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Date:   Fri, 21 Aug 2020 15:56:49 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Dan Williams <dan.j.williams@intel.com>
Cc:     Vishal Verma <vishal.l.verma@intel.com>, peterz@infradead.org,
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        joao.m.martins@oracle.com, linux-kernel@vger.kernel.org,
        linux-acpi@vger.kernel.org, dri-devel@lists.freedesktop.org
Subject: Re: [PATCH v4 15/23] device-dax: Add resize support
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On Sun, 02 Aug 2020 22:03:46 -0700 Dan Williams <dan.j.williams@intel.com> wrote:

> Make the device-dax 'size' attribute writable to allow capacity to be
> split between multiple instances in a region. The intended consumers of
> this capability are users that want to split a scarce memory resource
> between device-dax and System-RAM access, or users that want to have
> multiple security domains for a large region.
> 
> By default the hmem instance provider allocates an entire region to the
> first instance. The process of creating a new instance (assuming a
> region-id of 0) is find the region and trigger the 'create' attribute
> which yields an empty instance to configure. For example:
> 
>     cd /sys/bus/dax/devices
>     echo dax0.0 > dax0.0/driver/unbind
>     echo $new_size > dax0.0/size
>     echo 1 > $(readlink -f dax0.0)../dax_region/create
>     seed=$(cat $(readlink -f dax0.0)../dax_region/seed)
>     echo $new_size > $seed/size
>     echo dax0.0 > ../drivers/{device_dax,kmem}/bind
>     echo dax0.1 > ../drivers/{device_dax,kmem}/bind
> 
> Instances can be destroyed by:
> 
>     echo $device > $(readlink -f $device)../dax_region/delete

This userspace interface doesn't seem to be documented anywhere, so
there's nothing to update for this patch :(