profile result with unexpected big negative number #211

from memory_profiler import profile

NUM = 100000

class Person(object):
  def __init__(self, name):
    self.name = name

@profile
def run1():
  ps = []
  for i in range(NUM):
    ps.append(Person(str(i)))

@profile
def run2():
  r = []
  for _ in range(NUM):
    r.append({})

if __name__ == "__main__":
  run1()
  run2()

$ python -m memory_profiler demo.py
Filename: demo.py

Line #    Mem usage    Increment   Line Contents
================================================
    12     10.8 MiB     10.8 MiB   @profile
    13                             def run1():
    14     10.8 MiB      0.0 MiB       ps = []
    15     53.1 MiB   -744.4 MiB       for i in range(NUM):
    16     53.1 MiB   -711.9 MiB           ps.append(Person(str(i)))


Filename: demo.py

Line #    Mem usage    Increment   Line Contents
================================================
    18     14.8 MiB     14.8 MiB   @profile
    19                             def run2():
    20     14.8 MiB      0.0 MiB       r = []
    21     42.4 MiB    -47.0 MiB       for _ in range(NUM):
    22     42.4 MiB    -19.5 MiB           r.append({})

$ python -m memory_profiler demo.py
Filename: demo.py

Line #    Mem usage    Increment   Line Contents
================================================
    12     10.7 MiB     10.7 MiB   @profile
    13                             def run1():
    14     10.7 MiB      0.0 MiB       ps = []
    15     15.1 MiB      0.3 MiB       for i in range(NUM):
    16     15.1 MiB      4.0 MiB           ps.append(Person(str(i)))


Filename: demo.py

Line #    Mem usage    Increment   Line Contents
================================================
    18     11.6 MiB     11.6 MiB   @profile
    19                             def run2():
    20     11.6 MiB      0.0 MiB       r = []
    21     14.2 MiB      0.0 MiB       for _ in range(NUM):
    22     14.2 MiB      2.6 MiB           r.append({})