Added memory pressure monitor for linux.

base/memory/memory_pressure_monitor_chromeos.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_MEMORY_PRESSURE_MONITOR_CHROMEOS_H_
-#define BASE_MEMORY_MEMORY_PRESSURE_MONITOR_CHROMEOS_H_
-
-#include "base/base_export.h"
-#include "base/files/scoped_file.h"
-#include "base/gtest_prod_util.h"
-#include "base/macros.h"
-#include "base/memory/memory_pressure_listener.h"
-#include "base/memory/memory_pressure_monitor.h"
-#include "base/memory/weak_ptr.h"
-#include "base/timer/timer.h"
-
-namespace base {
-namespace chromeos {
-
-class TestMemoryPressureMonitor;
-
-////////////////////////////////////////////////////////////////////////////////
-// MemoryPressureMonitor
-//
-// A class to handle the observation of our free memory. It notifies the
-// MemoryPressureListener of memory fill level changes, so that it can take
-// action to reduce memory resources accordingly.
-//
-class BASE_EXPORT MemoryPressureMonitor : public base::MemoryPressureMonitor {
- public:
-  using GetUsedMemoryInPercentCallback = int (*)();
-
-  // There are two memory pressure events:
-  // MODERATE - which will mainly release caches.
-  // CRITICAL - which will discard tabs.
-  // The |MemoryPressureThresholds| enum selects the strategy of firing these
-  // events: A conservative strategy will keep as much content in memory as
-  // possible (causing the system to swap to zram) and an aggressive strategy
-  // will release memory earlier to avoid swapping.
-  enum MemoryPressureThresholds {
-    // Use the system default.
-    THRESHOLD_DEFAULT = 0,
-    // Try to keep as much content in memory as possible.
-    THRESHOLD_CONSERVATIVE = 1,
-    // Discard caches earlier, allowing to keep more tabs in memory.
-    THRESHOLD_AGGRESSIVE_CACHE_DISCARD = 2,
-    // Discard tabs earlier, allowing the system to get faster.
-    THRESHOLD_AGGRESSIVE_TAB_DISCARD = 3,
-    // Discard caches and tabs earlier to allow the system to be faster.
-    THRESHOLD_AGGRESSIVE = 4
-  };
-
-  explicit MemoryPressureMonitor(MemoryPressureThresholds thresholds);
-  ~MemoryPressureMonitor() override;
-
-  // Redo the memory pressure calculation soon and call again if a critical
-  // memory pressure prevails. Note that this call will trigger an asynchronous
-  // action which gives the system time to release memory back into the pool.
-  void ScheduleEarlyCheck();
-
-  // Get the current memory pressure level.
-  MemoryPressureListener::MemoryPressureLevel GetCurrentPressureLevel() const
-      override;
-
-  // Returns a type-casted version of the current memory pressure monitor. A
-  // simple wrapper to base::MemoryPressureMonitor::Get.
-  static MemoryPressureMonitor* Get();
-
- private:
-  friend TestMemoryPressureMonitor;
-  // Starts observing the memory fill level.
-  // Calls to StartObserving should always be matched with calls to
-  // StopObserving.
-  void StartObserving();
-
-  // Stop observing the memory fill level.
-  // May be safely called if StartObserving has not been called.
-  void StopObserving();
-
-  // The function which gets periodically called to check any changes in the
-  // memory pressure. It will report pressure changes as well as continuous
-  // critical pressure levels.
-  void CheckMemoryPressure();
-
-  // The function periodically checks the memory pressure changes and records
-  // the UMA histogram statistics for the current memory pressure level.
-  void CheckMemoryPressureAndRecordStatistics();
-
-  // Get the memory pressure in percent (virtual for testing).
-  virtual int GetUsedMemoryInPercent();
-
-  // The current memory pressure.
-  base::MemoryPressureListener::MemoryPressureLevel
-      current_memory_pressure_level_;
-
-  // A periodic timer to check for resource pressure changes. This will get
-  // replaced by a kernel triggered event system (see crbug.com/381196).
-  base::RepeatingTimer<MemoryPressureMonitor> timer_;
-
-  // To slow down the amount of moderate pressure event calls, this counter
-  // gets used to count the number of events since the last event occured.
-  int moderate_pressure_repeat_count_;
-
-  // The thresholds for moderate and critical pressure.
-  const int moderate_pressure_threshold_percent_;
-  const int critical_pressure_threshold_percent_;
-
-  // File descriptor used to detect low memory condition.
-  ScopedFD low_mem_file_;
-
-  base::WeakPtrFactory<MemoryPressureMonitor> weak_ptr_factory_;
-
-  DISALLOW_COPY_AND_ASSIGN(MemoryPressureMonitor);
-};
-
-}  // namespace chromeos
-}  // namespace base
-
-#endif  // BASE_MEMORY_MEMORY_PRESSURE_MONITOR_CHROMEOS_H_