Profiling the Dune node

Memory profiling the OCaml heap

  • Install an OCaml switch with the statmemprof patch:

    4.04.2+statistical-memprof or 4.06.0+statistical-memprof

  • Install statmemprof-emacs.

  • Enable loading statmemprof into the node.

    Add the statmemprof-emacs package as a dependency to the main package, and add let () = Statmemprof_emacs.start 1E-4 30 5 to the file.


    • sampling_rate is the sampling rate of the profiler. Good value: 1e-4.
    • callstack_size is the size of the fragment of the call stack which is captured for each sampled allocation.
    • min_sample_print is the minimum number of samples under which the location of an allocation is not displayed.
  • Load sturgeon into emacs, by adding this to your .emacs:

(let ((opam-share (ignore-errors (car (process-lines "opam" "config" "var" "share")))))
 (when (and opam-share (file-directory-p opam-share))
  (add-to-list 'load-path (expand-file-name "emacs/site-lisp" opam-share))))

(require 'sturgeon)
  • Launch the node then connect to it with sturgeon.

    If the process is launched with pid 1234 then

  M-x sturgeon-connect

(tab-completion works for finding the socket name)

Memory profiling the C heap

  • Install valgrind and massif-visualizer
valgrind --tool=massif dune-node run ...
  • Stop with Ctrl-C then display with

Performance profiling

  • Install perf (the linux-perf package for debian).

    If the package does not exist for your current kernel, a previous version can be used. Substitute the perf command to perf_4.9 if your kernel is 4.9).

  • Run the node, find the pid.

  • Attach perf with perf record -p pid --call-stack dwarf.

    Then stop capturing with Ctrl-C. This can represent a lot of data. Don’t do that for too long. If this is too much you can remove the --call-stack dwarf to get something more manageable, but interpreting the information can be harder.

  • display the result with perf report