Modify how the background process LRU list is handled.

A long time ago, we had a concept of an "empty" process -- this was
a process that didn't have any interesting components in it, which
would be placed below everything else in the LRU list.

Empty processes didn't work out well, because you could get into
bad situations where you have filled your LRU list with things that
have hidden activities, pushing empty processes to the bottom and
being immediately killed as soon as they go into the list.  So this
was removed.

This change brings the concept back, but in a slightly different
form, to address a more specific problem: for people who are switching
between N different applications, we would like to try to keep those
activities available in RAM in a consistent manner.  Currently the
previous activities would be killed often quickly and suprisingly,
even on devices with lots of RAM.  This is for two reasons:

(1) As you sit in one application, other things going on in the
background will go to the top of the LRU list, pushing down the
previous apps you have visited, even though you aren't aware at all
of these other things executing.
(2) There is a hard limit on the number of background processes
(currently 16) after which they are killed regardless of the amount
of available RAM.  This is desireable because if there is lots of
RAM we can end up with tons and tons of processes sitting around,
not really serving any purpose, but using up resources.

To improve the situation, we have again a concept of "empty" processes
but now it means one with no activities.  Processes that aren't empty
but in the background list are called hidden.  We maintain these as
two parallel lists, each getting half of the process limit: so with
a 16 process limit, you can have at most 8 empty and 8 hidden processes.

This allows us to consistently keep up to 8 recent applications around
for fast app switching; we will also keep around 8 other processes to
make it more efficient for background work to execute again if it needs
to.

Change-Id: Iee06e45efc20787da6a1e50020e5421c28204bd7

Author: Dianne Hackborn

services/java/com/android/server/am/ActivityManagerService.java

@@ -685,6 +685,18 @@ private class Identity {
      */
     int mLruSeq = 0;
 
+    /**
+     * Keep track of the non-hidden/empty process we last found, to help
+     * determine how to distribute hidden/empty processes next time.
+     */
+    int mNumNonHiddenProcs = 0;
+
+    /**
+     * Keep track of the number of hidden procs, to balance oom adj
+     * distribution between those and empty procs.
+     */
+    int mNumHiddenProcs = 0;
+
     /**
      * Keep track of the number of service processes we last found, to
      * determine on the next iteration which should be B services.
@@ -9081,7 +9093,9 @@ boolean dumpProcessesLocked(FileDescriptor fd, PrintWriter pw, String[] args,
             pw.println("  mGoingToSleep=" + mMainStack.mGoingToSleep);
             pw.println("  mLaunchingActivity=" + mMainStack.mLaunchingActivity);
             pw.println("  mAdjSeq=" + mAdjSeq + " mLruSeq=" + mLruSeq);
-            pw.println("  mNumServiceProcs=" + mNumServiceProcs
+            pw.println("  mNumNonHiddenProcs=" + mNumNonHiddenProcs
+                    + " mNumHiddenProcs=" + mNumHiddenProcs
+                    + " mNumServiceProcs=" + mNumServiceProcs
                     + " mNewNumServiceProcs=" + mNewNumServiceProcs);
         }
 
@@ -9746,6 +9760,7 @@ public int compare(Pair<ProcessRecord, Integer> object1,
                 pw.print("    ");
                 pw.print("oom: max="); pw.print(r.maxAdj);
                 pw.print(" hidden="); pw.print(r.hiddenAdj);
+                pw.print(" empty="); pw.print(r.emptyAdj);
                 pw.print(" curRaw="); pw.print(r.curRawAdj);
                 pw.print(" setRaw="); pw.print(r.setRawAdj);
                 pw.print(" cur="); pw.print(r.curAdj);
@@ -11966,22 +11981,23 @@ private BroadcastQueue isReceivingBroadcast(ProcessRecord app) {
     }
 
     private final int computeOomAdjLocked(ProcessRecord app, int hiddenAdj,
-            ProcessRecord TOP_APP, boolean recursed, boolean doingAll) {
+            int emptyAdj, ProcessRecord TOP_APP, boolean recursed, boolean doingAll) {
         if (mAdjSeq == app.adjSeq) {
             // This adjustment has already been computed.  If we are calling
             // from the top, we may have already computed our adjustment with
             // an earlier hidden adjustment that isn't really for us... if
             // so, use the new hidden adjustment.
             if (!recursed && app.hidden) {
-                app.curAdj = app.curRawAdj = app.nonStoppingAdj = hiddenAdj;
+                app.curAdj = app.curRawAdj = app.nonStoppingAdj =
+                        app.hasActivities ? hiddenAdj : emptyAdj;
             }
             return app.curRawAdj;
         }
 
         if (app.thread == null) {
             app.adjSeq = mAdjSeq;
             app.curSchedGroup = Process.THREAD_GROUP_BG_NONINTERACTIVE;
-            return (app.curAdj=ProcessList.HIDDEN_APP_MAX_ADJ);
+            return (app.curAdj=app.curRawAdj=ProcessList.HIDDEN_APP_MAX_ADJ);
         }
 
         app.adjTypeCode = ActivityManager.RunningAppProcessInfo.REASON_UNKNOWN;
@@ -11998,6 +12014,7 @@ private final int computeOomAdjLocked(ProcessRecord app, int hiddenAdj,
             app.adjType = "fixed";
             app.adjSeq = mAdjSeq;
             app.curRawAdj = app.nonStoppingAdj = app.maxAdj;
+            app.hasActivities = false;
             app.foregroundActivities = false;
             app.keeping = true;
             app.curSchedGroup = Process.THREAD_GROUP_DEFAULT;
@@ -12008,12 +12025,15 @@ private final int computeOomAdjLocked(ProcessRecord app, int hiddenAdj,
             app.systemNoUi = true;
             if (app == TOP_APP) {
                 app.systemNoUi = false;
+                app.hasActivities = true;
             } else if (activitiesSize > 0) {
                 for (int j = 0; j < activitiesSize; j++) {
                     final ActivityRecord r = app.activities.get(j);
                     if (r.visible) {
                         app.systemNoUi = false;
-                        break;
+                    }
+                    if (r.app == app) {
+                        app.hasActivities = true;
                     }
                 }
             }
@@ -12022,6 +12042,7 @@ private final int computeOomAdjLocked(ProcessRecord app, int hiddenAdj,
 
         app.keeping = false;
         app.systemNoUi = false;
+        app.hasActivities = false;
 
         // Determine the importance of the process, starting with most
         // important to least, and assign an appropriate OOM adjustment.
@@ -12037,6 +12058,7 @@ private final int computeOomAdjLocked(ProcessRecord app, int hiddenAdj,
             app.adjType = "top-activity";
             foregroundActivities = true;
             interesting = true;
+            app.hasActivities = true;
         } else if (app.instrumentationClass != null) {
             // Don't want to kill running instrumentation.
             adj = ProcessList.FOREGROUND_APP_ADJ;
@@ -12058,21 +12080,13 @@ private final int computeOomAdjLocked(ProcessRecord app, int hiddenAdj,
             adj = ProcessList.FOREGROUND_APP_ADJ;
             schedGroup = Process.THREAD_GROUP_DEFAULT;
             app.adjType = "exec-service";
-        } else if (activitiesSize > 0) {
-            // This app is in the background with paused activities.
-            // We inspect activities to potentially upgrade adjustment further below.
-            adj = hiddenAdj;
-            schedGroup = Process.THREAD_GROUP_BG_NONINTERACTIVE;
-            app.hidden = true;
-            app.adjType = "bg-activities";
         } else {
-            // A very not-needed process.  If this is lower in the lru list,
-            // we will push it in to the empty bucket.
+            // Assume process is hidden (has activities); we will correct
+            // later if this is not the case.
             adj = hiddenAdj;
             schedGroup = Process.THREAD_GROUP_BG_NONINTERACTIVE;
             app.hidden = true;
-            app.empty = true;
-            app.adjType = "bg-empty";
+            app.adjType = "bg-activities";
         }
 
         boolean hasStoppingActivities = false;
@@ -12089,6 +12103,7 @@ private final int computeOomAdjLocked(ProcessRecord app, int hiddenAdj,
                     }
                     schedGroup = Process.THREAD_GROUP_DEFAULT;
                     app.hidden = false;
+                    app.hasActivities = true;
                     foregroundActivities = true;
                     break;
                 } else if (r.state == ActivityState.PAUSING || r.state == ActivityState.PAUSED) {
@@ -12106,9 +12121,20 @@ private final int computeOomAdjLocked(ProcessRecord app, int hiddenAdj,
                     foregroundActivities = true;
                     hasStoppingActivities = true;
                 }
+                if (r.app == app) {
+                    app.hasActivities = true;
+                }
             }
         }
 
+        if (adj == hiddenAdj && !app.hasActivities) {
+            // Whoops, this process is completely empty as far as we know
+            // at this point.
+            adj = emptyAdj;
+            app.empty = true;
+            app.adjType = "bg-empty";
+        }
+
         if (adj > ProcessList.PERCEPTIBLE_APP_ADJ) {
             if (app.foregroundServices) {
                 // The user is aware of this app, so make it visible.
@@ -12242,8 +12268,16 @@ private final int computeOomAdjLocked(ProcessRecord app, int hiddenAdj,
                                         myHiddenAdj = ProcessList.VISIBLE_APP_ADJ;
                                     }
                                 }
-                                clientAdj = computeOomAdjLocked(
-                                    client, myHiddenAdj, TOP_APP, true, doingAll);
+                                int myEmptyAdj = emptyAdj;
+                                if (myEmptyAdj > client.emptyAdj) {
+                                    if (client.emptyAdj >= ProcessList.VISIBLE_APP_ADJ) {
+                                        myEmptyAdj = client.emptyAdj;
+                                    } else {
+                                        myEmptyAdj = ProcessList.VISIBLE_APP_ADJ;
+                                    }
+                                }
+                                clientAdj = computeOomAdjLocked(client, myHiddenAdj,
+                                        myEmptyAdj, TOP_APP, true, doingAll);
                                 String adjType = null;
                                 if ((cr.flags&Context.BIND_ALLOW_OOM_MANAGEMENT) != 0) {
                                     // Not doing bind OOM management, so treat
@@ -12382,8 +12416,16 @@ private final int computeOomAdjLocked(ProcessRecord app, int hiddenAdj,
                             myHiddenAdj = ProcessList.FOREGROUND_APP_ADJ;
                         }
                     }
-                    int clientAdj = computeOomAdjLocked(
-                        client, myHiddenAdj, TOP_APP, true, doingAll);
+                    int myEmptyAdj = emptyAdj;
+                    if (myEmptyAdj > client.emptyAdj) {
+                        if (client.emptyAdj > ProcessList.FOREGROUND_APP_ADJ) {
+                            myEmptyAdj = client.emptyAdj;
+                        } else {
+                            myEmptyAdj = ProcessList.FOREGROUND_APP_ADJ;
+                        }
+                    }
+                    int clientAdj = computeOomAdjLocked(client, myHiddenAdj,
+                            myEmptyAdj, TOP_APP, true, doingAll);
                     if (adj > clientAdj) {
                         if (app.hasShownUi && app != mHomeProcess
                                 && clientAdj > ProcessList.PERCEPTIBLE_APP_ADJ) {
@@ -12796,9 +12838,10 @@ final void checkExcessivePowerUsageLocked(boolean doKills) {
         }
     }
 
-    private final boolean updateOomAdjLocked(
-            ProcessRecord app, int hiddenAdj, ProcessRecord TOP_APP, boolean doingAll) {
+    private final boolean updateOomAdjLocked(ProcessRecord app, int hiddenAdj,
+            int emptyAdj, ProcessRecord TOP_APP, boolean doingAll) {
         app.hiddenAdj = hiddenAdj;
+        app.emptyAdj = emptyAdj;
 
         if (app.thread == null) {
             return false;
@@ -12808,7 +12851,7 @@ private final boolean updateOomAdjLocked(
 
         boolean success = true;
 
-        computeOomAdjLocked(app, hiddenAdj, TOP_APP, false, doingAll);
+        computeOomAdjLocked(app, hiddenAdj, emptyAdj, TOP_APP, false, doingAll);
 
         if (app.curRawAdj != app.setRawAdj) {
             if (wasKeeping && !app.keeping) {
@@ -12895,7 +12938,8 @@ final boolean updateOomAdjLocked(ProcessRecord app) {
 
         mAdjSeq++;
 
-        boolean success = updateOomAdjLocked(app, app.hiddenAdj, TOP_APP, false);
+        boolean success = updateOomAdjLocked(app, app.hiddenAdj, app.emptyAdj,
+                TOP_APP, false);
         final boolean nowHidden = app.curAdj >= ProcessList.HIDDEN_APP_MIN_ADJ
             && app.curAdj <= ProcessList.HIDDEN_APP_MAX_ADJ;
         if (nowHidden != wasHidden) {
@@ -12923,43 +12967,91 @@ final void updateOomAdjLocked() {
         // how many slots we have for background processes; we may want
         // to put multiple processes in a slot of there are enough of
         // them.
-        int numSlots = ProcessList.HIDDEN_APP_MAX_ADJ - ProcessList.HIDDEN_APP_MIN_ADJ + 1;
-        int factor = (mLruProcesses.size()-4)/numSlots;
-        if (factor < 1) factor = 1;
-        int step = 0;
+        int numSlots = (ProcessList.HIDDEN_APP_MAX_ADJ
+                - ProcessList.HIDDEN_APP_MIN_ADJ + 1) / 2;
+        int emptyFactor = (mLruProcesses.size()-mNumNonHiddenProcs-mNumHiddenProcs)/numSlots;
+        if (emptyFactor < 1) emptyFactor = 1;
+        int hiddenFactor = (mNumHiddenProcs > 0 ? mNumHiddenProcs : 1)/numSlots;
+        if (hiddenFactor < 1) hiddenFactor = 1;
+        int stepHidden = 0;
+        int stepEmpty = 0;
+        final int emptyProcessLimit = mProcessLimit > 1 ? mProcessLimit / 2 : mProcessLimit;
+        final int hiddenProcessLimit = mProcessLimit > 1 ? mProcessLimit / 2 : mProcessLimit;
         int numHidden = 0;
+        int numEmpty = 0;
         int numTrimming = 0;
-        
+
+        mNumNonHiddenProcs = 0;
+        mNumHiddenProcs = 0;
+
         // First update the OOM adjustment for each of the
         // application processes based on their current state.
         int i = mLruProcesses.size();
         int curHiddenAdj = ProcessList.HIDDEN_APP_MIN_ADJ;
+        int nextHiddenAdj = curHiddenAdj+1;
+        int curEmptyAdj = ProcessList.HIDDEN_APP_MIN_ADJ;
+        int nextEmptyAdj = curEmptyAdj+2;
         while (i > 0) {
             i--;
             ProcessRecord app = mLruProcesses.get(i);
             //Slog.i(TAG, "OOM " + app + ": cur hidden=" + curHiddenAdj);
-            updateOomAdjLocked(app, curHiddenAdj, TOP_APP, true);
-            if (curHiddenAdj < ProcessList.HIDDEN_APP_MAX_ADJ
-                && app.curAdj == curHiddenAdj) {
-                step++;
-                if (step >= factor) {
-                    step = 0;
-                    curHiddenAdj++;
-                }
-            }
+            updateOomAdjLocked(app, curHiddenAdj, curEmptyAdj, TOP_APP, true);
             if (!app.killedBackground) {
-                if (app.curAdj >= ProcessList.HIDDEN_APP_MIN_ADJ) {
+                if (app.curRawAdj == curHiddenAdj && app.hasActivities) {
+                    // This process was assigned as a hidden process...  step the
+                    // hidden level.
+                    mNumHiddenProcs++;
+                    if (curHiddenAdj != nextHiddenAdj) {
+                        stepHidden++;
+                        if (stepHidden >= hiddenFactor) {
+                            stepHidden = 0;
+                            curHiddenAdj = nextHiddenAdj;
+                            nextHiddenAdj += 2;
+                            if (nextHiddenAdj > ProcessList.HIDDEN_APP_MAX_ADJ) {
+                                nextHiddenAdj = ProcessList.HIDDEN_APP_MAX_ADJ;
+                            }
+                        }
+                    }
                     numHidden++;
-                    if (numHidden > mProcessLimit) {
+                    if (numHidden > hiddenProcessLimit) {
                         Slog.i(TAG, "No longer want " + app.processName
                                 + " (pid " + app.pid + "): hidden #" + numHidden);
                         EventLog.writeEvent(EventLogTags.AM_KILL, app.pid,
                                 app.processName, app.setAdj, "too many background");
                         app.killedBackground = true;
                         Process.killProcessQuiet(app.pid);
                     }
+                } else {
+                    if (app.curRawAdj == curEmptyAdj || app.curRawAdj == curHiddenAdj) {
+                        // This process was assigned as an empty process...  step the
+                        // empty level.
+                        if (curEmptyAdj != nextEmptyAdj) {
+                            stepEmpty++;
+                            if (stepEmpty >= emptyFactor) {
+                                stepEmpty = 0;
+                                curEmptyAdj = nextEmptyAdj;
+                                nextEmptyAdj += 2;
+                                if (nextEmptyAdj > ProcessList.HIDDEN_APP_MAX_ADJ) {
+                                    nextEmptyAdj = ProcessList.HIDDEN_APP_MAX_ADJ;
+                                }
+                            }
+                        }
+                    } else if (app.curRawAdj < ProcessList.HIDDEN_APP_MIN_ADJ) {
+                        mNumNonHiddenProcs++;
+                    }
+                    if (app.curAdj >= ProcessList.HIDDEN_APP_MIN_ADJ) {
+                        numEmpty++;
+                        if (numEmpty > emptyProcessLimit) {
+                            Slog.i(TAG, "No longer want " + app.processName
+                                    + " (pid " + app.pid + "): empty #" + numEmpty);
+                            EventLog.writeEvent(EventLogTags.AM_KILL, app.pid,
+                                    app.processName, app.setAdj, "too many background");
+                            app.killedBackground = true;
+                            Process.killProcessQuiet(app.pid);
+                        }
+                    }
                 }
-                if (!app.killedBackground && app.isolated && app.services.size() <= 0) {
+                if (app.isolated && app.services.size() <= 0) {
                     // If this is an isolated process, and there are no
                     // services running in it, then the process is no longer
                     // needed.  We agressively kill these because we can by
@@ -12989,18 +13081,20 @@ final void updateOomAdjLocked() {
         // are managing to keep around is less than half the maximum we desire;
         // if we are keeping a good number around, we'll let them use whatever
         // memory they want.
-        if (numHidden <= (ProcessList.MAX_HIDDEN_APPS/2)) {
+        if (numHidden <= (ProcessList.MAX_HIDDEN_APPS/4)
+                && numEmpty <= (ProcessList.MAX_HIDDEN_APPS/4)) {
+            final int numHiddenAndEmpty = numHidden + numEmpty;
             final int N = mLruProcesses.size();
-            factor = numTrimming/3;
+            int factor = numTrimming/3;
             int minFactor = 2;
             if (mHomeProcess != null) minFactor++;
             if (mPreviousProcess != null) minFactor++;
             if (factor < minFactor) factor = minFactor;
-            step = 0;
+            int step = 0;
             int fgTrimLevel;
-            if (numHidden <= (ProcessList.MAX_HIDDEN_APPS/5)) {
+            if (numHiddenAndEmpty <= (ProcessList.MAX_HIDDEN_APPS/5)) {
                 fgTrimLevel = ComponentCallbacks2.TRIM_MEMORY_RUNNING_CRITICAL;
-            } else if (numHidden <= (ProcessList.MAX_HIDDEN_APPS/3)) {
+            } else if (numHiddenAndEmpty <= (ProcessList.MAX_HIDDEN_APPS/3)) {
                 fgTrimLevel = ComponentCallbacks2.TRIM_MEMORY_RUNNING_LOW;
             } else {
                 fgTrimLevel = ComponentCallbacks2.TRIM_MEMORY_RUNNING_MODERATE;