Large Dictionaries Not Released From Memory - Python + UbuntuI have a flask application running on Ubuntu which reads from a file and creates several large dictionaries. After the dictionaries are created and flask returns the request, the memory used for the dictionaries is not released back to the OS. This example shows the problem: https://gist.github.com/pawl/c3ed7663b94abec01d75
It's not really a Flask issue, but the Flask guys were super helpful when I asked why my large dictionary wasn't released from memory: https://github.com/mitsuhiko/flask/issues/1202
I dug even deeper and learned this is a Linux thing:
"Python returns memory to the OS on the heap (that allocates other objects than small objects) only on Windows, if you run on Linux, you can only see the total memory used by your program increase."
Turning it into a function and running it as a separate process: https://gist.github.com/pawl/95769724848269cff890
If you want to go even deeper down the rabbit hole, read these:
- "most malloc implementations will not release memory to the operating system, and the few that do, do not do it very easily" -http://stackoverflow.com/questions/2215259/will-malloc-implementations-return-free-ed-memory-back-to-the-system
- "We compiled a version of Python with TCMalloc that only uses mmap. When testing the new Python in one of our largest projects, we found that not only did Python give back memory to the OS correctly, it also had a reduced memory usage and no apparent CPU penalty for using mmap instead of brk." - http://pushingtheweb.com/2010/06/python-and-tcmalloc/