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Date:   Wed, 9 Feb 2022 08:29:56 -0400
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     Christoph Hellwig <hch@lst.de>
Cc:     Dan Williams <dan.j.williams@intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Felix Kuehling <Felix.Kuehling@amd.com>,
        Alex Deucher <alexander.deucher@amd.com>,
        Christian =?utf-8?B?S8O2bmln?= <christian.koenig@amd.com>,
        "Pan, Xinhui" <Xinhui.Pan@amd.com>,
        Ben Skeggs <bskeggs@redhat.com>,
        Karol Herbst <kherbst@redhat.com>,
        Lyude Paul <lyude@redhat.com>,
        Alistair Popple <apopple@nvidia.com>,
        Logan Gunthorpe <logang@deltatee.com>,
        Ralph Campbell <rcampbell@nvidia.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        amd-gfx list <amd-gfx@lists.freedesktop.org>,
        Maling list - DRI developers 
        <dri-devel@lists.freedesktop.org>, nouveau@lists.freedesktop.org,
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Subject: Re: [PATCH 7/8] mm: remove the extra ZONE_DEVICE struct page refcount
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On Wed, Feb 09, 2022 at 07:23:45AM +0100, Christoph Hellwig wrote:
> On Tue, Feb 08, 2022 at 07:30:11PM -0800, Dan Williams wrote:
> > Interesting. I had expected that to really fix the refcount problem
> > that fs/dax.c would need to start taking real page references as pages
> > were added to a mapping, just like page cache.
> 
> I think we should do that eventually.  But I think this series that
> just attacks the device private type and extends to the device coherent
> and p2p enhacements is a good first step to stop the proliferation of
> the one off refcount and to allow to deal with the fsdax pages in another
> more focuessed series.

It is nice, but the other series are still impacted by the fsdax mess
- they still stuff pages into ptes without proper refcounts and have
to carry nonsense to dance around this problem.

I certainly would be unhappy if the amd driver, for instance, gained
the fsdax problem as well and started pushing 4k pages into PMDs.

Jason