Python not giving free memory back to the os get's me in real problems ...

["Martin v. Löwis"]

> I'm a bit fuzzy on this, but I don't think there _is_ a
> practical way to "return memory to the OS" in many OSes.

That's not true at all. Most C libraries these days manage
to return memory to the operating system.

On Win32 (which the OP is most likely to use), the
operating system offers the VirtualFree function to
release memory to the operating system. In MSVCRT,
the small block allocator will invoke VirtualFree
inside __sbh_free_block, when a block group becomes
completely free on the C level; likewise,
_heap_free_region invokes VirtualFree, so does
_heapmin_region.

In glibc 2 on Linux, public_fREe will invoke munmap
to release the memory to the operating system if the
chunk being freed was mmap'ed. glibc allocates chunks
greater than mmap_threshold with mmap, which defaults
to 128kiB - so Python's obmalloc arenas fall under
that algorithm. For small blocks, glibc releases
topmost memory through sbrk when it gets more than
M_TRIM_THRESHOLD bytes (defaults to 128kiB as well).
This algorithm isn't used when MORECORE_CANNOT_TRIM
is defined, which it would only on systems where
sbrk does not support negative arguments.

Regards,
Martin