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 4F21924BBFD for ; Mon, 12 Jan 2026 14:38:20 +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=1768228700; cv=none; b=IOPtswTVYvWAo0jVo/6zBLUZ3TCEFUkpV0eEjZpUwlhlBPwXaS4UUwJiKWEkldcZm1PloTaGWl4HmEyDIBhhdm1o42DNEYJbeG120DcWBZPNvCUxfcDz5pebKPiR3O5+JVcvU0kUPcaK1NN49tO2lluYREHL4rYAsK9xj8GLDJM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768228700; c=relaxed/simple; bh=rKLvcERsBJ4zpdksZXzLU7auq/Wn8M6LOBhi2U8GWYw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=d0dVuKTxcZayj1EFPEukAkOKVUxPR7hUs2VT6phAVqLP3KLrVrFTEA05OtOKcfuXcg7BLChg1LB0rqp+Eet5TaIfP2w+rBbyt4mZrQy1KyO78avFxunLtlkbWyciTBflyLiOyjI0DsMeMsPaYHN702rcebUw3ocBN6IrP/0b6ds= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=NZknK8K1; 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="NZknK8K1" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4E91AC19421; Mon, 12 Jan 2026 14:38:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768228700; bh=rKLvcERsBJ4zpdksZXzLU7auq/Wn8M6LOBhi2U8GWYw=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=NZknK8K1hewsUuSF6mTjMMfDvF8rmFXVnZ+4jpro5YuP0oxWGmDJwvPOY0xcKvq47 fbPC0sXhqIq3RmbfeJd3oARTHBD2SEk1gtS865Ghrl66iKBtwBSj9pKceWQWf62oki dcwtGb4FmBwN31Ha6gxmoIH+yF9V95/QaVGgaAtV1fFVweAB56fpXH5zmEgi7NMzM+ Cqgbjhv1C587BWWcjqtAj/Pdgqzk6JzjDh2+FcAgOgUlvI5duFpI2cXWJoVbHTZTzZ Vy2CjL7zPkLIMiZQv7Hz+0aZacdn3Kj/GjcHTRwxkWt/omBIpGCh3RUgz7SbEMqYn9 Y5XiZOso8TqMw== Message-ID: Date: Mon, 12 Jan 2026 09:38:13 -0500 Precedence: bulk X-Mailing-List: linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v2] NFSD: Add asynchronous write throttling support for UNSTABLE WRITEs To: NeilBrown Cc: Jeff Layton , Olga Kornievskaia , Dai Ngo , Tom Talpey , Mike Snitzer , Christoph Hellwig , linux-nfs@vger.kernel.org, Chuck Lever References: <20260109215613.25250-1-cel@kernel.org> <176802301025.16766.5819430775313248993@noble.neil.brown.name> <63566a53-ed5a-4c0b-920d-22219c750354@app.fastmail.com> <176808109160.2462021.5788018456330144196@noble.neil.brown.name> <176819131921.16766.16091990973366244227@noble.neil.brown.name> Content-Language: en-US From: Chuck Lever Organization: kernel.org In-Reply-To: <176819131921.16766.16091990973366244227@noble.neil.brown.name> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 1/11/26 11:15 PM, NeilBrown wrote: >>> What exactly is "the memory problem"? Do you have specific symptoms you >>> are trying to address? Have you had NFS server run out of memory and >>> grind to a halt? >> Review the past 9 months of Mike's work on direct I/O, published on >> this mailing list. Hammerspace has measured this misbehavior and >> experienced server melt-down. Their solution is to avoid using the >> page cache entirely. > I didn't pay very close attention but I thought the assessment was that > adding lots of single-use pages to the page cache, and then having to > clean them out later, caused a lot of unnecessary work that was best > avoided, and that drop-behind addressed this. Drop-behind is too inefficient to be used here. This is why direct I/O is also an option. Direct I/O is measurably superior to drop-behind. > Are you trying to find another way to address the same problem? Yes. I don't think we can backport direct I/O, for example, to LTS kernels. I expect it will be important to have an alternative to the new I/O caching modes for this reason alone. -- Chuck Lever