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[209.85.208.181]) by smtp.gmail.com with ESMTPSA id q16sm284578lfc.179.2020.12.09.13.04.39 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 09 Dec 2020 13:04:39 -0800 (PST) Received: by mail-lj1-f181.google.com with SMTP id f11so4149995ljn.2 for ; Wed, 09 Dec 2020 13:04:39 -0800 (PST) X-Received: by 2002:a2e:6f17:: with SMTP id k23mr1768604ljc.411.1607547879048; Wed, 09 Dec 2020 13:04:39 -0800 (PST) MIME-Version: 1.0 References: <20201209163950.8494-1-will@kernel.org> <20201209163950.8494-2-will@kernel.org> <20201209184049.GA8778@willie-the-truck> <20201209203203.GU7338@casper.infradead.org> In-Reply-To: <20201209203203.GU7338@casper.infradead.org> From: Linus Torvalds Date: Wed, 9 Dec 2020 13:04:22 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 1/2] mm: Allow architectures to request 'old' entries when prefaulting To: Matthew Wilcox Cc: Will Deacon , Linux Kernel Mailing List , Linux-MM , Linux ARM , Catalin Marinas , Jan Kara , Minchan Kim , Andrew Morton , "Kirill A . Shutemov" , Vinayak Menon , Android Kernel Team Content-Type: text/plain; charset="UTF-8" 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 9, 2020 at 12:32 PM Matthew Wilcox wrote: > > If a filesystem has put an Uptodate page into the page cache, the > rest of the kernel can read it without telling the filesystem. XFS does the same thing for xfs_file_read_iter() too. Not that I disagree with you - when you mmap a file, once it's mapped you see the data without any lock anyway. So it's all kinds of pointless to serialize the page fault, because that's simply not relevant. The lock will be gone by the time the user actually sees the data. But hey, the XFS people have their opinions. Linus