Re: [ndctl PATCH v7 08/13] Documentation/daxctl: add a man page for daxctl-reconfigure-device

["Verma, Vishal L" <vishal.l.verma@intel.com>]

On Thu, 2019-07-25 at 19:46 -0700, Dan Williams wrote:
> On Wed, Jul 24, 2019 at 2:57 PM Vishal Verma <vishal.l.verma@intel.com> wrote:
> > Add a man page describing the new daxctl-reconfigure-device command.
> > 
> > Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
> > Cc: Dave Hansen <dave.hansen@linux.intel.com>
> > Cc: Dan Williams <dan.j.williams@intel.com>
> > Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
> > ---
> >  Documentation/daxctl/Makefile.am              |   3 +-
> >  .../daxctl/daxctl-reconfigure-device.txt      | 139 ++++++++++++++++++
> >  2 files changed, 141 insertions(+), 1 deletion(-)
> >  create mode 100644 Documentation/daxctl/daxctl-reconfigure-device.txt
> > 
[..]
> > +* 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 --no-online dax0.0
> 
> Any reason to use --no-online in this example? Presumably some-service
> may not start if node2 has no online memory.
> 
Yep just a copy/paste typo, removing it.
> 
> > +[
> > +  {
> > +    "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 allows for the dax
> 
> s/allows/arranges/

ok.

> 
> > +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. If dax-class is
> > +in use (via the dax_pmem_compat driver), the reconfiguration will fail. See
> > +linkdaxctl:daxctl-migrate-device-model[1] for more information.
> 
> Let's make sure that do_reconfig() bails with a common error message
> for the compat case and quote that message here. You can check that by
> comparing the device path 'subsystem' to /sys/class/dax. I.e.
> 
> # ls -l /dev/dax0.0
> crw------- 1 root root 253, 4 Jul 25 12:22 /dev/dax0.0
> 
> # readlink -f /sys/dev/char/253\:4/subsystem
> /sys/class/dax
> 
> ...it will be /sys/bus/dax otherwise.

Hm,. currently the failure is just:
libdaxctl: daxctl_dev_enable: dax3.0: failed to enable

Should we check the subsystem as above programatically, and print a
better error in daxctl-reconfigure-device?

> 
> > +
> > +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.
> 
> Probably need to mention that the system might online the memory even
> if this is specified, or for extra credit, coordinate with that
> auto-online facility to arrange for it to be skipped.

Good point, added a note regarding this.

> 
> > +
> > +-O::
> > +--attempt-offline::
> > +       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.
> 
> As mentioned in patch 7, this sounds like --force to me.

Done.

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