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Subject: Re: [PATCH 2/2] xen: don't use page->lru for ZONE_DEVICE memory
To:     =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= <roger.pau@citrix.com>
Cc:     Jason Andryuk <jandryuk@gmail.com>,
        xen-devel <xen-devel@lists.xenproject.org>,
        open list <linux-kernel@vger.kernel.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Stefano Stabellini <sstabellini@kernel.org>
References: <20201207133024.16621-1-jgross@suse.com>
 <20201207133024.16621-3-jgross@suse.com>
 <CAKf6xpuqdY=TctOjNsnTTexeBpkV+HMkOHFsAd4vxUudBpxizA@mail.gmail.com>
 <72bc4417-076c-78f0-9c7e-5a9c95e79fb2@suse.com>
 <20201210111454.dxykvyktzwr3fjyk@Air-de-Roger>
From:   =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= <jgross@suse.com>
Message-ID: <7425aed6-ff6f-873a-b629-b9c7058e9b13@suse.com>
Date:   Thu, 10 Dec 2020 12:25:51 +0100
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From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= <jgross@suse.com>
To: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= <roger.pau@citrix.com>
Cc: Jason Andryuk <jandryuk@gmail.com>,
 xen-devel <xen-devel@lists.xenproject.org>,
 open list <linux-kernel@vger.kernel.org>,
 Boris Ostrovsky <boris.ostrovsky@oracle.com>,
 Stefano Stabellini <sstabellini@kernel.org>
Message-ID: <7425aed6-ff6f-873a-b629-b9c7058e9b13@suse.com>
Subject: Re: [PATCH 2/2] xen: don't use page->lru for ZONE_DEVICE memory
References: <20201207133024.16621-1-jgross@suse.com>
 <20201207133024.16621-3-jgross@suse.com>
 <CAKf6xpuqdY=TctOjNsnTTexeBpkV+HMkOHFsAd4vxUudBpxizA@mail.gmail.com>
 <72bc4417-076c-78f0-9c7e-5a9c95e79fb2@suse.com>
 <20201210111454.dxykvyktzwr3fjyk@Air-de-Roger>
In-Reply-To: <20201210111454.dxykvyktzwr3fjyk@Air-de-Roger>

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On 10.12.20 12:14, Roger Pau Monn=C3=A9 wrote:
> On Tue, Dec 08, 2020 at 07:45:00AM +0100, J=C3=BCrgen Gro=C3=9F wrote:
>> On 07.12.20 21:48, Jason Andryuk wrote:
>>> On Mon, Dec 7, 2020 at 8:30 AM Juergen Gross <jgross@suse.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 mem=
ory")
>>>> Signed-off-by: Juergen Gross <jgross@suse.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).
>=20
> 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?

I think so, yes, as we are owner of that page and we were fine to use
lru, too.

>=20
> If that's fine, add my:
>=20
> Acked-by: Roger Pau Monn=C3=A9 <roger.pau@citrix.com>
>=20
> To both patches, and thank you very much for fixing this!

UR welcome. :-)


Juergen

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