[vm, gc] Account for unbounded number of images pages in the compactor.

Bug: #41974
Change-Id: I23201f28e5d1e2ba298611206fc3eb0a9a989c2b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/155241
Reviewed-by: Alexander Markov <[email protected]>
Commit-Queue: Ryan Macnak <[email protected]>

Author: rmacnak-google

runtime/vm/heap/compactor.cc

@@ -569,29 +569,27 @@ void CompactorTask::PlanMoveToContiguousSize(intptr_t size) {
 }
 
 void GCCompactor::SetupImagePageBoundaries() {
-  for (intptr_t i = 0; i < kMaxImagePages; i++) {
-    image_page_ranges_[i].base = 0;
-    image_page_ranges_[i].size = 0;
-  }
-  intptr_t next_offset = 0;
+  MallocGrowableArray<ImagePageRange> ranges(4);
+
   OldPage* image_page = Dart::vm_isolate()->heap()->old_space()->image_pages_;
   while (image_page != NULL) {
-    RELEASE_ASSERT(next_offset <= kMaxImagePages);
-    image_page_ranges_[next_offset].base = image_page->object_start();
-    image_page_ranges_[next_offset].size =
-        image_page->object_end() - image_page->object_start();
+    ImagePageRange range = {image_page->object_start(),
+                            image_page->object_end()};
+    ranges.Add(range);
     image_page = image_page->next();
-    next_offset++;
   }
   image_page = heap_->old_space()->image_pages_;
   while (image_page != NULL) {
-    RELEASE_ASSERT(next_offset <= kMaxImagePages);
-    image_page_ranges_[next_offset].base = image_page->object_start();
-    image_page_ranges_[next_offset].size =
-        image_page->object_end() - image_page->object_start();
+    ImagePageRange range = {image_page->object_start(),
+                            image_page->object_end()};
+    ranges.Add(range);
     image_page = image_page->next();
-    next_offset++;
   }
+
+  ranges.Sort(CompareImagePageRanges);
+  intptr_t image_page_count;
+  ranges.StealBuffer(&image_page_ranges_, &image_page_count);
+  image_page_hi_ = image_page_count - 1;
 }
 
 DART_FORCE_INLINE
@@ -602,8 +600,17 @@ void GCCompactor::ForwardPointer(ObjectPtr* ptr) {
   }
 
   uword old_addr = ObjectLayout::ToAddr(old_target);
-  for (intptr_t i = 0; i < kMaxImagePages; i++) {
-    if ((old_addr - image_page_ranges_[i].base) < image_page_ranges_[i].size) {
+  intptr_t lo = 0;
+  intptr_t hi = image_page_hi_;
+  while (lo <= hi) {
+    intptr_t mid = (hi - lo + 1) / 2 + lo;
+    ASSERT(mid >= lo);
+    ASSERT(mid <= hi);
+    if (old_addr < image_page_ranges_[mid].start) {
+      hi = mid - 1;
+    } else if (old_addr >= image_page_ranges_[mid].end) {
+      lo = mid + 1;
+    } else {
       return;  // Not moved (unaligned image page).
     }
   }

runtime/vm/heap/compactor.h

@@ -28,7 +28,7 @@ class GCCompactor : public ValueObject,
       : HandleVisitor(thread),
         ObjectPointerVisitor(thread->isolate_group()),
         heap_(heap) {}
-  ~GCCompactor() {}
+  ~GCCompactor() { free(image_page_ranges_); }
 
   void Compact(OldPage* pages, FreeList* freelist, Mutex* mutex);
 
@@ -47,13 +47,21 @@ class GCCompactor : public ValueObject,
   Heap* heap_;
 
   struct ImagePageRange {
-    uword base;
-    uword size;
+    uword start;
+    uword end;
   };
-  // There are up to 4 images to consider:
-  // {instructions, data} x {vm isolate, current isolate}
-  static const intptr_t kMaxImagePages = 4;
-  ImagePageRange image_page_ranges_[kMaxImagePages];
+  static int CompareImagePageRanges(const ImagePageRange* a,
+                                    const ImagePageRange* b) {
+    if (a->start < b->start) {
+      return -1;
+    } else if (a->start == b->start) {
+      return 0;
+    } else {
+      return 1;
+    }
+  }
+  intptr_t image_page_hi_ = 0;
+  ImagePageRange* image_page_ranges_ = nullptr;
 
   // The typed data views whose inner pointer must be updated after sliding is
   // complete.

tests/standalone/fragmentation_deferred_load_lib1.dart

@@ -0,0 +1,7 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+foo() {
+  return "one!";
+}

tests/standalone/fragmentation_deferred_load_lib2.dart

@@ -0,0 +1,7 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+foo() {
+  return "two!";
+}

tests/standalone/fragmentation_deferred_load_lib3.dart

@@ -0,0 +1,7 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+foo() {
+  return "three!";
+}

tests/standalone/fragmentation_deferred_load_test.dart

@@ -0,0 +1,40 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// VMOptions=--use_compactor
+
+// Each loading unit creates more image pages in the heap, which unfortunately
+// cannot be aligned stronger than virtual memory page alignment, so the
+// compactor must detect references to these image pages separately. Before
+// these loading units were implemented, the compactor could assume a small
+// upper bound on the number of image pages.
+
+import "package:expect/expect.dart";
+import "fragmentation_deferred_load_lib1.dart" deferred as lib1;
+import "fragmentation_deferred_load_lib2.dart" deferred as lib2;
+import "fragmentation_deferred_load_lib3.dart" deferred as lib3;
+
+main() async {
+  await lib1.loadLibrary();
+  Expect.equals("one!", lib1.foo());
+  await lib2.loadLibrary();
+  Expect.equals("two!", lib2.foo());
+  await lib3.loadLibrary();
+  Expect.equals("three!", lib3.foo());
+
+  final List<List?> arrays = [];
+  // Fill up heap with alternate large-small items.
+  for (int i = 0; i < 500000; i++) {
+    arrays.add(new List<dynamic>.filled(260, null));
+    arrays.add(new List<dynamic>.filled(1, null));
+  }
+  // Clear the large items so that the heap is full of 260-word gaps.
+  for (int i = 0; i < arrays.length; i += 2) {
+    arrays[i] = null;
+  }
+  // Allocate a lot of 300-word objects that don't fit in the gaps.
+  for (int i = 0; i < 600000; i++) {
+    arrays.add(new List<dynamic>.filled(300, null));
+  }
+}

tests/standalone_2/fragmentation_deferred_load_lib1.dart

@@ -0,0 +1,7 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+foo() {
+  return "one!";
+}

tests/standalone_2/fragmentation_deferred_load_lib2.dart

@@ -0,0 +1,7 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+foo() {
+  return "two!";
+}

tests/standalone_2/fragmentation_deferred_load_lib3.dart

@@ -0,0 +1,7 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+foo() {
+  return "three!";
+}

tests/standalone_2/fragmentation_deferred_load_test.dart

@@ -0,0 +1,40 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// VMOptions=--use_compactor
+
+// Each loading unit creates more image pages in the heap, which unfortunately
+// cannot be aligned stronger than virtual memory page alignment, so the
+// compactor must detect references to these image pages separately. Before
+// these loading units were implemented, the compactor could assume a small
+// upper bound on the number of image pages.
+
+import "package:expect/expect.dart";
+import "fragmentation_deferred_load_lib1.dart" deferred as lib1;
+import "fragmentation_deferred_load_lib2.dart" deferred as lib2;
+import "fragmentation_deferred_load_lib3.dart" deferred as lib3;
+
+main() async {
+  await lib1.loadLibrary();
+  Expect.equals("one!", lib1.foo());
+  await lib2.loadLibrary();
+  Expect.equals("two!", lib2.foo());
+  await lib3.loadLibrary();
+  Expect.equals("three!", lib3.foo());
+
+  final List<List> arrays = [];
+  // Fill up heap with alternate large-small items.
+  for (int i = 0; i < 500000; i++) {
+    arrays.add(new List(260));
+    arrays.add(new List(1));
+  }
+  // Clear the large items so that the heap is full of 260-word gaps.
+  for (int i = 0; i < arrays.length; i += 2) {
+    arrays[i] = null;
+  }
+  // Allocate a lot of 300-word objects that don't fit in the gaps.
+  for (int i = 0; i < 600000; i++) {
+    arrays.add(new List(300));
+  }
+}