Move rabbit_memory_monitor:memory_use/1 to vm_memory_monitor

The function is renamed to get_memory_use/1 in the process, to match
other functions in the vm_memory_monitor module.

The file_handle_cache uses that function. By moving it to
vm_memory_monitor, we remove a dependency of file_handle_cache on a
rabbit_* module. This will allow us to move both file_handle_cache and
vm_memory_monitor to rabbitmq-common and help remove a dependency in the
Erlang client on the broker because the former calls
file_handle_cache:obtain/0.

To sum up the situation before this commit with a graph:

  amqp_network_connection --[depends on]--> file_handle_cache
            (amqp_client)                   (rabbit)

        file_handle_cache --[depends on]--> rabbit_memory_monitor
                 (rabbit)                   (rabbit)

And the situation we want to reach after the move:

  amqp_network_connection --[depends on]--> file_handle_cache
            (amqp_client)                   (rabbit_common)

        file_handle_cache --[depends on]--> vm_memory_monitor
          (rabbit_common)                   (rabbit_common)

    rabbit_memory_monitor --[depends on]--> vm_memory_monitor
                 (rabbit)                   (rabbit_common)

[#118490793]

Author: dumbbell

src/file_handle_cache.erl

@@ -1040,7 +1040,7 @@ tune_read_buffer_limit(Handle = #handle{read_buffer            = Buf,
                                                  end, Lim)}.
 
 maybe_reduce_read_cache(SparedRefs) ->
-    case rabbit_memory_monitor:memory_use(bytes) of
+    case vm_memory_monitor:get_memory_use(bytes) of
         {_, infinity}                             -> ok;
         {MemUse, MemLimit} when MemUse < MemLimit -> ok;
         {MemUse, MemLimit}                        -> reduce_read_cache(

src/rabbit_memory_monitor.erl

@@ -89,18 +89,8 @@ conserve_resources(Pid, disk, {_, Conserve, Node}) when node(Pid) =:= Node ->
 conserve_resources(_Pid, _Source, _Conserve) ->
     ok.
 
-memory_use(bytes) ->
-    MemoryLimit = vm_memory_monitor:get_memory_limit(),
-    {erlang:memory(total), case MemoryLimit > 0.0 of
-                               true  -> MemoryLimit;
-                               false -> infinity
-                           end};
-memory_use(ratio) ->
-    MemoryLimit = vm_memory_monitor:get_memory_limit(),
-    case MemoryLimit > 0.0 of
-        true  -> erlang:memory(total) / MemoryLimit;
-        false -> infinity
-    end.
+memory_use(Type) ->
+    vm_memory_monitor:get_memory_use(Type).
 
 %%----------------------------------------------------------------------------
 %% Gen_server callbacks

src/vm_memory_monitor.erl

@@ -35,7 +35,7 @@
 -export([get_total_memory/0, get_vm_limit/0,
          get_check_interval/0, set_check_interval/1,
          get_vm_memory_high_watermark/0, set_vm_memory_high_watermark/1,
-         get_memory_limit/0]).
+         get_memory_limit/0, get_memory_use/1]).
 
 %% for tests
 -export([parse_line_linux/1]).
@@ -73,6 +73,8 @@
 -spec get_vm_memory_high_watermark() -> vm_memory_high_watermark().
 -spec set_vm_memory_high_watermark(vm_memory_high_watermark()) -> 'ok'.
 -spec get_memory_limit() -> non_neg_integer().
+-spec get_memory_use(bytes) -> {non_neg_integer(),  float() | infinity};
+                    (ratio) -> float() | infinity.
 
 %%----------------------------------------------------------------------------
 %% Public API
@@ -106,6 +108,19 @@ set_vm_memory_high_watermark(Fraction) ->
 get_memory_limit() ->
     gen_server:call(?MODULE, get_memory_limit, infinity).
 
+get_memory_use(bytes) ->
+    MemoryLimit = get_memory_limit(),
+    {erlang:memory(total), case MemoryLimit > 0.0 of
+                               true  -> MemoryLimit;
+                               false -> infinity
+                           end};
+get_memory_use(ratio) ->
+    MemoryLimit = get_memory_limit(),
+    case MemoryLimit > 0.0 of
+        true  -> erlang:memory(total) / MemoryLimit;
+        false -> infinity
+    end.
+
 %%----------------------------------------------------------------------------
 %% gen_server callbacks
 %%----------------------------------------------------------------------------