[Mac] Collect real-time memory pressure stats, in an energy-efficient way

base/memory/memory_pressure_monitor_mac_unittest.cc

Index: base/memory/memory_pressure_monitor_mac_unittest.cc
diff --git a/base/memory/memory_pressure_monitor_mac_unittest.cc b/base/memory/memory_pressure_monitor_mac_unittest.cc
index b7c29cd13cb59025ae230c7007a937f81badc456..9d251f011e9959d1ea5f52482546e382155e993e 100644
--- a/base/memory/memory_pressure_monitor_mac_unittest.cc
+++ b/base/memory/memory_pressure_monitor_mac_unittest.cc
@@ -4,7 +4,11 @@
 
 #include "base/memory/memory_pressure_monitor_mac.h"
 
+#include "base/bind.h"
+#include "base/bind_helpers.h"
+#include "base/mac/scoped_cftyperef.h"
 #include "base/macros.h"
+#include "base/test/histogram_tester.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace base {
@@ -12,43 +16,87 @@ namespace mac {
 
 class TestMemoryPressureMonitor : public MemoryPressureMonitor {
  public:
-  using MemoryPressureMonitor::MemoryPressureLevelForMacMemoryPressure;
+  using MemoryPressureMonitor::MemoryPressureLevelForMacMemoryPressureLevel;
+
+  // A HistogramTester for verifying correct UMA stat generation.
+  base::HistogramTester tester;
 
   TestMemoryPressureMonitor() { }
 
+  // Clears the next run loop update time so that the next pass of the run
+  // loop checks the memory pressure level immediately. Normally there's a
+  // 5 second delay between pressure readings.
+  void ResetRunLoopUpdateTime() { next_run_loop_update_time_ = 0; }
+
+  // Access to the last-recorded memory pressure level.
+  MemoryPressureListener::MemoryPressureLevel LastPressureLevel() {
+    return last_pressure_level_;
+  }
+
+  // Sets the last UMA stat report time. Time spent in memory pressure is
+  // recorded in 5-second "ticks" from the last time statistics were recorded.
+  void SetLastStatisticReportTime(CFTimeInterval time) {
+    last_statistic_report_time_ = time;
+  }
+
+  // Sets the raw macOS memory pressure level read by the memory pressure
+  // monitor.
+  int macos_pressure_level_for_testing_;
+
+  // Exposes the UpdatePressureLevel() method for testing.
+  void UpdatePressureLevel() { MemoryPressureMonitor::UpdatePressureLevel(); }
+
+  // Returns the number of seconds left over from the last UMA tick
+  // calculation.
+  int SubTickSeconds() { return subtick_seconds_; }
+
+  // Returns the number of seconds per UMA tick.
+  static int GetSecondsPerUMATick() {
+    return MemoryPressureMonitor::GetSecondsPerUMATick();
+  }
+
  private:
   DISALLOW_COPY_AND_ASSIGN(TestMemoryPressureMonitor);
+
+  int GetMacMemoryPressureLevel() override {
+    return macos_pressure_level_for_testing_;
+  }
 };
 
 TEST(MacMemoryPressureMonitorTest, MemoryPressureFromMacMemoryPressure) {
-  EXPECT_EQ(MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE,
-            TestMemoryPressureMonitor::
-                MemoryPressureLevelForMacMemoryPressure(
-                    DISPATCH_MEMORYPRESSURE_NORMAL));
-  EXPECT_EQ(MemoryPressureListener::MEMORY_PRESSURE_LEVEL_MODERATE,
-            TestMemoryPressureMonitor::
-                MemoryPressureLevelForMacMemoryPressure(
-                    DISPATCH_MEMORYPRESSURE_WARN));
-  EXPECT_EQ(MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL,
-            TestMemoryPressureMonitor::
-                MemoryPressureLevelForMacMemoryPressure(
-                    DISPATCH_MEMORYPRESSURE_CRITICAL));
-  EXPECT_EQ(MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE,
-            TestMemoryPressureMonitor::
-                MemoryPressureLevelForMacMemoryPressure(0));
-  EXPECT_EQ(MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE,
-            TestMemoryPressureMonitor::
-                MemoryPressureLevelForMacMemoryPressure(3));
-  EXPECT_EQ(MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE,
-            TestMemoryPressureMonitor::
-                MemoryPressureLevelForMacMemoryPressure(5));
-  EXPECT_EQ(MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE,
-            TestMemoryPressureMonitor::
-                MemoryPressureLevelForMacMemoryPressure(-1));
+  EXPECT_EQ(
+      MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE,
+      TestMemoryPressureMonitor::MemoryPressureLevelForMacMemoryPressureLevel(
+          DISPATCH_MEMORYPRESSURE_NORMAL));
+  EXPECT_EQ(
+      MemoryPressureListener::MEMORY_PRESSURE_LEVEL_MODERATE,
+      TestMemoryPressureMonitor::MemoryPressureLevelForMacMemoryPressureLevel(
+          DISPATCH_MEMORYPRESSURE_WARN));
+  EXPECT_EQ(
+      MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL,
+      TestMemoryPressureMonitor::MemoryPressureLevelForMacMemoryPressureLevel(
+          DISPATCH_MEMORYPRESSURE_CRITICAL));
+  EXPECT_EQ(
+      MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE,
+      TestMemoryPressureMonitor::MemoryPressureLevelForMacMemoryPressureLevel(
+          0));
+  EXPECT_EQ(
+      MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE,
+      TestMemoryPressureMonitor::MemoryPressureLevelForMacMemoryPressureLevel(
+          3));
+  EXPECT_EQ(
+      MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE,
+      TestMemoryPressureMonitor::MemoryPressureLevelForMacMemoryPressureLevel(
+          5));
+  EXPECT_EQ(
+      MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE,
+      TestMemoryPressureMonitor::MemoryPressureLevelForMacMemoryPressureLevel(
+          -1));
 }
 
 TEST(MacMemoryPressureMonitorTest, CurrentMemoryPressure) {
   TestMemoryPressureMonitor monitor;
+
   MemoryPressureListener::MemoryPressureLevel memory_pressure =
       monitor.GetCurrentPressureLevel();
   EXPECT_TRUE(memory_pressure ==
@@ -59,5 +107,124 @@ TEST(MacMemoryPressureMonitorTest, CurrentMemoryPressure) {
                   MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL);
 }
 
+TEST(MacMemoryPressureMonitorTest, MemoryPressureConversion) {
+  TestMemoryPressureMonitor monitor;
+
+  monitor.macos_pressure_level_for_testing_ = DISPATCH_MEMORYPRESSURE_NORMAL;
+  MemoryPressureListener::MemoryPressureLevel memory_pressure =
+      monitor.GetCurrentPressureLevel();
+  EXPECT_EQ(memory_pressure,
+            MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE);
+
+  monitor.macos_pressure_level_for_testing_ = DISPATCH_MEMORYPRESSURE_WARN;
+  memory_pressure = monitor.GetCurrentPressureLevel();
+  EXPECT_EQ(memory_pressure,
+            MemoryPressureListener::MEMORY_PRESSURE_LEVEL_MODERATE);
+
+  monitor.macos_pressure_level_for_testing_ = DISPATCH_MEMORYPRESSURE_CRITICAL;
+  memory_pressure = monitor.GetCurrentPressureLevel();
+  EXPECT_EQ(memory_pressure,
+            MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL);
+}
+
+TEST(MacMemoryPressureMonitorTest, MemoryPressureRunLoopChecking) {
+  TestMemoryPressureMonitor monitor;
+
+  // To test grabbing the memory presure at the end of the run loop, we have to
+  // run the run loop, but to do that the run loop needs a run loop source. Add
+  // a timer as the source. We know that the exit observer is attached to
+  // the kMessageLoopExclusiveRunLoopMode mode, so use that mode.
+  ScopedCFTypeRef<CFRunLoopTimerRef> timer_ref(CFRunLoopTimerCreate(
+      NULL, CFAbsoluteTimeGetCurrent() + 10, 0, 0, 0, nullptr, nullptr));
+  CFRunLoopAddTimer(CFRunLoopGetCurrent(), timer_ref,
+                    kMessageLoopExclusiveRunLoopMode);
+
+  monitor.macos_pressure_level_for_testing_ = DISPATCH_MEMORYPRESSURE_WARN;
+  monitor.ResetRunLoopUpdateTime();
+  CFRunLoopRunInMode(kMessageLoopExclusiveRunLoopMode, 0, true);
+  EXPECT_EQ(monitor.LastPressureLevel(),
+            MemoryPressureListener::MEMORY_PRESSURE_LEVEL_MODERATE);
+
+  monitor.macos_pressure_level_for_testing_ = DISPATCH_MEMORYPRESSURE_CRITICAL;
+  monitor.ResetRunLoopUpdateTime();
+  CFRunLoopRunInMode(kMessageLoopExclusiveRunLoopMode, 0, true);
+  EXPECT_EQ(monitor.LastPressureLevel(),
+            MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL);
+
+  monitor.macos_pressure_level_for_testing_ = DISPATCH_MEMORYPRESSURE_NORMAL;
+  monitor.ResetRunLoopUpdateTime();
+  CFRunLoopRunInMode(kMessageLoopExclusiveRunLoopMode, 0, true);
+  EXPECT_EQ(monitor.LastPressureLevel(),
+            MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE);
+
+  CFRunLoopRemoveTimer(CFRunLoopGetCurrent(), timer_ref,
+                       kMessageLoopExclusiveRunLoopMode);
+}
+
+TEST(MacMemoryPressureMonitorTest, RecordMemoryPressureStats) {
+  TestMemoryPressureMonitor monitor;
+  const char* kHistogram = "Memory.PressureLevel";
+  CFTimeInterval now = CFAbsoluteTimeGetCurrent();
+  const int seconds_per_tick =
+      TestMemoryPressureMonitor::GetSecondsPerUMATick();
+
+  // Set the initial pressure level.
+  monitor.macos_pressure_level_for_testing_ = DISPATCH_MEMORYPRESSURE_NORMAL;
+  // Incur one UMA tick of time (and include one extra second of elapsed time).
+  monitor.SetLastStatisticReportTime(now - (seconds_per_tick + 1));
+  monitor.UpdatePressureLevel();
+  monitor.tester.ExpectTotalCount(kHistogram, 1);
+  monitor.tester.ExpectBucketCount(kHistogram, 0, 1);
+  // The report time above included an extra second so there should be 1
+  // sub-tick second left over.
+  EXPECT_EQ(1, monitor.SubTickSeconds());
+
+  // Simulate sitting in normal pressure for 1 second less than 6 UMA tick
+  // seconds and then elevating to warning. With the left over sub-tick second
+  // from above, the total elapsed ticks should be an even 6 UMA ticks.
+  monitor.macos_pressure_level_for_testing_ = DISPATCH_MEMORYPRESSURE_WARN;
+  monitor.SetLastStatisticReportTime(now - (seconds_per_tick * 6 - 1));
+  monitor.UpdatePressureLevel();
+  monitor.tester.ExpectTotalCount(kHistogram, 7);
+  monitor.tester.ExpectBucketCount(kHistogram, 0, 7);
+  monitor.tester.ExpectBucketCount(kHistogram, 1, 0);
+  EXPECT_EQ(0, monitor.SubTickSeconds());
+
+  // Simulate sitting in warning pressure for 20 UMA ticks and 2 seconds, and
+  // then elevating to critical.
+  monitor.macos_pressure_level_for_testing_ = DISPATCH_MEMORYPRESSURE_CRITICAL;
+  monitor.SetLastStatisticReportTime(now - (20 * seconds_per_tick + 2));
+  monitor.UpdatePressureLevel();
+  monitor.tester.ExpectTotalCount(kHistogram, 27);
+  monitor.tester.ExpectBucketCount(kHistogram, 0, 7);
+  monitor.tester.ExpectBucketCount(kHistogram, 1, 20);
+  monitor.tester.ExpectBucketCount(kHistogram, 2, 0);
+  EXPECT_EQ(2, monitor.SubTickSeconds());

[lgrey, 2017/02/22 21:33:40]

I wonder if we should always be rounding up for consistency.

[shrike, 2017/02/22 23:56:25]

I think if we do, and if we get a lot of subtick_seconds_ (they could be
generated, for example, by other code calling GetCurrentPressureLevel() ), we
could end up mis-computing time spent in pressure levels. Currently we show
users in memory pressure something like 5% of the time, which is 3 seconds out
of every minute. It doesn't take many extra seconds per minute to skew that. I
don't know, maybe unrealistic, but I think we should leave it unless you see a
big problem with it.

[lgrey, 2017/02/23 15:49:29]

Nah, no problem. I guess the inaccuracy is baked in from quantizing to 5 seconds
and it's just a question of whether the old level is overcounted or the new
level.

+
+  // A quick update while critical - the stats should not budge because less
+  // than 1 tick of time has elapsed.
+  monitor.macos_pressure_level_for_testing_ = DISPATCH_MEMORYPRESSURE_CRITICAL;
+  monitor.SetLastStatisticReportTime(now - 1);
+  monitor.UpdatePressureLevel();
+  monitor.tester.ExpectTotalCount(kHistogram, 27);
+  monitor.tester.ExpectBucketCount(kHistogram, 0, 7);
+  monitor.tester.ExpectBucketCount(kHistogram, 1, 20);
+  monitor.tester.ExpectBucketCount(kHistogram, 2, 0);
+  EXPECT_EQ(3, monitor.SubTickSeconds());
+
+  // A quick change back to normal. Less than 1 tick of time has elapsed, but
+  // in this case the pressure level changed, so the critical bucket should
+  // get another sample (otherwise we could miss quick level changes).
+  monitor.macos_pressure_level_for_testing_ = DISPATCH_MEMORYPRESSURE_NORMAL;
+  monitor.SetLastStatisticReportTime(now - 1);
+  monitor.UpdatePressureLevel();
+  monitor.tester.ExpectTotalCount(kHistogram, 28);
+  monitor.tester.ExpectBucketCount(kHistogram, 0, 7);
+  monitor.tester.ExpectBucketCount(kHistogram, 1, 20);
+  monitor.tester.ExpectBucketCount(kHistogram, 2, 1);
+  // When less than 1 tick of time has elapsed but the pressure level changed,
+  // the subtick remainder gets zeroed out.
+  EXPECT_EQ(0, monitor.SubTickSeconds());
+}
 }  // namespace mac
 }  // namespace base