Add partitionAllocActualSize() for predicting actual size of allocation

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 164 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 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;
 static const uint32_t kCookieValue = 0xDEADBEEFu;
@@ skipping 363 matching lines @@
 
     ptr = partitionCookieFreePointerAdjust(ptr);
     ASSERT(partitionPointerIsValid(ptr));
     PartitionPage* page = partitionPointerToPage(ptr);
     spinLockLock(&root->lock);
     partitionFreeWithPage(ptr, page);
     spinLockUnlock(&root->lock);
 #endif
 }
 
+ALWAYS_INLINE bool partitionBucketIsDirectMapped(PartitionBucket* bucket)
+{
+    return !bucket->numSystemPagesPerSlotSpan;
+}
+
+ALWAYS_INLINE size_t partitionDirectMapSize(size_t size)
+{
+    // Caller must check that the size is not above the kGenericMaxDirectMapped
+    // limit before calling. This also guards against integer overflow in the
+    // calculation here.
+    ASSERT(size <= kGenericMaxDirectMapped);
+    return (size + kSystemPageOffsetMask) & kSystemPageBaseMask;
+}
+
+ALWAYS_INLINE size_t partitionAllocActualSize(PartitionRootGeneric* root, size_t size)
+{
+#if defined(MEMORY_TOOL_REPLACES_ALLOCATOR)
+    return size;
+#else
+    ASSERT(root->initialized);
+    size = partitionCookieSizeAdjustAdd(size);
+    PartitionBucket* bucket = partitionGenericSizeToBucket(root, size);
+    if (LIKELY(!partitionBucketIsDirectMapped(bucket))) {
+        size = bucket->slotSize;
+    } else if (size > kGenericMaxDirectMapped) {
+        // Too large to allocate => return the size unchanged.
+    } else {
+        ASSERT(bucket == &PartitionRootBase::gPagedBucket);
+        size = partitionDirectMapSize(size);
+    }
+    return partitionCookieSizeAdjustSubtract(size);
+#endif
+}
+
 ALWAYS_INLINE bool partitionAllocSupportsGetSize()
 {
 #if defined(MEMORY_TOOL_REPLACES_ALLOCATOR)
     return false;
 #else
     return true;
 #endif
 }
 
 ALWAYS_INLINE size_t partitionAllocGetSize(void* ptr)
@@ skipping 38 matching lines @@
 using WTF::SizeSpecificPartitionAllocator;
 using WTF::PartitionAllocatorGeneric;
 using WTF::PartitionRoot;
 using WTF::partitionAllocInit;
 using WTF::partitionAllocShutdown;
 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