JEMALLOC(3)                       User Manual                      JEMALLOC(3)



NAME
       jemalloc - general purpose memory allocation functions

LIBRARY
       This manual describes jemalloc
       5.1.0-0-g61efbda7098de6fe64c362d309824864308c36d4. More information can
       be found at the jemalloc website[1].

SYNOPSIS
       #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
       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)
           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.

       MALLOCX_ALIGN(a)
           Align the memory allocation to start at an address that is a
           multiple of a, where a is a power of two. This macro does not
           validate that a is a power of 2.

       MALLOCX_ZERO
           Initialize newly allocated memory to contain zero bytes. In the
           growing reallocation case, the real size prior to reallocation
           defines the boundary between untouched bytes and those that are
           initialized to contain zero bytes. If this macro is absent, newly
           allocated memory is uninitialized.

       MALLOCX_TCACHE(tc)
           Use the thread-specific cache (tcache) specified by the identifier
           tc, which must have been acquired via the tcache.create mallctl.
           This macro does not validate that tc specifies a valid identifier.

       MALLOCX_TCACHE_NONE
           Do not use a thread-specific cache (tcache). Unless
           MALLOCX_TCACHE(tc) or MALLOCX_TCACHE_NONE is specified, an
           automatically managed tcache will be used under many circumstances.
           This macro cannot be used in the same flags argument as
           MALLOCX_TCACHE(tc).

       MALLOCX_ARENA(a)
           Use the arena specified by the index a. This macro has no effect
           for regions that were allocated via an arena other than the one
           specified. This macro does not validate that a specifies an arena
           index in the valid range.

       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_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", "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. 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, 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
       allbox tab(:); lB rB lB.  T{ Category T}:T{ Spacing T}:T{ Size T} l r l
       ^ r l ^ r l ^ r l ^ r l ^ r l ^ r l ^ r l ^ r l l r l ^ r l ^ r l ^ r l
       ^ r l ^ r l ^ r l ^ r l ^ r l ^ r l ^ r l ^ r l ^ r l ^ r l ^ r l ^ r
       l.  T{ Small T}:T{ lg T}:T{ [8] T} :T{ 16 T}:T{ [16, 32, 48, 64, 80,
       96, 112, 128] T} :T{ 32 T}:T{ [160, 192, 224, 256] T} :T{ 64 T}:T{
       [320, 384, 448, 512] T} :T{ 128 T}:T{ [640, 768, 896, 1024] T} :T{ 256
       T}:T{ [1280, 1536, 1792, 2048] T} :T{ 512 T}:T{ [2560, 3072, 3584,
       4096] T} :T{ 1 KiB T}:T{ [5 KiB, 6 KiB, 7 KiB, 8 KiB] T} :T{ 2 KiB
       T}:T{ [10 KiB, 12 KiB, 14 KiB] T} T{ Large T}:T{ 2 KiB T}:T{ [16 KiB]
       T} :T{ 4 KiB T}:T{ [20 KiB, 24 KiB, 28 KiB, 32 KiB] T} :T{ 8 KiB T}:T{
       [40 KiB, 48 KiB, 54 KiB, 64 KiB] T} :T{ 16 KiB T}:T{ [80 KiB, 96 KiB,
       112 KiB, 128 KiB] T} :T{ 32 KiB T}:T{ [160 KiB, 192 KiB, 224 KiB, 256
       KiB] T} :T{ 64 KiB T}:T{ [320 KiB, 384 KiB, 448 KiB, 512 KiB] T} :T{
       128 KiB T}:T{ [640 KiB, 768 KiB, 896 KiB, 1 MiB] T} :T{ 256 KiB T}:T{
       [1280 KiB, 1536 KiB, 1792 KiB, 2 MiB] T} :T{ 512 KiB T}:T{ [2560 KiB, 3
       MiB, 3584 KiB, 4 MiB] T} :T{ 1 MiB T}:T{ [5 MiB, 6 MiB, 7 MiB, 8 MiB]
       T} :T{ 2 MiB T}:T{ [10 MiB, 12 MiB, 14 MiB, 16 MiB] T} :T{ 4 MiB T}:T{
       [20 MiB, 24 MiB, 28 MiB, 32 MiB] T} :T{ 8 MiB T}:T{ [40 MiB, 48 MiB, 56
       MiB, 64 MiB] T} :T{ ...  T}:T{ ...  T} :T{ 512 PiB T}:T{ [2560 PiB, 3
       EiB, 3584 PiB, 4 EiB] T} :T{ 1 EiB T}:T{ [5 EiB, 6 EiB, 7 EiB] T}


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>.*  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-
           Return the jemalloc version string.

       epoch (uint64_t) rw
           If a value is passed in, refresh the data from which the mallctl*()
           functions report values, and increment the epoch. Return the
           current epoch. This is useful for detecting whether another thread
           caused a refresh.

       background_thread (bool) rw
           Enable/disable internal background worker threads. When set to
           true, background threads are created on demand (the number of
           background threads will be no more than the number of CPUs or
           active arenas). Threads run periodically, and handle purging
           asynchronously. When switching off, background threads are
           terminated synchronously. Note that after fork(2) function, the
           state in the child process will be disabled regardless the state in
           parent process. See stats.background_thread for related stats.
           opt.background_thread can be used to set the default option. This
           option is only available on selected pthread-based platforms.

       max_background_threads (size_t) rw
           Maximum number of background worker threads that will be created.
           This value is capped at opt.max_background_threads at startup.

       config.cache_oblivious (bool) r-
           --enable-cache-oblivious was specified during build configuration.

       config.debug (bool) r-
           --enable-debug 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.malloc_conf (const char *) r-
           Embedded configure-time-specified run-time options string, empty
           unless --with-malloc-conf 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.utrace (bool) r-
           --enable-utrace 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. Note that runtime option warnings are not included (see
           opt.abort_conf for that). The process will call abort(3) in these
           cases. This option is disabled by default unless --enable-debug is
           specified during configuration, in which case it is enabled by
           default.

       opt.abort_conf (bool) r-
           Abort-on-invalid-configuration enabled/disabled. If true, invalid
           runtime options are fatal. The process will call abort(3) in these
           cases. This option is disabled by default unless --enable-debug is
           specified during configuration, in which case it is enabled by
           default.

       opt.metadata_thp (const char *) r-
           Controls whether to allow jemalloc to use transparent huge page
           (THP) for internal metadata (see stats.metadata).  "always" allows
           such usage.  "auto" uses no THP initially, but may begin to do so
           when metadata usage reaches certain level. The default is
           "disabled".

       opt.retain (bool) r-
           If true, retain unused virtual memory for later reuse rather than
           discarding it by calling munmap(2) or equivalent (see
           stats.retained for related details). This option is disabled by
           default unless discarding virtual memory is known to trigger
           platform-specific performance problems, e.g. for [64-bit] Linux,
           which has a quirk in its virtual memory allocation algorithm that
           causes semi-permanent VM map holes under normal jemalloc operation.
           Although munmap(2) causes issues on 32-bit Linux as well, retaining
           virtual memory for 32-bit Linux is disabled by default due to the
           practical possibility of address space exhaustion.

       opt.dss (const char *) r-
           dss (sbrk(2)) allocation precedence as related to mmap(2)
           allocation. The following settings are supported if sbrk(2) is
           supported by the operating system: "disabled", "primary", and
           "secondary"; otherwise only "disabled" is supported. The default is
           "secondary" if sbrk(2) is supported by the operating system;
           "disabled" otherwise.

       opt.narenas (unsigned) r-
           Maximum number of arenas to use for automatic multiplexing of
           threads and arenas. The default is four times the number of CPUs,
           or one if there is a single CPU.

       opt.percpu_arena (const char *) r-
           Per CPU arena mode. Use the "percpu" setting to enable this
           feature, which uses number of CPUs to determine number of arenas,
           and bind threads to arenas dynamically based on the CPU the thread
           runs on currently.  "phycpu" setting uses one arena per physical
           CPU, which means the two hyper threads on the same CPU share one
           arena. Note that no runtime checking regarding the availability of
           hyper threading is done at the moment. When set to "disabled",
           narenas and thread to arena association will not be impacted by
           this option. The default is "disabled".

       opt.background_thread (const bool) r-
           Internal background worker threads enabled/disabled. Because of
           potential circular dependencies, enabling background thread using
           this option may cause crash or deadlock during initialization. For
           a reliable way to use this feature, see background_thread for
           dynamic control options and details. This option is disabled by
           default.

       opt.max_background_threads (const size_t) r-
           Maximum number of background threads that will be created if
           background_thread is set. Defaults to number of cpus.

       opt.dirty_decay_ms (ssize_t) r-
           Approximate time in milliseconds from the creation of a set of
           unused dirty pages until an equivalent set of unused dirty pages is
           purged (i.e. converted to muzzy via e.g.  madvise(...MADV_FREE) if
           supported by the operating system, or converted to clean otherwise)
           and/or reused. Dirty pages are defined as previously having been
           potentially written to by the application, and therefore consuming
           physical memory, yet having no current use. The pages are
           incrementally purged according to a sigmoidal decay curve that
           starts and ends with zero purge rate. A decay time of 0 causes all
           unused dirty pages to be purged immediately upon creation. A decay
           time of -1 disables purging. The default decay time is 10 seconds.
           See arenas.dirty_decay_ms and arena.<i>.dirty_decay_ms for related
           dynamic control options. See opt.muzzy_decay_ms for a description
           of muzzy pages.

       opt.muzzy_decay_ms (ssize_t) r-
           Approximate time in milliseconds from the creation of a set of
           unused muzzy pages until an equivalent set of unused muzzy pages is
           purged (i.e. converted to clean) and/or reused. Muzzy pages are
           defined as previously having been unused dirty pages that were
           subsequently purged in a manner that left them subject to the
           reclamation whims of the operating system (e.g.
           madvise(...MADV_FREE)), and therefore in an indeterminate state.
           The pages are incrementally purged according to a sigmoidal decay
           curve that starts and ends with zero purge rate. A decay time of 0
           causes all unused muzzy pages to be purged immediately upon
           creation. A decay time of -1 disables purging. The default decay
           time is 10 seconds. See arenas.muzzy_decay_ms and
           arena.<i>.muzzy_decay_ms for related dynamic control options.

       opt.lg_extent_max_active_fit (size_t) r-
           When reusing dirty extents, this determines the (log base 2 of the)
           maximum ratio between the size of the active extent selected (to
           split off from) and the size of the requested allocation. This
           prevents the splitting of large active extents for smaller
           allocations, which can reduce fragmentation over the long run
           (especially for non-active extents). Lower value may reduce
           fragmentation, at the cost of extra active extents. The default
           value is 6, which gives a maximum ratio of 64 (2^6).

       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.  opt.stats_print_opts can be combined to
           specify output options. If --enable-stats is specified during
           configuration, this has the potential to cause deadlock for a
           multi-threaded process that exits while one or more threads are
           executing in the memory allocation functions. Furthermore, atexit()
           may allocate memory during application initialization and then
           deadlock internally when jemalloc in turn calls atexit(), so this
           option is not universally usable (though the application can
           register its own atexit() function with equivalent functionality).
           Therefore, this option should only be used with care; it is
           primarily intended as a performance tuning aid during application
           development. This option is disabled by default.

       opt.stats_print_opts (const char *) r-
           Options (the opts string) to pass to the malloc_stats_print() at
           exit (enabled through opt.stats_print). See available options in
           malloc_stats_print(). Has no effect unless opt.stats_print is
           enabled. The default is "".

       opt.junk (const char *) r- [--enable-fill]
           Junk filling. If set to "alloc", each byte of uninitialized
           allocated memory will be initialized to 0xa5. If set to "free", all
           deallocated memory will be initialized to 0x5a. If set to "true",
           both allocated and deallocated memory will be initialized, and if
           set to "false", junk filling be disabled entirely. This is intended
           for debugging and will impact performance negatively. This option
           is "false" by default unless --enable-debug is specified during
           configuration, in which case it is "true" by default.

       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 rallocx() calls do not zero memory that was previously
           allocated. This is intended for debugging and will impact
           performance negatively. This option is disabled by default.

       opt.utrace (bool) r- [--enable-utrace]
           Allocation tracing based on utrace(2) enabled/disabled. This option
           is disabled by default.

       opt.xmalloc (bool) r- [--enable-xmalloc]
           Abort-on-out-of-memory enabled/disabled. If enabled, rather than
           returning failure for any allocation function, display a diagnostic
           message on STDERR_FILENO and cause the program to drop core (using
           abort(3)). If an application is designed to depend on this
           behavior, set the option at compile time by including the following
           in the source code:

               malloc_conf = "xmalloc:true";

           This option is disabled by default.

       opt.tcache (bool) r-
           Thread-specific caching (tcache) enabled/disabled. When there are
           multiple threads, each thread uses a tcache for objects up to a
           certain size. Thread-specific caching allows many allocations to be
           satisfied without performing any thread synchronization, at the
           cost of increased memory use. See the opt.lg_tcache_max option for
           related tuning information. This option is enabled by default.

       opt.lg_tcache_max (size_t) r-
           Maximum size class (log base 2) to cache in the thread-specific
           cache (tcache). 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.thp (const char *) r-
           Transparent hugepage (THP) mode. Settings "always", "never" and
           "default" are available if THP is supported by the operating
           system. The "always" setting enables transparent hugepage for all
           user memory mappings with MADV_HUGEPAGE; "never" ensures no
           transparent hugepage with MADV_NOHUGEPAGE; the default setting
           "default" makes no changes. Note that: this option does not affect
           THP for jemalloc internal metadata (see opt.metadata_thp); in
           addition, for arenas with customized extent_hooks, this option is
           bypassed as it is implemented as part of the default extent hooks.

       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
           jeprof command, which is based on the pprof that is developed as
           part of the gperftools package[3]. See HEAP PROFILE FORMAT for heap
           profile format documentation.

       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.prof_thread_active_init (bool) r- [--enable-prof]
           Initial setting for thread.prof.active in newly created threads.
           The initial setting for newly created threads can also be changed
           during execution via the prof.thread_active_init mallctl. This
           option is enabled by default.

       opt.lg_prof_sample (size_t) r- [--enable-prof]
           Average interval (log base 2) between allocation samples, as
           measured in bytes of allocation activity. Increasing the sampling
           interval decreases profile fidelity, but also decreases the
           computational overhead. The default sample interval is 512 KiB
           (2^19 B).

       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]
           Set the initial state of prof.gdump, which when enabled triggers a
           memory profile dump every time the total virtual memory exceeds the
           previous maximum. 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. Note that
           atexit() may allocate memory during application initialization and
           then deadlock internally when jemalloc in turn calls atexit(), so
           this option is not universally usable (though the application can
           register its own atexit() function with equivalent functionality).
           This option is disabled by default.

       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. If the
           specified arena was not initialized beforehand (see the
           arena.i.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/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) --
           Flush calling thread's thread-specific cache (tcache). This
           interface releases all cached objects and internal data structures
           associated with the calling thread's tcache. Ordinarily, this
           interface need not be called, since automatic periodic incremental
           garbage collection occurs, and the thread cache is automatically
           discarded when a thread exits. However, garbage collection is
           triggered by allocation activity, so it is possible for a thread
           that stops allocating/deallocating to retain its cache
           indefinitely, in which case the developer may find manual flushing
           useful.

       thread.prof.name (const char *) r- or -w [--enable-prof]
           Get/set the descriptive name associated with the calling thread in
           memory profile dumps. An internal copy of the name string is
           created, so the input string need not be maintained after this
           interface completes execution. The output string of this interface
           should be copied for non-ephemeral uses, because multiple
           implementation details can cause asynchronous string deallocation.
           Furthermore, each invocation of this interface can only read or
           write; simultaneous read/write is not supported due to string
           lifetime limitations. The name string must be nil-terminated and
           comprised only of characters in the sets recognized by isgraph(3)
           and isblank(3).

       thread.prof.active (bool) rw [--enable-prof]
           Control whether sampling is currently active for the calling
           thread. This is an activation mechanism in addition to prof.active;
           both must be active for the calling thread to sample. This flag is
           enabled by default.

       tcache.create (unsigned) r-
           Create an explicit thread-specific cache (tcache) and return an
           identifier that can be passed to the MALLOCX_TCACHE(tc) macro to
           explicitly use the specified cache rather than the automatically
           managed one that is used by default. Each explicit cache can be
           used by only one thread at a time; the application must assure that
           this constraint holds.

       tcache.flush (unsigned) -w
           Flush the specified thread-specific cache (tcache). The same
           considerations apply to this interface as to thread.tcache.flush,
           except that the tcache will never be automatically discarded.

       tcache.destroy (unsigned) -w
           Flush the specified thread-specific cache (tcache) and make the
           identifier available for use during a future tcache creation.

       arena.<i>.initialized (bool) r-
           Get whether the specified arena's statistics are initialized (i.e.
           the arena was initialized prior to the current epoch). This
           interface can also be nominally used to query whether the merged
           statistics corresponding to MALLCTL_ARENAS_ALL are initialized
           (always true).

       arena.<i>.decay (void) --
           Trigger decay-based purging of unused dirty/muzzy pages for arena
           <i>, or for all arenas if <i> equals MALLCTL_ARENAS_ALL. The
           proportion of unused dirty/muzzy pages to be purged depends on the
           current time; see opt.dirty_decay_ms and opt.muzy_decay_ms for
           details.

       arena.<i>.purge (void) --
           Purge all unused dirty pages for arena <i>, or for all arenas if
           <i> equals MALLCTL_ARENAS_ALL.

       arena.<i>.reset (void) --
           Discard all of the arena's extant allocations. This interface can
           only be used with arenas explicitly created via arenas.create. None
           of the arena's discarded/cached allocations may accessed afterward.
           As part of this requirement, all thread caches which were used to
           allocate/deallocate in conjunction with the arena must be flushed
           beforehand.

       arena.<i>.destroy (void) --
           Destroy the arena. Discard all of the arena's extant allocations
           using the same mechanism as for arena.<i>.reset (with all the same
           constraints and side effects), merge the arena stats into those
           accessible at arena index MALLCTL_ARENAS_DESTROYED, and then
           completely discard all metadata associated with the arena. Future
           calls to arenas.create may recycle the arena index. Destruction
           will fail if any threads are currently associated with the arena as
           a result of calls to thread.arena.

       arena.<i>.dss (const char *) rw
           Set the precedence of dss allocation as related to mmap allocation
           for arena <i>, or for all arenas if <i> equals MALLCTL_ARENAS_ALL.
           See opt.dss for supported settings.

       arena.<i>.dirty_decay_ms (ssize_t) rw
           Current per-arena approximate time in milliseconds from the
           creation of a set of unused dirty pages until an equivalent set of
           unused dirty pages is purged and/or reused. Each time this
           interface is set, all currently unused dirty pages are considered
           to have fully decayed, which causes immediate purging of all unused
           dirty pages unless the decay time is set to -1 (i.e. purging
           disabled). See opt.dirty_decay_ms for additional information.

       arena.<i>.muzzy_decay_ms (ssize_t) rw
           Current per-arena approximate time in milliseconds from the
           creation of a set of unused muzzy pages until an equivalent set of
           unused muzzy pages is purged and/or reused. Each time this
           interface is set, all currently unused muzzy pages are considered
           to have fully decayed, which causes immediate purging of all unused
           muzzy pages unless the decay time is set to -1 (i.e. purging
           disabled). See opt.muzzy_decay_ms for additional information.

       arena.<i>.retain_grow_limit (size_t) rw
           Maximum size to grow retained region (only relevant when opt.retain
           is enabled). This controls the maximum increment to expand virtual
           memory, or allocation through arena.<i>extent_hooks. In particular,
           if customized extent hooks reserve physical memory (e.g. 1G huge
           pages), this is useful to control the allocation hook's input size.
           The default is no limit.

       arena.<i>.extent_hooks (extent_hooks_t *) rw
           Get or set the extent management hook functions for arena <i>. The
           functions must be capable of operating on all extant extents
           associated with arena <i>, usually by passing unknown extents to
           the replaced functions. In practice, it is feasible to control
           allocation for arenas explicitly created via arenas.create such
           that all extents originate from an application-supplied extent
           allocator (by specifying the custom extent hook functions during
           arena creation), but the automatically created arenas will have
           already created extents prior to the application having an
           opportunity to take over extent allocation.

               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-
           Current limit on number of arenas.

       arenas.dirty_decay_ms (ssize_t) rw
           Current default per-arena approximate time in milliseconds from the
           creation of a set of unused dirty pages until an equivalent set of
           unused dirty pages is purged and/or reused, used to initialize
           arena.<i>.dirty_decay_ms during arena creation. See
           opt.dirty_decay_ms for additional information.

       arenas.muzzy_decay_ms (ssize_t) rw
           Current default per-arena approximate time in milliseconds from the
           creation of a set of unused muzzy pages until an equivalent set of
           unused muzzy pages is purged and/or reused, used to initialize
           arena.<i>.muzzy_decay_ms during arena creation. See
           opt.muzzy_decay_ms for additional information.

       arenas.quantum (size_t) r-
           Quantum size.

       arenas.page (size_t) r-
           Page size.

       arenas.tcache_max (size_t) r-
           Maximum thread-cached size class.

       arenas.nbins (unsigned) r-
           Number of bin size classes.

       arenas.nhbins (unsigned) r-
           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 slab.

       arenas.bin.<i>.slab_size (size_t) r-
           Number of bytes per slab.

       arenas.nlextents (unsigned) r-
           Total number of large size classes.

       arenas.lextent.<i>.size (size_t) r-
           Maximum size supported by this large size class.

       arenas.create (unsigned, extent_hooks_t *) rw
           Explicitly create a new arena outside the range of automatically
           managed arenas, with optionally specified extent hooks, and return
           the new arena index.

       arenas.lookup (unsigned, void*) rw
           Index of the arena to which an allocation belongs to.

       prof.thread_active_init (bool) rw [--enable-prof]
           Control the initial setting for thread.prof.active in newly created
           threads. See the opt.prof_thread_active_init option for additional
           information.

       prof.active (bool) rw [--enable-prof]
           Control whether sampling is currently active. See the
           opt.prof_active option for additional information, as well as the
           interrelated thread.prof.active mallctl.

       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.gdump (bool) rw [--enable-prof]
           When enabled, trigger a memory profile dump every time the total
           virtual memory exceeds the previous maximum. Profiles are dumped to
           files named according to the pattern
           <prefix>.<pid>.<seq>.u<useq>.heap, where <prefix> is controlled by
           the opt.prof_prefix option.

       prof.reset (size_t) -w [--enable-prof]
           Reset all memory profile statistics, and optionally update the
           sample rate (see opt.lg_prof_sample and prof.lg_sample).

       prof.lg_sample (size_t) r- [--enable-prof]
           Get the current sample rate (see opt.lg_prof_sample).

       prof.interval (uint64_t) r- [--enable-prof]
           Average number of bytes allocated between interval-based profile
           dumps. See the opt.lg_prof_interval option for additional
           information.

       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. This does not include stats.arenas.<i>.pdirty,
           stats.arenas.<i>.pmuzzy, nor pages entirely devoted to allocator
           metadata.

       stats.metadata (size_t) r- [--enable-stats]
           Total number of bytes dedicated to metadata, which comprise base
           allocations used for bootstrap-sensitive allocator metadata
           structures (see stats.arenas.<i>.base) and internal allocations
           (see stats.arenas.<i>.internal). Transparent huge page (enabled
           with opt.metadata_thp) usage is not considered.

       stats.metadata_thp (size_t) r- [--enable-stats]
           Number of transparent huge pages (THP) used for metadata. See
           stats.metadata and opt.metadata_thp) for details.

       stats.resident (size_t) r- [--enable-stats]
           Maximum number of bytes in physically resident data pages mapped by
           the allocator, comprising all pages dedicated to allocator
           metadata, pages backing active allocations, and unused dirty pages.
           This is a maximum rather than precise because pages may not
           actually be physically resident if they correspond to demand-zeroed
           virtual memory that has not yet been touched. This is a multiple of
           the page size, and is larger than stats.active.

       stats.mapped (size_t) r- [--enable-stats]
           Total number of bytes in active extents mapped by the allocator.
           This is larger than stats.active. This does not include inactive
           extents, even those that contain unused dirty pages, which means
           that there is no strict ordering between this and stats.resident.

       stats.retained (size_t) r- [--enable-stats]
           Total number of bytes in virtual memory mappings that were retained
           rather than being returned to the operating system via e.g.
           munmap(2) or similar. Retained virtual memory is typically
           untouched, decommitted, or purged, so it has no strongly associated
           physical memory (see extent hooks for details). Retained memory is
           excluded from mapped memory statistics, e.g.  stats.mapped.

       stats.background_thread.num_threads (size_t) r- [--enable-stats]
           Number of background threads running currently.

       stats.background_thread.num_runs (uint64_t) r- [--enable-stats]
           Total number of runs from all background threads.

       stats.background_thread.run_interval (uint64_t) r- [--enable-stats]
           Average run interval in nanoseconds of background threads.

       stats.mutexes.ctl.{counter}; (counter specific type) r-
       [--enable-stats]
           Statistics on ctl mutex (global scope; mallctl related).  {counter}
           is one of the counters below:

               num_ops (uint64_t): Total number of lock acquisition operations
               on this mutex.

               num_spin_acq (uint64_t): Number of times the mutex was
               spin-acquired. When the mutex is currently locked and cannot be
               acquired immediately, a short period of spin-retry within
               jemalloc will be performed. Acquired through spin generally
               means the contention was lightweight and not causing context
               switches.

               num_wait (uint64_t): Number of times the mutex was
               wait-acquired, which means the mutex contention was not solved
               by spin-retry, and blocking operation was likely involved in
               order to acquire the mutex. This event generally implies higher
               cost / longer delay, and should be investigated if it happens
               often.

               max_wait_time (uint64_t): Maximum length of time in nanoseconds
               spent on a single wait-acquired lock operation. Note that to
               avoid profiling overhead on the common path, this does not
               consider spin-acquired cases.

               total_wait_time (uint64_t): Cumulative time in nanoseconds
               spent on wait-acquired lock operations. Similarly,
               spin-acquired cases are not considered.

               max_num_thds (uint32_t): Maximum number of threads waiting on
               this mutex simultaneously. Similarly, spin-acquired cases are
               not considered.

               num_owner_switch (uint64_t): Number of times the current mutex
               owner is different from the previous one. This event does not
               generally imply an issue; rather it is an indicator of how
               often the protected data are accessed by different threads.

       stats.mutexes.background_thread.{counter} (counter specific type) r-
       [--enable-stats]
           Statistics on background_thread mutex (global scope;
           background_thread related).  {counter} is one of the counters in
           mutex profiling counters.

       stats.mutexes.prof.{counter} (counter specific type) r-
       [--enable-stats]
           Statistics on prof mutex (global scope; profiling related).
           {counter} is one of the counters in mutex profiling counters.

       stats.mutexes.reset (void) -- [--enable-stats]
           Reset all mutex profile statistics, including global mutexes, arena
           mutexes and bin mutexes.

       stats.arenas.<i>.dss (const char *) r-
           dss (sbrk(2)) allocation precedence as related to mmap(2)
           allocation. See opt.dss for details.

       stats.arenas.<i>.dirty_decay_ms (ssize_t) r-
           Approximate time in milliseconds from the creation of a set of
           unused dirty pages until an equivalent set of unused dirty pages is
           purged and/or reused. See opt.dirty_decay_ms for details.

       stats.arenas.<i>.muzzy_decay_ms (ssize_t) r-
           Approximate time in milliseconds from the creation of a set of
           unused muzzy pages until an equivalent set of unused muzzy pages is
           purged and/or reused. See opt.muzzy_decay_ms for details.

       stats.arenas.<i>.nthreads (unsigned) r-
           Number of threads currently assigned to arena.

       stats.arenas.<i>.uptime (uint64_t) r-
           Time elapsed (in nanoseconds) since the arena was created. If <i>
           equals 0 or MALLCTL_ARENAS_ALL, this is the uptime since malloc
           initialization.

       stats.arenas.<i>.pactive (size_t) r-
           Number of pages in active extents.

       stats.arenas.<i>.pdirty (size_t) r-
           Number of pages within unused extents that are potentially dirty,
           and for which madvise() or similar has not been called. See
           opt.dirty_decay_ms for a description of dirty pages.

       stats.arenas.<i>.pmuzzy (size_t) r-
           Number of pages within unused extents that are muzzy. See
           opt.muzzy_decay_ms for a description of muzzy pages.

       stats.arenas.<i>.mapped (size_t) r- [--enable-stats]
           Number of mapped bytes.

       stats.arenas.<i>.retained (size_t) r- [--enable-stats]
           Number of retained bytes. See stats.retained for details.

       stats.arenas.<i>.base (size_t) r- [--enable-stats]
           Number of bytes dedicated to bootstrap-sensitive allocator metadata
           structures.

       stats.arenas.<i>.internal (size_t) r- [--enable-stats]
           Number of bytes dedicated to internal allocations. Internal
           allocations differ from application-originated allocations in that
           they are for internal use, and that they are omitted from heap
           profiles.

       stats.arenas.<i>.metadata_thp (size_t) r- [--enable-stats]
           Number of transparent huge pages (THP) used for metadata. See
           opt.metadata_thp for details.

       stats.arenas.<i>.resident (size_t) r- [--enable-stats]
           Maximum number of bytes in physically resident data pages mapped by
           the arena, comprising all pages dedicated to allocator metadata,
           pages backing active allocations, and unused dirty pages. This is a
           maximum rather than precise because pages may not actually be
           physically resident if they correspond to demand-zeroed virtual
           memory that has not yet been touched. This is a multiple of the
           page size.

       stats.arenas.<i>.dirty_npurge (uint64_t) r- [--enable-stats]
           Number of dirty page purge sweeps performed.

       stats.arenas.<i>.dirty_nmadvise (uint64_t) r- [--enable-stats]
           Number of madvise() or similar calls made to purge dirty pages.

       stats.arenas.<i>.dirty_purged (uint64_t) r- [--enable-stats]
           Number of dirty pages purged.

       stats.arenas.<i>.muzzy_npurge (uint64_t) r- [--enable-stats]
           Number of muzzy page purge sweeps performed.

       stats.arenas.<i>.muzzy_nmadvise (uint64_t) r- [--enable-stats]
           Number of madvise() or similar calls made to purge muzzy pages.

       stats.arenas.<i>.muzzy_purged (uint64_t) r- [--enable-stats]
           Number of muzzy 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 times a small allocation was requested from
           the arena's bins, whether to fill the relevant tcache if opt.tcache
           is enabled, or to directly satisfy an allocation request otherwise.

       stats.arenas.<i>.small.ndalloc (uint64_t) r- [--enable-stats]
           Cumulative number of times a small allocation was returned to the
           arena's bins, whether to flush the relevant tcache if opt.tcache is
           enabled, or to directly deallocate an allocation otherwise.

       stats.arenas.<i>.small.nrequests (uint64_t) r- [--enable-stats]
           Cumulative number of allocation requests satisfied by all bin size
           classes.

       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 times a large extent was allocated from the
           arena, whether to fill the relevant tcache if opt.tcache is enabled
           and the size class is within the range being cached, or to directly
           satisfy an allocation request otherwise.

       stats.arenas.<i>.large.ndalloc (uint64_t) r- [--enable-stats]
           Cumulative number of times a large extent was returned to the
           arena, whether to flush the relevant tcache if opt.tcache is
           enabled and the size class is within the range being cached, or to
           directly deallocate an allocation otherwise.

       stats.arenas.<i>.large.nrequests (uint64_t) r- [--enable-stats]
           Cumulative number of allocation requests satisfied by all large
           size classes.

       stats.arenas.<i>.bins.<j>.nmalloc (uint64_t) r- [--enable-stats]
           Cumulative number of times a bin region of the corresponding size
           class was allocated from the arena, whether to fill the relevant
           tcache if opt.tcache is enabled, or to directly satisfy an
           allocation request otherwise.

       stats.arenas.<i>.bins.<j>.ndalloc (uint64_t) r- [--enable-stats]
           Cumulative number of times a bin region of the corresponding size
           class was returned to the arena, whether to flush the relevant
           tcache if opt.tcache is enabled, or to directly deallocate an
           allocation otherwise.

       stats.arenas.<i>.bins.<j>.nrequests (uint64_t) r- [--enable-stats]
           Cumulative number of allocation requests satisfied by bin regions
           of the corresponding size class.

       stats.arenas.<i>.bins.<j>.curregs (size_t) r- [--enable-stats]
           Current number of regions for this size class.

       stats.arenas.<i>.bins.<j>.nfills (uint64_t) r-
           Cumulative number of tcache fills.

       stats.arenas.<i>.bins.<j>.nflushes (uint64_t) r-
           Cumulative number of tcache flushes.

       stats.arenas.<i>.bins.<j>.nslabs (uint64_t) r- [--enable-stats]
           Cumulative number of slabs created.

       stats.arenas.<i>.bins.<j>.nreslabs (uint64_t) r- [--enable-stats]
           Cumulative number of times the current slab from which to allocate
           changed.

       stats.arenas.<i>.bins.<j>.curslabs (size_t) r- [--enable-stats]
           Current number of slabs.

       stats.arenas.<i>.bins.<j>.mutex.{counter} (counter specific type) r-
       [--enable-stats]
           Statistics on arena.<i>.bins.<j> mutex (arena bin scope; bin
           operation related).  {counter} is one of the counters in mutex
           profiling counters.

       stats.arenas.<i>.lextents.<j>.nmalloc (uint64_t) r- [--enable-stats]
           Cumulative number of times a large extent of the corresponding size
           class was allocated from the arena, whether to fill the relevant
           tcache if opt.tcache is enabled and the size class is within the
           range being cached, or to directly satisfy an allocation request
           otherwise.

       stats.arenas.<i>.lextents.<j>.ndalloc (uint64_t) r- [--enable-stats]
           Cumulative number of times a large extent of the corresponding size
           class was returned to the arena, whether to flush the relevant
           tcache if opt.tcache is enabled and the size class is within the
           range being cached, or to directly deallocate an allocation
           otherwise.

       stats.arenas.<i>.lextents.<j>.nrequests (uint64_t) r- [--enable-stats]
           Cumulative number of allocation requests satisfied by large extents
           of the corresponding size class.

       stats.arenas.<i>.lextents.<j>.curlextents (size_t) r- [--enable-stats]
           Current number of large allocations for this size class.

       stats.arenas.<i>.mutexes.large.{counter} (counter specific type) r-
       [--enable-stats]
           Statistics on arena.<i>.large mutex (arena scope; large allocation
           related).  {counter} is one of the counters in mutex profiling
           counters.

       stats.arenas.<i>.mutexes.extent_avail.{counter} (counter specific type)
       r- [--enable-stats]
           Statistics on arena.<i>.extent_avail mutex (arena scope; extent
           avail related).  {counter} is one of the counters in mutex
           profiling counters.

       stats.arenas.<i>.mutexes.extents_dirty.{counter} (counter specific
       type) r- [--enable-stats]
           Statistics on arena.<i>.extents_dirty mutex (arena scope; dirty
           extents related).  {counter} is one of the counters in mutex
           profiling counters.

       stats.arenas.<i>.mutexes.extents_muzzy.{counter} (counter specific
       type) r- [--enable-stats]
           Statistics on arena.<i>.extents_muzzy mutex (arena scope; muzzy
           extents related).  {counter} is one of the counters in mutex
           profiling counters.

       stats.arenas.<i>.mutexes.extents_retained.{counter} (counter specific
       type) r- [--enable-stats]
           Statistics on arena.<i>.extents_retained mutex (arena scope;
           retained extents related).  {counter} is one of the counters in
           mutex profiling counters.

       stats.arenas.<i>.mutexes.decay_dirty.{counter} (counter specific type)
       r- [--enable-stats]
           Statistics on arena.<i>.decay_dirty mutex (arena scope; decay for
           dirty pages related).  {counter} is one of the counters in mutex
           profiling counters.

       stats.arenas.<i>.mutexes.decay_muzzy.{counter} (counter specific type)
       r- [--enable-stats]
           Statistics on arena.<i>.decay_muzzy mutex (arena scope; decay for
           muzzy pages related).  {counter} is one of the counters in mutex
           profiling counters.

       stats.arenas.<i>.mutexes.base.{counter} (counter specific type) r-
       [--enable-stats]
           Statistics on arena.<i>.base mutex (arena scope; base allocator
           related).  {counter} is one of the counters in mutex profiling
           counters.

       stats.arenas.<i>.mutexes.tcache_list.{counter} (counter specific type)
       r- [--enable-stats]
           Statistics on arena.<i>.tcache_list mutex (arena scope; tcache to
           arena association related). This mutex is expected to be accessed
           less often.  {counter} is one of the counters in mutex profiling
           counters.

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.

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
           The 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 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
           newp is not NULL, and newlen is too large or too small.
           Alternatively, *oldlenp is too large or too small; in this case as
           much data as possible are read despite the error.

       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.

       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
           If 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

       To specify in the source that only one arena should be automatically
       created:

           malloc_conf = "narenas:1";

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 Evans

NOTES
        1. jemalloc website
           http://jemalloc.net/

        2. JSON format
           http://www.json.org/

        3. gperftools package
           http://code.google.com/p/gperftools/



jemalloc 5.1.0-0-g61efbda7098d    05/08/2018                       JEMALLOC(3)

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