From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=213.95.11.211 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793783868; b=eosYFX2b9AM4DQUjndibgjf/wsFnp4CWZGUL2e/N1+g8wcTVhFU41pRQONoe3+jKYyzY uZzYbix6IB7iGl8KC1JH8R66UfDBv7t/Fh/eOusRJDKtA9bZUTc1S4I4xaoH7N8Vl1W4n QkBNll5CzVOB7cQ6Zo5sKFE6FhXenGJaZkmZLo94/lTbt0sVbGgszciXjKyBT+f9ZFOgi yX7wI8JSUSBX/f9wNPFnFQVtGiEh9Is9DrwflRoCapjlxOs4KgI8hveO59m219wqD0ncT tHg9eCiSPqp+ggUPygHLkzgsGjpKFfhew81EF8Hy/8pUj8JWJtI3JzfRlaMr29EOP/A== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793783868; h=DMARC-Filter:Received:Date:From:To:Cc:Subject:Message-ID:References: MIME-Version:Content-Type:Content-Disposition:In-Reply-To:User-Agent; bh=2j+fNl2kk6EUtKkWbcK+QC3SrWBZ1R/JSeRG1EGPR8o=; b=L4nBv+azvk68NACn3oUcwm6rC+1MonCuF3M7ZHG0pCdXf4jmpuPBrlr63bp1Z4ZOLs20 7F9r0Z/DFw4RSO2rV5yaIHitMVPatAu65npMOS36c3glNvYPIlnPvu/Us3m7I9/rLo4x8 pLBFD3u2vTn36AaPaTO3+MVjpr5+MYB4LVSdqAaSgLJcgmvzwEiyWKuPf5e12g/Fe8IpW 4XhnM64iDdy0BPIfsd0Q54ZpJyefiUkTew9TajYY6cR1sPb48HITBwaVpnNz+TGMHri+w 1a64gwgi5s97NQzmOfwmbb3kDuCPAhZzDCgNJe88850gfI1Qa5gTPGLnzFQHkxksCSw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=lst.de; spf=pass smtp.mailfrom=lst.de; arc=none smtp.remote-ip=213.95.11.211 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) (using TLSv1.2 with cipher ECDHE-ECDSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CD367606A33F; Wed, 4 Nov 2026 09:17:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org CD367606A33F Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lst.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=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-Mailing-List: linux-nfs@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list 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) 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.