[erlang-questions] Erlang proccess memory usage

[Wenqiang Song]

Hi,

I'm experimenting with Erlang process and found something that not
expected.

What I do is creating 1M Erlang processes and measure memory usage. Code is
as follow:
-module(generator).
-export([start/0, generator/2, loop/0]).

start() ->
    Pid = self(),
    spawn( fun()->generator(19,Pid) end ),
    count (1).

count (Num) ->
    receive
add ->
%    io:format("Oopss, ~n"),
    if
0 =:= ( Num rem 10000 ) -> io:format("Count ~p~n", [Num]);
 true -> Q = 3
    end,
    count (Num + 1);
 _ ->
    io:format("haha, ~n")
    after 30000 ->
    io:format("Count ~p~n", [Num]),
    count (Num)
    end.
loop() ->
    receive
_ ->
    io:format("Oops ~n"),
%    proc_lib:hibernate(?MODULE, loop(), [])
    loop()
    end.
generator( 0, Pid ) ->
    Pid ! add,
%    proc_lib:hibernate(?MODULE, loop(), []);
    loop();
generator( Depth, Pid ) ->
    spawn( fun()->generator(Depth - 1, Pid) end),
    spawn( fun()->generator(Depth - 1, Pid) end),
    Pid ! add,
%    io:format("Depth: ~p, pid: ~p~n", [Depth, Pid]),
%    proc_lib:hibernate(?MODULE, loop(), []).
    loop().
===============End of Code=============
2> i(0,58,0).
[{current_function,{generator,loop,0}},
 {initial_call,{erlang,apply,2}},
 {status,waiting},
 {message_queue_len,0},
 {messages,[]},
 {links,[]},
 {dictionary,[]},
 {trap_exit,false},
 {error_handler,error_handler},
 {priority,normal},
 {group_leader,<0.25.0>},
 {total_heap_size,233},
 {heap_size,233},
 {stack_size,1},
 {reductions,9},
 {garbage_collection,[{min_bin_vheap_size,46368},
                      {min_heap_size,233},
                      {fullsweep_after,65535},
                      {minor_gcs,0}]},
 {suspending,[]}]

3> memory().
[{total,2759895784},
 {processes,2751081712},
 {processes_used,2751067504},
 {system,8814072},
 {atom,615121},
 {atom_used,589205},
 {binary,8608},
 {code,5845747},
 {ets,270928}]

Total memory usage is about 2.7G. While when I use i() and i(pid) I saw that
each process only uses about 233 bytes. I can't find where the memory is
used. Any idea?

Thanks
Andy
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