linux-kernel - Re: [RFC PATCH v3 0/2] mm: remove extra ZONE

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Message-ID: <YJ0mVAK7OjwIGnMe@casper.infradead.org>
Date:   Thu, 13 May 2021 14:15:00 +0100
From:   Matthew Wilcox <willy@...radead.org>
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>,
        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 0/2] mm: remove extra ZONE_DEVICE struct page
 refcount

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?