Memory management under OCAML

Memory management under OCAML

[David McClain]

I am trying to understand the behavior of the interactive OCAML system. If I
repeatedly perform the following line:

    let x = Array.create 1000000 0.0;;

then each subsequent execution should shadow the previous ones making them
unreachable. Yet the GC never collects the old bindings, even after I
manually perform Gc.full_major() or Gc.compact().  Why is this?

In another vein, whenever I start OCAML in interactive mode on WinNT 4.0 it
grabs about 10 MBytes (give or take some). Yet when I compile my own code in
native code OCAMLOPT, my programs typically grab about 100 MBytes or so,
even before any overt memory allocations occur. Why is this? Should I even
be concerned about it? and is there a mechanism to preallocate a fixed
amount of heap for the runtime images I create?

D. McClain
Sr. Scientist
Raytheon Systems Co.
Tucson, AZ

Re: Memory management under OCAML

[Ching-Tsun Chou]

   I am trying to understand the behavior of the interactive OCAML system. If I
   repeatedly perform the following line:

       let x = Array.create 1000000 0.0;;

   then each subsequent execution should shadow the previous ones making them
   unreachable. Yet the GC never collects the old bindings, even after I
   manually perform Gc.full_major() or Gc.compact().  Why is this?

Some time ago I observed the same thing and asked the same question.
To see the answer, go to the archive of Caml mailing list and search
for the thread "What exactly can be GC'ed?"

- Ching Tsun

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