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pablogsal

opened on Oct 21, 2024

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In #125703 @markshannon has raised that he is unhappy about the performance implications of where these hooks are placed and in a call we discussed that he has some ideas on how to make them more performant by moving them elsewhere or adapting then.

I am opening this issue to track and sync about these improvements for 3.14 and beyond.

Reacted by Carol Willing and Erlend E. Aasland

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1. pablogsal

   added

   performancePerformance or resource usagePerformance or resource usage

   on Oct 21, 2024
2. markshannon commented on Oct 25, 2024

   

   markshannon

   on Oct 25, 2024

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   I think we can fix the performance issues by raising the level at which allocation/free goes through a function pointer.

   Instead of a malloc-like interface void *malloc(size_t size), we should be returning partially initialized objects.
   PyObject *obj_malloc(PyTypeObject *tp, size_t size, size_t presize) would allocate a chunk of memory size + presize, returning a PyObject * pointing to that memory + presize, with the ob_type field set to tp and the ob_refcount set to one.

   This is low-enough level to be fully general, but with enough context to support tracemalloc.

   I think we would need the following implementations, switchable at runtime:

   • default
   • tracemalloc
   • custom (used when the underlying PEP 445 allocator is changed)
   • custom-tracemalloc (used when the underlying PEP 445 allocator is changed)
   • freethreading
   • freethreading-tracemalloc

   We don't need (or want) to switch between the free-threading and default allocators, but it keeps the rest of the code simpler if they have the same interface.
3. markshannon commented on Apr 7, 2025

   

   markshannon

   on Apr 7, 2025

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   Having played around with this a bit, I'm going with a slightly different design.

   All allocations and deallocations will go through a single (inline) function taking the threadstate as well as the type and sizes.
   This will allocate from per-size freelists, then fall back to the basic malloc/free functions.
   This works as we can disable, or re-enable, the freelists when PyRefTracer_SetTracer or PyMem_SetAllocator are called.
4. picnixz

   added

   type-featureA feature request or enhancementA feature request or enhancement

   interpreter-core(Objects, Python, Grammar, and Parser dirs)(Objects, Python, Grammar, and Parser dirs)

   on Apr 7, 2025

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