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_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.
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_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.
M_MMAP_MAX
- The maximum number of chunks to allocate with
mmap. Setting this
to zero disables all use of mmap.
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