Forward-port generational GC

Feature or enhancement

Proposal:

It was decided to revert the incremental GC and restore the generational GC from Python 3.13.

After discussing with @nascheme, we plan to forward-port the generational GC from 3.13 with minimal changes.

Here is the plan:

3.14

1. Forward-port the generational GC from 3.13 with minimal changes
2. Backport the heap_size calculation logic

3.15

1. Forward port from 3.14
2. Backport weakref's callbacks changes (b6b99bf, 350c58b, 654b8d9)
3. Backport changes required for pystats (c98c5b3)
4. Backport GC frame for Tachyon (336366f)
5. Backport extended data for callbacks: duration, candidates (598d4c6, 227b9d3)
6. Backport gc-stats from external processes (Add a module for monitoring GC statistics #146527)

AFAICT, these are all the changes that need to be forward-ported or backported for the 3.14 and 3.15.

Has this already been discussed elsewhere?

I have already discussed this feature proposal on Discourse

Links to previous discussion of this feature:

https://discuss.python.org/t/reverting-the-incremental-gc-in-python-3-14-and-3-15/107014

Linked PRs

• [3.14] GH-148726: Forward-port generational GC #148720
• GH-148726: Forward-port generational GC. #148746
• [3.14] GH-148726: Forward-port generational GC (another way) #148772
• [3.14] GH-148726: Add heap_size to _gc_runtime_state #149025
• GH-148726: Add heap_size to generational GC #149195
• gh-148726: Document the GC change in What's New in Python 3.14 #149209
• [3.14] gh-148726: Document the GC change in What's New in Python 3.14 (GH-149209) #149249
• gh-148726: Add gc changes to What's New #149398