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Date:   Thu, 13 Aug 2020 11:49:46 +0200
From:   Daniel Vetter <daniel@ffwll.ch>
To:     Roger Pau =?iso-8859-1?Q?Monn=E9?= <roger.pau@citrix.com>
Cc:     Christoph Hellwig <hch@infradead.org>,
        linux-kernel@vger.kernel.org,
        Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        Dan Carpenter <dan.carpenter@oracle.com>, Wei Liu <wl@xen.org>,
        Yan Yankovskyi <yyankovskyi@gmail.com>,
        dri-devel@lists.freedesktop.org, xen-devel@lists.xenproject.org,
        linux-mm@kvack.org, David Hildenbrand <david@redhat.com>,
        Michal Hocko <mhocko@kernel.org>,
        Dan Williams <dan.j.williams@intel.com>
Subject: Re: [PATCH v4 2/2] xen: add helpers to allocate unpopulated memory
Message-ID: <20200813094946.GJ2352366@phenom.ffwll.local>
Mail-Followup-To: Roger Pau =?iso-8859-1?Q?Monn=E9?= <roger.pau@citrix.com>,
        Christoph Hellwig <hch@infradead.org>, linux-kernel@vger.kernel.org,
        Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>,
        David Airlie <airlied@linux.ie>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        Dan Carpenter <dan.carpenter@oracle.com>, Wei Liu <wl@xen.org>,
        Yan Yankovskyi <yyankovskyi@gmail.com>,
        dri-devel@lists.freedesktop.org, xen-devel@lists.xenproject.org,
        linux-mm@kvack.org, David Hildenbrand <david@redhat.com>,
        Michal Hocko <mhocko@kernel.org>,
        Dan Williams <dan.j.williams@intel.com>
References: <20200811094447.31208-1-roger.pau@citrix.com>
 <20200811094447.31208-3-roger.pau@citrix.com>
 <20200813073337.GA16160@infradead.org>
 <20200813075420.GC975@Air-de-Roger>
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On Thu, Aug 13, 2020 at 09:54:20AM +0200, Roger Pau Monn? wrote:
> On Thu, Aug 13, 2020 at 08:33:37AM +0100, Christoph Hellwig wrote:
> > On Tue, Aug 11, 2020 at 11:44:47AM +0200, Roger Pau Monne wrote:
> > > If enabled (because ZONE_DEVICE is supported) the usage of the new
> > > functionality untangles Xen balloon and RAM hotplug from the usage of
> > > unpopulated physical memory ranges to map foreign pages, which is the
> > > correct thing to do in order to avoid mappings of foreign pages depend
> > > on memory hotplug.
> > 
> > So please just select ZONE_DEVICE if this is so much better rather
> > than maintaining two variants.
> 
> We still need to other variant for Arm at least, so both need to be
> maintained anyway, even if we force ZONE_DEVICE on x86.

Why does arm not have ZONE_DEVICE?
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch