Enabling profiling automatically disables any existing profiling to
  another or the same file.
Profiling writes the call stack to the specified file every time
  malloc is called to allocate a large vector object or to
  allocate a page of memory for small objects. The size of a page of
  memory and the size above which malloc is used for vectors are
  compile-time constants, by default 2000 and 128 bytes respectively.
The profiler tracks allocations, some of which will be to previously
  used memory and will not increase the total memory use of R.