OomAdjuster: demote previous process to cached after configurable timeout

Previous processes shouldn't stay out of cached indefinitely; they
should be eventually moved to cached and allowed to be restricted and
frozen. Add a configurable timeout to decide when the previous app
should move to cached.

The default timeout is 60s.

Bug: 261065790
Test: atest MockingOomAdjusterTests

Change-Id: I2a999bbf5915467343441afcf276437e34459051

2 files changed, 44 insertions, 15 deletions

diff --git a/services/core/java/com/android/server/am/ActivityManagerConstants.java b/services/core/java/com/android/server/am/ActivityManagerConstants.java
index 70f07a9eee6f..b0a2912b5413 100644
--- a/services/core/java/com/android/server/am/ActivityManagerConstants.java
+++ b/services/core/java/com/android/server/am/ActivityManagerConstants.java
@@ -129,6 +129,7 @@ final class ActivityManagerConstants extends ContentObserver {
     static final String KEY_KILL_BG_RESTRICTED_CACHED_IDLE = "kill_bg_restricted_cached_idle";
     static final String KEY_KILL_BG_RESTRICTED_CACHED_IDLE_SETTLE_TIME =
             "kill_bg_restricted_cached_idle_settle_time";
+    static final String KEY_MAX_PREVIOUS_TIME = "max_previous_time";
     /**
      * Note this key is on {@link DeviceConfig#NAMESPACE_ACTIVITY_MANAGER_COMPONENT_ALIAS}.
      * @see #mEnableComponentAlias
@@ -192,6 +193,7 @@ final class ActivityManagerConstants extends ContentObserver {
     private static final float DEFAULT_FGS_START_DENIED_LOG_SAMPLE_RATE = 1; // 100%
     private static final long DEFAULT_PROCESS_KILL_TIMEOUT_MS = 10 * 1000;
     private static final long DEFAULT_NETWORK_ACCESS_TIMEOUT_MS = 200; // 0.2 sec
+    private static final long DEFAULT_MAX_PREVIOUS_TIME = 60 * 1000; // 60s
 
     static final long DEFAULT_BACKGROUND_SETTLE_TIME = 60 * 1000;
     static final long DEFAULT_KILL_BG_RESTRICTED_CACHED_IDLE_SETTLE_TIME_MS = 60 * 1000;
@@ -522,6 +524,9 @@ final class ActivityManagerConstants extends ContentObserver {
     public long TOP_TO_ALMOST_PERCEPTIBLE_GRACE_DURATION =
             DEFAULT_TOP_TO_ALMOST_PERCEPTIBLE_GRACE_DURATION;
 
+    // How long a process can remain at previous oom_adj before dropping to cached
+    public static long MAX_PREVIOUS_TIME = DEFAULT_MAX_PREVIOUS_TIME;
+
     /**
      * The minimum time we allow between crashes, for us to consider this
      * application to be bad and stop its services and reject broadcasts.
@@ -1144,6 +1149,10 @@ final class ActivityManagerConstants extends ContentObserver {
                                 break;
                             case KEY_TOP_TO_FGS_GRACE_DURATION:
                                 updateTopToFgsGraceDuration();
+                                break;
+                            case KEY_MAX_PREVIOUS_TIME:
+                                updateMaxPreviousTime();
+                                break;
                             default:
                                 break;
                         }
@@ -1790,6 +1799,7 @@ final class ActivityManagerConstants extends ContentObserver {
                 DEFAULT_LOW_SWAP_THRESHOLD_PERCENT);
     }
 
+
     private void updateTopToFgsGraceDuration() {
         TOP_TO_FGS_GRACE_DURATION = DeviceConfig.getLong(
                 DeviceConfig.NAMESPACE_ACTIVITY_MANAGER,
@@ -1797,6 +1807,13 @@ final class ActivityManagerConstants extends ContentObserver {
                 DEFAULT_TOP_TO_FGS_GRACE_DURATION);
     }
 
+    private void updateMaxPreviousTime() {
+        MAX_PREVIOUS_TIME = DeviceConfig.getLong(
+                DeviceConfig.NAMESPACE_ACTIVITY_MANAGER,
+                KEY_MAX_PREVIOUS_TIME,
+                DEFAULT_MAX_PREVIOUS_TIME);
+    }
+
     private void updateMinAssocLogDuration() {
         MIN_ASSOC_LOG_DURATION = DeviceConfig.getLong(
                 DeviceConfig.NAMESPACE_ACTIVITY_MANAGER, KEY_MIN_ASSOC_LOG_DURATION,
diff --git a/services/core/java/com/android/server/am/OomAdjuster.java b/services/core/java/com/android/server/am/OomAdjuster.java
index f75b62a96c81..df4c3c2e304b 100644
--- a/services/core/java/com/android/server/am/OomAdjuster.java
+++ b/services/core/java/com/android/server/am/OomAdjuster.java
@@ -1961,25 +1961,37 @@ public class OomAdjuster {
                 }
             }
         }
-
         if (state.getCachedIsPreviousProcess() && state.getCachedHasActivities()) {
-            if (adj > PREVIOUS_APP_ADJ) {
-                // This was the previous process that showed UI to the user.
-                // We want to try to keep it around more aggressively, to give
-                // a good experience around switching between two apps.
-                adj = PREVIOUS_APP_ADJ;
+            // This was the previous process that showed UI to the user.  We want to
+            // try to keep it around more aggressively, to give a good experience
+            // around switching between two apps. However, we don't want to keep the
+            // process in this privileged state indefinitely. Eventually, allow the
+            // app to be demoted to cached.
+            if ((state.getSetProcState() == PROCESS_STATE_LAST_ACTIVITY
+                    && (state.getLastStateTime() + mConstants.MAX_PREVIOUS_TIME) < now)) {
+                procState = PROCESS_STATE_LAST_ACTIVITY;
                 schedGroup = SCHED_GROUP_BACKGROUND;
-                state.setCached(false);
-                state.setAdjType("previous");
+                state.setAdjType("previous-expired");
+                adj = CACHED_APP_MIN_ADJ;
                 if (DEBUG_OOM_ADJ_REASON || logUid == appUid) {
-                    reportOomAdjMessageLocked(TAG_OOM_ADJ, "Raise adj to prev: " + app);
+                    reportOomAdjMessageLocked(TAG_OOM_ADJ, "Expire prev adj: " + app);
                 }
-            }
-            if (procState > PROCESS_STATE_LAST_ACTIVITY) {
-                procState = PROCESS_STATE_LAST_ACTIVITY;
-                state.setAdjType("previous");
-                if (DEBUG_OOM_ADJ_REASON || logUid == appUid) {
-                    reportOomAdjMessageLocked(TAG_OOM_ADJ, "Raise procstate to prev: " + app);
+            } else {
+                if (adj > PREVIOUS_APP_ADJ) {
+                    adj = PREVIOUS_APP_ADJ;
+                    schedGroup = SCHED_GROUP_BACKGROUND;
+                    state.setCached(false);
+                    state.setAdjType("previous");
+                    if (DEBUG_OOM_ADJ_REASON || logUid == appUid) {
+                        reportOomAdjMessageLocked(TAG_OOM_ADJ, "Raise adj to prev: " + app);
+                    }
+                }
+                if (procState > PROCESS_STATE_LAST_ACTIVITY) {
+                    procState = PROCESS_STATE_LAST_ACTIVITY;
+                    state.setAdjType("previous");
+                    if (DEBUG_OOM_ADJ_REASON || logUid == appUid) {
+                        reportOomAdjMessageLocked(TAG_OOM_ADJ, "Raise procstate to prev: " + app);
+                    }
                 }
             }
         }