- Use the unused top of old-space pages when allocating.

vm/pages.cc

Index: vm/pages.cc
===================================================================
--- vm/pages.cc	(revision 6398)
+++ vm/pages.cc	(working copy)
@@ -70,6 +70,7 @@
       pages_(NULL),
       pages_tail_(NULL),
       large_pages_(NULL),
+      bump_page_(NULL),
       max_capacity_(max_capacity),
       capacity_(0),
       in_use_(0),
@@ -99,6 +100,7 @@
     pages_tail_->set_next(page);
   }
   pages_tail_ = page;
+  bump_page_ = NULL;  // Reenable scanning of pages for bump allocation.
   capacity_ += kPageSize;
 }
 
@@ -136,17 +138,28 @@
 
 
 uword PageSpace::TryBumpAllocate(intptr_t size) {
-  HeapPage* page = pages_tail_;
-  if (page == NULL) {
+  if (pages_tail_ == NULL) {
     return 0;
   }
-  uword result = page->top();
-  intptr_t remaining_space = page->end() - result;
-  if (remaining_space < size) {
-    return 0;
+  uword result = pages_tail_->TryBumpAllocate(size);
+  if (result != 0) {
+    return result;
   }
-  page->set_top(result + size);
-  return result;
+  if (bump_page_ == NULL) {
+    // The bump page has not yet been used: Start at the beginning of the list.
+    bump_page_ = pages_;
+  }
+  // The last page has already been attempted above.
+  while (bump_page_ != pages_tail_) {
+    ASSERT(bump_page_->next() != NULL);
+    result = bump_page_->TryBumpAllocate(size);
+    if (result != 0) {
+      return result;
+    }
+    bump_page_ = bump_page_->next();
+  }
+  // Ran through all of the pages trying to bump allocate: Give up.
+  return 0;
 }
 
 
@@ -264,6 +277,8 @@
   GCMarker marker(heap_);
   marker.MarkObjects(isolate, this, invoke_api_callbacks);
 
+  // Reset the bump allocation page to unused.
+  bump_page_ = NULL;
   // Reset the freelists and setup sweeping.
   freelist_.Reset();
   GCSweeper sweeper(heap_);
@@ -271,7 +286,8 @@
 
   HeapPage* page = pages_;
   while (page != NULL) {
-    in_use += sweeper.SweepPage(page, &freelist_);
+    intptr_t page_in_use = sweeper.SweepPage(page, &freelist_);
+    in_use += page_in_use;

[ricow1, 2012/04/11 10:23:30]

Why this change? (easier debugging?)

[Ivan Posva, 2012/04/11 11:56:52]

Yes, and preparation for the next step. Freeing of normal pages if they are
completely empty.

     page = page->next();
   }