Whippet GC notes on Guile, heuristics, and heap growth

Greets all! Another brief note today. I have gotten Guile working with one of the Nofl-based collectors, specifically the one that scans all edges conservatively ( heap-conservative-mmc / heap-conservative-parallel-mmc ). Hurrah! It was a pleasant surprise how easy it was to switch—from the user’s point of view, you just pass --with-gc=heap-conservative-parallel-mmc to Guile’s build (on the wip-whippet branch); when developing I also pass --with-gc-debug , and I had a couple bugs to fix—but, but, there are still some issues. Today’s note thinks through the ones related to heap sizing heuristics. growable heaps Whippet has three heap sizing strategies: fixed, growable, and adaptive (MemBalancer). The adaptive policy is the one I would like in the long term; it will grow the heap for processes with a high allocation rate, and shrink when they go idle. However I won’t really be able to test heap shrinking until I get precise tracing of heap edges, which will allow me to evacuate sparse ... Read full article.