(libc.info.gz) Malloc Tunable Parameters
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3.2.2.8 Malloc Tunable Parameters
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You can adjust some parameters for dynamic memory allocation with the
'mallopt' function. This function is the general SVID/XPG interface,
defined in 'malloc.h'.
-- Function: int mallopt (int PARAM, int VALUE)
Preliminary: | MT-Unsafe init const:mallopt | AS-Unsafe init lock |
AC-Unsafe init lock | POSIX Safety Concepts.
When calling 'mallopt', the PARAM argument specifies the parameter
to be set, and VALUE the new value to be set. Possible choices for
PARAM, as defined in 'malloc.h', are:
'M_MMAP_MAX'
The maximum number of chunks to allocate with 'mmap'. Setting
this to zero disables all use of 'mmap'.
'M_MMAP_THRESHOLD'
All chunks larger than this value are allocated outside the
normal heap, using the 'mmap' system call. This way it is
guaranteed that the memory for these chunks can be returned to
the system on 'free'. Note that requests smaller than this
threshold might still be allocated via 'mmap'.
'M_PERTURB'
If non-zero, memory blocks are filled with values depending on
some low order bits of this parameter when they are allocated
(except when allocated by 'calloc') and freed. This can be
used to debug the use of uninitialized or freed heap memory.
Note that this option does not guarantee that the freed block
will have any specific values. It only guarantees that the
content the block had before it was freed will be overwritten.
'M_TOP_PAD'
This parameter determines the amount of extra memory to obtain
from the system when a call to 'sbrk' is required. It also
specifies the number of bytes to retain when shrinking the
heap by calling 'sbrk' with a negative argument. This
provides the necessary hysteresis in heap size such that
excessive amounts of system calls can be avoided.
'M_TRIM_THRESHOLD'
This is the minimum size (in bytes) of the top-most,
releasable chunk that will cause 'sbrk' to be called with a
negative argument in order to return memory to the system.
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