Pool implementation for zone segments

src/zone/zone.cc

Index: src/zone/zone.cc
diff --git a/src/zone/zone.cc b/src/zone/zone.cc
index 4272e17fd2eba2ef2389350b15ae05fd6abfed31..5b458c6746c124e8561a5406e6d472ddabc7e7ee 100644
--- a/src/zone/zone.cc
+++ b/src/zone/zone.cc
@@ -51,7 +51,6 @@ Zone::Zone(AccountingAllocator* allocator)
 
 Zone::~Zone() {
   DeleteAll();
-  DeleteKeptSegment();
 
   DCHECK(segment_bytes_allocated_ == 0);
 }
@@ -92,73 +91,35 @@ void* Zone::New(size_t size) {
 }
 
 void Zone::DeleteAll() {
-  // Find a segment with a suitable size to keep around.
-  Segment* keep = nullptr;
-  // Traverse the chained list of segments, zapping (in debug mode)
-  // and freeing every segment except the one we wish to keep.
+  // Traverse the chained list of segments and return them all to the allocator.
   for (Segment* current = segment_head_; current;) {
     Segment* next = current->next();
-    if (!keep && current->size() <= kMaximumKeptSegmentSize) {
-      // Unlink the segment we wish to keep from the list.
-      keep = current;
-      keep->set_next(nullptr);
-    } else {
-      size_t size = current->size();
-#ifdef DEBUG
-      // Un-poison first so the zapping doesn't trigger ASan complaints.
-      ASAN_UNPOISON_MEMORY_REGION(current, size);
-#endif
-      current->ZapContents();
-      segment_bytes_allocated_ -= size;
-      allocator_->FreeSegment(current);
-    }
+    size_t size = current->size();
+
+    // Un-poison the segment content so we can re-use or zap it later.
+    ASAN_UNPOISON_MEMORY_REGION(current->start(), current->capacity());
+
+    segment_bytes_allocated_ -= size;
+    allocator_->ReturnSegment(current);
     current = next;
   }
 
-  // If we have found a segment we want to keep, we must recompute the
-  // variables 'position' and 'limit' to prepare for future allocate
-  // attempts. Otherwise, we must clear the position and limit to
-  // force a new segment to be allocated on demand.
-  if (keep) {
-    Address start = keep->start();
-    position_ = RoundUp(start, kAlignment);
-    limit_ = keep->end();
-    // Un-poison so we can re-use the segment later.
-    ASAN_UNPOISON_MEMORY_REGION(start, keep->capacity());
-    keep->ZapContents();
-  } else {
-    position_ = limit_ = 0;
-  }
+  position_ = limit_ = 0;
 
   allocation_size_ = 0;
   // Update the head segment to be the kept segment (if any).
-  segment_head_ = keep;
-}
-
-void Zone::DeleteKeptSegment() {
-  DCHECK(segment_head_ == nullptr || segment_head_->next() == nullptr);
-  if (segment_head_ != nullptr) {
-    size_t size = segment_head_->size();
-#ifdef DEBUG
-    // Un-poison first so the zapping doesn't trigger ASan complaints.
-    ASAN_UNPOISON_MEMORY_REGION(segment_head_, size);
-#endif
-    segment_head_->ZapContents();
-    segment_bytes_allocated_ -= size;
-    allocator_->FreeSegment(segment_head_);
-    segment_head_ = nullptr;
-  }
-
-  DCHECK(segment_bytes_allocated_ == 0);
+  segment_head_ = nullptr;
 }
 
 // Creates a new segment, sets it size, and pushes it to the front
 // of the segment chain. Returns the new segment.
-Segment* Zone::NewSegment(size_t size) {
-  Segment* result = allocator_->AllocateSegment(size);
-  segment_bytes_allocated_ += size;
+Segment* Zone::NewSegment(size_t requested_size) {
+  Segment* result = allocator_->GetSegment(requested_size);
+  DCHECK_GE(result->size(), requested_size);
+  segment_bytes_allocated_ += result->size();
   if (result != nullptr) {
-    result->Initialize(segment_head_, size, this);
+    result->set_zone(this);
+    result->set_next(segment_head_);
     segment_head_ = result;
   }
   return result;