- Do not bump allocate in old-space pages. Always use

vm/pages.h

Index: vm/pages.h
===================================================================
--- vm/pages.h	(revision 13711)
+++ vm/pages.h	(working copy)
@@ -31,9 +31,6 @@
   uword start() const { return reinterpret_cast<uword>(this); }
   uword end() const { return memory_->end(); }
 
-  uword top() const { return top_; }
-  void set_top(uword top) { top_ = top; }
-
   uword first_object_start() const {
     return (reinterpret_cast<uword>(this) + sizeof(HeapPage));
   }
@@ -44,16 +41,6 @@
     used_ += size;
   }
 
-  uword TryBumpAllocate(intptr_t size) {
-    uword result = top();
-    intptr_t remaining_space = end() - result;
-    if (remaining_space < size) {
-      return 0;
-    }
-    set_top(result + size);
-    return result;
-  }
-
   void VisitObjects(ObjectVisitor* visitor) const;
   void VisitObjectPointers(ObjectPointerVisitor* visitor) const;
 
@@ -72,7 +59,7 @@
   VirtualMemory* memory_;
   HeapPage* next_;
   uword used_;
-  uword top_;
+  uword alignment_;  // Needed to allocate old objects with kOldObjectAlignment.

[cshapiro, 2012/10/17 02:53:22]

This is a bit confusing.  Is this member referenced anywhere or is it just
padding?  It looks new, but I do not see anything that references it elsewhere
in this change.

If this is just padding, a compile time assert should check the alignment. 
Renaming this to padding_ would be more descriptive as well.

An alternative is to round up in first_object_start and do away with this member
all together.  That would seem to be more robust and would make a nice location
for a static or dynamic assert.

[Ivan Posva, 2012/10/18 17:34:21]

It is padding, which I tried to convey with the name alignment_.
I will reuse this slot for the end of the last object which corresponds to
memory_->end() for regularly sized pages and end of the object for large pages.
I have added a dynamic assert in allocation to ensure that all newly allocated
objects in PageSpace do have the required alignment.

 
   friend class PageSpace;
 
@@ -216,7 +203,7 @@
  private:
   static const intptr_t kAllocatablePageSize = kPageSize - sizeof(HeapPage);
 
-  void AllocatePage();
+  HeapPage* AllocatePage();
   void FreePage(HeapPage* page, HeapPage* previous_page);
   HeapPage* AllocateLargePage(intptr_t size);
   void FreeLargePage(HeapPage* page, HeapPage* previous_page);
@@ -229,8 +216,6 @@
     return increase <= (max_capacity_ - capacity_);
   }
 
-  uword TryBumpAllocate(intptr_t size);
-
   FreeList freelist_;
 
   Heap* heap_;
@@ -241,13 +226,6 @@
 
   PeerTable peer_table_;
 
-  // Page being used for bump allocation.
-  // The value has different meanings:
-  // NULL: Still bump allocating from last allocated fresh page.
-  // !NULL: Last page that had enough room to bump allocate, when we reach the
-  // tail page, we give up bump allocating.
-  HeapPage* bump_page_;
-
   // Various sizes being tracked for this generation.
   intptr_t max_capacity_;
   intptr_t capacity_;