PartitionAlloc: Make in-place realloc() less likely to happen

Source/wtf/PartitionAlloc.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 165 matching lines @@
 // In terms of allocation sizes, order 0 covers 0, order 1 covers 1, order 2
 // covers 2->3, order 3 covers 4->7, order 4 covers 8->15.
 static const size_t kGenericMinBucketedOrder = 4; // 8 bytes.
 static const size_t kGenericMaxBucketedOrder = 20; // Largest bucketed order is 1<<(20-1) (storing 512KB -> almost 1MB)
 static const size_t kGenericNumBucketedOrders = (kGenericMaxBucketedOrder - kGenericMinBucketedOrder) + 1;
 static const size_t kGenericNumBucketsPerOrderBits = 3; // Eight buckets per order (for the higher orders), e.g. order 8 is 128, 144, 160, ..., 240
 static const size_t kGenericNumBucketsPerOrder = 1 << kGenericNumBucketsPerOrderBits;
 static const size_t kGenericSmallestBucket = 1 << (kGenericMinBucketedOrder - 1);
 static const size_t kGenericMaxBucketSpacing = 1 << ((kGenericMaxBucketedOrder - 1) - kGenericNumBucketsPerOrderBits);
 static const size_t kGenericMaxBucketed = (1 << (kGenericMaxBucketedOrder - 1)) + ((kGenericNumBucketsPerOrder - 1) * kGenericMaxBucketSpacing);
-static const size_t kGenericMinDirectMappedDownsize = 16 * kPartitionPageSize; // Limit when downsizing a direct mapping using realloc().
+static const size_t kGenericMinDirectMappedDownsize = kGenericMaxBucketed + 1; // Limit when downsizing a direct mapping using realloc().
 static const size_t kGenericMaxDirectMapped = INT_MAX - kSystemPageSize;
 static const size_t kBitsPerSizet = sizeof(void*) * CHAR_BIT;
 
 // Constants for the memory reclaim logic.
 static const size_t kMaxFreeableSpans = 16;
 
 #ifndef NDEBUG
 // These two byte values match tcmalloc.
 static const unsigned char kUninitializedByte = 0xAB;
 static const unsigned char kFreedByte = 0xCD;
@@ skipping 461 matching lines @@
 using WTF::partitionAlloc;
 using WTF::partitionFree;
 using WTF::partitionAllocGeneric;
 using WTF::partitionFreeGeneric;
 using WTF::partitionReallocGeneric;
 using WTF::partitionAllocActualSize;
 using WTF::partitionAllocSupportsGetSize;
 using WTF::partitionAllocGetSize;
 
 #endif // WTF_PartitionAlloc_h