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Analysis of Andriod low on memory printing principle

2022-07-28 12:59:00 【Private dishes】

The source code is based on ：Android R

0. Preface 

02-09 17:15:20.886446  1164 13478 I ActivityManager: Low on memory:
02-09 17:15:20.887069  1164 13478 I ActivityManager:   ntv   ??  986102: [email protected]_64 (pid 389) native
02-09 17:15:20.887069  1164 13478 I ActivityManager:   ntv   ??   54670: logd (pid 261) native
02-09 17:15:20.887069  1164 13478 I ActivityManager:   ntv   ??   17231: surfaceflinger (pid 421) native
02-09 17:15:20.887069  1164 13478 I ActivityManager:   ntv   ??   10194: zygote (pid 367) native
02-09 17:15:20.887069  1164 13478 I ActivityManager:   ntv   ??   10051: webview_zygote (pid 1696) native
02-09 17:15:20.887069  1164 13478 I ActivityManager:   ntv   ??    9442: qcrild (pid 716) native
02-09 17:15:20.887069  1164 13478 I ActivityManager:   ntv   ??    8538: qcrild (pid 681) native
02-09 17:15:20.887069  1164 13478 I ActivityManager:   ntv   ??    7767: cameraserver (pid 578) native
02-09 17:15:20.887069  1164 13478 I ActivityManager:   ntv   ??    7081: audioserver (pid 418) native
02-09 17:15:20.887069  1164 13478 I ActivityManager:   ntv   ??    6399: mediaserver (pid 647) native
02-09 17:15:20.887069  1164 13478 I ActivityManager:   ntv   ??    6032: zygote64 (pid 366) native
02-09 17:15:20.887069  1164 13478 I ActivityManager:   ntv   ??    5666: netmgrd (pid 673) native
02-09 17:15:20.887069  1164 13478 I ActivityManager:   ntv   ??    4992: media.metrics (pid 645) native
02-09 17:15:20.887069  1164 13478 I ActivityManager:   ntv   ??    4738: media.swcodec (pid 678) native
02-09 17:15:20.887069  1164 13478 I ActivityManager:   ntv   ??    4687: init (pid 1) native
02-09 17:15:20.887069  1164 13478 I ActivityManager:   ntv   ??    4634: [email protected] (pid 393) native
02-09 17:15:20.887069  1164 13478 I ActivityManager:   ntv   ??    4579: android.hardware.audio.service (pid 386) native
02-09 17:15:20.887069  1164 13478 I ActivityManager:   ntv   ??    4565: media.extractor (pid 637) native
02-09 17:15:20.887069  1164 13478 I ActivityManager:   ntv   ??    4131: imsdaemon (pid 668) native

...

02-09 17:15:20.887217  1164 13478 I ActivityManager:   vis    IMPF    7024: com.android.smspush (pid 2446) service
02-09 17:15:20.887217  1164 13478 I ActivityManager:                        com.android.smspush/.WapPushManager<=Proc{1902:com.android.phone/1001}
02-09 17:15:20.887217  1164 13478 I ActivityManager:   prcp   IMPB   65781: com.sohu.inputmethod.sogou (pid 11697) service
02-09 17:15:20.887217  1164 13478 I ActivityManager:                        com.sohu.inputmethod.sogou/.SogouIME<=Proc{1164:system/1000}
02-09 17:15:20.887217  1164 13478 I ActivityManager:   prcp   IMPB   13053: com.android.webview:sandboxed_process0:org.chromium.content.app.SandboxedProcessService0:0 (pid 12509) service
02-09 17:15:20.887217  1164 13478 I ActivityManager:                        com.sohu.inputmethod.sogou/org.chromium.content.app.SandboxedProcessService0:0<=Proc{11697:com.sohu.inputmethod.sogou/u0a151}
02-09 17:15:20.887217  1164 13478 I ActivityManager:   svc    SVC    22194: com.sohu.inputmethod.sogou:push_service (pid 12588) started-services
02-09 17:15:20.887217  1164 13478 I ActivityManager:   prev   LAST   19057: com.android.packageinstaller (pid 11380) previous
02-09 17:15:20.887217  1164 13478 I ActivityManager:            2227718: TOTAL

Recently, I often encounter logcat Print in Low on memory, Here we will analyze the source code .

It is roughly divided into the following parts ：

  • log What is the basis of the information in ？
  • In addition to this information, what are the key points ？
  • The log How to trigger printing ？

1. reportMemUsage

log The characters in are easy to find from the source code , And information processing is all in reportMemUsage in , Because there are many function processing logics , Here the analysis is carried out in sections .

Code path ：frameworks/base/services/core/java/com/android/server/am/AMS.java

    void reportMemUsage(ArrayList<ProcessMemInfo> memInfos) {

Parameters are discussed below , Here we think it is the result of all processes ProcessMemInfo.

step1. Arrangement ProcessMemInfo

        final SparseArray<ProcessMemInfo> infoMap = new SparseArray<>(memInfos.size());
        for (int i=0, N=memInfos.size(); i<N; i++) {
            ProcessMemInfo mi = memInfos.get(i);
            infoMap.put(mi.pid, mi);
        }

take ProcessMemInfo Save to new SparseArray in .

step2. to update CPU state

Then, through the function updateCpuStatsNow() Update at this point CPU state , The code of the function is not posted , You can check the source code if you are interested , Also in AMS.java in .

The main attention is to member variables mProcessCpuTracker, adopt update Function update data ：

    void updateCpuStatsNow() {
        synchronized (mProcessCpuTracker) {
            ...
                mProcessCpuTracker.update();

---->upodate()

frameworks/base/core/java/com/android/internal/os/ProcessCpuTracker.java

    public void update() {
        ...

        if (Process.readProcFile("/proc/stat", SYSTEM_CPU_FORMAT,
                null, sysCpu, null)) {
            ...

        }

        ...

        try {
            mCurPids = collectStats("/proc", -1, mFirst, mCurPids, mProcStats);
        } finally {
            StrictMode.setThreadPolicy(savedPolicy);
        }

        ...

        final float[] loadAverages = mLoadAverageData;
        if (Process.readProcFile("/proc/loadavg", LOAD_AVERAGE_FORMAT,
                null, null, loadAverages)) {
            ...
        }

        ...
    }
  • Read /proc/stat Node related information , for example user time、system time、io wait time、irq time、idle time etc. ;
  • collectStats collect /proc All process information under the directory ;
  • Read /proc/loadavg Node information ,dumpsys cpuinfo perhaps ANR It will be printed when ;

step3. Acquisition process PSS

        for (int i = 0; i < statsCount; i++) {
            ProcessCpuTracker.Stats st = stats.get(i);
            long pss = Debug.getPss(st.pid, swaptrackTmp, memtrackTmp);
            if (pss > 0) {
                if (infoMap.indexOfKey(st.pid) < 0) {
                    ProcessMemInfo mi = new ProcessMemInfo(st.name, st.pid,
                            ProcessList.NATIVE_ADJ, -1, "native", null);
                    mi.pss = pss;
                    mi.swapPss = swaptrackTmp[1];
                    mi.memtrack = memtrackTmp[0];
                    memInfos.add(mi);
                }
            }
        }

        long totalPss = 0;
        long totalSwapPss = 0;
        long totalMemtrack = 0;
        for (int i=0, N=memInfos.size(); i<N; i++) {
            ProcessMemInfo mi = memInfos.get(i);
            if (mi.pss == 0) {
                mi.pss = Debug.getPss(mi.pid, swaptrackTmp, memtrackTmp);
                mi.swapPss = swaptrackTmp[1];
                mi.memtrack = memtrackTmp[0];
            }
            totalPss += mi.pss;
            totalSwapPss += mi.swapPss;
            totalMemtrack += mi.memtrack;
        }

step4. Yes ProcessMemInfo according to oom adj Sort 

        Collections.sort(memInfos, new Comparator<ProcessMemInfo>() {
            @Override public int compare(ProcessMemInfo lhs, ProcessMemInfo rhs) {
                if (lhs.oomAdj != rhs.oomAdj) {
                    return lhs.oomAdj < rhs.oomAdj ? -1 : 1;
                }
                if (lhs.pss != rhs.pss) {
                    return lhs.pss < rhs.pss ? 1 : -1;
                }
                return 0;
            }
        });

If oom adj There is a small to large order , If oom adj identical , According to pss From big to small .

step5. to update tag builder

stay reportMemUsage There are several important in this function StringBuilder object , These objects contain late logcat and DropBox Information required for document printing .

there tag builder, It's for later drop box Prepare information .

for (int i=0, N=memInfos.size(); i<N; i++) {
            ProcessMemInfo mi = memInfos.get(i);

            if (mi.oomAdj >= ProcessList.CACHED_APP_MIN_ADJ) {
                cachedPss += mi.pss;
            }

            if (mi.oomAdj != ProcessList.NATIVE_ADJ
                    && (mi.oomAdj < ProcessList.SERVICE_ADJ
                            || mi.oomAdj == ProcessList.HOME_APP_ADJ
                            || mi.oomAdj == ProcessList.PREVIOUS_APP_ADJ)) {
                if (lastOomAdj != mi.oomAdj) {
                    lastOomAdj = mi.oomAdj;
                    if (mi.oomAdj <= ProcessList.FOREGROUND_APP_ADJ) {
                        tag.append(" / ");
                    }
                    if (mi.oomAdj >= ProcessList.FOREGROUND_APP_ADJ) {
                        if (firstLine) {
                            stack.append(":");
                            firstLine = false;
                        }
                        stack.append("\n\t at ");
                    } else {
                        stack.append("$");
                    }
                } else {
                    tag.append(" ");
                    stack.append("$");
                }
                if (mi.oomAdj <= ProcessList.FOREGROUND_APP_ADJ) {
                    appendMemBucket(tag, mi.pss, mi.name, false);
                }
                appendMemBucket(stack, mi.pss, mi.name, true);
                if (mi.oomAdj >= ProcessList.FOREGROUND_APP_ADJ
                        && ((i+1) >= N || memInfos.get(i+1).oomAdj != lastOomAdj)) {
                    stack.append("(");
                    for (int k=0; k<DUMP_MEM_OOM_ADJ.length; k++) {
                        if (DUMP_MEM_OOM_ADJ[k] == mi.oomAdj) {
                            stack.append(DUMP_MEM_OOM_LABEL[k]);
                            stack.append(":");
                            stack.append(DUMP_MEM_OOM_ADJ[k]);
                        }
                    }
                    stack.append(")");
                }
            }

step6. to update full Native builder and short Native builder、java builder

            appendMemInfo(fullNativeBuilder, mi);
            if (mi.oomAdj == ProcessList.NATIVE_ADJ) {
                // The short form only has native processes that are >= 512K.
                if (mi.pss >= 512) {
                    appendMemInfo(shortNativeBuilder, mi);
                } else {
                    extraNativeRam += mi.pss;
                    extraNativeMemtrack += mi.memtrack;
                }
            } else {
                // Short form has all other details, but if we have collected RAM
                // from smaller native processes let's dump a summary of that.
                if (extraNativeRam > 0) {
                    appendBasicMemEntry(shortNativeBuilder, ProcessList.NATIVE_ADJ,
                            -1, extraNativeRam, extraNativeMemtrack, "(Other native)");
                    shortNativeBuilder.append('\n');
                    extraNativeRam = 0;
                }
                appendMemInfo(fullJavaBuilder, mi);
            }
  • In memory 512KB Above native Process information will be stored in shortNativeBuilder in ;
  • In memory 512KB Below is the sum of Statistics , And finally Other native The form is spliced in shortNativeBuilder;
  • Java Process information is placed in fullJavaBuilder in ;
        fullJavaBuilder.append("           ");
        ProcessList.appendRamKb(fullJavaBuilder, totalPss);
        fullJavaBuilder.append(": TOTAL");
        if (totalMemtrack > 0) {
            fullJavaBuilder.append(" (");
            fullJavaBuilder.append(stringifyKBSize(totalMemtrack));
            fullJavaBuilder.append(" memtrack)");
        } else {
        }
        fullJavaBuilder.append("\n");

  stay fullJavaBuilder Finally, add the last total pss. There could be total memtrack.

step7. Read /proc/meminfo Information 

        MemInfoReader memInfo = new MemInfoReader();
        memInfo.readMemInfo();
        final long[] infos = memInfo.getRawInfo();

Read meminfo Store in MemInfoReader Member variable in mInfos in , Through interface getRawInfo obtain ;

step8. according to meminfo to update MemInfoBuilder

Too much code , No more , Take a look log：

02-09 17:15:20.887254  1164 13478 I ActivityManager:   MemInfo:   192,372K slab,    13,844K shmem,    70,432K vm alloc,    44,800K page tables    30,704K kernel stack
02-09 17:15:20.887254  1164 13478 I ActivityManager:                  880K buffers,   349,444K cached,   286,888K mapped, 1,012,108K free
02-09 17:15:20.887254  1164 13478 I ActivityManager:   ZRAM:   166,244K RAM, 1,572,860K swap total, 1,047,972K swap free
02-09 17:15:20.887254  1164 13478 I ActivityManager:   Free RAM: 1,126,524K
02-09 17:15:20.887254  1164 13478 I ActivityManager:        ION:   149,764K
02-09 17:15:20.887254  1164 13478 I ActivityManager:   Used RAM: 2,615,922K
02-09 17:15:20.887254  1164 13478 I ActivityManager:   Lost RAM:  -671,218K

step9. logcat Print 

        Slog.i(TAG, "Low on memory:");
        Slog.i(TAG, shortNativeBuilder.toString());
        Slog.i(TAG, fullJavaBuilder.toString());
        Slog.i(TAG, memInfoBuilder.toString());

Here is the logcat See the print , Three main aspects ：

  • shortNativeBuilder Count all items greater than 512KB Of native The process of , Others are less than 512KB Of native Will be with other appear ;
  • fullJavaBuilder Statistics of all java Information about the process ;
  • memInfoBuilder Count the current process /proc/meminfo;

Be careful logcat Medium 

02-09 17:15:20.887217  1164 13478 I ActivityManager:   pers   PER    83753: com.android.systemui (pid 1520) fixed
02-09 17:15:20.887217  1164 13478 I ActivityManager:   pers   PER    51579: com.android.phone (pid 1902) fixed

Be careful TAG The last two columns ,pers、PER They correspond to each other oom adj and proc state.

Let's start with oom adj Corresponding string：

  • cch     ----  CACHED_APP_MIN_ADJ
  • svcb   ---- SERVICE_B_ADJ
  • prev   ---- PREVIOUS_APP_ADJ
  • home ---- HOME_APP_ADJ
  • svc    ---- SERVICE_ADJ
  • hvy    ---- HEAVY_WEIGHT_APP_ADJ
  • bkup  ---- BACKUP_APP_ADJ
  • prcl    ---- PERCEPTIBLE_LOW_APP_ADJ
  • prcp   ---- PERCEPTIBLE_APP_ADJ
  • vis     ---- VISIBLE_APP_ADJ
  • fg      ---- FOREGROUND_APP_ADJ
  • psvc  ---- PERSISTENT_SERVICE_ADJ
  • pers  ---- PERSISTENT_PROC_ADJ
  • sys    ---- SYSTEM_ADJ
  • ntv    ---- NATIVE_ADJ

And then look at proc state Corresponding string：

  • PER    ---- PROCESS_STATE_PERSISTENT
  • PERU ---- PROCESS_STATE_PERSISTENT_UI
  • TOP    ---- PROCESS_STATE_TOP
  • BTOP  ---- PROCESS_STATE_BOUND_TOP
  • FGS    ---- PROCESS_STATE_FOREGROUND_SERVICE
  • BFGS  ---- PROCESS_STATE_BOUND_FOREGROUND_SERVICE
  • IMPF   ---- PROCESS_STATE_IMPORTANT_FOREGROUND
  • IMPB   ---- PROCESS_STATE_IMPORTANT_BACKGROUND
  • TRNB  ---- PROCESS_STATE_TRANSIENT_BACKGROUND
  • BKUP  ---- PROCESS_STATE_BACKUP
  • SVC    ---- PROCESS_STATE_SERVICE
  • RCVR  ---- PROCESS_STATE_RECEIVER
  • TPSL   ---- PROCESS_STATE_TOP_SLEEPING
  • HVY    ---- PROCESS_STATE_HEAVY_WEIGHT
  • HOME ---- PROCESS_STATE_HOME
  • LAST   ---- PROCESS_STATE_LAST_ACTIVITY
  • CAC    ---- PROCESS_STATE_CACHED_ACTIVITY
  • CACC ---- PROCESS_STATE_CACHED_ACTIVITY_CLIENT
  • CRE   ---- PROCESS_STATE_CACHED_RECENT
  • CEM   ---- PROCESS_STATE_CACHED_EMPTY
  • NONE ---- PROCESS_STATE_CACHED_EMPTY
  • other     ---- ??

step10. Arrangement dropBuilder

Pass above stack builder、fullNativeBuilder、fullJavaBuilder、memInfoBuilder Arrangement dropBuilder Used to output drop box.

2. Trigger reportMemUsage

Next, analyze the reasons for triggering these printing .

2.1 reportMemUsage From message REPORT_MEM_USAGE_MSG

From the code context , Trigger reportMemUsage() There's only one place , Namely MainHandler Medium REPORT_MEM_USAGE_MSG news ：

            case REPORT_MEM_USAGE_MSG: {
                final ArrayList<ProcessMemInfo> memInfos = (ArrayList<ProcessMemInfo>)msg.obj;
                Thread thread = new Thread() {
                    @Override public void run() {
                        reportMemUsage(memInfos);
                    }
                };
                thread.start();
                break;
            }

This message comes with a parameter , Namely reportMemUsage() Parameters in function , in addition , This function is in a Separate threads In the implementation of .

2.2 Message from doLowMemReportIfNeededLocked issue

in addition , There is only one place to send this message , Namely doLowMemReportIfNeededLocked()：

    final void doLowMemReportIfNeededLocked(ProcessRecord dyingProc) {
        // If there are no longer any background processes running,
        // and the app that died was not running instrumentation,
        // then tell everyone we are now low on memory.
        if (!mProcessList.haveBackgroundProcessLocked()) {
            boolean doReport = "1".equals(SystemProperties.get(SYSTEM_DEBUGGABLE, "0"));
            if (doReport) {
                long now = SystemClock.uptimeMillis();
                if (now < (mLastMemUsageReportTime+5*60*1000)) {
                    doReport = false;
                } else {
                    mLastMemUsageReportTime = now;
                }
            }
            final ArrayList<ProcessMemInfo> memInfos
                    = doReport ? new ArrayList<ProcessMemInfo>(mProcessList.getLruSizeLocked())
                    : null;
            EventLogTags.writeAmLowMemory(mProcessList.getLruSizeLocked());
            long now = SystemClock.uptimeMillis();
            for (int i = mProcessList.mLruProcesses.size() - 1; i >= 0; i--) {
                ProcessRecord rec = mProcessList.mLruProcesses.get(i);
                if (rec == dyingProc || rec.thread == null) {
                    continue;
                }
                if (doReport) {
                    memInfos.add(new ProcessMemInfo(rec.processName, rec.pid, rec.setAdj,
                            rec.setProcState, rec.adjType, rec.makeAdjReason()));
                }
                if ((rec.lastLowMemory+mConstants.GC_MIN_INTERVAL) <= now) {
                    // The low memory report is overriding any current
                    // state for a GC request.  Make sure to do
                    // heavy/important/visible/foreground processes first.
                    if (rec.setAdj <= ProcessList.HEAVY_WEIGHT_APP_ADJ) {
                        rec.lastRequestedGc = 0;
                    } else {
                        rec.lastRequestedGc = rec.lastLowMemory;
                    }
                    rec.reportLowMemory = true;
                    rec.lastLowMemory = now;
                    mProcessesToGc.remove(rec);
                    addProcessToGcListLocked(rec);
                }
            }
            if (doReport) {
                Message msg = mHandler.obtainMessage(REPORT_MEM_USAGE_MSG, memInfos);
                mHandler.sendMessage(msg);
            }
            scheduleAppGcsLocked();
        }
    }

The details of this function need attention ：

  • Need to print mem usage, need ro.debuggable Yes, it is 1 Of , The default value is 0. That's it Printing will only appear in user debug or engine edition ;
  • Printed on 5 It will only appear once in minutes ;
  • The printed memory information will only be the current or process ;

2.3 doLowMemReportIfNeededLocked Trigger

Trigger source of function ：

  • killAllBackgroundProcesses()      The function is AMS External interface function of , It is used for users to actively call
  • appDiedLocked()    This paper mainly analyzes the trigger process of this function

2.4 appDiedLocked

    private final class AppDeathRecipient implements IBinder.DeathRecipient {
        final ProcessRecord mApp;
        final int mPid;
        final IApplicationThread mAppThread;

        AppDeathRecipient(ProcessRecord app, int pid,
                IApplicationThread thread) {
            ...
        }

        @Override
        public void binderDied() {
            ...
            synchronized(ActivityManagerService.this) {
                appDiedLocked(mApp, mPid, mAppThread, true, null);
            }
        }
    }

If you want to see appDiedLocked This method , The first thing to know is that ActivityThread.main() in , Starting from here, the process will be bound from this method after creation AMS, stay AMS By calling AMS.attachApplicationLocked() This method starts binding , In this method, there will be right ApplicationThreadProxy Binding notification ：

    private boolean attachApplicationLocked(@NonNull IApplicationThread thread,
            int pid, int callingUid, long startSeq) {
        ...

        final String processName = app.processName;
        try {
            AppDeathRecipient adr = new AppDeathRecipient(
                    app, pid, thread);
            thread.asBinder().linkToDeath(adr, 0);
            app.deathRecipient = adr;
        } catch (RemoteException e) {
            ...
        }

        ...

among IApplicationThread thread Is in ActivityThread The process created in belongs to the newly created process （ For example, new app The process of ）.client Namely ApplicationThreadProxy object , The object is AMS in ,AMS Is in system_server in . So when we binder server When you die （app Process death ） We system_server The process will be notified , Then do something about it .

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