[Python-Dev] Modify PyMem_Malloc to use pymalloc for performance

[M.-A. Lemburg]

On 03.02.2016 22:03, Victor Stinner wrote:
> Hi,
> 
> There is an old discussion about the performance of PyMem_Malloc()
> memory allocator. CPython is stressing a lot memory allocators. Last
> time I made statistics, it was for the PEP 454:
> "For example, the Python test suites calls malloc() , realloc() or
> free() 270,000 times per second in average."
> https://www.python.org/dev/peps/pep-0454/#log-calls-to-the-memory-allocator
> 
> I proposed a simple change: modify PyMem_Malloc() to use the pymalloc
> allocator which is faster for allocation smaller than 512 bytes, or
> fallback to malloc() (which is the current internal allocator of
> PyMem_Malloc()).
> 
> This tiny change makes Python up to 6% faster on some specific (macro)
> benchmarks, and it doesn't seem to make Python slower on any
> benchmark:
> http://bugs.python.org/issue26249#msg259445
> 
> Do you see any drawback of using pymalloc for PyMem_Malloc()?

Yes: You cannot free memory allocated using pymalloc with the
standard C lib free().

It would be better to go through the list of PyMem_*() calls
in Python and replace them with PyObject_*() calls, where
possible.

> Does anyone recall the rationale to have two families to memory allocators?

The PyMem_*() APIs were needed to have a cross-platform malloc()
implementation which returns standard C lib free()able memory,
but also behaves well when passing 0 as size.

-- 
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