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Date:   Wed, 7 Oct 2020 22:17:02 -0700
From:   Ram Pai <linuxram@us.ibm.com>
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>,
        Matthew Wilcox <willy@infradead.org>,
        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 2/2] mm: remove extra ZONE_DEVICE struct page
 refcount
Message-ID: <20201008051702.GA4773@ram-ibm-com.ibm.com>
Reply-To: Ram Pai <linuxram@us.ibm.com>
References: <20201001181715.17416-1-rcampbell@nvidia.com>
 <20201001181715.17416-3-rcampbell@nvidia.com>
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On Thu, Oct 01, 2020 at 11:17:15AM -0700, Ralph Campbell 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.


I was hoping this patch would resolve a page-reference issue that we run
into at random times while migrating a page to a device page backed by
secure-memory.

Unfortunately I continue to see the problem. There is a reference
held on that page, which fails the migration.

FYI
RP