Add flag-guarded disabling of default .art file madvise

The compressed .art app image file is read just once during process
startup. As such, there is little benefit to running a full madvise
before starting decompression, and in some cases this actually leads
to (slightly) worse latency.

Use a flag to control the default value for the ART runtime's
`-XMadviseWillNeedArtFileSize` configuration. Previously, this
was set via a makefile default to be UINT_MAX. This default is preserved
in the runtime, where the new aconfig flag disables this default
and turns off .art file madvise (unless the property is explicitly
configured for a particular device).

After ramping and validating performance impact, we may consider
deprecating and removing this ART runtime flag completely.

Flag: android.os.disable_madvise_artfile_default
Test: m
Test: adb shell aflags enable android.os.disable_madvise_artfile_default
   && adb shell setprop dalvik.vm.extra-opts -verbose:startup
   && adb logcat | grep Madvise
Bug: 382110550
Change-Id: I16170215da0d06a0fd110112fc17b03002939621

2 files changed, 9 insertions, 3 deletions

diff --git a/core/jni/Android.bp b/core/jni/Android.bp
index 411315ee2800..817284d3bf78 100644
--- a/core/jni/Android.bp
+++ b/core/jni/Android.bp
@@ -288,6 +288,7 @@ cc_library_shared_for_libandroid_runtime {
             ],
 
             static_libs: [
+                "android.os.flags-aconfig-cc",
                 "libasync_safe",
                 "libbinderthreadstateutils",
                 "libdmabufinfo",
diff --git a/core/jni/AndroidRuntime.cpp b/core/jni/AndroidRuntime.cpp
index 3bfc1028dd6a..0e4da86b7cc3 100644
--- a/core/jni/AndroidRuntime.cpp
+++ b/core/jni/AndroidRuntime.cpp
@@ -22,6 +22,7 @@
 #include <android-base/parsebool.h>
 #include <android-base/properties.h>
 #include <android/graphics/jni_runtime.h>
+#include <android_os.h>
 #include <android_runtime/AndroidRuntime.h>
 #include <assert.h>
 #include <binder/IBinder.h>
@@ -887,9 +888,13 @@ int AndroidRuntime::startVm(JavaVM** pJavaVM, JNIEnv** pEnv, bool zygote, bool p
                        madviseWillNeedFileSizeOdex,
                        "-XMadviseWillNeedOdexFileSize:");
 
-    parseRuntimeOption("dalvik.vm.madvise.artfile.size",
-                       madviseWillNeedFileSizeArt,
-                       "-XMadviseWillNeedArtFileSize:");
+    // Historically, dalvik.vm.madvise.artfile.size was set to UINT_MAX by default. With the
+    // disable_madvise_art_default flag rollout, we use this default only when the flag is disabled.
+    // TODO(b/382110550): Remove this property/flag entirely after validating and ramping.
+    const char* madvise_artfile_size_default =
+            android::os::disable_madvise_artfile_default() ? "" : "4294967295";
+    parseRuntimeOption("dalvik.vm.madvise.artfile.size", madviseWillNeedFileSizeArt,
+                       "-XMadviseWillNeedArtFileSize:", madvise_artfile_size_default);
 
     /*
      * Profile related options.