PartitionAlloc: Count direct mapped pages as committed

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
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 #if defined(MEMORY_TOOL_REPLACES_ALLOCATOR)
 #include <stdlib.h>
 #endif
 
 #if ENABLE(ASSERT)
 #include <string.h>
 #endif
 
 namespace WTF {
 
-// Maximum size of a partition's mappings. 2046MB. Note that the total amount of
-// bytes allocatable at the API will be smaller. This is because things like
-// guard pages, metadata, page headers and wasted space come out of the total.
-// The 2GB is not necessarily contiguous in virtual address space.
+// Maximum size of a partition's committed memory. 2046MB. Note that the total
+// amount of bytes allocatable at the API will be slightly smaller. This is
+// because things like wasted space come out of the total. The 2GB is not
+// necessarily contiguous in virtual address space.
 static const size_t kMaxPartitionSize = 2046u * 1024u * 1024u;
 
 // Allocation granularity of sizeof(void*) bytes.
 static const size_t kAllocationGranularity = sizeof(void*);
 static const size_t kAllocationGranularityMask = kAllocationGranularity - 1;
 static const size_t kBucketShift = (kAllocationGranularity == 8) ? 3 : 2;
 
 // Underlying partition storage pages are a power-of-two size. It is typical
 // for a partition page to be based on multiple system pages. Most references to
 // "page" refer to partition pages.
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 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