[K/N] Re-enable mutator assist

Also remove disabling of GC scheduling during GC

kotlin-native/runtime/src/alloc/custom/cpp/Heap.cpp

@@ -116,6 +116,12 @@ std::vector<ObjHeader*> Heap::GetAllocatedObjects() noexcept {
     return unfinalized;
 }
 
+// This overhead is calculated under the assumption that each thread holds on
+// to one almost empty page of each page type currently in use. Thus, the
+// per-thread-overhead is the sum of the page sizes of the page types that the
+// Heap has currently allocated, i.e., whose PageStores are not empty. This
+// estimate has two-sided error, and there are still pathological allocation
+// patterns that would lead to constant GC triggering.
 size_t Heap::EstimateOverheadPerThread() noexcept {
     size_t overHeadPerThread = 0;
     if (!nextFitPages_.isEmpty()) overHeadPerThread += NEXT_FIT_PAGE_SIZE;

kotlin-native/runtime/src/gcScheduler/adaptive/cpp/GCSchedulerImpl.hpp

@@ -64,7 +64,6 @@ public:
 
     void onGCStart() noexcept {
         regularIntervalPacer_.OnPerformFullGC();
-        heapGrowthController_.unsetBoundaries();
         timer_.restart(config_.regularGcInterval());
     }
 

kotlin-native/runtime/src/gcScheduler/common/cpp/GCSchedulerConfig.hpp

@@ -40,7 +40,7 @@ struct GCSchedulerConfig {
     std::atomic<double> heapTriggerCoefficient = 0.9;
     // See `mutatorAssists()`.
     std::atomic<std::underlying_type_t<MutatorAssists>> mutatorAssistsImpl =
-            static_cast<std::underlying_type_t<MutatorAssists>>(MutatorAssists::kDisable);
+            static_cast<std::underlying_type_t<MutatorAssists>>(MutatorAssists::kDefault);
 
     std::chrono::microseconds regularGcInterval() const { return std::chrono::microseconds(regularGcIntervalMicroseconds.load()); }
 

kotlin-native/runtime/src/gcScheduler/common/cpp/HeapGrowthController.hpp

@@ -31,10 +31,6 @@ public:
         triggerHeapBytes_ = targetHeapBytes_ * config_.heapTriggerCoefficient.load(std::memory_order_relaxed);
     }
 
-    void unsetBoundaries() noexcept {
-        targetHeapBytes_ = triggerHeapBytes_ = std::numeric_limits<int64_t>::max();
-    }
-
     // Can be called by any thread.
     MemoryBoundary boundaryForHeapSize(size_t totalAllocatedBytes) noexcept {
         if (totalAllocatedBytes >= targetHeapBytes_) {