Re-land "Concurrently unmap free pages."

src/heap/heap.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/heap/heap.h"
 
 #include "src/accessors.h"
 #include "src/api.h"
 #include "src/base/bits.h"
 #include "src/base/once.h"
@@ skipping 117 matching lines @@
       old_generation_size_at_last_gc_(0),
       gcs_since_last_deopt_(0),
       allocation_sites_scratchpad_length_(0),
       ring_buffer_full_(false),
       ring_buffer_end_(0),
       promotion_queue_(this),
       configured_(false),
       current_gc_flags_(Heap::kNoGCFlags),
       external_string_table_(this),
       chunks_queued_for_free_(NULL),
+      pending_unmap_job_semaphore_(0),
       gc_callbacks_depth_(0),
       deserialization_complete_(false),
       concurrent_sweeping_enabled_(false),
       strong_roots_list_(NULL) {
 // Allow build-time customization of the max semispace size. Building
 // V8 with snapshots and a non-default max semispace size is much
 // easier if you can define it as part of the build environment.
 #if defined(V8_MAX_SEMISPACE_SIZE)
   max_semi_space_size_ = reserved_semispace_size_ = V8_MAX_SEMISPACE_SIZE;
 #endif
@@ skipping 6346 matching lines @@
     heap_->FinalizeExternalString(ExternalString::cast(new_space_strings_[i]));
   }
   new_space_strings_.Free();
   for (int i = 0; i < old_space_strings_.length(); ++i) {
     heap_->FinalizeExternalString(ExternalString::cast(old_space_strings_[i]));
   }
   old_space_strings_.Free();
 }
 
 
+class Heap::UnmapFreeMemoryTask : public v8::Task {
+ public:
+  UnmapFreeMemoryTask(Heap* heap, MemoryChunk* head)
+      : heap_(heap), head_(head) {}
+  virtual ~UnmapFreeMemoryTask() {}
+
+ private:
+  // v8::Task overrides.
+  void Run() override {
+    heap_->FreeQueuedChunks(head_);
+    heap_->pending_unmap_job_semaphore_.Signal();
+  }
+
+  Heap* heap_;
+  MemoryChunk* head_;
+
+  DISALLOW_COPY_AND_ASSIGN(UnmapFreeMemoryTask);
+};
+
+
+void Heap::WaitUntilUnmappingOfFreeChunksCompleted() {
+  // We start an unmap job after sweeping and after compaction.
+  pending_unmap_job_semaphore_.Wait();
+  pending_unmap_job_semaphore_.Wait();
+}
+
+
 void Heap::QueueMemoryChunkForFree(MemoryChunk* chunk) {
+  // PreFree logically frees the memory chunk. However, the actual freeing
+  // will happen on a separate thread sometime later.
+  isolate_->memory_allocator()->PreFreeMemory(chunk);
+
+  // The chunks added to this queue will be freed by a concurrent thread.
   chunk->set_next_chunk(chunks_queued_for_free_);
   chunks_queued_for_free_ = chunk;
 }
 
 
 void Heap::FilterStoreBufferEntriesOnAboutToBeFreedPages() {
   if (chunks_queued_for_free_ == NULL) return;
   MemoryChunk* next;
   MemoryChunk* chunk;
   for (chunk = chunks_queued_for_free_; chunk != NULL; chunk = next) {
     next = chunk->next_chunk();
     chunk->SetFlag(MemoryChunk::ABOUT_TO_BE_FREED);
   }
-  isolate_->heap()->store_buffer()->Compact();
-  isolate_->heap()->store_buffer()->Filter(MemoryChunk::ABOUT_TO_BE_FREED);
+  store_buffer()->Compact();
+  store_buffer()->Filter(MemoryChunk::ABOUT_TO_BE_FREED);
 }
 
 
 void Heap::FreeQueuedChunks() {
-  MemoryChunk* next;
-  MemoryChunk* chunk;
-  for (chunk = chunks_queued_for_free_; chunk != NULL; chunk = next) {
-    next = chunk->next_chunk();
-    isolate_->memory_allocator()->Free(chunk);
+  if (chunks_queued_for_free_ != NULL) {
+    V8::GetCurrentPlatform()->CallOnBackgroundThread(
+        new UnmapFreeMemoryTask(this, chunks_queued_for_free_),
+        v8::Platform::kShortRunningTask);
+    chunks_queued_for_free_ = NULL;
+  } else {
+    // If we do not have anything to unmap, we just signal the semaphore
+    // that we are done.
+    pending_unmap_job_semaphore_.Signal();
   }
-  chunks_queued_for_free_ = NULL;
 }
 
 
+void Heap::FreeQueuedChunks(MemoryChunk* list_head) {
+  MemoryChunk* next;
+  MemoryChunk* chunk;
+  for (chunk = list_head; chunk != NULL; chunk = next) {
+    next = chunk->next_chunk();
+    isolate_->memory_allocator()->PerformFreeMemory(chunk);
+  }
+}
+
+
 void Heap::RememberUnmappedPage(Address page, bool compacted) {
   uintptr_t p = reinterpret_cast<uintptr_t>(page);
   // Tag the page pointer to make it findable in the dump file.
   if (compacted) {
     p ^= 0xc1ead & (Page::kPageSize - 1);  // Cleared.
   } else {
     p ^= 0x1d1ed & (Page::kPageSize - 1);  // I died.
   }
   remembered_unmapped_pages_[remembered_unmapped_pages_index_] =
       reinterpret_cast<Address>(p);
@@ skipping 180 matching lines @@
     *object_type = "CODE_TYPE";                                                \
     *object_sub_type = "CODE_AGE/" #name;                                      \
     return true;
     CODE_AGE_LIST_COMPLETE(COMPARE_AND_RETURN_NAME)
 #undef COMPARE_AND_RETURN_NAME
   }
   return false;
 }
 }  // namespace internal
 }  // namespace v8