changed default buffer limit parameters:

Fluentd core:
  buffer_chunk_limit 256MB -> 8MB
  buffer_queue_limit 128 -> 256

buf_memory:
  buffer_chunk_limit 32MB -> 8MB
  buffer_queue_limit 32 -> 64

out_file:
  buffer_chunk_limit -> 256MB

lib/fluent/buffer.rb

@@ -127,8 +127,11 @@ def enable_parallel(b=true)
     @parallel_pop = b
   end
 
-  config_param :buffer_chunk_limit, :size, :default => 256*1024*1024
-  config_param :buffer_queue_limit, :integer, :default => 128
+  # This configuration assumes plugins to send records to a remote server.
+  # Local file based plugins which should provide more reliability and efficiency
+  # should override buffer_chunk_limit with a larger size.
+  config_param :buffer_chunk_limit, :size, :default => 8*1024*1024
+  config_param :buffer_queue_limit, :integer, :default => 256
 
   alias chunk_limit buffer_chunk_limit
   alias chunk_limit= buffer_chunk_limit=

lib/fluent/plugin/buf_memory.rb

@@ -68,9 +68,9 @@ def initialize
     super
   end
 
-  # overwrite default buffer_chunk_limit and buffer_queue_limit
-  config_set_default :buffer_chunk_limit, 32*1024*1024
-  config_set_default :buffer_queue_limit, 32
+  # Overwrite default BasicBuffer#buffer_queue_limit
+  # to limit total memory usage upto 512MB.
+  config_set_default :buffer_queue_limit, 64
 
   def configure(conf)
     super

lib/fluent/plugin/out_file.rb

@@ -62,6 +62,9 @@ def configure(conf)
       conf['buffer_path'] ||= "#{@path}.*"
     end
 
+    # override default buffer_chunk_limit
+    conf['buffer_chunk_limit'] ||= '256m'
+
     super
 
     @timef = TimeFormatter.new(@time_format, @localtime)