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<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE erlref SYSTEM "erlref.dtd">
<erlref>
<header>
<copyright>
<year>2007</year><year>2013</year>
<holder>Ericsson AB. All Rights Reserved.</holder>
</copyright>
<legalnotice>
The contents of this file are subject to the Erlang Public License,
Version 1.1, (the "License"); you may not use this file except in
compliance with the License. You should have received a copy of the
Erlang Public License along with this software. If not, it can be
retrieved online at http://www.erlang.org/.
Software distributed under the License is distributed on an "AS IS"
basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
the License for the specific language governing rights and limitations
under the License.
</legalnotice>
<title>erts_alloc_config</title>
<prepared>Rickard Green</prepared>
<docno>1</docno>
<date>07-05-30</date>
<rev>1</rev>
<file>erts_alloc_config.sgml</file>
</header>
<module>erts_alloc_config</module>
<modulesummary>Configuration tool for erts_alloc</modulesummary>
<description>
<note>
<p><c>erts_alloc_config</c> is currently an experimental
tool and might be subject to backward incompatible
changes.</p>
</note>
<p><seealso marker="erts:erts_alloc">erts_alloc(3)</seealso> is an
Erlang Run-Time System internal memory allocator library.
<c>erts_alloc_config</c> is intended to be used to aid creation
of an <seealso marker="erts:erts_alloc">erts_alloc(3)</seealso>
configuration that is suitable for a limited number of runtime
scenarios. The configuration that <c>erts_alloc_config</c>
produce is intended as a suggestion, and may need to be
adjusted manually.</p>
<p>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.</p>
<p>The current implementation of <c>erts_alloc_config</c> concentrate
on configuration of multi-block carriers. Information gathered
when a runtime scenario is saved is mainly current and maximum use
of multi-block carriers. If a parameter that change the use of
multi-block carriers is changed, a previously generated
configuration is invalid and <c>erts_alloc_config</c> needs
to be run again. It is mainly the single block carrier threshold
that effects the use of multi-block carriers, but other
single-block carrier parameters might as well. If another value of
a single block carrier parameter than the default is desired, use
the desired value when running <c>erts_alloc_config</c>.</p>
<p>A configuration is created in the following way:</p>
<list type="bulleted">
<item>
<p>Pass the <seealso marker="erts:erts_alloc#Mea">+Mea config</seealso>
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 <c>erts_alloc_config</c> from
doing its job. Note, you should <em>not</em> use this flag
when using the created configuration. Also note that it is
important that you use the same
<seealso marker="erts:erl#+S">amount of schedulers</seealso>
when creating the configuration as you are going the use on
the system using the configuration.</p>
</item>
<item>
<p>Run your applications with different scenarios (the more
the better) and save information about each scenario by calling
<seealso marker="#save_scenario/0">save_scenario/0</seealso>.
It may be hard to know when the applications are at an (for
<c>erts_alloc_config</c>) important runtime scenario. A good
approach may therefore be to call
<seealso marker="#save_scenario/0">save_scenario/0</seealso>
repeatedly, e.g. once every tenth second. Note that it is
important that your applications reach the runtime scenarios
that are important for <c>erts_alloc_config</c> when you are
saving scenarios; otherwise, the configuration may perform
bad.</p>
</item>
<item>
<p>When you have covered all scenarios, call
<seealso marker="#make_config/1">make_config/1</seealso>
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
<seealso marker="erts:erl#args_file">-args_file FileName</seealso>
to the <seealso marker="erts:erl">erl(1)</seealso> command.</p>
</item>
<item>
<p>The configuration produced by <c>erts_alloc_config</c> may
need to be manually adjusted as already stated. Do not modify the
file produced by <c>erts_alloc_config</c>; instead, put your
modifications in another file and load this file after the
file produced by <c>erts_alloc_config</c>. That is, put the
<seealso marker="erts:erl#args_file">-args_file FileName</seealso>
argument that reads your modification file later on the
command-line than the
<seealso marker="erts:erl#args_file">-args_file FileName</seealso>
argument that reads the configuration file produced by
<c>erts_alloc_config</c>. If a memory allocation parameter
appear multiple times, the last version of will be used, i.e.,
you can override parameters in the configuration file produced
by <c>erts_alloc_config</c>. Doing it this way simplifies
things when you want to rerun <c>erts_alloc_config</c>.</p>
</item>
</list>
<note>
<p>The configuration created by <c>erts_alloc_config</c> 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
<c>erts_alloc_config</c> 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 <c>erts_alloc_config</c> if the Erlang
runtime system used is changed.</p>
</note>
<p><c>erts_alloc_config</c> saves information about runtime scenarios
and performs computations in a server that is automatically
started. The server register itself under the name
<c>'__erts_alloc_config__'</c>.</p>
</description>
<funcs>
<func>
<name>save_scenario() -> ok | {error, Error}</name>
<fsummary>Saves information about current runtime scenario</fsummary>
<type>
<v>Error = term()</v>
</type>
<desc>
<p><c>save_scenario/0</c> saves information about the current
runtime scenario. This information will later be used when
<seealso marker="#make_config/0">make_config/0</seealso>,
or <seealso marker="#make_config/1">make_config/1</seealso>
is called.</p>
<p>The first time <c>save_scenario/0</c> is called a server
will be started. This server will save runtime scenarios. All
saved scenarios can be removed by calling
<seealso marker="#make_config/0">stop/0</seealso>.</p>
</desc>
</func>
<func>
<name>make_config() -> ok | {error, Error}</name>
<fsummary>Creates an erts_alloc configuration</fsummary>
<type>
<v>Error = term()</v>
</type>
<desc>
<p>This is the same as calling
<seealso marker="#make_config/1">make_config(group_leader())</seealso>.</p>
</desc>
</func>
<func>
<name>make_config(FileNameOrIODev) -> ok | {error, Error}</name>
<fsummary>Creates an erts_alloc configuration</fsummary>
<type>
<v>FileNameOrIODev = string() | io_device()</v>
<v>Error = term()</v>
</type>
<desc>
<p><c>make_config/1</c> uses the information previously saved by
<seealso marker="#save_scenario/0">save_scenario/0</seealso>
in order to produce an <c>erts_alloc</c> configuration. At
least one scenario have had to be saved. All scenarios
previously saved will be used when creating the
configuration. </p>
<p>If <c>FileNameOrIODev</c> is a <c>string()</c>,
<c>make_config/1</c> will use <c>FileNameOrIODev</c> as a
filename. A file named <c>FileNameOrIODev</c> is created and
the configuration will be written to that file. If
<c>FileNameOrIODev</c> is an
<seealso marker="stdlib:io">io_device()</seealso> (see the
documentation of the module
<seealso marker="stdlib:io">io</seealso>), the configuration
will be written to the io device.</p>
</desc>
</func>
<func>
<name>stop() -> ok | {error, Error}</name>
<fsummary></fsummary>
<type>
<v>Error = term()</v>
</type>
<desc>
<p>Stops the server that saves runtime scenarios.</p>
</desc>
</func>
</funcs>
<section>
<title>See Also</title>
<p><seealso marker="erts:erts_alloc">erts_alloc(3)</seealso>,
<seealso marker="erts:erl">erl(1)</seealso>,
<seealso marker="stdlib:io">io(3)</seealso></p>
</section>
</erlref>
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