Fix performance issue in Red Black Tree init

src/snmalloc/ds_core/redblacktree.h

@@ -101,7 +101,7 @@ namespace snmalloc
       H ptr;
 
     public:
-      ChildRef() : ptr(nullptr) {}
+      constexpr ChildRef() = default;
 
       ChildRef(H p) : ptr(p) {}
 
@@ -232,7 +232,15 @@ namespace snmalloc
     struct RBStep
     {
       ChildRef node;
-      bool dir = false;
+      bool dir;
+
+      // Default constructor needed for Array<RBStep, 128>.
+      constexpr RBStep() = default;
+
+      // Remove copy constructors to avoid accidentally copying and mutating the
+      // path.
+      RBStep(const RBStep& other) = delete;
+      RBStep& operator=(const RBStep& other) = delete;
 
       /**
        * Update the step to point to a new node and direction.

src/snmalloc/mem/metadata.h

@@ -282,6 +282,11 @@ namespace snmalloc
       uintptr_t* val;
 
     public:
+      /**
+       * Uninitialised constructor.
+       */
+      BackendStateWordRef() = default;
+
       /**
        * Constructor, wraps a `uintptr_t`.  Note that this may be used outside
        * of the meta entry by code wishing to provide uniform storage to things

src/test/perf/large_alloc/large_alloc.cc

@@ -0,0 +1,83 @@
+#include <snmalloc/snmalloc.h>
+#include <test/measuretime.h>
+#include <test/setup.h>
+
+using namespace snmalloc;
+
+static constexpr size_t ALLOC_SIZE = 800 * 1024; // 800 KB
+static constexpr size_t ITERATIONS = 100000;
+
+void test_alloc_dealloc_cycle()
+{
+  {
+    MeasureTime m;
+    m << "Alloc/dealloc 800KB x " << ITERATIONS;
+
+    for (size_t i = 0; i < ITERATIONS; i++)
+    {
+      void* p = snmalloc::alloc(ALLOC_SIZE);
+      SNMALLOC_CHECK(p != nullptr);
+      snmalloc::dealloc(p);
+    }
+  }
+
+  snmalloc::debug_check_empty();
+}
+
+void test_batch_alloc_then_dealloc()
+{
+  static constexpr size_t BATCH = 128;
+
+  void* ptrs[BATCH];
+
+  MeasureTime m;
+  m << "Batch alloc then dealloc 800KB x " << BATCH;
+  for (size_t j = 0; j < ITERATIONS / BATCH; j++)
+  {
+    for (size_t i = 0; i < BATCH; i++)
+    {
+      ptrs[i] = snmalloc::alloc(ALLOC_SIZE);
+      SNMALLOC_CHECK(ptrs[i] != nullptr);
+    }
+
+    for (size_t i = 0; i < BATCH; i++)
+    {
+      snmalloc::dealloc(ptrs[i]);
+    }
+  }
+
+  snmalloc::debug_check_empty();
+}
+
+void test_alloc_dealloc_with_touch()
+{
+  {
+    MeasureTime m;
+    m << "Alloc/touch/dealloc 800KB x " << ITERATIONS;
+
+    for (size_t i = 0; i < ITERATIONS; i++)
+    {
+      char* p = static_cast<char*>(snmalloc::alloc(ALLOC_SIZE));
+      SNMALLOC_CHECK(p != nullptr);
+      // Touch every 4KiB  and last bytes to ensure pages are faulted in
+      for (size_t offset = 0; offset < ALLOC_SIZE; offset += 4096)
+      {
+        p[offset] = 1;
+      }
+      snmalloc::dealloc(p);
+    }
+  }
+
+  snmalloc::debug_check_empty();
+}
+
+int main(int, char**)
+{
+  setup();
+
+  test_alloc_dealloc_cycle();
+  test_batch_alloc_then_dealloc();
+  test_alloc_dealloc_with_touch();
+
+  return 0;
+}