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mtmalloc(3malloc)
mtmalloc(3MALLOC) Memory Allocation Library Functions mtmalloc(3MALLOC)
NAME
mtmalloc, mallocctl - MT hot memory allocator
SYNOPSIS
cc [ flag ... ] file ... -lmtmalloc [ library ... ]
#include <stdlib.h>
void *malloc(size_t size);
void *calloc(size_t nelem, size_t elsize);
void *memalign(size_t alignment, size_t size);
void *realloc(void *ptr, size_t size);
void *valloc(size_t size);
size_t malloc_usable_size(void *ptr);
void free(void *ptr);
#include <mtmalloc.h>
void mallocctl(int cmd, long value);
DESCRIPTION
These functions provide a simple general-purpose memory allocation
package that is suitable for use in high performance multithreaded ap‐
plications. The suggested use of this library is in multithreaded ap‐
plications; it can be used for single threaded applications, but there
is no advantage in doing so. This library cannot be dynamically loaded
with dlopen(3C) during runtime because there must be only one manager
of the process heap.
They operate as described on the malloc(3C) manual page, except for the
following differences:
o Additional options for these functions are available via the
mallocctl() function and the MTMALLOC_OPTIONS environment
variable, as described below.
o A freed pointer that is passed to free() or realloc() will
send a SIGABRT signal to the calling process, unless this
behavior is disabled via the mallocctl() function or the MT‐
MALLOC_OPTIONS environment variable.
o Support for using adi(7) is not available.
The mallocctl() function controls the behavior of the mtmalloc library.
The options fall into two general classes, debugging options and per‐
formance options.
MTDOUBLEFREE Allows double free of a pointer. Setting value to 1
means yes and 0 means no. The default behavior of
double free results in a core dump.
MTDEBUGPATTERN Writes misaligned data into the buffer after free().
When the buffer is reallocated, the contents are ver‐
ified to ensure that there was no access to the
buffer after the free. If the buffer has been dirt‐
ied, a SIGABRT signal is delivered to the process.
Setting value to 1 means yes and 0 means no. The de‐
fault behavior is to not write misaligned data. The
pattern used is 0xdeadbeef. Use of this option re‐
sults in a performance penalty.
MTINITBUFFER Writes misaligned data into the newly allocated
buffer. This option is useful for detecting some ac‐
cesses before initialization. Setting value to 1
means yes and 0 means no. The default behavior is to
not write misaligned data to the newly allocated
buffer. The pattern used is 0xbaddcafe. Use of this
option results in a performance penalty.
MTCHUNKSIZE This option changes the size of allocated memory when
a pool has exhausted all available memory in the
buffer. Increasing this value allocates more memory
for the application. A substantial performance gain
can occur because the library makes fewer calls to
the OS for more memory. Acceptable number values are
between 9 and 256. The default value is 9 for 32-bit
code and 64 for 64-bit code. This value is multiplied
by 8192.
MTEXCLUSIVE This option is now a no-op as all threads have an ex‐
clusive set of caches.
MTREALFREE This option sets the threshold for calling mad‐
vise(3C) with MADV_FREE. Calling madvise() will re‐
sult in the memory associated with the allocation be‐
ing returned to the kernel. When freed, allocations
greater than value*pagesize will have madvise()
called. If value is less than 2, it will be set to 2.
ENVIRONMENT VARIABLES
MTMALLOC_OPTIONS
A comma separated list of options. The supported options are:
MTEXCLUSIVE=Y
This is a no-op. All threads have exclusive access to a set of
caches.
MTMAXCACHE=16, 17, 18, 19, 20, or 21
By default, allocations less than 2^16 bytes are allocated from
buckets indexed by thread ID. Using this MTMALLOC_OPTION set‐
ting, variable size of the cached allocations can be increased
to 2^17, 2^18, 2^18, 2^19, 2^20, or 2^21 by setting MTMAXCACHE
to 17, 18, 19, 20, or 21. If MTMAXCACHE is set to less than 16,
it is reset to 16. If MTMAXCACHE is set to more than 21, then
it is reset to 21. This all occurs silently.
MTCHUNKSIZE=xx
Allocation buckets are sized by the chunk size and the size of
the allocation request. The default setting is 9 for 32-bit ap‐
plications and 64 for 64 bit applications. For the cost of ad‐
dress space, performance can sometimes be enhanced by increas‐
ing this parameter. For more information, see the malloc‐
ctl(3MALLOC) man page.
MTREALFREE=xx
If xx > 1, set the threshold for calling madvise(3C) with
MADV_FREE. Calling madvise() will result in the memory associ‐
ated with the allocation being returned to the kernel. When
freed, allocations greater than xx*pagesize will have madvise()
called. If xx is less than 2, it will be set to 2.
MTDEBUGPATTERN=Y
Writes misaligned data into the buffer after free(). When the
buffer is reallocated, the contents are verified to ensure that
there was no access to the buffer after the free. If the buffer
has been dirtied, a SIGABRT signal is delivered to the process.
The default behavior is not to write misaligned data. The pat‐
tern used is 0xdeadbeef. Use of this option results in a per‐
formance penalty.
MTINITBUFFER=Y
Writes misaligned data into the newly allocated buffer. This
option is useful for detecting some accesses before initializa‐
tion. The default behavior is not to write misaligned data to
the newly allocated buffer. The pattern used is 0xbaddcafe. Use
of this option results in a performance penalty.
MTDOUBLEFREE=Y
Allows double free of a pointer. The default behavior of double
free results in a core dump.
USAGE
See malloc(3C) for an overview and comparison of all the allocation li‐
braries provided by Oracle Solaris.
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ MT-LevelSafe
SEE ALSO
brk(2), getrlimit(2), dlopen(3C), madvise(3C), malloc(3C), sig‐
nal.h(3HEAD), libmtmalloc(3LIB), attributes(7)
WARNINGS
Undefined results will occur if the size requested for a block of mem‐
ory exceeds the maximum size of a process's heap. This information may
be obtained using the getrlimit() function.
Oracle Solaris 11.4 7 Feb 2019 mtmalloc(3MALLOC)