This time, we pass the 2 parameter, asking the program to perform larger allocations (greater than MMAP_THRESHOLD):

$ ./malloc_brk_test 2
                              init_brk =        0x2209000
 #: malloc(       n) =        heap_ptr           cur_brk   delta 
                                                      [cur_brk-init_brk]
[...]

 3: malloc(  136168) =   0x7f57288cd010         0x222a000 [135168]
Arena 0:
system bytes     =     135168
in use bytes     =       5792
Total (incl. mmap):
system bytes     =     274432
in use bytes     =     145056
max mmap regions =          1
max mmap bytes   =     139264

 4: malloc( 1048576) =   0x7f57287c7010         0x222a000 [135168]
Arena 0:
system bytes     =     135168
in use bytes     =       5792
Total (incl. mmap):
system bytes     =    1327104
in use bytes     =    1197728
max mmap regions =          2
max mmap bytes   =    1191936

$                     

(Note that the preceding code we have clipped the output of the first two small allocations and only show the relevant large ones).

Now, we allocate 132 KB (point 3 in the preceding output); some thing to take note of are as follows:

• The allocations (#3 and #4) are for 132 KB and 1 MB – both above the MMAP_THRESHOLD (value of 128 KB)
• The (arena 0) heap in-use bytes (5,792) has not changed at all across these two allocations, indicating that heap memory has not been used
• The max mmap regions and max mmap bytes numbers have changed to positive values (from zero), indicating the use of mmap-ed memory

A couple of remaining scenarios will be examined later.