GH-126491: GC: Mark objects reachable from roots before doing cycle collection by markshannon · Pull Request #126502 · python/cpython

markshannon · 2024-11-06T14:23:37Z

This PR:

Performs a marking step before the incremental cycle collection
Rescans the stack before each increment
Removes lazy dict tracking as the lazy tracking optimization no longer pays off.

Performance is excellent. Speedup is 4%, with a 100% speedup on one GC benchmark.

Stats show the GC is run more frequently and collects more objects, but does only ~60% of the work.

This PR also:

Makes detaching an object's dict a bit more robust in case of a memory error.
Increases the threshold in a GC test. This test is to check for uncontrolled growth, so the exact threshold doesn't matter.

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