[heap] Some small PagedNewSpace fixes

Bug: v8:12612
Change-Id: Ibd20ba65e81b86239e254b945c4c6c9c6137b714
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3822687
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82354}

src/heap/new-spaces.cc

@@ -948,6 +948,7 @@ void PagedSpaceForNewSpace::Shrink() {
       Page* current_page = page;
       page = page->next_page();
       if (current_page->allocated_bytes() == 0) {
+        memory_chunk_list().Remove(current_page);
         ReleasePage(current_page);
       }
     }
@@ -981,8 +982,9 @@ void PagedSpaceForNewSpace::ReleasePage(Page* page) {
 }
 
 bool PagedSpaceForNewSpace::AddFreshPage() {
-  if (TotalCapacity() >= MaximumCapacity()) return false;
-  return TryExpandImpl();
+  DCHECK_LE(TotalCapacity(), MaximumCapacity());
+  if (current_capacity_ >= target_capacity_) return false;
+  return EnsureCurrentCapacity();
 }
 
 bool PagedSpaceForNewSpace::EnsureCurrentCapacity() {
@@ -1035,7 +1037,7 @@ PagedNewSpace::~PagedNewSpace() {
 void PagedNewSpace::Verify(Isolate* isolate) const {
   const Page* first_page = paged_space_.first_page();
 
-  VerifyImpl(isolate, first_page, first_page->area_start());
+  if (first_page) VerifyImpl(isolate, first_page, first_page->area_start());
 
   // Check paged-spaces.
   VerifyPointersVisitor visitor(heap());

src/heap/new-spaces.h

@@ -584,7 +584,7 @@ class V8_EXPORT_PRIVATE PagedSpaceForNewSpace final : public PagedSpaceBase {
 
   // Reset the allocation pointer.
   void EvacuatePrologue();
-  void EvacuateEpilogue() {}
+  void EvacuateEpilogue() { allocated_linear_areas_ = 0; }
 
   // When inline allocation stepping is active, either because of incremental
   // marking, idle scavenge, or allocation statistics gathering, we 'interrupt'
@@ -613,6 +613,12 @@ class V8_EXPORT_PRIVATE PagedSpaceForNewSpace final : public PagedSpaceBase {
   void RemovePage(Page* page) final;
   void ReleasePage(Page* page) final;
 
+  size_t ExternalBackingStoreBytes(ExternalBackingStoreType type) const final {
+    if (type == ExternalBackingStoreType::kArrayBuffer)
+      return heap()->YoungArrayBufferBytes();
+    return external_backing_store_bytes_[type];
+  }
+
 #ifdef VERIFY_HEAP
   void Verify(Isolate* isolate, ObjectVisitor* visitor) const final;
 #endif
@@ -681,12 +687,9 @@ class V8_EXPORT_PRIVATE PagedNewSpace final : public NewSpace {
   }
 
   // Return the available bytes without growing.
-  // TODO(v8:12612): Rethink this method. In SemiSpaceNewSpace available memory
-  // was contiguous memory. With PagedNewSpace it is the sum of blocks in the
-  // freelist. Available() returning X does not guarantee that an object of size
-  // lower than X can be allocated without growing as it might still not fit in
-  // any block in the freelist.
-  size_t Available() const final { return paged_space_.Available(); }
+  size_t Available() const final {
+    return paged_space_.Available() + limit() - top();
+  }
 
   size_t ExternalBackingStoreBytes(ExternalBackingStoreType type) const final {
     return paged_space_.ExternalBackingStoreBytes(type);