Don't pre-initialize Class.name fields in boot images

The Class.name field is normally allocated and set dynamically when
required. We were pre-initializing it for non-app-images in order to
reduce dirty pages. It turns out that without this very few classes
would ever get this field initialized (~2% according to tests while
running a few apps). No longer pre-initializing the field reduces the
size of each boot image by ~600kb.

This partially reverts commit d418edaf4d.

Prior to the change the smaps entry for an art file look like this:

701cd000-70303000 rw-p 00000000 103:1d 5505036                           /data/dalvik-cache/arm64/system@framework@boot-core-libart.art
Size:               1240 kB
KernelPageSize:        4 kB
MMUPageSize:           4 kB
Rss:                 720 kB
Pss:                 190 kB
Shared_Clean:        548 kB
Shared_Dirty:          0 kB
Private_Clean:        44 kB
Private_Dirty:       128 kB
Referenced:          720 kB
Anonymous:           128 kB

With this change running the same program gives us the following smaps
entry:

6fc83000-6fdae000 rw-p 00000000 103:1d 6684684                           /data/dalvik-cache/arm64/system@framework@boot-core-libart.art
Size:               1196 kB
KernelPageSize:        4 kB
MMUPageSize:           4 kB
Rss:                 672 kB
Pss:                 195 kB
Shared_Clean:        496 kB
Shared_Dirty:          0 kB
Private_Clean:        48 kB
Private_Dirty:       128 kB
Referenced:          672 kB
Anonymous:           128 kB

All relevant measures of memory use are either improved or remain
unchanged. (NB private_clean is the amount of memory that another process
could cause to be dirtied by writing to it. It is not relevant to this
change.)

Bug: 32635074
Test: ./tools/field-null-percent/check-null-fields.py 'Ljava/lang/Class;.name:Ljava/lang/String;'
Test: Builds and boots
Test: Examine smaps for both old and new version.

Change-Id: I96aaeb782715db5c1e035bdf76331b4253c74ce6

2 files changed, 0 insertions, 23 deletions

diff --git a/dex2oat/linker/image_writer.cc b/dex2oat/linker/image_writer.cc
index 6a134548a9..685174dedd 100644
--- a/dex2oat/linker/image_writer.cc
+++ b/dex2oat/linker/image_writer.cc
@@ -213,10 +213,6 @@ bool ImageWriter::PrepareImageAddressSpace(TimingLogger* timings) {
       // since the cookie field contains long pointers to DexFiles which are not deterministic.
       // b/34090128
       ClearDexFileCookies();
-    } else {
-      TimingLogger::ScopedTiming t("ComputeLazyFieldsForImageClasses", timings);
-      // Avoid for app image since this may increase RAM and image size.
-      ComputeLazyFieldsForImageClasses();  // Add useful information
     }
   }
   {
@@ -753,21 +749,6 @@ bool ImageWriter::AllocMemory() {
   return true;
 }
 
-class ImageWriter::ComputeLazyFieldsForClassesVisitor : public ClassVisitor {
- public:
-  bool operator()(ObjPtr<Class> c) override REQUIRES_SHARED(Locks::mutator_lock_) {
-    StackHandleScope<1> hs(Thread::Current());
-    mirror::Class::ComputeName(hs.NewHandle(c));
-    return true;
-  }
-};
-
-void ImageWriter::ComputeLazyFieldsForImageClasses() {
-  ClassLinker* class_linker = Runtime::Current()->GetClassLinker();
-  ComputeLazyFieldsForClassesVisitor visitor;
-  class_linker->VisitClassesWithoutClassesLock(&visitor);
-}
-
 static bool IsBootClassLoaderClass(ObjPtr<mirror::Class> klass)
     REQUIRES_SHARED(Locks::mutator_lock_) {
   return klass->GetClassLoader() == nullptr;
diff --git a/dex2oat/linker/image_writer.h b/dex2oat/linker/image_writer.h
index e45023e6dc..f4557467b6 100644
--- a/dex2oat/linker/image_writer.h
+++ b/dex2oat/linker/image_writer.h
@@ -429,10 +429,6 @@ class ImageWriter final {
   // Debug aid that list of requested image classes.
   void DumpImageClasses();
 
-  // Preinitializes some otherwise lazy fields (such as Class name) to avoid runtime image dirtying.
-  void ComputeLazyFieldsForImageClasses()
-      REQUIRES_SHARED(Locks::mutator_lock_);
-
   // Visit all class loaders.
   void VisitClassLoaders(ClassLoaderVisitor* visitor) REQUIRES_SHARED(Locks::mutator_lock_);