JEMALLOC(3) | User Manual | JEMALLOC(3) |
jemalloc - general purpose memory allocation functions
This manual describes jemalloc 5.2.1-0-gea6b3e973b477b8061e0076bb257dbd7f3faa756. More information can be found at the jemalloc website[1].
#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 *aligned_alloc(size_t alignment, size_t size);
void *realloc(void *ptr, size_t size);
void free(void *ptr);
void *mallocx(size_t size, int flags);
void *rallocx(void *ptr, size_t size, int flags);
size_t xallocx(void *ptr, size_t size, size_t extra, int flags);
size_t sallocx(void *ptr, int flags);
void dallocx(void *ptr, int flags);
void sdallocx(void *ptr, size_t size, int flags);
size_t nallocx(size_t size, int flags);
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_stats_print(void (*write_cb) (void *, const char *), void *cbopaque, const char *opts);
size_t malloc_usable_size(const void *ptr);
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 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 *).
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.
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 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:
MALLOCX_LG_ALIGN(la)
MALLOCX_ALIGN(a)
MALLOCX_ZERO
MALLOCX_TCACHE(tc)
MALLOCX_TCACHE_NONE
MALLOCX_ARENA(a)
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.
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.
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).
The sallocx() function returns the real size of the allocation at ptr.
The dallocx() function causes the memory referenced by ptr to be made available for future allocations.
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().
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.
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; 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... */ }
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.
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.
Once, when the first call is made to one of the memory allocation routines, the allocator initializes its internals based in part on various options that can be specified at compile- or run-time.
The string specified via --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.
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 sbrk(2) is supported by the operating system, this allocator uses both mmap(2) and sbrk(2), in that order of preference; otherwise only mmap(2) is used.
This allocator uses multiple arenas in order to reduce lock contention for threaded programs on multi-processor systems. This works well with regard to threading scalability, but incurs some costs. There is a small fixed per-arena overhead, and additionally, arenas manage memory completely independently of each other, which means a small fixed increase in overall memory fragmentation. These overheads are not generally an issue, given the number of arenas normally used. Note that using substantially more arenas than the default is not likely to improve performance, mainly due to reduced cache performance. However, it may make sense to reduce the number of arenas if an application does not make much use of the allocation functions.
In addition to multiple arenas, this allocator supports thread-specific caching, in order to make it possible to completely avoid synchronization for most allocation requests. Such caching allows very fast allocation in the common case, but it increases memory usage and fragmentation, since a bounded number of objects can remain allocated in each thread cache.
Memory is conceptually broken into extents. Extents are always aligned to multiples of the page size. This alignment makes it possible to find metadata for user objects quickly. User objects are broken into two categories according to size: small and large. Contiguous small objects comprise a slab, which resides within a single extent, whereas large objects each have their own extents backing them.
Small objects are managed in groups by slabs. Each slab maintains a bitmap to track which regions are in use. Allocation requests that are no more than half the quantum (8 or 16, depending on architecture) are rounded up to the nearest power of two that is at least 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.
Allocations are packed tightly together, which can be an issue for multi-threaded applications. If you need to assure that allocations do not suffer from cacheline sharing, round your allocation requests up to the nearest multiple of the cacheline size, or specify cacheline alignment when allocating.
The 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 arena.<i>.extent_hooks). Growth only succeeds if the trailing memory is currently available, and the extent allocator supports merging.
Assuming 4 KiB pages and a 16-byte quantum on a 64-bit system, the size classes in each category are as shown in Table 1.
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, 54 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] |
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>.* and
arena.<i>.{initialized,purge,decay,dss}, <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 epoch mallctl, which controls refreshing of cached dynamic statistics.
version (const char *) r-
epoch (uint64_t) rw
background_thread (bool) rw
max_background_threads (size_t) rw
config.cache_oblivious (bool) r-
config.debug (bool) r-
config.fill (bool) r-
config.lazy_lock (bool) r-
config.malloc_conf (const char *) r-
config.prof (bool) r-
config.prof_libgcc (bool) r-
config.prof_libunwind (bool) r-
config.stats (bool) r-
config.utrace (bool) r-
config.xmalloc (bool) r-
opt.abort (bool) r-
opt.confirm_conf (bool) r-
opt.abort_conf (bool) r-
opt.metadata_thp (const char *) r-
opt.retain (bool) r-
opt.dss (const char *) r-
opt.narenas (unsigned) r-
opt.oversize_threshold (size_t) r-
opt.percpu_arena (const char *) r-
opt.background_thread (bool) r-
opt.max_background_threads (size_t) r-
opt.dirty_decay_ms (ssize_t) r-
opt.muzzy_decay_ms (ssize_t) r-
opt.lg_extent_max_active_fit (size_t) r-
opt.stats_print (bool) r-
opt.stats_print_opts (const char *) r-
opt.junk (const char *) r- [--enable-fill]
opt.zero (bool) r- [--enable-fill]
opt.utrace (bool) r- [--enable-utrace]
opt.xmalloc (bool) r- [--enable-xmalloc]
malloc_conf = "xmalloc:true";
This option is disabled by default.
opt.tcache (bool) r-
opt.lg_tcache_max (size_t) r-
opt.thp (const char *) r-
opt.prof (bool) r- [--enable-prof]
opt.prof_prefix (const char *) r- [--enable-prof]
opt.prof_active (bool) r- [--enable-prof]
opt.prof_thread_active_init (bool) r- [--enable-prof]
opt.lg_prof_sample (size_t) r- [--enable-prof]
opt.prof_accum (bool) r- [--enable-prof]
opt.lg_prof_interval (ssize_t) r- [--enable-prof]
opt.prof_gdump (bool) r- [--enable-prof]
opt.prof_final (bool) r- [--enable-prof]
opt.prof_leak (bool) r- [--enable-prof]
thread.arena (unsigned) rw
thread.allocated (uint64_t) r- [--enable-stats]
thread.allocatedp (uint64_t *) r- [--enable-stats]
thread.deallocated (uint64_t) r- [--enable-stats]
thread.deallocatedp (uint64_t *) r- [--enable-stats]
thread.tcache.enabled (bool) rw
thread.tcache.flush (void) --
thread.prof.name (const char *) r- or -w [--enable-prof]
thread.prof.active (bool) rw [--enable-prof]
tcache.create (unsigned) r-
tcache.flush (unsigned) -w
tcache.destroy (unsigned) -w
arena.<i>.initialized (bool) r-
arena.<i>.decay (void) --
arena.<i>.purge (void) --
arena.<i>.reset (void) --
arena.<i>.destroy (void) --
arena.<i>.dss (const char *) rw
arena.<i>.dirty_decay_ms (ssize_t) rw
arena.<i>.muzzy_decay_ms (ssize_t) rw
arena.<i>.retain_grow_limit (size_t) rw
arena.<i>.extent_hooks (extent_hooks_t *) rw
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.
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 arena.<i>.dss setting irrelevant.
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.
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 arena.<i>.destroy).
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.
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.
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.
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.
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.
arenas.narenas (unsigned) r-
arenas.dirty_decay_ms (ssize_t) rw
arenas.muzzy_decay_ms (ssize_t) rw
arenas.quantum (size_t) r-
arenas.page (size_t) r-
arenas.tcache_max (size_t) r-
arenas.nbins (unsigned) r-
arenas.nhbins (unsigned) r-
arenas.bin.<i>.size (size_t) r-
arenas.bin.<i>.nregs (uint32_t) r-
arenas.bin.<i>.slab_size (size_t) r-
arenas.nlextents (unsigned) r-
arenas.lextent.<i>.size (size_t) r-
arenas.create (unsigned, extent_hooks_t *) rw
arenas.lookup (unsigned, void*) rw
prof.thread_active_init (bool) rw [--enable-prof]
prof.active (bool) rw [--enable-prof]
prof.dump (const char *) -w [--enable-prof]
prof.gdump (bool) rw [--enable-prof]
prof.reset (size_t) -w [--enable-prof]
prof.lg_sample (size_t) r- [--enable-prof]
prof.interval (uint64_t) r- [--enable-prof]
stats.allocated (size_t) r- [--enable-stats]
stats.active (size_t) r- [--enable-stats]
stats.metadata (size_t) r- [--enable-stats]
stats.metadata_thp (size_t) r- [--enable-stats]
stats.resident (size_t) r- [--enable-stats]
stats.mapped (size_t) r- [--enable-stats]
stats.retained (size_t) r- [--enable-stats]
stats.background_thread.num_threads (size_t) r- [--enable-stats]
stats.background_thread.num_runs (uint64_t) r- [--enable-stats]
stats.background_thread.run_interval (uint64_t) r- [--enable-stats]
stats.mutexes.ctl.{counter}; (counter specific type) r- [--enable-stats]
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.
stats.mutexes.background_thread.{counter} (counter specific type) r- [--enable-stats]
stats.mutexes.prof.{counter} (counter specific type) r- [--enable-stats]
stats.mutexes.reset (void) -- [--enable-stats]
stats.arenas.<i>.dss (const char *) r-
stats.arenas.<i>.dirty_decay_ms (ssize_t) r-
stats.arenas.<i>.muzzy_decay_ms (ssize_t) r-
stats.arenas.<i>.nthreads (unsigned) r-
stats.arenas.<i>.uptime (uint64_t) r-
stats.arenas.<i>.pactive (size_t) r-
stats.arenas.<i>.pdirty (size_t) r-
stats.arenas.<i>.pmuzzy (size_t) r-
stats.arenas.<i>.mapped (size_t) r- [--enable-stats]
stats.arenas.<i>.retained (size_t) r- [--enable-stats]
stats.arenas.<i>.extent_avail (size_t) r- [--enable-stats]
stats.arenas.<i>.base (size_t) r- [--enable-stats]
stats.arenas.<i>.internal (size_t) r- [--enable-stats]
stats.arenas.<i>.metadata_thp (size_t) r- [--enable-stats]
stats.arenas.<i>.resident (size_t) r- [--enable-stats]
stats.arenas.<i>.dirty_npurge (uint64_t) r- [--enable-stats]
stats.arenas.<i>.dirty_nmadvise (uint64_t) r- [--enable-stats]
stats.arenas.<i>.dirty_purged (uint64_t) r- [--enable-stats]
stats.arenas.<i>.muzzy_npurge (uint64_t) r- [--enable-stats]
stats.arenas.<i>.muzzy_nmadvise (uint64_t) r- [--enable-stats]
stats.arenas.<i>.muzzy_purged (uint64_t) r- [--enable-stats]
stats.arenas.<i>.small.allocated (size_t) r- [--enable-stats]
stats.arenas.<i>.small.nmalloc (uint64_t) r- [--enable-stats]
stats.arenas.<i>.small.ndalloc (uint64_t) r- [--enable-stats]
stats.arenas.<i>.small.nrequests (uint64_t) r- [--enable-stats]
stats.arenas.<i>.small.nfills (uint64_t) r- [--enable-stats]
stats.arenas.<i>.small.nflushes (uint64_t) r- [--enable-stats]
stats.arenas.<i>.large.allocated (size_t) r- [--enable-stats]
stats.arenas.<i>.large.nmalloc (uint64_t) r- [--enable-stats]
stats.arenas.<i>.large.ndalloc (uint64_t) r- [--enable-stats]
stats.arenas.<i>.large.nrequests (uint64_t) r- [--enable-stats]
stats.arenas.<i>.large.nfills (uint64_t) r- [--enable-stats]
stats.arenas.<i>.large.nflushes (uint64_t) r- [--enable-stats]
stats.arenas.<i>.bins.<j>.nmalloc (uint64_t) r- [--enable-stats]
stats.arenas.<i>.bins.<j>.ndalloc (uint64_t) r- [--enable-stats]
stats.arenas.<i>.bins.<j>.nrequests (uint64_t) r- [--enable-stats]
stats.arenas.<i>.bins.<j>.curregs (size_t) r- [--enable-stats]
stats.arenas.<i>.bins.<j>.nfills (uint64_t) r-
stats.arenas.<i>.bins.<j>.nflushes (uint64_t) r-
stats.arenas.<i>.bins.<j>.nslabs (uint64_t) r- [--enable-stats]
stats.arenas.<i>.bins.<j>.nreslabs (uint64_t) r- [--enable-stats]
stats.arenas.<i>.bins.<j>.curslabs (size_t) r- [--enable-stats]
stats.arenas.<i>.bins.<j>.nonfull_slabs (size_t) r- [--enable-stats]
stats.arenas.<i>.bins.<j>.mutex.{counter} (counter specific type) r- [--enable-stats]
stats.arenas.<i>.extents.<j>.n{extent_type} (size_t) r- [--enable-stats]
stats.arenas.<i>.extents.<j>.{extent_type}_bytes (size_t) r- [--enable-stats]
stats.arenas.<i>.lextents.<j>.nmalloc (uint64_t) r- [--enable-stats]
stats.arenas.<i>.lextents.<j>.ndalloc (uint64_t) r- [--enable-stats]
stats.arenas.<i>.lextents.<j>.nrequests (uint64_t) r- [--enable-stats]
stats.arenas.<i>.lextents.<j>.curlextents (size_t) r- [--enable-stats]
stats.arenas.<i>.mutexes.large.{counter} (counter specific type) r- [--enable-stats]
stats.arenas.<i>.mutexes.extent_avail.{counter} (counter specific type) r- [--enable-stats]
stats.arenas.<i>.mutexes.extents_dirty.{counter} (counter specific type) r- [--enable-stats]
stats.arenas.<i>.mutexes.extents_muzzy.{counter} (counter specific type) r- [--enable-stats]
stats.arenas.<i>.mutexes.extents_retained.{counter} (counter specific type) r- [--enable-stats]
stats.arenas.<i>.mutexes.decay_dirty.{counter} (counter specific type) r- [--enable-stats]
stats.arenas.<i>.mutexes.decay_muzzy.{counter} (counter specific type) r- [--enable-stats]
stats.arenas.<i>.mutexes.base.{counter} (counter specific type) r- [--enable-stats]
stats.arenas.<i>.mutexes.tcache_list.{counter} (counter specific type) r- [--enable-stats]
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.
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: ]
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>
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.
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:
EINVAL
ENOMEM
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
ENOMEM
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 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.
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.
The sallocx() function returns the real size of the allocation pointed to by ptr.
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.
The mallctl(), mallctlnametomib(), and mallctlbymib() functions return 0 on success; otherwise they return an error value. The functions will fail if:
EINVAL
ENOENT
EPERM
EAGAIN
EFAULT
The malloc_usable_size() function returns the usable size of the allocation pointed to by ptr.
The following environment variable affects the execution of the allocation functions:
MALLOC_CONF
To dump core whenever a problem occurs:
ln -s 'abort:true' /etc/malloc.conf
To specify in the source that only one arena should be automatically created:
malloc_conf = "narenas:1";
madvise(2), mmap(2), sbrk(2), utrace(2), alloca(3), atexit(3), getpagesize(3)
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”).
Jason Evans
03/27/2021 | jemalloc 5.2.1-0-gea6b3e973b47 |