Reverting the incremental GC in Python 3.14 and 3.15

[tim.one (Tim Peters)]

As requested by @hugovk, I started a new topic yesterday to discuss ideas for rehabilitating inc gc:

Improving incremental gc

Incremental gc is being reverted for 3.14, to be replaced with the older 3-gen collector, and the same will be true of 3.15: Inc gc seemed to be primarily aimed at reducing “stop the world” long pauses, and has had some success at that. But it came at the cost of sometimes greatly increasing memory use, as trash cycles pile up waiting for the incremental collector to get to them. I wrote a toy app to explore the limits (link to a public gist): Toy cyclic gc code · GitHub . Don’t be put off…

He wants to keep this topic focused on 3.14/3.15. So please continue this in the new topic (or create your own).

@markshannon

Adding the gen0 collection to the increment is trivial; it’s a three line change

@nas already posted a patch there that that does that (plus some more)..

However, by itself doesn’t fix the problem: too many garbage cycles span multiple young collections.

It’s nevertheless a major improvement (slashing peak memory use) on the stress tests we have so far. A promising start .

@nas;a original 3-gen design was focused on timely collection of shorter-lived cycles, and I’m confident that moving, as you suggest, back closer to that will pay off. It’s the gen2 collections that caused “long pauses”.