Re: [ndctl PATCH 04/10] libdaxctl: add an API to determine if memory is movable

From: Dan Williams <dan.j.williams@intel.com>
To: Vishal Verma <vishal.l.verma@intel.com>
Cc: linux-nvdimm <linux-nvdimm@lists.01.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Ben Olson <ben.olson@intel.com>,
	Michal Biesek <michal.biesek@intel.com>
Subject: Re: [ndctl PATCH 04/10] libdaxctl: add an API to determine if memory is movable
Date: Fri, 18 Oct 2019 11:54:44 -0700	[thread overview]
Message-ID: <CAPcyv4hb7vPbWhb3R5fyJH0H5OqRmhtVr=_D0tiYrkc_r8HpaQ@mail.gmail.com> (raw)
In-Reply-To: <20191002234925.9190-5-vishal.l.verma@intel.com>

On Wed, Oct 2, 2019 at 4:49 PM Vishal Verma <vishal.l.verma@intel.com> wrote:
>
> By default, daxctl always attempts to online new memory sections as
> 'movable' so that routine kernel allocations aren't serviced from this
> memory, and the memory is later removable via hot-unplug.
>
> System configuration, or other agents (such as udev rules) may race
> 'daxctl' to online memory, and this may result in the memory not being
> 'movable'. Add an interface to query the movability of a memory object
> associated with a dax device.
>
> This is in preparation to both display a 'movable' attribute in device
> listings, as well as optionally allowing memory to be onlined as
> non-movable.
>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Reported-by: Ben Olson <ben.olson@intel.com>
> Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
> ---
>  daxctl/lib/libdaxctl-private.h | 20 +++++++++
>  daxctl/lib/libdaxctl.c         | 77 ++++++++++++++++++++++++++++++++--
>  daxctl/lib/libdaxctl.sym       |  5 +++
>  daxctl/libdaxctl.h             |  1 +
>  4 files changed, 100 insertions(+), 3 deletions(-)
>
> diff --git a/daxctl/lib/libdaxctl-private.h b/daxctl/lib/libdaxctl-private.h
> index 7ba3c46..82939bb 100644
> --- a/daxctl/lib/libdaxctl-private.h
> +++ b/daxctl/lib/libdaxctl-private.h
> @@ -44,6 +44,25 @@ enum memory_op {
>         MEM_SET_ONLINE,
>         MEM_IS_ONLINE,
>         MEM_COUNT,
> +       MEM_FIND_ZONE,

This is private so the naming is not too big a concern, but isn't this
a MEM_GET_ZONE? A find operation to me is something that can succeed
to find nothing, whereas a get operation fail assumes the association
can always be retrieved barring exceptional conditions.
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