Clean up and clarify PartitionAlloc

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 123 matching lines @@
 // constant values, we pack _all_ partitionAllocGeneric() sizes perfectly up
 // against the end of a system page.
 static const size_t kPartitionPageShift = 14; // 16KB
 static const size_t kPartitionPageSize = 1 << kPartitionPageShift;
 static const size_t kPartitionPageOffsetMask = kPartitionPageSize - 1;
 static const size_t kPartitionPageBaseMask = ~kPartitionPageOffsetMask;
 static const size_t kMaxPartitionPagesPerSlotSpan = 4;
 
 // To avoid fragmentation via never-used freelist entries, we hand out partition
 // freelist sections gradually, in units of the dominant system page size.
-// What we're actually doing is avoiding filling the full partition page
-// (typically 16KB) will freelist pointers right away. Writing freelist
-// pointers will fault and dirty a private page, which is very wasteful if we
-// never actually store objects there.
+// What we're actually doing is avoiding filling the full partition page (16 KB)
+// with freelist pointers right away. Writing freelist pointers will fault and
+// dirty a private page, which is very wasteful if we never actually store
+// objects there.
 static const size_t kNumSystemPagesPerPartitionPage = kPartitionPageSize / kSystemPageSize;
 static const size_t kMaxSystemPagesPerSlotSpan = kNumSystemPagesPerPartitionPage * kMaxPartitionPagesPerSlotSpan;
 
 // We reserve virtual address space in 2MB chunks (aligned to 2MB as well).
 // These chunks are called "super pages". We do this so that we can store
 // metadata in the first few pages of each 2MB aligned section. This leads to
 // a very fast free(). We specifically choose 2MB because this virtual address
 // block represents a full but single PTE allocation on ARM, ia32 and x64.
 //
 // The layout of the super page is as follows. The sizes below are the same
@@ skipping 561 matching lines @@
 
     ptr = partitionCookieFreePointerAdjust(ptr);
     ASSERT(partitionPointerIsValid(ptr));
     PartitionPage* page = partitionPointerToPage(ptr);
     spinLockLock(&root->lock);
     partitionFreeWithPage(ptr, page);
     spinLockUnlock(&root->lock);
 #endif
 }
 
-ALWAYS_INLINE size_t partitionDirectMapSize(size_t size)
+ALWAYS_INLINE size_t partitionRoundUpToSystemPage(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);
+        size = partitionRoundUpToSystemPage(size);
     }
     return partitionCookieSizeAdjustSubtract(size);
 #endif
 }
 
 ALWAYS_INLINE bool partitionAllocSupportsGetSize()
 {
 #if defined(MEMORY_TOOL_REPLACES_ALLOCATOR)
     return false;
 #else
@@ skipping 48 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