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Tue, 17 Feb 2026 11:21:20 -0500 (EST) Date: Tue, 17 Feb 2026 11:21:20 -0500 From: Andres Freund To: Pankaj Raghav Cc: Jan Kara , Ojaswin Mujoo , linux-xfs@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, lsf-pc@lists.linux-foundation.org, djwong@kernel.org, john.g.garry@oracle.com, willy@infradead.org, hch@lst.de, ritesh.list@gmail.com, Luis Chamberlain , dchinner@redhat.com, Javier Gonzalez , gost.dev@samsung.com, tytso@mit.edu, p.raghav@samsung.com, vi.shah@samsung.com Subject: Re: [LSF/MM/BPF TOPIC] Buffered atomic writes Message-ID: References: <7cf3f249-453d-423a-91d1-dfb45c474b78@linux.dev> <4627056f-2ab9-4ff1-bca0-5d80f8f0bbab@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4627056f-2ab9-4ff1-bca0-5d80f8f0bbab@linux.dev> X-Rspamd-Queue-Id: 02397C0005 X-Stat-Signature: 8wcbuzz54c7984tje4uiz4qwpxrhfrq9 X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1771345282-299264 X-HE-Meta: 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 zwgnwCig CaLBOMEpZWVNQGV23esB9TEEYNP9lBVDa/NZoN0qNFEjZ0nB0jcTDUtAk+UAVmRvPCoiyGNgkl9e0dfva6I5dgChrDv6iiQrRa6NVcsswO66mP/SooW01KVCvlCCP0fHrfG8Rnc3ANd1csEfyP1lEyYy8VNqVw1g7SRV40Lbui1W4I/jBli/+FCFJ4iJCbiDjpZ4y3P4VFnb+k7tK7LM36TZpW2uXxGrAm53rgSwXQRUqf6dAjIcV4Ylm3wT3R0tz6lj/Ylg9JAqk5nlRD7GLbrJhKAXrvgensRgg3tsKrjdrvOBIu61BMEDoFZLqQSAJ50cax+KCXJF6PyoZAlZ6w/LoDiYtOnRE9WnaYzK5HLPaEYqU/Eex1cDmTnMhM0PO1uLW8QvcpT1xD9duid6guQq+GseTb0UJIDsRAB0Wf1ir3K0PZ1HNQchzDA== 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: List-Subscribe: List-Unsubscribe: Hi, On 2026-02-17 13:42:35 +0100, Pankaj Raghav wrote: > On 2/17/2026 1:06 PM, Jan Kara wrote: > > On Mon 16-02-26 10:45:40, Andres Freund wrote: > > > (*) As it turns out, it often seems to improves write throughput as well, if > > > writeback is triggered by memory pressure instead of SYNC_FILE_RANGE_WRITE, > > > linux seems to often trigger a lot more small random IO. > > > > > > > So immediately writing them might be ok as long as we don't remove those > > > > pages from the page cache like we do in RWF_UNCACHED. > > > > > > Yes, it might. I actually often have wished for something like a > > > RWF_WRITEBACK flag... > > > > I'd call it RWF_WRITETHROUGH but otherwise it makes sense. > > > > One naive question: semantically what will be the difference between > RWF_DSYNC and RWF_WRITETHROUGH? So RWF_DSYNC will be the sync version and > RWF_WRITETHOUGH will be an async version where we kick off writeback > immediately in the background and return? Besides sync vs async: If the device has a volatile write cache, RWF_DSYNC will trigger flushes for the entire write cache or do FUA writes for just the RWF_DSYNC write. Which wouldn't be needed for RWF_WRITETHROUGH, right? I don't know if there will be devices that have a volatile write cache with atomicity support for > 4kB, so maybe that's a distinction that's irrelevant in practice for Postgres. But for 4kB writes, the difference in throughput and individual IO latency you get from many SSDs between using FUA writes / cache flushes and not doing so are enormous. Greetings, Andres Freund