Issue #19571 has been updated by ko1 (Koichi Sasada). Could you make clear the following? * Please describe how the new parameter is used and how the current implementation calculate without new parameter. * my understanding is this parameter is used for the major GC condition. * This new parameter can reduce major GC count (and this is why the figures show the results) * Can we compare the major GC counts, uncollectible objects count and memory footprint? * Could you try with other parameters, from 0.10 to 0.50 for example? Maybe this proposal is based on the assumption that "we can't collect uncollectible objects in many cases so the collection rate (== major GC counts) should be reduced". I agree this assumption in general. Can we make some kind of evidence? Trivial comment: This parameter is ratio for the "old objects" so I'm not sure it makes sense. ---------------------------------------- Feature #19571: Add REMEMBERED_WB_UNPROTECTED_OBJECTS_LIMIT_RATIO to the GC https://bugs.ruby-lang.org/issues/19571#change-102623 * Author: peterzhu2118 (Peter Zhu) * Status: Open * Priority: Normal ---------------------------------------- GitHub PR: https://github.com/ruby/ruby/pull/7577 The proposed PR adds the environment variable `RUBY_GC_HEAP_REMEMBERED_WB_UNPROTECTED_OBJECTS_LIMIT_RATIO` which is used to calculate the `remembered_wb_unprotected_objects_limit` using a ratio of `old_objects`. This should improve performance by reducing major GC because, in a major GC, we mark all of the old objects, so we should have more uncollectible WB unprotected objects before starting a major GC. The default has been set to 0.01 (1% of old objects). On one of [Shopify's highest traffic Ruby apps, Storefront Renderer](https://shopify.engineering/how-shopify-reduced-storefront-response-times-re...), we saw significant improvements after deploying this patch in production. In the graphs below, we have the `tuned` group which uses `RUBY_GC_HEAP_REMEMBERED_WB_UNPROTECTED_OBJECTS_LIMIT_RATIO=0.01` (the default value), and an `untuned` group, which turns this feature off with `RUBY_GC_HEAP_REMEMBERED_WB_UNPROTECTED_OBJECTS_LIMIT_RATIO=0`. We see that the tuned group spends significantly less time in GC, on average 0.67x of the time compared to the untuned group and 0.49x for p99. We see this improvement in GC time translate to improvements in response times. The average response time is now 0.96x of the time compared to the untuned group and 0.86x for p99.  ---Files-------------------------------- Screenshot 2023-04-03 at 11.39.06 AM.png (554 KB) -- https://bugs.ruby-lang.org/