base: Discardable memory types.

base/memory/discardable_memory.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_MEMORY_DISCARDABLE_MEMORY_H_
 #define BASE_MEMORY_DISCARDABLE_MEMORY_H_
 
+#include <vector>
+
 #include "base/base_export.h"
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
 
 namespace base {
 
+enum DiscardableMemoryType {
+  DISCARDABLE_MEMORY_NONE,
+  DISCARDABLE_MEMORY_ANDROID,

[reveman, 2013/12/13 18:21:53]

Follow up patches will replace this with DISCARDABLE_MEMORY_ASHMEM, which will
be supported on both android and chromeos.

+  DISCARDABLE_MEMORY_MAC,

[reveman, 2013/12/13 18:21:53]

We might want to rename this to DISCARDABLE_MEMORY_VM or
DISCARDABLE_MEMORY_VM_PURGEABLE in a follow up patch and move the implementation
out of _mac.cc if we need some implementation specific unit tests.

+  DISCARDABLE_MEMORY_EMULATED
+};
+
 enum LockDiscardableMemoryStatus {

[reveman, 2013/12/16 21:05:51]

How about we rename this to DiscardableMemoryLockStatus and use
DISCARDABLE_MEMORY_LOCK_STATUS_ prefix for all values? The prefix for the type
values above would then become DISCARDABLE_MEMORY_TYPE_.

[Philippe, 2013/12/17 14:28:21]

SGTM

[reveman, 2013/12/18 08:12:38]

Done.

   DISCARDABLE_MEMORY_FAILED = -1,
   DISCARDABLE_MEMORY_PURGED = 0,
   DISCARDABLE_MEMORY_SUCCESS = 1
 };
 
 // Platform abstraction for discardable memory. DiscardableMemory is used to
 // cache large objects without worrying about blowing out memory, both on mobile
 // devices where there is no swap, and desktop devices where unused free memory
 // should be used to help the user experience. This is preferable to releasing
 // memory in response to an OOM signal because it is simpler, though it has less
@@ skipping 20 matching lines @@
 //   - Linux: http://lwn.net/Articles/452035/
 //   - Mac: http://trac.webkit.org/browser/trunk/Source/WebCore/platform/mac/PurgeableBufferMac.cpp
 //          the comment starting with "vm_object_purgable_control" at
 //            http://www.opensource.apple.com/source/xnu/xnu-792.13.8/osfmk/vm/vm_object.c
 //
 // Thread-safety: DiscardableMemory instances are not thread-safe.
 class BASE_EXPORT DiscardableMemory {
  public:
   virtual ~DiscardableMemory() {}
 
-  // Check whether the system supports discardable memory natively. Returns
-  // false if the support is emulated.
-  static bool SupportedNatively();
+  // Get system supported discardable memory types. Preferred type at the front
+  // of vector.
+  static const std::vector<DiscardableMemoryType>& GetSupportedTypes();
+
+  // Set the current discardable memory type.
+  static void SetType(DiscardableMemoryType type);
+
+  // Get the current discardable memory type.
+  static DiscardableMemoryType GetType();
 
   static scoped_ptr<DiscardableMemory> CreateLockedMemory(size_t size);
 
   // Locks the memory so that it will not be purged by the system. Returns
   // DISCARDABLE_MEMORY_SUCCESS on success. If the return value is
   // DISCARDABLE_MEMORY_FAILED then this object should be discarded and
   // a new one should be created. If the return value is
   // DISCARDABLE_MEMORY_PURGED then the memory is present but any data that
   // was in it is gone.
   virtual LockDiscardableMemoryStatus Lock() WARN_UNUSED_RESULT = 0;
 
   // Unlocks the memory so that it can be purged by the system. Must be called
   // after every successful lock call.
   virtual void Unlock() = 0;
 
   // Returns the memory address held by this object. The object must be locked
   // before calling this. Otherwise, this will cause a DCHECK error.
   virtual void* Memory() const = 0;
 
   // Testing utility calls.
 
   // Check whether a purge of all discardable memory in the system is supported.
   // Use only for testing!
   static bool PurgeForTestingSupported();

[reveman, 2013/12/13 18:21:53]

This is now only true if all supported types can be purged.

 
   // Purge all discardable memory in the system. This call has global effects
   // across all running processes, so it should only be used for testing!
   static void PurgeForTesting();

[reveman, 2013/12/13 18:21:53]

This is now purging all supported types and not just the current one.

I think we should remove this from the general DiscardableMemory API unless it
can be supported by all types. Implementation specific test can be used for this
instead.

 };
 
 }  // namespace base
 
 #endif  // BASE_MEMORY_DISCARDABLE_MEMORY_H_