Track large array buffer allocations.

src/objects.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <memory>
 #include <sstream>
@@ skipping 19445 matching lines @@
   // are currently being constructed in the |ArrayBufferTracker|. The
   // registration method below handles the case of registering a buffer that has
   // already been promoted.
   array_buffer->set_backing_store(data);
 
   if (data && !is_external) {
     isolate->heap()->RegisterNewArrayBuffer(*array_buffer);
   }
 }
 
+namespace {
+
+template <class T>
+int log2Value(T value) {

[bbudge, 2017/03/31 19:01:18]

Rather than roll your own, you could use the functions in v8/src/base/bits.h
(count leading zeroes to get the log)

https://cs.chromium.org/chromium/src/v8/src/base/bits.h?rcl=21a7487c06f10629d...

[kschimpf, 2017/03/31 19:31:52]

Thanks for the pointer. I agree that I shouldn't roll my own. However, I was
unable to find an integer-based log2, and I didn't think of counting leading
zeros. Changing.

Question: Should I do this same simplification to bad allocation sizes (in CL
https://codereview.chromium.org/2786913004 )?

+  int count = 0;
+  T base = 0;
+  while (value > base) {
+    ++count;
+    value >>= 1;
+  }
+  return count;
+}
+
+}  // namespace
 
 bool JSArrayBuffer::SetupAllocatingData(Handle<JSArrayBuffer> array_buffer,
                                         Isolate* isolate,
                                         size_t allocated_length,
                                         bool initialize, SharedFlag shared) {
   void* data;
   CHECK(isolate->array_buffer_allocator() != NULL);
   // Prevent creating array buffers when serializing.
   DCHECK(!isolate->serializer_enabled());
   if (allocated_length != 0) {
+    constexpr size_t MinBigAllocation = 1 << 20;

[bbudge, 2017/03/31 19:01:18]

nit: convention is to prefix 'k' to constants

[kschimpf, 2017/03/31 19:31:52]

Good point. I suffer from spending too many years in LLVM conventions! Fixing.

+    if (allocated_length >= MinBigAllocation)
+      isolate->counters()->big_array_buffer_allocations()->AddSample(
+          log2Value(allocated_length));
     if (initialize) {
       data = isolate->array_buffer_allocator()->Allocate(allocated_length);
     } else {
       data = isolate->array_buffer_allocator()->AllocateUninitialized(
           allocated_length);
     }
     if (data == NULL) return false;
   } else {
     data = NULL;
   }
@@ skipping 923 matching lines @@
       // depend on this.
       return DICTIONARY_ELEMENTS;
     }
     DCHECK_LE(kind, LAST_ELEMENTS_KIND);
     return kind;
   }
 }
 
 }  // namespace internal
 }  // namespace v8