android系統定期釋放catch內存

1、在init.rc中定義一個服務
service drop_caches /sbin/busybox sh /system/bin/flushcache.sh
user root
group root system
disabled
oneshot
flushcache.sh文件內容：
#!/system/bin/busybox sh
/system/bin/log -t pagecache “flush page cache”
echo 1 > /proc/sys/vm/drop_caches
2、在ActivityManagerService.java文件中每個15秒定期檢查內核大小，超過一定值時定期釋放內存，如下：

static final int FIRST_ACTIVITY_STACK_MSG = 100;
    static final int FIRST_BROADCAST_QUEUE_MSG = 200;
    static final int FIRST_COMPAT_MODE_MSG = 300;
    static final int FIRST_SUPERVISOR_STACK_MSG = 100;

    static ServiceThread sKillThread = null;
    static KillHandler sKillHandler = null;

   static final int SW_FLUSH_PAGECACHE_MSG = 400;
    static final int SW_SEND_MSG_DELAYED = 15*1000;
    //static final int SW_MEM_FLUSH_THRESTHOD1 =  80000;// =< 512M 25%
    //static final int SW_MEM_FLUSH_THRESTHOD2 =  90000;// > 512M  38%
    static final int SW_MEM_FLUSH_THRESTHOD1 =  614400;// 600M 25%
    static final int SW_MEM_FLUSH_THRESTHOD2 =  665600;//  650M  //768000;//750M 38%
    CompatModeDialog mCompatModeDialog;
    UnsupportedDisplaySizeDialog mUnsupportedDisplaySizeDialog;
    long mLastMemUsageReportTime = 0;
final class MainHandler extends Handler {
        public MainHandler(Looper looper) {
            super(looper, null, true);
        }
	 private void flushPageCache() {
            MemInfoReader memInfo = new MemInfoReader();
            memInfo.readMemInfo();
	     //Log.d(TAG,"TotalSize=" + memInfo.getTotalSizeKb()*1024 + ", CachedSize=" + memInfo.getCachedSizeKb()*1024 + ",freeSize=" + memInfo.getZramTotalSizeKb()*1024 + ",zramSize=" + memInfo.getZramTotalSizeKb()*1024 + ",kernelSize=" + memInfo.getKernelUsedSizeKb()*1024);//, nativeTotalPss*1024);
	     Log.d(TAG,"TotalSizeKB=" + memInfo.getTotalSizeKb() + ", CachedSizeKB=" + memInfo.getCachedSizeKb() + ",freeSizeKB=" + memInfo.getFreeSizeKb() + ",zramSizeKB=" + memInfo.getZramTotalSizeKb() + ",kernelSizeKB=" + memInfo.getKernelUsedSizeKb());//, nativeTotalPss*1024);
	    //if( (memInfo.getTotalSizeKb() <= 524288 && memInfo.getCachedSizeKb() > SW_MEM_FLUSH_THRESTHOD1) ||
          //      (memInfo.getTotalSizeKb() > 524288 && memInfo.getCachedSizeKb() > SW_MEM_FLUSH_THRESTHOD2) ) {
		//524288KB=512M
		//getTotalSizeKb<=1.751GB && getCachedSizeKb>600MB or
		//getTotalSizeKb>1.600GB && getCachedSizeKb>650MB or
		  if( (memInfo.getTotalSizeKb() <= 524288 && memInfo.getCachedSizeKb() > SW_MEM_FLUSH_THRESTHOD1) ||
                (memInfo.getTotalSizeKb() > 524288 && memInfo.getCachedSizeKb() > SW_MEM_FLUSH_THRESTHOD2) ) {
		//Log.d(TAG,"TotalSize="+memInfo.getTotalSizeKb()*1024+", CachedSize="+memInfo.getCachedSizeKb()*1024+",zramKb="+ zramKb*1024+",kernelKb="+kernelKb*1024);//, nativeTotalPss*1024);
			SystemProperties.set("ctl.start", "drop_caches");
			Log.d(TAG,"start clean cache...");
            }

	    Log.v(TAG,"cached = " + memInfo.getCachedSizeKb() + "KB");
            Message msg = Message.obtain();
            msg.what    = SW_FLUSH_PAGECACHE_MSG;
            mHandler.sendMessageDelayed(msg, SW_SEND_MSG_DELAYED);
            return;
        }
        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
	    case SW_FLUSH_PAGECACHE_MSG: {
			flushPageCache();
			 break;
		}
            case UPDATE_CONFIGURATION_MSG: {
                final ContentResolver resolver = mContext.getContentResolver();
                Settings.System.putConfigurationForUser(resolver, (Configuration) msg.obj,
                        msg.arg1);
            } break;
…………………………………………………………………………………………………………………………………………….
public ActivityManagerService(Context systemContext) {
        mContext = systemContext;
        mFactoryTest = FactoryTest.getMode();
………………………………………………………………………………………………………………………………………………
  new Thread() {
            @Override
            public void run() {
                mProcessCpuTracker.init();
            }
        }.start();

        mCompatModePackages = new CompatModePackages(this, systemDir, mHandler);
        mIntentFirewall = new IntentFirewall(new IntentFirewallInterface(), mHandler);
        mStackSupervisor = new ActivityStackSupervisor(this);
        mActivityStarter = new ActivityStarter(this, mStackSupervisor);
        mRecentTasks = new RecentTasks(this, mStackSupervisor);

        mProcessCpuThread = new Thread("CpuTracker") {
            @Override
            public void run() {
                while (true) {
                    try {
                        try {
                            synchronized(this) {
                                final long now = SystemClock.uptimeMillis();
                                long nextCpuDelay = (mLastCpuTime.get()+MONITOR_CPU_MAX_TIME)-now;
                                long nextWriteDelay = (mLastWriteTime+BATTERY_STATS_TIME)-now;
                                //Slog.i(TAG, "Cpu delay=" + nextCpuDelay
                                //        + ", write delay=" + nextWriteDelay);
                                if (nextWriteDelay < nextCpuDelay) {
                                    nextCpuDelay = nextWriteDelay;
                                }
                                if (nextCpuDelay > 0) {
                                    mProcessCpuMutexFree.set(true);
                                    this.wait(nextCpuDelay);
                                }
                            }
                        } catch (InterruptedException e) {
                        }
                        updateCpuStatsNow();
                    } catch (Exception e) {
                        Slog.e(TAG, "Unexpected exception collecting process stats", e);
                    }
                }
            }
        };
	if(SystemProperties.getBoolean("ro.config.low_ram", false) ||
		SystemProperties.getBoolean("sys.mem.opt", false) ) {
		Message msg = Message.obtain();
		msg.what = SW_FLUSH_PAGECACHE_MSG;
		mHandler.sendMessage(msg);
	}
        Watchdog.getInstance().addMonitor(this);
        Watchdog.getInstance().addThread(mHandler);
``