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Sun, 15 Feb 2026 01:01:58 -0800 (PST) Received: from localhost ([2a0d:6fc2:4b0a:db00:eb98:5335:fc91:c4bc]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43796abd793sm18612064f8f.25.2026.02.15.01.01.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 15 Feb 2026 01:01:58 -0800 (PST) Date: Sun, 15 Feb 2026 11:01:57 +0200 From: Amir Goldstein To: Pankaj Raghav , Andres Freund Cc: 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, jack@suse.cz, ojaswin@linux.ibm.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: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam12 X-Stat-Signature: 4qy9w7o7o4i5xwmxj31r4ceztez1u5ec X-Rspamd-Queue-Id: 5F495A000B X-Rspam-User: X-HE-Tag: 1771146121-208694 X-HE-Meta: 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 ZlKBBTY/ 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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: List-Subscribe: List-Unsubscribe: On Fri, Feb 13, 2026 at 11:20:36AM +0100, Pankaj Raghav wrote: > Hi all, > > Atomic (untorn) writes for Direct I/O have successfully landed in kernel > for ext4 and XFS[1][2]. However, extending this support to Buffered I/O > remains a contentious topic, with previous discussions often stalling due to > concerns about complexity versus utility. > > I would like to propose a session to discuss the concrete use cases for > buffered atomic writes and if possible, talk about the outstanding > architectural blockers blocking the current RFCs[3][4]. > > ## Use Case: > > A recurring objection to buffered atomics is the lack of a convincing use > case, with the argument that databases should simply migrate to direct I/O. > We have been working with PostgreSQL developer Andres Freund, who has > highlighted a specific architectural requirement where buffered I/O remains > preferable in certain scenarios. > > While Postgres recently started to support direct I/O, optimal performance > requires a large, statically configured user-space buffer pool. This becomes > problematic when running many Postgres instances on the same hardware, a > common deployment scenario. Statically partitioning RAM for direct I/O > caches across many instances is inefficient compared to allowing the kernel > page cache to dynamically balance memory pressure between instances. > > The other use case is using postgres as part of a larger workload on one > instance. Using up enough memory for postgres' buffer pool to make DIO use > viable is often not realistic, because some deployments require a lot of > memory to cache database IO, while others need a lot of memory for > non-database caching. > > Enabling atomic writes for this buffered workload would allow Postgres to > disable full-page writes [5]. For direct I/O, this has shown to reduce > transaction variability; for buffered I/O, we expect similar gains, > alongside decreased WAL bandwidth and storage costs for WAL archival. As a > side note, for most workloads full page writes occupy a significant portion > of WAL volume. > > Andres has agreed to attend LSFMM this year to discuss these requirements. > Andres, If you wish to attend LSFMM, please request an invite via the Google form: https://forms.gle/hUgiEksr8CA1migCA Thanks, Amir.