Add threshold to downgrade compaction when swap is low

This patch introduces a threshold that allows compaction
system to downgrade full compactions into file only compactions
which do not cause compactions to happen as a way to reduce
pressure on swap thus aiming for a reduction in overall cpu
usage during high memory pressure scenarios as finding new
pages will likely be harder when the swap is low.

Bug: 226458732
Test: Manual. Verified that compaction runs artificially using different
thresholds and logging.

Change-Id: I12b460174c857f6750c9a173997c66381e4a1dc3

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

@@ -152,6 +152,11 @@ public final class CachedAppOptimizer {
     static final int SET_FROZEN_PROCESS_MSG = 3;
     static final int REPORT_UNFREEZE_MSG = 4;
 
+    // When free swap falls below this percentage threshold any full (file + anon)
+    // compactions will be downgraded to file only compactions to reduce pressure
+    // on swap resources as file.
+    static final double COMPACT_DOWNGRADE_FREE_SWAP_THRESHOLD = 0.2;
+
     static final int DO_FREEZE = 1;
     static final int REPORT_UNFREEZE = 2;
 
@@ -544,6 +549,11 @@ public final class CachedAppOptimizer {
 
     static private native void cancelCompaction();
 
+    /**
+     * Retrieves the free swap percentage.
+     */
+    static private native double getFreeSwapPercent();
+
     /**
      * Reads the flag value from DeviceConfig to determine whether app compaction
      * should be enabled, and starts the freeze/compaction thread if needed.
@@ -1338,6 +1348,18 @@ public final class CachedAppOptimizer {
                         default:
                             break;
                     }
+                    // Downgrade compaction if facing swap memory pressure
+                    if (action.equals(mCompactActionFull)) {
+                        double swapUsagePercent = getFreeSwapPercent();
+                        if (swapUsagePercent < COMPACT_DOWNGRADE_FREE_SWAP_THRESHOLD) {
+                            Slog.d(TAG_AM,
+                                    "Downgraded compaction to file only due to low swap."
+                                            + " Swap Free% " + swapUsagePercent);
+                            action = mCompactActionSome;
+                            pendingAction = COMPACT_PROCESS_SOME;
+                        }
+                    }
+
                     try {
                         Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "Compact "
                                 + ((pendingAction == COMPACT_PROCESS_SOME) ? "some" : "full")

services/core/jni/com_android_server_am_CachedAppOptimizer.cpp

@@ -37,6 +37,7 @@
 #include <sys/pidfd.h>
 #include <sys/stat.h>
 #include <sys/syscall.h>
+#include <sys/sysinfo.h>
 #include <sys/types.h>
 #include <unistd.h>
 
@@ -305,6 +306,16 @@ static void com_android_server_am_CachedAppOptimizer_cancelCompaction(JNIEnv*, j
     }
 }
 
+static jdouble com_android_server_am_CachedAppOptimizer_getFreeSwapPercent(JNIEnv*, jobject) {
+    struct sysinfo memoryInfo;
+    int error = sysinfo(&memoryInfo);
+    if(error == -1) {
+        LOG(ERROR) << "Could not check free swap space";
+        return 0;
+    }
+    return (double)memoryInfo.freeswap / (double)memoryInfo.totalswap;
+}
+
 static void com_android_server_am_CachedAppOptimizer_compactProcess(JNIEnv*, jobject, jint pid,
                                                                     jint compactionFlags) {
     compactProcessOrFallback(pid, compactionFlags);
@@ -358,6 +369,8 @@ static const JNINativeMethod sMethods[] = {
         /* name, signature, funcPtr */
         {"cancelCompaction", "()V",
          (void*)com_android_server_am_CachedAppOptimizer_cancelCompaction},
+        {"getFreeSwapPercent", "()D",
+         (void*)com_android_server_am_CachedAppOptimizer_getFreeSwapPercent},
         {"compactSystem", "()V", (void*)com_android_server_am_CachedAppOptimizer_compactSystem},
         {"compactProcess", "(II)V", (void*)com_android_server_am_CachedAppOptimizer_compactProcess},
         {"freezeBinder", "(IZ)I", (void*)com_android_server_am_CachedAppOptimizer_freezeBinder},