Revision c15a9e401a4f42b412c04a3919f2d40a64f4861a authored by Jared Wein on 11 December 2012, 23:55:25 UTC, committed by Jared Wein on 11 December 2012, 23:55:25 UTC
1 parent a98f790
GonkMemoryPressureMonitoring.cpp
/* -*- 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/FileUtils.h"
#include "mozilla/Monitor.h"
#include "mozilla/Preferences.h"
#include "mozilla/Services.h"
#include "nsIObserver.h"
#include "nsIObserverService.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)
using namespace mozilla;
namespace {
class MemoryPressureRunnable : public nsRunnable
{
public:
NS_IMETHOD Run()
{
MOZ_ASSERT(NS_IsMainThread());
LOG("Dispatching low-memory memory-pressure event");
nsCOMPtr<nsIObserverService> os = services::GetObserverService();
if (os) {
os->NotifyObservers(nullptr, "memory-pressure",
NS_LITERAL_STRING("low-memory").get());
}
return NS_OK;
}
};
/**
* 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_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 PRUnichar* 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());
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, NS_ARRAY_LENGTH(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().
nsRefPtr<MemoryPressureRunnable> memoryPressureRunnable =
new MemoryPressureRunnable();
NS_DispatchToMainThread(memoryPressureRunnable);
// Manually check lowMemFd until we observe that memory pressure is over.
// We won't fire any more memory-pressure events until we observe that
// we're no longer under pressure.
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);
} while (memoryPressure);
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;
}
Monitor mMonitor;
uint32_t mPollMS;
bool mShuttingDown;
ScopedClose mShutdownPipeRead;
ScopedClose mShutdownPipeWrite;
};
NS_IMPL_THREADSAFE_ISUPPORTS2(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
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