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<!-- refpage --><center><h1>erts_alloc_config</h1></center>
<h3>MODULE</h3>
<div class="REFBODY">erts_alloc_config</div>
<h3>MODULE SUMMARY</h3>
<div class="REFBODY">Configuration tool for erts_alloc</div>
<h3>DESCRIPTION</h3>
<div class="REFBODY"><p>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p><span class="code">erts_alloc_config</span> is currently an experimental
tool and might be subject to backward incompatible
changes.</p>
</p></div>
</div>
<p><span class="bold_code"><a href="javascript:erlhref('../../../../doc/../','erts','erts_alloc.html');">erts_alloc(3)</a></span> is an
Erlang Run-Time System internal memory allocator library.
<span class="code">erts_alloc_config</span> is intended to be used to aid creation
of an <span class="bold_code"><a href="javascript:erlhref('../../../../doc/../','erts','erts_alloc.html');">erts_alloc(3)</a></span>
configuration that is suitable for a limited number of runtime
scenarios. The configuration that <span class="code">erts_alloc_config</span>
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 <span class="code">erts_alloc_config</span> 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 <span class="code">erts_alloc_config</span> 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 <span class="code">erts_alloc_config</span>.</p>
<p>A configuration is created in the following way:</p>
<ul>
<li>
<p>Pass the <span class="bold_code"><a href="javascript:erlhref('../../../../doc/../','erts','erts_alloc.html#Mea');">+Mea config</a></span>
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 <span class="code">erts_alloc_config</span> from
doing its job. Note, you should <strong>not</strong> use this flag
when using the created configuration. Also note that it is
important that you use the same
<span class="bold_code"><a href="javascript:erlhref('../../../../doc/../','erts','erl.html#+S');">amount of schedulers</a></span>
when creating the configuration as you are going the use on
the system using the configuration.</p>
</li>
<li>
<p>Run your applications with different scenarios (the more
the better) and save information about each scenario by calling
<span class="bold_code"><a href="#save_scenario-0">save_scenario/0</a></span>.
It may be hard to know when the applications are at an (for
<span class="code">erts_alloc_config</span>) important runtime scenario. A good
approach may therefore be to call
<span class="bold_code"><a href="#save_scenario-0">save_scenario/0</a></span>
repeatedly, e.g. once every tenth second. Note that it is
important that your applications reach the runtime scenarios
that are important for <span class="code">erts_alloc_config</span> when you are
saving scenarios; otherwise, the configuration may perform
bad.</p>
</li>
<li>
<p>When you have covered all scenarios, call
<span class="bold_code"><a href="#make_config-1">make_config/1</a></span>
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
<span class="bold_code"><a href="javascript:erlhref('../../../../doc/../','erts','erl.html#args_file');">-args_file FileName</a></span>
to the <span class="bold_code"><a href="javascript:erlhref('../../../../doc/../','erts','erl.html');">erl(1)</a></span> command.</p>
</li>
<li>
<p>The configuration produced by <span class="code">erts_alloc_config</span> may
need to be manually adjusted as already stated. Do not modify the
file produced by <span class="code">erts_alloc_config</span>; instead, put your
modifications in another file and load this file after the
file produced by <span class="code">erts_alloc_config</span>. That is, put the
<span class="bold_code"><a href="javascript:erlhref('../../../../doc/../','erts','erl.html#args_file');">-args_file FileName</a></span>
argument that reads your modification file later on the
command-line than the
<span class="bold_code"><a href="javascript:erlhref('../../../../doc/../','erts','erl.html#args_file');">-args_file FileName</a></span>
argument that reads the configuration file produced by
<span class="code">erts_alloc_config</span>. 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 <span class="code">erts_alloc_config</span>. Doing it this way simplifies
things when you want to rerun <span class="code">erts_alloc_config</span>.</p>
</li>
</ul>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>The configuration created by <span class="code">erts_alloc_config</span> 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
<span class="code">erts_alloc_config</span> 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 <span class="code">erts_alloc_config</span> if the Erlang
runtime system used is changed.</p>
</p></div>
</div>
<p><span class="code">erts_alloc_config</span> saves information about runtime scenarios
and performs computations in a server that is automatically
started. The server register itself under the name
<span class="code">'__erts_alloc_config__'</span>.</p>
</p></div>
<h3>EXPORTS</h3>
<p><a name="save_scenario-0"><span class="bold_code">save_scenario() -> ok | {error, Error}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Error = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p><span class="code">save_scenario/0</span> saves information about the current
runtime scenario. This information will later be used when
<span class="bold_code"><a href="#make_config-0">make_config/0</a></span>,
or <span class="bold_code"><a href="#make_config-1">make_config/1</a></span>
is called.</p>
<p>The first time <span class="code">save_scenario/0</span> is called a server
will be started. This server will save runtime scenarios. All
saved scenarios can be removed by calling
<span class="bold_code"><a href="#make_config-0">stop/0</a></span>.</p>
</p></div>
<p><a name="make_config-0"><span class="bold_code">make_config() -> ok | {error, Error}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Error = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>This is the same as calling
<span class="bold_code"><a href="#make_config-1">make_config(group_leader())</a></span>.</p>
</p></div>
<p><a name="make_config-1"><span class="bold_code">make_config(FileNameOrIODev) -> ok | {error, Error}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">FileNameOrIODev = string() | io_device()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Error = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p><span class="code">make_config/1</span> uses the information previously saved by
<span class="bold_code"><a href="#save_scenario-0">save_scenario/0</a></span>
in order to produce an <span class="code">erts_alloc</span> configuration. At
least one scenario have had to be saved. All scenarios
previously saved will be used when creating the
configuration. </p>
<p>If <span class="code">FileNameOrIODev</span> is a <span class="code">string()</span>,
<span class="code">make_config/1</span> will use <span class="code">FileNameOrIODev</span> as a
filename. A file named <span class="code">FileNameOrIODev</span> is created and
the configuration will be written to that file. If
<span class="code">FileNameOrIODev</span> is an
<span class="bold_code"><a href="javascript:erlhref('../../../../doc/../','stdlib','io.html');">io_device()</a></span> (see the
documentation of the module
<span class="bold_code"><a href="javascript:erlhref('../../../../doc/../','stdlib','io.html');">io</a></span>), the configuration
will be written to the io device.</p>
</p></div>
<p><a name="stop-0"><span class="bold_code">stop() -> ok | {error, Error}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Error = term()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Stops the server that saves runtime scenarios.</p>
</p></div>
<h3><a name="id68748">See Also</a></h3>
<div class="REFBODY">
<p><span class="bold_code"><a href="javascript:erlhref('../../../../doc/../','erts','erts_alloc.html');">erts_alloc(3)</a></span>,
<span class="bold_code"><a href="javascript:erlhref('../../../../doc/../','erts','erl.html');">erl(1)</a></span>,
<span class="bold_code"><a href="javascript:erlhref('../../../../doc/../','stdlib','io.html');">io(3)</a></span></p>
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