[erlang-questions] High memory consumption inside docker

[Lukas Larsson]

Hello,

You want to start the emulator with the "+Mim true +Mis true" flags and
then use instrument (http://erlang.org/doc/man/instrument.html) to inspect
what is going on. The most interesting for you should be something like:

lists:reverse(lists:keysort(2,instrument:memory_status(types))).

For example:

erl +Mis true +Mim true
Erlang/OTP 19 [DEVELOPMENT] [erts-8.0] [source-9946a17] [64-bit]
[smp:16:16] [async-threads:10] [hipe] [kernel-poll:false]
1> lists:reverse(lists:keysort(2,instrument:memory_status(types))).
[{timer_wheel,[{sizes,8391792,8391792,8391792},
               {blocks,16,16,16}]},
 {code,[{sizes,3463220,3463220,3469945},{blocks,84,84,84}]},
 {proc_tab,[{sizes,3145791,3145791,3145791},{blocks,1,1,1}]},
 {heap,[{sizes,1882920,1932208,3456120},{blocks,26,28,28}]},
 {pre_alloc_data,[{sizes,1032303,1032303,1032303},
                  {blocks,17,17,17}]},
 {port_tab,[{sizes,786495,786495,786495},{blocks,1,1,1}]},
 {old_heap,[{sizes,679872,682880,2941656},{blocks,10,11,11}]},
 {scheduler_data,[{sizes,673141,673141,673141},
                  {blocks,3,3,3}]},
 {export_entry,[{sizes,462528,462528,462528},
                {blocks,2628,2628,2628}]},
 {literal,[{sizes,379648,379648,379648},{blocks,84,84,84}]},
 {ethread_long_lived,[{sizes,326016,326016,326016},
                      {blocks,283,283,283}]},
 {atom_entry,[{sizes,304840,304840,304840},
              {blocks,7621,7621,7621}]},
 {beam_register,[{sizes,264544,264544,264544},
                 {blocks,32,32,32}]},
 {export_tab,[{sizes,162888,162888,162888},
              {blocks,15,15,15}]},
 {hipe_data,[{sizes,148464,148464,148464},{blocks,18,18,18}]},
 {ethread_standard,[{sizes,133487,133487,133487},
                    {blocks,6,6,6}]},
 {db_term,[{sizes,119568,119568,119568},
           {blocks,388,388,388}]},
 {atom_tab,[{sizes,112232,112232,121472},{blocks,10,10,10}]},
 {atom_text,[{sizes,98328,98328,98328},{blocks,3,3,3}]},
 {db_tabs,[{sizes,82023,82023,82023},{blocks,3,3,3}]},
 {drv_internal,[{sizes,79352,79352,79608},{blocks,4,4,19}]},
 {db_segment,[{sizes,51744,51744,53824},{blocks,19,19,...}]},
 {fun_entry,[{sizes,51568,51568,...},{blocks,586,...}]},
 {drv_binary,[{sizes,47774,...},{blocks,...}]},
 {driver_event_state,[{sizes,...},{...}]},
 {module_tab,[{...}|...]},
 {module_entry,[...]},
 {proc,...},
 {...}|...]

So in the above we can see that the timer wheel structures take the most
memory and then code, proc tab etc etc.

Lukas

On Tue, Mar 29, 2016 at 2:01 PM, Michał Muskała <michal@REDACTED> wrote:

> Hello everybody,
>
> This is a followup from the elixir mailing list:
>
> https://groups.google.com/forum/#!msg/elixir-lang-talk/TqIcSVkHBxs/N1nWRWW9BwAJ
> There were several issues involved in that particular problem, but one
> of them might be of interest to the people here as well, as it's
> generally erlang-related rather than tied to elixir or any package in
> particular.
>
> The issue comes down to unusually high memory consumption for erlang,
> specifically the system part from erlang:memory/0. The output below
> shows values when running outside docker and inside:
>
> Outside docker:
> erl -eval 'io:format("~w~n", [erlang:memory()]), init:stop().' -noshell
>
> [{total,15182640},{processes,3799768},{processes_used,3797720},{system,11382872},{atom,194289},{atom_used,169621},{binary,78344},{code,3868184},{ets,229416}]
>
> Inside docker's official erlang image (debian based)
> docker run --rm -it erlang:18-slim erl -eval 'io:format("~w~n",
> [erlang:memory()]), init:stop().' -noshell
>
> [{total,111303160},{processes,3799768},{processes_used,3797720},{system,107503392},{atom,194289},{atom_used,169584},{binary,595608},{code,3860673},{ets,239464}]
>
> Inside minimal alpine linux erlang image
> docker run --rm -it msaraiva/erlang erl -eval 'io:format("~w~n",
> [erlang:memory()]), init:stop().' -noshell
>
> [{total,111432888},{processes,3748312},{processes_used,3746312},{system,107684576},{atom,194289},{atom_used,169869},{binary,596568},{code,3847723},{ets,185296}]
>
> As you can see all the values except for system are very similar, with
> system being almost 10x as large. The issue is also consistent across
> different images. While outside docker a simple shell uses around
> 15MB, inside docker it grows to 80MB.
> I tried to investigate the issue further using recon, and it looks
> like the excessive memory is allocated with ll_alloc, although I have
> to admit I'm out of my depth here.
>
> I'll be thankful for any help or indications where I could dig deeper.
>
> Michał.
> _______________________________________________
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>
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