Oilpan: Discard unused system pages when sweeping NormalPageHeaps

third_party/WebKit/Source/wtf/PageAllocator.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 108 matching lines @@
 // A read or write to a discarded page will not fault.
 // Reading from a discarded page may return the original page content, or a
 // page full of zeroes.
 // Writing to a discarded page is the only guaranteed way to tell the system
 // that the page is required again. Once written to, the content of the page is
 // guaranteed stable once more. After being written to, the page content may be
 // based on the original page content, or a page of zeroes.
 // len must be a multiple of kSystemPageSize bytes.
 WTF_EXPORT void discardSystemPages(void* addr, size_t len);
 
+WTF_EXPORT ALWAYS_INLINE uintptr_t roundUpToSystemPage(uintptr_t address)
+{
+    return (address + kSystemPageOffsetMask) & kSystemPageBaseMask;
+}
+
+WTF_EXPORT ALWAYS_INLINE uintptr_t roundDownToSystemPage(uintptr_t address)
+{
+    return address & kSystemPageBaseMask;
+}
+
 } // namespace WTF
 
 #endif // WTF_PageAllocator_h