Eliminate ?MEMORY_LIMIT_SCALING and make the ratio at which we page configurable. Note that I have changed the representation from a ratio-of-a-ratio to just a plain ratio (i.e. propertion of total memory, not proportion of the high watermark). I believe this will be easier to understand. Hence also the name vm_memory_paging_watermark, chosen by analogy with vm_memory_high_watermark.

2 files changed, 5 insertions, 17 deletions

diff --git a/ebin/rabbit_app.in b/ebin/rabbit_app.in
index 339fa69eae..b28214aff0 100644
--- a/ebin/rabbit_app.in
+++ b/ebin/rabbit_app.in
@@ -19,6 +19,7 @@
          {ssl_listeners, []},
          {ssl_options, []},
          {vm_memory_high_watermark, 0.4},
+         {vm_memory_paging_watermark, 0.2},
          {disk_free_limit, 1000000000}, %% 1GB
          {msg_store_index_module, rabbit_msg_store_ets_index},
          {backing_queue_module, rabbit_variable_queue},
diff --git a/src/rabbit_memory_monitor.erl b/src/rabbit_memory_monitor.erl
index 117ff95a97..a2df255cae 100644
--- a/src/rabbit_memory_monitor.erl
+++ b/src/rabbit_memory_monitor.erl
@@ -43,17 +43,6 @@
 -define(DEFAULT_UPDATE_INTERVAL, 2500).
 -define(TABLE_NAME, ?MODULE).
 
-%% Because we have a feedback loop here, we need to ensure that we
-%% have some space for when the queues don't quite respond as fast as
-%% we would like, or when there is buffering going on in other parts
-%% of the system. In short, we aim to stay some distance away from
-%% when the memory alarms will go off, which cause backpressure (of
-%% some sort) on producers. Note that all other Thresholds are
-%% relative to this scaling.
--define(MEMORY_LIMIT_SCALING, 0.4).
-
--define(LIMIT_THRESHOLD, 0.5). %% don't limit queues when mem use is < this
-
 %% 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
@@ -207,15 +196,13 @@ internal_update(State = #state { queue_durations = Durations,
                                  desired_duration = DesiredDurationAvg,
                                  queue_duration_sum = Sum,
                                  queue_duration_count = Count }) ->
-    MemoryLimit = ?MEMORY_LIMIT_SCALING * vm_memory_monitor:get_memory_limit(),
-    MemoryRatio = case MemoryLimit > 0.0 of
-                      true  -> erlang:memory(total) / MemoryLimit;
-                      false -> infinity
-                  end,
+    {ok, LimitThreshold} =
+        application:get_env(rabbit, vm_memory_paging_watermark),
+    MemoryRatio = erlang:memory(total) / vm_memory_monitor:get_total_memory(),
     DesiredDurationAvg1 =
         if MemoryRatio =:= infinity ->
                 0.0;
-           MemoryRatio < ?LIMIT_THRESHOLD orelse Count == 0 ->
+           MemoryRatio < LimitThreshold orelse Count == 0 ->
                 infinity;
            MemoryRatio < ?SUM_INC_THRESHOLD ->
                 ((Sum + ?SUM_INC_AMOUNT) / Count) / MemoryRatio;