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Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: References: <20230123173007.325544-1-dhowells@redhat.com> <20230123173007.325544-11-dhowells@redhat.com> <31f7d71d-0eb9-2250-78c0-2e8f31023c66@nvidia.com> <84721e8d-d40e-617c-b75e-ead51c3e1edf@nvidia.com> <852117.1674567983@warthog.procyon.org.uk> <852914.1674568628@warthog.procyon.org.uk> <859142.1674569510@warthog.procyon.org.uk> <864109.1674570473@warthog.procyon.org.uk> To: Jason Gunthorpe Cc: dhowells@redhat.com, John Hubbard , Al Viro , Christoph Hellwig , Matthew Wilcox , Jens Axboe , Jan Kara , Jeff Layton , Logan Gunthorpe , linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Christoph Hellwig , linux-mm@kvack.org Subject: Re: [PATCH v8 10/10] mm: Renumber FOLL_PIN and FOLL_GET down MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <875205.1674572365.1@warthog.procyon.org.uk> Date: Tue, 24 Jan 2023 14:59:25 +0000 Message-ID: <875206.1674572365@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 1CEC140016 X-Stat-Signature: h6efyaxeibbtgnbewskqh3xxqz5ge7hg X-HE-Tag: 1674572372-448938 X-HE-Meta: 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 odwEvYyk voWVJjBFArL+IU1+OSqXRj62T33URO+GYvUVuqgfTRS3i3PE1KNmumIajvsMF1FUBzunCSBCBMpYxuvVu86bynSTcmTcPSNkOYWparozy0hS2dSXqk2o56n00Igcd2AZdYw5/7gAwAT1XXp+laxQzXqg4itmmDv8MkA2k1qQPZeNs6DNuglfWf82jDBqXrclO1kLte2w4pcfSNmkXAVBreY9zgFiWNpSVe8ZQSlmkvX1HnRqdAhGGegeGpg== 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: Jason Gunthorpe wrote: > What is the 3rd state? Consider a network filesystem message generated for a direct I/O that the network filesystem does zerocopy on. You may have an sk_buff that has fragments from one or more of three different sources: (1) Fragments consisting of specifically allocated pages, such as the IP/UDP/TCP headers that have refs taken on them. (2) Fragments consisting of zerocopy kernel buffers that has neither refs nor pins belonging to the sk_buff. iov_iter_extract_pages() will not take pins when extracting from, say, an XARRAY-type or KVEC-type iterator. iov_iter_extract_mode() will return 0. (3) Fragments consisting of zerocopy user buffers that have pins taken on them belonging to the sk_buff. iov_iter_extract_pages() will take pins when extracting from, say, a UBUF-type or IOVEC-type iterator. iov_iter_extract_mode() will return FOLL_PIN (at the moment). So you have three states: Ref'd, pinned and no-retention. David