[heap] Add flag to synchronize runtime allocations in old space

Add flag FLAG_concurrent_allocation that when enabled protects all runtime allocations in the old space with a mutex. Prerequisite for concurrent allocation. Still disabled by default.

Bug: v8:10315
Change-Id: I37e59b3d51fe3aad112f0b556ea867cc0a2496e2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2140937
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67075}

src/flags/flag-definitions.h

@@ -917,6 +917,7 @@ DEFINE_BOOL_READONLY(array_buffer_extension, V8_ARRAY_BUFFER_EXTENSION_BOOL,
 DEFINE_IMPLICATION(array_buffer_extension, always_promote_young_mc)
 DEFINE_BOOL(concurrent_array_buffer_sweeping, true,
             "concurrently sweep array buffers")
+DEFINE_BOOL(concurrent_allocation, false, "concurrently allocate in old space")
 DEFINE_BOOL(local_heaps, false, "allow heap access from background tasks")
 DEFINE_BOOL(parallel_marking, true, "use parallel marking in atomic pause")
 DEFINE_INT(ephemeron_fixpoint_iterations, 10,

src/heap/spaces.cc

@@ -3787,6 +3787,13 @@ bool PagedSpace::SlowRefillLinearAllocationArea(int size_in_bytes,
   VMState<GC> state(heap()->isolate());
   RuntimeCallTimerScope runtime_timer(
       heap()->isolate(), RuntimeCallCounterId::kGC_Custom_SlowAllocateRaw);
+  base::Optional<base::MutexGuard> optional_mutex;
+
+  if (FLAG_concurrent_allocation && origin != AllocationOrigin::kGC &&
+      identity() == OLD_SPACE) {
+    optional_mutex.emplace(&allocation_mutex_);
+  }
+
   return RawSlowRefillLinearAllocationArea(size_in_bytes, origin);
 }
 

src/heap/spaces.h

@@ -2588,6 +2588,9 @@ class V8_EXPORT_PRIVATE PagedSpace
   // Mutex guarding any concurrent access to the space.
   base::Mutex space_mutex_;
 
+  // Mutex guarding concurrent allocation.
+  base::Mutex allocation_mutex_;
+
   friend class IncrementalMarking;
   friend class MarkCompactCollector;