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erts_alloc_config(3)	   Erlang Module Definition	  erts_alloc_config(3)

       erts_alloc_config - Configuration tool for erts_alloc

       erts_alloc_config  is  currently	an experimental	tool and might be sub-
       ject to backward	incompatible changes.

       erts_alloc(3) is	an Erlang Run-Time System  internal  memory  allocator
       library.	erts_alloc_config is intended to be used to aid	creation of an
       erts_alloc(3) configuration that	is suitable for	a  limited  number  of
       runtime	scenarios. The configuration that erts_alloc_config produce is
       intended	as a suggestion, and may need to be adjusted manually.

       The configuration is created based on information  about	 a  number  of
       runtime	scenarios. It is obviously impossible to foresee every runtime
       scenario	that can occur.	The important scenarios	are those  that	 cause
       maximum	or  minimum  load  on specific memory allocators. Load in this
       context is total	size of	memory blocks allocated.

       The current implementation of erts_alloc_config concentrate on configu-
       ration  of  multi-block	carriers.  Information gathered	when a runtime
       scenario	is saved is mainly current and maximum use of multi-block car-
       riers.  If  a  parameter	that change the	use of multi-block carriers is
       changed,	a previously generated configuration is	invalid	 and  erts_al-
       loc_config needs	to be run again. It is mainly the single block carrier
       threshold that effects the use of multi-block carriers, but other  sin-
       gle-block  carrier parameters might as well. If another value of	a sin-
       gle block carrier parameter than	the default is desired,	 use  the  de-
       sired value when	running	erts_alloc_config.

       A configuration is created in the following way:

	 * Pass	the +Mea config	command-line flag to the Erlang	runtime	system
	   you are going to use	for creation of	the  allocator	configuration.
	   It  will disable features that prevent erts_alloc_config from doing
	   its job. Note, you should not use this flag when using the  created
	   configuration. Also note that it is important that you use the same
	   amount of schedulers	when creating the configuration	as you are go-
	   ing the use on the system using the configuration.

	 * Run	your  applications with	different scenarios (the more the bet-
	   ter)	and save information about each	scenario by calling  save_sce-
	   nario/0.  It	 may  be  hard to know when the	applications are at an
	   (for	erts_alloc_config) important runtime scenario. A good approach
	   may	therefore be to	call save_scenario/0 repeatedly, e.g. once ev-
	   ery tenth second. Note that it is important that your  applications
	   reach  the runtime scenarios	that are important for erts_alloc_con-
	   fig when you	are saving scenarios; otherwise, the configuration may
	   perform bad.

	 * When	you have covered all scenarios,	call make_config/1 in order to
	   create a configuration. The configuration is	written	to a file that
	   you	have  chosen.  This configuration file can later be read by an
	   Erlang runtime-system at startup. Pass the  command	line  argument
	   -args_file FileName to the erl(1) command.

	 * The configuration produced by erts_alloc_config may need to be man-
	   ually adjusted as already stated. Do	not modify the	file  produced
	   by  erts_alloc_config;  instead,  put your modifications in another
	   file	and load this file after the file produced by  erts_alloc_con-
	   fig.	 That is, put the -args_file FileName argument that reads your
	   modification	file later on the  command-line	 than  the  -args_file
	   FileName  argument  that  reads  the	configuration file produced by
	   erts_alloc_config. If a memory allocation parameter appear multiple
	   times, the last version of will be used, i.e., you can override pa-
	   rameters in the configuration file produced	by  erts_alloc_config.
	   Doing it this way simplifies	things when you	want to	rerun erts_al-

       The configuration created by erts_alloc_config may  perform  bad,  ever
       horrible,  for  runtime scenarios that are very different from the ones
       saved when creating the configuration. You are, therefore,  advised  to
       rerun  erts_alloc_config	if the applications run	when the configuration
       was made	are changed, or	if the load on the applications	 have  changed
       since  the  configuration  was  made.  You  are	also  advised to rerun
       erts_alloc_config if the	Erlang runtime system used is changed.

       erts_alloc_config saves information about runtime  scenarios  and  per-
       forms  computations  in	a  server  that	 is automatically started. The
       server register itself under the	name '__erts_alloc_config__'.

       save_scenario() -> ok | {error, Error}


		 Error = term()

	      save_scenario/0 saves information	about the current runtime sce-
	      nario.  This  information	will later be used when	make_config/0,
	      or make_config/1 is called.

	      The first	time  save_scenario/0  is  called  a  server  will  be
	      started. This server will	save runtime scenarios.	All saved sce-
	      narios can be removed by calling stop/0.

       make_config() ->	ok | {error, Error}


		 Error = term()

	      This is the same as calling make_config(group_leader()).

       make_config(FileNameOrIODev) -> ok | {error, Error}


		 FileNameOrIODev = string() | io_device()
		 Error = term()

	      make_config/1 uses the information previously saved by save_sce-
	      nario/0  in  order  to  produce  an erts_alloc configuration. At
	      least one	scenario have had to be	saved.	All  scenarios	previ-
	      ously saved will be used when creating the configuration.

	      If  FileNameOrIODev  is a	string(), make_config/1	will use File-
	      NameOrIODev as a filename. A file	named FileNameOrIODev is  cre-
	      ated  and	 the  configuration  will  be written to that file. If
	      FileNameOrIODev is an io_device()	(see the documentation of  the
	      module io), the configuration will be written to the io device.

       stop() -> ok | {error, Error}


		 Error = term()

	      Stops the	server that saves runtime scenarios.

       erts_alloc(3), erl(1), io(3)

Ericsson AB		     runtime_tools 1.13.2	  erts_alloc_config(3)


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