From 629b26c5196bfdc8d188d768472de71c341c71ef Mon Sep 17 00:00:00 2001
From: "hpayer@chromium.org"
 <hpayer@chromium.org@ce2b1a6d-e550-0410-aec6-3dcde31c8c00>
Date: Mon, 14 Oct 2013 09:48:44 +0000
Subject: [PATCH] Use pages from lower to higher addresses in new space.

This CL constitutes the invariant that the top pointer in new space is always larger than objects allocated since the last new space garbage collection.

BUG=
R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/26865004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@17185 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
---
 src/spaces.cc | 33 ++++++++++++---------------------
 1 file changed, 12 insertions(+), 21 deletions(-)

diff --git a/src/spaces.cc b/src/spaces.cc
index b7fa32d..d8aecf3 100644
--- a/src/spaces.cc
+++ b/src/spaces.cc
@@ -1527,20 +1527,18 @@ void SemiSpace::TearDown() {
 bool SemiSpace::Commit() {
   ASSERT(!is_committed());
   int pages = capacity_ / Page::kPageSize;
-  Address end = start_ + maximum_capacity_;
-  Address start = end - pages * Page::kPageSize;
-  if (!heap()->isolate()->memory_allocator()->CommitBlock(start,
+  if (!heap()->isolate()->memory_allocator()->CommitBlock(start_,
                                                           capacity_,
                                                           executable())) {
     return false;
   }
 
-  NewSpacePage* page = anchor();
-  for (int i = 1; i <= pages; i++) {
+  NewSpacePage* current = anchor();
+  for (int i = 0; i < pages; i++) {
     NewSpacePage* new_page =
-      NewSpacePage::Initialize(heap(), end - i * Page::kPageSize, this);
-    new_page->InsertAfter(page);
-    page = new_page;
+      NewSpacePage::Initialize(heap(), start_ + i * Page::kPageSize, this);
+    new_page->InsertAfter(current);
+    current = new_page;
   }
 
   committed_ = true;
@@ -1584,20 +1582,18 @@ bool SemiSpace::GrowTo(int new_capacity) {
   int pages_before = capacity_ / Page::kPageSize;
   int pages_after = new_capacity / Page::kPageSize;
 
-  Address end = start_ + maximum_capacity_;
-  Address start = end - new_capacity;
   size_t delta = new_capacity - capacity_;
 
   ASSERT(IsAligned(delta, OS::AllocateAlignment()));
   if (!heap()->isolate()->memory_allocator()->CommitBlock(
-      start, delta, executable())) {
+      start_ + capacity_, delta, executable())) {
     return false;
   }
   capacity_ = new_capacity;
   NewSpacePage* last_page = anchor()->prev_page();
   ASSERT(last_page != anchor());
-  for (int i = pages_before + 1; i <= pages_after; i++) {
-    Address page_address = end - i * Page::kPageSize;
+  for (int i = pages_before; i < pages_after; i++) {
+    Address page_address = start_ + i * Page::kPageSize;
     NewSpacePage* new_page = NewSpacePage::Initialize(heap(),
                                                       page_address,
                                                       this);
@@ -1617,25 +1613,20 @@ bool SemiSpace::ShrinkTo(int new_capacity) {
   ASSERT(new_capacity >= initial_capacity_);
   ASSERT(new_capacity < capacity_);
   if (is_committed()) {
-    // Semispaces grow backwards from the end of their allocated capacity,
-    // so we find the before and after start addresses relative to the
-    // end of the space.
-    Address space_end = start_ + maximum_capacity_;
-    Address old_start = space_end - capacity_;
     size_t delta = capacity_ - new_capacity;
     ASSERT(IsAligned(delta, OS::AllocateAlignment()));
 
     MemoryAllocator* allocator = heap()->isolate()->memory_allocator();
-    if (!allocator->UncommitBlock(old_start, delta)) {
+    if (!allocator->UncommitBlock(start_ + new_capacity, delta)) {
       return false;
     }
 
     int pages_after = new_capacity / Page::kPageSize;
     NewSpacePage* new_last_page =
-        NewSpacePage::FromAddress(space_end - pages_after * Page::kPageSize);
+        NewSpacePage::FromAddress(start_ + (pages_after - 1) * Page::kPageSize);
     new_last_page->set_next_page(anchor());
     anchor()->set_prev_page(new_last_page);
-    ASSERT((current_page_ <= first_page()) && (current_page_ >= new_last_page));
+    ASSERT((current_page_ >= first_page()) && (current_page_ <= new_last_page));
   }
 
   capacity_ = new_capacity;
-- 
2.7.4