Logs memory usage by specific parts of erlang VM at a time

Log format:

```
14:03:28.892 [info] EPP proxy memory usage total: 31.04 MB, processes:
8.60 MB, processes_used: 8.59 MB, system: 22.43 MB, atom: 492.61 KB,
atom_used: 468.70 KB, binary: 893.20 KB, code: 8.16 MB, ets: 1.18 MB.
```

apps/epp_proxy/src/epp_proxy_sup.erl

@@ -57,10 +57,14 @@ init([]) ->
     PoolSupervisor = #{id => epp_pool_supervisor,
 		       type => supervisor, modules => [epp_pool_supervisor],
 		       start => {epp_pool_supervisor, start_link, []}},
+    MemoryMonitor = #{id => memory_monitor, type => worker,
+		      modules => [memory_monitor],
+		      start => {memory_monitor, start_link, []}},
+    SharedSpecs = [TLSAcceptor, PoolSupervisor,
+		   MemoryMonitor],
     ChildrenSpec = case ?DevMode of
-		     {ok, true} ->
-			 [TCPAcceptor, TLSAcceptor, PoolSupervisor];
-		     _ -> [TLSAcceptor, PoolSupervisor]
+		     {ok, true} -> [TCPAcceptor | SharedSpecs];
+		     _ -> SharedSpecs
 		   end,
     {ok, {SupFlags, ChildrenSpec}}.
 

apps/epp_proxy/src/memory_monitor.erl

@@ -0,0 +1,95 @@
+%%%-------------------------------------------------------------------
+%%% @doc
+%%%
+%%% @end
+%%% Created: 20 Feb 2020
+%%%-------------------------------------------------------------------
+-module(memory_monitor).
+
+-behaviour(gen_server).
+
+-define(TEN_MINUTES_IN_MS, 10 * 30 * 1000).
+
+-define(THIRTY_MINUTES_IN_MS, 30 * 30 * 1000).
+
+-define(ONE_HOUR_IN_MS, 60 * 60 * 1000).
+
+-export([init/1, start_link/0]).
+
+-export([code_change/3, handle_call/3, handle_cast/2,
+	 handle_info/2, terminate/2]).
+
+-export([log_memory/0]).
+
+-record(state, {timer_ref  :: timer:tref()}).
+
+-type state() :: #state{}.
+
+-spec start_link() -> ignore | {error, _} | {ok, pid()}.
+
+start_link() ->
+    gen_server:start_link({local, ?MODULE}, ?MODULE, [],
+			  []).
+
+-spec init([]) -> {ok, state()}.
+
+init([]) ->
+    {ok, TimerReference} =
+	timer:send_interval(?THIRTY_MINUTES_IN_MS, log_usage),
+    erlang:send(self(), log_usage),
+    {ok, #state{timer_ref = TimerReference}}.
+
+%%%-------------------------------------------------------------------
+%%% GenServer callbacks
+%%%-------------------------------------------------------------------
+-spec handle_call(_, _, State) -> {stop,
+				   not_implemented, State}.
+
+handle_call(_M, _F, State) ->
+    {stop, not_implemented, State}.
+
+-spec handle_cast(_, State) -> {stop, not_implemented,
+				State}.
+
+handle_cast(_M, State) ->
+    {stop, not_implemented, State}.
+
+-spec handle_info(log_usage, _) -> {noreply, _}.
+
+handle_info(log_usage, State) ->
+    ok = log_memory(), {noreply, State}.
+
+-spec terminate(_, state()) -> ok.
+
+terminate(_Reason, State) ->
+    {ok, cancel} = timer:cancel(State#state.timer_ref), ok.
+
+-spec code_change(_, _, _) -> {ok, _}.
+
+code_change(_OldVersion, State, _Extra) -> {ok, State}.
+
+%%%-------------------------------------------------------------------
+%%% Internal functions
+%%%-------------------------------------------------------------------
+log_memory() ->
+    Mem = erlang:memory(),
+    Values = lists:map(fun ({Name, Value}) ->
+			       List = io_lib:format("~s: ~s",
+						    [Name,
+						     human_filesize(Value)]),
+			       binary:list_to_bin(List)
+		       end,
+		       Mem),
+    Values,
+    lager:info("EPP proxy memory usage ~s.",
+	       [lists:join(", ", Values)]).
+
+human_filesize(Size) ->
+    human_filesize(Size,
+		   ["B", "KB", "MB", "GB", "TB", "PB"]).
+
+human_filesize(S, [_ | [_ | _] = L]) when S >= 1024 ->
+    human_filesize(S / 1024, L);
+human_filesize(S, [M | _]) ->
+    List = io_lib:format("~.2f ~s", [float(S), M]),
+    binary:list_to_bin(List).