base: Add soft memory limit to DiscardableMemoryManager.

base/memory/discardable_memory_manager.h

 // Copyright 2014 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_MANAGER_H_
 #define BASE_MEMORY_DISCARDABLE_MEMORY_MANAGER_H_
 
 #include "base/base_export.h"
 #include "base/containers/hash_tables.h"
 #include "base/containers/mru_cache.h"
 #include "base/memory/memory_pressure_listener.h"
 #include "base/synchronization/lock.h"
+#include "base/time/time.h"
 
 namespace base {
 namespace internal {
 
 // This interface is used by the DiscardableMemoryManager class to provide some
 // level of userspace control over discardable memory allocations.
 class DiscardableMemoryManagerAllocation {
  public:
   // Allocate and acquire a lock that prevents the allocation from being purged
   // by the system. Returns true if memory was previously allocated and is still
@@ skipping 33 matching lines @@
 // The DiscardableMemoryManager manages a collection of
 // DiscardableMemoryManagerAllocation instances. It is used on platforms that
 // need some level of userspace control over discardable memory. It keeps track
 // of all allocation instances (in case they need to be purged), and the total
 // amount of allocated memory (in case this forces a purge). When memory usage
 // reaches the limit, the manager purges the LRU memory.
 //
 // When notified of memory pressure, the manager either purges the LRU memory --
 // if the pressure is moderate -- or all discardable memory if the pressure is
 // critical.
+//
+// When notified that idle, the manager purges memory not used since the hard

[willchan no longer on Chromium, 2014/07/07 22:28:08]

Fix comment not to mention idle, but requested to reduce memory? Or just delete
this comment since the ReduceMemoryUsage() function already describes it well.

[reveman, 2014/07/07 23:49:03]

Done.

+// memory limit cutoff.
 class BASE_EXPORT_PRIVATE DiscardableMemoryManager {
  public:
   typedef DiscardableMemoryManagerAllocation Allocation;
 
   DiscardableMemoryManager(size_t memory_limit,
-                           size_t bytes_to_keep_under_moderate_pressure);
-  ~DiscardableMemoryManager();
+                           size_t soft_memory_limit,
+                           size_t bytes_to_keep_under_moderate_pressure,
+                           TimeDelta hard_memory_limit_expiration_time);
+  virtual ~DiscardableMemoryManager();
 
   // Call this to register memory pressure listener. Must be called on a thread
   // with a MessageLoop current.
   void RegisterMemoryPressureListener();
 
   // Call this to unregister memory pressure listener.
   void UnregisterMemoryPressureListener();
 
   // The maximum number of bytes of memory that may be allocated before we force
-  // a purge. If this amount is zero, it is interpreted as having no limit at
-  // all.
+  // a purge.
   void SetMemoryLimit(size_t bytes);
 
+  // The number of bytes of memory that may be allocated but unused for the hard
+  // limit expiration time without getting purged.
+  void SetSoftMemoryLimit(size_t bytes);
+
   // Sets the amount of memory to keep when we're under moderate pressure.
   void SetBytesToKeepUnderModeratePressure(size_t bytes);
 
+  // Sets the memory usage cutoff time for hard memory limit.
+  void SetHardMemoryLimitExpirationTime(
+      TimeDelta hard_memory_limit_expiration_time);
+
+  // This will attempt to reduce memory footprint until within soft memory
+  // limit. Returns true if there's no need to call this again until allocations
+  // have been used.
+  bool ReduceMemoryUsage();
+
   // Adds the given allocation to the manager's collection.
   void Register(Allocation* allocation, size_t bytes);
 
   // Removes the given allocation from the manager's collection.
   void Unregister(Allocation* allocation);
 
   // Returns false if an error occurred. Otherwise, returns true and sets
   // |purged| to indicate whether or not allocation has been purged since last
   // use.
   bool AcquireLock(Allocation* allocation, bool* purged);
@@ skipping 16 matching lines @@
   // Returns total amount of allocated discardable memory. This should only be
   // used by tests.
   size_t GetBytesAllocatedForTest() const;
 
  private:
   struct AllocationInfo {
     explicit AllocationInfo(size_t bytes) : bytes(bytes), purgable(false) {}
 
     const size_t bytes;
     bool purgable;
+    TimeTicks last_usage;
   };
   typedef HashingMRUCache<Allocation*, AllocationInfo> AllocationMap;
 
   // This can be called as a hint that the system is under memory pressure.
   void OnMemoryPressure(
       MemoryPressureListener::MemoryPressureLevel pressure_level);
 
-  // Purges memory until usage is within
+  // Purges memory until usage is less or equal to
   // |bytes_to_keep_under_moderate_pressure_|.
-  void Purge();
+  void PurgeUntilWithinBytesToKeepUnderModeratePressure();
 
-  // Purges least recently used memory until usage is less or equal to |limit|.
+  // Purges memory not used since |hard_memory_limit_expiration_time_| before
+  // "right now" until usage is less or equal to |soft_memory_limit_|.
+  // Returns true if total amount of memory is less or equal to soft memory
+  // limit.
+  bool PurgeIfNotUsedSinceHardLimitCutoffUntilWithinSoftMemoryLimit();
+
+  // Purges memory that has not been used since |timestamp| until usage is less
+  // or equal to |limit|.
   // Caller must acquire |lock_| prior to calling this function.
-  void PurgeLRUWithLockAcquiredUntilUsageIsWithin(size_t limit);
-
-  // Ensures that we don't allocate beyond our memory limit. Caller must acquire
-  // |lock_| prior to calling this function.
-  void EnforcePolicyWithLockAcquired();
+  void PurgeIfNotUsedSinceTimestampUntilUsageIsWithinLimitWithLockAcquired(
+      TimeTicks timestamp,
+      size_t limit);
 
   // Called when a change to |bytes_allocated_| has been made.
-  void BytesAllocatedChanged() const;
+  void BytesAllocatedChanged(size_t new_bytes_allocated) const;
+
+  // Virtual for tests.
+  virtual TimeTicks Now() const;
 
   // Needs to be held when accessing members.
   mutable Lock lock_;
 
   // A MRU cache of all allocated bits of memory. Used for purging.
   AllocationMap allocations_;
 
   // The total amount of allocated memory.
   size_t bytes_allocated_;
 
   // The maximum number of bytes of memory that may be allocated.
   size_t memory_limit_;
 
+  // The number of bytes of memory that may be allocated but not used for
+  // |hard_memory_limit_expiration_time_| amount of time when receiving an idle
+  // notification.
+  size_t soft_memory_limit_;
+
   // Under moderate memory pressure, we will purge memory until usage is within
   // this limit.
   size_t bytes_to_keep_under_moderate_pressure_;
 
   // Allows us to be respond when the system reports that it is under memory
   // pressure.
   scoped_ptr<MemoryPressureListener> memory_pressure_listener_;
 
+  // Amount of time it takes for an allocation to become affected by
+  // |soft_memory_limit_|.
+  TimeDelta hard_memory_limit_expiration_time_;
+
   DISALLOW_COPY_AND_ASSIGN(DiscardableMemoryManager);
 };
 
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_MEMORY_DISCARDABLE_MEMORY_MANAGER_H_