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
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index 0000000000000000000000000000000000000000..f5601503d805096fe021ed46f33a81091df6ba57
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+++ b/base/win/memory_pressure_monitor.cc
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+// 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() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
+  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() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
+  timer_.Start(FROM_HERE,
+               TimeDelta::FromMilliseconds(kPollingIntervalMs),
+               Bind(&MemoryPressureMonitor::
+                        CheckMemoryPressureAndRecordStatistics,
+                    weak_ptr_factory_.GetWeakPtr()));
+}
+
+void MemoryPressureMonitor::StopObserving() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
+  // If StartObserving failed, StopObserving will still get called.
+  timer_.Stop();
+  weak_ptr_factory_.InvalidateWeakPtrs();
+}
+
+void MemoryPressureMonitor::CheckMemoryPressure() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
+  // Get the previous pressure level and update the current one.
+  MemoryPressureLevel old_pressure = current_memory_pressure_level_;
+  current_memory_pressure_level_ = CalculateCurrentPressureLevel();
+
+  // |notify| will be set to true if MemoryPressureListeners need to be
+  // notified of a memory pressure level state change.
+  bool notify = false;
+  switch (current_memory_pressure_level_) {
+    case MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE:
+      break;
+
+    case MemoryPressureListener::MEMORY_PRESSURE_LEVEL_MODERATE: {

[grt (UTC plus 2), 2015/05/06 16:31:09]

nit: remove unneeded braces here and on line 143

+      if (old_pressure != current_memory_pressure_level_) {
+        // This is a new transition to moderate pressure so notify.
+        moderate_pressure_repeat_count_ = 0;

[grt (UTC plus 2), 2015/05/06 16:31:09]

nit: it looks like you can move this assignment down to line 152 or so and
simplify this case to:
      // Notify if this is a new transition to moderate or if moderate
      // is sustained over the cooldown period.
      notify = (old_pressure != current_memory_pressure_level_ ||
                ++moderate_pressure_repeat_count_ ==
                    kModeratePressureCooldownCycles);
just tossing this out there; it's your call.

[chrisha, 2015/05/06 16:59:04]

I personally like the expanded statement as is because I find it easier to read
naturally, and it's possible to put breakpoints on them. YMMV.

(Plus the moderate_pressure_repeat_count_ = 0 still has to be done...)

[grt (UTC plus 2), 2015/05/06 18:14:57]

nod.
The first part of my suggestion was to move that down near the point of
notification around line 152. One questionable benefit of doing so is that it
puts the clearing of the count down by the notification itself where it's not
likely to accidentally get messed up if the logic around these parts ever
changes. If the invariant is "the count will always be zero when a notification
is sent," then it seems logical to me to put the zeroing close to the notifying.

Anyway, I'm fine the way it is, just clarifying my thinking.

+        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_);
+}
+
+void MemoryPressureMonitor::CheckMemoryPressureAndRecordStatistics() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
+  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 const DWORDLONG kMBBytes = 1024 * 1024;
+  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 memory.
+#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