Merge changes from topic "CacheOomRanker-new-features-sc-qpr1-dev" into sc-qpr1-dev

* changes:
  Use Process.getRss instead of mProfile.getLastRss in CacheOomRanker.
  Change CacheOomRanker's "uses" feature.
  Fix race condition when using mPreserveTopNApps.
  Allow CacheOomRanker to rerank when there's <8 processes in the cache.
  Fix CacheOomRankerTest.

core/java/android/app/ActivityManager.java

@@ -771,6 +771,11 @@ public class ActivityManager {
         return procState >= PROCESS_STATE_TRANSIENT_BACKGROUND;
     }
 
+    /** @hide Should this process state be considered in the cache? */
+    public static final boolean isProcStateCached(int procState) {
+        return procState >= PROCESS_STATE_CACHED_ACTIVITY;
+    }
+
     /** @hide Is this a foreground service type? */
     public static boolean isForegroundService(int procState) {
         return procState == PROCESS_STATE_FOREGROUND_SERVICE;

services/core/java/com/android/server/am/CacheOomRanker.java

@@ -16,6 +16,8 @@
 
 package com.android.server.am;
 
+import android.os.Process;
+import android.os.SystemClock;
 import android.provider.DeviceConfig;
 import android.util.Slog;
 
@@ -38,21 +40,40 @@ public class CacheOomRanker {
     private static final boolean DEFAULT_USE_OOM_RE_RANKING = false;
     @VisibleForTesting
     static final String KEY_OOM_RE_RANKING_NUMBER_TO_RE_RANK = "oom_re_ranking_number_to_re_rank";
-    @VisibleForTesting static final int DEFAULT_OOM_RE_RANKING_NUMBER_TO_RE_RANK = 8;
+    @VisibleForTesting
+    static final int DEFAULT_OOM_RE_RANKING_NUMBER_TO_RE_RANK = 8;
+    @VisibleForTesting
+    static final String KEY_OOM_RE_RANKING_PRESERVE_TOP_N_APPS =
+            "oom_re_ranking_preserve_top_n_apps";
+    @VisibleForTesting
+    static final int DEFAULT_PRESERVE_TOP_N_APPS = 3;
+    @VisibleForTesting
+    static final String KEY_OOM_RE_RANKING_USE_FREQUENT_RSS = "oom_re_ranking_rss_use_frequent_rss";
+    @VisibleForTesting
+    static final boolean DEFAULT_USE_FREQUENT_RSS = true;
+    @VisibleForTesting
+    static final String KEY_OOM_RE_RANKING_RSS_UPDATE_RATE_MS = "oom_re_ranking_rss_update_rate_ms";
+    @VisibleForTesting
+    static final long DEFAULT_RSS_UPDATE_RATE_MS = 10_000; // 10 seconds
     @VisibleForTesting
     static final String KEY_OOM_RE_RANKING_LRU_WEIGHT = "oom_re_ranking_lru_weight";
-    @VisibleForTesting static final float DEFAULT_OOM_RE_RANKING_LRU_WEIGHT = 0.35f;
+    @VisibleForTesting
+    static final float DEFAULT_OOM_RE_RANKING_LRU_WEIGHT = 0.35f;
     @VisibleForTesting
     static final String KEY_OOM_RE_RANKING_USES_WEIGHT = "oom_re_ranking_uses_weight";
-    @VisibleForTesting static final float DEFAULT_OOM_RE_RANKING_USES_WEIGHT = 0.5f;
+    @VisibleForTesting
+    static final float DEFAULT_OOM_RE_RANKING_USES_WEIGHT = 0.5f;
     @VisibleForTesting
     static final String KEY_OOM_RE_RANKING_RSS_WEIGHT = "oom_re_ranking_rss_weight";
-    @VisibleForTesting static final float DEFAULT_OOM_RE_RANKING_RSS_WEIGHT = 0.15f;
+    @VisibleForTesting
+    static final float DEFAULT_OOM_RE_RANKING_RSS_WEIGHT = 0.15f;
 
     private static final Comparator<RankedProcessRecord> SCORED_PROCESS_RECORD_COMPARATOR =
             new ScoreComparator();
     private static final Comparator<RankedProcessRecord> CACHE_USE_COMPARATOR =
             new CacheUseComparator();
+    private static final Comparator<RankedProcessRecord> RSS_COMPARATOR =
+            new RssComparator();
     private static final Comparator<RankedProcessRecord> LAST_RSS_COMPARATOR =
             new LastRssComparator();
     private static final Comparator<RankedProcessRecord> LAST_ACTIVITY_TIME_COMPARATOR =
@@ -61,20 +82,33 @@ public class CacheOomRanker {
     private final Object mPhenotypeFlagLock = new Object();
 
     private final ActivityManagerService mService;
+    private final ProcessDependencies mProcessDependencies;
     private final ActivityManagerGlobalLock mProcLock;
     private final Object mProfilerLock;
 
     @GuardedBy("mPhenotypeFlagLock")
     private boolean mUseOomReRanking = DEFAULT_USE_OOM_RE_RANKING;
+    @GuardedBy("mPhenotypeFlagLock")
+    @VisibleForTesting
+    int mPreserveTopNApps = DEFAULT_PRESERVE_TOP_N_APPS;
+    @GuardedBy("mPhenotypeFlagLock")
+    @VisibleForTesting
+    boolean mUseFrequentRss = DEFAULT_USE_FREQUENT_RSS;
+    @GuardedBy("mPhenotypeFlagLock")
+    @VisibleForTesting
+    long mRssUpdateRateMs = DEFAULT_RSS_UPDATE_RATE_MS;
     // Weight to apply to the LRU ordering.
     @GuardedBy("mPhenotypeFlagLock")
-    @VisibleForTesting float mLruWeight = DEFAULT_OOM_RE_RANKING_LRU_WEIGHT;
+    @VisibleForTesting
+    float mLruWeight = DEFAULT_OOM_RE_RANKING_LRU_WEIGHT;
     // Weight to apply to the ordering by number of times the process has been added to the cache.
     @GuardedBy("mPhenotypeFlagLock")
-    @VisibleForTesting float mUsesWeight = DEFAULT_OOM_RE_RANKING_USES_WEIGHT;
+    @VisibleForTesting
+    float mUsesWeight = DEFAULT_OOM_RE_RANKING_USES_WEIGHT;
     // Weight to apply to the ordering by RSS used by the processes.
     @GuardedBy("mPhenotypeFlagLock")
-    @VisibleForTesting float mRssWeight = DEFAULT_OOM_RE_RANKING_RSS_WEIGHT;
+    @VisibleForTesting
+    float mRssWeight = DEFAULT_OOM_RE_RANKING_RSS_WEIGHT;
 
     // Positions to replace in the lru list.
     @GuardedBy("mPhenotypeFlagLock")
@@ -93,6 +127,12 @@ public class CacheOomRanker {
                                 updateUseOomReranking();
                             } else if (KEY_OOM_RE_RANKING_NUMBER_TO_RE_RANK.equals(name)) {
                                 updateNumberToReRank();
+                            } else if (KEY_OOM_RE_RANKING_PRESERVE_TOP_N_APPS.equals(name)) {
+                                updatePreserveTopNApps();
+                            } else if (KEY_OOM_RE_RANKING_USE_FREQUENT_RSS.equals(name)) {
+                                updateUseFrequentRss();
+                            } else if (KEY_OOM_RE_RANKING_RSS_UPDATE_RATE_MS.equals(name)) {
+                                updateRssUpdateRateMs();
                             } else if (KEY_OOM_RE_RANKING_LRU_WEIGHT.equals(name)) {
                                 updateLruWeight();
                             } else if (KEY_OOM_RE_RANKING_USES_WEIGHT.equals(name)) {
@@ -106,9 +146,15 @@ public class CacheOomRanker {
             };
 
     CacheOomRanker(final ActivityManagerService service) {
+        this(service, new ProcessDependenciesImpl());
+    }
+
+    @VisibleForTesting
+    CacheOomRanker(final ActivityManagerService service, ProcessDependencies processDependencies) {
         mService = service;
         mProcLock = service.mProcLock;
         mProfilerLock = service.mAppProfiler.mProfilerLock;
+        mProcessDependencies = processDependencies;
     }
 
     /** Load settings from device config and register a listener for changes. */
@@ -159,6 +205,31 @@ public class CacheOomRanker {
         return mScoredProcessRecords == null ? 0 : mScoredProcessRecords.length;
     }
 
+    @GuardedBy("mPhenotypeFlagLock")
+    private void updatePreserveTopNApps() {
+        int preserveTopNApps = DeviceConfig.getInt(DeviceConfig.NAMESPACE_ACTIVITY_MANAGER,
+                KEY_OOM_RE_RANKING_PRESERVE_TOP_N_APPS, DEFAULT_PRESERVE_TOP_N_APPS);
+        if (preserveTopNApps < 0) {
+            Slog.w(OomAdjuster.TAG,
+                    "Found negative value for preserveTopNApps, setting to default: "
+                            + preserveTopNApps);
+            preserveTopNApps = DEFAULT_PRESERVE_TOP_N_APPS;
+        }
+        mPreserveTopNApps = preserveTopNApps;
+    }
+
+    @GuardedBy("mPhenotypeFlagLock")
+    private void updateRssUpdateRateMs() {
+        mRssUpdateRateMs = DeviceConfig.getLong(DeviceConfig.NAMESPACE_ACTIVITY_MANAGER,
+                KEY_OOM_RE_RANKING_RSS_UPDATE_RATE_MS, DEFAULT_RSS_UPDATE_RATE_MS);
+    }
+
+    @GuardedBy("mPhenotypeFlagLock")
+    private void updateUseFrequentRss() {
+        mUseFrequentRss = DeviceConfig.getBoolean(DeviceConfig.NAMESPACE_ACTIVITY_MANAGER,
+                KEY_OOM_RE_RANKING_USE_FREQUENT_RSS, DEFAULT_USE_FREQUENT_RSS);
+    }
+
     @GuardedBy("mPhenotypeFlagLock")
     private void updateLruWeight() {
         mLruWeight = DeviceConfig.getFloat(DeviceConfig.NAMESPACE_ACTIVITY_MANAGER,
@@ -183,9 +254,39 @@ public class CacheOomRanker {
      */
     @GuardedBy({"mService", "mProcLock"})
     void reRankLruCachedAppsLSP(ArrayList<ProcessRecord> lruList, int lruProcessServiceStart) {
+        // The lruList is a list of processes ordered by how recently they were used. The
+        // least-recently-used apps are at the beginning of the list. We keep track of two
+        // indices in the lruList:
+        //
+        // getNumberToReRank=5, preserveTopNApps=3, lruProcessServiceStart=7,
+        // lruList=
+        //   0: app A       ^
+        //   1: app B       | These apps are re-ranked, as they are the first five apps (see
+        //   2: app C       | getNumberToReRank), excluding...
+        //   3: app D       v
+        //   4: app E       ^
+        //   5: app F       | The three most-recently-used apps in the cache (see preserveTopNApps).
+        //   6: app G       v
+        //   7: service A   ^
+        //   8: service B   | Everything beyond lruProcessServiceStart is ignored, as these aren't
+        //   9: service C   | apps.
+        //  10: activity A  |
+        //      ...         |
+        //
+        // `numProcessesEvaluated` moves across the apps (indices 0-6) or until we've found enough
+        // apps to re-rank, and made sure none of them are in the top `preserveTopNApps` apps.
+        // Re-ranked apps are copied into `scoredProcessRecords`, where the re-ranking calculation
+        // happens.
+        //
+        // Note that some apps in the `lruList` can be skipped, if they don't pass
+        //`appCanBeReRanked`.
+
         float lruWeight;
         float usesWeight;
         float rssWeight;
+        int preserveTopNApps;
+        boolean useFrequentRss;
+        long rssUpdateRateMs;
         int[] lruPositions;
         RankedProcessRecord[] scoredProcessRecords;
 
@@ -193,6 +294,9 @@ public class CacheOomRanker {
             lruWeight = mLruWeight;
             usesWeight = mUsesWeight;
             rssWeight = mRssWeight;
+            preserveTopNApps = mPreserveTopNApps;
+            useFrequentRss = mUseFrequentRss;
+            rssUpdateRateMs = mRssUpdateRateMs;
             lruPositions = mLruPositions;
             scoredProcessRecords = mScoredProcessRecords;
         }
@@ -202,52 +306,98 @@ public class CacheOomRanker {
             return;
         }
 
+        int numProcessesEvaluated = 0;
         // Collect the least recently used processes to re-rank, only rank cached
         // processes further down the list than mLruProcessServiceStart.
-        int cachedProcessPos = 0;
+        int numProcessesReRanked = 0;
-        for (int i = 0; i < lruProcessServiceStart
+        while (numProcessesEvaluated < lruProcessServiceStart
-                && cachedProcessPos < scoredProcessRecords.length; ++i) {
+                && numProcessesReRanked < scoredProcessRecords.length) {
-            ProcessRecord app = lruList.get(i);
+            ProcessRecord process = lruList.get(numProcessesEvaluated);
             // Processes that will be assigned a cached oom adj score.
-            if (!app.isKilledByAm() && app.getThread() != null && app.mState.getCurAdj()
+            if (appCanBeReRanked(process)) {
-                    >= ProcessList.UNKNOWN_ADJ) {
+                scoredProcessRecords[numProcessesReRanked].proc = process;
-                scoredProcessRecords[cachedProcessPos].proc = app;
+                scoredProcessRecords[numProcessesReRanked].score = 0.0f;
-                scoredProcessRecords[cachedProcessPos].score = 0.0f;
+                lruPositions[numProcessesReRanked] = numProcessesEvaluated;
-                lruPositions[cachedProcessPos] = i;
+                ++numProcessesReRanked;
-                ++cachedProcessPos;
+            }
+            ++numProcessesEvaluated;
+        }
+
+        // Count how many apps we're not re-ranking (up to preserveTopNApps).
+        int numProcessesNotReRanked = 0;
+        while (numProcessesEvaluated < lruProcessServiceStart
+                && numProcessesNotReRanked < preserveTopNApps) {
+            ProcessRecord process = lruList.get(numProcessesEvaluated);
+            if (appCanBeReRanked(process)) {
+                numProcessesNotReRanked++;
+            }
+            numProcessesEvaluated++;
+        }
+        // Exclude the top `preserveTopNApps` apps from re-ranking.
+        if (numProcessesNotReRanked < preserveTopNApps) {
+            numProcessesReRanked -= preserveTopNApps - numProcessesNotReRanked;
+            if (numProcessesReRanked < 0) {
+                numProcessesReRanked = 0;
             }
         }
 
-        // TODO maybe ensure a certain number above this in the cache before re-ranking.
+        if (useFrequentRss) {
-        if (cachedProcessPos < scoredProcessRecords.length)  {
+            // Update RSS values for re-ranked apps.
-            // Ignore we don't have enough processes to worry about re-ranking.
+            long nowMs = SystemClock.elapsedRealtime();
-            return;
+            for (int i = 0; i < numProcessesReRanked; ++i) {
+                RankedProcessRecord scoredProcessRecord = scoredProcessRecords[i];
+                long sinceUpdateMs =
+                        nowMs - scoredProcessRecord.proc.mState.getCacheOomRankerRssTimeMs();
+                if (scoredProcessRecord.proc.mState.getCacheOomRankerRss() != 0
+                        && sinceUpdateMs < rssUpdateRateMs) {
+                    continue;
+                }
+
+                long[] rss = mProcessDependencies.getRss(scoredProcessRecord.proc.getPid());
+                if (rss == null || rss.length == 0) {
+                    Slog.e(
+                            OomAdjuster.TAG,
+                            "Process.getRss returned bad value, not re-ranking: "
+                                    + Arrays.toString(rss));
+                    return;
+                }
+                // First element is total RSS:
+                // frameworks/base/core/jni/android_util_Process.cpp:1192
+                scoredProcessRecord.proc.mState.setCacheOomRankerRss(rss[0], nowMs);
+                scoredProcessRecord.proc.mProfile.setLastRss(rss[0]);
+            }
         }
 
         // Add scores for each of the weighted features we want to rank based on.
         if (lruWeight > 0.0f) {
             // This doesn't use the LRU list ordering as after the first re-ranking
             // that will no longer be lru.
-            Arrays.sort(scoredProcessRecords, LAST_ACTIVITY_TIME_COMPARATOR);
+            Arrays.sort(scoredProcessRecords, 0, numProcessesReRanked,
+                    LAST_ACTIVITY_TIME_COMPARATOR);
             addToScore(scoredProcessRecords, lruWeight);
         }
         if (rssWeight > 0.0f) {
-            synchronized (mService.mAppProfiler.mProfilerLock) {
+            if (useFrequentRss) {
-                Arrays.sort(scoredProcessRecords, LAST_RSS_COMPARATOR);
+                Arrays.sort(scoredProcessRecords, 0, numProcessesReRanked, RSS_COMPARATOR);
+            } else {
+                synchronized (mService.mAppProfiler.mProfilerLock) {
+                    Arrays.sort(scoredProcessRecords, 0, numProcessesReRanked, LAST_RSS_COMPARATOR);
+                }
             }
             addToScore(scoredProcessRecords, rssWeight);
         }
         if (usesWeight > 0.0f) {
-            Arrays.sort(scoredProcessRecords, CACHE_USE_COMPARATOR);
+            Arrays.sort(scoredProcessRecords, 0, numProcessesReRanked, CACHE_USE_COMPARATOR);
             addToScore(scoredProcessRecords, usesWeight);
         }
 
         // Re-rank by the new combined score.
-        Arrays.sort(scoredProcessRecords, SCORED_PROCESS_RECORD_COMPARATOR);
+        Arrays.sort(scoredProcessRecords, 0, numProcessesReRanked,
+                SCORED_PROCESS_RECORD_COMPARATOR);
 
         if (ActivityManagerDebugConfig.DEBUG_OOM_ADJ) {
             boolean printedHeader = false;
-            for (int i = 0; i < scoredProcessRecords.length; ++i) {
+            for (int i = 0; i < numProcessesReRanked; ++i) {
                 if (scoredProcessRecords[i].proc.getPid()
                         != lruList.get(lruPositions[i]).getPid()) {
                     if (!printedHeader) {
@@ -260,12 +410,18 @@ public class CacheOomRanker {
             }
         }
 
-        for (int i = 0; i < scoredProcessRecords.length; ++i) {
+        for (int i = 0; i < numProcessesReRanked; ++i) {
             lruList.set(lruPositions[i], scoredProcessRecords[i].proc);
             scoredProcessRecords[i].proc = null;
         }
     }
 
+    private static boolean appCanBeReRanked(ProcessRecord process) {
+        return !process.isKilledByAm()
+                && process.getThread() != null
+                && process.mState.getCurAdj() >= ProcessList.UNKNOWN_ADJ;
+    }
+
     private static void addToScore(RankedProcessRecord[] scores, float weight) {
         for (int i = 1; i < scores.length; ++i) {
             scores[i].score += i * weight;
@@ -305,6 +461,16 @@ public class CacheOomRanker {
         }
     }
 
+    private static class RssComparator implements Comparator<RankedProcessRecord> {
+        @Override
+        public int compare(RankedProcessRecord o1, RankedProcessRecord o2) {
+            // High RSS first to match least recently used.
+            return Long.compare(
+                    o2.proc.mState.getCacheOomRankerRss(),
+                    o1.proc.mState.getCacheOomRankerRss());
+        }
+    }
+
     private static class LastRssComparator implements Comparator<RankedProcessRecord> {
         @Override
         public int compare(RankedProcessRecord o1, RankedProcessRecord o2) {
@@ -317,4 +483,18 @@ public class CacheOomRanker {
         public ProcessRecord proc;
         public float score;
     }
+
+    /**
+     * Interface for mocking {@link Process} static methods.
+     */
+    interface ProcessDependencies {
+        long[] getRss(int pid);
+    }
+
+    private static class ProcessDependenciesImpl implements ProcessDependencies {
+        @Override
+        public long[] getRss(int pid) {
+            return Process.getRss(pid);
+        }
+    }
 }

services/core/java/com/android/server/am/ProcessStateRecord.java

@@ -342,6 +342,20 @@ final class ProcessStateRecord {
     @GuardedBy("mService")
     private int mCacheOomRankerUseCount;
 
+    /**
+     * Process memory usage (RSS).
+     *
+     * Periodically populated by {@code CacheOomRanker}, stored in this object to cache the values.
+     */
+    @GuardedBy("mService")
+    private long mCacheOomRankerRss;
+
+    /**
+     * The last time, in milliseconds since boot, since {@link #mCacheOomRankerRss} was updated.
+     */
+    @GuardedBy("mService")
+    private long mCacheOomRankerRssTimeMs;
+
     /**
      * Whether or not this process is reachable from given process.
      */
@@ -577,6 +591,10 @@ final class ProcessStateRecord {
 
     @GuardedBy({"mService", "mProcLock"})
     void setSetProcState(int setProcState) {
+        if (ActivityManager.isProcStateCached(mSetProcState)
+                && !ActivityManager.isProcStateCached(setProcState)) {
+            mCacheOomRankerUseCount++;
+        }
         mSetProcState = setProcState;
     }
 
@@ -840,12 +858,7 @@ final class ProcessStateRecord {
 
     @GuardedBy("mService")
     void setCached(boolean cached) {
-        if (mCached != cached) {
+        mCached = cached;
-            mCached = cached;
-            if (cached) {
-                ++mCacheOomRankerUseCount;
-            }
-        }
     }
 
     @GuardedBy("mService")
@@ -1151,6 +1164,21 @@ final class ProcessStateRecord {
         return mLastInvisibleTime;
     }
 
+    public void setCacheOomRankerRss(long rss, long rssTimeMs) {
+        mCacheOomRankerRss = rss;
+        mCacheOomRankerRssTimeMs = rssTimeMs;
+    }
+
+    @GuardedBy("mService")
+    public long getCacheOomRankerRss() {
+        return mCacheOomRankerRss;
+    }
+
+    @GuardedBy("mService")
+    public long getCacheOomRankerRssTimeMs() {
+        return mCacheOomRankerRssTimeMs;
+    }
+
     @GuardedBy({"mService", "mProcLock"})
     void dump(PrintWriter pw, String prefix, long nowUptime) {
         if (mReportedInteraction || mFgInteractionTime != 0) {

services/tests/mockingservicestests/src/com/android/server/am/CacheOomRankerTest.java

@@ -21,12 +21,16 @@ import static android.app.ActivityManager.PROCESS_STATE_BOUND_FOREGROUND_SERVICE
 import static com.google.common.truth.Truth.assertThat;
 
 import static org.mockito.Mockito.doReturn;
+import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.spy;
 
+import android.app.ActivityManager;
+import android.app.IApplicationThread;
 import android.content.ComponentName;
 import android.content.Context;
 import android.content.pm.ApplicationInfo;
 import android.content.pm.PackageManagerInternal;
+import android.os.Environment;
 import android.os.Handler;
 import android.os.HandlerThread;
 import android.os.Process;
@@ -48,8 +52,14 @@ import org.mockito.Mock;
 import org.mockito.junit.MockitoJUnitRunner;
 
 import java.io.File;
-import java.time.Duration;
+import java.time.Instant;
+import java.time.LocalDate;
+import java.time.ZoneOffset;
+import java.time.temporal.ChronoUnit;
 import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.Executor;
 import java.util.concurrent.TimeUnit;
@@ -60,8 +70,11 @@ import java.util.concurrent.TimeUnit;
  * Build/Install/Run:
  * atest FrameworksMockingServicesTests:CacheOomRankerTest
  */
+@SuppressWarnings("GuardedBy") // No tests are concurrent, so no need to test locking.
 @RunWith(MockitoJUnitRunner.class)
 public class CacheOomRankerTest {
+    private static final Instant NOW = LocalDate.of(2021, 1, 1).atStartOfDay(
+            ZoneOffset.UTC).toInstant();
 
     @Mock
     private AppOpsService mAppOpsService;
@@ -82,6 +95,7 @@ public class CacheOomRankerTest {
     private int mNextUid = 30000;
     private int mNextPackageUid = 40000;
     private int mNextPackageName = 1;
+    private Map<Integer, Long> mPidToRss;
 
     private TestExecutor mExecutor = new TestExecutor();
     private CacheOomRanker mCacheOomRanker;
@@ -107,7 +121,15 @@ public class CacheOomRankerTest {
         LocalServices.removeServiceForTest(PackageManagerInternal.class);
         LocalServices.addService(PackageManagerInternal.class, mPackageManagerInt);
 
-        mCacheOomRanker = new CacheOomRanker(mAms);
+        mPidToRss = new HashMap<>();
+        mCacheOomRanker = new CacheOomRanker(
+                mAms,
+                pid -> {
+                    Long rss = mPidToRss.get(pid);
+                    assertThat(rss).isNotNull();
+                    return new long[]{rss};
+                }
+        );
         mCacheOomRanker.init(mExecutor);
     }
 
@@ -134,6 +156,15 @@ public class CacheOomRankerTest {
         assertThat(mCacheOomRanker.getNumberToReRank())
                 .isEqualTo(CacheOomRanker.DEFAULT_OOM_RE_RANKING_NUMBER_TO_RE_RANK + 2);
 
+        mExecutor.init();
+        DeviceConfig.setProperty(DeviceConfig.NAMESPACE_ACTIVITY_MANAGER,
+                CacheOomRanker.KEY_OOM_RE_RANKING_PRESERVE_TOP_N_APPS,
+                Integer.toString(CacheOomRanker.DEFAULT_PRESERVE_TOP_N_APPS + 1),
+                false);
+        mExecutor.waitForLatch();
+        assertThat(mCacheOomRanker.mPreserveTopNApps)
+                .isEqualTo(CacheOomRanker.DEFAULT_PRESERVE_TOP_N_APPS + 1);
+
         mExecutor.init();
         DeviceConfig.setProperty(DeviceConfig.NAMESPACE_ACTIVITY_MANAGER,
                 CacheOomRanker.KEY_OOM_RE_RANKING_LRU_WEIGHT,
@@ -165,6 +196,9 @@ public class CacheOomRankerTest {
     @Test
     public void reRankLruCachedApps_lruImpactsOrdering() throws InterruptedException {
         setConfig(/* numberToReRank= */ 5,
+                /* preserveTopNApps= */ 0,
+                /* useFrequentRss= */ true,
+                /* rssUpdateRateMs= */ 0,
                 /* usesWeight= */ 0.0f,
                 /* pssWeight= */ 0.0f,
                 /* lruWeight= */1.0f);
@@ -172,36 +206,40 @@ public class CacheOomRankerTest {
         ProcessList list = new ProcessList();
         ArrayList<ProcessRecord> processList = list.getLruProcessesLSP();
         ProcessRecord lastUsed40MinutesAgo = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
-                Duration.ofMinutes(40).toMillis(), 10 * 1024L, 1000);
+                NOW.minus(40, ChronoUnit.MINUTES).toEpochMilli(), 10 * 1024L, 1000);
         processList.add(lastUsed40MinutesAgo);
         ProcessRecord lastUsed42MinutesAgo = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
-                Duration.ofMinutes(42).toMillis(), 20 * 1024L, 2000);
+                NOW.minus(42, ChronoUnit.MINUTES).toEpochMilli(), 20 * 1024L, 2000);
         processList.add(lastUsed42MinutesAgo);
         ProcessRecord lastUsed60MinutesAgo = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
-                Duration.ofMinutes(60).toMillis(), 1024L, 10000);
+                NOW.minus(60, ChronoUnit.MINUTES).toEpochMilli(), 1024L, 10000);
         processList.add(lastUsed60MinutesAgo);
         ProcessRecord lastUsed15MinutesAgo = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
-                Duration.ofMinutes(15).toMillis(), 100 * 1024L, 10);
+                NOW.minus(15, ChronoUnit.MINUTES).toEpochMilli(), 100 * 1024L, 10);
         processList.add(lastUsed15MinutesAgo);
         ProcessRecord lastUsed17MinutesAgo = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
-                Duration.ofMinutes(17).toMillis(), 1024L, 20);
+                NOW.minus(17, ChronoUnit.MINUTES).toEpochMilli(), 1024L, 20);
         processList.add(lastUsed17MinutesAgo);
         // Only re-ranking 5 entries so this should stay in most recent position.
         ProcessRecord lastUsed30MinutesAgo = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
-                Duration.ofMinutes(30).toMillis(), 1024L, 20);
+                NOW.minus(30, ChronoUnit.MINUTES).toEpochMilli(), 1024L, 20);
         processList.add(lastUsed30MinutesAgo);
+        list.setLruProcessServiceStartLSP(processList.size());
 
         mCacheOomRanker.reRankLruCachedAppsLSP(processList, list.getLruProcessServiceStartLOSP());
 
         // First 5 ordered by least recently used first, then last processes position unchanged.
         assertThat(processList).containsExactly(lastUsed60MinutesAgo, lastUsed42MinutesAgo,
                 lastUsed40MinutesAgo, lastUsed17MinutesAgo, lastUsed15MinutesAgo,
-                lastUsed30MinutesAgo);
+                lastUsed30MinutesAgo).inOrder();
     }
 
     @Test
     public void reRankLruCachedApps_rssImpactsOrdering() throws InterruptedException {
         setConfig(/* numberToReRank= */ 6,
+                /* preserveTopNApps= */ 0,
+                /* useFrequentRss= */ true,
+                /* rssUpdateRateMs= */ 0,
                 /* usesWeight= */ 0.0f,
                 /* pssWeight= */ 1.0f,
                 /* lruWeight= */ 0.0f);
@@ -209,151 +247,477 @@ public class CacheOomRankerTest {
         ProcessList list = new ProcessList();
         ArrayList<ProcessRecord> processList = list.getLruProcessesLSP();
         ProcessRecord rss10k = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
-                Duration.ofMinutes(40).toMillis(), 10 * 1024L, 1000);
+                NOW.minus(40, ChronoUnit.MINUTES).toEpochMilli(), 10 * 1024L, 1000);
         processList.add(rss10k);
         ProcessRecord rss20k = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
-                Duration.ofMinutes(42).toMillis(), 20 * 1024L, 2000);
+                NOW.minus(42, ChronoUnit.MINUTES).toEpochMilli(), 20 * 1024L, 2000);
         processList.add(rss20k);
         ProcessRecord rss1k = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
-                Duration.ofMinutes(60).toMillis(), 1024L, 10000);
+                NOW.minus(60, ChronoUnit.MINUTES).toEpochMilli(), 1024L, 10000);
         processList.add(rss1k);
         ProcessRecord rss100k = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
-                Duration.ofMinutes(15).toMillis(), 100 * 1024L, 10);
+                NOW.minus(15, ChronoUnit.MINUTES).toEpochMilli(), 100 * 1024L, 10);
         processList.add(rss100k);
         ProcessRecord rss2k = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
-                Duration.ofMinutes(17).toMillis(), 2 * 1024L, 20);
+                NOW.minus(17, ChronoUnit.MINUTES).toEpochMilli(), 2 * 1024L, 20);
         processList.add(rss2k);
         ProcessRecord rss15k = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
-                Duration.ofMinutes(30).toMillis(), 15 * 1024L, 20);
+                NOW.minus(30, ChronoUnit.MINUTES).toEpochMilli(), 15 * 1024L, 20);
         processList.add(rss15k);
         // Only re-ranking 6 entries so this should stay in most recent position.
         ProcessRecord rss16k = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
-                Duration.ofMinutes(30).toMillis(), 16 * 1024L, 20);
+                NOW.minus(30, ChronoUnit.MINUTES).toEpochMilli(), 16 * 1024L, 20);
         processList.add(rss16k);
+        list.setLruProcessServiceStartLSP(processList.size());
 
         mCacheOomRanker.reRankLruCachedAppsLSP(processList, list.getLruProcessServiceStartLOSP());
 
         // First 6 ordered by largest pss, then last processes position unchanged.
         assertThat(processList).containsExactly(rss100k, rss20k, rss15k, rss10k, rss2k, rss1k,
-                rss16k);
+                rss16k).inOrder();
     }
 
+    @Test
+    public void reRankLruCachedApps_rssImpactsOrdering_cachedRssValues()
+            throws InterruptedException {
+        setConfig(/* numberToReRank= */ 6,
+                /* preserveTopNApps= */ 0,
+                /* useFrequentRss= */ true,
+                /* rssUpdateRateMs= */ 10000000,
+                /* usesWeight= */ 0.0f,
+                /* pssWeight= */ 1.0f,
+                /* lruWeight= */ 0.0f);
+
+        ProcessList list = new ProcessList();
+        ArrayList<ProcessRecord> processList = list.getLruProcessesLSP();
+        ProcessRecord rss10k = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(40, ChronoUnit.MINUTES).toEpochMilli(), 10 * 1024L, 1000);
+        processList.add(rss10k);
+        ProcessRecord rss20k = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(42, ChronoUnit.MINUTES).toEpochMilli(), 20 * 1024L, 2000);
+        processList.add(rss20k);
+        ProcessRecord rss1k = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(60, ChronoUnit.MINUTES).toEpochMilli(), 1024L, 10000);
+        processList.add(rss1k);
+        ProcessRecord rss100k = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(15, ChronoUnit.MINUTES).toEpochMilli(), 100 * 1024L, 10);
+        processList.add(rss100k);
+        ProcessRecord rss2k = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(17, ChronoUnit.MINUTES).toEpochMilli(), 2 * 1024L, 20);
+        processList.add(rss2k);
+        ProcessRecord rss15k = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(30, ChronoUnit.MINUTES).toEpochMilli(), 15 * 1024L, 20);
+        processList.add(rss15k);
+        // Only re-ranking 6 entries so this should stay in most recent position.
+        ProcessRecord rss16k = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(30, ChronoUnit.MINUTES).toEpochMilli(), 16 * 1024L, 20);
+        processList.add(rss16k);
+        list.setLruProcessServiceStartLSP(processList.size());
+
+        mCacheOomRanker.reRankLruCachedAppsLSP(processList, list.getLruProcessServiceStartLOSP());
+        // First 6 ordered by largest pss, then last processes position unchanged.
+        assertThat(processList).containsExactly(rss100k, rss20k, rss15k, rss10k, rss2k, rss1k,
+                rss16k).inOrder();
+
+        // Clear mPidToRss so that Process.getRss calls fail.
+        mPidToRss.clear();
+        // Mix up the process list to ensure that CacheOomRanker actually re-ranks.
+        Collections.swap(processList, 0, 1);
+
+        mCacheOomRanker.reRankLruCachedAppsLSP(processList, list.getLruProcessServiceStartLOSP());
+        // Re ranking is the same.
+        assertThat(processList).containsExactly(rss100k, rss20k, rss15k, rss10k, rss2k, rss1k,
+                rss16k).inOrder();
+    }
+
+    @Test
+    public void reRankLruCachedApps_rssImpactsOrdering_profileRss()
+            throws InterruptedException {
+        setConfig(/* numberToReRank= */ 6,
+                /* preserveTopNApps= */ 0,
+                /* useFrequentRss= */ false,
+                /* rssUpdateRateMs= */ 10000000,
+                /* usesWeight= */ 0.0f,
+                /* pssWeight= */ 1.0f,
+                /* lruWeight= */ 0.0f);
+
+        ProcessList list = new ProcessList();
+        ArrayList<ProcessRecord> processList = list.getLruProcessesLSP();
+        ProcessRecord rss10k = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(40, ChronoUnit.MINUTES).toEpochMilli(), 0L, 1000);
+        rss10k.mProfile.setLastRss(10 * 1024L);
+        processList.add(rss10k);
+        ProcessRecord rss20k = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(42, ChronoUnit.MINUTES).toEpochMilli(), 0L, 2000);
+        rss20k.mProfile.setLastRss(20 * 1024L);
+        processList.add(rss20k);
+        ProcessRecord rss1k = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(60, ChronoUnit.MINUTES).toEpochMilli(), 0L, 10000);
+        rss1k.mProfile.setLastRss(1024L);
+        processList.add(rss1k);
+        ProcessRecord rss100k = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(15, ChronoUnit.MINUTES).toEpochMilli(), 0L, 10);
+        rss100k.mProfile.setLastRss(100 * 1024L);
+        processList.add(rss100k);
+        ProcessRecord rss2k = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(17, ChronoUnit.MINUTES).toEpochMilli(), 0L, 20);
+        rss2k.mProfile.setLastRss(2 * 1024L);
+        processList.add(rss2k);
+        ProcessRecord rss15k = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(30, ChronoUnit.MINUTES).toEpochMilli(), 15 * 1024L, 20);
+        rss15k.mProfile.setLastRss(15 * 1024L);
+        processList.add(rss15k);
+        // Only re-ranking 6 entries so this should stay in most recent position.
+        ProcessRecord rss16k = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(30, ChronoUnit.MINUTES).toEpochMilli(), 16 * 1024L, 20);
+        rss16k.mProfile.setLastRss(16 * 1024L);
+        processList.add(rss16k);
+        list.setLruProcessServiceStartLSP(processList.size());
+
+        // This should not be used, as RSS values are taken from mProfile.
+        mPidToRss.clear();
+
+        mCacheOomRanker.reRankLruCachedAppsLSP(processList, list.getLruProcessServiceStartLOSP());
+        // First 6 ordered by largest pss, then last processes position unchanged.
+        assertThat(processList).containsExactly(rss100k, rss20k, rss15k, rss10k, rss2k, rss1k,
+                rss16k).inOrder();
+
+        // Clear mPidToRss so that Process.getRss calls fail.
+        mPidToRss.clear();
+        // Mix up the process list to ensure that CacheOomRanker actually re-ranks.
+        Collections.swap(processList, 0, 1);
+
+        mCacheOomRanker.reRankLruCachedAppsLSP(processList, list.getLruProcessServiceStartLOSP());
+        // Re ranking is the same.
+        assertThat(processList).containsExactly(rss100k, rss20k, rss15k, rss10k, rss2k, rss1k,
+                rss16k).inOrder();
+    }
+
+
     @Test
     public void reRankLruCachedApps_usesImpactsOrdering() throws InterruptedException {
         setConfig(/* numberToReRank= */ 4,
+                /* preserveTopNApps= */ 0,
+                /* useFrequentRss= */ true,
+                /* rssUpdateRateMs= */ 0,
                 /* usesWeight= */ 1.0f,
                 /* pssWeight= */ 0.0f,
                 /* lruWeight= */ 0.0f);
 
         ProcessList list = new ProcessList();
-        list.setLruProcessServiceStartLSP(1);
         ArrayList<ProcessRecord> processList = list.getLruProcessesLSP();
         ProcessRecord used1000 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
-                Duration.ofMinutes(40).toMillis(), 10 * 1024L, 1000);
+                NOW.minus(40, ChronoUnit.MINUTES).toEpochMilli(), 10 * 1024L, 1000);
         processList.add(used1000);
         ProcessRecord used2000 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
-                Duration.ofMinutes(42).toMillis(), 20 * 1024L, 2000);
+                NOW.minus(42, ChronoUnit.MINUTES).toEpochMilli(), 20 * 1024L, 2000);
         processList.add(used2000);
         ProcessRecord used10 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
-                Duration.ofMinutes(15).toMillis(), 100 * 1024L, 10);
+                NOW.minus(15, ChronoUnit.MINUTES).toEpochMilli(), 100 * 1024L, 10);
         processList.add(used10);
         ProcessRecord used20 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
-                Duration.ofMinutes(17).toMillis(), 2 * 1024L, 20);
+                NOW.minus(17, ChronoUnit.MINUTES).toEpochMilli(), 2 * 1024L, 20);
         processList.add(used20);
         // Only re-ranking 6 entries so last two should stay in most recent position.
         ProcessRecord used500 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
-                Duration.ofMinutes(30).toMillis(), 15 * 1024L, 500);
+                NOW.minus(30, ChronoUnit.MINUTES).toEpochMilli(), 15 * 1024L, 500);
         processList.add(used500);
         ProcessRecord used200 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
-                Duration.ofMinutes(30).toMillis(), 16 * 1024L, 200);
+                NOW.minus(30, ChronoUnit.MINUTES).toEpochMilli(), 16 * 1024L, 200);
         processList.add(used200);
+        list.setLruProcessServiceStartLSP(processList.size());
 
         mCacheOomRanker.reRankLruCachedAppsLSP(processList, list.getLruProcessServiceStartLOSP());
 
         // First 4 ordered by uses, then last processes position unchanged.
         assertThat(processList).containsExactly(used10, used20, used1000, used2000, used500,
-                used200);
+                used200).inOrder();
     }
 
     @Test
-    public void reRankLruCachedApps_notEnoughProcesses() throws InterruptedException {
+    public void reRankLruCachedApps_fewProcesses() throws InterruptedException {
-        setConfig(/* numberToReRank= */ 4,
-                /* usesWeight= */ 0.5f,
-                /* pssWeight= */ 0.2f,
-                /* lruWeight= */ 0.3f);
-
-        ProcessList list = new ProcessList();
-        ArrayList<ProcessRecord> processList = list.getLruProcessesLSP();
-        ProcessRecord unknownAdj1 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
-                Duration.ofMinutes(40).toMillis(), 10 * 1024L, 1000);
-        processList.add(unknownAdj1);
-        ProcessRecord unknownAdj2 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
-                Duration.ofMinutes(42).toMillis(), 20 * 1024L, 2000);
-        processList.add(unknownAdj2);
-        ProcessRecord unknownAdj3 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
-                Duration.ofMinutes(15).toMillis(), 100 * 1024L, 10);
-        processList.add(unknownAdj3);
-        ProcessRecord foregroundAdj = nextProcessRecord(ProcessList.FOREGROUND_APP_ADJ,
-                Duration.ofMinutes(17).toMillis(), 2 * 1024L, 20);
-        processList.add(foregroundAdj);
-        ProcessRecord serviceAdj = nextProcessRecord(ProcessList.SERVICE_ADJ,
-                Duration.ofMinutes(30).toMillis(), 15 * 1024L, 500);
-        processList.add(serviceAdj);
-        ProcessRecord systemAdj = nextProcessRecord(ProcessList.SYSTEM_ADJ,
-                Duration.ofMinutes(30).toMillis(), 16 * 1024L, 200);
-        processList.add(systemAdj);
-
-        // 6 Processes but only 3 in eligible for cache so no re-ranking.
-        mCacheOomRanker.reRankLruCachedAppsLSP(processList, list.getLruProcessServiceStartLOSP());
-
-        // All positions unchanged.
-        assertThat(processList).containsExactly(unknownAdj1, unknownAdj2, unknownAdj3,
-                foregroundAdj, serviceAdj, systemAdj);
-    }
-
-    @Test
-    public void reRankLruCachedApps_notEnoughNonServiceProcesses() throws InterruptedException {
         setConfig(/* numberToReRank= */ 4,
+                /* preserveTopNApps= */ 0,
+                /* useFrequentRss= */ true,
+                /* rssUpdateRateMs= */ 0,
                 /* usesWeight= */ 1.0f,
                 /* pssWeight= */ 0.0f,
                 /* lruWeight= */ 0.0f);
 
         ProcessList list = new ProcessList();
-        list.setLruProcessServiceStartLSP(4);
         ArrayList<ProcessRecord> processList = list.getLruProcessesLSP();
         ProcessRecord used1000 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
-                Duration.ofMinutes(40).toMillis(), 10 * 1024L, 1000);
+                NOW.minus(40, ChronoUnit.MINUTES).toEpochMilli(), 10 * 1024L, 1000);
         processList.add(used1000);
         ProcessRecord used2000 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
-                Duration.ofMinutes(42).toMillis(), 20 * 1024L, 2000);
+                NOW.minus(42, ChronoUnit.MINUTES).toEpochMilli(), 20 * 1024L, 2000);
         processList.add(used2000);
         ProcessRecord used10 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
-                Duration.ofMinutes(15).toMillis(), 100 * 1024L, 10);
+                NOW.minus(15, ChronoUnit.MINUTES).toEpochMilli(), 100 * 1024L, 10);
         processList.add(used10);
-        ProcessRecord used20 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+        ProcessRecord foregroundAdj = nextProcessRecord(ProcessList.FOREGROUND_APP_ADJ,
-                Duration.ofMinutes(17).toMillis(), 2 * 1024L, 20);
+                NOW.minus(17, ChronoUnit.MINUTES).toEpochMilli(), 2 * 1024L, 20);
-        processList.add(used20);
+        processList.add(foregroundAdj);
-        ProcessRecord used500 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+        ProcessRecord serviceAdj = nextProcessRecord(ProcessList.SERVICE_ADJ,
-                Duration.ofMinutes(30).toMillis(), 15 * 1024L, 500);
+                NOW.minus(30, ChronoUnit.MINUTES).toEpochMilli(), 15 * 1024L, 500);
-        processList.add(used500);
+        processList.add(serviceAdj);
-        ProcessRecord used200 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+        ProcessRecord systemAdj = nextProcessRecord(ProcessList.SYSTEM_ADJ,
-                Duration.ofMinutes(30).toMillis(), 16 * 1024L, 200);
+                NOW.minus(30, ChronoUnit.MINUTES).toEpochMilli(), 16 * 1024L, 200);
-        processList.add(used200);
+        processList.add(systemAdj);
+        list.setLruProcessServiceStartLSP(processList.size());
 
         mCacheOomRanker.reRankLruCachedAppsLSP(processList, list.getLruProcessServiceStartLOSP());
 
-        // All positions unchanged.
+        // 6 processes, only 3 in eligible for cache, so only those are re-ranked.
-        assertThat(processList).containsExactly(used1000, used2000, used10, used20, used500,
+        assertThat(processList).containsExactly(used10, used1000, used2000,
-                used200);
+                foregroundAdj, serviceAdj, systemAdj).inOrder();
     }
 
-    private void setConfig(int numberToReRank, float useWeight, float pssWeight, float lruWeight)
+    @Test
+    public void reRankLruCachedApps_fewNonServiceProcesses() throws InterruptedException {
+        setConfig(/* numberToReRank= */ 4,
+                /* preserveTopNApps= */ 0,
+                /* useFrequentRss= */ true,
+                /* rssUpdateRateMs= */ 0,
+                /* usesWeight= */ 1.0f,
+                /* pssWeight= */ 0.0f,
+                /* lruWeight= */ 0.0f);
+
+        ProcessList list = new ProcessList();
+        ArrayList<ProcessRecord> processList = list.getLruProcessesLSP();
+        ProcessRecord used1000 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(40, ChronoUnit.MINUTES).toEpochMilli(), 10 * 1024L, 1000);
+        processList.add(used1000);
+        ProcessRecord used2000 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(42, ChronoUnit.MINUTES).toEpochMilli(), 20 * 1024L, 2000);
+        processList.add(used2000);
+        ProcessRecord used10 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(15, ChronoUnit.MINUTES).toEpochMilli(), 100 * 1024L, 10);
+        processList.add(used10);
+        ProcessRecord service1 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(17, ChronoUnit.MINUTES).toEpochMilli(), 2 * 1024L, 20);
+        processList.add(service1);
+        ProcessRecord service2 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(30, ChronoUnit.MINUTES).toEpochMilli(), 15 * 1024L, 500);
+        processList.add(service2);
+        ProcessRecord service3 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(30, ChronoUnit.MINUTES).toEpochMilli(), 16 * 1024L, 200);
+        processList.add(service3);
+        list.setLruProcessServiceStartLSP(3);
+
+        mCacheOomRanker.reRankLruCachedAppsLSP(processList, list.getLruProcessServiceStartLOSP());
+
+        // Services unchanged, rest re-ranked.
+        assertThat(processList).containsExactly(used10, used1000, used2000, service1, service2,
+                service3).inOrder();
+    }
+
+    @Test
+    public void reRankLruCachedApps_manyProcessesThenFew() throws InterruptedException {
+        setConfig(/* numberToReRank= */ 6,
+                /* preserveTopNApps= */ 0,
+                /* useFrequentRss= */ true,
+                /* rssUpdateRateMs= */ 0,
+                /* usesWeight= */ 1.0f,
+                /* pssWeight= */ 0.0f,
+                /* lruWeight= */ 0.0f);
+
+        ProcessList set1List = new ProcessList();
+        ArrayList<ProcessRecord> set1ProcessList = set1List.getLruProcessesLSP();
+        ProcessRecord set1Used1000 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(40, ChronoUnit.MINUTES).toEpochMilli(), 10 * 1024L, 1000);
+        set1ProcessList.add(set1Used1000);
+        ProcessRecord set1Used2000 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(42, ChronoUnit.MINUTES).toEpochMilli(), 20 * 1024L, 2000);
+        set1ProcessList.add(set1Used2000);
+        ProcessRecord set1Used10 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(15, ChronoUnit.MINUTES).toEpochMilli(), 100 * 1024L, 10);
+        set1ProcessList.add(set1Used10);
+        ProcessRecord set1Uses20 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(17, ChronoUnit.MINUTES).toEpochMilli(), 2 * 1024L, 20);
+        set1ProcessList.add(set1Uses20);
+        ProcessRecord set1Uses500 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(30, ChronoUnit.MINUTES).toEpochMilli(), 15 * 1024L, 500);
+        set1ProcessList.add(set1Uses500);
+        ProcessRecord set1Uses200 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(30, ChronoUnit.MINUTES).toEpochMilli(), 16 * 1024L, 200);
+        set1ProcessList.add(set1Uses200);
+        set1List.setLruProcessServiceStartLSP(set1ProcessList.size());
+
+        mCacheOomRanker.reRankLruCachedAppsLSP(set1ProcessList,
+                set1List.getLruProcessServiceStartLOSP());
+        assertThat(set1ProcessList).containsExactly(set1Used10, set1Uses20, set1Uses200,
+                set1Uses500, set1Used1000, set1Used2000).inOrder();
+
+        ProcessList set2List = new ProcessList();
+        ArrayList<ProcessRecord> set2ProcessList = set2List.getLruProcessesLSP();
+        ProcessRecord set2Used1000 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(40, ChronoUnit.MINUTES).toEpochMilli(), 10 * 1024L, 1000);
+        set2ProcessList.add(set2Used1000);
+        ProcessRecord set2Used2000 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(42, ChronoUnit.MINUTES).toEpochMilli(), 20 * 1024L, 2000);
+        set2ProcessList.add(set2Used2000);
+        ProcessRecord set2Used10 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(15, ChronoUnit.MINUTES).toEpochMilli(), 100 * 1024L, 10);
+        set2ProcessList.add(set2Used10);
+        ProcessRecord set2ForegroundAdj = nextProcessRecord(ProcessList.FOREGROUND_APP_ADJ,
+                NOW.minus(17, ChronoUnit.MINUTES).toEpochMilli(), 2 * 1024L, 20);
+        set2ProcessList.add(set2ForegroundAdj);
+        ProcessRecord set2ServiceAdj = nextProcessRecord(ProcessList.SERVICE_ADJ,
+                NOW.minus(30, ChronoUnit.MINUTES).toEpochMilli(), 15 * 1024L, 500);
+        set2ProcessList.add(set2ServiceAdj);
+        ProcessRecord set2SystemAdj = nextProcessRecord(ProcessList.SYSTEM_ADJ,
+                NOW.minus(30, ChronoUnit.MINUTES).toEpochMilli(), 16 * 1024L, 200);
+        set2ProcessList.add(set2SystemAdj);
+        set2List.setLruProcessServiceStartLSP(set2ProcessList.size());
+
+        mCacheOomRanker.reRankLruCachedAppsLSP(set2ProcessList,
+                set2List.getLruProcessServiceStartLOSP());
+        assertThat(set2ProcessList).containsExactly(set2Used10, set2Used1000, set2Used2000,
+                set2ForegroundAdj, set2ServiceAdj, set2SystemAdj).inOrder();
+    }
+
+    @Test
+    public void reRankLruCachedApps_preservesTopNApps() throws InterruptedException {
+        setConfig(/* numberToReRank= */ 6,
+                /* preserveTopNApps= */ 3,
+                /* useFrequentRss= */ true,
+                /* rssUpdateRateMs= */ 0,
+                /* usesWeight= */ 1.0f,
+                /* pssWeight= */ 0.0f,
+                /* lruWeight= */ 0.0f);
+
+        ProcessList list = new ProcessList();
+        ArrayList<ProcessRecord> processList = list.getLruProcessesLSP();
+        ProcessRecord used1000 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(40, ChronoUnit.MINUTES).toEpochMilli(), 10 * 1024L, 1000);
+        processList.add(used1000);
+        ProcessRecord used2000 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(42, ChronoUnit.MINUTES).toEpochMilli(), 20 * 1024L, 2000);
+        processList.add(used2000);
+        ProcessRecord used10 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(15, ChronoUnit.MINUTES).toEpochMilli(), 100 * 1024L, 10);
+        processList.add(used10);
+        // Preserving the top 3 processes, so these should not be re-ranked.
+        ProcessRecord used20 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(17, ChronoUnit.MINUTES).toEpochMilli(), 2 * 1024L, 20);
+        processList.add(used20);
+        ProcessRecord used500 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(30, ChronoUnit.MINUTES).toEpochMilli(), 15 * 1024L, 500);
+        processList.add(used500);
+        ProcessRecord used200 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(30, ChronoUnit.MINUTES).toEpochMilli(), 16 * 1024L, 200);
+        processList.add(used200);
+        list.setLruProcessServiceStartLSP(processList.size());
+
+        mCacheOomRanker.reRankLruCachedAppsLSP(processList, list.getLruProcessServiceStartLOSP());
+
+        // First 3 ordered by uses, then last processes position unchanged.
+        assertThat(processList).containsExactly(used10, used1000, used2000, used20, used500,
+                used200).inOrder();
+    }
+
+    @Test
+    public void reRankLruCachedApps_preservesTopNApps_allAppsUnchanged()
+            throws InterruptedException {
+        setConfig(/* numberToReRank= */ 6,
+                /* preserveTopNApps= */ 100,
+                /* useFrequentRss= */ true,
+                /* rssUpdateRateMs= */ 0,
+                /* usesWeight= */ 1.0f,
+                /* pssWeight= */ 0.0f,
+                /* lruWeight= */ 0.0f);
+
+        ProcessList list = new ProcessList();
+        ArrayList<ProcessRecord> processList = list.getLruProcessesLSP();
+        ProcessRecord used1000 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(40, ChronoUnit.MINUTES).toEpochMilli(), 10 * 1024L, 1000);
+        processList.add(used1000);
+        ProcessRecord used2000 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(42, ChronoUnit.MINUTES).toEpochMilli(), 20 * 1024L, 2000);
+        processList.add(used2000);
+        ProcessRecord used10 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(15, ChronoUnit.MINUTES).toEpochMilli(), 100 * 1024L, 10);
+        processList.add(used10);
+        ProcessRecord used20 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(17, ChronoUnit.MINUTES).toEpochMilli(), 2 * 1024L, 20);
+        processList.add(used20);
+        ProcessRecord used500 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(30, ChronoUnit.MINUTES).toEpochMilli(), 15 * 1024L, 500);
+        processList.add(used500);
+        ProcessRecord used200 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(30, ChronoUnit.MINUTES).toEpochMilli(), 16 * 1024L, 200);
+        processList.add(used200);
+        list.setLruProcessServiceStartLSP(processList.size());
+
+        mCacheOomRanker.reRankLruCachedAppsLSP(processList, list.getLruProcessServiceStartLOSP());
+
+        // Nothing reordered, as we preserve the top 100 apps.
+        assertThat(processList).containsExactly(used1000, used2000, used10, used20, used500,
+                used200).inOrder();
+    }
+
+    @Test
+    public void reRankLruCachedApps_preservesTopNApps_negativeReplacedWithDefault()
+            throws InterruptedException {
+        setConfig(/* numberToReRank= */ 6,
+                /* preserveTopNApps= */ -100,
+                /* useFrequentRss= */ true,
+                /* rssUpdateRateMs= */ 0,
+                /* usesWeight= */ 1.0f,
+                /* pssWeight= */ 0.0f,
+                /* lruWeight= */ 0.0f);
+
+        ProcessList list = new ProcessList();
+        ArrayList<ProcessRecord> processList = list.getLruProcessesLSP();
+        ProcessRecord used1000 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(40, ChronoUnit.MINUTES).toEpochMilli(), 10 * 1024L, 1000);
+        processList.add(used1000);
+        ProcessRecord used2000 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(42, ChronoUnit.MINUTES).toEpochMilli(), 20 * 1024L, 2000);
+        processList.add(used2000);
+        ProcessRecord used10 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(15, ChronoUnit.MINUTES).toEpochMilli(), 100 * 1024L, 10);
+        processList.add(used10);
+        // Negative preserveTopNApps interpreted as the default (3), so the last three are unranked.
+        ProcessRecord used20 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(17, ChronoUnit.MINUTES).toEpochMilli(), 2 * 1024L, 20);
+        processList.add(used20);
+        ProcessRecord used500 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(30, ChronoUnit.MINUTES).toEpochMilli(), 15 * 1024L, 500);
+        processList.add(used500);
+        ProcessRecord used200 = nextProcessRecord(ProcessList.UNKNOWN_ADJ,
+                NOW.minus(30, ChronoUnit.MINUTES).toEpochMilli(), 16 * 1024L, 200);
+        processList.add(used200);
+        list.setLruProcessServiceStartLSP(processList.size());
+
+        mCacheOomRanker.reRankLruCachedAppsLSP(processList, list.getLruProcessServiceStartLOSP());
+
+        // First 3 apps re-ranked, as preserveTopNApps is interpreted as 3.
+        assertThat(processList).containsExactly(used10, used1000, used2000, used20, used500,
+                used200).inOrder();
+    }
+
+    private void setConfig(int numberToReRank, int preserveTopNApps, boolean useFrequentRss,
+            long rssUpdateRateMs, float usesWeight, float pssWeight, float lruWeight)
             throws InterruptedException {
         mExecutor.init(4);
         DeviceConfig.setProperty(DeviceConfig.NAMESPACE_ACTIVITY_MANAGER,
                 CacheOomRanker.KEY_OOM_RE_RANKING_NUMBER_TO_RE_RANK,
                 Integer.toString(numberToReRank),
                 false);
+        DeviceConfig.setProperty(DeviceConfig.NAMESPACE_ACTIVITY_MANAGER,
+                CacheOomRanker.KEY_OOM_RE_RANKING_PRESERVE_TOP_N_APPS,
+                Integer.toString(preserveTopNApps),
+                false);
+        DeviceConfig.setProperty(DeviceConfig.NAMESPACE_ACTIVITY_MANAGER,
+                CacheOomRanker.KEY_OOM_RE_RANKING_USE_FREQUENT_RSS,
+                Boolean.toString(useFrequentRss),
+                false);
+        DeviceConfig.setProperty(DeviceConfig.NAMESPACE_ACTIVITY_MANAGER,
+                CacheOomRanker.KEY_OOM_RE_RANKING_RSS_UPDATE_RATE_MS,
+                Long.toString(rssUpdateRateMs),
+                false);
         DeviceConfig.setProperty(DeviceConfig.NAMESPACE_ACTIVITY_MANAGER,
                 CacheOomRanker.KEY_OOM_RE_RANKING_LRU_WEIGHT,
                 Float.toString(lruWeight),
@@ -364,17 +728,19 @@ public class CacheOomRankerTest {
                 false);
         DeviceConfig.setProperty(DeviceConfig.NAMESPACE_ACTIVITY_MANAGER,
                 CacheOomRanker.KEY_OOM_RE_RANKING_USES_WEIGHT,
-                Float.toString(useWeight),
+                Float.toString(usesWeight),
                 false);
         mExecutor.waitForLatch();
         assertThat(mCacheOomRanker.getNumberToReRank()).isEqualTo(numberToReRank);
+        assertThat(mCacheOomRanker.mUseFrequentRss).isEqualTo(useFrequentRss);
+        assertThat(mCacheOomRanker.mRssUpdateRateMs).isEqualTo(rssUpdateRateMs);
         assertThat(mCacheOomRanker.mRssWeight).isEqualTo(pssWeight);
-        assertThat(mCacheOomRanker.mUsesWeight).isEqualTo(useWeight);
+        assertThat(mCacheOomRanker.mUsesWeight).isEqualTo(usesWeight);
         assertThat(mCacheOomRanker.mLruWeight).isEqualTo(lruWeight);
     }
 
     private ProcessRecord nextProcessRecord(int setAdj, long lastActivityTime, long lastRss,
-            int returnedToCacheCount) {
+            int wentToForegroundCount) {
         ApplicationInfo ai = new ApplicationInfo();
         ai.packageName = "a.package.name" + mNextPackageName++;
         ProcessRecord app = new ProcessRecord(mAms, ai, ai.packageName + ":process", mNextUid++);
@@ -382,14 +748,20 @@ public class CacheOomRankerTest {
         app.info.uid = mNextPackageUid++;
         // Exact value does not mater, it can be any state for which compaction is allowed.
         app.mState.setSetProcState(PROCESS_STATE_BOUND_FOREGROUND_SERVICE);
-        app.mState.setSetAdj(setAdj);
+        app.mState.setCurAdj(setAdj);
         app.setLastActivityTime(lastActivityTime);
-        app.mProfile.setLastRss(lastRss);
+        mPidToRss.put(app.getPid(), lastRss);
         app.mState.setCached(false);
-        for (int i = 0; i < returnedToCacheCount; ++i) {
+        for (int i = 0; i < wentToForegroundCount; ++i) {
-            app.mState.setCached(false);
+            app.mState.setSetProcState(ActivityManager.PROCESS_STATE_FOREGROUND_SERVICE);
-            app.mState.setCached(true);
+            app.mState.setSetProcState(ActivityManager.PROCESS_STATE_CACHED_RECENT);
         }
+        // Sets the thread returned by ProcessRecord#getThread, which we use to check whether the
+        // app is currently launching.
+        ProcessStatsService processStatsService = new ProcessStatsService(
+                mock(ActivityManagerService.class), new File(Environment.getDataSystemCeDirectory(),
+                "procstats"));
+        app.makeActive(mock(IApplicationThread.class), processStatsService);
         return app;
     }