Add memory pressure monitor for Linux.

components/memory_pressure/direct_memory_pressure_calculator_linux.cc

Index: components/memory_pressure/direct_memory_pressure_calculator_linux.cc
diff --git a/components/memory_pressure/direct_memory_pressure_calculator_linux.cc b/components/memory_pressure/direct_memory_pressure_calculator_linux.cc
new file mode 100644
index 0000000000000000000000000000000000000000..f1dbc01f16f9628a3290cea569710d7f0f6a18cd
--- /dev/null
+++ b/components/memory_pressure/direct_memory_pressure_calculator_linux.cc
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+// Copyright 2016 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/direct_memory_pressure_calculator_linux.h"
+
+#include "base/process/process_metrics.h"
+#include "base/sys_info.h"
+
+namespace memory_pressure {
+
+namespace {
+
+static const int kKiBperMiB = 1024;
+
+}  // namespace
+
+// Thresholds at which we consider the system being under moderate/critical
+// memory pressure. They represent the percentage of system memory in use.
+const int DirectMemoryPressureCalculator::kDefaultModerateThresholdPc = 70;
+const int DirectMemoryPressureCalculator::kDefaultCriticalThresholdPc = 90;
+
+DirectMemoryPressureCalculator::DirectMemoryPressureCalculator()
+    : moderate_threshold_mb_(0), critical_threshold_mb_(0) {
+  InferThresholds();
+}
+
+DirectMemoryPressureCalculator::DirectMemoryPressureCalculator(
+    int moderate_threshold_mb,
+    int critical_threshold_mb)
+    : moderate_threshold_mb_(moderate_threshold_mb),
+      critical_threshold_mb_(critical_threshold_mb) {
+  DCHECK_GE(moderate_threshold_mb_, critical_threshold_mb_);
+  DCHECK_LE(0, critical_threshold_mb_);
+}
+
+DirectMemoryPressureCalculator::MemoryPressureLevel
+DirectMemoryPressureCalculator::CalculateCurrentPressureLevel() {
+  base::SystemMemoryInfoKB mem_info = {};
+  if (!GetSystemMemoryInfo(&mem_info))
+    return MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE;
+
+  // How much system memory is actively available for use right now, in MBs.
+  int phys_free = mem_info.free / kKiBperMiB;
+
+  // Determine if the physical memory is under critical memory pressure.
+  if (phys_free <= critical_threshold_mb_)
+    return MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL;
+
+  // Determine if the physical memory is under moderate memory pressure.
+  if (phys_free <= moderate_threshold_mb_)
+    return MemoryPressureListener::MEMORY_PRESSURE_LEVEL_MODERATE;
+
+  // No memory pressure was detected.
+  return MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE;
+}
+
+bool DirectMemoryPressureCalculator::GetSystemMemoryInfo(
+    base::SystemMemoryInfoKB* mem_info) const {
+  return base::GetSystemMemoryInfo(mem_info);
+}
+
+void DirectMemoryPressureCalculator::InferThresholds() {
+  base::SystemMemoryInfoKB mem_info = {};
+  if (!GetSystemMemoryInfo(&mem_info))
+    return;
+
+  moderate_threshold_mb_ =
+      mem_info.total * (100 - kDefaultModerateThresholdPc) / 100 / kKiBperMiB;
+  critical_threshold_mb_ =
+      mem_info.total * (100 - kDefaultCriticalThresholdPc) / 100 / kKiBperMiB;
+}
+
+}  // namespace memory_pressure