[Python-Dev] Looking for master thesis ideas involving Python

"Martin v. Löwis" martin at v.loewis.de
Sun Nov 2 19:18:53 EST 2003

Armin Rigo wrote:
>>If you put all objects of the same type into a pool, you really want
>>all objects to have the same side, inside a pool. With that
>>assumption, garbage objects can be reallocated without causing
>>fragmentation. If objects in a pool have different sizes, it is not
>>possible to have an efficient reallocation strategy.
> "Not easy" would have been more appropriate.  It is still basically what
> malloc() does.

That's why I said "efficient". What malloc basically does is not 
efficient. It gets worse if, at reallocation time, you are not only 
bound by size, but also by type. E.g. if you have deallocated a tuple of
10 elements, and then reallocate a tuple of 6, the wasted space can only
hold a tuple of 1 element, nothing else.

> One way would be to use Python's current memory allocator, by adapting it to
> sort objects into pools not only according to size but also according to type.  
> What seems to me like a good solution would be to use one relatively large
> "arena" per type and Python's memory allocator to subdivide each arena.  If
> each arena starts at a pointer address which is properly aligned, then
> *(p&MASK) gives you the type of any object, and possibly even without much
> cache-miss overhead because there are not so many arenas in total (probably
> only 1-2 per type in common cases, and arenas can be large).

So where do you put strings with 100,000 elements (characters)? Or any 
other object that exceeds an arena in size?


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