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 #if defined(COMPILER_GCC)
  42 namespace BASE_HASH_NAMESPACE {
  43 template <>
  44 struct hash<base::internal::DiscardableMemoryManagerAllocation*> {
  45   size_t operator()(
  46       base::internal::DiscardableMemoryManagerAllocation* ptr) const {
  47     return hash<size_t>()(reinterpret_cast<size_t>(ptr));
  48   }
  49 };
  50 }  // namespace BASE_HASH_NAMESPACE
  51 #endif  // COMPILER
  52
  53 namespace base {
  54 namespace internal {
  55
  56 // The DiscardableMemoryManager manages a collection of
  57 // DiscardableMemoryManagerAllocation instances. It is used on platforms that
  58 // need some level of userspace control over discardable memory. It keeps track
  59 // of all allocation instances (in case they need to be purged), and the total
  60 // amount of allocated memory (in case this forces a purge). When memory usage
  61 // reaches the limit, the manager purges the LRU memory.
  62 class BASE_EXPORT_PRIVATE DiscardableMemoryManager {
  63  public:
  64   typedef DiscardableMemoryManagerAllocation Allocation;
  65
  66   DiscardableMemoryManager(size_t memory_limit,
  67                            size_t soft_memory_limit,
  68                            TimeDelta hard_memory_limit_expiration_time);
  69   virtual ~DiscardableMemoryManager();
  70
  71   // The maximum number of bytes of memory that may be allocated before we force
  72   // a purge.
  73   void SetMemoryLimit(size_t bytes);
  74
  75   // The number of bytes of memory that may be allocated but unused for the hard
  76   // limit expiration time without getting purged.
  77   void SetSoftMemoryLimit(size_t bytes);
  78
  79   // Sets the memory usage cutoff time for hard memory limit.
  80   void SetHardMemoryLimitExpirationTime(
  81       TimeDelta hard_memory_limit_expiration_time);
  82
  83   // This will attempt to reduce memory footprint until within soft memory
  84   // limit. Returns true if there's no need to call this again until allocations
  85   // have been used.
  86   bool ReduceMemoryUsage();
  87
  88   // This can be called to attempt to reduce memory footprint until within
  89   // limit for bytes to keep under moderate pressure.
  90   void ReduceMemoryUsageUntilWithinLimit(size_t bytes);
  91
  92   // Adds the given allocation to the manager's collection.
  93   void Register(Allocation* allocation, size_t bytes);
  94
  95   // Removes the given allocation from the manager's collection.
  96   void Unregister(Allocation* allocation);
  97
  98   // Returns false if an error occurred. Otherwise, returns true and sets
  99   // |purged| to indicate whether or not allocation has been purged since last
 100   // use.
 101   bool AcquireLock(Allocation* allocation, bool* purged);
 102
 103   // Release a previously acquired lock on allocation. This allows the manager
 104   // to purge it if necessary.
 105   void ReleaseLock(Allocation* allocation);
 106
 107   // Purges all discardable memory.
 108   void PurgeAll();
 109
 110   // Returns true if allocation has been added to the manager's collection. This
 111   // should only be used by tests.
 112   bool IsRegisteredForTest(Allocation* allocation) const;
 113
 114   // Returns true if allocation can be purged. This should only be used by
 115   // tests.
 116   bool CanBePurgedForTest(Allocation* allocation) const;
 117
 118   // Returns total amount of allocated discardable memory. This should only be
 119   // used by tests.
 120   size_t GetBytesAllocatedForTest() const;
 121
 122  private:
 123   struct AllocationInfo {
 124     explicit AllocationInfo(size_t bytes) : bytes(bytes), purgable(false) {}
 125
 126     const size_t bytes;
 127     bool purgable;
 128     TimeTicks last_usage;
 129   };
 130   typedef HashingMRUCache<Allocation*, AllocationInfo> AllocationMap;
 131
 132   // Purges memory not used since |hard_memory_limit_expiration_time_| before
 133   // "right now" until usage is less or equal to |soft_memory_limit_|.
 134   // Returns true if total amount of memory is less or equal to soft memory
 135   // limit.
 136   bool PurgeIfNotUsedSinceHardLimitCutoffUntilWithinSoftMemoryLimit();
 137
 138   // Purges memory that has not been used since |timestamp| until usage is less
 139   // or equal to |limit|.
 140   // Caller must acquire |lock_| prior to calling this function.
 141   void PurgeIfNotUsedSinceTimestampUntilUsageIsWithinLimitWithLockAcquired(
 142       TimeTicks timestamp,
 143       size_t limit);
 144
 145   // Called when a change to |bytes_allocated_| has been made.
 146   void BytesAllocatedChanged(size_t new_bytes_allocated) const;
 147
 148   // Virtual for tests.
 149   virtual TimeTicks Now() const;
 150
 151   // Needs to be held when accessing members.
 152   mutable Lock lock_;
 153
 154   // A MRU cache of all allocated bits of memory. Used for purging.
 155   AllocationMap allocations_;
 156
 157   // The total amount of allocated memory.
 158   size_t bytes_allocated_;
 159
 160   // The maximum number of bytes of memory that may be allocated.
 161   size_t memory_limit_;
 162
 163   // The number of bytes of memory that may be allocated but not used for
 164   // |hard_memory_limit_expiration_time_| amount of time when receiving an idle
 165   // notification.
 166   size_t soft_memory_limit_;
 167
 168   // Amount of time it takes for an allocation to become affected by
 169   // |soft_memory_limit_|.
 170   TimeDelta hard_memory_limit_expiration_time_;
 171
 172   DISALLOW_COPY_AND_ASSIGN(DiscardableMemoryManager);
 173 };
 174
 175 }  // namespace internal
 176 }  // namespace base
 177
 178 #endif  // BASE_MEMORY_DISCARDABLE_MEMORY_MANAGER_H_