From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EA56A34D4CE for ; Wed, 22 Oct 2025 18:39:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761158372; cv=none; b=BBzw/5+c4thUCdjSeW83RsNdM/Hvg+wzLz71Zk+vlkZPTMBPksX72IIn0ajpJrbd4KuLWYIUZ/E8VtCPpT/c+8+Y5lKlMMzgUBQeWlww6atXF1bdkcuDb7DNCO4+Yypg2YT0mHXb+l7niutkefoq7gM4KfGdHh4GS1NjG0K6TkM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761158372; c=relaxed/simple; bh=jXb1y2G4IGUVwg06cMQeMu1rZ393ryy3gHMnTiySGzE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=PMrpGIMIe1eUJH7yMFb1EcCm/KavIMxQ/B53YyYfhTOU9flDrlMU/U9W6N7DKhdWcF2rzP/L4gLuklC4wYeoalVay85/c7DZqmkgp5qKJ05zGoaSKHHOv/KqU5bUL3rcJLueeZoUd87zn7CPBwvMUa5U5w9OH34w3VUGyC3IHW4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=b4R0Pw4Y; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="b4R0Pw4Y" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4A681C113D0; Wed, 22 Oct 2025 18:39:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1761158371; bh=jXb1y2G4IGUVwg06cMQeMu1rZ393ryy3gHMnTiySGzE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=b4R0Pw4Y5KrhlzpFpWlRQ/sCu5ITTV9MlZCWOqoyhyDVK2wLIts+2pLhynPUaTYzp 2U0KB5qHIIMFdC2m2vxz5Gdtbf67MStrnlDDm7SbTD5WTKPF4EooPh+JcmRAYC/+UI CPkVEA5wQlP2xa0SuKZ4sDq7+m/52GVpbdrTjxlmJZJwDB8fpbmXQ/3l3iLr/TSYkn pMoTysPRAKam4EjGBOZNxiKhByhWCmmVbExcrkqHjkIojHwAii2h9LXEjr7rzyqTSn R7I9i5caZ3nrb4E6ktF+3duX+JztR+cCHIXtAsCIwlz9F2pU3+weUl0DMy7JEBaaUg JXk8DX92G93SQ== Date: Wed, 22 Oct 2025 14:39:30 -0400 From: Mike Snitzer To: Tom Talpey Cc: Chuck Lever , NeilBrown , Jeff Layton , Olga Kornievskaia , Dai Ngo , linux-nfs@vger.kernel.org, Chuck Lever Subject: Re: [RFC PATCH] NFSD: Make FILE_SYNC WRITEs comply with spec Message-ID: References: <20251022162237.26727-1-cel@kernel.org> <63c79d16-fec8-47f2-ace3-0b8fd4f41528@talpey.com> <2d204966-abd4-4aa2-90ed-ffd69f059384@talpey.com> Precedence: bulk X-Mailing-List: linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2d204966-abd4-4aa2-90ed-ffd69f059384@talpey.com> On Wed, Oct 22, 2025 at 02:25:42PM -0400, Tom Talpey wrote: > On 10/22/2025 1:46 PM, Mike Snitzer wrote: > > On Wed, Oct 22, 2025 at 01:22:52PM -0400, Tom Talpey wrote: > > > There needs to be some statement of the performance consequences of > > > removing this "optimization". I'm going to predict it's significant > > > on rotating media, and should not go unmeasured. > > > > I agree that rotational storage will likely see an impact. But > > Linux's more recent (now like 14 years ago) FLUSH+FUA rework really > > helped improve things -- that was a major undertaking where Christoph, > > Jens and others really did a fantastic job of breathing new life into > > Linux performance on modern rotational storage. > > I agree, but I think honesty requires it to be measured. Writing > the metadata has to wait for the data to make it to the same storage, > this can roughly double the total latency. If it's small (NVMe), great. > > This kind of "optimization" was tried by pretty much every server > vendor in the early NFSv3 days, I recall many amusing scenes at > old Connectathons where the schemes, or completely unaware servers > were exposed. There was no place to hide when operation latencies > were measured in tens of milliseconds. Same game today, just shifted. > > > Related blast from the past: https://lwn.net/Articles/457667/ > > > > My point: may not be as grim as we think... > > but there is a difference between SATA rotational storage and > > "enterprise" rotational storage (e.g. NetApp or EMC fronted by > > elaborate caching that is configured to report wbc=0 because they have > > battery backed cache) > > Yep. But this is upstream, right? It can't assume. Correct, but catering to really old and slow rotational storage isn't (or shouldn't be) a priority. > To be clear - I totally agree with the change. Only concern is > stating why it's so important, in the face of performance. Yes. In the end, data safety is priority 1, eeking out best performance is secondary. I think all of us can agree on that (even those who have really old/slow rotational storage that will get whiplash from this change). Mike