The Tor Browser: widget/gonk/GonkMemoryPressureMonitoring.cpp@6474c204b198 (annotated)

widget/gonk/GonkMemoryPressureMonitoring.cpp@6474c204b198 (annotated)

widget/gonk/GonkMemoryPressureMonitoring.cpp

Wed, 31 Dec 2014 06:09:35 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Wed, 31 Dec 2014 06:09:35 +0100
changeset 0: 6474c204b198
permissions: -rw-r--r--

Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.

 /* -*- 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 "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 "nsThreadUtils.h"
 #include <errno.h>
 #include <fcntl.h>
 #include <poll.h>
 #include <android/log.h>
 #define LOG(args...)  \
   __android_log_print(ANDROID_LOG_INFO, "GonkMemoryPressure" , ## args)
 #ifdef MOZ_NUWA_PROCESS
 #include "ipc/Nuwa.h"
 #endif
 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
   : public nsIRunnable
   , public nsIObserver
 {
 public:
   MemoryPressureWatcher()
     : mMonitor("MemoryPressureWatcher")
     , mShuttingDown(false)
   {
   }
   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, /* holdsWeak */ false);
     // 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.
     mPollMS = Preferences::GetUint("gonk.systemMemoryPressureRecoveryPollMS",
                                    /* default */ 5000);
     int pipes[2];
     NS_ENSURE_STATE(!pipe(pipes));
     mShutdownPipeRead = pipes[0];
     mShutdownPipeWrite = pipes[1];
     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()
   {
     MOZ_ASSERT(!NS_IsMainThread());
 #ifdef MOZ_NUWA_PROCESS
     if (IsNuwaProcess()) {
       NS_ASSERTION(NuwaMarkCurrentThread != nullptr,
                    "NuwaMarkCurrentThread is undefined!");
       NuwaMarkCurrentThread(nullptr, nullptr);
     }
 #endif
     int lowMemFd = open("/sys/kernel/mm/lowmemkiller/notify_trigger_active",
                         O_RDONLY | O_CLOEXEC);
     NS_ENSURE_STATE(lowMemFd != -1);
     ScopedClose autoClose(lowMemFd);
     nsresult rv = CheckForMemoryPressure(lowMemFd, nullptr);
     NS_ENSURE_SUCCESS(rv, rv);
     while (true) {
       // Wait for a notification on lowMemFd or for data to be written to
       // mShutdownPipeWrite.  (poll(lowMemFd, POLLPRI) blocks until we're under
       // memory pressure.)
       struct pollfd pollfds[2];
       pollfds[0].fd = lowMemFd;
       pollfds[0].events = POLLPRI;
       pollfds[1].fd = mShutdownPipeRead;
       pollfds[1].events = POLLIN;
       int pollRv;
       do {
         pollRv = poll(pollfds, ArrayLength(pollfds), /* timeout */ -1);
       } while (pollRv == -1 && errno == EINTR);
       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 lowMemFd 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().
       // We use low-memory-no-forward because each process has its own watcher
       // and thus there is no need for the main process to forward this event.
       rv = DispatchMemoryPressure(MemPressure_New);
       NS_ENSURE_SUCCESS(rv, rv);
       // Manually check lowMemFd 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.
       bool memoryPressure;
       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(lowMemFd, &memoryPressure);
         NS_ENSURE_SUCCESS(rv, rv);
         if (memoryPressure) {
           rv = DispatchMemoryPressure(MemPressure_Ongoing);
           NS_ENSURE_SUCCESS(rv, rv);
           continue;
         }
       } while (false);
       LOG("Memory pressure is over.");
     }
     return NS_OK;
   }
 private:
   /**
    * Read from aLowMemFd, which we assume corresponds to the
    * notify_trigger_active sysfs node, and determine whether we're currently
    * under memory pressure.
    *
    * We don't expect this method to block.
    */
   nsresult CheckForMemoryPressure(int aLowMemFd, bool* aOut)
   {
     if (aOut) {
       *aOut = false;
     }
     lseek(aLowMemFd, 0, SEEK_SET);
     char buf[2];
     int nread;
     do {
       nread = read(aLowMemFd, buf, sizeof(buf));
     } while(nread == -1 && errno == EINTR);
     NS_ENSURE_STATE(nread == 2);
     // The notify_trigger_active sysfs node should contain either "0\n" or
     // "1\n".  The latter indicates memory pressure.
     if (aOut) {
       *aOut = buf[0] == '1' && buf[1] == '\n';
     }
     return NS_OK;
   }
   /**
    * 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;
   bool mShuttingDown;
   ScopedClose mShutdownPipeRead;
   ScopedClose mShutdownPipeWrite;
 };
 NS_IMPL_ISUPPORTS(MemoryPressureWatcher, nsIRunnable, nsIObserver);
 } // anonymous namespace
 namespace mozilla {
 void
 InitGonkMemoryPressureMonitoring()
 {
   // memoryPressureWatcher is held alive by the observer service.
   nsRefPtr<MemoryPressureWatcher> memoryPressureWatcher =
     new MemoryPressureWatcher();
   NS_ENSURE_SUCCESS_VOID(memoryPressureWatcher->Init());
   nsCOMPtr<nsIThread> thread;
   NS_NewThread(getter_AddRefs(thread), memoryPressureWatcher);
 }
 } // namespace mozilla

The Tor Browser / annotate

widget/gonk/GonkMemoryPressureMonitoring.cpp@6474c204b198 (annotated)

widget/gonk/GonkMemoryPressureMonitoring.cpp