Added memory pressure monitor for linux.

base/memory/memory_pressure_monitor_linux.h

Index: base/memory/memory_pressure_monitor_linux.h
diff --git a/base/memory/memory_pressure_monitor_chromeos.h b/base/memory/memory_pressure_monitor_linux.h
similarity index 85%
copy from base/memory/memory_pressure_monitor_chromeos.h
copy to base/memory/memory_pressure_monitor_linux.h
index ff8992a56314ae33b29bac7dc4c40c20f6af42b6..bb6486d9ad44be91dbdc829947487ed2a822ac21 100644
--- a/base/memory/memory_pressure_monitor_chromeos.h
+++ b/base/memory/memory_pressure_monitor_linux.h
@@ -1,12 +1,11 @@
-// 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"
@@ -15,7 +14,7 @@
 #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;
 
@@ -50,7 +49,7 @@ class BASE_EXPORT MemoryPressureMonitor : public base::MemoryPressureMonitor {
     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
@@ -59,8 +58,8 @@ class BASE_EXPORT MemoryPressureMonitor : public base::MemoryPressureMonitor {
   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.
@@ -101,19 +100,12 @@ class BASE_EXPORT MemoryPressureMonitor : public base::MemoryPressureMonitor {
   // 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_