diff --git a/src/emqx_misc.erl b/src/emqx_misc.erl
index 75db4227f..eb6a25377 100644
--- a/src/emqx_misc.erl
+++ b/src/emqx_misc.erl
@@ -224,15 +224,18 @@ tune_heap_size(#{max_heap_size := MaxHeapSize}) ->
                                         });
 tune_heap_size(undefined) -> ok.
 
-%% We multiply the size with factor ?OOM_FACTOR, to give the
-%% process a chance to suicide by `check_oom/1`
 must_kill_heap_size(Size) ->
+    %% We set the max allowed heap size by `erlang:process_flag(max_heap_size, #{size => Size})`,
+    %% where the `Size` cannot be set to an integer lager than `(1 bsl 59) - 1` on a 64-bit system,
+    %% or `(1 bsl 27) - 1` on a 32-bit system.
     MaxAllowedSize = case erlang:system_info(wordsize) of
         8 -> % arch_64
             (1 bsl 59) - 1;
         4 -> % arch_32
             (1 bsl 27) - 1
     end,
+    %% We multiply the size with factor ?OOM_FACTOR, to give the
+    %% process a chance to suicide by `check_oom/1`
     case ceil(Size * ?OOM_FACTOR) of
         Size0 when Size0 >= MaxAllowedSize -> MaxAllowedSize;
         Size0 -> Size0