erts_alloc_config(3erl) Erlang Module Definition erts_alloc_config(3erl)
NAME
erts_alloc_config - Configuration tool for erts_alloc
DESCRIPTION
Note:
erts_alloc_config is currently an experimental tool and might be sub-
ject to backward incompatible changes.
erts_alloc(3erl) 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(3erl) 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-
loc_config.
Note:
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__'.
EXPORTS
save_scenario() -> ok | {error, Error}
Types:
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}
Types:
Error = term()
This is the same as calling make_config(group_leader()).
make_config(FileNameOrIODev) -> ok | {error, Error}
Types:
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}
Types:
Error = term()
Stops the server that saves runtime scenarios.
SEE ALSO
erts_alloc(3erl), erl(1), io(3erl)
Ericsson AB runtime_tools 1.15 erts_alloc_config(3erl)