Add UMA stats to get the quality of service of memory pressure handling scheme in ChromeOS.

base/chromeos/memory_pressure_observer_chromeos.cc

 // 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.
 
 #include "base/chromeos/memory_pressure_observer_chromeos.h"
 
 #include "base/message_loop/message_loop.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/process/process_metrics.h"
 #include "base/time/time.h"
 
 namespace base {
 
 namespace {
 
 // The time between memory pressure checks. While under critical pressure, this
 // is also the timer to repeat cleanup attempts.
 const int kMemoryPressureIntervalMs = 1000;
 
 // The time which should pass between two moderate memory pressure calls.
 const int kModerateMemoryPressureCooldownMs = 10000;
 
 // Number of event polls before the next moderate pressure event can be sent.
 const int kModerateMemoryPressureCooldown =
     kModerateMemoryPressureCooldownMs / kMemoryPressureIntervalMs;
 
 // Threshold constants to emit pressure events.
 const int kNormalMemoryPressureModerateThresholdPercent = 60;
 const int kNormalMemoryPressureCriticalThresholdPercent = 90;
 const int kAggressiveMemoryPressureModerateThresholdPercent = 35;
 const int kAggressiveMemoryPressureCriticalThresholdPercent = 70;
 
+// Number of memory pressure levels. Should update this value if more memory
+// pressure level is introduced in MemoryPressureListener::MemoryPressureLevel.

[Mr4D (OOO till 08-26), 2015/02/04 00:11:19]

... if more memory pressure levels are introduced ...

Looking at the constants, there is a -1 .. 2. I think it would be a good idea to
map the pressure values to a new enum and store that instead (e.g. like
UMAMemoryPressureLevel). The new enum could then also have something like a
UMA_MEMORY_PRESSURE_MAX value which denotes the upper limit which is cleaner
than this.

+const int kNumMemoryPressureLevels = 3;
+
 // Converts a |MemoryPressureThreshold| value into a used memory percentage for
 // the moderate pressure event.
 int GetModerateMemoryThresholdInPercent(
     MemoryPressureObserverChromeOS::MemoryPressureThresholds thresholds) {
   return thresholds == MemoryPressureObserverChromeOS::
                            THRESHOLD_AGGRESSIVE_CACHE_DISCARD ||
          thresholds == MemoryPressureObserverChromeOS::THRESHOLD_AGGRESSIVE
              ? kAggressiveMemoryPressureModerateThresholdPercent
              : kNormalMemoryPressureModerateThresholdPercent;
 }
 
 // Converts a |MemoryPressureThreshold| value into a used memory percentage for
 // the critical pressure event.
 int GetCriticalMemoryThresholdInPercent(
     MemoryPressureObserverChromeOS::MemoryPressureThresholds thresholds) {
   return thresholds == MemoryPressureObserverChromeOS::
                            THRESHOLD_AGGRESSIVE_TAB_DISCARD ||
          thresholds == MemoryPressureObserverChromeOS::THRESHOLD_AGGRESSIVE
              ? kAggressiveMemoryPressureCriticalThresholdPercent
              : kNormalMemoryPressureCriticalThresholdPercent;
 }
 
+// Record UMA histogram statistics for the current memory pressure level.
+void RecordMemoryStatistics(
+    MemoryPressureListener::MemoryPressureLevel memory_pressure_level) {
+  UMA_HISTOGRAM_ENUMERATION("ChromeOS.MemoryPressureLevel",
+                            memory_pressure_level, kNumMemoryPressureLevels);
+}
+
 // Converts free percent of memory into a memory pressure value.
 MemoryPressureListener::MemoryPressureLevel GetMemoryPressureLevelFromFillLevel(
     int actual_fill_level,
     int moderate_threshold,
     int critical_threshold) {
   if (actual_fill_level < moderate_threshold)
     return MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE;
   return actual_fill_level < critical_threshold
              ? MemoryPressureListener::MEMORY_PRESSURE_LEVEL_MODERATE
              : MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL;
@@ skipping 21 matching lines @@
 void MemoryPressureObserverChromeOS::ScheduleEarlyCheck() {
   MessageLoop::current()->PostTask(
       FROM_HERE,
       Bind(&MemoryPressureObserverChromeOS::CheckMemoryPressure,
            weak_ptr_factory_.GetWeakPtr()));
 }
 
 void MemoryPressureObserverChromeOS::StartObserving() {
   timer_.Start(FROM_HERE,
                TimeDelta::FromMilliseconds(kMemoryPressureIntervalMs),
-               Bind(&MemoryPressureObserverChromeOS::CheckMemoryPressure,
+               Bind(&MemoryPressureObserverChromeOS::
+                        CheckMemoryPressureAndRecordStatistics,
                     weak_ptr_factory_.GetWeakPtr()));
 }
 
 void MemoryPressureObserverChromeOS::StopObserving() {
   // If StartObserving failed, StopObserving will still get called.
   timer_.Stop();
 }
 
+void MemoryPressureObserverChromeOS::CheckMemoryPressureAndRecordStatistics() {
+  CheckMemoryPressure();
+  RecordMemoryStatistics(current_memory_pressure_level_);

[Mr4D (OOO till 08-26), 2015/02/04 00:11:19]

In this case you can pull the content of the function into this function and add
a switch statement to convert the MemoryPressureLevel into a
UMAMemoryPressureLevel here. I would say that there is no need to create a
function with a single call which gets only called from one place.

+}
+
 void MemoryPressureObserverChromeOS::CheckMemoryPressure() {
   MemoryPressureListener::MemoryPressureLevel old_pressure =
       current_memory_pressure_level_;
   current_memory_pressure_level_ =
       GetMemoryPressureLevelFromFillLevel(GetUsedMemoryInPercent(),
                                           moderate_pressure_threshold_percent_,
                                           critical_pressure_threshold_percent_);
   // In case there is no memory pressure we do not notify.
   if (current_memory_pressure_level_ ==
       MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE) {
@@ skipping 54 matching lines @@
   // Available memory is the sum of free, swap and easy reclaimable memory.
   int available_memory =
       info.free + info.swap_free / kSwapWeight + file_memory;
 
   DCHECK(available_memory < total_memory);
   int percentage = ((total_memory - available_memory) * 100) / total_memory;
   return percentage;
 }
 
 }  // namespace base