[heap] Add methods for freeing all LABs

This CL adds Heap::FreeLinearAllocationAreas to free all local
allocation buffers (LABs). We use this to give up LABs for a local GC.
The second method Heap::FreeSharedLinearAllocationAreas is used to free
all LABs in the shared heap for shared GCs and in the future also on
isolate shutdown.

Bug: v8:10315
Change-Id: Ie5cbb68c95fae027055aeaf4458473b04b15b18c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3279681Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77900}

src/heap/heap.cc

@@ -2273,9 +2273,7 @@ void Heap::PerformSharedGarbageCollection(Isolate* initiator,
   DCHECK_NOT_NULL(isolate()->global_safepoint());
 
   isolate()->global_safepoint()->IterateClientIsolates([](Isolate* client) {
-    Heap* client_heap = client->heap();
-    client_heap->shared_old_allocator_->FreeLinearAllocationArea();
-    client_heap->shared_map_allocator_->FreeLinearAllocationArea();
+    client->heap()->FreeSharedLinearAllocationAreas();
   });
 
   PerformGarbageCollection(GarbageCollector::MARK_COMPACTOR);
@@ -3536,6 +3534,26 @@ void Heap::MakeHeapIterable() {
   // iterable up to top().
 }
 
+void Heap::FreeLinearAllocationAreas() {
+  safepoint()->IterateLocalHeaps(
+      [](LocalHeap* local_heap) { local_heap->FreeLinearAllocationArea(); });
+
+  PagedSpaceIterator spaces(this);
+  for (PagedSpace* space = spaces.Next(); space != nullptr;
+       space = spaces.Next()) {
+    space->FreeLinearAllocationArea();
+  }
+
+  // New space is bump-pointer allocation only and therefore guaranteed to be
+  // iterable up to top().
+}
+
+void Heap::FreeSharedLinearAllocationAreas() {
+  if (!isolate()->shared_isolate()) return;
+  shared_old_allocator_->FreeLinearAllocationArea();
+  shared_map_allocator_->FreeLinearAllocationArea();
+}
+
 namespace {
 
 double ComputeMutatorUtilizationImpl(double mutator_speed, double gc_speed) {

src/heap/heap.h

@@ -1785,6 +1785,12 @@ class Heap {
   // with the allocation memento of the object at the top
   void EnsureFillerObjectAtTop();
 
+  // Free all LABs in the heap.
+  void FreeLinearAllocationAreas();
+
+  // Free all shared LABs.
+  void FreeSharedLinearAllocationAreas();
+
   // Performs garbage collection in a safepoint.
   // Returns the number of freed global handles.
   size_t PerformGarbageCollection(

src/heap/mark-compact.cc

@@ -919,16 +919,14 @@ void MarkCompactCollector::Prepare() {
     StartMarking();
   }
 
+  heap_->FreeLinearAllocationAreas();
+
   PagedSpaceIterator spaces(heap());
   for (PagedSpace* space = spaces.Next(); space != nullptr;
        space = spaces.Next()) {
     space->PrepareForMarkCompact();
   }
 
-  // Fill and reset all background thread LABs
-  heap_->safepoint()->IterateLocalHeaps(
-      [](LocalHeap* local_heap) { local_heap->FreeLinearAllocationArea(); });
-
   // All objects are guaranteed to be initialized in atomic pause
   if (heap()->new_lo_space()) {
     heap()->new_lo_space()->ResetPendingObject();

src/heap/paged-spaces.cc

@@ -860,10 +860,6 @@ void PagedSpace::UpdateInlineAllocationLimit(size_t min_size) {
 // OldSpace implementation
 
 void PagedSpace::PrepareForMarkCompact() {
-  // We don't have a linear allocation area while sweeping.  It will be restored
-  // on the first allocation after the sweep.
-  FreeLinearAllocationArea();
-
   // Clear the free list before a full GC---it will be rebuilt afterward.
   free_list_->Reset();
 }