1 files changed, 194 insertions, 0 deletions
diff --git a/xpcom/base/AvailableMemoryTracker.cpp b/xpcom/base/AvailableMemoryTracker.cpp
new file mode 100644
index 0000000000..5e75f26ac6
--- /dev/null
+++ b/xpcom/base/AvailableMemoryTracker.cpp
@@ -0,0 +1,194 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/AvailableMemoryTracker.h"
+
+#if defined(XP_WIN)
+#  include "mozilla/WindowsVersion.h"
+#  include "nsIMemoryReporter.h"
+#endif
+
+#include "nsIObserver.h"
+#include "nsIObserverService.h"
+#include "nsIRunnable.h"
+#include "nsISupports.h"
+#include "nsThreadUtils.h"
+#include "nsXULAppAPI.h"
+
+#include "mozilla/Mutex.h"
+#include "mozilla/ResultExtensions.h"
+#include "mozilla/Services.h"
+
+#if defined(MOZ_MEMORY)
+#  include "mozmemory.h"
+#endif  // MOZ_MEMORY
+
+using namespace mozilla;
+
+Atomic<uint32_t, MemoryOrdering::Relaxed> sNumLowPhysicalMemEvents;
+
+namespace {
+
+#if defined(XP_WIN)
+
+#  if (NTDDI_VERSION < NTDDI_WINBLUE) || \
+      (NTDDI_VERSION == NTDDI_WINBLUE && !defined(WINBLUE_KBSPRING14))
+// Definitions for heap optimization that require the Windows SDK to target the
+// Windows 8.1 Update
+static const HEAP_INFORMATION_CLASS HeapOptimizeResources =
+    static_cast<HEAP_INFORMATION_CLASS>(3);
+
+static const DWORD HEAP_OPTIMIZE_RESOURCES_CURRENT_VERSION = 1;
+
+typedef struct _HEAP_OPTIMIZE_RESOURCES_INFORMATION {
+  DWORD Version;
+  DWORD Flags;
+} HEAP_OPTIMIZE_RESOURCES_INFORMATION, *PHEAP_OPTIMIZE_RESOURCES_INFORMATION;
+#  endif
+
+static int64_t LowMemoryEventsPhysicalDistinguishedAmount() {
+  return sNumLowPhysicalMemEvents;
+}
+
+class LowEventsReporter final : public nsIMemoryReporter {
+  ~LowEventsReporter() {}
+
+ public:
+  NS_DECL_ISUPPORTS
+
+  NS_IMETHOD CollectReports(nsIHandleReportCallback* aHandleReport,
+                            nsISupports* aData, bool aAnonymize) override {
+    // clang-format off
+    MOZ_COLLECT_REPORT(
+      "low-memory-events/physical", KIND_OTHER, UNITS_COUNT_CUMULATIVE,
+      LowMemoryEventsPhysicalDistinguishedAmount(),
+"Number of low-physical-memory events fired since startup. We fire such an "
+"event when a windows low memory resource notification is signaled. The "
+"machine will start to page if it runs out of physical memory.  This may "
+"cause it to run slowly, but it shouldn't cause it to crash.");
+    // clang-format on
+
+    return NS_OK;
+  }
+};
+
+NS_IMPL_ISUPPORTS(LowEventsReporter, nsIMemoryReporter)
+
+#endif  // defined(XP_WIN)
+
+/**
+ * This runnable is executed in response to a memory-pressure event; we spin
+ * the event-loop when receiving the memory-pressure event in the hope that
+ * other observers will synchronously free some memory that we'll be able to
+ * purge here.
+ */
+class nsJemallocFreeDirtyPagesRunnable final : public Runnable {
+  ~nsJemallocFreeDirtyPagesRunnable() = default;
+
+#if defined(XP_WIN)
+  void OptimizeSystemHeap();
+#endif
+
+ public:
+  NS_DECL_NSIRUNNABLE
+
+  nsJemallocFreeDirtyPagesRunnable()
+      : Runnable("nsJemallocFreeDirtyPagesRunnable") {}
+};
+
+NS_IMETHODIMP
+nsJemallocFreeDirtyPagesRunnable::Run() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+#if defined(MOZ_MEMORY)
+  jemalloc_free_dirty_pages();
+#endif
+
+#if defined(XP_WIN)
+  OptimizeSystemHeap();
+#endif
+
+  return NS_OK;
+}
+
+#if defined(XP_WIN)
+void nsJemallocFreeDirtyPagesRunnable::OptimizeSystemHeap() {
+  // HeapSetInformation exists prior to Windows 8.1, but the
+  // HeapOptimizeResources information class does not.
+  if (IsWin8Point1OrLater()) {
+    HEAP_OPTIMIZE_RESOURCES_INFORMATION heapOptInfo = {
+        HEAP_OPTIMIZE_RESOURCES_CURRENT_VERSION};
+
+    ::HeapSetInformation(nullptr, HeapOptimizeResources, &heapOptInfo,
+                         sizeof(heapOptInfo));
+  }
+}
+#endif  // defined(XP_WIN)
+
+/**
+ * The memory pressure watcher is used for listening to memory-pressure events
+ * and reacting upon them. We use one instance per process currently only for
+ * cleaning up dirty unused pages held by jemalloc.
+ */
+class nsMemoryPressureWatcher final : public nsIObserver {
+  ~nsMemoryPressureWatcher() = default;
+
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIOBSERVER
+
+  void Init();
+};
+
+NS_IMPL_ISUPPORTS(nsMemoryPressureWatcher, nsIObserver)
+
+/**
+ * Initialize and subscribe to the memory-pressure events. We subscribe to the
+ * observer service in this method and not in the constructor because we need
+ * to hold a strong reference to 'this' before calling the observer service.
+ */
+void nsMemoryPressureWatcher::Init() {
+  nsCOMPtr<nsIObserverService> os = services::GetObserverService();
+
+  if (os) {
+    os->AddObserver(this, "memory-pressure", /* ownsWeak */ false);
+  }
+}
+
+/**
+ * Reacts to all types of memory-pressure events, launches a runnable to
+ * free dirty pages held by jemalloc.
+ */
+NS_IMETHODIMP
+nsMemoryPressureWatcher::Observe(nsISupports* aSubject, const char* aTopic,
+                                 const char16_t* aData) {
+  MOZ_ASSERT(!strcmp(aTopic, "memory-pressure"), "Unknown topic");
+
+  nsCOMPtr<nsIRunnable> runnable = new nsJemallocFreeDirtyPagesRunnable();
+
+  NS_DispatchToMainThread(runnable);
+
+  return NS_OK;
+}
+
+}  // namespace
+
+namespace mozilla {
+namespace AvailableMemoryTracker {
+
+void Init() {
+  // The watchers are held alive by the observer service.
+  RefPtr<nsMemoryPressureWatcher> watcher = new nsMemoryPressureWatcher();
+  watcher->Init();
+
+#if defined(XP_WIN)
+  RegisterLowMemoryEventsPhysicalDistinguishedAmount(
+      LowMemoryEventsPhysicalDistinguishedAmount);
+#endif  // defined(XP_WIN)
+}
+
+}  // namespace AvailableMemoryTracker
+}  // namespace mozilla