Reland of "[heap] Switch to 500k pages"

src/heap/spaces.h

Index: src/heap/spaces.h
diff --git a/src/heap/spaces.h b/src/heap/spaces.h
index c035342bfa85058dd9be34024e17cbc6d5722be3..192f61a65d6bd13b48c4020b8303706c5133074f 100644
--- a/src/heap/spaces.h
+++ b/src/heap/spaces.h
@@ -234,7 +234,15 @@ class MemoryChunk {
     IN_TO_SPACE,    // All pages in new space has one of these two set.
     NEW_SPACE_BELOW_AGE_MARK,
     EVACUATION_CANDIDATE,
-    NEVER_EVACUATE,  // May contain immortal immutables.
+
+    // |NEVER_EVACUATE|: A page tagged with this flag will never be selected
+    // for evacuation. Typically used for immortal immovable pages.
+    NEVER_EVACUATE,
+
+    // |NEVER_SWEEP|: A page tagged with this flag will be ignored by the
+    // sweeper. The memory will always be accounted for as allocated. Typically
+    // used for immortal immovable pages.
+    NEVER_SWEEP,
 
     // Large objects can have a progress bar in their page header. These object
     // are scanned in increments and will be kept black while being scanned.
@@ -689,7 +697,7 @@ class Page : public MemoryChunk {
   // account.
   // TODO(hpayer): This limit should be way smaller but we currently have
   // short living objects >256K.
-  static const int kMaxRegularHeapObjectSize = 600 * KB;
+  static const int kMaxRegularHeapObjectSize = 400 * KB;
 
   static inline Page* ConvertNewToOld(Page* old_page, PagedSpace* new_owner);
 
@@ -1270,6 +1278,8 @@ class MemoryAllocator {
                              intptr_t commit_area_size,
                              Executability executable, Space* space);
 
+  void ShrinkChunk(MemoryChunk* chunk, size_t bytes_to_shrink);
+
   Address ReserveAlignedMemory(size_t requested, size_t alignment,
                                base::VirtualMemory* controller);
   Address AllocateAlignedMemory(size_t reserve_size, size_t commit_size,
@@ -1575,6 +1585,7 @@ class AllocationStats BASE_EMBEDDED {
     capacity_ -= size_in_bytes;
     size_ -= size_in_bytes;
     CHECK_GE(size_, 0);
+    CHECK_GE(capacity_, 0);
   }
 
   // Allocate from available bytes (available -> size).
@@ -2140,6 +2151,10 @@ class PagedSpace : public Space {
   iterator begin() { return iterator(anchor_.next_page()); }
   iterator end() { return iterator(&anchor_); }
 
+  // Shrink immortal immovable pages of the space to be exactly the size needed
+  // using the high water mark.
+  void ShrinkImmortalImmovablePages();
+
  protected:
   // PagedSpaces that should be included in snapshots have different, i.e.,
   // smaller, initial pages.