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[2003:cb:c707:5e00:9e97:86d:5ed5:bb95]) by smtp.gmail.com with ESMTPSA id d3-20020adfe2c3000000b002bc7fcf08ddsm2385220wrj.103.2023.01.26.15.44.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 26 Jan 2023 15:44:09 -0800 (PST) Message-ID: Date: Fri, 27 Jan 2023 00:44:08 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0 Subject: Re: [PATCH v11 2/8] iov_iter: Add a function to extract a page list from an iterator To: Al Viro , David Howells Cc: Christoph Hellwig , Matthew Wilcox , Jens Axboe , Jan Kara , Jeff Layton , Jason Gunthorpe , Logan Gunthorpe , linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Christoph Hellwig , John Hubbard References: <20230126141626.2809643-1-dhowells@redhat.com> <20230126141626.2809643-3-dhowells@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: D365240007 X-Stat-Signature: hknkck9nfggk37guh6gqi68zxtgsigff X-HE-Tag: 1674776655-872395 X-HE-Meta: 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 NVupIFNo 8vQE508D+eb4TC8f4QYs/Ho7qprc62D/B/aWjM5hSdPuH9ErOt8rppoR8l72x3mXyFGR1Rzg3xlVACc240UtZdYouw2ptYCbUGkyJONWdOHWG5EtYeWIdVgdYHSV1CDLiStMrSVehKjWxBiWO8AjayqQZ7WBtH/KVI2M8wH8cIQP4Buj/BxCcGU3KzGi7fEjLz5vSKrCm/2um85WBG66kXuIy8boGTubMLqgNBJRjrq4+fEwdvWPFhP3n3ZNdCTwcQfhxd6n5JV+aQdUt2+3MyEZchSeEmeQMjFHUxqZnUkBrOx0zPOTuACYT1C5eiuzTNc/jvyxTE+NNPvU+j9IxhvsWZcEhGb0TG943DNyf5IGEr9jIjawuWTylynd1JAb/NssOz/d+mq/hujux7PIJhEoQzHhZH6xdGjY85mCDX2m0CFt62AXfUXA25DwvJWwekIYQocJ5hB0/NFM3jhv8Wfq+4j7ar/r4lACQWCd9TSdOC2bJXkHZO6aW0Zg7G6AkqdMd X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 26.01.23 23:36, Al Viro wrote: > On Thu, Jan 26, 2023 at 09:59:36PM +0000, Al Viro wrote: >> On Thu, Jan 26, 2023 at 02:16:20PM +0000, David Howells wrote: >> >>> +/** >>> + * iov_iter_extract_will_pin - Indicate how pages from the iterator will be retained >>> + * @iter: The iterator >>> + * >>> + * Examine the iterator and indicate by returning true or false as to how, if >>> + * at all, pages extracted from the iterator will be retained by the extraction >>> + * function. >>> + * >>> + * %true indicates that the pages will have a pin placed in them that the >>> + * caller must unpin. This is must be done for DMA/async DIO to force fork() >>> + * to forcibly copy a page for the child (the parent must retain the original >>> + * page). >>> + * >>> + * %false indicates that no measures are taken and that it's up to the caller >>> + * to retain the pages. >>> + */ >>> +static inline bool iov_iter_extract_will_pin(const struct iov_iter *iter) >>> +{ >>> + return user_backed_iter(iter); >>> +} >>> + >> >> Wait a sec; why would we want a pin for pages we won't be modifying? >> A reference - sure, but... > > After having looked through the earlier iterations of the patchset - > sorry, but that won't fly for (at least) vmsplice(). There we can't > pin those suckers; We'll need a way to pass FOLL_LONGTERM to pin_user_pages_fast() to handle such long-term pinning as vmsplice() needs. But the release path (unpin) will be the same. -- Thanks, David / dhildenb