1 files changed, 359 insertions, 0 deletions
diff --git a/widget/gonk/GonkMemoryPressureMonitoring.cpp b/widget/gonk/GonkMemoryPressureMonitoring.cpp
new file mode 100644
index 000000000..0fafb37cf
--- /dev/null
+++ b/widget/gonk/GonkMemoryPressureMonitoring.cpp
@@ -0,0 +1,359 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=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 <android/log.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <poll.h>
+#include <sys/sysinfo.h>
+
+#include "GonkMemoryPressureMonitoring.h"
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/FileUtils.h"
+#include "mozilla/Monitor.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/ProcessPriorityManager.h"
+#include "mozilla/Services.h"
+#include "nsIObserver.h"
+#include "nsIObserverService.h"
+#include "nsMemoryPressure.h"
+#include "nsPrintfCString.h"
+#include "nsThreadUtils.h"
+
+#define LOG(args...)  \
+  __android_log_print(ANDROID_LOG_INFO, "GonkMemoryPressure" , ## args)
+
+using namespace mozilla;
+
+namespace {
+
+/**
+ * MemoryPressureWatcher watches sysfs from its own thread to notice when the
+ * system is under memory pressure.  When we observe memory pressure, we use
+ * MemoryPressureRunnable to notify observers that they should release memory.
+ *
+ * When the system is under memory pressure, we don't want to constantly fire
+ * memory-pressure events.  So instead, we try to detect when sysfs indicates
+ * that we're no longer under memory pressure, and only then start firing events
+ * again.
+ *
+ * (This is a bit problematic because we can't poll() to detect when we're no
+ * longer under memory pressure; instead we have to periodically read the sysfs
+ * node.  If we remain under memory pressure for a long time, this means we'll
+ * continue waking up to read from the node for a long time, potentially wasting
+ * battery life.  Hopefully we don't hit this case in practice!  We write to
+ * logcat each time we go around this loop so it's at least noticable.)
+ *
+ * Shutting down safely is a bit of a chore.  XPCOM won't shut down until all
+ * threads exit, so we need to exit the Run() method below on shutdown.  But our
+ * thread might be blocked in one of two situations: We might be poll()'ing the
+ * sysfs node waiting for memory pressure to occur, or we might be asleep
+ * waiting to read() the sysfs node to see if we're no longer under memory
+ * pressure.
+ *
+ * To let us wake up from the poll(), we poll() not just the sysfs node but also
+ * a pipe, which we write to on shutdown.  To let us wake up from sleeping
+ * between read()s, we sleep by Wait()'ing on a monitor, which we notify on
+ * shutdown.
+ */
+class MemoryPressureWatcher final
+  : public nsIRunnable
+  , public nsIObserver
+{
+public:
+  MemoryPressureWatcher()
+    : mMonitor("MemoryPressureWatcher")
+    , mLowMemTriggerKB(0)
+    , mPageSize(0)
+    , mShuttingDown(false)
+    , mTriggerFd(-1)
+    , mShutdownPipeRead(-1)
+    , mShutdownPipeWrite(-1)
+  {
+  }
+
+  NS_DECL_THREADSAFE_ISUPPORTS
+
+  nsresult Init()
+  {
+    nsCOMPtr<nsIObserverService> os = services::GetObserverService();
+    NS_ENSURE_STATE(os);
+
+    // The observer service holds us alive.
+    os->AddObserver(this, NS_XPCOM_SHUTDOWN_OBSERVER_ID, /* ownsWeak */ false);
+
+    // Initialize the internal state
+    mPageSize = sysconf(_SC_PAGESIZE);
+    ReadPrefs();
+    nsresult rv = OpenFiles();
+    NS_ENSURE_SUCCESS(rv, rv);
+    SetLowMemTrigger(mSoftLowMemTriggerKB);
+
+    return NS_OK;
+  }
+
+  NS_IMETHOD Observe(nsISupports* aSubject, const char* aTopic,
+                     const char16_t* aData)
+  {
+    MOZ_ASSERT(strcmp(aTopic, NS_XPCOM_SHUTDOWN_OBSERVER_ID) == 0);
+    LOG("Observed XPCOM shutdown.");
+
+    MonitorAutoLock lock(mMonitor);
+    mShuttingDown = true;
+    mMonitor.Notify();
+
+    int rv;
+    do {
+      // Write something to the pipe; doesn't matter what.
+      uint32_t dummy = 0;
+      rv = write(mShutdownPipeWrite, &dummy, sizeof(dummy));
+    } while(rv == -1 && errno == EINTR);
+
+    return NS_OK;
+  }
+
+  NS_IMETHOD Run() override
+  {
+    MOZ_ASSERT(!NS_IsMainThread());
+
+    int triggerResetTimeout = -1;
+    bool memoryPressure;
+    nsresult rv = CheckForMemoryPressure(&memoryPressure);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    while (true) {
+      // Wait for a notification on mTriggerFd or for data to be written to
+      // mShutdownPipeWrite.  (poll(mTriggerFd, POLLPRI) blocks until we're
+      // under memory pressure or until we time out, the time out is used
+      // to adjust the trigger level after a memory pressure event.)
+      struct pollfd pollfds[2];
+      pollfds[0].fd = mTriggerFd;
+      pollfds[0].events = POLLPRI;
+      pollfds[1].fd = mShutdownPipeRead;
+      pollfds[1].events = POLLIN;
+
+      int pollRv = MOZ_TEMP_FAILURE_RETRY(
+        poll(pollfds, ArrayLength(pollfds), triggerResetTimeout)
+      );
+
+      if (pollRv == 0) {
+        // Timed out, adjust the trigger and update the timeout.
+        triggerResetTimeout = AdjustTrigger(triggerResetTimeout);
+        continue;
+      }
+
+      if (pollfds[1].revents) {
+        // Something was written to our shutdown pipe; we're outta here.
+        LOG("shutting down (1)");
+        return NS_OK;
+      }
+
+      // If pollfds[1] isn't happening, pollfds[0] ought to be!
+      if (!(pollfds[0].revents & POLLPRI)) {
+        LOG("Unexpected revents value after poll(): %d. "
+            "Shutting down GonkMemoryPressureMonitoring.", pollfds[0].revents);
+        return NS_ERROR_FAILURE;
+      }
+
+      // POLLPRI on mTriggerFd indicates that we're in a low-memory situation.
+      // We could read lowMemFd to double-check, but we've observed that the
+      // read sometimes completes after the memory-pressure event is over, so
+      // let's just believe the result of poll().
+      rv = DispatchMemoryPressure(MemPressure_New);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      // Move to the hard level if we're on the soft one.
+      if (mLowMemTriggerKB > mHardLowMemTriggerKB) {
+        SetLowMemTrigger(mHardLowMemTriggerKB);
+      }
+
+      // Manually check mTriggerFd until we observe that memory pressure is
+      // over.  We won't fire any more low-memory events until we observe that
+      // we're no longer under pressure. Instead, we fire low-memory-ongoing
+      // events, which cause processes to keep flushing caches but will not
+      // trigger expensive GCs and other attempts to save memory that are
+      // likely futile at this point.
+      do {
+        {
+          MonitorAutoLock lock(mMonitor);
+
+          // We need to check mShuttingDown before we wait here, in order to
+          // catch a shutdown signal sent after we poll()'ed mShutdownPipeRead
+          // above but before we started waiting on the monitor.  But we don't
+          // need to check after we wait, because we'll either do another
+          // iteration of this inner loop, in which case we'll check
+          // mShuttingDown, or we'll exit this loop and do another iteration
+          // of the outer loop, in which case we'll check the shutdown pipe.
+          if (mShuttingDown) {
+            LOG("shutting down (2)");
+            return NS_OK;
+          }
+          mMonitor.Wait(PR_MillisecondsToInterval(mPollMS));
+        }
+
+        LOG("Checking to see if memory pressure is over.");
+        rv = CheckForMemoryPressure(&memoryPressure);
+        NS_ENSURE_SUCCESS(rv, rv);
+
+        if (memoryPressure) {
+          rv = DispatchMemoryPressure(MemPressure_Ongoing);
+          NS_ENSURE_SUCCESS(rv, rv);
+          continue;
+        }
+      } while (false);
+
+      if (XRE_IsParentProcess()) {
+        // The main process will try to adjust the trigger.
+        triggerResetTimeout = mPollMS * 2;
+      }
+
+      LOG("Memory pressure is over.");
+    }
+
+    return NS_OK;
+  }
+
+protected:
+  ~MemoryPressureWatcher() {}
+
+private:
+  void ReadPrefs() {
+    // While we're under memory pressure, we periodically read()
+    // notify_trigger_active to try and see when we're no longer under memory
+    // pressure.  mPollMS indicates how many milliseconds we wait between those
+    // read()s.
+    Preferences::AddUintVarCache(&mPollMS,
+      "gonk.systemMemoryPressureRecoveryPollMS", /* default */ 5000);
+
+    // We have two values for the notify trigger, a soft one which is triggered
+    // before we start killing background applications and an hard one which is
+    // after we've killed background applications but before we start killing
+    // foreground ones.
+    Preferences::AddUintVarCache(&mSoftLowMemTriggerKB,
+      "gonk.notifySoftLowMemUnderKB", /* default */ 43008);
+    Preferences::AddUintVarCache(&mHardLowMemTriggerKB,
+      "gonk.notifyHardLowMemUnderKB", /* default */ 14336);
+  }
+
+  nsresult OpenFiles() {
+    mTriggerFd = open("/sys/kernel/mm/lowmemkiller/notify_trigger_active",
+                      O_RDONLY | O_CLOEXEC);
+    NS_ENSURE_STATE(mTriggerFd != -1);
+
+    int pipes[2];
+    NS_ENSURE_STATE(!pipe(pipes));
+    mShutdownPipeRead = pipes[0];
+    mShutdownPipeWrite = pipes[1];
+    return NS_OK;
+  }
+
+  /**
+   * Set the low memory trigger to the specified value, this can be done by
+   * the main process alone.
+   */
+  void SetLowMemTrigger(uint32_t aValue) {
+    if (XRE_IsParentProcess()) {
+      nsPrintfCString str("%ld", (aValue * 1024) / mPageSize);
+      if (WriteSysFile("/sys/module/lowmemorykiller/parameters/notify_trigger",
+                       str.get())) {
+        mLowMemTriggerKB = aValue;
+      }
+    }
+  }
+
+  /**
+   * Read from the trigger file descriptor and determine whether we're
+   * currently under memory pressure.
+   *
+   * We don't expect this method to block.
+   */
+  nsresult CheckForMemoryPressure(bool* aOut)
+  {
+    *aOut = false;
+
+    lseek(mTriggerFd, 0, SEEK_SET);
+
+    char buf[2];
+    int nread = MOZ_TEMP_FAILURE_RETRY(read(mTriggerFd, buf, sizeof(buf)));
+    NS_ENSURE_STATE(nread == 2);
+
+    // The notify_trigger_active sysfs node should contain either "0\n" or
+    // "1\n".  The latter indicates memory pressure.
+    *aOut = (buf[0] == '1');
+    return NS_OK;
+  }
+
+  int AdjustTrigger(int timeout)
+  {
+    if (!XRE_IsParentProcess()) {
+      return -1; // Only the main process can adjust the trigger.
+    }
+
+    struct sysinfo info;
+    int rv = sysinfo(&info);
+    if (rv < 0) {
+      return -1; // Without system information we're blind, bail out.
+    }
+
+    size_t freeMemory = (info.freeram * info.mem_unit) / 1024;
+
+    if (freeMemory > mSoftLowMemTriggerKB) {
+      SetLowMemTrigger(mSoftLowMemTriggerKB);
+      return -1; // Trigger adjusted, wait indefinitely.
+    }
+
+    // Wait again but double the duration, max once per day.
+    return std::min(86400000, timeout * 2);
+  }
+
+  /**
+   * Dispatch the specified memory pressure event unless a high-priority
+   * process is present. If a high-priority process is present then it's likely
+   * responding to an urgent event (an incoming call or message for example) so
+   * avoid wasting CPU time responding to low-memory events.
+   */
+  nsresult DispatchMemoryPressure(MemoryPressureState state)
+  {
+    if (ProcessPriorityManager::AnyProcessHasHighPriority()) {
+      return NS_OK;
+    }
+
+    return NS_DispatchMemoryPressure(state);
+  }
+
+  Monitor mMonitor;
+  uint32_t mPollMS; // Ongoing pressure poll delay
+  uint32_t mSoftLowMemTriggerKB; // Soft memory pressure level
+  uint32_t mHardLowMemTriggerKB; // Hard memory pressure level
+  uint32_t mLowMemTriggerKB; // Current value of the trigger
+  size_t mPageSize;
+  bool mShuttingDown;
+
+  ScopedClose mTriggerFd;
+  ScopedClose mShutdownPipeRead;
+  ScopedClose mShutdownPipeWrite;
+};
+
+NS_IMPL_ISUPPORTS(MemoryPressureWatcher, nsIRunnable, nsIObserver);
+
+} // namespace
+
+namespace mozilla {
+
+void
+InitGonkMemoryPressureMonitoring()
+{
+  // memoryPressureWatcher is held alive by the observer service.
+  RefPtr<MemoryPressureWatcher> memoryPressureWatcher =
+    new MemoryPressureWatcher();
+  NS_ENSURE_SUCCESS_VOID(memoryPressureWatcher->Init());
+
+  nsCOMPtr<nsIThread> thread;
+  NS_NewNamedThread("MemoryPressure", getter_AddRefs(thread),
+                    memoryPressureWatcher);
+}
+
+} // namespace mozilla