JEMALLOC(3) | User Manual | JEMALLOC(3) |
NAME¶
jemalloc - general purpose memory allocation functionsLIBRARY¶
This manual describes jemalloc 3.0.0-0-gfc9b1dbf69f59d7ecfc4ac68da9847e017e1d046. More information can be found at the jemalloc website[1].SYNOPSIS¶
#include <stdlib.h> #include <jemalloc/jemalloc.h>
Standard API¶
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
*aligned_alloc(size_t alignment,
size_t size);
void
*realloc(void *ptr,
size_t size);
void
free(void *ptr);
Non-standard API¶
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;
Experimental API¶
int
allocm(void **ptr, size_t *rsize,
size_t size, int flags);
int
rallocm(void **ptr, size_t *rsize,
size_t size, size_t extra,
int flags);
int
sallocm(const void *ptr,
size_t *rsize, int flags);
int
dallocm(void *ptr, int flags);
int
nallocm(size_t *rsize, size_t size,
int flags);
DESCRIPTION¶
Standard API¶
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 aligned_alloc function allocates size bytes of memory such that the allocation's base address is an even multiple of alignment. The requested alignment must be a power of 2. Behavior is undefined if size is not an integral multiple of alignment. 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.Non-standard API¶
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... */ }
Experimental API¶
The experimental API is subject to change or removal without regard for backward compatibility. If --disable-experimental is specified during configuration, the experimental API is omitted. The allocm, rallocm, sallocm, dallocm , and nallocm 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 << la). This macro does not
validate that 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_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 option is absent, newly allocated
memory is uninitialized.
ALLOCM_NO_MOVE
For 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. Behavior is undefined if size is 0.
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) bytes, though inability to allocate the extra byte(s) will not
by itself result in failure. Behavior is undefined if size is 0,
or if ( 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.
The nallocm function allocates no memory, but it performs the same
size computation as the allocm function, and if rsize is
not NULL it sets *rsize to the real size of the allocation that
would result from the equivalent allocm function call. Behavior
is undefined if size is 0.
TUNING¶
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.IMPLEMENTATION NOTES¶
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 mmap(2) and sbrk(2), in that order of preference; otherwise only mmap(2) is used. This allocator uses multiple arenas in order to reduce lock contention for threaded programs on multi-processor systems. This works well with regard to threading scalability, but incurs some costs. There is a small fixed per-arena overhead, and additionally, arenas manage memory completely independently of each other, which means a small fixed increase in overall memory fragmentation. These overheads are not generally an issue, given the number of arenas normally used. Note that using substantially more arenas than the default is not likely to improve performance, mainly due to reduced cache performance. However, it may make sense to reduce the number of arenas if an application does not make much use of the allocation functions. In addition to multiple arenas, 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. 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 small object size classes are multiples of the quantum, spaced such that internal fragmentation is limited to approximately 25% for all but the smallest size classes. Allocation requests that are larger than the maximum small 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.Category | Spacing | Size |
Small | lg | [8] |
16 | [16, 32, 48, ..., 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] | |
Large | 4 KiB | [4 KiB, 8 KiB, 12 KiB, ..., 4072 KiB] |
Huge | 4 MiB | [4 MiB, 8 MiB, 12 MiB, ...] |
MALLCTL NAMESPACE¶
The following names are defined in the namespace accessible via theReturn 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.fill" ( bool) r-
--enable-fill was specified during
build configuration.
"config.lazy_lock" ( bool) r-
--enable-lazy-lock was specified during
build configuration.
"config.mremap" ( bool) r-
--enable-mremap was specified during
build configuration.
"config.munmap" ( bool) r-
--enable-munmap 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.tcache" ( bool) r-
--disable-tcache was not specified
during build configuration.
"config.tls" ( bool) r-
--disable-tls was not specified during
build configuration.
"config.utrace" ( bool) r-
--enable-utrace was specified during
build configuration.
"config.valgrind" ( bool) r-
--enable-valgrind was 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_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.quarantine" ( size_t) r- [--enable-fill]
Per thread quarantine size in bytes. If
non-zero, each thread maintains a FIFO object quarantine that stores up to the
specified number of bytes of memory. The quarantined memory is not freed until
it is released from quarantine, though it is immediately junk-filled if the
"opt.junk" option is enabled. This feature is of particular use in
combination with Valgrind[2], which can detect attempts to access
quarantined objects. This is intended for debugging and will impact
performance negatively. The default quarantine size is 0.
"opt.redzone" ( bool) r- [--enable-fill]
Redzones enabled/disabled. If enabled, small
allocations have redzones before and after them. Furthermore, if the
"opt.junk" option is enabled, the redzones are checked for
corruption during deallocation. However, the primary intended purpose of this
feature is to be used in combination with Valgrind[2], which needs
redzones in order to do effective buffer overflow/underflow detection. This
option is intended for debugging and will impact performance negatively. This
option is disabled 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.utrace" ( bool) r- [--enable-utrace]
Allocation tracing based on utrace(2)
enabled/disabled. This option is disabled by default.
"opt.valgrind" ( bool) r- [--enable-valgrind]
Valgrind[2] support enabled/disabled.
If enabled, several other options are automatically modified during options
processing to work well with Valgrind: "opt.junk" and
"opt.zero" are set to false, "opt.quarantine" is set to 16
MiB, and "opt.redzone" is set to true. 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:
This option is disabled by default.
"opt.tcache" ( bool) r- [--enable-tcache]
malloc_conf = "xmalloc:true";
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_max" option for related
tuning information. This option is enabled by default.
"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. 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_interval" option for information on interval-triggered
profile dumping, the "opt.prof_gdump" option for information on
high-water-triggered profile dumping, and the "opt.prof_final"
option for final profile dumping. Profile output is compatible with the
included pprof Perl script, which originates from the gperftools
package[3].
"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.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 512 KiB (2^19 B).
"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. This option is disabled by default.
"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_final" ( 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 "opt.prof_prefix" option. This option is enabled
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.prof" option for information on analyzing
heap profile output. This option is disabled by default.
"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.
"thread.tcache.enabled" ( bool) rw [--enable-tcache]
Enable/disable calling thread's tcache. The
tcache is implicitly flushed as a side effect of becoming disabled (see
"thread.tcache.flush").
"thread.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.
"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.page" ( size_t) r-
Page size.
"arenas.tcache_max" ( size_t) r- [--enable-tcache]
Maximum thread-cached size class.
"arenas.nbins" ( unsigned) r-
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.
"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.
"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 or similar has not been called.
"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 or similar calls made to purge dirty
pages.
"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>.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>.curruns" ( size_t) r-
[--enable-stats]
Current number of runs for this size
class.
DEBUGGING MALLOC PROBLEMS¶
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. However, jemalloc does integrate with the most excellent Valgrind[2] tool if the --enable-valgrind configuration option is enabled and the "opt.valgrind" option is enabled.DIAGNOSTIC MESSAGES¶
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>:”.RETURN VALUES¶
Standard API¶
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: EINVALThe alignment parameter is not a power
of 2 at least as large as sizeof( void *).
ENOMEM
Memory allocation error.
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:
EINVAL
The alignment parameter is not a power
of 2.
ENOMEM
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.
Non-standard API¶
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: EINVALnewp 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.
ENOMEM
*oldlenp is too short to hold the
requested value.
ENOENT
name or mib specifies an
unknown/invalid value.
EPERM
Attempt to read or write void value, or
attempt to write read-only value.
EAGAIN
A memory allocation failure occurred.
EFAULT
An interface with side effects failed in some
way not directly related to mallctl* read/write
processing.
Experimental API¶
The allocm, rallocm, sallocm, dallocm , and nallocm functions return ALLOCM_SUCCESS on success; otherwise they return an error value. The allocm, rallocm, and nallocm functions will fail if: ALLOCM_ERR_OOMOut 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_ERR_NOT_MOVED
ALLOCM_NO_MOVE was specified, but the
reallocation request could not be serviced without moving the object.
ENVIRONMENT¶
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.
EXAMPLES¶
To dump core whenever a problem occurs:ln -s 'abort:true' /etc/malloc.conf
malloc_conf = "lg_chunk:24";
SEE ALSO¶
madvise(2), mmap(2), sbrk(2), utrace(2), alloca(3), atexit(3), getpagesize(3)STANDARDS¶
The malloc, calloc, realloc, and free functions conform to ISO/IEC 9899:1990 (“ISO C90”). The posix_memalign function conforms to IEEE Std 1003.1-2001 (“POSIX.1”).AUTHOR¶
Jason EvansNOTES¶
- 1.
- jemalloc website
- 2.
- Valgrind
- 3.
- gperftools package
05/11/2012 | jemalloc 3.0.0-0-gfc9b1dbf69f5 |