- Free completely empty pages as part of sweep.

vm/pages.cc

Index: vm/pages.cc
===================================================================
--- vm/pages.cc	(revision 6528)
+++ vm/pages.cc	(working copy)
@@ -68,7 +68,6 @@
     : freelist_(),
       heap_(heap),
       pages_(NULL),
-      pages_tail_(NULL),
       large_pages_(NULL),
       bump_page_(NULL),
       max_capacity_(max_capacity),
@@ -94,12 +93,8 @@
 
 void PageSpace::AllocatePage() {
   HeapPage* page = HeapPage::Allocate(kPageSize, is_executable_);
-  if (pages_ == NULL) {
-    pages_ = page;
-  } else {
-    pages_tail_->set_next(page);
-  }
-  pages_tail_ = page;
+  page->set_next(pages_);
+  pages_ = page;
   bump_page_ = NULL;  // Reenable scanning of pages for bump allocation.
   capacity_ += kPageSize;
 }
@@ -115,6 +110,19 @@
 }
 
 
+void PageSpace::FreePage(HeapPage* page, HeapPage* previous_page) {
+  capacity_ -= page->memory_->size();
+  // Remove the page from the list.
+  if (previous_page != NULL) {
+    previous_page->set_next(page->next());
+  } else {
+    pages_ = page->next();
+  }
+  // TODO(iposva): Consider adding to a pool of empty pages.
+  page->Deallocate();
+}
+
+
 void PageSpace::FreeLargePage(HeapPage* page, HeapPage* previous_page) {
   capacity_ -= page->memory_->size();
   // Remove the page from the list.
@@ -138,21 +146,12 @@
 
 
 uword PageSpace::TryBumpAllocate(intptr_t size) {
-  if (pages_tail_ == NULL) {
-    return 0;
-  }
-  uword result = pages_tail_->TryBumpAllocate(size);
-  if (result != 0) {
-    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);
+  while (bump_page_ != NULL) {
+    uword result = bump_page_->TryBumpAllocate(size);
     if (result != 0) {
       return result;
     }
@@ -284,14 +283,22 @@
   GCSweeper sweeper(heap_);
   intptr_t in_use = 0;
 
+  HeapPage* prev_page = NULL;
   HeapPage* page = pages_;
   while (page != NULL) {
     intptr_t page_in_use = sweeper.SweepPage(page, &freelist_);
-    in_use += page_in_use;
-    page = page->next();
+    HeapPage* next_page = page->next();
+    if (page_in_use == 0) {
+      FreePage(page, prev_page);
+    } else {
+      in_use += page_in_use;
+      prev_page = page;
+    }
+    // Advance to the next page.
+    page = next_page;
   }
 
-  HeapPage* prev_page = NULL;
+  prev_page = NULL;
   page = large_pages_;
   while (page != NULL) {
     intptr_t page_in_use = sweeper.SweepLargePage(page);