EdenCollections are a lot cheaper than FullCollections on average, but there's still room for improvement. I gathered some GC phase timing logs while browsing around on a few JS-heavy-ish websites and wrote a tool to parse the output and sort by average time spent in each phase. Here's what it looks like: Eden FinishingCollection Eden 0.0 avg UpdateAllocationLimits Eden 0.0 avg ResetAllocators Eden 0.0 avg RememberCurrentlyExecutingCodeBlocks Eden 0.0 avg NotifyIncrementalSweeper Eden 0.0 avg FinalizeDFGWorklists Eden 0.0 avg SnapshotMarkedSpace Eden 0.0 avg SweepingArrayBuffers Eden 0.0 avg VisitHandleStack Eden 0.0 avg MarkingException Eden 0.0 avg MarkingArgumentBuffers Eden 0.0 avg VisitTempSortVectors Eden 0.0 avg VisitSmallStrings Eden 0.0 avg GatherScratchBufferRoots Eden 0.0 avg FlushWriteBarrierBuffer Eden 0.0 avg FlushOldStructureIDTables Eden 0.0 avg ClearLivenessData Eden 0.01 avg VisitProtectedObjects Eden 0.02 avg ClearRememberedSet Eden 0.03 avg TraceCodeBlocksAndJITStubRoutines Eden 0.05 avg ClearUnmarkedExecutables Eden 0.09 avg ReapingWeakHandles Eden 0.11 avg DeleteSourceProviderCaches Eden 0.15 avg GatherStackRoots Eden 0.15 avg StopAllocation Eden 0.24 avg Convergence Eden 0.25 avg VisitStrongHandles Eden 0.38 avg CopyBackingStores Eden 0.41 avg DeleteCodeBlocks Eden 0.44 avg VisitingLiveWeakHandles Eden 0.52 avg VisitConservativeRoots Eden 1.25 avg FinalizeUnconditionalFinalizers Eden 1.53 avg MarkRoots Eden 2.99 avg Collect Eden 5.89 avg Note: Some of these phases are sub-phases of other phases. Times are in milliseconds. A bunch of these phases seem to have low-hanging fruit. Things like converting iteration over linked lists to iteration over vectors, skipping phases during EdenCollections, etc. I've already done a few things along these lines. This bug is just to keep track of the various things that could help.