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[2003:cb:c704:1100:65a0:c03a:142a:f914]) by smtp.gmail.com with ESMTPSA id n13-20020a5d67cd000000b002bdcce37d31sm33258092wrw.99.2023.01.23.05.24.13 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 23 Jan 2023 05:24:14 -0800 (PST) Message-ID: Date: Mon, 23 Jan 2023 14:24:13 +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 v7 2/8] iov_iter: Add a function to extract a page list from an iterator Content-Language: en-US To: David Howells Cc: 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 , John Hubbard , linux-mm@kvack.org References: <7bbcccc9-6ebf-ffab-7425-2a12f217ba15@redhat.com> <246ba813-698b-8696-7f4d-400034a3380b@redhat.com> <20230120175556.3556978-1-dhowells@redhat.com> <20230120175556.3556978-3-dhowells@redhat.com> <3814749.1674474663@warthog.procyon.org.uk> <3903251.1674479992@warthog.procyon.org.uk> From: David Hildenbrand Organization: Red Hat In-Reply-To: <3903251.1674479992@warthog.procyon.org.uk> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 23.01.23 14:19, David Howells wrote: > David Hildenbrand wrote: > >> Switching from FOLL_GET to FOLL_PIN was in the works by John H. Not sure what >> the status is. Interestingly, Documentation/core-api/pin_user_pages.rst >> already documents that "CASE 1: Direct IO (DIO)" uses FOLL_PIN ... which does, >> unfortunately, no reflect reality yet. > > Yeah - I just came across that. > > Should iov_iter.c then switch entirely to using pin_user_pages(), rather than > get_user_pages()? In which case my patches only need keep track of > pinned/not-pinned and never "got". That would be the ideal case: whenever intending to access page content, use FOLL_PIN instead of FOLL_GET. The issue that John was trying to sort out was that there are plenty of callsites that do a simple put_page() instead of calling unpin_user_page(). IIRC, handling that correctly in existing code -- what was pinned must be released via unpin_user_page() -- was the biggest workitem. Not sure how that relates to your work here (that's why I was asking): if you could avoid FOLL_GET, that would be great :) -- Thanks, David / dhildenb