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Date: Mon, 5 Oct 2020 09:40:02 -0700 From: Ralph Campbell <rcampbell@...dia.com> To: Christoph Hellwig <hch@....de> 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>, 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 10/1/20 10:59 PM, Christoph Hellwig wrote: > 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. >> >> Signed-off-by: Ralph Campbell <rcampbell@...dia.com> > > Looks good, > > Reviewed-by: Christoph Hellwig <hch@....de> Thanks for the review. I still have reservations about making this an official patch. Did you see the updated cover letter? Basically, I'm concerned about ZONE_DEVICE struct pages being inserted into the process page table with a zero reference count with vmf_insert_mixed(). If it is to be a non-zero reference count, then DAX, pmem, and other uses of ZONE_DEVICE pages need to be changed (or vmf_insert_mixed()) to inc/dec in appropriate places but I don't feel I know that code well enough to make those changes.
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