Lower limit for external allocation and improve tracing.

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index 43c83e40a5aecfd74ed46f00ec678dde9d9436cb..0eb75f4f30f2a95086fa05f128de7244be971fa1 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -6620,7 +6620,12 @@ bool Heap::ConfigureHeap(int max_semispace_size,
   max_semispace_size_ = RoundUpToPowerOf2(max_semispace_size_);
   reserved_semispace_size_ = RoundUpToPowerOf2(reserved_semispace_size_);
   initial_semispace_size_ = Min(initial_semispace_size_, max_semispace_size_);
-  external_allocation_limit_ = 16 * max_semispace_size_;
+
+  // The external allocation limit should be below 256 MB on all architectures
+  // to avoid unnecessary low memory notifications, as that is the threshold
+  // for some embedders.
+  external_allocation_limit_ = 12 * max_semispace_size_;
+  ASSERT(external_allocation_limit_ <= 256 * MB);
 
   // The old generation is paged and needs at least one page for each space.
   int paged_space_count = LAST_PAGED_SPACE - FIRST_PAGED_SPACE + 1;