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 19455 matching lines @@
 
 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 kMinBigAllocation = 1 << 20;
+    if (allocated_length >= kMinBigAllocation) {
+      isolate->counters()->array_buffer_big_allocations()->AddSample(
+          static_cast<int>(
+              sizeof(size_t) == 32
+                  ? (32 - base::bits::CountLeadingZeros32(allocated_length))
+                  : (64 - base::bits::CountLeadingZeros64(allocated_length))));

[bbudge, 2017/03/31 20:52:28]

You could also just do:

sizeof(uint64_t) * kBitsPerByte -
base::bits::CountLeadingZeros64(allocated_length) - 1

-1 if you wish to map 1 to 0, 2 to 1 etc. I'm not clear on how histograms work
for ranges.

[Mircea Trofin, 2017/03/31 21:01:38]

The pointer sizes are something that may be fishable out of globals.h and you
can use constants then.

[kschimpf, 2017/03/31 21:11:02]

The recommendation is NOT to use value 0 in UMA histograms since that value is
where all out of range data goes. Chrome documentation recommends starting with
1. That is why I did not subtract 1.

Simplifying as suggested otherwise.

[kschimpf, 2017/03/31 21:11:02]

size_t is the number of bytes. Using uint64_t, as Bill suggests, fixes the
issue.

+    }
     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