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 CONFIGU‐
       RATION 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 con‐
       figuration 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-al‐
locating 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 en‐
abled 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 by‐
pass all of the CPU caches and force the write requests to flow directly to the Integrated Memory Con‐
troller without delay.

The rpmemd dynamically choose the appropriate persistency method and the flushing to persistence primi‐
tive 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.