1 files changed, 282 insertions, 0 deletions
diff --git a/xpcom/base/AvailableMemoryWatcherLinux.cpp b/xpcom/base/AvailableMemoryWatcherLinux.cpp
new file mode 100644
index 0000000000..04927b7d46
--- /dev/null
+++ b/xpcom/base/AvailableMemoryWatcherLinux.cpp
@@ -0,0 +1,282 @@
+/* -*- 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 "AvailableMemoryWatcher.h"
+#include "AvailableMemoryWatcherUtils.h"
+#include "mozilla/Services.h"
+#include "mozilla/StaticPrefs_browser.h"
+#include "mozilla/Unused.h"
+#include "nsAppRunner.h"
+#include "nsIObserverService.h"
+#include "nsISupports.h"
+#include "nsITimer.h"
+#include "nsIThread.h"
+#include "nsMemoryPressure.h"
+
+namespace mozilla {
+
+// Linux has no native low memory detection. This class creates a timer that
+// polls for low memory and sends a low memory notification if it notices a
+// memory pressure event.
+class nsAvailableMemoryWatcher final : public nsITimerCallback,
+                                       public nsINamed,
+                                       public nsAvailableMemoryWatcherBase {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_NSITIMERCALLBACK
+  NS_DECL_NSIOBSERVER
+  NS_DECL_NSINAMED
+
+  nsresult Init() override;
+  nsAvailableMemoryWatcher();
+
+  void HandleLowMemory();
+  void MaybeHandleHighMemory();
+
+ private:
+  ~nsAvailableMemoryWatcher() = default;
+  void StartPolling(const MutexAutoLock&);
+  void StopPolling(const MutexAutoLock&);
+  void ShutDown();
+  void UpdateCrashAnnotation(const MutexAutoLock&);
+  static bool IsMemoryLow();
+
+  nsCOMPtr<nsITimer> mTimer MOZ_GUARDED_BY(mMutex);
+  nsCOMPtr<nsIThread> mThread MOZ_GUARDED_BY(mMutex);
+
+  bool mPolling MOZ_GUARDED_BY(mMutex);
+  bool mUnderMemoryPressure MOZ_GUARDED_BY(mMutex);
+
+  // Polling interval to check for low memory. In high memory scenarios,
+  // default to 5000 ms between each check.
+  static const uint32_t kHighMemoryPollingIntervalMS = 5000;
+
+  // Polling interval to check for low memory. Default to 1000 ms between each
+  // check. Use this interval when memory is low,
+  static const uint32_t kLowMemoryPollingIntervalMS = 1000;
+};
+
+// A modern version of linux should keep memory information in the
+// /proc/meminfo path.
+static const char* kMeminfoPath = "/proc/meminfo";
+
+nsAvailableMemoryWatcher::nsAvailableMemoryWatcher()
+    : mPolling(false), mUnderMemoryPressure(false) {}
+
+nsresult nsAvailableMemoryWatcher::Init() {
+  nsresult rv = nsAvailableMemoryWatcherBase::Init();
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  MutexAutoLock lock(mMutex);
+  mTimer = NS_NewTimer();
+  nsCOMPtr<nsIThread> thread;
+  // We have to make our own thread here instead of using the background pool,
+  // because some low memory scenarios can cause the background pool to fill.
+  rv = NS_NewNamedThread("MemoryPoller", getter_AddRefs(thread));
+  if (NS_FAILED(rv)) {
+    NS_WARNING("Couldn't make a thread for nsAvailableMemoryWatcher.");
+    // In this scenario we can't poll for low memory, since we can't dispatch
+    // to our memory watcher thread.
+    return rv;
+  }
+  mThread = thread;
+
+  // Set the crash annotation to its initial state.
+  UpdateCrashAnnotation(lock);
+
+  StartPolling(lock);
+
+  return NS_OK;
+}
+
+already_AddRefed<nsAvailableMemoryWatcherBase> CreateAvailableMemoryWatcher() {
+  RefPtr watcher(new nsAvailableMemoryWatcher);
+
+  if (NS_FAILED(watcher->Init())) {
+    return do_AddRef(new nsAvailableMemoryWatcherBase);
+  }
+
+  return watcher.forget();
+}
+
+NS_IMPL_ISUPPORTS_INHERITED(nsAvailableMemoryWatcher,
+                            nsAvailableMemoryWatcherBase, nsITimerCallback,
+                            nsIObserver, nsINamed);
+
+void nsAvailableMemoryWatcher::StopPolling(const MutexAutoLock&)
+    MOZ_REQUIRES(mMutex) {
+  if (mPolling && mTimer) {
+    // stop dispatching memory checks to the thread.
+    mTimer->Cancel();
+    mPolling = false;
+  }
+}
+
+// Check /proc/meminfo for low memory. Largely C method for reading
+// /proc/meminfo.
+/* static */
+bool nsAvailableMemoryWatcher::IsMemoryLow() {
+  MemoryInfo memInfo{0, 0};
+  nsresult rv = ReadMemoryFile(kMeminfoPath, memInfo);
+
+  if (NS_FAILED(rv) || (memInfo.memAvailable == 0) || (memInfo.memTotal == 0)) {
+    // If memAvailable cannot be found, then we are using an older system.
+    // We can't accurately poll on this.
+    // If memTotal is zero we can't calculate how much memory we're using.
+    return false;
+  }
+
+  unsigned long memoryAsPercentage =
+      (memInfo.memAvailable * 100) / memInfo.memTotal;
+
+  return memoryAsPercentage <=
+             StaticPrefs::browser_low_commit_space_threshold_percent() ||
+         memInfo.memAvailable <
+             StaticPrefs::browser_low_commit_space_threshold_mb() * 1024;
+}
+
+void nsAvailableMemoryWatcher::ShutDown() {
+  nsCOMPtr<nsIThread> thread;
+  {
+    MutexAutoLock lock(mMutex);
+    if (mTimer) {
+      mTimer->Cancel();
+      mTimer = nullptr;
+    }
+    thread = mThread.forget();
+  }
+  // thread->Shutdown() spins a nested event loop while waiting for the thread
+  // to end. But the thread might execute some previously dispatched event that
+  // wants to lock our mutex, too, before arriving at the shutdown event.
+  if (thread) {
+    thread->Shutdown();
+  }
+}
+
+// We will use this to poll for low memory.
+NS_IMETHODIMP
+nsAvailableMemoryWatcher::Notify(nsITimer* aTimer) {
+  MutexAutoLock lock(mMutex);
+  if (!mThread) {
+    // If we've made it this far and there's no  |mThread|,
+    // we might have failed to dispatch it for some reason.
+    MOZ_ASSERT(mThread);
+    return NS_ERROR_FAILURE;
+  }
+  nsresult rv = mThread->Dispatch(
+      NS_NewRunnableFunction("MemoryPoller", [self = RefPtr{this}]() {
+        if (self->IsMemoryLow()) {
+          self->HandleLowMemory();
+        } else {
+          self->MaybeHandleHighMemory();
+        }
+      }));
+
+  if NS_FAILED (rv) {
+    NS_WARNING("Cannot dispatch memory polling event.");
+  }
+  return NS_OK;
+}
+
+void nsAvailableMemoryWatcher::HandleLowMemory() {
+  MutexAutoLock lock(mMutex);
+  if (!mTimer) {
+    // We have been shut down from outside while in flight.
+    return;
+  }
+  if (!mUnderMemoryPressure) {
+    mUnderMemoryPressure = true;
+    UpdateCrashAnnotation(lock);
+    // Poll more frequently under memory pressure.
+    StartPolling(lock);
+  }
+  UpdateLowMemoryTimeStamp();
+  // We handle low memory offthread, but we want to unload
+  // tabs only from the main thread, so we will dispatch this
+  // back to the main thread.
+  // Since we are doing this async, we don't need to unlock the mutex first;
+  // the AutoLock will unlock the mutex when we finish the dispatch.
+  NS_DispatchToMainThread(NS_NewRunnableFunction(
+      "nsAvailableMemoryWatcher::OnLowMemory",
+      [self = RefPtr{this}]() { self->mTabUnloader->UnloadTabAsync(); }));
+}
+
+void nsAvailableMemoryWatcher::UpdateCrashAnnotation(const MutexAutoLock&)
+    MOZ_REQUIRES(mMutex) {
+  CrashReporter::AnnotateCrashReport(
+      CrashReporter::Annotation::LinuxUnderMemoryPressure,
+      mUnderMemoryPressure);
+}
+
+// If memory is not low, we may need to dispatch an
+// event for it if we have been under memory pressure.
+// We can also adjust our polling interval.
+void nsAvailableMemoryWatcher::MaybeHandleHighMemory() {
+  MutexAutoLock lock(mMutex);
+  if (!mTimer) {
+    // We have been shut down from outside while in flight.
+    return;
+  }
+  if (mUnderMemoryPressure) {
+    RecordTelemetryEventOnHighMemory(lock);
+    NS_NotifyOfEventualMemoryPressure(MemoryPressureState::NoPressure);
+    mUnderMemoryPressure = false;
+    UpdateCrashAnnotation(lock);
+  }
+  StartPolling(lock);
+}
+
+// When we change the polling interval, we will need to restart the timer
+// on the new interval.
+void nsAvailableMemoryWatcher::StartPolling(const MutexAutoLock& aLock)
+    MOZ_REQUIRES(mMutex) {
+  uint32_t pollingInterval = mUnderMemoryPressure
+                                 ? kLowMemoryPollingIntervalMS
+                                 : kHighMemoryPollingIntervalMS;
+  if (!mPolling) {
+    // Restart the timer with the new interval if it has stopped.
+    // For testing, use a small polling interval.
+    if (NS_SUCCEEDED(
+            mTimer->InitWithCallback(this, gIsGtest ? 10 : pollingInterval,
+                                     nsITimer::TYPE_REPEATING_SLACK))) {
+      mPolling = true;
+    }
+  } else {
+    mTimer->SetDelay(gIsGtest ? 10 : pollingInterval);
+  }
+}
+
+// Observe events for shutting down and starting/stopping the timer.
+NS_IMETHODIMP
+nsAvailableMemoryWatcher::Observe(nsISupports* aSubject, const char* aTopic,
+                                  const char16_t* aData) {
+  nsresult rv = nsAvailableMemoryWatcherBase::Observe(aSubject, aTopic, aData);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  if (strcmp(aTopic, "xpcom-shutdown") == 0) {
+    ShutDown();
+  } else {
+    MutexAutoLock lock(mMutex);
+    if (mTimer) {
+      if (strcmp(aTopic, "user-interaction-active") == 0) {
+        StartPolling(lock);
+      } else if (strcmp(aTopic, "user-interaction-inactive") == 0) {
+        StopPolling(lock);
+      }
+    }
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsAvailableMemoryWatcher::GetName(nsACString& aName) {
+  aName.AssignLiteral("nsAvailableMemoryWatcher");
+  return NS_OK;
+}
+
+}  // namespace mozilla