[heap] Add a flag to enable memory reducer for small heaps

Bug: chromium:933107
Change-Id: Ie3a485447f96228d5c8d7fc169c9aabf8ccf6599
Reviewed-on: https://chromium-review.googlesource.com/c/1477057Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59658}

src/flag-definitions.h

@@ -768,6 +768,8 @@ DEFINE_BOOL(verify_heap_skip_remembered_set, false,
 #endif
 DEFINE_BOOL(move_object_start, true, "enable moving of object starts")
 DEFINE_BOOL(memory_reducer, true, "use memory reducer")
+DEFINE_BOOL(memory_reducer_for_small_heaps, true,
+            "use memory reducer for small heaps")
 DEFINE_INT(heap_growing_percent, 0,
            "specifies heap growing factor as (1 + heap_growing_percent/100)")
 DEFINE_INT(v8_os_page_size, 0, "override OS page size (in KBytes)")

src/heap/heap.cc

@@ -4689,7 +4689,8 @@ void Heap::NotifyOldGenerationExpansion() {
   const size_t kMemoryReducerActivationThreshold = 1 * MB;
   if (old_generation_capacity_after_bootstrap_ && ms_count_ == 0 &&
       OldGenerationCapacity() >= old_generation_capacity_after_bootstrap_ +
-                                     kMemoryReducerActivationThreshold) {
+                                     kMemoryReducerActivationThreshold &&
+      FLAG_memory_reducer_for_small_heaps) {
     MemoryReducer::Event event;
     event.type = MemoryReducer::kPossibleGarbage;
     event.time_ms = MonotonicallyIncreasingTimeInMs();