linux-kernel - Re: [RFC PATCH v3 2/2] mm: remove extra ZONE

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Message-ID: <20201008051702.GA4773@ram-ibm-com.ibm.com>
Date:   Wed, 7 Oct 2020 22:17:02 -0700
From:   Ram Pai <linuxram@...ibm.com>
To:     Ralph Campbell <rcampbell@...dia.com>
Cc:     linux-mm@...ck.org, kvm-ppc@...r.kernel.org,
        nouveau@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Dan Williams <dan.j.williams@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Matthew Wilcox <willy@...radead.org>,
        Jerome Glisse <jglisse@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Alistair Popple <apopple@...dia.com>,
        Christoph Hellwig <hch@....de>,
        Jason Gunthorpe <jgg@...dia.com>,
        Bharata B Rao <bharata@...ux.ibm.com>,
        Zi Yan <ziy@...dia.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Paul Mackerras <paulus@...abs.org>,
        Ben Skeggs <bskeggs@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH v3 2/2] mm: remove extra ZONE_DEVICE struct page
 refcount

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