Python resident memory retention & Evan Jones' improvements

Matt Ernst matt.ernst at
Sat Oct 3 23:33:14 CEST 2009

On Oct 2, 4:47 pm, Andrew MacIntyre <andy... at>
> There are two things you need to be aware of in this situation:
> - not all Python's memory is allocated through Python's specialised
>    malloc() - int and float objects in particular (in 2.x at least) are
>    allocated directly via a privately managed free list, and any
>    allocation requiring more than 256 bytes is directed to the platform
>    malloc().  Any memory not allocated via Python's malloc() is not
>    subject to the memory release facility referred to above.
>    Python 2.6 does improve the management of memory consumed by int and
>    float objects via the garbage collector.
> - while Python attempts to maximally utilise memory arenas to improve
>    the chances of being able to free them, Python's malloc() does not do
>    any compaction of memory (ie moving allocations between arenas) within
>    existing arenas.  Nor does garbage collection do this.  So fragmented
>    allocations can cause the retention of nearly empty arenas.
> I suspect that what you see with the second test script above is caused
> by some sort of fragmentation.

Thank you for the explanation. Since my real application uses many
small objects, it makes sense that memory cannot be reclaimed in the
absence of compaction.


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