Revert of [heap] Switch to 500k pages

src/snapshot/snapshot-common.cc

Index: src/snapshot/snapshot-common.cc
diff --git a/src/snapshot/snapshot-common.cc b/src/snapshot/snapshot-common.cc
index 959ac56fa98aa6a182062c76126f53e24c6bb193..fed45d16b6c3528d241284765bbeb8631c489617 100644
--- a/src/snapshot/snapshot-common.cc
+++ b/src/snapshot/snapshot-common.cc
@@ -31,6 +31,19 @@
   return index < num_contexts;
 }
 
+
+uint32_t Snapshot::SizeOfFirstPage(Isolate* isolate, AllocationSpace space) {
+  DCHECK(space >= FIRST_PAGED_SPACE && space <= LAST_PAGED_SPACE);
+  if (!isolate->snapshot_available()) {
+    return static_cast<uint32_t>(MemoryAllocator::PageAreaSize(space));
+  }
+  uint32_t size;
+  int offset = kFirstPageSizesOffset + (space - FIRST_PAGED_SPACE) * kInt32Size;
+  memcpy(&size, isolate->snapshot_blob()->data + offset, kInt32Size);
+  return size;
+}
+
+
 bool Snapshot::Initialize(Isolate* isolate) {
   if (!isolate->snapshot_available()) return false;
   base::ElapsedTimer timer;
@@ -76,8 +89,25 @@
   return Handle<Context>::cast(result);
 }
 
-void ProfileDeserialization(const SnapshotData* startup_snapshot,
-                            const List<SnapshotData*>* context_snapshots) {
+void UpdateMaxRequirementPerPage(
+    uint32_t* requirements,
+    Vector<const SerializedData::Reservation> reservations) {
+  int space = 0;
+  uint32_t current_requirement = 0;
+  for (const auto& reservation : reservations) {
+    current_requirement += reservation.chunk_size();
+    if (reservation.is_last()) {
+      requirements[space] = std::max(requirements[space], current_requirement);
+      current_requirement = 0;
+      space++;
+    }
+  }
+  DCHECK_EQ(i::Serializer::kNumberOfSpaces, space);
+}
+
+void CalculateFirstPageSizes(const SnapshotData* startup_snapshot,
+                             const List<SnapshotData*>* context_snapshots,
+                             uint32_t* sizes_out) {
   if (FLAG_profile_deserialization) {
     int startup_total = 0;
     PrintF("Deserialization will reserve:\n");
@@ -91,6 +121,36 @@
         context_total += reservation.chunk_size();
       }
       PrintF("%10d bytes per context #%d\n", context_total, i);
+    }
+  }
+
+  uint32_t startup_requirements[i::Serializer::kNumberOfSpaces];
+  uint32_t context_requirements[i::Serializer::kNumberOfSpaces];
+  for (int space = 0; space < i::Serializer::kNumberOfSpaces; space++) {
+    startup_requirements[space] = 0;
+    context_requirements[space] = 0;
+  }
+
+  UpdateMaxRequirementPerPage(startup_requirements,
+                              startup_snapshot->Reservations());
+  for (const auto& context_snapshot : *context_snapshots) {
+    UpdateMaxRequirementPerPage(context_requirements,
+                                context_snapshot->Reservations());
+  }
+
+  for (int space = 0; space < i::Serializer::kNumberOfSpaces; space++) {
+    // If the space requirement for a page is less than a page size, we consider
+    // limiting the size of the first page in order to save memory on startup.
+    uint32_t required = startup_requirements[space] +
+                        2 * context_requirements[space] +
+                        Page::kObjectStartOffset;
+    // Add a small allowance to the code space for small scripts.
+    if (space == CODE_SPACE) required += 32 * KB;
+
+    if (space >= FIRST_PAGED_SPACE && space <= LAST_PAGED_SPACE) {
+      uint32_t max_size =
+          MemoryAllocator::PageAreaSize(static_cast<AllocationSpace>(space));
+      sizes_out[space - FIRST_PAGED_SPACE] = std::min(required, max_size);
     }
   }
 }
@@ -106,9 +166,13 @@
     total_length += context_snapshot->RawData().length();
   }
 
-  ProfileDeserialization(startup_snapshot, context_snapshots);
+  uint32_t first_page_sizes[kNumPagedSpaces];
+  CalculateFirstPageSizes(startup_snapshot, context_snapshots,
+                          first_page_sizes);
 
   char* data = new char[total_length];
+  memcpy(data + kFirstPageSizesOffset, first_page_sizes,
+         kNumPagedSpaces * kInt32Size);
   memcpy(data + kNumberOfContextsOffset, &num_contexts, kInt32Size);
   int payload_offset = StartupSnapshotOffset(num_contexts);
   int payload_length = startup_snapshot->RawData().length();