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[2003:cb:c704:1100:65a0:c03a:142a:f914]) by smtp.gmail.com with ESMTPSA id 21-20020a05600c26d500b003d9b87296a9sm10216753wmv.25.2023.01.23.06.20.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 23 Jan 2023 06:20:43 -0800 (PST) Message-ID: <77f3fc56-05d8-def0-e518-0906c729e7df@redhat.com> Date: Mon, 23 Jan 2023 15:20:41 +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 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> <3911637.1674481111@warthog.procyon.org.uk> From: David Hildenbrand Organization: Red Hat In-Reply-To: <3911637.1674481111@warthog.procyon.org.uk> 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-Rspamd-Queue-Id: BE6A1120007 X-Stat-Signature: m53qqfm1g83tqn38x1i7bjeytqsmt7ph X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1674483648-942158 X-HE-Meta: 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 1u+6K1AN 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 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 23.01.23 14:38, David Howells wrote: > David Hildenbrand wrote: > >> 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 :) > > Well, it simplifies things a bit. > > I can make the new iov_iter_extract_pages() just do "pin" or "don't pin" and > do no ref-getting at all. Things can be converted over to "unpin the pages or > doing nothing" as they're converted over to using iov_iter_extract_pages() > from iov_iter_get_pages*(). > > The block bio code then only needs a single bit of state: pinned or not > pinned. Unfortunately, I'll have to let BIO experts comment on that :) I only know the MM side of things here. > > For cifs RDMA, do I need to make it pass in FOLL_LONGTERM? And does that need > a special cleanup? Anything that holds pins "possibly forever" should that. vmsplice() is another example that should use it, once properly using FOLL_PIN. [FOLL_GET | FOLL_LONGTERM is not really used/defined with semantics] > > sk_buff fragment handling could still be tricky. I'm thinking that in that > code I'll need to store FOLL_GET/PIN in the bottom two bits of the frag page > pointer. Sometimes it allocates a new page and attaches it (have ref); > sometimes it does zerocopy to/from a page (have pin) and sometimes it may be > pointing to a kernel buffer (don't pin or ref). > > David > -- Thanks, David / dhildenb