NAME
jemalloc - general purpose memory allocation functions
LIBRARY
This manual describes jemalloc 4.2.1-0-g3de035335255d553bdb344c32ffdb603816195d8. More information can be found at the jemalloc website[1].
The following configuration options are enabled in libc's built-in jemalloc: --enable-fill, --enable-lazy-lock, --enable-munmap, --enable-stats, --enable-tcache, --enable-tls, --enable-utrace, and --enable-xmalloc. Additionally, --enable-debug is enabled in development versions of FreeBSD (controlled by the MALLOC_PRODUCTION make variable).
SYNOPSIS
#include <stdlib.h> #include <malloc_np.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
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;
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 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.
Non-standard API
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, &bin_size, &len, NULL, 0); /* Do something with bin_size... */ }
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”, “l”, and “h” can be specified to omit per size class statistics for bins, large objects, and huge 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 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.
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 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.
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 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, 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. Multiple small and large objects can reside within a single chunk, whereas huge objects each have one or more chunks backing them. Each chunk that contains small and/or large objects 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 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, large size classes are smaller than the chunk size (see the "opt.lg_chunk" option), and huge size classes extend from the chunk 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 and huge allocations in place, as long as the pre-size and post-size are both large or both huge. In such cases shrinkage always succeeds for large size classes, but for huge size classes the chunk allocator must support splitting (see "arena.<i>.chunk_hooks"). Growth only succeeds if the trailing memory is currently available, and additionally for huge size classes the chunk allocator must support merging.
Assuming 2 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 | 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] | |
Huge | 256 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] |
MALLCTL NAMESPACE
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-
"epoch" (uint64_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.munmap" (bool) r-
"config.prof" (bool) r-
"config.prof_libgcc" (bool) r-
"config.prof_libunwind" (bool) r-
"config.stats" (bool) r-
"config.tcache" (bool) r-
"config.tls" (bool) r-
"config.utrace" (bool) r-
"config.valgrind" (bool) r-
"config.xmalloc" (bool) r-
"opt.abort" (bool) r-
"opt.dss" (const char *) r-
"opt.lg_chunk" (size_t) r-
"opt.narenas" (unsigned) r-
"opt.purge" (const char *) r-
"opt.lg_dirty_mult" (ssize_t) r-
"opt.decay_time" (ssize_t) r-
"opt.stats_print" (bool) r-
"opt.junk" (const char *) r- [--enable-fill]
"opt.quarantine" (size_t) r- [--enable-fill]
"opt.redzone" (bool) 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- [--enable-tcache]
"opt.lg_tcache_max" (size_t) r- [--enable-tcache]
"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 [--enable-tcache]
"thread.tcache.flush" (void) -- [--enable-tcache]
"thread.prof.name" (const char *) r- or -w [--enable-prof]
"thread.prof.active" (bool) rw [--enable-prof]
"tcache.create" (unsigned) r- [--enable-tcache]
"tcache.flush" (unsigned) -w [--enable-tcache]
"tcache.destroy" (unsigned) -w [--enable-tcache]
"arena.<i>.purge" (void) --
"arena.<i>.decay" (void) --
"arena.<i>.reset" (void) --
"arena.<i>.dss" (const char *) rw
"arena.<i>.lg_dirty_mult" (ssize_t) rw
"arena.<i>.decay_time" (ssize_t) rw
"arena.<i>.chunk_hooks" (chunk_hooks_t) rw
typedef struct { chunk_alloc_t *alloc; chunk_dalloc_t *dalloc; chunk_commit_t *commit; chunk_decommit_t *decommit; chunk_purge_t *purge; chunk_split_t *split; chunk_merge_t *merge; } chunk_hooks_t;
The chunk_hooks_t structure comprises function pointers which are described individually below. jemalloc uses these functions to manage chunk 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 chunks for later reuse. Cleanup attempts cascade from deallocation to decommit to purging, which gives the chunk management functions opportunities to reject the most permanent cleanup operations in favor of less permanent (and often less costly) operations. The chunk splitting and merging operations can also be opted out of, but this is mainly intended to support platforms on which virtual memory mappings provided by the operating system kernel do not automatically coalesce and split, e.g. Windows.
typedef void *(chunk_alloc_t)(void *chunk, size_t size, size_t alignment, bool *zero, bool *commit, unsigned arena_ind);
A chunk allocation function conforms to the chunk_alloc_t type and upon success returns a pointer to size bytes of mapped memory on behalf of arena arena_ind such that the chunk's base address is a multiple of alignment, as well as setting *zero to indicate whether the chunk is zeroed and *commit to indicate whether the chunk is committed. Upon error the function returns NULL and leaves *zero and *commit unmodified. The size parameter is always a multiple of the chunk size. The alignment parameter is always a power of two at least as large as the chunk size. Zeroing is mandatory if *zero is true upon function entry. Committing is mandatory if *commit is true upon function entry. If chunk is not NULL, the returned pointer must be chunk 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 chunk allocation function makes the arena's "arena.<i>.dss" setting irrelevant.
typedef bool (chunk_dalloc_t)(void *chunk, size_t size, bool committed, unsigned arena_ind);
A chunk deallocation function conforms to the chunk_dalloc_t type and deallocates a chunk of given 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 chunk remains mapped, in the same commit state, and available for future use, in which case it will be automatically retained for later reuse.
typedef bool (chunk_commit_t)(void *chunk, size_t size, size_t offset, size_t length, unsigned arena_ind);
A chunk commit function conforms to the chunk_commit_t type and commits zeroed physical memory to back pages within a chunk of given 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 (chunk_decommit_t)(void *chunk, size_t size, size_t offset, size_t length, unsigned arena_ind);
A chunk decommit function conforms to the chunk_decommit_t type and decommits any physical memory that is backing pages within a chunk of given 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 chunk 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 (chunk_purge_t)(void *chunk, size_tsize, size_t offset, size_t length, unsigned arena_ind);
A chunk purge function conforms to the chunk_purge_t type and optionally discards physical pages within the virtual memory mapping associated with chunk of given size at offset bytes, extending for length on behalf of arena arena_ind, returning false if pages within the purged virtual memory range will be zero-filled the next time they are accessed.
typedef bool (chunk_split_t)(void *chunk, size_t size, size_t size_a, size_t size_b, bool committed, unsigned arena_ind);
A chunk split function conforms to the chunk_split_t type and optionally splits chunk of given size into two adjacent chunks, 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 chunk remains unsplit and therefore should continue to be operated on as a whole.
typedef bool (chunk_merge_t)(void *chunk_a, size_t size_a, void *chunk_b, size_t size_b, bool committed, unsigned arena_ind);
A chunk merge function conforms to the chunk_merge_t type and optionally merges adjacent chunks, chunk_a of given size_a and chunk_b of given size_b into one contiguous chunk, 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 chunks remain distinct mappings and therefore should continue to be operated on independently.
"arenas.narenas" (unsigned) r-
"arenas.initialized" (bool *) r-
"arenas.lg_dirty_mult" (ssize_t) rw
"arenas.decay_time" (ssize_t) rw
"arenas.quantum" (size_t) r-
"arenas.page" (size_t) r-
"arenas.tcache_max" (size_t) r- [--enable-tcache]
"arenas.nbins" (unsigned) r-
"arenas.nhbins" (unsigned) r- [--enable-tcache]
"arenas.bin.<i>.size" (size_t) r-
"arenas.bin.<i>.nregs" (uint32_t) r-
"arenas.bin.<i>.run_size" (size_t) r-
"arenas.nlruns" (unsigned) r-
"arenas.lrun.<i>.size" (size_t) r-
"arenas.nhchunks" (unsigned) r-
"arenas.hchunk.<i>.size" (size_t) r-
"arenas.extend" (unsigned) r-
"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.cactive" (size_t *) r- [--enable-stats]
"stats.allocated" (size_t) r- [--enable-stats]
"stats.active" (size_t) r- [--enable-stats]
"stats.metadata" (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.arenas.<i>.dss" (const char *) r-
"stats.arenas.<i>.lg_dirty_mult" (ssize_t) r-
"stats.arenas.<i>.decay_time" (ssize_t) r-
"stats.arenas.<i>.nthreads" (unsigned) r-
"stats.arenas.<i>.pactive" (size_t) r-
"stats.arenas.<i>.pdirty" (size_t) r-
"stats.arenas.<i>.mapped" (size_t) r- [--enable-stats]
"stats.arenas.<i>.retained" (size_t) r- [--enable-stats]
"stats.arenas.<i>.metadata.mapped" (size_t) r- [--enable-stats]
"stats.arenas.<i>.metadata.allocated" (size_t) r- [--enable-stats]
"stats.arenas.<i>.npurge" (uint64_t) r- [--enable-stats]
"stats.arenas.<i>.nmadvise" (uint64_t) r- [--enable-stats]
"stats.arenas.<i>.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>.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>.huge.allocated" (size_t) r- [--enable-stats]
"stats.arenas.<i>.huge.nmalloc" (uint64_t) r- [--enable-stats]
"stats.arenas.<i>.huge.ndalloc" (uint64_t) r- [--enable-stats]
"stats.arenas.<i>.huge.nrequests" (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- [--enable-stats --enable-tcache]
"stats.arenas.<i>.bins.<j>.nflushes" (uint64_t) r- [--enable-stats --enable-tcache]
"stats.arenas.<i>.bins.<j>.nruns" (uint64_t) r- [--enable-stats]
"stats.arenas.<i>.bins.<j>.nreruns" (uint64_t) r- [--enable-stats]
"stats.arenas.<i>.bins.<j>.curruns" (size_t) r- [--enable-stats]
"stats.arenas.<i>.lruns.<j>.nmalloc" (uint64_t) r- [--enable-stats]
"stats.arenas.<i>.lruns.<j>.ndalloc" (uint64_t) r- [--enable-stats]
"stats.arenas.<i>.lruns.<j>.nrequests" (uint64_t) r- [--enable-stats]
"stats.arenas.<i>.lruns.<j>.curruns" (size_t) r- [--enable-stats]
"stats.arenas.<i>.hchunks.<j>.nmalloc" (uint64_t) r- [--enable-stats]
"stats.arenas.<i>.hchunks.<j>.ndalloc" (uint64_t) r- [--enable-stats]
"stats.arenas.<i>.hchunks.<j>.nrequests" (uint64_t) r- [--enable-stats]
"stats.arenas.<i>.hchunks.<j>.curhchunks" (size_t) r- [--enable-stats]
HEAP PROFILE FORMAT
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>
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.
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:
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.
Non-standard API
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.
ENVIRONMENT
The following environment variable affects the execution of the allocation functions:
MALLOC_CONF
EXAMPLES
To dump core whenever a problem occurs:
ln -s 'abort:true' /etc/malloc.conf
To specify in the source a chunk size that is 16 MiB:
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”).
HISTORY
The malloc_usable_size and posix_memalign functions first appeared in FreeBSD 7.0.
The aligned_alloc, malloc_stats_print, and mallctl* functions first appeared in FreeBSD 10.0.
The *allocx functions first appeared in FreeBSD 11.0.
AUTHOR
Jason Evans
NOTES
- 1.
- jemalloc website
- 2.
- Valgrind
- 3.
- gperftools package