linux-kernel - Re: [PATCH RFC 0/6] nfsd: allow for a dynamically-sized threadpool

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <53080a86-df29-4321-8b51-c5af565cc6f2@app.fastmail.com>
Date: Sat, 13 Dec 2025 14:34:48 -0500
From: "Chuck Lever" <cel@...nel.org>
To: "Jeff Layton" <jlayton@...nel.org>,
 "Chuck Lever" <chuck.lever@...cle.com>, NeilBrown <neil@...wn.name>,
 "Olga Kornievskaia" <okorniev@...hat.com>, "Dai Ngo" <Dai.Ngo@...cle.com>,
 "Tom Talpey" <tom@...pey.com>, "Trond Myklebust" <trondmy@...nel.org>,
 "Anna Schumaker" <anna@...nel.org>
Cc: linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 0/6] nfsd: allow for a dynamically-sized threadpool



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.
>
> 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.
>
> 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.

An important consideration!


> The series is based on a set of draft patches by Neil. There are a
> number of changes from his work:
>
> 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.

My concern is whether one or more clients can force this mechanism
to continue creating threads until resource exhaustion causes a
denial of service.

I'm not convinced that setting a minimum number of threads is all
that interesting. Can you elaborate on why you chose that design?


-- 
Chuck Lever