Why is 'malloced_memory' lower than 'used_heap

In every example of v8.getHeapStatistics() the malloced_memory seems to be lower than used_heap_size:

{
  total_heap_size: 7326976,
  total_heap_size_executable: 4194304,
  total_physical_size: 7326976,
  total_available_size: 1152656,
  used_heap_size: 3476208,
  heap_size_limit: 1535115264,
  malloced_memory: 16384,
  peak_malloced_memory: 1127496,
  does_zap_garbage: 0,
  number_of_native_contexts: 1,
  number_of_detached_contexts: 0
}

How can malloced_memory be lower than used_heap_size? Isn't used_heap_size a subset of malloced_memory?

My assumptions (obviously incorrect, unless malloced_memory is in KB and used_heap_size is in B):

malloced_memory: total memory acquired from the OS (needed to create the V8 heap, store Buffers, etc.).
used_heap_size: the total size of all objects on the V8 heap (including uncollected garbage).

CodePudding user response：

(V8 developer here.)

Memory for the managed heap is mmaped, not malloced, so it's not expected to be a subset.