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Date:   Thu, 13 May 2021 14:15:00 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Ralph Campbell <rcampbell@nvidia.com>
Cc:     linux-mm@kvack.org, kvm-ppc@vger.kernel.org,
        nouveau@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        Dan Williams <dan.j.williams@intel.com>,
        Ira Weiny <ira.weiny@intel.com>,
        Jerome Glisse <jglisse@redhat.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Alistair Popple <apopple@nvidia.com>,
        Christoph Hellwig <hch@lst.de>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Bharata B Rao <bharata@linux.ibm.com>,
        Zi Yan <ziy@nvidia.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Yang Shi <yang.shi@linux.alibaba.com>,
        Paul Mackerras <paulus@ozlabs.org>,
        Ben Skeggs <bskeggs@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [RFC PATCH v3 0/2] mm: remove extra ZONE_DEVICE struct page
 refcount
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References: <20201001181715.17416-1-rcampbell@nvidia.com>
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On Thu, Oct 01, 2020 at 11:17:13AM -0700, Ralph Campbell wrote:
> This is still an RFC because after looking at the pmem/dax code some
> more, I realized that the ZONE_DEVICE struct pages are being inserted
> into the process' page tables with vmf_insert_mixed() and a zero
> refcount on the ZONE_DEVICE struct page. This is sort of OK because
> insert_pfn() increments the reference count on the pgmap which is what
> prevents memunmap_pages() from freeing the struct pages and it doesn't
> check for a non-zero struct page reference count.
> But, any calls to get_page() will hit the VM_BUG_ON_PAGE() that
> checks for a reference count == 0.

This seems to have gone quiet.  What needs to happen to resurrect this?