Replaced different means of zone pooling/reusing by one zone segment pool

src/zone/zone.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/zone/zone.h"
 
 #include <cstring>
 
 #include "src/v8.h"
 
@@ skipping 33 matching lines @@
 Zone::Zone(AccountingAllocator* allocator)
     : allocation_size_(0),
       segment_bytes_allocated_(0),
       position_(0),
       limit_(0),
       allocator_(allocator),
       segment_head_(nullptr) {}
 
 Zone::~Zone() {
   DeleteAll();
-  DeleteKeptSegment();
 
   DCHECK(segment_bytes_allocated_ == 0);
 }
 
 void* Zone::New(size_t size) {
   // Round up the requested size to fit the alignment.
   size = RoundUp(size, kAlignment);
 
   // If the allocation size is divisible by 8 then we return an 8-byte aligned
   // address.
@@ skipping 25 matching lines @@
   allocation_size_ += size;
   return reinterpret_cast<void*>(result);
 }
 
 void Zone::DeleteAll() {
 #ifdef DEBUG
   // Constant byte value used for zapping dead memory in debug mode.
   static const unsigned char kZapDeadByte = 0xcd;
 #endif
 
-  // 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.

[Michael Starzinger, 2016/09/20 10:35:39]

nit: Lets drop the "except the one we wish to keep" part from the comment.

   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();
+    size_t size = current->size();
 #ifdef DEBUG
-      // Un-poison first so the zapping doesn't trigger ASan complaints.
-      ASAN_UNPOISON_MEMORY_REGION(current, size);
-      // Zap the entire current segment (including the header).
-      memset(current, kZapDeadByte, size);
+    // Un-poison first so the zapping doesn't trigger ASan complaints.
+    ASAN_UNPOISON_MEMORY_REGION(current, size);
+    // Zap the entire current segment (including the header).
+    memset(current, kZapDeadByte, size);
 #endif
-      segment_bytes_allocated_ -= size;
-      allocator_->ReturnSegment(current);
-    }
+    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());
-#ifdef DEBUG
-    // Zap the contents of the kept segment (but not the header).
-    memset(start, kZapDeadByte, keep->capacity());
-#endif
-  } 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() {
-#ifdef DEBUG
-  // Constant byte value used for zapping dead memory in debug mode.
-  static const unsigned char kZapDeadByte = 0xcd;
-#endif
-
-  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);
-    // Zap the entire kept segment (including the header).
-    memset(segment_head_, kZapDeadByte, size);
-#endif
-    segment_bytes_allocated_ -= size;
-    allocator_->ReturnSegment(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_->GetSegment(size);
   segment_bytes_allocated_ += size;
   if (result != nullptr) {
     result->Initialize(segment_head_, size, this);
     segment_head_ = result;
@@ skipping 52 matching lines @@
   // size bytes + header and alignment padding)
   DCHECK(reinterpret_cast<uintptr_t>(position_) >=
          reinterpret_cast<uintptr_t>(result));
   limit_ = segment->end();
   DCHECK(position_ <= limit_);
   return result;
 }
 
 }  // namespace internal
 }  // namespace v8