Finch:increase max_old_space_size to 4 GB based on availability of physical memory

This is for the finch experiment CL 1592792 V8HugeMaxOldGenerationSize
(--js-flags="huge_max_old_generation_size").
The purpose of this finch is to support web apps that require more heap
space for their data sets.

The current max_old_space_size is 2 GB. This CL increases the size to 4 GB for
64-bit systems with a physical memory size bigger than 16 GB. This CL does not
change MaxGrowingFactor. HeapController::kMaxSize is still set to 2GB so the
GC schedule remains the same.

All tests from "tools\dev\gm.py x64.release.check" passes in my local machine
with FLAG_increase_max_old_space_size forced to true.

Bug:958974

Change-Id: I9d916d75c0b16342040dd1336e28e423e5bcc474
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1592129
Commit-Queue: Maggie Chen <magchen@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61297}

src/flag-definitions.h

@@ -742,6 +742,9 @@ DEFINE_BOOL(experimental_new_space_growth_heuristic, false,
             "Grow the new space based on the percentage of survivors instead "
             "of their absolute value.")
 DEFINE_SIZE_T(max_old_space_size, 0, "max size of the old space (in Mbytes)")
+DEFINE_BOOL(huge_max_old_generation_size, false,
+            "Increase max size of the old space to 4 GB for x64 systems with"
+            "the physical memory bigger than 16 GB")
 DEFINE_SIZE_T(initial_old_space_size, 0, "initial old space size (in Mbytes)")
 DEFINE_BOOL(gc_global, false, "always perform global GCs")
 DEFINE_INT(random_gc_interval, 0,

src/heap/heap.cc

@@ -216,8 +216,18 @@ size_t Heap::ComputeMaxOldGenerationSize(uint64_t physical_memory) {
   size_t computed_size = static_cast<size_t>(physical_memory / i::MB /
                                              old_space_physical_memory_factor *
                                              kPointerMultiplier);
-  return Max(Min(computed_size, HeapController::kMaxSize),
-             HeapController::kMinSize);
+  size_t max_size_in_mb = HeapController::kMaxSize;
+
+  // Finch experiment: Increase the heap size from 2GB to 4GB for 64-bit
+  // systems with physical memory bigger than 16GB.
+  constexpr bool x64_bit = Heap::kPointerMultiplier >= 2;
+  if (FLAG_huge_max_old_generation_size && x64_bit &&
+      physical_memory / GB > 16) {
+    DCHECK_LE(max_size_in_mb, 4096);
+    max_size_in_mb = 4096;  // 4GB
+  }
+
+  return Max(Min(computed_size, max_size_in_mb), HeapController::kMinSize);
 }
 
 size_t Heap::Capacity() {