When I worked on a Python app that did real-time processing of (very large) lists of python dicts, merely processing them in a list comprehension caused "leaks" causing unbound virtual memory growth. The issue was that that for small allocations, eg. interned strings, malloc would use the "brk" call rather than "mmap". "brk" simply bumps the top of heap pointer, so if a more long-lived object gets allocated during the time of the comprehension it creates high-water marks in the heap.

The solution at the time was to process the large lists in smaller chunks at a time to make it less likely that a small longer lived object would be allocated in the middle, preventing later cleanup. However, a better solution would probably have been to rewrite parts of the app in a less allocation-happy language.