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%% This Source Code Form is subject to the terms of the Mozilla Public
%% License, v. 2.0. If a copy of the MPL was not distributed with this
%% file, You can obtain one at https://mozilla.org/MPL/2.0/.
%%
%% Copyright (c) 2007-2020 VMware, Inc. or its affiliates. All rights reserved.
%%
%% This module handles the node-wide memory statistics.
%% It receives statistics from all queues, counts the desired
%% queue length (in seconds), and sends this information back to
%% queues.
-module(rabbit_memory_monitor).
-behaviour(gen_server2).
-export([start_link/0, register/2, deregister/1,
report_ram_duration/2, stop/0, conserve_resources/3, memory_use/1]).
-export([init/1, handle_call/3, handle_cast/2, handle_info/2,
terminate/2, code_change/3]).
-record(process, {pid, reported, sent, callback, monitor}).
-record(state, {timer, %% 'internal_update' timer
queue_durations, %% ets #process
queue_duration_sum, %% sum of all queue_durations
queue_duration_count, %% number of elements in sum
desired_duration, %% the desired queue duration
disk_alarm %% disable paging, disk alarm has fired
}).
-define(SERVER, ?MODULE).
-define(TABLE_NAME, ?MODULE).
%% If all queues are pushed to disk (duration 0), then the sum of
%% their reported lengths will be 0. If memory then becomes available,
%% unless we manually intervene, the sum will remain 0, and the queues
%% will never get a non-zero duration. Thus when the mem use is <
%% SUM_INC_THRESHOLD, increase the sum artificially by SUM_INC_AMOUNT.
-define(SUM_INC_THRESHOLD, 0.95).
-define(SUM_INC_AMOUNT, 1.0).
-define(EPSILON, 0.000001). %% less than this and we clamp to 0
%%----------------------------------------------------------------------------
%% Public API
%%----------------------------------------------------------------------------
-spec start_link() -> rabbit_types:ok_pid_or_error().
start_link() ->
gen_server2:start_link({local, ?SERVER}, ?MODULE, [], []).
-spec register(pid(), {atom(),atom(),[any()]}) -> 'ok'.
register(Pid, MFA = {_M, _F, _A}) ->
gen_server2:call(?SERVER, {register, Pid, MFA}, infinity).
-spec deregister(pid()) -> 'ok'.
deregister(Pid) ->
gen_server2:cast(?SERVER, {deregister, Pid}).
-spec report_ram_duration
(pid(), float() | 'infinity') -> number() | 'infinity'.
report_ram_duration(Pid, QueueDuration) ->
gen_server2:call(?SERVER,
{report_ram_duration, Pid, QueueDuration}, infinity).
-spec stop() -> 'ok'.
stop() ->
gen_server2:cast(?SERVER, stop).
%% Paging should be enabled/disabled only in response to disk resource alarms
%% for the current node.
conserve_resources(Pid, disk, {_, Conserve, Node}) when node(Pid) =:= Node ->
gen_server2:cast(Pid, {disk_alarm, Conserve});
conserve_resources(_Pid, _Source, _Conserve) ->
ok.
memory_use(Type) ->
vm_memory_monitor:get_memory_use(Type).
%%----------------------------------------------------------------------------
%% Gen_server callbacks
%%----------------------------------------------------------------------------
init([]) ->
{ok, Interval} = application:get_env(rabbit, memory_monitor_interval),
{ok, TRef} = timer:send_interval(Interval, update),
Ets = ets:new(?TABLE_NAME, [set, private, {keypos, #process.pid}]),
Alarms = rabbit_alarm:register(self(), {?MODULE, conserve_resources, []}),
{ok, internal_update(
#state { timer = TRef,
queue_durations = Ets,
queue_duration_sum = 0.0,
queue_duration_count = 0,
desired_duration = infinity,
disk_alarm = lists:member(disk, Alarms)})}.
handle_call({report_ram_duration, Pid, QueueDuration}, From,
State = #state { queue_duration_sum = Sum,
queue_duration_count = Count,
queue_durations = Durations,
desired_duration = SendDuration }) ->
[Proc = #process { reported = PrevQueueDuration }] =
ets:lookup(Durations, Pid),
gen_server2:reply(From, SendDuration),
{Sum1, Count1} =
case {PrevQueueDuration, QueueDuration} of
{infinity, infinity} -> {Sum, Count};
{infinity, _} -> {Sum + QueueDuration, Count + 1};
{_, infinity} -> {Sum - PrevQueueDuration, Count - 1};
{_, _} -> {Sum - PrevQueueDuration + QueueDuration,
Count}
end,
true = ets:insert(Durations, Proc #process { reported = QueueDuration,
sent = SendDuration }),
{noreply, State #state { queue_duration_sum = zero_clamp(Sum1),
queue_duration_count = Count1 }};
handle_call({register, Pid, MFA}, _From,
State = #state { queue_durations = Durations }) ->
MRef = erlang:monitor(process, Pid),
true = ets:insert(Durations, #process { pid = Pid, reported = infinity,
sent = infinity, callback = MFA,
monitor = MRef }),
{reply, ok, State};
handle_call(_Request, _From, State) ->
{noreply, State}.
handle_cast({disk_alarm, Alarm}, State = #state{disk_alarm = Alarm}) ->
{noreply, State};
handle_cast({disk_alarm, Alarm}, State) ->
{noreply, internal_update(State#state{disk_alarm = Alarm})};
handle_cast({deregister, Pid}, State) ->
{noreply, internal_deregister(Pid, true, State)};
handle_cast(stop, State) ->
{stop, normal, State};
handle_cast(_Request, State) ->
{noreply, State}.
handle_info(update, State) ->
{noreply, internal_update(State)};
handle_info({'DOWN', _MRef, process, Pid, _Reason}, State) ->
{noreply, internal_deregister(Pid, false, State)};
handle_info(_Info, State) ->
{noreply, State}.
terminate(_Reason, #state { timer = TRef }) ->
timer:cancel(TRef),
ok.
code_change(_OldVsn, State, _Extra) ->
{ok, State}.
%%----------------------------------------------------------------------------
%% Internal functions
%%----------------------------------------------------------------------------
zero_clamp(Sum) when Sum < ?EPSILON -> 0.0;
zero_clamp(Sum) -> Sum.
internal_deregister(Pid, Demonitor,
State = #state { queue_duration_sum = Sum,
queue_duration_count = Count,
queue_durations = Durations }) ->
case ets:lookup(Durations, Pid) of
[] -> State;
[#process { reported = PrevQueueDuration, monitor = MRef }] ->
true = case Demonitor of
true -> erlang:demonitor(MRef);
false -> true
end,
{Sum1, Count1} =
case PrevQueueDuration of
infinity -> {Sum, Count};
_ -> {zero_clamp(Sum - PrevQueueDuration),
Count - 1}
end,
true = ets:delete(Durations, Pid),
State #state { queue_duration_sum = Sum1,
queue_duration_count = Count1 }
end.
internal_update(State = #state{queue_durations = Durations,
desired_duration = DesiredDurationAvg,
disk_alarm = DiskAlarm}) ->
DesiredDurationAvg1 = desired_duration_average(State),
ShouldInform = should_inform_predicate(DiskAlarm),
case ShouldInform(DesiredDurationAvg, DesiredDurationAvg1) of
true -> inform_queues(ShouldInform, DesiredDurationAvg1, Durations);
false -> ok
end,
State#state{desired_duration = DesiredDurationAvg1}.
desired_duration_average(#state{disk_alarm = true}) ->
infinity;
desired_duration_average(#state{disk_alarm = false,
queue_duration_sum = Sum,
queue_duration_count = Count}) ->
{ok, LimitThreshold} =
application:get_env(rabbit, vm_memory_high_watermark_paging_ratio),
MemoryRatio = memory_use(ratio),
if MemoryRatio =:= infinity ->
0.0;
MemoryRatio < LimitThreshold orelse Count == 0 ->
infinity;
MemoryRatio < ?SUM_INC_THRESHOLD ->
((Sum + ?SUM_INC_AMOUNT) / Count) / MemoryRatio;
true ->
(Sum / Count) / MemoryRatio
end.
inform_queues(ShouldInform, DesiredDurationAvg, Durations) ->
true =
ets:foldl(
fun (Proc = #process{reported = QueueDuration,
sent = PrevSendDuration,
callback = {M, F, A}}, true) ->
case ShouldInform(PrevSendDuration, DesiredDurationAvg)
andalso ShouldInform(QueueDuration, DesiredDurationAvg) of
true -> ok = erlang:apply(
M, F, A ++ [DesiredDurationAvg]),
ets:insert(
Durations,
Proc#process{sent = DesiredDurationAvg});
false -> true
end
end, true, Durations).
%% In normal use, we only inform queues immediately if the desired
%% duration has decreased, we want to ensure timely paging.
should_inform_predicate(false) -> fun greater_than/2;
%% When the disk alarm has gone off though, we want to inform queues
%% immediately if the desired duration has *increased* - we want to
%% ensure timely stopping paging.
should_inform_predicate(true) -> fun (D1, D2) -> greater_than(D2, D1) end.
greater_than(infinity, infinity) -> false;
greater_than(infinity, _D2) -> true;
greater_than(_D1, infinity) -> false;
greater_than(D1, D2) -> D1 > D2.
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