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Date: Wed, 7 Jan 2026 08:55:01 +0100
From: Christoph Hellwig <hch@lst.de>
To: Chuck Lever <cel@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>, Mike Snitzer <snitzer@kernel.org>,
	linux-nfs@vger.kernel.org, Chuck Lever <chuck.lever@oracle.com>,
	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>
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On Fri, Dec 19, 2025 at 09:11:04AM -0500, Chuck Lever wrote:
> From: Chuck Lever <chuck.lever@oracle.com>
> 
> 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.