From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 2A725606D811 for ; Wed, 4 Nov 2026 09:17:50 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 44F476B05C0; Wed, 4 Nov 2026 04:17:49 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 400146B05C1; Wed, 4 Nov 2026 04:17:49 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 33CFD6B05C2; Wed, 4 Nov 2026 04:17:49 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 0C7E46B05C0 for ; Wed, 4 Nov 2026 04:17:49 -0500 (EST) Received: from smtpin15.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 831A440697 for ; Wed, 4 Nov 2026 09:17:48 +0000 (UTC) X-FDA: 85396884216.15.AD613B6 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by imf21.hostedemail.com (Postfix) with ESMTP id C86011C0004 for ; 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imf21.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=lst.de; spf=pass (imf21.hostedemail.com: domain of hch@lst.de designates 213.95.11.211 as permitted sender) smtp.mailfrom=hch@lst.de Received: by verein.lst.de (Postfix, from userid 2407) id 5149E68BFE; Wed, 4 Nov 2026 10:17:41 +0100 (CET) Date: Wed, 4 Nov 2026 10:17:40 +0100 From: Christoph Hellwig To: Mike Snitzer Cc: Matthew Wilcox , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Chuck Lever , Jeff Layton , linux-nfs@vger.kernel.org, NeilBrown , Olga Kornievskaia , Dai Ngo , Tom Talpey , Christoph Hellwig , Jens Axboe , Jonathan Corbet Subject: Re: [PATCH v10 0/7] mm, iomap, NFSD: stop uncached writes reading back shared pages Message-ID: <20261104091740.GB31130@lst.de> References: <20261103211754.35352-1-snitzer@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261103211754.35352-1-snitzer@kernel.org> User-Agent: Mutt/1.5.17 (2007-11-01) X-Stat-Signature: pj9ww5wqnth6ny9wogioe7qs4kzzp698 X-Rspam-User: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: C86011C0004 X-HE-Tag: 1793783866-539369 X-HE-Meta: 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 6mOMlJPU xyXlUkEXTqSXaKbKsNXJVcNaoavhapj2eKzv4L/fZSkw48fHslDLO4x+5EHO8wsN7Um4RHaG+vmxmpO3ujWsIW3jKKvKL3LryCvC6PUd89+SLuVWErJRQSxwyVGfNgqFWrLlm4/N1Tu8HWCUbQZriniz6hiir+JPYdbgob4qIswAoO6k= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Tue, Nov 03, 2026 at 04:17:47PM -0500, Mike Snitzer wrote: > Hi, > > An uncached (RWF_DONTCACHE) buffered write drops each folio it writes > once the folio is written back. A folio that the write covers only > partly is shared with the neighbouring write. If it is dropped before > the neighbour writes its part, the neighbour reads it back from disk > first. 32 threads writing interleaved records to one XFS file, 4 KiB > pages, before and after 5/7: Very colourful terminology here. Who is "the neighbour". How do we know a "neighbour" exists and what it wants to do? In general if the user gave a very clear indication that the data should not be cached, it is a bit awkward to second uess that. Especially if the expectations are not very clearly documented.