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Date:   Mon, 7 Feb 2022 18:25:15 -0800
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Subject: Re: [PATCH 7/8] mm: remove the extra ZONE_DEVICE struct page refcount
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To:     Christoph Hellwig <hch@lst.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Dan Williams <dan.j.williams@intel.com>
Cc:     Felix Kuehling <Felix.Kuehling@amd.com>,
        Alex Deucher <alexander.deucher@amd.com>,
        =?UTF-8?Q?Christian_K=c3=b6nig?= <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>, Jason Gunthorpe <jgg@ziepe.ca>,
        Alistair Popple <apopple@nvidia.com>,
        Logan Gunthorpe <logang@deltatee.com>,
        linux-kernel@vger.kernel.org, amd-gfx@lists.freedesktop.org,
        dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org,
        nvdimm@lists.linux.dev, linux-mm@kvack.org
References: <20220207063249.1833066-1-hch@lst.de>
 <20220207063249.1833066-8-hch@lst.de>
From:   Ralph Campbell <rcampbell@nvidia.com>
In-Reply-To: <20220207063249.1833066-8-hch@lst.de>
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On 2/6/22 22:32, Christoph Hellwig wrote:
> ZONE_DEVICE struct pages have an extra reference count that complicates
> the code for put_page() and several places in the kernel that need to
> check the reference count to see that a page is not being used (gup,
> compaction, migration, etc.). Clean up the code so the reference count
> doesn't need to be treated specially for ZONE_DEVICE pages.
>
> Note that this excludes the special idle page wakeup for fsdax pages,
> which still happens at refcount 1.  This is a separate issue and will
> be sorted out later.  Given that only fsdax pages require the
> notifiacation when the refcount hits 1 now, the PAGEMAP_OPS Kconfig
> symbol can go away and be replaced with a FS_DAX check for this hook
> in the put_page fastpath.
>
> Based on an earlier patch from Ralph Campbell <rcampbell@nvidia.com>.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Thanks for working on this, definite step forward.

Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>