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Wed, 18 Feb 2026 17:42:20 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id H2z8KPz5lWnlbAAAD6G6ig (envelope-from ); Wed, 18 Feb 2026 17:42:20 +0000 Received: by quack3.suse.cz (Postfix, from userid 1000) id 6949BA08CF; Wed, 18 Feb 2026 18:42:05 +0100 (CET) Date: Wed, 18 Feb 2026 18:42:05 +0100 From: Jan Kara To: Ojaswin Mujoo Cc: Pankaj Raghav , linux-xfs@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, lsf-pc@lists.linux-foundation.org, Andres Freund , djwong@kernel.org, john.g.garry@oracle.com, willy@infradead.org, hch@lst.de, ritesh.list@gmail.com, jack@suse.cz, 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-pc] [LSF/MM/BPF TOPIC] Buffered atomic writes Message-ID: References: <7cf3f249-453d-423a-91d1-dfb45c474b78@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: wmr6pg9ed5sqkfc9wsnjz1ionb1d96ji X-Rspam-User: X-Rspamd-Queue-Id: 6710C40008 X-Rspamd-Server: rspam01 X-HE-Tag: 1771436542-581406 X-HE-Meta: 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 9BD2KtEn 7HiZ5SVC0n7XAof6uQqqhhNRYfIi4wzGdkB3KvjsBtpxLdGEiGhzgeTmZRcM0dSNyKjM5NuSbH7RZtUWS1cCcsblt691II8dJW0p0len262rwxFanQBdBwqsYgwHspv8rEh4m1k9OQ6UuzGB9Xgj+eEXuhscg6u1QQ+wNatQcRA8Fy8zNnRLOTwzgUAjsZiTOHIgIl9vmEtBN0dAKrDU3QwqNjbEK5tNJ15tNXeYgob2D8NS9lU1L4nxXYGxoJ2ZrQEu5Qf11XjaKY1MjRewU2wecpgwtqD4WvGQAuWysMQZes3ZiARJj5up3U26zY7QYNAlUSomLBC+Z9r4zZ6fcPNyJIOEuCcHs4HHjb/9F67eQtBpe3T1B8xDgaKiAjDpgSiBDLaaWX9aKMuNtLkVBfODFa4A7JggjBdzS 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 Tue 17-02-26 22:50:17, Ojaswin Mujoo wrote: > On Mon, Feb 16, 2026 at 10:52:35AM +0100, Pankaj Raghav wrote: > > Hmm, IIUC, postgres will write their dirty buffer cache by combining multiple DB > > pages based on `io_combine_limit` (typically 128kb). 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. > > Yep, and Ive not looked at the code path much but I think if we really > care about the user not changing the data b/w write and writeback then > we will probably need to start the writeback while holding the folio > lock, which is currently not done in RWF_UNCACHED. That isn't enough. submit_bio() returning isn't enough to guaranteed DMA to the device has happened. And until it happens, modifying the pagecache page means modifying the data the disk will get. The best is probably to transition pages to writeback state and deal with it as with any other requirement for stable pages. Honza -- Jan Kara SUSE Labs, CR