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c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1767772508; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=59/y5JO3AIg0gecJqYz1Tn984ys7mhUu5h078woniVM=; b=MOSnIFWoSp1MAt/63T0h8QD1/+KyUCmFVVRk+4lUvOkLLUJO6kK4//ollSpR8BDWI/cVQi S282clmP9qKjvbC3TihFqfCpbqTAJiyUQMv4sht2jeJWU9wxYWCsXCeTDyarlu81OJp/cs VkXFoc0QlJPe+cF9+1TpVx/WbzO2gMw= Received: by verein.lst.de (Postfix, from userid 2407) id 3E576227AA8; Wed, 7 Jan 2026 08:55:02 +0100 (CET) Date: Wed, 7 Jan 2026 08:55:01 +0100 From: Christoph Hellwig To: Chuck Lever Cc: Christoph Hellwig , Mike Snitzer , linux-nfs@vger.kernel.org, Chuck Lever , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Subject: Re: [RFC PATCH 1/2] NFSD: Add aggressive write throttling control Message-ID: <20260107075501.GA19005@lst.de> References: <20251219141105.1247093-1-cel@kernel.org> <20251219141105.1247093-2-cel@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251219141105.1247093-2-cel@kernel.org> User-Agent: Mutt/1.5.17 (2007-11-01) X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: C310640003 X-Stat-Signature: 49x7j13dobj41hfjmzkesk39fqjzh1m7 X-Rspam-User: X-HE-Tag: 1767772507-928696 X-HE-Meta: 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 e0xV3RiD hZUKdWVQnNdVLEkbM1QyklFEqOK85vDtRACNXi1x6bE9l6oeQY0aebycRt6bkiFx0E3GWn0tVZ/TcZzFh2bxoBoVcFDI0HTUI+e5uLrzJ4gWMb+bBMb481TZMnA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Dec 19, 2025 at 09:11:04AM -0500, Chuck Lever wrote: > From: Chuck Lever > > On NFS servers with fast network links but slow storage, clients can > generate WRITE requests faster than the server can flush payloads to > durable storage. This can push the server into memory exhaustion as > dirty pages accumulate across hundreds of concurrent NFSD threads. > > The existing dirty page throttling (balance_dirty_pages()) uses > per-task accounting with default ratelimits that allow each thread > to dirty ~32 pages before throttling occurs. With many NFSD threads, > this allows significant dirty page accumulation before any > throttling kicks in. What makes NFSD so special here vs say a userspace process with a bunch of threads? Also what is the actual problem we're trying to solve? I kinda hate having this stuff in NFSD when there's nothing specific about nfs serving here.