Add some support for promptly purging pages.

base/allocator/partition_allocator/page_allocator.h

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_ALLOCATOR_PARTITION_ALLOCATOR_PAGE_ALLOCATOR_H
 #define BASE_ALLOCATOR_PARTITION_ALLOCATOR_PAGE_ALLOCATOR_H
 
 #include <stdint.h>
 
 #include <cstddef>
@@ skipping 57 matching lines @@
 // The pages will be readable and writeable.
 // len must be a multiple of kSystemPageSize bytes.
 // The result bool value indicates whether the permission
 // change succeeded or not. You must check the result
 // (in most cases you need to CHECK that it is true).
 BASE_EXPORT WARN_UNUSED_RESULT bool SetSystemPagesAccessible(void* address,
                                                              size_t length);
 
 // Decommit one or more system pages. Decommitted means that the physical memory
 // is released to the system, but the virtual address space remains reserved.
-// System pages are re-committed by calling recommitSystemPages(). Touching
+// System pages are re-committed by calling RecommitSystemPages(). Touching
 // a decommitted page _may_ fault.
 // Clients should not make any assumptions about the contents of decommitted
 // system pages, before or after they write to the page. The only guarantee
 // provided is that the contents of the system page will be deterministic again
 // after recommitting and writing to it. In particlar note that system pages are
-// not guaranteed to be zero-filled upon re-commit. len must be a multiple of
-// kSystemPageSize bytes.
-BASE_EXPORT void DecommitSystemPages(void* address, size_t length);
+// not guaranteed to be zero-filled upon re-commit. |len| must be a multiple of
+// |kSystemPageSize| bytes.
+//
+// |purge_hint| is an optional hint to signal that the system pages can
+// be discarded from process memory right away. By supplying |true|, the
+// implementation makes an OS-specific best effort to decommit the system pages
+// sooner from the process. Even with |purge_hint| set to |true|, it is not
+// guaranteed that the decommitted system pages will be zero-filled upon
+// recommit.
+BASE_EXPORT void DecommitSystemPages(void* address,
+                                     size_t length,
+                                     bool purge_hint = false);
 
 // Recommit one or more system pages. Decommitted system pages must be
 // recommitted before they are read are written again.
 // Note that this operation may be a no-op on some platforms.
 // len must be a multiple of kSystemPageSize bytes.
 BASE_EXPORT void RecommitSystemPages(void* address, size_t length);
 
 // Discard one or more system pages. Discarding is a hint to the system that
 // the page is no longer required. The hint may:
 // - Do nothing.
@@ skipping 18 matching lines @@
 ALWAYS_INLINE uintptr_t RoundDownToSystemPage(uintptr_t address) {
   return address & kSystemPageBaseMask;
 }
 
 // Returns errno (or GetLastError code) when mmap (or VirtualAlloc) fails.
 BASE_EXPORT uint32_t GetAllocPageErrorCode();
 
 }  // namespace base
 
 #endif  // BASE_ALLOCATOR_PARTITION_ALLOCATOR_PAGE_ALLOCATOR_H