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To:     Jason Andryuk <jandryuk@gmail.com>
Cc:     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>
From:   =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= <jgross@suse.com>
Subject: Re: [PATCH 2/2] xen: don't use page->lru for ZONE_DEVICE memory
Message-ID: <72bc4417-076c-78f0-9c7e-5a9c95e79fb2@suse.com>
Date:   Tue, 8 Dec 2020 07:45:00 +0100
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From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= <jgross@suse.com>
To: Jason Andryuk <jandryuk@gmail.com>
Cc: 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: <72bc4417-076c-78f0-9c7e-5a9c95e79fb2@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>
In-Reply-To: <CAKf6xpuqdY=TctOjNsnTTexeBpkV+HMkOHFsAd4vxUudBpxizA@mail.gmail.com>

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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 memor=
y")
>> Signed-off-by: Juergen Gross <jgross@suse.com>
>=20
> 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).

Juergen

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