Bound individual size of allocation to put in free list

If we use partialKeyLen, then the difference between partialKeyCapacity
and partialKeyLen will slowly grow. We have 3 padding bytes in Node now.

ConflictSet.cpp

@@ -174,18 +174,16 @@ struct Node {
   Node *parent = nullptr;
   Entry entry;
   int32_t partialKeyLen = 0;
-  int16_t numChildren : 15 = 0;
-  bool entryPresent : 1 = false;
+  int16_t numChildren = 0;
+  bool entryPresent = false;
   uint8_t parentsIndex = 0;
   /* end section that's copied to the next node */
 
   Type type;
-#ifndef NDEBUG
-  // Leaving this uninitialized is intentional and necessary to expect asserts
-  // to pass. Basically it needs to be preserved when going to the free list and
-  // back.
+
+  // Leaving this uninitialized is intentional and necessary for correctness.
+  // Basically it needs to be preserved when going to the free list and back.
   int32_t partialKeyCapacity;
-#endif
 
   uint8_t *partialKey();
 };
@@ -262,7 +260,8 @@ static_assert(sizeof(Node4) < kMinChildrenNode4 * kBytesPerKey);
 
 // Bounds memory usage in free list, but does not account for memory for partial
 // keys.
-template <class T, size_t kMemoryBound = (1 << 20)>
+template <class T, int64_t kMemoryBound = (1 << 20),
+          int64_t kMaxIndividual = (1 << 10)>
 struct BoundedFreeListAllocator {
   static_assert(sizeof(T) >= sizeof(void *));
   static_assert(std::derived_from<T, Node>);
@@ -274,24 +273,22 @@ struct BoundedFreeListAllocator {
 #endif
     if (freeList != nullptr) {
       T *n = (T *)freeList;
-      VALGRIND_MAKE_MEM_DEFINED(n, sizeof(T));
-      if (n->partialKeyLen >= partialKeyCapacity) {
-        memcpy(&freeList, freeList, sizeof(freeList));
-        --freeListSize;
-        VALGRIND_MAKE_MEM_UNDEFINED(n, sizeof(T));
-#ifndef NDEBUG
-        VALGRIND_MAKE_MEM_DEFINED(&n->partialKeyCapacity,
-                                  sizeof(n->partialKeyCapacity));
-#endif
+      VALGRIND_MAKE_MEM_UNDEFINED(n, sizeof(T));
+      VALGRIND_MAKE_MEM_DEFINED(&n->partialKeyCapacity,
+                                sizeof(n->partialKeyCapacity));
+      VALGRIND_MAKE_MEM_DEFINED(freeList, sizeof(freeList));
+      memcpy(&freeList, freeList, sizeof(freeList));
+      freeListBytes -= sizeof(T) + n->partialKeyCapacity;
+      if (n->partialKeyCapacity >= partialKeyCapacity) {
         return new (n) T;
+      } else {
+        // The intent is to filter out too-small nodes in the freelist
+        free(n);
       }
-      VALGRIND_MAKE_MEM_NOACCESS(n, sizeof(T));
     }
 
     auto *result = new (safe_malloc(sizeof(T) + partialKeyCapacity)) T;
-#ifndef NDEBUG
     result->partialKeyCapacity = partialKeyCapacity;
-#endif
     return result;
   }
 
@@ -300,12 +297,13 @@ struct BoundedFreeListAllocator {
     --liveAllocations;
 #endif
     static_assert(std::is_trivially_destructible_v<T>);
-    if (freeListSize == kMaxFreeListSize) {
+    if (sizeof(T) + p->partialKeyCapacity > kMaxIndividual ||
+        freeListBytes >= kMemoryBound) {
       return free(p);
     }
     memcpy((void *)p, &freeList, sizeof(freeList));
     freeList = p;
-    ++freeListSize;
+    freeListBytes += sizeof(T) + p->partialKeyCapacity;
     VALGRIND_MAKE_MEM_NOACCESS(freeList, sizeof(T));
   }
 
@@ -323,10 +321,10 @@ struct BoundedFreeListAllocator {
 #endif
 
 private:
-  static constexpr int kMaxFreeListSize = kMemoryBound / sizeof(T);
-  int freeListSize = 0;
+  int64_t freeListBytes = 0;
   void *freeList = nullptr;
 #if SHOW_MEMORY
+  // TODO Track partial key bytes
   int64_t maxLiveAllocations = 0;
   int64_t liveAllocations = 0;
 #endif