PEP 848 Proposes Generational Incremental Garbage Collection for CPython

PEP 848 outlines a new cyclic garbage collector for CPython that is both generational and incremental. It will alternate between young and incremental old collections, focusing on specific parts of the heap where garbage is most concentrated.

The proposed collector aims to reduce GC pause times by up to a factor of 100 in programs with large heaps, alongside a 3-5% overall performance improvement on the pyperformance benchmark suite. Peak memory use is expected to decrease for larger heaps but may increase for smaller, shorter-lived programs.

The current generational collector is inefficient due to scanning live objects, examining objects too frequently, and performing full heap scans, leading to long pause times. The new design targets older objects and performs incremental scans, increasing effectiveness and reducing pauses.

The collector design prioritizes total program run time, maximum GC pause time, and peak memory use. It divides the heap into three generations (Nursery, Aging, Old) and further splits them into spaces, with a specific alternating algorithm for collecting increments of the old generation and the oldest young generation space. The existing non-incremental collector will remain an option.