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 E8AEA1A83F9; Sat, 13 Dec 2025 21:35:22 +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=1765661723; cv=none; b=gxl8F8rSUicf6P3IzhZzpjD1WYS7AQqKNk/DdAhipnaHqqIr26OjKU7dnFbqF2yj7j3Y2ADeV+dZKTc4gjYp241ygRr4nAZAqnsZBB0ErCGzNDeu2yMMpJ2TH5Z4yz7xxJjpRM3GigbOHIlLfh8XP8igSw3x56i6B27ENRILMcA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765661723; c=relaxed/simple; bh=m8q3UCFLf7V04fENheYu1xfh1KxdNGvGfzMyrAOboEg=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=uZWS5LuZoJuQqL/m+/tHM6BwTxVT3yo50jgxWEhVjNQEfzNFlJGVrQgdsfCSqnzPVgg4kjrdqr/ZAUZ+gQ4i55sD3ir+NgZVwT8O+uMu3kopkY5ZcdQVEMymyZnEV59abpYDyY3KPHvOn3YjGTge1QF/epzaeV6FoBXjtfEWCDM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=RK3FdrSL; 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="RK3FdrSL" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 977B6C4CEFB; Sat, 13 Dec 2025 21:35:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1765661722; bh=m8q3UCFLf7V04fENheYu1xfh1KxdNGvGfzMyrAOboEg=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=RK3FdrSLBjn3sDc0ybBo+HkjUpBTuPhXTWGKpOVpB/Fp/Jo56C2NQf5BSBclE+kh+ QgnbTxi0c3Br3mzzQz5uIDoPOgInaSAne3nzdebBdMmbFZg8gdUs0pIUe0Adzf56Ed KJfxMMMiSIhJKA/1QCTW3BY6G9SaBp8RMvLh/A8gM6UpoatBCEVnKgpIucSutQb+TP Y4a4RXOgY+UiZccL0Y6il6DDXZCiBYxMMmywCTj+bKsu+HdA7ERzfG8dLqmlQoSgac PWVhbK9yYlDBcFO4+812GYaxAYLpQL+alUvE1wYHfhCC9soinVEcdjdzwRlakZqpme ay8Hvqgu4Ry2A== Message-ID: <2d56440cd9747988358e1d3e1d0b981626329f62.camel@kernel.org> Subject: Re: [PATCH RFC 0/6] nfsd: allow for a dynamically-sized threadpool From: Jeff Layton To: Chuck Lever , Chuck Lever , NeilBrown , Olga Kornievskaia , Dai Ngo , Tom Talpey , Trond Myklebust , Anna Schumaker Cc: linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org Date: Sun, 14 Dec 2025 06:35:18 +0900 In-Reply-To: <53080a86-df29-4321-8b51-c5af565cc6f2@app.fastmail.com> References: <20251213-nfsd-dynathread-v1-0-de755e59cbc4@kernel.org> <53080a86-df29-4321-8b51-c5af565cc6f2@app.fastmail.com> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv 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linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Sat, 2025-12-13 at 14:34 -0500, Chuck Lever wrote: >=20 > On Fri, Dec 12, 2025, at 5:39 PM, Jeff Layton wrote: > > This patchset changes nfsd to dynamically size its threadpool as > > needed. The main user-visible change is the addition of new controls > > that allow the admin to set a minimum number of threads. > >=20 > > When the minimum is set to a non-zero value, the traditional "threads" > > setting is interpreted as a maximum number of threads instead of a > > static count. The server will start the minimum number of threads, and > > then ramp up the thread count as needed. When the server is idle, it > > will gradually ramp down the thread count. > >=20 > > This control scheme should allow us to sanely switch between kernels > > that do and do not support dynamic threading. In the case where dynamic > > threading is not supported, the user will just get the static maximum > > number of threads. >=20 > An important consideration! >=20 >=20 > > The series is based on a set of draft patches by Neil. There are a > > number of changes from his work: > >=20 > > 1/ his original series was based around a new setting that defined a > > maximum number of threads. This one instead adds a control to define a > > minimum number of threads. >=20 > My concern is whether one or more clients can force this mechanism > to continue creating threads until resource exhaustion causes a > denial of service. >=20 The old "threads" setting is repurposed as a maximum when "min-theads" is set. If someone sets "threads" high enough that they can drive the machine into resource exhaustion, then that's an administrative error IMO. > I'm not convinced that setting a minimum number of threads is all > that interesting. Can you elaborate on why you chose that design? >=20 The main reason to do dynamic threading is that NFS activity can be spotty. Servers often have periods where they are very busy and other times where they are idle. Today, admins usually just set "threads" to the maximum number that they think they will ever need to deal with this. This is a waste of resources when nfsd is idle, of course. For a dedicated NFS server that isn't doing anything else, that's usually considered acceptable. So, I see the dynamic threading as mostly useful for machines that are running nfsd as a "side job". e.g. -- a compute-heavy server that runs nfsd in order to make its results available to other hosts. In those cases, it makes sense to allow the thread count to ramp down when no one is accessing nfsd so that those resources can be used for other things. With that in mind, it makes sense to repurpose "threads" as a maximum, since that reflects the reality for most people today. So, the new control should have the effect of setting a minimum number of threads. =20 For my own testing, I've mostly set min-threads to 1. We could certainly convert this into a "dynamic-threading" bool setting and just hardcode the minimum to 1 or some other value in that case, but I think it makes sense to allow the flexibility to set the value higher, at least until we have a better feeling for how this affects performance. Thanks for taking a look! --=20 Jeff Layton