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[184.145.4.219]) by smtp.gmail.com with ESMTPSA id o10sm15018668qki.72.2021.05.19.05.21.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 19 May 2021 05:21:09 -0700 (PDT) Date: Wed, 19 May 2021 08:21:08 -0400 From: Peter Xu To: Alistair Popple Cc: linux-mm@kvack.org, nouveau@lists.freedesktop.org, bskeggs@redhat.com, akpm@linux-foundation.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, jhubbard@nvidia.com, rcampbell@nvidia.com, jglisse@redhat.com, jgg@nvidia.com, hch@infradead.org, daniel@ffwll.ch, willy@infradead.org, bsingharora@gmail.com, Christoph Hellwig Subject: Re: [PATCH v8 5/8] mm: Device exclusive memory access Message-ID: References: <20210407084238.20443-1-apopple@nvidia.com> <47694715.suB6H4Uo8R@nvdebian> <2217153.lfGrokb94b@nvdebian> MIME-Version: 1.0 In-Reply-To: <2217153.lfGrokb94b@nvdebian> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Authentication-Results: imf15.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=aadB3nSK; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf15.hostedemail.com: domain of peterx@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=peterx@redhat.com X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: A7FD9A0003BA X-Stat-Signature: otemt35h41hcx3oaiga1t96kjtewmxd3 X-HE-Tag: 1621426871-219822 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, May 19, 2021 at 09:35:10PM +1000, Alistair Popple wrote: > I think the approach you are describing is similar to what > migrate_vma_collect()/migrate_vma_unamp() does now and I think it could be > made to work. I ended up going with the GUP+unmap approach in part because > Christoph suggested it but primarily because it required less code especially > given we needed to call something to fault the page in/break COW anyway (or > extend what was there to call handle_mm_fault(), etc.). I see, thank. Would you mind add a short paragraph in the commit message talking about these two solutions and why we choose the GUP way? -- Peter Xu