Added memory pressure monitor for linux.

base/memory/memory_pressure_monitor_linux.h

-// Copyright 2014 The Chromium Authors. All rights reserved.
+// Copyright 2015 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_
+#ifndef BASE_MEMORY_MEMORY_PRESSURE_MONITOR_LINUX_H_
+#define BASE_MEMORY_MEMORY_PRESSURE_MONITOR_LINUX_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 {
+namespace nix {

[chrisha, 2015/07/24 13:25:46]

This doesn't feel like the right namespace.

In fact, we probably shouldn't even have this namespace, nor should we have a
MemoryPressureMonitor base class.

We've been wanting to clean this up for a while by removing the base class,
putting all header stuff in a single .h file, with OS differences hidden behind
precompiler conditionals. Then, common implementation bits (there might be some)
in a .cc, and OS specific implementation details in _win.cc, _mac.cc, _linux.cc,
_chromeos.cc. Look at base/process/process_info.* for an example.

[proberge, 2015/07/24 19:03:10]

Done, but note that my C++ is very rusty and that I most likely made several
design mistakes during the refactor. Please don't hold back on your comments.

 
 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.
 //
@@ skipping 12 matching lines @@
     // 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
   };

[chrisha, 2015/07/24 13:25:46]

This ends up copying a *lot* from the ChromeOS pressure monitor. It would be
simpler if there was one we could reuse from those two platforms, as they are
going to be mostly the same. Any slight differences in logic would be easily
hidden behind precompiler conditionals, no?

[proberge, 2015/07/24 19:03:10]

Removed some more logic. If we were to merge the two into one file (with
precompiler conditionals), wouldn't it be confusing for it to be in
memory_pressure_listener.cc ?

 
-  explicit MemoryPressureMonitor(MemoryPressureThresholds thresholds);
+  MemoryPressureMonitor();
   ~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;
+  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.
@@ skipping 20 matching lines @@
       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 nix
 }  // namespace base
 
-#endif  // BASE_MEMORY_MEMORY_PRESSURE_MONITOR_CHROMEOS_H_
+#endif  // BASE_MEMORY_MEMORY_PRESSURE_MONITOR_LINUX_H_