base/memory/discardable_memory_manager.h

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef BASE_MEMORY_DISCARDABLE_MEMORY_MANAGER_H_
   6 #define BASE_MEMORY_DISCARDABLE_MEMORY_MANAGER_H_
   7
   8 #include "base/base_export.h"
   9 #include "base/containers/hash_tables.h"
  10 #include "base/containers/mru_cache.h"
  11 #include "base/synchronization/lock.h"
  12 #include "base/time/time.h"
  13
  14 namespace base {
  15 namespace internal {
  16
  17 // This interface is used by the DiscardableMemoryManager class to provide some
  18 // level of userspace control over discardable memory allocations.
  19 class DiscardableMemoryManagerAllocation {
  20  public:
  21   // Allocate and acquire a lock that prevents the allocation from being purged
  22   // by the system. Returns true if memory was previously allocated and is still
  23   // resident.
  24   virtual bool AllocateAndAcquireLock() = 0;
  25
  26   // Release a previously acquired lock on the allocation so that it can be
  27   // purged by the system.
  28   virtual void ReleaseLock() = 0;
  29
  30   // Explicitly purge this allocation. It is illegal to call this while a lock
  31   // is acquired on the allocation.
  32   virtual void Purge() = 0;
  33
  34  protected:
  35   virtual ~DiscardableMemoryManagerAllocation() {}
  36 };
  37
  38 }  // namespace internal
  39 }  // namespace base
  40
  41 namespace base {
  42 namespace internal {
  43
  44 // The DiscardableMemoryManager manages a collection of
  45 // DiscardableMemoryManagerAllocation instances. It is used on platforms that
  46 // need some level of userspace control over discardable memory. It keeps track
  47 // of all allocation instances (in case they need to be purged), and the total
  48 // amount of allocated memory (in case this forces a purge). When memory usage
  49 // reaches the limit, the manager purges the LRU memory.
  50 class BASE_EXPORT_PRIVATE DiscardableMemoryManager {
  51  public:
  52   typedef DiscardableMemoryManagerAllocation Allocation;
  53
  54   DiscardableMemoryManager(size_t memory_limit,
  55                            size_t soft_memory_limit,
  56                            TimeDelta hard_memory_limit_expiration_time);
  57   virtual ~DiscardableMemoryManager();
  58
  59   // The maximum number of bytes of memory that may be allocated before we force
  60   // a purge.
  61   void SetMemoryLimit(size_t bytes);
  62
  63   // The number of bytes of memory that may be allocated but unused for the hard
  64   // limit expiration time without getting purged.
  65   void SetSoftMemoryLimit(size_t bytes);
  66
  67   // Sets the memory usage cutoff time for hard memory limit.
  68   void SetHardMemoryLimitExpirationTime(
  69       TimeDelta hard_memory_limit_expiration_time);
  70
  71   // This will attempt to reduce memory footprint until within soft memory
  72   // limit. Returns true if there's no need to call this again until allocations
  73   // have been used.
  74   bool ReduceMemoryUsage();
  75
  76   // This can be called to attempt to reduce memory footprint until within
  77   // limit for bytes to keep under moderate pressure.
  78   void ReduceMemoryUsageUntilWithinLimit(size_t bytes);
  79
  80   // Adds the given allocation to the manager's collection.
  81   void Register(Allocation* allocation, size_t bytes);
  82
  83   // Removes the given allocation from the manager's collection.
  84   void Unregister(Allocation* allocation);
  85
  86   // Returns false if an error occurred. Otherwise, returns true and sets
  87   // |purged| to indicate whether or not allocation has been purged since last
  88   // use.
  89   bool AcquireLock(Allocation* allocation, bool* purged);
  90
  91   // Release a previously acquired lock on allocation. This allows the manager
  92   // to purge it if necessary.
  93   void ReleaseLock(Allocation* allocation);
  94
  95   // Purges all discardable memory.
  96   void PurgeAll();
  97
  98   // Returns true if allocation has been added to the manager's collection. This
  99   // should only be used by tests.
 100   bool IsRegisteredForTest(Allocation* allocation) const;
 101
 102   // Returns true if allocation can be purged. This should only be used by
 103   // tests.
 104   bool CanBePurgedForTest(Allocation* allocation) const;
 105
 106   // Returns total amount of allocated discardable memory. This should only be
 107   // used by tests.
 108   size_t GetBytesAllocatedForTest() const;
 109
 110  private:
 111   struct AllocationInfo {
 112     explicit AllocationInfo(size_t bytes) : bytes(bytes), purgable(false) {}
 113
 114     const size_t bytes;
 115     bool purgable;
 116     TimeTicks last_usage;
 117   };
 118   typedef HashingMRUCache<Allocation*, AllocationInfo> AllocationMap;
 119
 120   // Purges memory not used since |hard_memory_limit_expiration_time_| before
 121   // "right now" until usage is less or equal to |soft_memory_limit_|.
 122   // Returns true if total amount of memory is less or equal to soft memory
 123   // limit.
 124   bool PurgeIfNotUsedSinceHardLimitCutoffUntilWithinSoftMemoryLimit();
 125
 126   // Purges memory that has not been used since |timestamp| until usage is less
 127   // or equal to |limit|.
 128   // Caller must acquire |lock_| prior to calling this function.
 129   void PurgeIfNotUsedSinceTimestampUntilUsageIsWithinLimitWithLockAcquired(
 130       TimeTicks timestamp,
 131       size_t limit);
 132
 133   // Called when a change to |bytes_allocated_| has been made.
 134   void BytesAllocatedChanged(size_t new_bytes_allocated) const;
 135
 136   // Virtual for tests.
 137   virtual TimeTicks Now() const;
 138
 139   // Needs to be held when accessing members.
 140   mutable Lock lock_;
 141
 142   // A MRU cache of all allocated bits of memory. Used for purging.
 143   AllocationMap allocations_;
 144
 145   // The total amount of allocated memory.
 146   size_t bytes_allocated_;
 147
 148   // The maximum number of bytes of memory that may be allocated.
 149   size_t memory_limit_;
 150
 151   // The number of bytes of memory that may be allocated but not used for
 152   // |hard_memory_limit_expiration_time_| amount of time when receiving an idle
 153   // notification.
 154   size_t soft_memory_limit_;
 155
 156   // Amount of time it takes for an allocation to become affected by
 157   // |soft_memory_limit_|.
 158   TimeDelta hard_memory_limit_expiration_time_;
 159
 160   DISALLOW_COPY_AND_ASSIGN(DiscardableMemoryManager);
 161 };
 162
 163 }  // namespace internal
 164 }  // namespace base
 165
 166 #endif  // BASE_MEMORY_DISCARDABLE_MEMORY_MANAGER_H_