linux-kernel - Re: [PATCH 2/2] xen: don't use page->lru for ZONE

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Date:   Thu, 10 Dec 2020 12:14:54 +0100
From:   Roger Pau Monné <roger.pau@...rix.com>
To:     Jürgen Groß <jgross@...e.com>
CC:     Jason Andryuk <jandryuk@...il.com>,
        xen-devel <xen-devel@...ts.xenproject.org>,
        open list <linux-kernel@...r.kernel.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>
Subject: Re: [PATCH 2/2] xen: don't use page->lru for ZONE_DEVICE memory

On Tue, Dec 08, 2020 at 07:45:00AM +0100, Jürgen Groß wrote:
> On 07.12.20 21:48, Jason Andryuk wrote:
> > On Mon, Dec 7, 2020 at 8:30 AM Juergen Gross <jgross@...e.com> wrote:
> > > 
> > > Commit 9e2369c06c8a18 ("xen: add helpers to allocate unpopulated
> > > memory") introduced usage of ZONE_DEVICE memory for foreign memory
> > > mappings.
> > > 
> > > Unfortunately this collides with using page->lru for Xen backend
> > > private page caches.
> > > 
> > > Fix that by using page->zone_device_data instead.
> > > 
> > > Fixes: 9e2369c06c8a18 ("xen: add helpers to allocate unpopulated memory")
> > > Signed-off-by: Juergen Gross <jgross@...e.com>
> > 
> > Would it make sense to add BUG_ON(is_zone_device_page(page)) and the
> > opposite as appropriate to cache_enq?
> 
> No, I don't think so. At least in the CONFIG_ZONE_DEVICE case the
> initial list in a PV dom0 is populated from extra memory (basically
> the same, but not marked as zone device memory explicitly).

I assume it's fine for us to then use page->zone_device_data even if
the page is not explicitly marked as ZONE_DEVICE memory?

If that's fine, add my:

Acked-by: Roger Pau Monné <roger.pau@...rix.com>

To both patches, and thank you very much for fixing this!

Roger.