Create MemoryPressureStatsCollector.

components/memory_pressure/memory_pressure_stats_collector.cc

Index: components/memory_pressure/memory_pressure_stats_collector.cc
diff --git a/components/memory_pressure/memory_pressure_stats_collector.cc b/components/memory_pressure/memory_pressure_stats_collector.cc
new file mode 100644
index 0000000000000000000000000000000000000000..e068665ee1e210eee4bdea28df99265a37b306de
--- /dev/null
+++ b/components/memory_pressure/memory_pressure_stats_collector.cc
@@ -0,0 +1,173 @@
+// 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.
+
+#include "components/memory_pressure/memory_pressure_stats_collector.h"
+
+#include "base/metrics/histogram.h"
+#include "base/time/default_tick_clock.h"
+
+namespace memory_pressure {
+
+namespace {
+
+using MemoryPressureLevel = MemoryPressureListener::MemoryPressureLevel;
+
+// A special memory pressure level that is used to indicate that the stats
+// collector has not yet been called.
+const MemoryPressureLevel MEMORY_PRESSURE_LEVEL_INVALID =
+    static_cast<MemoryPressureLevel>(
+        MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE - 1);
+
+// Converts a memory pressure level to an UMA enumeration value.
+MemoryPressureLevelUMA MemoryPressureLevelToUmaEnumValue(
+    MemoryPressureLevel level) {
+  switch (level) {
+    case MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE:
+      return UMA_MEMORY_PRESSURE_LEVEL_NONE;
+    case MemoryPressureListener::MEMORY_PRESSURE_LEVEL_MODERATE:
+      return UMA_MEMORY_PRESSURE_LEVEL_MODERATE;
+    case MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL:
+      return UMA_MEMORY_PRESSURE_LEVEL_CRITICAL;
+  }
+  NOTREACHED();
+  return UMA_MEMORY_PRESSURE_LEVEL_COUNT;
+}
+
+// Converts an UMA enumeration value to a memory pressure level.
+MemoryPressureLevel MemoryPressureLevelFromUmaEnumValue(
+    MemoryPressureLevelUMA level) {
+  switch (level) {
+    case UMA_MEMORY_PRESSURE_LEVEL_NONE:
+      return MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE;
+    case UMA_MEMORY_PRESSURE_LEVEL_MODERATE:
+      return MemoryPressureListener::MEMORY_PRESSURE_LEVEL_MODERATE;
+    case UMA_MEMORY_PRESSURE_LEVEL_CRITICAL:
+      return MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL;
+  }
+  NOTREACHED();
+  return MEMORY_PRESSURE_LEVEL_INVALID;
+}
+
+}  // namespace
+
+MemoryPressureStatsCollector::MemoryPressureStatsCollector()
+    : reporting_delegate_(new UmaReportingDelegate()),
+      tick_clock_(new base::DefaultTickClock()),
+      last_pressure_level_(MEMORY_PRESSURE_LEVEL_INVALID) {}
+
+void MemoryPressureStatsCollector::UpdateStatistics(
+    MemoryPressureLevel current_pressure_level) {
+  base::TimeTicks now = tick_clock_->NowTicks();
+
+  // Special case: first call to the collector. Observations have just started
+  // so there's nothing to report.
+  if (last_pressure_level_ == MEMORY_PRESSURE_LEVEL_INVALID) {
+    last_pressure_level_ = current_pressure_level;
+    last_update_time_ = now;
+    return;
+  }
+
+  // If the pressure level has transitioned then report this.
+  if (last_pressure_level_ != current_pressure_level) {
+    reporting_delegate_->ReportLevelChange(last_pressure_level_,
+                                           current_pressure_level);
+  }
+
+  // Increment the appropriate cumulative bucket.
+  int index = MemoryPressureLevelToUmaEnumValue(current_pressure_level);
+  base::TimeDelta time_since_update = now - last_update_time_;
+  unreported_cumulative_time_[index] += time_since_update;
+
+  // Update last pressure related state.
+  last_pressure_level_ = current_pressure_level;
+  last_update_time_ = now;
+
+  // Make reports about the amount of time spent cumulatively at each level.
+  for (size_t i = 0; i < arraysize(unreported_cumulative_time_); ++i) {
+    if (unreported_cumulative_time_[i].is_zero())
+      continue;
+    reporting_delegate_->ReportCumulativeTime(
+        MemoryPressureLevelFromUmaEnumValue(
+            static_cast<MemoryPressureLevelUMA>(i)),
+        &unreported_cumulative_time_[i]);
+  }
+}
+
+namespace {
+
+// Enumeration of UMA pressure level changes. This needs to be kept in sync
+// with histograms.xml and the memory pressure levels defined in
+// MemoryPressureListener.
+enum MemoryPressureLevelChangeUMA {
+  UMA_MEMORY_PRESSURE_LEVEL_CHANGE_NONE_TO_MODERATE = 0,
+  UMA_MEMORY_PRESSURE_LEVEL_CHANGE_NONE_TO_CRITICAL = 1,
+  UMA_MEMORY_PRESSURE_LEVEL_CHANGE_MODERATE_TO_CRITICAL = 2,
+  UMA_MEMORY_PRESSURE_LEVEL_CHANGE_CRITICAL_TO_MODERATE = 3,
+  UMA_MEMORY_PRESSURE_LEVEL_CHANGE_CRITICAL_TO_NONE = 4,
+  UMA_MEMORY_PRESSURE_LEVEL_CHANGE_MODERATE_TO_NONE = 5,
+  // This must be the last value in the enum.
+  UMA_MEMORY_PRESSURE_LEVEL_CHANGE_COUNT
+};
+
+// Converts a pressure state change to an UMA enumeration value.
+MemoryPressureLevelChangeUMA MemoryPressureLevelChangeToUmaEnumValue(
+    MemoryPressureLevel old_level,
+    MemoryPressureLevel new_level) {
+  switch (old_level) {
+    case MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE: {
+      if (new_level == MemoryPressureListener::MEMORY_PRESSURE_LEVEL_MODERATE)
+        return UMA_MEMORY_PRESSURE_LEVEL_CHANGE_NONE_TO_MODERATE;
+      if (new_level == MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL)
+        return UMA_MEMORY_PRESSURE_LEVEL_CHANGE_NONE_TO_CRITICAL;
+    }
+    case MemoryPressureListener::MEMORY_PRESSURE_LEVEL_MODERATE: {
+      if (new_level == MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE)
+        return UMA_MEMORY_PRESSURE_LEVEL_CHANGE_MODERATE_TO_NONE;
+      if (new_level == MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL)
+        return UMA_MEMORY_PRESSURE_LEVEL_CHANGE_MODERATE_TO_CRITICAL;
+    }
+    case MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL: {
+      if (new_level == MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE)
+        return UMA_MEMORY_PRESSURE_LEVEL_CHANGE_CRITICAL_TO_MODERATE;
+      if (new_level == MemoryPressureListener::MEMORY_PRESSURE_LEVEL_MODERATE)
+        return UMA_MEMORY_PRESSURE_LEVEL_CHANGE_CRITICAL_TO_MODERATE;
+    }
+  }
+  NOTREACHED();
+  return UMA_MEMORY_PRESSURE_LEVEL_CHANGE_COUNT;
+}
+
+}  // namespace
+
+void MemoryPressureStatsCollector::UmaReportingDelegate::ReportCumulativeTime(
+    MemoryPressureLevel pressure_level,
+    base::TimeDelta* time) {
+  // Extract the number of seconds and leave behind the milliseconds.
+  int64 seconds = time->InSeconds();
+  *time -= base::TimeDelta::FromSeconds(seconds);
+
+  // Increment the histogram for each second spent in the given state.
+  for (int64 i = 0; i < seconds; ++i) {
+    UMA_HISTOGRAM_ENUMERATION("Memory.PressureLevel",

[rkaplow, 2015/09/03 17:22:36]

alexei - is there a more efficient way to add N enums instead of just looping?
Since in this case N can be pretty large (up to thousands)

[rkaplow, 2015/09/03 17:22:36]

We're already writing to this in other places eg.
base/memory/memory_pressure_monitor_win.cc.
How does this interact right now?

[chrisha, 2015/09/03 20:00:45]

Turns out there is now! AddCount! But it's not exposed via any of the macros.
I've rewritten this to use the histograms directly, but maybe we should add a
UMA_HISTOGRAM_ENUMERATION_WITH_COUNT macro in histograms.h?

[chrisha, 2015/09/03 20:00:45]

No interaction at all. This component will replace the base implementation
entirely when it's ready. I'll switch them over wholesale at that point, and rip
out the base implementation. None of this component code is currently shipped
with Chrome.

[rkaplow, 2015/09/03 22:15:07]

Agreed. This is fine for now. Maybe add a TODO to change it in the future (to
your best guess of what the name would be kind of thing)

[rkaplow, 2015/09/03 22:15:07]

AH right - missed that this wasn't hooked up yet.

+                              MemoryPressureLevelToUmaEnumValue(pressure_level),
+                              UMA_MEMORY_PRESSURE_LEVEL_COUNT);
+#if defined(OS_CHROMEOS)
+    // Continue to emit the old metric on ChromeOS during the transition period.

[rkaplow, 2015/09/03 17:22:36]

describe a little more maybe how this is transitioning

[chrisha, 2015/09/03 20:00:45]

Actually, I've rethought this. When I switch to using the component I will
simultaneously deprecate the ChromeOS.MemoryPressureLevel histogram and refer
users to the standard Memory.PressureLevel one instead. At no point will I emit
both histograms.

Is this reasonable?

[rkaplow, 2015/09/03 22:15:07]

that sounds good.

+    UMA_HISTOGRAM_ENUMERATION("ChromeOS.MemoryPressureLevel",
+                              MemoryPressureLevelToUmaEnumValue(pressure_level),
+                              UMA_MEMORY_PRESSURE_LEVEL_COUNT);
+#endif
+  }
+}
+
+void MemoryPressureStatsCollector::UmaReportingDelegate::ReportLevelChange(
+    MemoryPressureLevel old_pressure_level,
+    MemoryPressureLevel new_pressure_level) {
+  UMA_HISTOGRAM_ENUMERATION("Memory.PressureLevelChange",
+                            MemoryPressureLevelChangeToUmaEnumValue(
+                                old_pressure_level, new_pressure_level),
+                            UMA_MEMORY_PRESSURE_LEVEL_CHANGE_COUNT);
+}
+
+}  // namespace memory_pressure