Create base::win::MemoryPressureMonitor class.

base/win/memory_pressure_monitor.cc

Index: base/win/memory_pressure_monitor.cc
diff --git a/base/win/memory_pressure_monitor.cc b/base/win/memory_pressure_monitor.cc
new file mode 100644
index 0000000000000000000000000000000000000000..26571a151eb56635db307e978bd45842ba362332
--- /dev/null
+++ b/base/win/memory_pressure_monitor.cc
@@ -0,0 +1,220 @@
+// 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 "base/win/memory_pressure_monitor.h"
+
+#include <windows.h>
+
+#include "base/metrics/histogram_macros.h"
+#include "base/single_thread_task_runner.h"
+#include "base/thread_task_runner_handle.h"
+#include "base/time/time.h"
+
+namespace base {
+namespace win {
+
+namespace {
+
+// TODO(chrisha): Explore the following constants further with an experiment.
+
+// Moderate and critical memory load percentages. These percentages are applied
+// to both system memory and virtual memory.
+const int kModerateThresholdPercent = 60;
+const int kCriticalThresholdPercent = 95;
+
+// Absolute system memory requirements. These are modeled after typical renderer
+// sizes on Windows sytems (rounded to the neared 10 MB). These are applied to
+// system memory only. Intended as a lower bound to the above percentages on
+// low-end systems. Taken from the Memory.Renderer UMA statistic.
+const int kModerateThresholdMb = 300;  // 95th percentile renderer size.
+const int kCriticalThresholdMb = 60;   // 50th percentile renderer size.
+
+// Enumeration of UMA memory pressure levels. This needs to be kept in sync with
+// histograms.xml and the memory pressure levels defined in
+// MemoryPressureListener.
+enum MemoryPressureLevelUMA {
+  UMA_MEMORY_PRESSURE_LEVEL_NONE = 0,
+  UMA_MEMORY_PRESSURE_LEVEL_MODERATE = 1,
+  UMA_MEMORY_PRESSURE_LEVEL_CRITICAL = 2,
+  // This must be the last value in the enum.
+  UMA_MEMORY_PRESSURE_LEVEL_COUNT,
+};
+
+// Converts a memory pressure level to an UMA enumeration value.
+MemoryPressureLevelUMA MemoryPressureLevelToUmaEnumValue(
+    MemoryPressureListener::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_NONE;
+}
+
+}  // namespace
+
+// The following constants have been lifted from similar values in the ChromeOS
+// memory pressure monitor. The values were determined experimentally to ensure
+// sufficient responsiveness of the memory pressure subsystem, and minimal
+// overhead.
+const int MemoryPressureMonitor::kPollingIntervalMs = 1000;
+const int MemoryPressureMonitor::kModeratePressureCooldownMs = 10000;
+const int MemoryPressureMonitor::kModeratePressureCooldownCycles =
+    kModeratePressureCooldownMs / kPollingIntervalMs;
+
+MemoryPressureMonitor::MemoryPressureMonitor()
+    : current_memory_pressure_level_(
+          MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE),
+      moderate_pressure_repeat_count_(0),
+      weak_ptr_factory_(this) {
+  StartObserving();
+}
+
+MemoryPressureMonitor::~MemoryPressureMonitor() {
+  StopObserving();
+}
+
+void MemoryPressureMonitor::CheckMemoryPressureSoon() {
+  ThreadTaskRunnerHandle::Get()->PostTask(
+      FROM_HERE, Bind(&MemoryPressureMonitor::CheckMemoryPressure,
+                      weak_ptr_factory_.GetWeakPtr()));
+}
+
+MemoryPressureListener::MemoryPressureLevel
+MemoryPressureMonitor::GetCurrentPressureLevel() const {
+  return current_memory_pressure_level_;
+}
+
+void MemoryPressureMonitor::StartObserving() {
+  timer_.Start(FROM_HERE,
+               TimeDelta::FromMilliseconds(kPollingIntervalMs),
+               Bind(&MemoryPressureMonitor::
+                        CheckMemoryPressureAndRecordStatistics,
+                    weak_ptr_factory_.GetWeakPtr()));
+}
+
+void MemoryPressureMonitor::StopObserving() {
+  // If StartObserving failed, StopObserving will still get called.
+  timer_.Stop();
+  weak_ptr_factory_.InvalidateWeakPtrs();
+}
+
+void MemoryPressureMonitor::CheckMemoryPressure() {
+  // |notify| will be set to true if MemoryPressureListeners need to be
+  // notified of a memory pressure level state change.
+  bool notify = false;
+
+  base::AutoLock scoped_lock(lock_);
+  MemoryPressureLevel old_pressure = current_memory_pressure_level_;
+  current_memory_pressure_level_ = CalculateCurrentPressureLevel();
+
+  switch (current_memory_pressure_level_) {
+    case MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE:
+      break;
+
+    case MemoryPressureListener::MEMORY_PRESSURE_LEVEL_MODERATE: {
+      if (old_pressure != current_memory_pressure_level_) {
+        // This is a new transition to moderate pressure so notify.
+        moderate_pressure_repeat_count_ = 0;
+        notify = true;
+      } else {
+        // Already in moderate pressure, only notify if sustained over the
+        // cooldown period.
+        if (++moderate_pressure_repeat_count_ ==
+                kModeratePressureCooldownCycles) {
+          moderate_pressure_repeat_count_ = 0;
+          notify = true;
+        }
+      }
+    } break;
+
+    case MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL: {
+      // Always notify of critical pressure levels.
+      notify = true;
+    } break;
+  }
+
+  if (!notify)
+    return;
+
+  // Emit a notification of the current memory pressure level. This can only
+  // happen for moderate and critical pressure levels.
+  DCHECK_NE(MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE,
+            current_memory_pressure_level_);
+  MemoryPressureListener::NotifyMemoryPressure(current_memory_pressure_level_);

[grt (UTC plus 2), 2015/05/06 13:26:36]

this is called while the lock is held. is this needed?

[chrisha, 2015/05/06 15:09:57]

No longer applicable, lock removed.

+}
+
+void MemoryPressureMonitor::CheckMemoryPressureAndRecordStatistics() {
+  CheckMemoryPressure();
+
+  UMA_HISTOGRAM_ENUMERATION(
+      "Memory.PressureLevel",
+      MemoryPressureLevelToUmaEnumValue(current_memory_pressure_level_),
+      UMA_MEMORY_PRESSURE_LEVEL_COUNT);
+}
+
+MemoryPressureListener::MemoryPressureLevel
+MemoryPressureMonitor::CalculateCurrentPressureLevel() {
+  MEMORYSTATUSEX mem_status = {};
+  if (!GetSystemMemoryStatus(&mem_status))
+    return MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE;
+
+  // How much of the system's physical memory is actively being used by
+  // pages that are in the working sets of running programs.
+  int phys_load = mem_status.dwMemoryLoad;
+
+  // How much system memory is actively available for use right now, in MBs.
+  static DWORDLONG kMBBytes = 1024 * 1024;

[grt (UTC plus 2), 2015/05/06 13:26:36]

static const

[chrisha, 2015/05/06 15:09:57]

Done.

+  int phys_free = static_cast<int>(mem_status.ullAvailPhys / kMBBytes);
+
+  // Determine if the physical memory is under critical memory pressure.
+  if (phys_load > kCriticalThresholdPercent ||
+      phys_free < kCriticalThresholdMb) {
+    return MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL;
+  }
+
+  // On 64-bit platforms there is little value in calculating virtual memory
+  // pressure as it is at least 3 orders of magnitude larger than system

[grt (UTC plus 2), 2015/05/06 13:26:36]

is "system" the end of the sentence? please add a period.

[chrisha, 2015/05/06 15:09:57]

Done.

+#if !defined(ARCH_CPU_64_BITS)
+  // The virtual load of the current process. This is the percentage of virtual
+  // memory that is reserved or committed.
+  int virt_load = 100 - static_cast<int>(
+      100 * mem_status.ullAvailVirtual / mem_status.ullTotalVirtual);
+
+  // Determine if the virtual memory is under critical memory pressure.
+  if (virt_load > kCriticalThresholdPercent)
+    return MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL;
+
+  // Determine if the virtual memory is under moderate memory pressure.
+  if (virt_load > kModerateThresholdPercent)
+    return MemoryPressureListener::MEMORY_PRESSURE_LEVEL_MODERATE;
+#endif  // !defined(ARCH_CPU_64_BITS)
+
+  // Determine if the physical memory is under moderate memory pressure. This
+  // is done after the virtual memory checking to give that a chance to emit a
+  // critical pressure signal.
+  if (phys_load > kModerateThresholdPercent ||
+      phys_free < kModerateThresholdMb) {
+    return MemoryPressureListener::MEMORY_PRESSURE_LEVEL_MODERATE;
+  }
+
+  // No memory pressure was detected.
+  return MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE;
+}
+
+bool MemoryPressureMonitor::GetSystemMemoryStatus(
+    MEMORYSTATUSEX* mem_status) {
+  DCHECK(mem_status != nullptr);
+  mem_status->dwLength = sizeof(MEMORYSTATUSEX);
+  if (!::GlobalMemoryStatusEx(mem_status))
+    return false;
+  return true;
+}
+
+}  // namespace win
+}  // namespace base