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

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Message-ID: <7425aed6-ff6f-873a-b629-b9c7058e9b13@suse.com>
Date:   Thu, 10 Dec 2020 12:25:51 +0100
From:   Jürgen Groß <jgross@...e.com>
To:     Roger Pau Monné <roger.pau@...rix.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 10.12.20 12:14, Roger Pau Monné wrote:
> 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?

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

> 
> 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!

UR welcome. :-)


Juergen

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