From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ram Pai <linuxram@us.ibm.com>
Subject: Re: [RFC PATCH v3 2/2] mm: remove extra ZONE_DEVICE struct page
 refcount
Date: Wed, 7 Oct 2020 22:17:02 -0700
Message-ID: <20201008051702.GA4773@ram-ibm-com.ibm.com>
References: <20201001181715.17416-1-rcampbell@nvidia.com>
 <20201001181715.17416-3-rcampbell@nvidia.com>
Reply-To: Ram Pai <linuxram@us.ibm.com>
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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>
List-Id: nouveau.vger.kernel.org

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