Ubuntu Manpage: daxctl-reconfigure-device - Reconfigure a dax device into a different mode

NAME

       daxctl-reconfigure-device - Reconfigure a dax device into a different mode

SYNOPSIS

       daxctl reconfigure-device <dax0.0> [<dax1.0>...<daxY.Z>] [<options>]

EXAMPLES

       •   Reconfigure dax0.0 to system-ram mode, don’t online the memory

           # daxctl reconfigure-device --mode=system-ram --no-online dax0.0
           [
             {
               "chardev":"dax0.0",
               "size":16777216000,
               "target_node":2,
               "mode":"system-ram"
             }
           ]

       •   Reconfigure dax0.0 to devdax mode, attempt to offline the memory

           # daxctl reconfigure-device --human --mode=devdax --force dax0.0
           {
             "chardev":"dax0.0",
             "size":"15.63 GiB (16.78 GB)",
             "target_node":2,
             "mode":"devdax"
           }

       •   Reconfigure all dax devices on region0 to system-ram mode

           # daxctl reconfigure-device --mode=system-ram --region=0 all
           [
             {
               "chardev":"dax0.0",
               "size":16777216000,
               "target_node":2,
               "mode":"system-ram"
             },
             {
               "chardev":"dax0.1",
               "size":16777216000,
               "target_node":3,
               "mode":"system-ram"
             }
           ]

       •   Run a process called some-service using numactl to restrict its cpu nodes to 0 and 1,
           and  memory allocations to node 2 (determined using daxctl_dev_get_target_node() or
           daxctl list)

           # daxctl reconfigure-device --mode=system-ram dax0.0
           [
             {
               "chardev":"dax0.0",
               "size":16777216000,
               "target_node":2,
               "mode":"system-ram"
             }
           ]

           # numactl --cpunodebind=0-1 --membind=2 -- some-service --opt1 --opt2

DESCRIPTION

Reconfigure the operational mode of a dax device. This can be used to convert a regular
devdax mode device to the system-ram mode which arranges for the dax range to be
hot-plugged into the system as regular memory.

Note
This is a destructive operation. Any data on the dax device will be lost.

Note
Device reconfiguration depends on the dax-bus device model. See
daxctl-migrate-device-model(1) for more information. If dax-class is in use (via the
dax_pmem_compat driver), the reconfiguration will fail with an error such as the
following:

# daxctl reconfigure-device --mode=system-ram --region=0 all
libdaxctl: daxctl_dev_disable: dax3.0: error: device model is dax-class
dax3.0: disable failed: Operation not supported
error reconfiguring devices: Operation not supported
reconfigured 0 devices

daxctl-reconfigure-device nominally expects that it will online new memory blocks as
movable, so that kernel data doesn’t make it into this memory. However, there are other
potential agents that may be configured to automatically online new hot-plugged memory as
it appears. Most notably, these are the /sys/devices/system/memory/auto_online_blocks
configuration, or system udev rules. If such an agent races to online memory sections,
daxctl checks if the blocks were onlined as movable memory. If this was not the case, and
the memory blocks are found to be in a different zone, then a warning is displayed. If it
is desired that a different agent control the onlining of memory blocks, and the
associated memory zone, then it is recommended to use the --no-online option described
below. This will abridge the device reconfiguration operation to just hotplugging the
memory, and refrain from then onlining it.

OPTIONS

-r, --region=
Restrict the operation to devices belonging to the specified region(s). A device-dax
region is a contiguous range of memory that hosts one or more /dev/daxX.Y devices,
where X is the region id and Y is the device instance id.

-m, --mode=
Specify the mode to which the dax device(s) should be reconfigured.

• "system-ram": hotplug the device into system memory.

• "devdax": switch to the normal "device dax" mode. This requires the kernel to
support hot-unplugging kmem based memory. If this is not available, a reboot is
the only way to switch back to devdax mode.

-N, --no-online
By default, memory sections provided by system-ram devices will be brought online
automatically and immediately with the online_movable policy. Use this option to
disable the automatic onlining behavior.

--no-movable
--movable is the default. This can be overridden to online new memory such that is is
not movable. This allows any allocation to potentially be served from this memory.
This may preclude subsequent removal. With the --movable behavior (which is default),
kernel allocations will not consider this memory, and it will be reserved for
application use.

-f, --force
When converting from "system-ram" mode to "devdax", it is expected that all the memory
sections are first made offline. By default, daxctl won’t touch online memory. However
with this option, attempt to offline the memory on the NUMA node associated with the
dax device before converting it back to "devdax" mode.

-u, --human
By default the command will output machine-friendly raw-integer data. Instead, with
this flag, numbers representing storage size will be formatted as human readable
strings with units, other fields are converted to hexadecimal strings.

-v, --verbose
Emit more debug messages

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