I have a memory leak in a program using big arrays. With the goal of debugging
it I run into the memory_profiler module. Then I discovered something which is
surprising to me. Please consider the following script:
$ cat memtest.py
import gc
from memory_profiler import profile
@profile
def test1():
a = [0] * 1024 * 1024
del a
gc.collect() # nothing change if I comment this
@profile
def test2():
for i in range(10):
a = [0] * 1024 * 1024
del a
gc.collect() # nothing change if I comment this
test1()
test2()
Here is its output, on a Linux 64 bit machine:
$ python memtest.py
Filename: memtest.py
Line # Mem usage Increment Line Contents
================================================
5 @profile
6 9.250 MB 0.000 MB def test1():
7 17.246 MB 7.996 MB a = [0] * 1024 * 1024
8 9.258 MB -7.988 MB del a
9 9.258 MB 0.000 MB gc.collect() # nothing change if I
comment this
Filename: memtest.py
Line # Mem usage Increment Line Contents
================================================
12 @profile
13 9.262 MB 0.000 MB def test2():
14 17.270 MB 8.008 MB for i in range(10):
15 17.270 MB 0.000 MB a = [0] * 1024 * 1024
16 17.270 MB 0.000 MB del a
17 17.270 MB 0.000 MB gc.collect() # nothing change if I
comment this
In the first case the memory is released (even if strangely not
completely, 7.996 != 7.988), in the second case the memory is not. Why it is
so? I did expect gc.collect() to free the memory but it is completely
ininfluent. In the second cases there are 10 lists with 8 MB each, so
80 MB are allocated and 72 released, but 8 MB are still there apparently.
It does not look like a problem of mem_profile, this is what observe with
top too.
Any ideas?
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