TL;DR ╰> octane goes from 41859 -> 42414 ╰> octane has ~15% fewer nursery collections taking >500us The current patch is very simple: it moves the existing nursery collection code to Marking.cpp, uses a new JSTracer subclass to avoid the indirect call overhead, and specializes StoreBuffer::*::mark to skip DispatchToTracer. Microbenchmarks show that traversing a store buffer is roughly 2x faster with the patch applied. Further work is needed here: I want to experiment with using a mark stack instead of an inline list to see if I can eek out any further improvements. Also, we should be able to share some of this code with processMarkStackTop, somehow. https://treeherder.mozilla.org/#/jobs?repo=try&revision=5db59d84dabf

Missing a qref.

Comment on attachment 8601696 [details] [diff] [review] 18_custom_marking_for_nursery-v0.diff Review of attachment 8601696 [details] [diff] [review]: ----------------------------------------------------------------- This is great! ::: js/src/gc/Nursery-inl.h @@ +21,5 @@ > MOZ_ASSERT(isInside((void*)*ref)); > const gc::RelocationOverlay* overlay = reinterpret_cast<const gc::RelocationOverlay*>(*ref); > if (!overlay->isForwarded()) > return false; > /* This static cast from Cell* restricts T to valid (GC thing) types. */ This comment needs updating/removing.

Comment on attachment 8601696 [details] [diff] [review] 18_custom_marking_for_nursery-v0.diff >--- a/js/src/gc/Nursery.cpp >+++ b/js/src/gc/Nursery.cpp [...] >-struct TenureCount >+js::TenuringTracer::TenuringTracer(JSRuntime* rt, Nursery* nursery) >+ : JSTracer(rt, JSTracer::TracerKindTag::Tenuring, TraceWeakMapKeysValues) >+ , nursery_(*nursery) >+ , tenuredSize(0) >+ , head(nullptr) >+ , tail(&head) >+ , savedRuntimeNeedBarrier(rt->needsIncrementalBarrier()) >+#ifdef JS_GC_ZEAL >+ , verifyingPostBarriers(nullptr) >+#endif > { This "verifyingPostBarriers" initialization causes Werror build bustage for me, locally (with clang 3.7). The build warning (error) is: > js/src/gc/Nursery.cpp:383:27: error: implicit conversion of nullptr constant to 'bool' [-Werror,-Wnull-conversion] > , verifyingPostBarriers(nullptr) > ~^~~~~~~ > 1 error generated. Terrence, should this be s/nullptr/false/? Could you push a followup to fix?

Ah, terrence says on IRC that bug 1161353 (which just landed) will address comment 6.