rabbit_disk_monitor: Add config to tune polling interval

The polling interval (min, max and fast-rate) should be tuned
for use on different hardware. For example high-end machines with strong
network bandwidth should be tuning the fast-rate higher so that disk
space is checked more often, as with stronger resources the disk space
could fill up more rapidly than the default 250MB/sec predicts.

Author: the-mikedavis

deps/rabbit/priv/schema/rabbit.schema

@@ -1238,6 +1238,20 @@ fun(Conf) ->
     end
 end}.
 
+%% Tuning of disk monitor polling parameters
+{mapping, "disk_monitor.fast_rate", "rabbit.disk_monitor_fast_rate", [
+    %% Unit: KB/second, for example 250_000 for 250MB/sec.
+    {datatype, [integer]}
+]}.
+{mapping, "disk_monitor.min_interval", "rabbit.disk_monitor_min_interval", [
+    %% Unit: milliseconds.
+    {datatype, [integer]}
+]}.
+{mapping, "disk_monitor.max_interval", "rabbit.disk_monitor_max_interval", [
+    %% Unit: milliseconds.
+    {datatype, [integer]}
+]}.
+
 %% Per-queue-type / per-mount disk alarms
 {mapping, "disk_free_limits.$num.name", "rabbit.disk_free_limits", [
     {datatype, [binary]}

deps/rabbit/src/rabbit_disk_monitor.erl

@@ -36,8 +36,6 @@
 -define(DEFAULT_MIN_DISK_CHECK_INTERVAL, 100).
 -define(DEFAULT_MAX_DISK_CHECK_INTERVAL, 10000).
 -define(DEFAULT_DISK_FREE_LIMIT, 50000000).
-%% 250MB/s i.e. 250kB/ms
--define(FAST_RATE, (250 * 1000)).
 
 -record(mount,
         {%% name set in configuration
@@ -164,6 +162,10 @@ start_link(Args) ->
 init([Limit]) ->
     {ok, Retries} = application:get_env(rabbit, disk_monitor_failure_retries),
     {ok, Interval} = application:get_env(rabbit, disk_monitor_failure_retry_interval),
+    MinInterval = application:get_env(rabbit, disk_monitor_min_interval,
+                                      ?DEFAULT_MIN_DISK_CHECK_INTERVAL),
+    MaxInterval = application:get_env(rabbit, disk_monitor_max_interval,
+                                      ?DEFAULT_MAX_DISK_CHECK_INTERVAL),
     ?ETS_NAME = ets:new(?ETS_NAME, [protected, set, named_table]),
     ?MOUNT_ETS_NAME = ets:new(?MOUNT_ETS_NAME, [protected, set, named_table,
                                                 {keypos, #mount.name}]),
@@ -172,8 +174,8 @@ init([Limit]) ->
                     limit        = Limit,
                     retries      = Retries,
                     interval     = Interval},
-    State1 = set_min_check_interval(?DEFAULT_MIN_DISK_CHECK_INTERVAL, State0),
-    State2 = set_max_check_interval(?DEFAULT_MAX_DISK_CHECK_INTERVAL, State1),
+    State1 = set_min_check_interval(MinInterval, State0),
+    State2 = set_max_check_interval(MaxInterval, State1),
 
     State3 = enable(State2),
 
@@ -420,9 +422,13 @@ interval(#state{actual = DataDirAvailable,
                         (_Path, _Mount, Min) ->
                             Min
                     end, DataDirGap, Mounts),
-    IdealInterval = 2 * SmallestGap / ?FAST_RATE,
+    IdealInterval = 2 * SmallestGap / fast_rate(),
     trunc(erlang:max(MinInterval, erlang:min(MaxInterval, IdealInterval))).
 
+fast_rate() ->
+    %% 250MB/s i.e. 250kB/ms
+    application:get_env(rabbit, disk_monitor_fast_rate, 250_000).
+
 -spec mounts() -> mounts().
 mounts() ->
     case application:get_env(rabbit, disk_free_limits) of

deps/rabbit/test/config_schema_SUITE_data/rabbit.snippets

@@ -179,6 +179,15 @@ ssl_options.fail_if_no_peer_cert = true",
     "disk_free_limit.absolute = 2P",
     [{rabbit,[{disk_free_limit, "2P"}]}],
     []},
+  %% Disk monitor polling
+  {disk_monitor_tune_polling_parameters,
+    "disk_monitor.fast_rate = 1000000 # 1 GB/sec
+     disk_monitor.min_interval = 50
+     disk_monitor.max_interval = 20000",
+    [{rabbit,[{disk_monitor_fast_rate, 1_000_000},
+              {disk_monitor_min_interval, 50},
+              {disk_monitor_max_interval, 20_000}]}],
+    []},
 
  {default_users,
  "