[Caml-list] Out_of_memory exception in output_value

[Richard Jones <rich@annexia.org>]

I have a problem with a real program which tries to write an approx
200 MB data structure to disk using output_value.  The output_value
statement throws an Out_of_memory exception, even though the Unix
process itself is only using around 350 MB on a machine with plenty of
physical RAM and swap.

The test program below reproduces the problem.

Is there any way I can tell the memory allocator that it's allowed to
keep allocating memory, or work around this bug in another way?

Rich.

---
(* ocamlopt -w s unix.cmxa memtest.ml -o memtest *)

let arraylen = 200000
let stringlen = 1000

let () =
  prerr_endline "Creating big structure ...";
  let data = Array.init arraylen (fun i -> String.create stringlen) in
  prerr_endline "Sleeping for 5 seconds ...";
  Unix.sleep 5;
  prerr_endline "Saving big structure to a file ...";
  let chan = open_out_bin "/tmp/test.dat" in
  output_value chan data;
  close_out chan;
  ignore (Sys.command "ls -lh /tmp/test.dat")

---
$ ./memtest 
Creating big structure ...
Sleeping for 5 seconds ...
Saving big structure to a file ...
Fatal error: exception Out_of_memory

During the sleep:

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND           
 3098 rich      25   0  203m 198m 1640 S 43.4 42.0   0:03.21 memtest           

Just before the crash:

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND           
 3103 rich      18   0  333m 301m 1640 D  1.7 63.7   0:04.49 memtest           

-- 
Richard Jones. http://www.annexia.org/ http://www.j-london.com/
Merjis Ltd. http://www.merjis.com/ - improving website return on investment
http://www.winwinsales.co.uk/ - CRM improvement consultancy

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