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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id s3-20020a25b943000000b00cad44e2417esm726509ybm.64.2023.08.10.23.09.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 10 Aug 2023 23:09:09 -0700 (PDT) Date: Thu, 10 Aug 2023 23:08:54 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.attlocal.net To: Christoph Hellwig cc: Hugh Dickins , Christian Brauner , Andrew Morton , Oleksandr Tymoshenko , Carlos Maiolino , Jeff Layton , Chuck Lever , Jan Kara , Miklos Szeredi , Daniel Xu , Chris Down , Tejun Heo , Greg Kroah-Hartman , Matthew Wilcox , Pete Zaitcev , Helge Deller , Topi Miettinen , Yu Kuai , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH vfs.tmpfs 4/5] tmpfs: trivial support for direct IO In-Reply-To: Message-ID: <194ba8d1-767d-a153-419-7f124ab6d36c@google.com> References: <7c12819-9b94-d56-ff88-35623aa34180@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Stat-Signature: r7m38kjmzhbatj8sdis4tmgtsqtgeicf X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: EF4634000D X-Rspam-User: X-HE-Tag: 1691734150-579778 X-HE-Meta: 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 fKJVuNRu QAx3IA2z7OyHmQUSLVeBtOn3uAJP1ZxGa5t4Os/vATLvqsqhYLp9Vmnk8xi0b89GVIWC5K+1KIrazDBa9qkLKzFqnuWyngAcFKj3p4akxxF+LOmzXrIyxqla1vaq1nA07F8jb39c2nb/ZALNyFfRQLBw8PioZmoUcDPuAby+pHva01/MZwGVN/XmYTeWQbzz0HY3kAzbAmddj2je/uKGVAsI3jM8fPxXDfL0NVfugWx9P+mdKqbhWDfsn7fkl7R2YgE2WZlF4UiF5HpqRPr/+kZU9gDtFF++W5n7arZi04nWmx8/Gs1A0m+udt/0t21/IvIbfFt7FlWgTp3i0TmMyx6uj3YWveFtFrplJunrzahEmb4uPWmO/ukeURkOq/0AX9VpY 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, 9 Aug 2023, Christoph Hellwig wrote: > Please do not add a new ->direct_IO method. I'm currently working hard > on removing it, just set FMODE_CAN_ODIRECT and handle the fallback in > your read_iter/write_iter methods. Thanks for the input, I'd missed that FMODE_CAN_ODIRECT development. I can see why you would surely prefer not to have a .direct_IO added. But whether that's right for tmpfs at this time, I'll let you and all decide: I've tried and tested the v2 patch now, and will send it out shortly; but it has to add a shmem_file_write_iter(), where shmem was doing fine with generic_file_write_iter() + direct_IO() stub before. So my own feeling is that the v1 patch with shmem_direct_IO() was better, duplicating less code; but whatever, you can all decide between them. > > But if we just start claiming direct I/O support for file systems that > don't actually support it, I'm starting to seriously wonder why we > bother with the flag at all and don't just allow O_DIRECT opens > to always succeed.. Yes, I've wondered that way too, but don't have a strong opinion on it. Hugh