Ubuntu Manpage: rpmemd - librpmem target node process (EXPERIMENTAL)

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NAME

       rpmemd - librpmem target node process (EXPERIMENTAL)

SYNOPSIS

              $ rpmemd [--help] [--version] [<args>]

DESCRIPTION

       The  rpmemd  process  is  executed  on  target node by librpmem(7) library over ssh(1) and
       facilitates access to persistent memory over RDMA.  The rpmemd should not be run  manually
       under normal conditions.

OPTIONS

       Command  line options overwrite the default rpmemd configuration, the global configuration
       file and the user configuration file.

       -V, --version

       Displays rpmemd version and exits.

       -h, --help

       Prints synopsis and list of parameters and exits.

       -c, --config <path>

       Custom configuration file location.  If the custom configuration file is  provided  others
       are omitted.  See CONFIGURATION FILES section for details.

       All options described in CONFIGURATION FILES section are common for both the configuration
       file and the command line - the equivalent of the following line in the config file:

       option = value

       is

       --option value

       in the command line.

       The following command line options: –persist-apm, –persist-general and –use-syslog  should
       not  be  followed  by any value.  Presence of each of them in the command line turns on an
       appropriate option.  See CONFIGURATION FILES section for details.

       -r, --remove <poolset>

       Remove a pool described by given pool set file descriptor.  It is interpreted as a path to
       the pool set file relative to the pool set directory.

       -f, --force

       Ignore errors when removing a pool file using –remove option.

CONFIGURATION FILES

       The rpmemd searches for the configuration files with following priorities:

       • The global configuration file located in /etc/rpmemd/rpmemd.conf.

       • The user configuration file located in the user home directory ($HOME/.rpmemd.conf).

       The  rpmemd  can also read configuration from the custom configuration file provided using
       –config command line option.  See OPTIONS section for details.

       The default configuration is described in the DEFAULT CONFIGURATION section.

       The configuration file is a plain text file.  Each line  of  the  configuration  file  can
       store  only  one  configuration option defined as a key=value pair.  Empty lines and lines
       starting with # are omitted.

       The allowed options are:

       • log-file = <path> - log file location

       • poolset-dir = <path> - pool set files directory

       • persist-apm = {yes|no} - enable The Appliance Persistency Method.  This option  must  be
         set  only  if the target platform has non-allocating writes IO enabled.  See PERSISTENCY
         METHODS section for details.

       • persist-general = {yes|no} - enable The General Purpose Server Persistency Method.   See
         PERSISTENCY METHODS section for details.

       • use-syslog = {yes|no} - use syslog(3) for logging messages instead of log file

       • log-level = <level> - set log level value.  Accepted <level> values are:

         • err - error conditions

         • warn - warning conditions

         • notice - normal, but significant conditions

         • info - informational message

         • debug - debug-level message

       The  $HOME  sub-string  in  the  poolset-dir  path  is replaced with the current user home
       directory.

EXAMPLE

       Example of the configuration file:

              # This is an example of configuration file
              log-file = $HOME/.logs/rpmemd.log
              poolset-dir = $HOME/poolsets/
              persist-apm = yes
              persist-general = no
              use-syslog = no # Use log file instead of syslog
              log-level = info

DEFAULT CONFIGURATION

       The rpmemd default configuration is equivalent of the following configuration file:

              log-file = /var/log/rpmemd.log
              poolset-dir = $HOME
              persist-apm = no
              persist-general = yes
              use-syslog = yes
              log-level = err

PERSISTENCY METHODS

The librpmem(7) supports two methods for making data written to remote persistent memory
durable. The difference between the use of the two mechanisms is based on whether
librpmem(7) will make use of non-allocating writes on the remote node.

• The General Purpose Server Persistency Method does not have any requirements for the
platform on which the target daemon runs and can be enabled by administrator using the
persist-general option. This method utilize libpmem(7) persistency mechanisms on remote
node and requires additional communication between initiator and remote node using the
in-band connection.

• The Appliance Persistency Method requires non-allocating writes enabled on the platform
and can be enabled by administrator using persist-apm option. This method requires to
issue an RDMA READ operation after the RDMA WRITE operations performed on requested
chunk of memory.

“Non-allocating write requests” is the Intel Integrated IO Controller mode where all
incoming PCIe writes will utilize non-allocating buffers for the write requests.
Non-allocating writes are guaranteed to bypass all of the CPU caches and force the write
requests to flow directly to the Integrated Memory Controller without delay.

The rpmemd dynamically choose the appropriate persistency method and the flushing to
persistence primitive for GPSPM for each opened pool set name depending on available
persistency methods and whether all pool set parts are stored in the persistent memory.

If the Appliance Persistency Method is enabled and the pool set is stored in the
persistent memory rpmemd will use the Appliance Persistency Method. If the pool set is
NOT stored in the persistent memory it will fallback to the General Puropose Server
Persistency Method with pmem_msync(3).

If the General Puropose Server Persistency Method is enabled and the pool set is stored in
the persistent memory rpmemd will use pmem_persist(3). If the pool set is NOT stored in
the persistent momory it will use pmem_msync(3).

See pmem_persist(3) and pmem_msync(3) for more details.