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Message-ID: <CAPcyv4ijD+=3rje1CfSG4XKuRNfuAWOui93NQV09NmBte_gc0w@mail.gmail.com>
Date: Mon, 12 Oct 2020 14:14:07 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Ralph Campbell <rcampbell@...dia.com>
Cc: Linux MM <linux-mm@...ck.org>, kvm-ppc@...r.kernel.org,
nouveau@...ts.freedesktop.org,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
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>, 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: [PATCH v2] mm/hmm: make device private reference counts zero based
On Mon, Oct 12, 2020 at 10:46 AM Ralph Campbell <rcampbell@...dia.com> 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 device private pages, leaving DAX as still being
> a special case.
Please no half-step to removing the special casing...
[..]
> +void free_zone_device_page(struct page *page)
> +{
> + if (!is_device_private_page(page))
> return;
That seems too subtle to be acceptable to me. All ZONE_DEVICE pages
need to have the same relationship with respect to idle-ness and the
page reference count.
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