Re: [ndctl PATCH v2 10/12] cxl/memdev: Add {reserve,free}-dpa commands

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Thu, 14 Jul 2022 10:02:44 -0700
Dan Williams <dan.j.williams@intel.com> wrote:

> Add helper commands for managing allocations of DPA (device physical
> address) capacity on a set of CXL memory devices.
> 
> The main convenience this command affords is automatically picking the next
> decoder to allocate per-memdev.
> 
> For example, to allocate 256MiB from all endpoints that are covered by a
> given root decoder, and collect those resulting endpoint-decoders into an
> array:
> 
>   readarray -t mem < <(cxl list -M -d $decoder | jq -r ".[].memdev")
>   readarray -t endpoint < <(cxl reserve-dpa -t pmem ${mem[*]} -s $((256<<20)) |
>                             jq -r ".[] | .decoder.decoder")
> 
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Not a proper review as don't have time to dive into this today. But whilst glancing at it, noticed a typo below.

> diff --git a/Documentation/cxl/cxl-reserve-dpa.txt b/Documentation/cxl/cxl-reserve-dpa.txt
> new file mode 100644
> index 000000000000..560daf0cb277
> --- /dev/null
> +++ b/Documentation/cxl/cxl-reserve-dpa.txt
> @@ -0,0 +1,67 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +cxl-reserve-dpa(1)
> +==================
> +
> +NAME
> +----
> +cxl-reserve-dpa - allocate device-physical address space
> +
> +SYNOPSIS
> +--------
> +[verse]
> +'cxl reserve-dpa' <mem0> [<mem1>..<memN>] [<options>]
> +
> +The CXL region provisioning process proceeds in multiple steps. One of
> +the steps is identifying and reserving the DPA span that each member of
> +the interleave-set (region) contributes in advance of attaching that
> +allocation to a region. For development, test, and debug purposes this
> +command is a helper to find the next available decoder on endpoint
> +(memdev) and mark a span of DPA as busy.
> +
> +OPTIONS
> +-------
> +<memory device(s)>::
> +include::memdev-option.txt[]
> +
> +-d::
> +--decoder::
> +	Specify the decoder to attempt the allocation. The CXL specification
> +	mandates that allocations must be ordered by DPA and decoder instance.
> +	I.e. the lowest DPA allocation on the device is covered by deocder0, and

decoder0

> +	the last / highest DPA allocation is covered by the last decoder. This
> +	ordering is enforced by the kernel. By default the tool picks the 'next
> +	available' decoder.