Signal lmkd to start psi monitoring after boot.

To save CPU cycles during boot for low resource device a new
configuration is added to delay registration of psi monitoring until
boot is complete. ActivityManagerService will send an lmkd message to
start psi monitoring after boot.

Bug: 288566858
Test: Build, boot and verified boot logs to confirm the behavior.

Change-Id: Iee5cecdae54304b092c6a1801f3814e13a919be2

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

@@ -5061,6 +5061,10 @@ public class ActivityManagerService extends IActivityManager.Stub
             // Tell anyone interested that we are done booting!
             SystemProperties.set("sys.boot_completed", "1");
             SystemProperties.set("dev.bootcomplete", "1");
+
+            // Start PSI monitoring in LMKD if it was skipped earlier.
+            ProcessList.startPsiMonitoringAfterBoot();
+
             mUserController.onBootComplete(
                     new IIntentReceiver.Stub() {
                         @Override

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

@@ -357,6 +357,7 @@ public final class ProcessList {
     static final byte LMK_UPDATE_PROPS = 7;
     static final byte LMK_KILL_OCCURRED = 8; // Msg to subscribed clients on kill occurred event
     static final byte LMK_STATE_CHANGED = 9; // Msg to subscribed clients on state changed
+    static final byte LMK_START_MONITORING = 9; // Start monitoring if delayed earlier
 
     // Low Memory Killer Daemon command codes.
     // These must be kept in sync with async_event_type definitions in lmkd.h
@@ -1568,6 +1569,15 @@ public final class ProcessList {
         return true;
     }
 
+    /**
+     * {@hide}
+     */
+    public static void startPsiMonitoringAfterBoot() {
+        ByteBuffer buf = ByteBuffer.allocate(4);
+        buf.putInt(LMK_START_MONITORING);
+        writeLmkd(buf, null);
+    }
+
     private static boolean writeLmkd(ByteBuffer buf, ByteBuffer repl) {
         if (!sLmkdConnection.isConnected()) {
             // try to connect immediately and then keep retrying