
r-
[--enable-stats]
Get a pointer to the the value that is returned by the
"thread.allocated"
mallctl. This is useful for avoiding the overhead of repeated
mallctl*() calls.
thread.deallocated"
(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.
thread.deallocatedp"
(uint64_t *)
r-
[--enable-stats]
Get a pointer to the the value that is returned by the
"thread.deallocated"
mallctl. This is useful for avoiding the overhead of repeated
mallctl*() calls.
arenas.narenas"
(unsigned)
r-
Maximum number of arenas.
arenas.initialized"
(bool *)
r-
An array of
"arenas.narenas"
booleans. Each boolean indicates whether the corresponding arena is
initialized.
arenas.quantum"
(size_t)
r-
Quantum size.
arenas.cacheline"
(size_t)
r-
Assumed cacheline size.
arenas.subpage"
(size_t)
r-
Subpage size class interval.
arenas.pagesize"
(size_t)
r-
Page size.
arenas.chunksize"
(size_t)
r-
Chunk size.
arenas.tspace_min"
(size_t)
r-
Minimum tiny size class. Tiny size classes are powers of two.
arenas.tspace_max"
(size_t)
r-
Maximum tiny size class. Tiny size classes are powers of two.
arenas.qspace_min"
(size_t)
r-
Minimum quantum-spaced size class.
arenas.qspace_max"
(size_t)
r-
Maximum quantum-spaced size class.
arenas.cspace_min"
(size_t)
r-
Minimum cacheline-spaced size class.
arenas.cspace_max"
(size_t)
r-
Maximum cacheline-spaced size class.
arenas.sspace_min"
(size_t)
r-
Minimum subpage-spaced size class.
arenas.sspace_max"
(size_t)
r-
Maximum subpage-spaced size class.
arenas.tcache_max"
(size_t)
r-
[--enable-tcache]
Maximum thread-cached size class.
arenas.ntbins"
(unsigned)
r-
Number of tiny bin size classes.
arenas.nqbins"
(unsigned)
r-
Number of quantum-spaced bin size classes.
arenas.ncbins"
(unsigned)
r-
Number of cacheline-spaced bin size classes.
arenas.nsbins"
(unsigned)
r-
Number of subpage-spaced bin size classes.
arenas.nbins"
(unsigned)
r-
Total number of bin size classes.
arenas.nhbins"
(unsigned)
r-
[--enable-tcache]
Total number of thread cache bin size classes.
arenas.bin.<i>.size"
(size_t)
r-
Maximum size supported by size class.
arenas.bin.<i>.nregs"
(uint32_t)
r-
Number of regions per page run.
arenas.bin.<i>.run_size"
(size_t)
r-
Number of bytes per page run.
arenas.nlruns"
(size_t)
r-
Total number of large size classes.
arenas.lrun.<i>.size"
(size_t)
r-
Maximum size supported by this large size class.
arenas.purge"
(unsigned)
-w
Purge unused dirty pages for the specified arena, or for all arenas if none is specified.
prof.active"
(bool)
rw
[--enable-prof]
Control whether sampling is currently active. See the
"opt.prof_active"
option for additional information.
prof.dump"
(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
"opt.prof_prefix"
option.
prof.interval"
(uint64_t)
r-
[--enable-prof]
Average number of bytes allocated between
inverval-based profile dumps. See the
"opt.lg_prof_interval"
option for additional information.
stats.cactive"
(size_t *)
r-
[--enable-stats]
Pointer to a counter that contains an approximate count
of the current number of bytes in active pages. The estimate may be
high, but never low, because each arena rounds up to the nearest
multiple of the chunk size when computing its contribution to the
counter. Note that the
"epoch"
mallctl has no bearing
on this counter. Furthermore, counter consistency is maintained via
atomic operations, so it is necessary to use an atomic operation in
order to guarantee a consistent read when dereferencing the pointer.
stats.allocated"
(size_t)
r-
[--enable-stats]
Total number of bytes allocated by the application.
stats.active"
(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
"stats.allocated"
.
stats.mapped"
(size_t)
r-
[--enable-stats]
Total number of bytes in chunks mapped on behalf of the
application. This is a multiple of the chunk size, and is at least as
large as
"stats.active"
. This
does not include inactive chunks backed by swap files. his does not
include inactive chunks embedded in the DSS.
stats.chunks.current"
(size_t)
r-
[--enable-stats]
Total number of chunks actively mapped on behalf of the application. This does not include inactive chunks backed by swap files. This does not include inactive chunks embedded in the DSS.
stats.chunks.total"
(uint64_t)
r-
[--enable-stats]
Cumulative number of chunks allocated.
stats.chunks.high"
(size_t)
r-
[--enable-stats]
Maximum number of active chunks at any time thus far.
stats.huge.allocated"
(size_t)
r-
[--enable-stats]
Number of bytes currently allocated by huge objects.
stats.huge.nmalloc"
(uint64_t)
r-
[--enable-stats]
Cumulative number of huge allocation requests.
stats.huge.ndalloc"
(uint64_t)
r-
[--enable-stats]
Cumulative number of huge deallocation requests.
stats.arenas.<i>.nthreads"
(unsigned)
r-
Number of threads currently assigned to arena.
stats.arenas.<i>.pactive"
(size_t)
r-
Number of pages in active runs.
stats.arenas.<i>.pdirty"
(size_t)
r-
Number of pages within unused runs that are potentially
dirty, and for which madvise(...,
MADV_DONTNEED
stats.arenas.<i>.mapped"
(size_t)
r-
[--enable-stats]
Number of mapped bytes.
stats.arenas.<i>.npurge"
(uint64_t)
r-
[--enable-stats]
Number of dirty page purge sweeps performed.
stats.arenas.<i>.nmadvise"
(uint64_t)
r-
[--enable-stats]
Number of madvise(...,
MADV_DONTNEED
stats.arenas.<i>.npurged"
(uint64_t)
r-
[--enable-stats]
Number of pages purged.
stats.arenas.<i>.small.allocated"
(size_t)
r-
[--enable-stats]
Number of bytes currently allocated by small objects.
stats.arenas.<i>.small.nmalloc"
(uint64_t)
r-
[--enable-stats]
Cumulative number of allocation requests served by small bins.
stats.arenas.<i>.small.ndalloc"
(uint64_t)
r-
[--enable-stats]
Cumulative number of small objects returned to bins.
stats.arenas.<i>.small.nrequests"
(uint64_t)
r-
[--enable-stats]
Cumulative number of small allocation requests.
stats.arenas.<i>.large.allocated"
(size_t)
r-
[--enable-stats]
Number of bytes currently allocated by large objects.
stats.arenas.<i>.large.nmalloc"
(uint64_t)
r-
[--enable-stats]
Cumulative number of large allocation requests served directly by the arena.
stats.arenas.<i>.large.ndalloc"
(uint64_t)
r-
[--enable-stats]
Cumulative number of large deallocation requests served directly by the arena.
stats.arenas.<i>.large.nrequests"
(uint64_t)
r-
[--enable-stats]
Cumulative number of large allocation requests.
stats.arenas.<i>.bins.<j>.allocated"
(size_t)
r-
[--enable-stats]
Current number of bytes allocated by bin.
stats.arenas.<i>.bins.<j>.nmalloc"
(uint64_t)
r-
[--enable-stats]
Cumulative number of allocations served by bin.
stats.arenas.<i>.bins.<j>.ndalloc"
(uint64_t)
r-
[--enable-stats]
Cumulative number of allocations returned to bin.
stats.arenas.<i>.bins.<j>.nrequests"
(uint64_t)
r-
[--enable-stats]
Cumulative number of allocation requests.
stats.arenas.<i>.bins.<j>.nfills"
(uint64_t)
r-
[--enable-stats --enable-tcache]
Cumulative number of tcache fills.
stats.arenas.<i>.bins.<j>.nflushes"
(uint64_t)
r-
[--enable-stats --enable-tcache]
Cumulative number of tcache flushes.
stats.arenas.<i>.bins.<j>.nruns"
(uint64_t)
r-
[--enable-stats]
Cumulative number of runs created.
stats.arenas.<i>.bins.<j>.nreruns"
(uint64_t)
r-
[--enable-stats]
Cumulative number of times the current run from which to allocate changed.
stats.arenas.<i>.bins.<j>.highruns"
(size_t)
r-
[--enable-stats]
Maximum number of runs at any time thus far.
stats.arenas.<i>.bins.<j>.curruns"
(size_t)
r-
[--enable-stats]
Current number of runs.
stats.arenas.<i>.lruns.<j>.nmalloc"
(uint64_t)
r-
[--enable-stats]
Cumulative number of allocation requests for this size class served directly by the arena.
stats.arenas.<i>.lruns.<j>.ndalloc"
(uint64_t)
r-
[--enable-stats]
Cumulative number of deallocation requests for this size class served directly by the arena.
stats.arenas.<i>.lruns.<j>.nrequests"
(uint64_t)
r-
[--enable-stats]
Cumulative number of allocation requests for this size class.
stats.arenas.<i>.lruns.<j>.highruns"
(size_t)
r-
[--enable-stats]
Maximum number of runs at any time thus far for this size class.
stats.arenas.<i>.lruns.<j>.curruns"
(size_t)
r-
[--enable-stats]
Current number of runs for this size class.
swap.avail"
(size_t)
r-
[--enable-stats --enable-swap]
Number of swap file bytes that are currently not associated with any chunk (i.e. mapped, but otherwise completely unmanaged).
swap.prezeroed"
(bool)
rw
[--enable-swap]
If true, the allocator assumes that the swap file(s)
contain nothing but nil bytes. If this assumption is violated,
allocator behavior is undefined. This value becomes read-only after
"swap.fds"
is
successfully written to.
swap.nfds"
(size_t)
r-
[--enable-swap]
Number of file descriptors in use for swap.
swap.fds"
(int *)
r-
[--enable-swap]
When written to, the files associated with the
specified file descriptors are contiguously mapped via
mmap(2). The resulting virtual memory
region is preferred over anonymous
mmap(2) and
sbrk(2) memory. Note that if a file's
size is not a multiple of the page size, it is automatically truncated
to the nearest page size multiple. See the
"swap.prezeroed"
mallctl for specifying that the files are pre-zeroed.
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.
Programs often accidentally depend on “uninitialized”
memory actually being filled with zero bytes. Junk filling
(see the
"opt.junk"
option) tends to expose such bugs in the form of obviously incorrect
results and/or coredumps. Conversely, zero
filling (see the
"opt.zero"
option) eliminates
the symptoms of such bugs. Between these two options, it is usually
possible to quickly detect, diagnose, and eliminate such bugs.
This implementation does not provide much detail about the problems it detects, because the performance impact for storing such information would be prohibitive. There are a number of allocator implementations available on the Internet which focus on detecting and pinpointing problems by trading performance for extra sanity checks and detailed diagnostics.
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
"opt.abort"
option is set, most
warnings are treated as errors.
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.
All messages are prefixed by
“<jemalloc>: ”.
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.
The posix_memalign() function
returns the value 0 if successful; otherwise it returns an error value.
The posix_memalign() function will fail
if:
The alignment parameter is
not a power of 2 at least as large as
sizeof(void *).
Memory allocation error.
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.
The free() function returns no
value.
The malloc_usable_size() function
returns the usable size of the allocation pointed to by
ptr.
The mallctl(),
mallctlnametomib(), and
mallctlbymib() functions return 0 on
success; otherwise they return an error value. The functions will fail
if:
newp is not
NULL, and newlen is too
large or too small. Alternatively, *oldlenp
is too large or too small; in this case as much data as possible
are read despite the error.
*oldlenp is too short to
hold the requested value.
name or
mib specifies an unknown/invalid
value.
Attempt to read or write void value, or attempt to write read-only value.
A memory allocation failure occurred.
An interface with side effects failed in some way
not directly related to mallctl*()
read/write processing.
The allocm(),
rallocm(),
sallocm(), and
dallocm() functions return
ALLOCM_SUCCESS on success; otherwise they return an
error value. The allocm() and
rallocm() functions will fail if:
Out of memory. Insufficient contiguous memory was
available to service the allocation request. The
allocm() function additionally sets
*ptr to NULL, whereas
the rallocm() function leaves
*ptr unmodified.
The rallocm() function will also
fail if:
ALLOCM_NO_MOVE was specified,
but the reallocation request could not be serviced without moving
the object.
The following environment variable affects the execution of the allocation functions:
MALLOC_CONFIf the environment variable
MALLOC_CONF is set, the characters it contains
will be interpreted as options.