[heap] Add a flag to disable scavenge tasks.

Change-Id: I921cdcf7a1b9dc0d5f8ddcb94c5e374b1fb1c879
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2135626Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Hannes Payer <hpayer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66983}

src/flags/flag-definitions.h

@@ -891,6 +891,7 @@ DEFINE_BOOL(incremental_marking_wrappers, true,
             "use incremental marking for marking wrappers")
 DEFINE_BOOL(trace_unmapper, false, "Trace the unmapping")
 DEFINE_BOOL(parallel_scavenge, true, "parallel scavenge")
+DEFINE_BOOL(scavenge_task, true, "schedule scavenge tasks")
 DEFINE_BOOL(trace_parallel_scavenge, false, "trace parallel scavenge")
 DEFINE_BOOL(write_protect_code_memory, true, "write protect code memory")
 #ifdef V8_CONCURRENT_MARKING

src/heap/scavenge-job.cc

@@ -39,7 +39,7 @@ bool ScavengeJob::YoungGenerationSizeTaskTriggerReached(Heap* heap) {
 }
 
 void ScavengeJob::ScheduleTaskIfNeeded(Heap* heap) {
-  if (!task_pending_ && !heap->IsTearingDown() &&
+  if (FLAG_scavenge_task && !task_pending_ && !heap->IsTearingDown() &&
       YoungGenerationSizeTaskTriggerReached(heap)) {
     v8::Isolate* isolate = reinterpret_cast<v8::Isolate*>(heap->isolate());
     auto taskrunner =