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[209.85.208.175]) by smtp.gmail.com with ESMTPSA id f15sm283384lfg.258.2021.12.22.10.40.45 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 22 Dec 2021 10:40:46 -0800 (PST) Received: by mail-lj1-f175.google.com with SMTP id 207so5175473ljf.10 for ; Wed, 22 Dec 2021 10:40:45 -0800 (PST) X-Received: by 2002:a5d:6211:: with SMTP id y17mr2950577wru.97.1640198434545; Wed, 22 Dec 2021 10:40:34 -0800 (PST) MIME-Version: 1.0 References: <900b7d4a-a5dc-5c7b-a374-c4a8cc149232@redhat.com> <20211221190706.GG1432915@nvidia.com> <3e0868e6-c714-1bf8-163f-389989bf5189@redhat.com> <20211222124141.GA685@quack2.suse.cz> <4a28e8a0-2efa-8b5e-10b5-38f1fc143a98@redhat.com> <20211222144255.GE685@quack2.suse.cz> <505d3d0f-23ee-0eec-0571-8058b8eedb97@redhat.com> <20211222160846.GH685@quack2.suse.cz> In-Reply-To: <20211222160846.GH685@quack2.suse.cz> From: Linus Torvalds Date: Wed, 22 Dec 2021 10:40:18 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v1 06/11] mm: support GUP-triggered unsharing via FAULT_FLAG_UNSHARE (!hugetlb) To: Jan Kara Cc: David Hildenbrand , Jason Gunthorpe , Nadav Amit , Linux Kernel Mailing List , Andrew Morton , Hugh Dickins , David Rientjes , Shakeel Butt , John Hubbard , Mike Kravetz , Mike Rapoport , Yang Shi , "Kirill A . Shutemov" , Matthew Wilcox , Vlastimil Babka , Jann Horn , Michal Hocko , Rik van Riel , Roman Gushchin , Andrea Arcangeli , Peter Xu , Donald Dutile , Christoph Hellwig , Oleg Nesterov , Linux-MM , "open list:KERNEL SELFTEST FRAMEWORK" , "open list:DOCUMENTATION" Content-Type: text/plain; charset="UTF-8" Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=google header.b=REM7Dgpg; spf=pass (imf03.hostedemail.com: domain of torvalds@linuxfoundation.org designates 209.85.167.48 as permitted sender) smtp.mailfrom=torvalds@linuxfoundation.org; dmarc=none X-Rspamd-Queue-Id: 2A9E32001B X-Stat-Signature: ryrdo76mdi59756ak7e1e7a5u97jmq6b X-Rspamd-Server: rspam04 X-HE-Tag: 1640198448-939885 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, Dec 22, 2021 at 8:08 AM Jan Kara wrote: > > Well, but O_DIRECT reads must use FOLL_PIN in any case because they modify > page data (and so we need to detect them both for COW and filesystem needs). Well, O_DIRECT reads do, but not necessarily writes. And hey, even reads have been dodgy in the past when we didn't really have the pinning logic - there's been a lot of users that just wanted it to work for their particular use-case rather than in general and in all situations.. Linus