On Wed, Jan 26, 2022 at 05:44:54PM -0800, Dan Williams wrote:
> On Tue, Jan 18, 2022 at 12:20 PM <alison.schofi...@intel.com> wrote:
> >
> > From: Alison Schofield <alison.schofi...@intel.com>
> >
> > Users may want to change the partition layout of a memory
> > device using the CXL command line tool.
>
> How about:
>
> CXL devices may support both volatile and persistent memory capacity.
> The amount of device capacity set aside for each type is typically
> established at the factory, but some devices also allow for dynamic
> re-partitioning, add a command for this purpose.
Thanks!
>
> > Add a new CXL command,
> > 'cxl set-partition-info', that operates on a CXL memdev, or a
> > set of memdevs, and allows the user to change the partition
> > layout of the device(s).
> >
> > Synopsis:
> > Usage: cxl set-partition-info <mem0> [<mem1>..<memN>] [<options>]
>
> It's unfortunate that the specification kept the word "info" in the
> set-partition command name, let's leave it out of this name and just
> call this 'cxl set-partition'.
>
Will do.
> >
> > -v, --verbose turn on debug
> > -s, --volatile_size <n>
> > next volatile partition size in bytes
>
> Some users will come to this tool with the thought, "I want volatile
> capacity X", others "I want pmem capacity Y". All but the most
> advanced users will not understand how the volatile setting affects
> the pmem and vice versa, nor will they understand that capacity might
> be fixed and other capacity is dynamic.
I went very by the spec here, with those advance users in mind. I do
think the user with limited knowledge may get frustrated by the rules.
ie. like finding that their total capacity is not all partitionable
capacity. I looked at ipmctl goal setting, where they do percentages,
and didn't pursue - stuck with the spec.
I like this below. If user wants 100% of any type, no math needed. But,
anything else the user will have to specify a byte value.
> So how about a set of options like:
>
> -t, --type=<volatile,pmem>
> -s,--size=<size>
>
> ...where by default -t is 'pmem' and -s is '0' for 100% of the dynamic
> capacity set to PMEM.
>
I don't get the language "and -s is '0' for 100%", specifically, the
"-s is 0".
If -s is ommitted the default behavior will be to set 100% of the
partitionable capacity to type.
If both type and size are ommitted, 100% of partitionable capacity is
set to PMEM.
Humor me...are these right?
set-partition mem0
100% to pmem
set-partition mem0 -tpmem
100% to pmem
set-partition mem0 -tvolatile -s0
100% to pmem ^^ That's what I think a -s0 does?!?
set-partition mem0 -tvolatile
100% to volatile
set-partition mem0 -tvolatile -s256MB
256MB to volatile
Remainder to pmem
set-partition mem0 -s256MB
256MB to pmem
Remainder to volatile
Thanks!
> The tool can then help the user get what they want relative to
> whatever frame of reference led them to read the set-partition man
> page. The tool can figure out the details behind the scenes, or warn
> them if they want something impossible like setting PMEM capacity to
> 1GB on a device where 2GB of PMEM is statically allocated.
>
> This also helps with future proofing in case there are other types
> that come along.
>
Got it.
> >
> > The included MAN page explains how to find the partitioning
> > capabilities and restrictions of a CXL memory device.
> >
snip
> > +-------
> > +<memory device(s)>::
> > +include::memdev-option.txt[]
> > +
> > +-s::
> > +--size=::
>
> This is "--volatile_size" in the current patch, but that's moot with
> feedback to move to a --type + --size scheme.
Got it.
>
> > + Size in bytes of the volatile partition requested.
> > +
> > + Size must align to the devices partition_alignment_bytes.
> > + Use 'cxl list -m <memdev> -I' to find partition_alignment_bytes.
>
> This a static 256M, that can just be documented here.
>
My read of the spec says partition alignment is "Expressed in multiples
of 256MB", not static. Where is it defined as static?
> > +
> > + Size must be less than or equal to the device's partitionable
> > bytes.
> > + Calculate partitionable bytes by subracting the
> > volatile_only_bytes,
>
> s/subracting/subtracting/
>
> ...but rather than teaching the user to input valid values, tell them
> the validation and translation the tool will do on their behalf with
> the input based on type and the details they don't need to worry
> about.
Got it.
Thanks Dan.
