linux-kernel - Re: [PATCH v4 2/2] xen: add helpers to allocate unpopulated memory

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Message-ID: <20200813094946.GJ2352366@phenom.ffwll.local>
Date:   Thu, 13 Aug 2020 11:49:46 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Roger Pau Monné <roger.pau@...rix.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        linux-kernel@...r.kernel.org,
        Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Dan Carpenter <dan.carpenter@...cle.com>, Wei Liu <wl@....org>,
        Yan Yankovskyi <yyankovskyi@...il.com>,
        dri-devel@...ts.freedesktop.org, xen-devel@...ts.xenproject.org,
        linux-mm@...ck.org, David Hildenbrand <david@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH v4 2/2] xen: add helpers to allocate unpopulated memory

On Thu, Aug 13, 2020 at 09:54:20AM +0200, Roger Pau Monné 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