Make store buffer more robust to OOM.

src/heap/store-buffer.cc

Index: src/heap/store-buffer.cc
diff --git a/src/heap/store-buffer.cc b/src/heap/store-buffer.cc
index a73e0fa57772f387a9c25be16136b87563e1df9c..f6df80e0dab84235ce58f2ba8f2edb1ccd37d11c 100644
--- a/src/heap/store-buffer.cc
+++ b/src/heap/store-buffer.cc
@@ -33,6 +33,9 @@ StoreBuffer::StoreBuffer(Heap* heap)
 
 
 void StoreBuffer::SetUp() {
+  // Allocate 3x the buffer size, so that we can start the new store buffer
+  // aligned to 2x the size.  This lets us use a bit test to detect the end of
+  // the area.
   virtual_memory_ = new base::VirtualMemory(kStoreBufferSize * 3);
   uintptr_t start_as_int =
       reinterpret_cast<uintptr_t>(virtual_memory_->address());
@@ -40,17 +43,22 @@ void StoreBuffer::SetUp() {
       reinterpret_cast<Address*>(RoundUp(start_as_int, kStoreBufferSize * 2));
   limit_ = start_ + (kStoreBufferSize / kPointerSize);
 
+  // Reserve space for the larger old buffer.
   old_virtual_memory_ =
       new base::VirtualMemory(kOldStoreBufferLength * kPointerSize);
   old_top_ = old_start_ =
       reinterpret_cast<Address*>(old_virtual_memory_->address());
   // Don't know the alignment requirements of the OS, but it is certainly not
   // less than 0xfff.
-  DCHECK((reinterpret_cast<uintptr_t>(old_start_) & 0xfff) == 0);
-  int initial_length =
-      static_cast<int>(base::OS::CommitPageSize() / kPointerSize);
-  DCHECK(initial_length > 0);
-  DCHECK(initial_length <= kOldStoreBufferLength);
+  CHECK((reinterpret_cast<uintptr_t>(old_start_) & 0xfff) == 0);
+  CHECK(kStoreBufferSize >= base::OS::CommitPageSize());
+  // Initial size of the old buffer is as big as the buffer for new pointers.
+  // This means even if we later fail to enlarge the old buffer due to OOM from
+  // the OS, we will still be able to empty the new pointer buffer into the old
+  // buffer.
+  int initial_length = static_cast<int>(kStoreBufferSize / kPointerSize);
+  CHECK(initial_length > 0);
+  CHECK(initial_length <= kOldStoreBufferLength);
   old_limit_ = old_start_ + initial_length;
   old_reserved_limit_ = old_start_ + kOldStoreBufferLength;
 
@@ -116,11 +124,12 @@ void StoreBuffer::EnsureSpace(intptr_t space_needed) {
   while (old_limit_ - old_top_ < space_needed &&
          old_limit_ < old_reserved_limit_) {
     size_t grow = old_limit_ - old_start_;  // Double size.
-    if (!old_virtual_memory_->Commit(reinterpret_cast<void*>(old_limit_),
-                                     grow * kPointerSize, false)) {
-      V8::FatalProcessOutOfMemory("StoreBuffer::EnsureSpace");
+    if (old_virtual_memory_->Commit(reinterpret_cast<void*>(old_limit_),
+                                    grow * kPointerSize, false)) {
+      old_limit_ += grow;
+    } else {
+      break;
     }
-    old_limit_ += grow;
   }
 
   if (SpaceAvailable(space_needed)) return;